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Green concrete: Prospects and challenges
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DOI: 10.1016/j.conbuildmat.2017.09.008
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Review
Green concrete: Prospects and challenges
K.M. Liew a,b,⇑
, A.O. Sojobi a
, L.W. Zhang c,⇑
a
Department of Architecture and Civil Engineering, City University of Hong Kong, Kowloon, Hong Kong, China
b
City University of Hong Kong Shenzhen Research Institute, Nanshan District, Shenzhen 518057, Guangdong, China
c
School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
h i g h l i g h t s
Green concrete utilizes waste materials as SCM and aggregates in concrete.
It promotes effective waste management, GHG reduction and resource conservation.
Benefits: improved strength, workability, durability, pumpability, reduced cracking.
Benefits: reduction of construction maintenance costs and increased service life.
More R D, standards and large-scale demonstration projects are required.
a r t i c l e i n f o
Article history:
Received 28 April 2017
Received in revised form 29 August 2017
Accepted 1 September 2017
Available online 20 September 2017
Keywords:
Green concrete
High-volume fly ash concrete
Ultra-high performance concrete
Lightweight concrete
Geopolymer concrete
a b s t r a c t
Utilization of green concrete in construction is increasingly adopted by the construction industry owing
to the drawbacks of conventional concrete and the numerous inherent benefits of green concrete. The
increasing demand for green concrete has been spurred by demand for high quality concrete products,
desire of nations to reduce green-house gas emission, need for conservation of natural resources and lim-
ited landfill spaces. Green concrete comes in various forms such as high-volume fly ash concrete, ultra-
high performance concrete, geopolymer concrete, lightweight concrete to mention a few. Green concrete
offers numerous environmental, technical benefits and economic benefits such as high strength,
increased durability, improved workability and pumpability, reduced permeability, controlled bleeding,
superior resistance to acid attack, and reduction of plastic shrinkage cracking. These characteristics pro-
motes faster concrete production, reduction of curing waiting time, reduction of construction costs, early
project completion, reduction of maintenance costs and increased service life of construction projects.
Green concrete promotes sustainable and innovative use of waste materials and unconventional alterna-
tive materials in concrete. Suitable standards, more demonstration projects, as well as adequate training,
public awareness, cross-disciplinary collaborations and further research and developments are required
to promote global adoption of green concrete in large-scale infrastructure projects.
Ó 2017 Elsevier Ltd. All rights reserved.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1065
2. Common waste materials used as SCM in green concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1065
2.1. RHA as SCM in green concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1065
2.2. Silica fume as SCM in green concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1066
2.3. Fly ash as SCM in green concrete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1066
2.4. GGBFS as SCM in green concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1067
2.5. Waste glass as SCM in green concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1068
3. Activation techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1068
4. Production of green concrete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1069
5. Properties of green concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1069
http://dx.doi.org/10.1016/j.conbuildmat.2017.09.008
0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
⇑ Corresponding authors.
E-mail addresses: kmliew@cityu.edu.hk (K.M. Liew), zlvwen@hotmail.com (L.W. Zhang).
Construction and Building Materials 156 (2017) 1063–1095
Contents lists available at ScienceDirect
Construction and Building Materials
journal homepage: www.elsevier.com/locate/conbuildmat

5.1. Fresh properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1069
5.1.1. Slump and water requirement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1069
5.1.2. Setting time, flow, workability, segregation index, bleeding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1070
5.2. Hard properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1070
5.2.1. Compressive strength. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1070
5.2.2. Flexural strength. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1071
5.2.3. Splitting tensile strength and modulus of elasticity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1071
5.2.4. Shrinkage and creep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1072
5.3. Durability properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1074
5.3.1. Water absorption and porosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1074
5.3.2. Chloride penetration and alkali silica reaction (ASR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1074
5.3.3. Fire-resistance and chemical attack properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1076
6. Factors that influence properties of green concrete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078
6.1. SCM chemical composition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078
6.2. Water/binder (w/b) ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078
6.3. Curing medium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078
7. Binary, ternary and quarternary SCM mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078
8. Nomenclature and applications of green concrete utilized in concrete structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1079
8.1. HVFAC (High volume fly ash concrete) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1079
8.2. UHPC (Ultra high performance concrete) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1080
8.3. UHSC (Ultra high strength concrete) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1080
8.4. LWC (Lightweight concrete) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1081
8.5. HSC (High strength concrete) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1082
8.6. HPC (High performance concrete) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1082
8.7. GPC (Geopolymer concrete) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1083
9. Analytical and numerical modelling of green concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1083
10. Potential benefits of green concrete in early project completion and cost savings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1084
11. Future trends in production and application of green concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1086
12. Current challenges and obstacles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1087
13. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1087
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1087
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1087
Nomenclature
SCM Supplementary cementitious material
SF Silica fume
RHA Rice husk ash
GGBS GGBFS Ground granulated blast-furnace slag
WG Waste glass
NS Nano-silica
PPF Polypropylene fibres
BOFS Basic oxygen furnace slag
RAC Recycled aggregate concrete
FFA Fine fly ash
RHAC Rice husk ash concrete
FAC Fly ash concrete
FA-HSC Fly ash-based high strength concrete
SFC Silica fume concrete
UHPC Ultra-high performance concrete
WGC Waste glass concrete
GF Glass fume from waste glass
C3S (tricalcium silicate)
C2S (dicalcium silicate)
RHAC Rice husk ash concrete
SCC Self-consolidating concrete
HPC High-performance concrete
AA Alternative aggregates
OPC Ordinary Portland cement
RRHA Raw rice hush ash
NanoA Nano-Al2O3
CNI Calcium nitrite-based corrosion inhibitor
FA50L 50%Fly ash content
HVFAC High-volume fly ash concrete
HPSCC High performance self-consolidating concrete
FA Fly ash
CRT Cathode ray tube waste glass
GFRP Glass fibre reinforced polymer
CS Compressive strength
SP Superplasticizer
w/b water binder ratio
w/cm water-cementitious ratio
w/scm water-supplementary cementitious materials ratio
ASR Alkali silica reaction
RPC Reactive powder concrete
MK Metakaolin
SiO2ÀEff Effective amorphous silica content
Seff Effective surface area of SCM
CN Carbon nanotube
HSC High strength concrete
UHPC Ultra high strength concrete
LWC Lightweight concrete
BRAC Bacterial rice husk ash concrete
CRHA Rice husk ash from controlled burning
1064 K.M. Liew et al. / Construction and Building Materials 156 (2017) 1063–1095

1. Introduction
Globally, management of solid wastes poses a herculean chal-
lenge to developed and developing countries owing to industrial
growth, construction booms, rapid urbanization, and consumeric
lifestyle [1]. The demand for green concrete in construction indus-
try is spurred by increased regulations to reduce carbon footprint,
limit greenhouse gas emission and limited landfill spaces. In addi-
tion, the construction industry is embracing green construction
owing to project requirements for LEED (Leadership in Energy
and Environmental Design) certifications.
The present high demand for natural resources to meet infras-
tructural demands has created immense opportunities for the
use of waste materials to green infrastructure construction [2–5].
These waste materials play the roles of either supplementary
cementitious materials (SCM) or alternative aggregates (AA) in
green concrete and can be categorized as agricultural, industrial
and municipal wastes as shown in Fig. 1.
Though coined in Denmark in 1999, green concrete has been in
practical existence for several decades and centuries. Jin and Chen
[6] defined green concrete as concrete produced by utilizing alter-
native or recycled waste materials in order to reduce energy con-
sumption, environmental impact and natural resource
consumption. Green concrete is a concept of embracing and inte-
grating environmental considerations in concrete with respect to
raw material sourcing, mix design, structural design, construction
and maintenance of concrete structures [7].
The inherent drawbacks of traditional concrete include unsus-
tainable consumption of natural raw materials, low, early-age
compressive strength, environmental contamination [8–10].
On the other hand, green concrete exhibit numerous
advantages such as improvement in concrete properties, low
carbon footprint, conservation of natural resources, to mention a
few [11].
The major barriers for green concrete utilization in construction
are systemic lock-in, lower qualities of locally available materials,
increase in construction costs, and technical barriers [6,12].
In order to produce sustainable green concrete, technological
advances that are energy efficient, utilize low-carbon production
methods and novel cement formulations are required alongside
technical guidelines for their production and usage [13].
2. Common waste materials used as SCM in green concrete
The waste materials utilized in green concrete can be grouped
into three categories namely agricultural, industrial and municipal
wastes as depicted in Fig. 1. In order to utilize their pozzolanic
properties in green concrete, the waste materials are often acti-
vated through physical or chemical means or their combination
[14,15].
2.1. RHA as SCM in green concrete
Various studies have been carried out on the utilization of rice
husk ash (RHA) as supplementary cementitious material and sand
replacement in various concrete applications [14,16–20].
Utilization of RHA offers numerous benefits in concrete. A few
of the benefits include improvement of microstructure, void struc-
ture reformation, increased early age strength, by reducing the
width of the ITZ between paste and aggregate [21–23].
It was observed that the optimum parameters recommended
for RHA to maximize its pozzolanic properties in concrete varied
amongst different researches mainly because of the different con-
stituents utilized in combination with RHA, variation in the pro-
duction process and applications.
Despite many researches on RHA as SCM in concrete and mor-
tar, the relationship between the particle size and pozzolanic prop-
erties of RHA is not yet well understood. Previous researchers have
made attempt to explain their relationship with various degrees of
success. A positive relationship exist between Blaine specific sur-
face area (SSA) of RHA and its pozzolanicity but an inverse relation-
ship with median particle size ðd50Þ [24]. On the other hand, the
multilayered, angular and microporous surface of RHA was
reported to be the major factor controlling the pozzolanic reaction
[25].
In-depth literature studies revealed that the pozzolanic proper-
ties of RHA are influenced by its particle size and specific surface
area, percentage replacement of cement, and water-cement ratio.
In addition, it was observed that the influence of SSA of RHA often
supersedes that of particle size ðd50Þ. This finding was corroborated
in earlier studies [25–27]. Givi et al. [26] reported that 5 lm RHA
particle size with SSA of 36:47 m2
=g recorded the higher compres-
sive strength (CS) compared to 95 lm RHA particle size with SSA of
24 m2
=g. In a similar vein, the highest CS28 (51.8 MPa) was
obtained with the smallest RHA particle (11.5 lm) and the highest
SSA (30.4) by another researcher [25]. These values were higher
compared to the other samples with corresponding particle sizes
of 31.3 and 18.3 lm, BET SSA of 27.4 and 29.1 and corresponding
CS28 of 48.4 and 50.2 MPa respectively. The above results lend cre-
dence to the dominance and importance of SSA to both RHA poz-
zolanicity and compressive strength development of concrete.
Previous work by Cyr et al. [28]established that SCMs exhibit
both pozzolanic and physical effects, which can be quantified.
The pozzolanic contribution of SCM was reported in Eq. (1):
Dfpz ¼
apz
1 þ b
Seff
c ð1Þ
where Dfpz = pozzolanic contribution of SCM (RHA); apz = depth in
time of hydration; b = BET surface area of cement (Type 1 OPC),
which varies with water-cement ratio as shown in Fig. 2;
Seff = Effective surface area of SCM as shown in Eq. (2); c = 1.
Seff ¼ SsxgP ð2Þ
where Ss = SSA of RHA; gP = efficiency factor obtained from the
work of Cyr et al. [29]. Likewise, it was also reported that amor-
phous silica content of RHA can also be used to reliably assess the
pozzolanic potential of different RHA samples using Eq. (3) [27].
SiO2ÀEff ¼
Min ðp; pmaxÞ Á SiO2ÀAmorphous
1 À Minðp; pmaxÞ
ð3Þ
where SiO2ÀEff = effective amorphous silica content (%);SiO2ÀAmorphous
= amorphous silica content of RHA samples; p = % RHA replacement
of cement, which could reach up to maximum ðPmaxÞ. SiO2ÀEff is the
amount of amorphous SiO2 that is able to react, given the replace-
ment level p, maximum replacement level pmax and amorphous sil-
Agricultur
al wastes
Rice
husk
ash
Corn
cob
ash
Sawd
ust
ash
Industrial
wastes
Fly
ash
Silica
fume
Granula
ted
blast
furnace
slag
Municipal
wastes
Glass PlasƟcs Paper
Fig. 1. Categories of Wastes utilized in Green Concrete.
K.M. Liew et al. / Construction and Building Materials 156 (2017) 1063–1095 1065

ica content. The SiO2ÀEff result obtained was utilized in place Seff in
equation for comparison purposes.
Experimental data presented by Zunino and Lopez [27] were
used for analyses because they utilized RHA from different suppli-
ers with different d50, BET SSA and SiO2 amorphous content.
Although the experiment was conducted at 20% RHA replacement
of cement and 0.5 w/c ratio, it was extended to higher replacement
ratios using the formulas given above. Our results revealed that the
pozzolanic contribution of RHA varies with median particle size,
water-cement ratio, specific surface area and percentage RHA
replacement of cement as shown in Figs. 3–6.
In addition, the highest pozzolanic contribution occurred at
0.35 water-cement ratio, 30% cement replacement and
14.467 lm. This correspond with the maximum results obtained
by another study [30]. Furthermore, it was also observed that the
pozzolanic contribution increased with increasing BET SSA and
increasing reduction in median particle sizes. Therefore, in order
to enhance the pozzolanic contribution of RHA in concrete, RHA
particles with both smaller specific surface area and smaller parti-
cle sizes should be utilized to give maximum pozzolanic contribu-
tion. This implies smaller RHA particle sizes have the potential to
offer more pozzolanic contribution in concrete provided they have
higher SSA.
Furthermore, the potentials of RHA in concrete is yet to be fully
realized since most reported experiments in literature were con-
ducted at sub-optimal experimental conditions. Therefore, more
researches are needed to find cost-effective and affordable meth-
ods to improve the SSA of locally available RHA to encourage its
adoption and widespread utilization.
From Fig. 7, it was observed that the pozzolanic contribution
obtained using SiO2ÀEff proposed by Zunino and Lopez [27] gave
higher effective surface values at all median particle sizes com-
pared to the method using the SSAEff suggested by Cyr et al. [29].
Even though the two approaches showed similar trend up to med-
ian particle size of 20.644 lm, their results differed afterwards.
Calculation of pozzolanic contribution of RHA in concrete using
the SiO2ÀEff could be a better approach. This is also supported by
the fact that SiO2 constitutes about 80–90% of RHA by mass and
it is the major source of its pozzolanicity [26,30–32].
Therefore, in order to optimize the pozzolanic potentials of
RHA, proper attention must be paid to its production process as
well as its chemical composition alongside other concrete/cement
constituent materials utilized in RHAC [23,33].
Optimum grinding time for RHA depends on the incineration/
burning temperature it was subjected to, burning duration, type
of incineration equipment utilized, level of pre-treatment of the
RHA, the speed and type of grinding machine utilized.
The optimum cement replacement with RHA is governed by the
SSA of the RHA, RHA particle size, w/c ratio, presence of other SCM,
w=cm ratio, type, chemical and mineralogical composition of
cement and SCM utilized [21,34,35]. Other parameters that may
affect optimum cement replacement include type and dosage of
super plasticizer and target engineering properties to be opti-
mized, size of the concrete aggregates, porosity of the concrete
and pre-treatment and activation level of RHA.
Jamil et al. [35] reported that optimum replacement percentage
ratio of RHA in each type of cement varies as the % of C3S (trical-
cium silicate) and C2S (dicalcium silicate) varies with cement types
and the amount of CaðOHÞ2 produced during cement hydration.
The authors also mentioned that optimum replacement percentage
ratio of RHA will increase with increase in percentage of foreign
compounds in RH samples and also percentage of non-reactive
crystalline silica in RHA. In addition, the authors reported that par-
ticle size, SSA, pozzolanic reactivity and pore structure are the
main factors governing cement hydration and invariably cement
replacements in concrete. The ash type, grinding time and cement
percentage replacements effects and their interactions were also
reported to affect strength development of RHAC [36]. The authors
recommended Type 2 ash prepared at 650 °C, grinding time of
240 min and 20% or 40% cement replacement with RHA.
Negative impacts of RHA in concrete include reduction of flowa-
bility, high water requirement, flow blockage and increase in
superplasticizer requirements. Others include reduction of
strength at high RHA content, poor chloride permeability at high
RHA content and ASR reaction in alkaline solution. These negative
impacts can be ameliorated through careful optimization of the
production processes of RHA and RHAC and utilization of appropri-
ate optimum RHA contents for concrete applications.
2.2. Silica fume as SCM in green concrete
Silica fume (SF) has been used in various applications [37–44]
and acted as SCM, filler and healing agents. Benefits offered by SF
in concrete are improved flexural and compressive strengths,
increased pozzolanic activity, multi-range macroporosity proper-
ties, to mention a few [41,43–46]. Its multi-range macroporosity
properties allow its usage in the production of high-porosity
cement foams and multi-strength lightweight concrete (LWC). SF
was also found useful in increasing ultimate-load carrying capac-
ity, improved durability and impact resistance [37–40,47]. Opti-
mum dosage of SF ranges between 10 and 14% when used in
combination with materials such as steel fibres, nano-silica, recy-
cled aggregate [37,39,40].
One of the negative impacts of SF in concrete include reduction
in workability [48]. Also, SF was reported ineffective in reducing
creep [49] and caused reduction in long-term compressive
strength [50]. Increase in chloride-initiated reinforcement corro-
sion in marine environment was also reported and was found to
be mitigated at low w=c ratio [51].
2.3. Fly ash as SCM in green concrete
Previous studies have investigated the use of fly ash as SCM in
various concrete applications [52–58]. The benefits derived from
the use of fly ash were increase in compressive strength (CS), bulk
density and linear shrinkage, porosity reduction, improvement in
bending toughness and ductility [52,53,58].
In order to ensure satisfactory properties, curing time, curing
temperature and type of materials used in fly-ash concrete (FAC)
must be carefully selected [55,56]. Optimum production conditions
should also be utilized depending on exposure conditions of the
y = 21.86x + 35.46
R² = 0.974
0
20
40
60
80
100
120
140
160
0.35 0.4 0.5 0.57 0.7
BETSSA(m2/g)
w/c raƟo
Fig. 2. Variation of BET SSA of cement with w/c ratio [28].

envisaged FAC product [54,55,59,60]. The fly ash could be from
anthracite or bituminous coal, lignite or sub-bituminous coals [61].
Negative impacts of fly ash in high-volume fly ash concrete
(HVFAC) include extended setting times, slow strength develop-
ment, low early-age strength, construction delay, difficulties to
use in cold weather concreting and low resistance to deicer-salt
scaling carbonation [62]. Kurad et al. [63] also advised against high
volume applications of RHA in concrete to avoid retardation of
compressive strength development. In addition, high class C fly
ash can increase ASR in silica fume concrete (SFC) [64].
2.4. GGBFS as SCM in green concrete
Ground granulated blast furnace slag has been investigated for
use in production of geopolymer concrete (GPC) and alkali-
activated slag (AAS) cements [65,66]. The benefits of SF in concrete
0
1
2
3
4
5
6
7
14.467 19.123 19.623 20.644 20.953
PozzolaniccontribuƟon,fpz(MPa)
RHA median parƟcle size, D50 (μm)
0.35 w/c
0.4 w/c
0.5 w/c
0.57 w/c
0.7 w/c
Fig. 3. Variation of pozzolanic contribution with Particle size and water-cement ratio.
0
1
2
3
4
5
6
7
8
9
14.467 19.123 19.623 20.644 20.953
RHA ParƟcle Size, D50 (μm)
20%
30%
40%
50%
60%
Fig. 4. Variation of pozzolanic contribution with particle size at different percentage replacements.
0
1
2
3
4
5
6
7
8
9
23.582 31.284 52.114 114.523 128.85
BET SSA (m2/g)
20%
30%
40%
50%
60%
Fig. 5. Variation of pozzolanic contribution of RHA with BET SSA and percentage replacement.

are improvement in durability, enhancement of long-term CS to
mention a few [67,68].
Optimum OPC=GGBFS ratio of 4:1 at 0.3 water-binder ðw=bÞ
ratio and cement-sand ratio of 1:1.5 were recommended by Chi-
diac and Panesar [69,66]. Low percentage replacements and low
water-to-powder ratios were recommended to avoid bleeding,
shrinkage straining and obtain high CS [70,71].
GGBFS and fly ash were reported to initiate corrosion and
increase critical corrosion. On the contrary, laboratory evidence
and field practice have shown their usefulness in the achievement
of durable structures even in most aggressive natural environ-
ments [72,73]. In addition, it was reported that there is no need
for extra steel protection when these SCMs are utilized in concrete
[74]. However, it was pointed out that their combination should be
avoided and appropriate precautions in concrete technology
should be taken in their concrete applications as well.
2.5. Waste glass as SCM in green concrete
Waste glass has been utilized as SCM and fine aggregates in var-
ious applications such as ultra-lightweight fibre reinforced con-
crete, fired-clay bricks to mention a few [75–79]. Other
applications include glass-reinforced panels, structural repair con-
crete and fast-cured polymer concrete [80–83].
The benefits of the utilization of WG were improved CS, resis-
tance to freezing and thawing, chloride penetration and surface
scaling, good resistance to Na2CO3 and H2SO4 [84,85]. The recom-
mended optimum percentage as cement and fine aggregate
replacements were 5–10% and 7.5–25% respectively [80,86,87].
Negative impacts of waste glass in concrete include slump
reduction at high waste glass content as well as decrease in com-
pressive strength [88]. These impacts can be ameliorated by val-
orization of waste glass to become glass fume, usage of
appropriate w/c ratio and waste glass content.
3. Activation techniques
Activation is necessary to prevent slow and low, early-age
strength development and accelerate the pozzolanic reactivity of
SCMs in green concrete. Activation helps to achieve higher early
and later strength amongst other benefits [89]. Types of activation
techniques available in literature include mechanical activation,
chemical activation, curing/temperature activation, water-
controlled activation and SCM-controlled activation.
Mechanical activation involves grinding of SCM to smaller fine
particles to increase fineness and their effective specific surface
area. Chemical activation is the addition or utilization of chemical
substances to activate the pozzolanicity of cementitious materials
[90]. Curing/temperature activation refers to the use of curing
medium with age and temperature to achieve property develop-
ment of the concrete. The curing medium could be air, water, alter-
nating combination of both.
Temperature activation refers to the use of elevated tempera-
tures above room temperature to activate the reactivity of the con-
crete constituents. Commonly utilized activation media utilized in
temperature-controlled activation are air or water. SCM-controlled
activation involves the use of SCM or cement to accelerate poz-
zolanic reactions of the pozzolans. Elevated temperature curing
at 50 °C favours pozzolanic behaviour of glass particles which also
depends on the glass composition [91]. Particle size smaller than
25 lm was recommended.
Chemical activation is the most efficient and feasible activation
method [92]. Examples of chemical activators found in literature
utilized in green concrete are sodium sulphate anhydrite, sodium
silicate, acids such as HCl and H2SO4, CaCl2, Na2SO4, NaOH,
Na2CO3, CaðOHÞ2, K2SO4, TiO2, Calcium formate. The chemical acti-
vators could be added during grinding or combined with
temperature-controlled activation to reduce total materials costs
[92]. For instance, combination of grinding and addition of
Na2SO4 achieved higher strength than single activation [93].
Advantages of chemical activation include reduction of setting
time, early strength development, reduction of total material costs,
higher SiO2 content, lower alkali and unburned carbon contents,
better grindability and smaller particle size, achievement of
superior strength and enhancement of microstructural properties
[94–97]. Sometimes, chemical activation is combined with
temperature-controlled activation.
Other benefits of chemical activation include improved worka-
bility, reduced shrinkage and prevents deterioration of later-age
strength, improved pore structure, accelerated hydration and
improved flexural strength of self-compacting concrete, reduction
of pore size and total porosity [98,99]. Kawashima et al. [100]
reported that addition of nano-CaCO3 prepared through sonication
improved hydration rate, setting time and CS of self-consolidating
concrete. Achieved reduction in initial and final setting times as
well as improvement in CS through the use of colloidal nanosilica.
In another study, quicklime was recommended for High-volume fly
ash systems only, with positive contribution to both early and
later-age strength development [101]. Addition of quicklime
increased both early and later-strength of FA-based cementitious
sytems [102]. For WGC, lithium compounds were suggested to
limit ASR expansion [103].
SCM-controlled activation has been used to improve bond
strength, reduce the setting time, achieve early-age and high late
0
1
2
3
4
5
6
7
8
9
20% 30% 40% 50% 60%
RHA content (%)
14.467 μm
19.123 μm
19.623 μm
20.644 μm
20.953μm
Fig. 6. Variation of pozzolanic contribution of RHA with percentage replacement
using different particle sizes.
0
5
10
15
20
25
14.467 19.123 19.623 20.644 20.953
EffecƟvesurfacearea(m2/g)
RHA median parƟcle size, d50 (μm)
SiO2-eff
SSAeff
Fig. 7. Comparison of pozzolanic contribution using SiO2-Eff and SSAEff..

strength and reduce [104–108]. Commonly utilized SCMs include
OPC, nano-SiO2, GGBFS. Bernal et al. [109] advocate silicate-based
activators produced from SF or RHA in combination with aqueous
NaOH as an alternative to commercial-based activators. The
mechanical performance of the binders produced were similar to
those of commercial silicate solutions.
In order to achieve synergistic benefits, sometimes thermal and
mechanical activation are combined. The benefits of such method
include early-strength development, removal of inconsistencies
in the chemical and mineralogical properties of RHA [15,90].
According to Kumar et al. [110], the effects of mechanical acti-
vation depend on the type of activation device utilized. Their study
revealed that raw fly ash exhibited highest lime reactivity, fol-
lowed by vibratory mill fly ash, and then attrition mill fly ash.
Blanco et al. [111] suggested mechanical activation prior to chem-
ical activation to increase SSA and pozzolanic reactivity of SCM.
The type of activator used influences the microstructure of the
mortar or concrete and the resulting secondary products formed
[112]. Based on their results, in terms of CS, the order of preference
of alkali activator was NaOH + WG NaOH Na2CO3. They also
observed that, in fly-ash binders, the ratio of SiO2=Na2O and their
pH seems to play crucial roles in the reactivity of the cementitious
system and strength development of the binder. This finding was
corroborated by De Vargas et al. [113] who reported that
SiO2=Na2O played a major role in CS development, morphology
and microstructure of FA-based geopolymer system. Their results
revealed an increase in CS with increasing molar ratio, increasing
curing age and increasing curing temperature.
For SCM-controlled activation, addition of 5% SF to replace slag
improved CS up to 800 °C in AAS pastes [114]. Owing to its dilution
effect and pozzolanic reactivity, addition of 5–10% RHA to replace
cement was useful in the consumption of free lime, formation of
additional C-S-H resulting in increased CS [115]. In another study,
RHA addition in SF UHPC resulted in improved impermeability and
increased CS of 9.76%, 14.5% and 10.02% at 3, 28 and 120 days
[116]. Addition of nanosilica (NS) enhanced the structural perfor-
mance of FA-based GPC through the geopolymerization transfor-
mation of the amorphous phase of GPC to crystalline phase
without the need for thermal activation.
4. Production of green concrete
Production methods of green concrete differ depending on the
constituent materials to be utilized and the intended application.
In order to produce sustainable, green concrete with sufficient
workability, Müller et al. [117] suggested four basic steps namely:
I. Determining experimentally the relevant properties of the
selected concrete constituents
II. Determine the water/cement ratio based on desired cement
content and strength requirements
III. Optimize the grain size distribution of granular constituent
IV. Production and evaluation of the fresh concrete properties
based on achieved packing density and prediction compres-
sive strength
Optimization methods which can be applied in green concrete
include particle packing optimization using granular optimization
of all concrete constituent [117,118], statistical optimization using
microanalysis data and estimation of C-S-H contents [119], step-
by-step optimization method [120,121].
Other optimization methods include micro-proportioning opti-
mization of fines grading [122], particle size distribution method
[123], multi-objective simultaneous optimization using response
surface methodology (RSM) [124], box-behnken response surface
technique [125], response surface methodology using design-
expert software [126] and multicriteria optimization method for
the technical, economic and environmental aspects of green con-
crete [127].
The advantages of optimization in green concrete include min-
imization of air voids leading to attainment of maximum strength,
synergistic maximization of the properties of the constituent mate-
rials. In addition, for ternary blended cement concrete, Binici et al.
[128] suggested separately grinding each of the SCM constituents
to obtain higher compressive strengths.
5. Properties of green concrete
5.1. Fresh properties
5.1.1. Slump and water requirement
Slump test indicates the behavior of compacted concrete cone
under the action of gravitational force, which can also be seen as
a measure of the consistency or wetness of the concrete mix [129].
In order to produce HVFAC, Bentz et al. [130] recommended
optimum mixture proportioning and careful selection, evaluation
and combination of HRWRA (high-range water-reducing admix-
tures) alongside increasing aggregate volume fraction. Alaka and
Oyedele [131] obtained good workable HVFAC at low water-
binder ratio with superabundant dosage of superplasticizer (SP).
Yijin et al. [132] and Mukherjee et al. [133] recorded increase in
slump values with increasing fly ash replacements of cement,
which was attributed to high specific surface area and low specific
gravity of fly ash compared to Portland cement.
For rice husk ash (RHA), Keertana and Gobhiga [134] reported
decrease in slump with increasing RHA while Abalaka [135]
recorded increased slump up to 5% cement replacement with
RHA and decrease thereafter. For SF, Hunchate et al. [136] recorded
increasing slump up to 10% silica fume (SF) cement replacements
and decline thereafter while Amarkhail [137] obtained reduction
in slump values with up to 15% SF replacement of cement. With
respect to GGBFS, Karri et al. [138] and Arivalagan [139] reported
increase in slump values with increase in GGBFS contents. Tamila-
rasan et al. [129] reported optimum slump value of 55% GGBFS
replacement levels for grade 20 and grade 25 concretes. The
decrease in slump values was attributed to the high water absorp-
tion of RHA and often SP is added to enhance workability of RHA in
concrete.
Slump reduction is attributed to the high specific surface area of
the RHA and SF and high water absorption capacity as a result of
their macro-mesoporous nature and the concrete pore volume
[140]. Their slump reduction potential depends on their level of
reactivity and activation, level of fineness and water-cement ratio
and cement replacement ratio [140,141]. Abalaka [135] also men-
tioned that each SCM has its own optimum w=b ratio which would
give it its maximum reactivity. In addition, RHA had higher yield
stress and viscosity than SF and its particle shape is angular while
that of SF is spherical [140]. As a result, in their study, RHA exhib-
ited lower mini-slump flow compared to compared to SF. In
another study, SF exhibited higher flow compared to unground
RHA and was attributed to its spherical particle shape, its ability
to release adsorbed water from its microstructure and the amount
of fine particles it contains [142].
For waste glass, while Malik et al. [143] and Liang et al. [144]
reported increasing slump values at increasing waste glass replace-
ments of fine aggregate, Abdallah and Fan [145] reported decline in
slump values. The contrasting views may be due to the different
concrete mix ratios used, the physical properties of the concrete
constituents and the replacement levels investigated.

5.1.2. Setting time, flow, workability, segregation index, bleeding
Setting time determines the time available for transport, plac-
ing and compaction of cement/cementitious-based materials
[146]. The authors reported that the setting time of GGBFS-based
geopolymers vary with the calcium content, particle size and
Si=Al molar ratios. The initial setting time (IST) and final setting
time (FST) they obtained were 109–141 min and 155–327 min.
Bouzoubaa and Lachemi [147] reported that for FA-based SCC ini-
tial and final setting times ranged from 4:50–7:45 to 6:30–10:15 h
and were found to be 3–4 h longer than control. Brooks et al. [148]
reported that there is no linear relationship between setting times
and SCM percentage replacement owing to the influence of several
factors. In terms of difference between FST and IST, SF results were
found comparable to OPC and preferable to FA and GGBS.
Ravina and Mehta [149] reported delay in IST and FST from
20 min to 4 h 20 min and 1 h – 5 h 15 min in concrete depending
on the type and amount of FA utilized. The delay in setting time
was influenced by the sulphate and available alkali contents of
FA. Nochaiya et al. [150] reported IST and FST values of 145–
170 min and 215–235 min for Portland-FA cement pastes respec-
tively. Inclusion of SF increased the IST but led to reduction of
the FST at increasing SF contents from 5 to 10%.
Ikpong and Okpala [141] reported improvement in cohesive-
ness and flowability of RHA-modified concrete containing 30%
RHA replacement of cement. The IST increased from 2 h to 3.5 h
while the FST increased from 4 h to 4.5 h respectively. Lin et al.
[151] reported that WG recorded IST and FST values of 666–
1158 min and 765–1245 for increasing replacements of MK from
10 to 40%. Likewise, Wang [152] observed reduction in IST and
FST with increasing WG powder content of up to 50% cement
replacement in mortar at 0:485 w=b ratio. Combination of coarse
and fine WG resulted in longer IST and FST as well as higher slump
values. WG was recommended because of its impermeability,
enhanced flow properties and higher strength at elevated
temperatures.
Also, Bouzoubaa and Lachemi [147] reported that FA-based SCC
exhibit good deformability and stability. Increase in flow time was
observed with decrease in water content. Segregation index was
found to decrease with increasing FA content but increased with
SP dosage. A w=cm ratio of 0.45 was recommended to obtain
segregation-resistant FA-SCC. Shen [153] reported that smaller
aggregate size, continuous aggregate gradation, lower aggregate
density and higher paste viscosity and yield stress reduce dynamic
segregation.
According to Xie et al. [154], Fresh SCC made with UPFA (ultra-
pulverized fly ash) must meet the following requirements: 240–
270 mm slump, slump flow of 600–750 and L-box flow velocity
(VL) of 35–80 m/s. When the VL is 80 m=s, the viscosity is too
high to resist segregation and when it is 35 m/s, the viscosity is
too high to attain self-compacting. In order to produce HSSCC with
UPFA, the following were recommended: fineness of 500–
600 m2
=kg, UPFA content of 30–40%, total SCM content
P 500 kg=m3
, minimum sand ratio of 40% and appropriate water
content at optimum SP content. In addition, a low yield stress,
moderate viscosity and retention of kinetic energy of the flowable
mix by reducing the coarse aggregate fraction is essential to
achieve required fluidity, segregation resistance and prevent inter-
particle collision and blocking.
Rahman et al. [155] reported that RHA produced from uncon-
trolled burning can be utilized in low-cost housing construction
project. The RHA concrete up to 40% exhibited sieve segregation
of 0.04–8.2%, slump flow of 580–670 mm, passing abilities of
5.9–7 s (v-funnel) and 3.5–5.2 which met the requirements of
SCC. Wu et al. [156] reported utilization of fly ash as viscous mod-
ifier in production of self-compacting LWC with good workability.
The concrete exhibited segregation ratio (SR) of 4.4–5.6% and
aggregate segregation index (Iseg) of 2.9–4.2%, both of which are
15% specified for SCC.
In addition, Yazıcı [157] obtained lower slump flow at 30% and
40% cement replacements compared to SF, higher slump flow at
50% cement replacement and equal slump flow at 60% cement
replacement. The slump flow values for FA and SF vary from
750–800 mm to 765–825 mm respectively.
Bingöl and Tohumcu [158] showed that FA achieved better fill-
ing and passing ability in self-compacting concrete (SCC) compared
to SF. Based on their slump flow values, FA-based SCC could be
used for normal applications such as walls and columns while
the SF-based SCC can be utilized in slightly-reinforced concrete
structures. Ternary and quaternary SCMs were also found to
improve the filling and passing ability of self-compacting concrete
and met all the EFNARC requirements [159].
Workability is the ease of handling, placing, compacting and
finishing fresh concrete [104]. The authors demonstrated that
workability of GPC reduced with inclusion of GGBFS and FA and
reduction of activator to binder owing to accelerated reaction of
calcium and angular and spherical shapes of GGBFS and FA parti-
cles. Duval and Kadri [160] recommended 10% SF as the maximum
replacement for cement without affecting workability of SFC.
Msinjili et al. [161] reported that workability of fresh concrete
can be improved with the aid of polycarboxylate ethers and ligno-
sulphonate while Karthik et al. [162] recommended the use of bio-
additives. Improved workability and prolonged setting time were
observed in their applications. Ismail and Waliuddin [163]
reported good workability of concrete with finely ground 20%
RHA replacement of cement and hard workability at 30% RHA.
On the other hand, Khatri et al. [48] reported that SF marginally
decreased workability of concrete but contributed significantly to
improved mechanical properties.
The properties of fresh cement pastes and concrete is affected
by hot weather conditions [164]. Likewise, IST and FST decreases
with curing temperature increase. Ujhelyi and Ibrahim [165] men-
tioned that the use of 40% GGBS along with ground tuff (a natural
pozzolana) up to 20% was useful in preserving the properties of
concrete during hot-weather concreting conditions.
For WGC, slump flow, flow ratio and v-funnel increased with
increasing WG content [166]. Slump flow values of 670–880 mm,
670–740 mm, and 670–780 were obtained at increasing cement
contents of 350 kg=m3
, 400 kg=m3
and 450 kg=m3
.
Vinai et al. [167] recommended water-solid ratio range of 0.37–
0.41 and binder content 400 kg=m3
to avoid fast initial concrete
setting and significant strength reduction. Boukendakdji et al.
[168] recommended polycarboxylate-based SP to improve worka-
bility of SCC at optimum GGBFS content of 15%. The authors
advised that care should be taken in the use of mineral additives
owing to their tendency to reduce early strength when used as
cement replacement.
Bleeding is the movement of water to the surface of freshly
placed concrete and is noticeable when surface water exists on
fresh concrete surface [169]. The negative effects of bleeding
include variable concrete properties. According to Wainwright
and Ait-Aider [170], bleeding is influenced largely by the particle
size distribution of cement, fine content in concrete mix as well
as cement reactivity. The authors reported similar bleeding
between combination of 40% GGBS + 60% OPC and 100% OPC.
5.2. Hard properties
5.2.1. Compressive strength
In order to enhance easy comparison, the compressive strength
(CS) results obtained by different researchers for different green

concrete were plotted in Fig. 8 while the materials used were given
in Table 1. The three highest CS of 92.1 MPa, 80 MPa and 79 MPa
were achieved using SF + ns, SF only and RHA after 90 curing days
[39,171]. SF was corroborated by Benaicha et al. [172] to produce
high CS of 82.9 MPa after 28 days curing age.
Addition of lime to HVFAC and cement to GPC (geopolymer con-
crete) were shown to aid their CS development [59]. Low CS were
recorded with geopolymers produced with alkali activators which
was attributed to their high Si=Al ratio [17,173]. Hwang and Huynh
[17] noted that the development of compressive strength depends
on appropriate combination of NaOH concentration and RHA
content.
Kumar and Gupta [174] recorded CS of 0.2 MPa with Ca/Si ratio
of 0.106, Shatat [175] reported CS of 63.7 MPa at Ca=Si ratio of 0.89
while Chindaprasirt et al. [173] recorded 38 MPa with Ca=Si ratio
of 7.98 and 0.026 before and after geopolymerisation. Thus, it can
be inferred that high CS is obtained at intermediate Ca=Si between
0.85 and 1.0. Therefore, it is suggested that chemically complimen-
tary waste materials should be utilized in blended concrete appli-
cations to achieve optimum results.
5.2.2. Flexural strength
Flexural strength results obtained by various researchers for
green concrete differs as depicted in Fig. 9 while the materials were
shown in Table 2. The highest flexural strength of 10:97 N=mm2
was obtained by Mohseni et al. [176] with quarternary system of
Cement + RHA + NanoA + PPO, followed by Patil and Sangle [177]
who utilized Cement + 20% FA + 1.5% Steel fibres + water reducing
admixture and then Sathawane et al. [178] who used ternary sys-
tem of Cement + Fly ash + RHA. The lowest flexural strength was
recorded by Walczak et al. [179] with waste glass.
Differences in their flexural strengths can be attributed to dif-
ferences in the concrete mix design, pre-loading condition, com-
pressive strength, SCM and aggregate materials utilized.
Fibre-reinforced mortar containing RHA, nano-alumina, and
polypropylene fibres (PPF) obtained the highest flexural strength.
The high flexural strength was attributed to the presence of PPF,
which improved the ductility of the mortar by providing bridging
action, which enhanced the fracture energy and consequently flex-
ural strength of the mortar. On the other hand, the nano-Al2O3 (NA)
enhanced the load transfer from the matrix to the fibre. These syn-
ergistic interactions were responsible for the high flexural strength
of the fibre reinforced mortar. Similar effect was observed in pre-
stressed steel fibre-reinforced concrete beams, which obtained
the second highest flexural strength. This implies presence of fibres
enhances the energy absorption capacity of concrete structures
and consequently their flexural strength. Enhancement of flexural
strength of concrete by nano-Al2O3, polypropylene and steel fibres
was also corroborated by other studies [180–182].
Concrete mortar containing waste glass (CRT) and fluidized fly
ash recorded the least flexural strength. This concrete mixture
lacked the benefits of the bridging action of the fibres as well as
load –transfer benefits caused by nano-alumina.
5.2.3. Splitting tensile strength and modulus of elasticity
Splitting tensile strength (STS) obtained by different researchers
were displayed in Fig. 10. The highest STS of 5:3 N=mm2
was
obtained by Jalal et al. [39] with SF and NS followed by
5:07 N=mm2
obtained using waste glass [86].
FA-blended cements recorded low splitting tensile strength
(STS) which was linked to reduction in the quality of the ITZ [57]
and in order to meet the minimum requirements for use in struc-
tural lightweight concrete, Kockal and Ozturan [126] recom-
0
10
20
30
40
50
60
70
80
90
100
Compressivestrengthatdifferentcuringdays
(MPa)
Different SCMs uƟlized in green concrete
7
28
90
Fig. 8. Compressive strength at different curing days for different SCMs utilized in green concrete.
Table 1
Materials utilized in different green concrete in Fig. 8.
Author(s) Waste materials used as SCM Type of green
concrete/mortar
Çakır and
Sofyanlı
[37]
SF + RAC Recycled aggregate
concrete
Jalal et al. [39] SF + NS HPSCC
Xu et al. [171] RHA 30 min RHA blended paste
Xu et al. [171] SF RHA blended paste
Xu et al. [171] Raw RHA RHA blended paste
Mohseni et al.
[176]
Cement + RHA + NanoA + PPO Fiber-reinforced
mortar
Mohseni et al.
[176]
RHA only Fiber-reinforced
mortar
Yang et al.
[207]
RHA + BOFS RHA-based
composite
Bog˘a et al.
[213]
GGBFS + CNI GGBFS modified
concrete
FA50 L HVFAC
Aliabdo et al.
[86]
25%addition of waste glass powder
(45 MPa cement)
Glass powder
mortar
Aliabdo et al.
[86]
25%cement replacement with WG
powder (45 MPa cement)
Glass powder
mortar

mended curing period between 50 and 90 days. Benaicha et al.
[172] observed increase in modulus of elasticity (MOE) in SF-
modified concrete with increasing SF contents while Tatikonda
[183] recommended optimum RHA content of 5% to obtain maxi-
mum MOE irrespective of the cement/concrete grade used as dis-
played in Fig. 11.
In addition, Chik et al. [184] reported increase in MOE with
increasing rice husk content and recommended 15% optimum
RHA cement replacement which also gave the highest compressive
strength of 6:70 N=mm2
. Siddique and Kaur [185] reported that
MOE reduced with increasing elevated temperatures but increased
with GGBFS content as displayed in Fig. 12. Abdallah and Fan [145]
observed increase in MOE with curing age and with increased
waste glass content in concrete which was attributed to the higher
MOE of waste glass compared to natural glass.
5.2.4. Shrinkage and creep
Rovnaník et al. [186] reported increased shrinkage with
increased brick powder waste content because of the high water
absorption of brick powder waste as shown in Fig. 13. Kayali
[187] reported 33% reduction in shrinkage with fly ash aggregate
as well as 22% reduction in weight and 20% increase in strength.
This implies fly ash aggregate can be utilized in the production of
stronger and lighter green concrete with reduced transportation
costs especially for precast elements. Also, results by Haranki
[188] revealed that care must be taken in the selection and prepa-
ration of aggregate to be utilized in green concrete to minimize
shrinkage in green concrete.
According to Serdar et al. [189], the four major types of shrink-
age are plastic shrinkage, carbonation shrinkage, autogenous
0
2
4
6
8
10
12
Flexuralstrengthatdifferentcuringdays(MPa)
7
28
90
Fig. 9. Flexural strength at different curing days for different SCMs utilized in green concrete.
Table 2
Materials utilized in different green concrete in Fig. 9.
Author(s) Waste materials used as SCM Type of green concrete/mortar
Jalal et al. [39] SF + NS HPSCC
Mohseni et al. [176] Cement + RHA + NanoA + PPF Fiber-reinforced mortar
Mohseni et al. [176] RHA only Fiber-reinforced mortar
Yang et al. [207] RHA + BOF RHA-based composite
Benaicha et al. [172] Cement + Limestone filler + SF30 Self-compacting concrete
Benaicha et al. [172] Cement + Limestone filler Self-compacting concrete
Sathawane et al. [178] 22.5%FA + 7.5%RHA RHA + FA modified concrete
Walczak et al. [179] Cement + CRT80%+20%FFA + Expanded clay Waste glass concrete
Walczak et al. [179] Cement + CRT100%+Expanded clay Waste glass concrete
Patil and Sangle [177] Cement + 20%FA + 1.5%Steel fibres Prestressed steel fibre reinforced concrete beam
Patil and Sangle [177] Cement + 20%FA + 1.5%Steel fibres Non- Prestressed steel fibre reinforced concrete beam
Patil and Sangle [177] Cement + 20%FA + 0%Steel fibres Prestressed plain concrete beam
Karri et al. [138] GGBFS40% (M40) GGBFS concrete
Karri et al. [138] GGBFS40% (M20) GGBFS concrete
0
1
2
3
4
5
6
7
8
SF+RAC SF+NS WG
addiƟon
WG FA+RHA GGBFS GGBFS
Spliƫngtensilestrengthatdifferent
curingdays(N/mm2)
7
28
90
Fig. 10. Splitting tensile strength at different curing days for different SCMs utilized
in green concrete.

shrinkage and drying shrinkage. While the first two were caused
by poor curing and carbonation, the last two were caused by drying
and moisture loss. Creep is induced significantly by internal rela-
tive humidity (IRH) and increased with increasing RHA content
in concrete [190]. Addition of 10% SF was suggested to minimize
shrinkage and cracking potential of UHPC [191]. 15% RHA was rec-
ommended for optimum creep reduction. Creep reduction of
5560% can be achieved using HVFA of 55–65% fly ash content
[192].
Barrett et al. [193] suggested the use of pre-wetted LWAs in
HVFAC to induce internal curing effect resulting in improved
early-age strength as well as reduction in autogenous shrinkage
and tensile stresses. Atisß [194] stated that high strength HVFAC
with lower shrinkage compared to OPC and lower water consump-
tion can be utilized in construction of road pavement and large
industrial floors. Ling [195] recommended the use of limewater
and ultra-fine fly ash to augment the low-strength development
of HVFAC.
Drying shrinkage has a non-linear relationship with ambient
relative humidity (RH) [196]. The authors also reported that aggre-
gate grading and maximum aggregate size affects shrinkage strain.
The non-linear relationship grows with increasing aggregate size.
Drying shrinkage strain of ambient-cured specimens were com-
pared to heat-cured specimens [197].
Serdar et al. [189] recommended the utilization of quaternary
cement blends (FA, slag limestone) to obtain shrinkage and creep
deformation similar to CEM II cement and to minimize negative
impact of binary SCMs in concrete. In addition, Wallah and Rangan
[197] reported that the specific creep of FA-based GPC was that of
Portland cement concrete (PCC) because of block-polymerisation
concept. The concept describes the behaviour of the fly ash atoms
which acts as micro-aggregates in the system resulting in the
increase in the creep resistance of FA-based GPC compared to
PCC. The specific creep was observed to reduce with CS. This rela-
tionship was also reported by Folliard et al. [198]. The authors also
mentioned that early age creep tends to be higher than at later
ages. Wallah [199] reported that creep strain, creep coefficient
and specific creep of FA-based GPC decreased with increasing CS.
High creep strains were observed at early ages of HVFAC
because of slow strength development [62,200]. The low creep
strains of HVFAC was attributed to the ‘micro-aggregate effect’ of
the unreacted FA remaining in the concrete. As much as 50% creep
reduction was reported by combined effect of SP and HVFA [201].
Strain due to both creep and shrinkage is due to removal of
adsorbed water, applied stress, pore refinement and increase in
fine pores, and improvement in microstructure of the ITZ [48]. SF
decreased specific creep at all ages and long-term drying shrinkage
as well.
Gifford and Ward [202] reported that fly ash reduces creep by
increasing the elastic modulus and contributing to the total aggre-
gate as well as reduction of paste volume. Yuan and Cook [203]
reported high creep strain at high cement replacements with fly
ash while Lohtia et al. [204] recommended 15%FA replacement of
cement as optimum for strength, elasticity, shrinkage and creep.
Contrary to literatures, Klausen et al. [205] observed that FAC of
17% and 33% FA contents exhibited similar compressive and tensile
creep behaviour throughout the hardening phase. In addition, the
specific creep development was found to increase with fly ash
content.
Since water plays a crucial role in creep mechanism, addition of
SF is useful in restricting moisture movement [191]. However, the
authors reported that there is no interaction between creep and
shrinkage. According to Forth [206], tensile creep is about 2–3
0
5
10
15
20
25
30
35
40
45
50
0 5 10 15
ModulusofelasƟcityfordifferent
concretegrade(GPa)
Rice husk ash content (%)
60
80
100
Fig. 11. Modulus of elasticity for different concrete grades of RHA-modified
concrete [183].
0
5
10
15
20
25
30
35
40
45
50
0 20 40 60
ReducƟoninModulusofelasƟcityat
differentelevatedtemperature(%)
GGBFS cement replacement (%)
100
200
300
Fig. 12. Reduction in modulus of elasticity at different elevated temperature (°C) at
different GGBFS content [185].
0
1
2
3
4
5
6
04:00 03:01 1.5:1.5 00:04
Shrinkage(%)
Fly ash/Brick powder raƟo
Fig. 13. Effects of brick powder content on shrinkage [186].

times greater than compressive creep and that both are affected by
relative humidity. The author also reported that ultimate tensile
creep has a decreasing non-linear relationship with compressive
strength for different applied stresses and that the presence of
microcracks in the ITZ enhances tensile creep.
5.3. Durability properties
5.3.1. Water absorption and porosity
Yang et al. [207] recommended a maximum cement replace-
ment levels 6 60% in order to avoid adverse impact on the perfor-
mance of the concrete as a result of increased water demand of the
SCM. It was also noted that water absorption of ternary blends
cement comprising RHA and BOF produced by Yang et al. [207]
was less than that of ternary blend derived from fly ash and lime-
stone by Shafigh et al. [57].
Parghi and Alam [208] observed that water absorption reduced
with increase in recycled glass powder content while bulk density
decreases. Aliabdo et al. [59] reported that cement addition caused
decrease in both water absorption and porosity of GPC as revealed
in Fig. 14.
In another study by Aliabdo et al. [86], water absorption and
voids ratio was found to reduce with increase in waste glass pow-
der addition as a result of the pore filling and pozzolanic action of
waste glass powder. Investigation by Binici [209] revealed that
water absorption reduces with increase in alkali activation temper-
ature but the reduction exhibited differs from one material to
another as depicted in Fig. 15.
Tian and Zhang [210] reported that water absorption and
apparent porosity varies with different curing ages and fly ash-
cement ratios as displayed in Figs. 16 and 17. This implies that
SCM-cement ratio, the apparent porosity and water absorption of
the SCM used in a green concrete affects their mechanical perfor-
mance. Hesami et al. [21] also reported decrease in porosity with
increase in RHA combined with PPS, glass and steel fibres irrespec-
tive of water-cement ratio and recommended optimum RHA con-
tent of between 8 and 10% and water-cement ratio of 0.33.
Momtazi and Zanoosh [211] reported that waste rubber tire and
polypropylene fibre (PPF) can be used to reduce water absorption
of RHA-cement composite.
5.3.2. Chloride penetration and alkali silica reaction (ASR)
Siddique et al. [212] reported improved resistance to chloride
penetration with bacterial rice husk ash concrete (BRHAC) com-
pared to results obtained by Bog˘a et al. [213] as shown in Fig. 18
and recommended 10% RHA replacement of cement as optimum
value. Gastaldini et al. [34] revealed that lower chloride penetra-
tion was obtained at lower water/cement ratio of 0.5 compared
to 0.65 and that chloride penetration control of RHA was higher
compared to SF (see Fig. 19).
Parghi and Alam [208] recommended inclusion of 25% recycled
glass particle of size 300 lm in combination with 10% FA+ 10% SF
to make superior mortar with ASR expansion 10% specified by
ASTM C1260. Abdallah and Fan [145] reported increased reduction
in ASR expansion with increased waste glass content as natural
sand replacement with curing age. This occurrence was attributed
to reduction in available alkali due to the consumption of lime by
the silica in the finely grounded waste glass.
SF was also observed to exhibit about 40% and 14.3% chloride
penetration resistance more than RHA at the same cement replace-
ment ratio of 5% and 10% and w=b ratio of 0.6 and 3 days curing age
[34]. Chloride penetration resistance of 11.9% and 50% for RHA and
52.4% and 64.3% for SF at 5% and 10% cement replacements respec-
tively were recorded at 91 days–3 days curing age.
Hassan et al. [214] reported that SF achieved lowest chloride
penetration compared to FA and OPC at both early ages but compa-
rable characteristics with SF at long-term ages. In HPC, SF was
found to contribute more to permeability reduction (87%) and pore
reduction (25%) than CS. Rostami and Behfarnia [215] reported
chloride penetration resistance of 26.7%, 38.5% and 49.6% at 5%,
10% and 15% SF replacement of cement.
Zareei et al. [216] achieved 78.4% reduction in chloride penetra-
tion in HPC containing 25% RHA replacement of cement and 10%
microsilica from 4306 Coulumbs to 928 Coulombs. [157] achieved
52.36% reduction in chloride penetration from 19 mm to 9.5 mm
through the use of HVFA SCC containing 60% FA and 10% SF. They
reported that concrete cover of 20 mm concrete cover is not suffi-
cient to protect steel reinforcement from chloride ingress even in
high quality SCC.
Matos and Sousa-Coutinho [217] reported that SF and WG were
effective in reduction of ASR. A reduction of 76.85% reduction was
achieved at 20% WG content. Waste glass powder also achieved
52.47% reduction in chloride diffusion in mortar. An optimum of
10% WG content was recommended to achieve best durability
properties [152].
Siddique and Bennacer [169] reported improved chloride bind-
ing capacity with increasing GGBS content but it is affected by the
presence of sulfates. Cheng et al. [218] reported 81.9% chloride
penetration resistance using 60% GGBS replacement of cement at
w/cm ratio of 0.55 from 10271coulombs to 1864 coulombs. The
improvement in chloride penetration resistance was attributed to
pore refinement and densification of the concrete system.
Cracking potential can be minimized by limiting unrestrained
shrinkage of concrete mixtures [219]. Their results showed that
FA exhibited the greatest drying shrinkage compared to nanosilica
and GGBS cement. Also, chloride penetration was observed to
reduce with increasing curing age, increasing cement replacements
0
2
4
6
8
10
12
0% 5% 10% 15%
WaterabsorpƟon(%)
Porosity(%)
Cement addiƟon to Geopolymer concrete (%)
WA
Porosity
Fig. 14. Effects of cement addition in geopolymer concrete [59].

with RHA and SF but reduced with increasing w/b ratio. Balapour
et al. [220] reported that combination of nano-RHA (2.5%) and
micro-RHA (12.5%) produced the best chloride penetration resis-
tance. In fact, their combination achieved chloride penetration
resistance of 71.2% at 90 days compared to control. This value
was higher than 36.2% recorded by 2.5% nano-RHA utilized alone.
From the results above, it seems the order of preference in
terms of resistance to chloride penetration is GGBS RHA SF
FA WG. However, experiments are required to check or confirm
this order of preference for chloride penetration resistance using
the same experimental conditions such as similar cement replace-
ment levels, w/cm ratio, curing age at testing, amongst others for
accurate comparison purposes.
Alkali silica reaction is a concrete durability problem where sil-
ica forms in aggregates react with alkali pore solutions to form
expansive reaction products, resulting in deleterious concrete
cracking [221]. Effectiveness of any SCM to mitigate ASR depends
on the SCM composition (SiO2 and alkali content), SCM %, type of
alkali aggregate reaction, type and fineness of alkali-contents of
cement [222]. SCMs reduce ASR through pozzolanic reaction which
0
2
4
6
8
10
12
14
GGBFS Fly ash Silica sand Pumice
WaterabsorpƟon(%)atdifferent
acƟvaƟontemperature
Different materials used as alkali acƟvators
100
150
Fig. 15. Water absorption for different materials at varied activation temperatures (°C) [209].
0
5
10
15
20
25
28 days
3 months
6 months
10 months
WaterabsorpƟonatdifferentfly
ash-cementraƟos(%)
Water curing ages
1.2
1.6
2
Fig. 16. Water absorption of fly ash/bagasse composite at different curing ages and
fly ash-cement ratios [210].
21
22
23
24
25
26
27
28 days 3 months 6 months 10 months
Apparentporosityatdifferentflyash-
cementraƟos(%)
Water curing age
1.2
1.6
2
Fig. 17. Apparent porosity of fly ash/bagasse composite at different curing ages and
fly ash-cement ratios [210].
0
2000
4000
6000
8000
10000
12000
RHAC BRHAC GGBFS+CNI GGBFS+CNI GGBFS
Rapidchloridepermeabilityatdifferent
curingdays(Coulombs)
Different SCMs used in green concrete
7
28
56
90
Fig. 18. Rapid chloride penetration at different curing days for different SCMs.
0
10
20
30
40
50
60
0% 30% 40% 50%
Compressivestrengthatdifferent
curingages,differentconcretegrades
differentacidsoluƟons(N/mm2)
GGBFS replacement of cement
28M40H2SO4
28M40HCl
28M20H2SO4
28M20HCl
90M40H2SO4
90M40HCl
90M20H2SO4
90M20HCl
Fig. 19. Compressive strength at different GGBFS cement replacements, different
curing age, different grades of concrete in different acid solutions [138].

reduces concrete permeability and ASR consumption of available
alkali ions [223].
According to Christopher et al. [221], contrary views were pre-
sented concerning the effects of RHA on ASR in concrete. While
Hasparyk et al. [224] recommended between 12 and 15% of RHA
to control ASR, Le [225] reported that RHA contributes to ASR by
acting as micro-reactive aggregate to produce expansive ASR prod-
ucts. This contradiction was resolved by Zerbino et al. [226] who
reported that RHA can inhibit or promote ASR depending on its
particle size. Therefore, the authors recommended careful selection
of cement, equipment and mixing cycle, as well as adaptation of
the mixing process. In another study which spanned three years,
they observed stable mechanical properties at alkali contents
(Na2O) 3 kg=m3
. Their results were corroborated in another
study which revealed that RHA produced through controlled incin-
eration exhibited stronger ASR inhibition effect compared to resid-
ual RHA produced via uncontrolled burning [227]. ASR reductions
of 51.4% and 83.8% were obtained at 10 and 20% CRHA (RHA from
controlled burning) while reductions of 2.7%, 37.8%, 70.3% and
94.6% were produced at 10% 20%, 30% and 40% RRHA (RHA from
uncontrolled burning) cement replacements in mortar bars at w/
cm ratio of 0.47.
Le [225] reported that SF was more effective than RHA in miti-
gating ASR expansion in mortar. The suggested the use of RHA of
fine particle size 5.7 lm to mitigate ASR expansion.
At 20% cement replacement with SF, FA, WG, CRHA and RRHA,
the ASR expansion obtained were 0.01%, 0.02%, 0.02%, 0.06% and
0.23%, which corresponded to percentage reductions of 88.9%,
66%, 83.8% and 37.8% for FA, WG, CRHA and RRHA [64,88,227].
Furthermore, Oberholster and Westra [228] reported that SF
performed better than FA in mitigating ASR. At 20% cement
replacement, they obtained ASR values of 0:03%, 0:02% and 0.2
for SF, FA and cement. These results correspond to ASR reductions
of 85% and 65% respectively with reference to the control, which
lends credence to the superiority of SF over FA in mitigating ASR.
In another study, Buck [229] recorded ASR values of 0:15% and
0.47 at 30% GGBS cement replacement and 0% (control), which
corresponds to ASR reduction of 68:1%. Therefore, from the results
above, it seems the ranking of the SCMs in terms of ASR mitigation
is SF FA CRHA GGBS WG RRHA. Nevertheless, confirma-
tory laboratory and field investigations are required to confirm this
order of ranking.
Lindgård et al. [230] mentioned that SCMs low in calcium and
high in silica are the most effective in reducing pore solution alka-
linity and consequently ASR expansion. The authors called for reli-
able methods for satisfactory, accelerated and affordable testing
methods that resembles field conditions such as humidity, alkali
content and temperature.
ASR expansion was reported to decrease in concrete when WG
was utilized as fine aggregates as a result of reduction of available
lime [88]. ASR reductions of 66%, 41:7% and 16:7%were obtained
at 20%, 15% and 10%WG replacement of fine aggregate.
ASR expansion was investigated between 25 and 100% cement
replacements [231] and was found to depend on WG content and
glass colour. They recommended the use of FA and Li2CO3 for
reduction of ASR expansion. In contrast, Özkan and Yüksel [232]
mentioned that glass colour does not have significant influence
on both ASR and elevated temperature resistance. They advocated
the utilization of FA and GGBFS to reduce ASR expansion.
5.3.3. Fire-resistance and chemical attack properties
Karri et al. [138] investigated the effects of chemical acid attack
on GGBFS modified concrete at different curing ages using two
grades of concrete (20 and 40 MPa). CS increased for some of the
concrete as shown in Fig. 13 and may be due to chemical reactions
of the acid with the GGBFS and other concrete constituents. It was
suggested that GGBFS cement replacement should not exceed 40%
with respect to durability considerations and that the acid seems
to promote pozzolanic reactions in the GGBFS modified concrete.
SF had considerable influence on residual CS at 300°C.
Strength retention was 84:1%, 85:2%, 68:8% and 26:8% at 10%
SF replacement of cement in SFC, at elevated temperatures of
100, 200, 300 and 400°C. Their strength retention was greater than
the corresponding values of 84:1%, 85:2%, 68:8% and 26:8% exhib-
ited at 6% cement replacement [233]. The strength loss was attrib-
uted to weakening of the ITZ weakening of the bonding between
aggregate and paste and chemical decomposition of hydration
products. Also, strength recovery of 1.3–3.7% was observed at
200 °C. in all the concretes.
Bernal et al. [234] reported strength retention of 94:5%, 60:9%,
and 47:3%, for SF and 103:6%, 46:4%, and 48:2%, for RHA at
200 °C., 400 °C and 600 °C. The results showed that SF exhibited
higher strength retention than RHA. Only RHA-based system
retained measurable strength after 800 °C.
Rashad [235] reported CS of 45.92 MPa for HVFAC at 70% FA
replacement of cement and 400 °C., which was lower compared
to 67 MPa and 52 MPa for SF and RHA in alkali-activated pastes
reported by Bernal et al. [234] at the same temperature. In addi-
tion, increase in CS was observed at 400 °C in all the mixtures
and was attributed to the densification of the matrix. The increas-
ing strength loss recorded from 400 to 1000 °C. was attributed to
loss of water, increasing porosity and permeability. In addition,
HVFAC exhibited better fire performance compared to neat con-
crete while inclusion of GGBS showed negative effects on CS at ele-
vated temperature.
FA-GP showed low thermal stability at elevated temperatures
between 800 and 1000 °C, which was attributed to increase in
average pore size and replacement of amorphous structure with
crystalline Na-feldspars [98]. The Class F fly ash-based GP prepared
using Na activator recorded CS of 30 MPa, 33 MPa, 37 MPa, 38 MPa,
14 MPa and 12 MPa at 200 °C, 400 °C, 600 °C, 800 °C, 1000 °C and
1200 °C respectively. On the other hand, FA-GP prepared using
potassium silicate exhibited deterioration of CS after 1000 °C,
while the amorphous structure remained. This demonstrates that
Class F fly ash-based GP materials cannot be utilized in refractory
insulation applications as a result of the large reductions in CS
and high shrinkage between 800 °C and 1200 °C.
HSC made with SF ð15:4%Þ and FA (38:5% of cement content)
experienced CS reduction of 74:4% from 97.3 MPa to 24.9 MPa at
elevated temperature of 800 °C [236]. On the other hand, normal
concrete (NC) showed 54:7% reduction in CS at the same temper-
ature. The deterioration in both HSC and NC was linked to variation
in the pore structure.
HSC containing 9% SF wt. of cement recorded CS marginal
strength loss between 100 and 400 °C and significant loss between
55 and 80% after 400 °C [237]. Janotka and Nürnbergerová [238]
reported strength deterioration between 100 and 200 °C in HSC
with SF content of 7:53% by wt of cement at w=c ratio of 0.32
and was linked to pore-structure coarsening. Kong et al. [239]
reported that FA-GP pastes recorded 6% strength increase at CS
of 62.8 MPa and 11% mass loss at elevated temperature of
800 °C, compared to unexposed specimens. The CS increase was
attributed to the low moisture loss, presence of high proportion
of micropores and high solid-to-liquid ratio.
Reported that fly ash-to-activator ratio is the most critical
parameter for fire resistance and strength development in GPs
and suggested optimum combination of Na2SiO3=KOH of 2.5 and
FA=activator of 2.5. Increase in strength of GPs at elevated temper-
atures was attributed to both polymerization reaction and sinter-
ing. In another study, Kong and Sanjayan [240] revealed that

aggregate size and their rate of expansion are influential parame-
ters which affect the performance of GPC ate elevated temperature.
While small aggregates (10 mm) promote spalling and extensive
cracking, large aggregates (10 mm) were observed to be stable.
Pan et al. [241] reported 15% strength loss at temperatures
500 and 56% between 500 and 800 °C in fine glass powder mor-
tar. The strength loss was attributed to reduction in calcium
hydroxide (CH) in GP mortar, softening of glass content and higher
incompatibility between paste and sand particles.
Poon et al. [242] reported that PFA (pulverized FA) followed by
GGBS exhibited better performance at elevated temperature com-
pared to SF in concrete and could be utilized where there is high
risk of fire. Optimum cement replacements of cement by FA and
GGBS in HSC and NSC to retain maximum strength and durability
were 30% and 40% respectively [242]. In contrast, SFC with more
than 5% cement replacement should be avoided because of
explosive spalling.
Based on the results, the order of preference in terms of CS per-
formance at elevated temperature was FA GGBS SF. Average
strength loss were 44% and 60% in FA- and SF-based HSC and
GGBS-based NSC.
Rashad et al. [243] reported increasing residual strength at ele-
vated temperatures when GGBS was used as sand replacements in
AAS (alkali activated slag) mortar. Residual strength losses
obtained at 800 °C were 33:45%, 51:91%, 69:49%, and 90%, at
25%, 50%, 75%, and 100%, replacement of sand respectively. Also,
enhancement in residual strength at 200 and 400 °C were 19:31%,
79:26%, 89:73%, and 100:95%, and 20:89%, 64:28%, 71:86%, and
82:58%, at 25%, 50%, 75%, and 100%, replacement of sand respec-
tively. No micro-crack was found in the AAS mortar throughout all
the elevated temperature tests.
Tanyildizi and Coskun [244] investigated LWC incorporating 0,
10, 20, and 30% FA replacement of cement at elevated temperature
of 200, 400 and 800 °C. CS ranges of 38–48 MPa, 35–38 MPa and
14–23 MPa were recorded at 200, 400 and 800 °C. The percentage
retained strength obtained ranges from 91.09–98.95%, 80.23–
92.6% and 36.13–43.64% at 200, 400 and 800 °C respectively. The
loss in CS was linked to loss of hydration water at elevated temper-
atures. With respect to the splitting tensile strength (STS), the per-
centage STS retained ranges from 87.84–91.85%, 81.94–85.55% and
23.55–43.15% at 200, 400 and 800 °C respectively. Based on
ANOVA analysis, the most important experimental parameters
for STS and CS of FAC were heating degree and fly ash content
and their percentage contribution to CS development were
93:41% and for CS and 89:39% and 4:84%. In order to achieve opti-
mum CS and STS, the optimum FA content recommended was 30%.
Concrete made with fine waste glass replacing fine recorded the
highest CS compared to coarse WGC and combination of fine and
coarse WG [245]. Optimum WG content to achieve maximum CS
at both ambient and elevated temperature was 10% aggregate
replacement for the three combination types. CS of the three con-
crete converged close to 700 °C because of its closeness to the
melting temperature of waste glass, which is between 700 and
800 °C and the elimination of size effect in the softened state of
the glass aggregates. CS obtained for the fine WGC were 40.5, 35,
55, 42, 34.5 and 22 at 20, 60, 150, 300, 500 and 700 °C.
Pulverized FAC expressed relative strength improvement at 450
and 650 °C even though durability deteriorated from 250 °C [246].
CS loss was attributed to increased width of ITZ, increased total
porosity and coarsening of the hardened cement paste.
RHA is more effective than FA in resisting sulphate attack of
binary cement mortars. Surprisingly, the RHA mortar experienced
strength enhancement of 7% compared to 0% for FA after 90-day
immersion in 5% sodium sulphate solution and at 20% cement
replacement [247]. However, fly ash experienced higher strength
improvement of 8:8% compared to RHA which recorded 24:6%
strength reduction both at 40% cement replacement after 90 days.
Optimum RHA and FA replacement of cement to ensure CS reten-
tion and development is 20% and 40% respectively.
Chatveera and Lertwattanaruk [248] recommended 20% RHA
replacement of cement durability improvement in concrete and
enhancement of resistance to HCl and H2SO4. The resistance to acid
attack was observed to be directly proportional to the
ðSiO2 þ Al2O3 þ Fe2O3Þ=CaO ratio. The improved resistance of RHA
was also corroborated was attributed to the densification of its
microstructure, physical and pozzolanic effect as well as presence
of Al2O3 [227]. Strength improvement was also recorded at 25%
RHA replacement of cement with 0.1 H2SO4 [249].
Chemical resistance of FA and SF to several chemical such as
H2SO4, HNO3, acetic acid, H3PO4, Na2SO4, and MgSO4 was investi-
gated by [250]. They reported that SF had superior resistance at
higher cement replacement from 15%. SF exhibited lower strength
loss of 16:6% and 17:8% compared to 23:5% and 38:9% for FA at
15% and 22:5% cement replacements respectively.
Chemical resistance of FA is influenced by its fineness. CS
increased from 41.5, 53.5, 56, and 61.5 MPa for increasing Blaine
fineness of 3000, 3900, 4800 and 9300 cm3
/g [251]. The optimum
replacement level to achieve chemical acid resistance varies
depends on the type of acid and alkaline solutions involved
[252]. It seems the chemical acid resistance of FA was more effec-
tive at higher replacements compared to SF. The sulfate resistance
was linked to the prevention of ingress of sulfate ions into con-
crete, resulting in little formation of gypsum and/or ettringite in
concrete [253]. The level of resistance to chemical attack increases
with increasing cement content, lowering of w=c ratio and the uti-
lization of cement with C3A (tricalcium aluminate) content 7%
[254].
Chemical resistance of GGBS depends on high reactivity in the
presence of lime, availability of Ca in the pore solution and its dis-
tribution in the specimen [255]. GGBS performed better than FA on
exposure to leaching and sulphate attack [256]. The authors
reported that hydration of C3S and C2S in cements resulted in for-
mation of portlandite, which when released, facilitates ingress of
sulphate ions and produce expansive products such as gypsum
and ettringite. Likewise, GGBS performed better than FA in resist-
ing attack from MgSO4 as it recorded the higher CS28 [257].
Up to 50% GGBS can be used in concrete to achieve good
sulphate-resisting properties, minimize carbonation as well as
thermal cracking [258]. Also, concrete containing up to 70% GGBS
showed good resistance to thaumasite form of sulphate attack
(TSA) and their resistance was improved with the addition of small
amounts of calcium carbonate or calcium sulfate [259,260]. GGBS
exhibited stronger resistance to sulphate attack compared to fly
ash and the optimum cement replacement for GGBS was 40%
[261]. Even though GGBS has good resisting capability, O’Connell
et al. [262] pointed out that GGBS should not be utilized in
wastewater infrastructures because it cannot withstand the high
levels of sulphate and sulphuric acid attack.
Waste glass improved durability of WGC by maintaining weight
stability during sulphate attack [263]. In addition, field studies cov-
ering 6.7 years showed continuous improvement in mechanical
performance of slabs and walls made with WGC [264]. Glass fume
made from WG particles were observed to exhibit higher resis-
tance to sulphate attack [265].
Ganjian and Pouya [266] reported that OPC concrete performed
better than SFC when exposed to tidal environment while mixture
of SF and GGBS exhibited worse performance. Makhloufi et al.
[267] reported that mortar made with quaternary blends including
GGBS showed improved sulphate attack resistance than OPC con-
crete. Aziz et al. [268] reported that up to 30% GGBS improved
the durability of sulphate resisting cement (SRC) and can be used

to produce highly durable concrete. The improvement was attrib-
uted to decrease of total pore volume, free lime content, total chlo-
ride, total sulphate contents and, subsequently, increase in the
resistivity towards sulphate and chloride ions.
From the above results, it seems the preferable ranking of the
SCMs in terms of resistance to sulphate attack was
WG SF GGBS FA RHA. However, confirmatory laboratory
and field investigations are suggested to check this ranking.
6. Factors that influence properties of green concrete
6.1. SCM chemical composition
Comparison of the chemical composition of the five (5) different
SCMs and OPC revealed that, on the average, SF has the highest SiO2
(silica content), followed by RHA. Also, it was observed that fly ash
recorded the highest Al2O3 (alumina) content followed by GGBFS.
In terms of CaO (calcium oxide) content, OPC recorded the highest
value followed by GGBFS as depicted in Fig. 20.
6.2. Water/binder (w/b) ratio
Hu et al. [14] observed that higher water/cement ðw=cÞ ratio
leads to lower Ca=Si ratio, large pores, higher porosity of the C-S-
H gel which causes lower elastic modulus and lower hardness.
The authors recommended lower water-cement ratio and incorpo-
ration of admixtures to improve mechanical properties of cementi-
tious materials. The connection between lower porosity and lower
w/b ratio was also corroborated by Gao et al. [269] who also
observed that ITZ porosity decreases with increasing curing age,
decreasing water ratio and increasing aggregate content. Both
Hesami et al. [21] and Lian and Zhuge [270] recommended 0.33
as the optimum w=c ratio for pervious concrete pavement to
ensure full hydration and formation of strong cement pastes.
6.3. Curing medium
Yazıcı et al. [271] demonstrated that curing condition affects
the mechanical performance of reactive powder concrete (RPC).
Autoclaved curing gave the highest flexural strengths compared
to steam curing and standard curing as shown in Figs. 21 and 22.
Bog˘a et al. [213] also reported that increasing the curing periods
and applying standard water curing method resulted in significant
improvement in the mechanical properties of the concrete. Nath
and Sarker [272] reported that even though heat-curing provided
early-age strength, it is not replicable at available cast-in situ
construction.
According to Neupane [65], elevated temperature curing is not
cost-effective and practicable. Furthermore, results obtained by
Binici et al. [128] and Shafigh et al. [57] depicted in Fig. 23 revealed
that water curing obtained the highest CS at 90 days curing age
compared to autoclaving curing. Therefore, water curing is recom-
mended for curing green concrete to enable full hydration, chemi-
cal reaction and bonding of the constituents.
7. Binary, ternary and quarternary SCM mixtures
The concept of binary, ternary and quaternary SCM is to obtain
blended SCM with properties that are superior than the individual
SCM constituents. Utilization of such blended cements overcomes
the drawbacks associated with any of the individual constituent
and maximizes their individual strengths or advantages. While
Rakhimova and Rakhimov [66] recommended a component-wise
approach in the development and application of sustainable
cement and green concrete, Wang and Chen [273] presented a
simplex-centroid design method in determining the proportion of
various ternary blend SCM mixtures to achieve target strengths,
thereby reducing the need for trial and error mixes.
Mohamed [274] recommended ternary mix of cement with 10%
FA and 10% SF which obtained highest compressive strength in
SCC. Le and Ludwig [32] recommended ternary combination of
20% FA and 20% RHA to produce CS58 of approximately 130 MPa
which was recommended for usage in self-compacting high perfor-
mance concrete (SCHPC) which increased plastic viscosity and seg-
regation resistance but eliminated bleeding.
Deb et al. [275] investigated blending of GGBFS with low-
calcium Fly ash (Class F) and observed that the shrinkage reduced
with the increase in slag content and decrease in sodium silicate to
sodium hydroxide (SS=SH) ratio in GPC at room temperature.
In order derive the optimum benefits from the use of SCMs, it is
expedient that the combination and proportion of selected SCMs
for binary, ternary and quarternary SCM mixtures should be prop-
erly selected to maximize the synergistic positive effects and min-
imize or avoid the synergistic negative impacts. This is achievable
to some extent by taking into consideration the elemental compo-
sition of each SCM selected for combination, the individual
physico-chemical characteristics of each SCM and their effects on
concrete/mortar properties from available literatures.
0
20
40
60
80
100
SiO2 Al2O3 Fe2O3 CaO MgO SO3 Na2O K2O P205 TiO2 LOI
ComposiƟon(%)
Chemical composiƟon
FA WG GGBFS RHA SF OPC
Fig. 20. Comparison of chemical composition of different SCMs and OPC (Authors).

8. Nomenclature and applications of green concrete utilized in
concrete structures
Existing literatures on green concrete revealed the existence of
different nomenclatures for green concrete depending on the SCM
utilized, properties of the green concrete such as compressive
strength, performance levels, compactability and density as
depicted in Fig. 24. They include HVFAC (high-volume fly ash con-
crete), UHPC (ultra-high performance concrete), HPC (high perfor-
mance concrete), ultra-high strength concrete (UHSC), HSC (high
strength concrete), SCC (self-consolidating concrete), LWC (light-
weight concrete) and geopolymer concrete (GPC).
8.1. HVFAC (High volume fly ash concrete)
High-volume fly ash concrete (HVFAC) are concrete mixtures
containing a minimum of 40–50% fly ash by mass of cementitious
materials [133,276]. HVFAC with 50% cement replacement with fly
ash C was utilized in the construction of Computer Science Build-
ing at York University and Lower Notch Dam in Ontario, Canada
and Bayview high-rise apartment and was recommended for com-
mercial and residential construction applications [61,277].
The strength development of HVFAC depends on fly ash replace-
ment levels, water-to-cementitious material ratios and volume of
cement paste [278]. While Rashad [279] recommended usage of
fly ash as partial or full replacement of natural fine aggregate in
HVFAC where fly ash is abundantly available and there is shortage
of natural sand as fine aggregate, Li [106] recommended the addi-
tion of nano-SiO2 as an accelerating additive to facilitate the poz-
zolanic properties of fly ash to improve the early and long-term
strength gain.
Mehta [280] classified HVFAC into three categories namely low,
moderate and high strength HVFAC with minimum CS28 of 20, 30
and 40 and corresponding water-cement ratios of 0.9–1.3, 0.72–
0.83 and 0.5–0.7 respectively.
0
5
10
15
20
25
30
35
20 40 60
Flexuralstrength(Mpa)
GGBFS replacement of silica fume (%)
Bauxite Steam cured
Bauxite Autoclaved cured
Granite steam cured
Granite Autoclaved cured
Fig. 21. Effect of curing condition on Flexural strength and aggregate type [232].
0
50
100
150
200
250
300
350
20 40 60
Compressivestrength(Mpa)
GGBFS replacement of silica fume (%)
Bauxite autoclaved cured
Bauxite standard cured
Fig. 22. Comparison of compressive strength using autoclaved and standard curing
media [232].
0
10
20
30
40
50
Compressivestrengthatdifferentcuring
days(Mpa)
Different SCMs used in green concrete
90
56
28
Fig. 23. Compressive strength results for different curing methods.

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