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International Journal of Pavement Engineering
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gpav20
Performance evaluation of steel slag high
performance concrete for sustainable pavements
Ragaa T. Abd El-Hakim, Gamal M. Elgendy, Sherif M. El-Badawy & Mohamed
Amin
To cite this article: Ragaa T. Abd El-Hakim, Gamal M. Elgendy, Sherif M. El-Badawy & Mohamed
Amin (2021): Performance evaluation of steel slag high performance concrete for sustainable
pavements, International Journal of Pavement Engineering, DOI: 10.1080/10298436.2021.1922908
To link to this article: https://doi.org/10.1080/10298436.2021.1922908
Published online: 06 May 2021.
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3. different applications based on their different properties and
the purpose of use. There is some research evidence that SS
can be used successfully in unbound granular layers or
embankments for road pavements with minor gradation cor-
rections. It was reported that SS can match or sometimes
beat natural aggregates without representing a hazard for the
environment (Rohde, Peres Núñez et al. 2003; Pasetto and
Baldo 2010; Barišić, Netinger Grubeša et al. 2017; Shiha, El-
Badawy et al. 2020).
A comparative lifecycle assessment (LCA) was carried out
for six different concrete pavements (Anastasiou, Liapis et al.
2015). The parameters studied in the comparative LCA were
SS as an alternative to crushed limestone, as well as three
different binders: a pozzolanic Portland cement, a new hydrau-
lic road binder and a mixed-type binder consisting of Portland
cement and fly ash. The 40-year LCA results showed that rigid
pavements with high volume of alternative materials can
reduce carbon dioxide equivalent emissions to a large scale
compared to conventional concrete pavements. Therefore, sig-
nificantly enhance their environmental footprint.
Some types of steel slag may undergo expansion (volu-
metric instability) due to the hydration process of the free
CaO in the presence of water. This process forms Portlandite
(Ca (OH)₂) that have a lower density compared to CaO
(Wang 2016). In addition, other oxides such as the free
MgO hydrates. However, they require longer hydration
time as compared to CaO and can also cause expansion (Yil-
dirim and Prezzi 2011; Sorlini, Sanzeni et al. 2012).
Although steel slag has potentials for expansion, several
references have shown that ageing the steel slag properly
can mitigate this problem (Collins, Ciesielski et al. 1994).
The British and European standards did not stipulate a
specific duration for the weathering (ageing) process. How-
ever, some research studies reported that the duration
required for ageing in order to mitigate the expansion pro-
blem of steel slag is 3–18 months (Ameri and Behnood 2012;
Behnood and Ameri 2012; Sorlini, Sanzeni et al. 2012; Olu-
wasola, Hainin et al. 2014). (Wang 2016) suggested a usabil-
ity criterion to evaluate the suitability of steel slag in
confined applications such as concrete and asphalt mixtures.
This criterion relies mainly on the maximum expansion
force, the calculated tensile stress of a single slag particle,
and the allowable stress of the concrete or asphalt mixtures
using steel slag as aggregate replacement.
1.1. High performance concrete and its applications in
pavements
High-performance concrete (HPC) is concrete with special
properties: low shrinkage, low permeability, high workability,
high durability, and a high modulus of elasticity, or high
strength (Course 2018). The HPC usually consists of cement,
water, fine sand, superplasticizer, fly ash, or silica fume. Some-
times, quartz flour and fibre are added as well so that HPC
achieves ultra-strength and ultra-ductility, respectively. One
of the key elements of high-performance concrete is its low
water-to-cement ratio (Büyüköztürk and Lau 2002). An inves-
tigation of Ultra High Strength Concrete (UHSC, fc=125 MPa)
showed that its specific fracture energy increases with
temperature increase. This makes it suitable to be used in air-
port aprons subjected to hot jet blast from jet engine aircrafts
(Bamonte and Gambarova 2010). Using SS powder combined
with Super-plasticizer admixture, to produce economical HPC
to be used in pavement applications have shown enhanced
durability and reduced cement content. Different types of SS
along with SS cement and concrete with variable admixtures
dosage were studied in literature (Li, Kong et al. 2009). The
effectiveness of using SS powder for suppressing Alkali Aggre-
gate Reaction was also analysed. The results showed that prop-
erties and durability of concrete can be greatly improved by
using SS powder (Li, Kong et al. 2009). However, other
research studies reported that the SSP did not cause any sig-
nificant improvement on the mechanical properties of con-
crete (Lin, Wang et al. 2008; Yu, Wang et al. 2017; Han and
Zhang 2018; Liu and Guo 2018).
A comparison between three HPC mixtures was conducted;
HPC produced with SS, HPC produced with crystallized slag as
coarse aggregate and natural limestone aggregates HPC
(Biskri, Achoura et al. 2017). Ground granulated blast furnace
slag (GGBFS) and silica fume (SF) were added as supplemen-
tary cementing materials at water to cement ratio (w/c) of 0.27.
Mechanical strength properties at different ages and durability
indicators were tested. The results showed that the mineralogy,
morphology, and aggregate strength are substantial factors
affecting the compressive strength and durability of HPC.
The angularity and surface texture roughness of artificial
aggregates revived the bond between aggregates and hardened
cement paste and surged the strength of concrete (Biskri,
Achoura et al. 2017).
Microstructural enhancement techniques for cementitious
materials are used to develop Reactive Powder Concrete
(RPC), otherwise known as ultra-high-performance concrete
(UHPC). To decrease the cement and SF content of RPC by
using ultra-fine fly ash (UFFA) and steel slag powder, the
effect of these mineral admixtures on compressive strength
of RPC was investigated (Peng, Hu et al. 2010). The exper-
imental results indicate that the utilisation of UFFA and SS
in RPC is feasible and has prominent mechanical performance.
The microstructure analysis demonstrated that the excellent
mechanical properties of RPC containing SS and UFFA were
mainly attributed to the sequential hydration filling effect of
the compound system (Peng, Hu et al. 2010). Other research
showed that replacing cement with either SF or metakaolin
can improve the mechanical and physical properties of
UHPC (Amin and Tayeh 2020). HPC with early strength,
self-curing capabilities and low shrinkage may potentially
improve rigid pavement performance. A multi-scale exper-
imental programme examined the mechanical properties and
shrinkage behaviour of normal strength concrete (NSC) and
HPC. The results show that the use of HPC containing pre-
wetted lightweight aggregate can potentially reduce micro-
cracking and enhance overall pavement performance (Lopez,
Kahn et al. 2010).
It can easily be noticed that, virtually all research has been
done in the laboratory. Moreover, very limited studies evalu-
ated the long-term performance of concrete mixes containing
SS using the available performance prediction models or simu-
lations. This type of experiments/simulations generates a
2 R. T. ABD EL-HAKIM ET AL.
4. speculation about how the mix will behave on the long term
under actual climatic and traffic loading conditions.
2. Research significance and objectives
Construction of different pavement layers requires massive
quantities of materials. Consequently, the constructive use of
waste/by product materials in pavements preserves natural
resources and saves substantial areas of landfills. Steel Slag
has special features such as, high density, skid resistance,
wear resistance, crushing resistance and surface angularity.
These properties make it favourable as a road construction
material. In the last decade, there is a governmental tendency
in Egypt towards constructing more rigid pavements due to
two main reasons. The first reason is overloading whereas
more than 96% of freight transportation in Egypt is carried
out using trucks (Elshamly, Abd El-Hakim et al. 2017).
These trucks are usually loaded with excessive weights. The
second reason is the increased price and inferior quality of
the asphalt binder in Egypt. The Egyptian asphalt producers
do not manufacture modified asphalt. In the presence of
high temperatures and heavy loads, asphalt concrete mixtures
produced using these unmodified yet expensive asphalt bin-
ders, are more prone to premature rutting and with pavement
aging, excessive fatigue cracking is also expected. The prema-
ture deterioration in the early life of asphalt pavements
encouraged incorporating more rigid pavements in the
national road plan of Egypt. Consequently, the performance
prediction of such pavements became indispensable. Finally,
few research papers investigated using HPC in rigid pavement
road sections resting on subgrade soils. In addition, the pave-
ment performance evaluation using the state-of-the-art
AASHTOWare Pavement ME which is a key factor in pave-
ment design was seldom investigated in previous research
papers for such concrete mixes. The rigid pavement perform-
ance is not only a function of material properties and loads. It
is a combined function of climatic conditions which is a crucial
element for pavement performance in addition to the pre-
viously mentioned factors. These reasons motivated the
authors, not only to experimentally investigate the mixes man-
ufactured with steel slag coarse aggregate and steel slag pow-
der, but also to evaluate the performance of these mixtures
under typical traffic, climatic conditions and subgrade proper-
ties in Egypt.
The main objective of the current research is to evaluate the
properties of high-performance concrete (HPC) manufactured
with different percentages of EAFSS as a replacement of the
concrete coarse aggregate and steel slag powder as a partial
replacement of cement. The specific objectives are:
. Study the effect of using EAFSS on HPC physical and mech-
anical properties.
. Determine the optimum percentage of the EAFSS aggregate
in the pavement mixture.
. Evaluate the use of EAFSS powder as a mineral filler in rigid
pavement concrete mixtures
. Evaluate the performance of pavements containing steel
slag as a road construction material using the AASHTO-
Ware Pavement ME Design.
3. Materials and methods
3.1. Materials
A CEM I 52.5 N grade Ordinary Portland Cement (OPC) as
classified by ASTM C150 from Alarish Cement Company in
Egypt was used to produce the concrete mixtures (BS
2009a). The specific gravity of the cement was found to be
3.15 according to ESS 2421/2005 (ESS 2005).
Two aggregate types were used in this research: natural and
manufactured EAF steel slag aggregates. A natural crushed
dolomite stone coarse aggregate from Ataka mountain in
Suez city is used in this study. It has a nominal maximum
aggregate size (NMAS) of 12.5 mm. Testing of natural coarse
aggregate is carried out in accordance with the Egyptian Stan-
dard Specifications (1109/2008) (ESS 2008), and the Egyptian
Code ECCS 203–2008 (ECCS 2008). Natural siliceous sand
was used as a fine aggregate.
The steel slag used in this research is a local Electric Arc
Furnace Steel Slag (EAFSS) obtained from Ezz Steel Factory
in Suez city. The EAFSS is a by-product during melting of
steel scrap from the impurities and fluxing agents, which
form the liquid slag floating over the liquid crude iron or
steel in electric arc furnaces. The chemical composition of
the used EAFSS as obtained from the manufacturer is shown
in Table 1.
The EAFSS was manually crushed and sieved in the labora-
tory to maintain very similar gradation to the natural coarse
aggregate (NMAS = 12.5 mm). For the sake of mitigating
expansion of steel slag, the material was washed to accelerate
the hydration process of free lime and magnesia, and then
weathered in the laboratory for 6 months before use in the
mix production. Figure 1(a) shows the EAFSS used as coarse
aggregate replacement in this research. The colour of the slag
implies that this is an aged slag. As the figure shows, the
EAFSS possess a very rough surface texture with irregular
angular shape. This is also confirmed by the Scanning Electron
Microscopy (SEM) micrographs shown in Figures 1 (b) to 1 (d).
Los Angeles (LA) abrasion machine was used with other
tools to extensively crush another amount of EAFSS in order
to maintain an extra fine that passes from the standard US
Sieve #200. Steel slag was crushed into smaller size with a ham-
mer, then it was put in the LA machine with the twelve steel
balls (weight of the ball is about 390-440 gm) and the machine
was rotated till fine particles were formed. The third step of
this extensive crushing process was putting the steel slag
sand size product in the mill of an electric kitchen blinder
until getting extra fine steel slag particles. Only particles
Table 1. Chemical composition of the EAF steel slag (Ezz steel factory).
Constituent SiO₂ Fe₂ O₃ AL₂ O₃ Ca O Mg O Mn O Cr₂ O₃ P₂ O₅ Ti O₂ V₂O₅ SO₃
Composition% 13.1 36.8 5.51 33.03 5.03 4.18 0.77 0.74 0.60 0.10 0.14
INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING 3
5. passing the standard US Sieve #200 were used as steel slag
powder. This powder was denoted in this research as Steel
Slag Powder (SSP).
The gradation and physical properties of the investigated
aggregates (coarse, fine, and slag) are summarised in Table 2.
The results in Table 2 indicate that the EAFSS has a lower
absorption, higher specific gravity, higher density, better
abrasion, and better crushing coefficient compared to the dolo-
mite aggregate.
The mineral fillers used in this research are of two types,
locally produced silica fume (SF) from SICA Company in
Egypt, and the previously prepared SSP which was sieved
Figure 1. Investigated EAFSS as coarse aggregate replacement (a) Investigated Coarse Aggregate Size EAFSS (b)SEM Micrograph Magnified 50 times (c) SEM Micro-
graph Magnified 1500 times (d) SEM Micrograph Magnified 3000 times.
Table 2. Coarse and fine aggregate gradation and physical properties.
Sieve Analysis
Sieve size (mm) 19 12.5 9.5 4.75 2.36 1.18 0.6 0.3 0.15
Passing% Sand (fine) 100 100 100 95 78.5 72.5 45 10 0
Dolomite (coarse) 100 98 73 6.5 0 0 0 0 0
Steel Slag 100 97 66 5.5 0 0 0 0 0
Physical Properties
Property Sand Dolomite Steel Slag Specification limits
Water Absorption, % 1.20 2.00 0.80 2.5% maximum***
*SSD Specific Gravity 2.67 2.71 3.18
Clay and fine dust content % 0.60 0.97 - 4% maximum **
Bulk Density, kg/m³ 1664 1630 1885
Impact Coefficient, % — 12.0 6.30 30% maximum ***
Los Angles Abrasion, % — 17.9 13.30 30% maximum **
Crushing Coefficient, % — 21.0 11.10 30% maximum **
*SSD = Saturated Surface Dry.
**Limits of ESS 1109/2008(ESS 2008).
***Limits of ECCS203-2008 (ECCS 2008).
4 R. T. ABD EL-HAKIM ET AL.
6. until 100% of this powder passed from the standard US Sieve
#200. The same SSP used in this study was used in another
study as mineral filler in Hot Mix Asphalt (Awed, Tarbay
et al. 2020) and the Transmission Electron Microscopy (TEM)
was performed on it. Transmission Electron Microscopy
(TEM)TEM isused to characterise morphology and crystalline
structure of the SSP. The TEM images of the SSP particles
depicted in Figure 2 show that the the particle sizes range
from 51 to 146 nm.
The SF used in this work was locally obtained from SICA
Company in Egypt having a silica content of 99.1%. The phys-
ical properties and chemical compositions of the invistigated
SF as provided by the manufacturer are shown in Table 3.
A locally produced high performance superplasticizer aqu-
eous solution admixture of modified polycarboxylate basis (Vis-
cocrete-5930L) was used to increase workability and viscosity of
the investigated concrete mixes. The Viscocrete-5930L complies
with the ASTM-C-494 types G and F(ASTM 1999), and BS EN
934 part 2: 2009 (BS 2009a). The dosage of the admixture was
adjusted to minimise the water/binder ratio.
The factorial of the investigated concrete mixes is summar-
ised in Table 4. The mixtures factorial was achieved by repla-
cing different amounts of the dolomite coarse aggregates,
normally used in the manufacture of concrete in Egypt, by
EAFSS in increments of 25% (by weight of coarse aggregate)
until all the natural aggregates are totally replaced by the
steel slag. The control mix (H0) has zero percent steel slag
(100% dolomite coarse aggregate). Mixes H1, H2, H3 and
H4 were prepared by substituting the dolomite coarse aggre-
gate by EAFSS in percentages of 25, 50, 75 and 100% by weight
of coarse aggregate, respectively. Mixes from H5 to H12were
manufactured using 50% EAFSS and 50% dolomite coarse
aggregate. It will be seen from the results section that, the
best mechanical properties achieved was for Mix H2 with
50% EAFSS replacement. The experimental programme was
expanded to investigate the effect of mineral filler materials
and cement content. The siliceous sand (fine aggregate) per-
centage was kept constant at 40% of the total weight of aggre-
gate for all mixes. To investigate the effect of cement content,
cement content of 400 kg/m³ was used for H5, H7 and H10,
500 kg/m³ was used for H0 to H4, H8 and H11, while
600 kg/m³ was used for H6, H9 and H12. Water to binder
materials ratio (w/b) was kept constant at 0.3, mineral filler
materials content (SF or SSP or both) was fixed at 20% from
the weight of cement. The superplasticizer (SP) dosage was
kept constant at 3% from the weight of binder materials
(cement plus mineral filler materials).
Table 5 represents the volumetric ratios of all the investi-
gated mixes.
3.2. Experimental work
All concrete samples were mechanically mixed. The slump test
was conducted on the fresh concrete according to ASTM C 143
(ASTM 2003) to evaluate workability. Drying shrinkage and
initial and final setting time tests were conducted on moratr
according to ASTM C 157–08 (ASTM 2008) and Egyptian
Code ECCS 203–2008 (ECCS 2008) respectively. Then, for
each concrete mix, the following testes were completed:
. Compressive strength according to ASTM C 192 (ASTM
2007)at 7, 14, 28, 56 and 90 days on 15 cubes (3 cubes for
each age of 15 × 15 × 15 cm).
Figure 2. TEM images of the investigated steel slag powder (Awed, Tarbay et al. 2020).
Table 3. Properties of silica fume.
Properties Silica fume
Physical
Specific gravity 2.14
Bulk unit weight (Kg/m3
) 393
Specific area (cm2
/gm) 20150
Colour Light Grey
Chemical compositions (%)
Silicon dioxide (SiO2) 99.1
Aluminum oxide (Al2O3) 0.11
Ferric oxide (Fe2O3) 0.32
Calcium oxide (CaO) 0.12
Magnesium oxide (MgO) 0.17
Sulphur trioxide (SO3) 0.10
Potassium oxide (K2O) 0.15
Sodium oxide (Na2O) 0.10
Loss on Ignition (LOI) 0.45
INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING 5
7. . Indirect tensile strength according to ASTM C 496 (ASTM
2004)at 28 days on 3 cylinders (15 cm diameter and 30 cm
height).
. Flexural strength according to ASTM C78 (ASTM 2002a) at
28 days on 3 beams (10 × 10 × 50 cm).
. Static modulus of elasticity according to ASTM C469
(ASTM 2002b) at 28 days on 1 cylinder (15 cm diameter
and 30 cm height).
. Coefficient of permeability at 28 days on 1 cube (10 × 10 ×
10 cm) using the German water permeability apparatus
(GWP).
. Coefficient of thermal conductivity at 28 days on 2 samples
(10 × 10 × 3 cm) using a manufactured device.
4. Results and analyses
The ensuing subsections present the analysis and discussion of
the conduced testing programme results on the investigated
mixtures.
4.1 Fresh concrete properties (Slump test)
The slump of the designed HPC incorporated with EAFSS, SF
and SSP is presented in Figure 3 (a,b). Figure 3 (a) shows a lin-
ear decrease in consistency with the increase in the replacement
percentage of EAFSS aggregate for mixes H0 to H4. The reason
is due to the surface texture, shape, porosity, and the heavy
specific weight of the EAFSS aggregates. The effect of cement
content and mineral materials on slump were also studied
and presented in Figure 3 (b). This figure shows that the
effect of the SF on mix consistency is lower than SSP probably
due to the extra fine particles of the silica fume. It is observed
that the slump of the 500 kg/m3
cement mixtures with 20%
SF, 10% SF+10% SSP, and 20% SSP are 7.4, 8.2, and 8.8 cm,
respectively. This is attributed to the fact that, when the SSP
is used in HPC, it slightly increases the stress state between par-
ticles, aggregate, and mortar. In addition, the specific surface
area of the 600 kg/m3
cement is higher than that of the
400 kg/m3
or 500 kg/m3
of cement, resulting in reduced
slump values as shown in Figure 3 (b) (Wang, Yu et al. 2019;
Li, Cheng et al. 2020). In these figures the bar charts represent
the average results of three replicate testing results while the
standard deviation of the results is denoted by ‘I’ on the bars.
4.2. Initial and final setting time
Initial and final setting time test was carried out according to
(ESS 2005). The initial and final setting times of the blended
cement paste mixed with SSP are found to be similar to
those of pure cement paste, but they are delayed to different
degrees. The greater the percentage of SSP, the later both the
emerge of initial setting time and final setting time as shown
in Figure 4. It can be notedthat SSP retard the hydration of
Table 4. Factorial of the produced concrete mixtures.
Concrete
mix
w/b
ratio
Cement content
Kg/m³
* Coarse
aggregates (60%
of the total
aggregate mass)
**Mineral filler
EAFSS replacement percentage of coarse
aggregate mass Mix purpose
Dolomite EAFSS
H0 Control 0.3 500 60% 0% 20% SF 0% Control Mix
H1 500 45% 15% 25% Effect of EAFSS Replacement
H2 500 30% 30% 50%
H3 500 15% 45% 75%
H4 500 0% 60% 100%
H5 400 30% 30% 50% Effect of mineral Filler Type
and Content
H6 600
H7 400 10%SF+10% SSP
H8 500 10% SF+10% SSP
H9 600 10% SF+10% SSP
H10 400 20% SSP
H11 500
H12 600
Table 5. Volumetric proportions of concrete mixtures.
Concrete constituents (kg/m3
)
Mixture ID Cement Sand Dolomite Steel Slag SF SSP SP Water
H0 (Control) 500 644.6 966.9 0.00 100 0 18.0 180
H1 500 658.8 741.1 247.10 100 0 18.0 180
H2 500 674.4 505.8 505.80 100 0 18.0 180
H3 500 690.0 258.75 776.25 100 0 18.0 180
H4 500 707.1 0 1060.70 100 0 18.0 180
H5 400 765.0 573.75 573.75 80 0 14.4 144
H6 600 583.8 437.85 437.85 120 0 21.6 216
H7 400 771.9 578.9 578.90 40 40 14.4 144
H8 500 683.0 512.25 512.25 50 50 18.0 180
H9 600 594.1 445.6 445.60 60 60 21.6 216
H10 400 778.8 584.1 584.10 0 80 14.4 144
H11 500 691.6 518.7 518.70 0 100 18.0 180
H12 600 604.5 453.4 453.40 0 120 21.6 216
6 R. T. ABD EL-HAKIM ET AL.
8. Portland cement before one day age. The effect of SSP on the
hydration system of Portland cement is closely related to its
mineral phases, fineness and surface shape. In the hydration
process of the blended cement paste mixed with steel slag pow-
der, parts of these components participate in or influence the
hydration system and changes its characteristics compared to
the characteristics of the hydration system of pure cement.
The retarding effect of steel slag on the early hydration process
of cement is due to its high content of MgO, MnO, and P2O5.
Research works indicate that the presence of MgO and MnO
can retard the early hydration process of clinker (Zheng, Xue-
hua et al. 1992; Péra, Ambroise et al. 1999; Altun and Yılmaz
2002; Shuguang, Yongjia et al. 2006).
4.3. Drying shrinkage
Drying shrinkage strain test was carried out according to
ASTM C 157–08 and ECCS 203–2008 (ASTM 2008; ECCS
2008)to determine the drying shrinkage strains at 1, 7, 14, 21
and 28 days. The drying shrinkage was tested as the length
change of 25 ×25×285 mm beams.
The drying shrinkage of HPC sample measured as a func-
tion of time up to 28 days are presented in Figure 5. It can
be seen that the shrinkage of HPC in the first seven days is fas-
ter. The difference of total shrinkage of each sample is
insignificant, and a clear distinction could be observed
among all the HPC mixtures at seven days. Afterwards, the
shrinkagerate gradually decreases, and the specimens continue
to shrink up to 14 days to 28 days. Due to the low w/bin HPC,
the mixed water is quickly consumed at the early stage of
hydration, inducing rapid decrease of relative humidity inside
the system. In addition, outside moisture does not easily
exchange with the inner moisture of HPC due to the lower
porosity and dense microstructure of HPC (Meng and Khayat
2017, 2018; Li, Cheng et al. 2020). As a result, the early shrink-
age development of HPC is comparatively rapid compared
tothe normal Portland cement concrete.
The shrinkage of all specimens is smaller than 420 micro
strain at the age of up to 28 days. For instance, the drying
shrinkage values of HPC with 10% and 20% SSP at 28 days
are 334 and 298 micro strain, respectively. Compared with
HPC without SSP, the total shrinkage of HPC with 10% and
Figure 3: Workability of investigated high performance fresh concrete mixtures (a): Effect of %EAFSS on Slump for Mixes H0 to H4 (b): Effect of Cement Content and
Mineral Materials on Slump.
Figure 4. Effect of mineral materials content on setting time. Figure 5. Effect of mineral materials content on drying shrinkage.
INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING 7
9. 20% SSP at 28 days are reduced by 13.3% and 22.6%, respect-
ively. While, the shrinkage at 28 days of HPC with 20% SF is
approximately 9.1% higher than that without the SF. This
can be attributed to multiple reasons such as the shortening
of early-age period of the concrete and the cement dilution
effect (Liu and Wang 2017). In addition, both the accelerated
cement hydration and the refinement of pore structure
owing to the changed particle packing of binder can contribute
to this result. Eventually, the drying shrinkage of HPC incor-
porating SSP is lower than the control group.
4.4. Unit weight
The unit weight of the steel slag coarse aggregate concrete var-
ied from 2.48 t/m³ (H0) to 2.80 t/m³ (H4). The results are
shown in Table 7. In general, it increased with the increase
in the slag replacement percentage due to the higher specific
gravity of the steel slag aggregates.
4.5. Permeability
The coefficient of permeability was measured according to BS
EN 12390-8: 2009 as shown in Figure 6 (a). The sample used
was 10×10×10 cm cube which was previously dried in 110 ̊C
oven. A sealed pressure chamber is attached to the concrete
surface using anchors. The chamber is filled with de-aerated
water, and the required water pressure is applied to the surface.
The amount of water which penetrates the concrete surface is
measured by keeping the pressure constant using the
micrometer gauge with an attached pin by which the water
leaving the chamber was substituted. The detailed procedure
and calculations are discussed in (BS 2009b).
Figure 6 (b) illustrates the effect of replacement of steel slag
coarse aggregate on the coefficient of permeability. As shown
from the figure, increasing the replacement percentage of
EAFSS decreased the permeability of concrete. The coefficient
of permeability decreased from (2.60×10−3
mm/sec) for H0 to
(2.2×10−3
mm/sec) for H2, then it was found to slightly
increase with increasing the EAFSS. It is worth mentioning
that the decrease in permeability coefficient with the increase
in EAFSS aggregate up to 50% replacement substantiates the
improvement of the pervious concrete properties at this repla-
cement ratio. This lower concrete permeability indicates lower
interconnected air voids, and hence better strength and
durability.
4.6. Compressive strength
The incorporation of steel slag and traditional dolomite aggre-
gates combined with admixtures enhanced the compressive
strength to produce HPC. The testing results show a slight
increase in the compressive strength with the increase in
EAFSS of up to 50% replacement and then it decreased slightly,
even though, all EAFSS mixes have nearly a compressive
strength of 100 MPa or more. The mix with 50% steel slag
(H2) recorded the highest increase in compressive strength at
all ages compared to the control mix (H0). Figure 7 shows the
effect of EFASS replacement percentage on compressive
strength at different ages. Using SSP powder with or instead
of SF was found to slightly reduce the compressive strength at
all ages, although it is still higher than the control mix. This is
due to the effect of mineral and chemical admixtures, also SF
effect on compressive strength is greater than that of SSP.
The analysis of the results confirms that the SSP has a neg-
ligible pozzolanic activity as compared to the SF which agree
with other studies (Rashad 2019; Brand and Fanijo 2020).
SSP is less active than cement and contains large amounts of
calcium and magnesium oxides (as shown in Table 1). The
main minerals of steel slag, used in this research, include
iron oxide (Fe₂ O₃, 36.8%), 33.03% of calcium oxide (CaO),
5.03% magnesium oxide (MgO)and 4.18% manganese oxide
(MnO). The cementitious properties of ordinary cement
mainly come from the minerals of tricalcium silicate (C3S)
and C2S. The previous mineral phases play a negative role in
Figure 6. Equipment and results of the permeability test (a) Water Permeability Apparatus (b) Effect of % Slag on Conc. Permeability after 28-Days.
8 R. T. ABD EL-HAKIM ET AL.
10. the cementitious properties of steel slag to a certain extent. In
order to improve the early activity of steel slag, choosing
proper mineral admixture and chemical activators to modify
steel slag is necessary (Guo and Shi 2013). Some research
studies speculated that cement containing SSP yield concrete
with inferior mechanical properties (Lin, Wang et al. 2008;
Yu, Wang et al. 2017). The fluidity of SSP cement mortar con-
taining SSP and the compressive strength of concrete with
different contents of SSP have been studied by (Liu and Guo
2018). The cement containing SSP mortar was found to have
higher fluidity while the compressive strength of concrete
was reported to decrease insignificantly for the samples with
SSP less than 10%. (Han and Zhang 2018) evaluated the com-
position, morphology of hydration products along with the
compressive strength of a five-year-old concrete containing
SSP. The study reported lower compressive strength for the
SSP concrete. In addition, many SSP particles were not fully
hydrated even after this long period of time.
On the other hand, the compressive strength development
of concrete with SF additive is mainly due to its filler effect,
pozzolanic reaction with Ca(OH)2 and the hastening of the
Portland cement hydration (Said-Mansour, Kadri et al.
2011). Due to its very fine particles, it fills the voids between
the relatively larger particles of the cement yielding a dense
particle packing at the aggregate-paste interface. Moreover,
the pozzolanic reaction of SF with Ca(OH)2 produces
additional C–S-H gel which contributes to the strength gain.
The pozzolanic and filler effects of SF in concrete can be
confirmed from the microstructural characterisation study
conducted by (Said-Mansour, Kadri et al. 2011). As literature
studies showed, SiO2, which is the main component of SF, con-
sumes Ca(OH)2 to form C—S—H gel. Thus, SF has some poz-
zolanic activity and works as a supplementary cementitious
material (Amin 2018; Amin and Tayeh 2020). However, steel
slag is less active than cement and the gel of steel slag com-
pounding with cement is looser which may negatively affect
the mechanical properties of concrete (Liu and Wang 2017;
Yu, Wang et al. 2017). Finally, the larger surface area of the
finer SF particles accelerates the hydration process of the
Portland cement thus improving the pozzolanic reaction rate
(Kadri, Kenai et al. 2011). This, in turn, leads to the improve-
ment in compressive strength.
It can be observed that all mixes of 50% steel slag and
cement contents of 500 kg/m3
or more, recorded compressive
strength higher than 100 MPa after 90 days putting them in
the ultra-high strength concrete category (Elgendy, Elagamy
et al. 2020). On the other hand, all EAFSS concrete mixes
recorded compressive strength higher than 60 MPa after 90
days which is the required minimum strength of HPC (Course
2018; PCA 2019).
The increase in the compressive strength, especially in the
mixes of 50% steel slag coarse aggregate, can be attributed to
the unique morphological characteristics and angularity of
the steel slag particles shown previously in Figure 1 which
led to increase in the mechanical bond between the aggregate
and cement paste as reported in literature (Tarbay, Azam et al.
2019) along with the reduced amount of interconnected voids.
In addition, the rigidity of both EAFSS aggregate and the
cement paste, makes the resulting concrete behaves as a single
unit yielding stronger concrete.
The results of this study show that the optimum content of
cement lies in the vicinity of 600 kg/m3
. Figure 8 shows the
effect of cement content on the compressive strength of similar
mixes prepared with cement and mineral materials. According
to these results, the compressive strength growth from 400 Kg/
m3
to 500 and 600 Kg/m3
is between 15.22% and 34.17%.
These results proved that cement content of 600 Kg/m3
is
the optimum content for compressive strength in case of
incorporation of 20%SF. The reason for this phenomenon is
that SF undergoes a secondary hydration reaction with Ca
(OH)2, the hydration product of cement, to form (C—S—H)
gel, contributing in the development of compressive strength
(Wongkeo and Chaipanich 2010; Wongkeo, Thongsanitgarn
et al. 2014)
In addition, it is observed from Figure 8 that the compres-
sive strength of HPC with SF is 13.7% greater than that of HPC
with SSP. This is because the influences of SSP on the compres-
sive strength of concrete is reflected in two aspects: on the one
Figure 7. Effect of EAFSS percentage on compressive strength at different ages.
INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING 9
11. hand, the amount of cement is reduced relatively after the
incorporation of SSP, and the activity index of SSP is lower
than that of cement, so the amount of C—S—H produced by
hydration reaction is reduced relatively at the same time,
resulting in the reduction of concrete compressive strength.
On the other hand, the micro-filler effect (Atahan and
Dikme 2011; Hengyan and Wenzhong 2012), the SSP, can
fill the gaps in the cement and increase the compactness of
the concrete, therefore the strength of the concrete increases
to some extent. Under the synergetic effect of the two factors,
the compressive strength of concrete shows a downward trend,
and only when the content of SSP is 20%, the compressive
strength of concrete with 500 kg/m3
cement content decreased
slightly, indicating that the low activity of SSP is stronger than
the filling effect with respect to the influence on compressive
strength of concrete.
A few earlier studies have used the indentation test to inves-
tigate the interfacial transition zone (ITZ) of cementitious
materials with EAFSS aggregates. The studies have shown
improvement in concrete strength and ITZ characteristics by
using EAFSS aggregates (Yuji 1987; Montgomery and Wang
1991; Arribas, Santamaria et al. 2015; Pang, Zhou et al. 2016;
Brand and Roesler 2018). Furthermore, factors affecting the
concrete properties are aggregate type, source, and properties
such as gradation, shape, surface texture, porosity, and phase
composition (Mehta and Monteiro 2014; Brand and Roesler
2018). For example, the chemical reaction between cement
and EAFSS aggregates as well as the rough surface texture
were the main reasons for enhancing the concrete strength
(Yuji 1987; Montgomery and Wang 1991; Arribas, Santamaria
et al. 2015; Pang, Zhou et al. 2016; Brand and Roesler 2018).
4.7. Splitting tensile strength, flexures strength, and
modulus of elasticity
The values of splitting tensile strength at 28 days for concrete
mixes (H0 to H4) improved significantly with the increase of
EAFSS until 50% replacement (H2 mix) as shown in Figure
9 (a). Adding more than 50% EAFSS led to a very slight
decrease in the splitting tensile strength with the results still
higher than that of the control mix. The improvement at the
50% EAFSS was about 46.5% compared to the control mix.
The increase in the indirect tensile strength can be attributed
to the rough surface and high angularity of the steel slag
which led to increase in the mechanical bond between the
aggregate and the cement paste.
The flexural strength results are shown in Figure 9 (b) while
the modulus of elasticity results are given in Figure 9 (c). Simi-
lar to the indirect tensile strength results, both flexural strength
and modulus of elasticity of the mixes increased with the
increase in the EAFSS aggregate up to 50% then it slightly
decreased. It should be noted that the results of 100% replace-
ment are still higher than those of the control mix. This
increase can be attributed to the angularity and surface rough-
ness of the EAFSS as well as the lower interconnected voids
causing increased bond between aggregates and cement paste.
4.8. Thermal conductivity
The thermal conductivity coefficient of the concrete specimens
was estimated by using the device shown in Figure 10 (a)
which was manually assembled by using 10×10 cm steel plate
electric heater between two concrete specimens 10×10×3 cm
as shown in Figure 10 (b). The other faces of specimens
were covered by two steel plates 10×10 cm while all other
parts of specimens were thermally insulated to force the heat
to pass through the thickness of specimens only. The two
faces of the heater and the two steel plates were connected to
a temperature recorder through four thermocouples, as
shown in Figure 10 (b), to record the temperature on the
two faces of each specimen The difference in temperature
(Δt) was measured at steady state when no variation in temp-
erature happen over time. The coefficient of thermal conduc-
tivity (K) is calculated from Fourier’s equation(Saylor 2018):
K =
Q × t
A × DT
(1)
where: K: is the coefficient of thermal conductivity×10−3
W/
m.K; Q: is the power applied, Q = I ×V = V²/R (R is the resist-
ance of the heater which measured at 7.3 Ω, and V is the
applied voltage); A: is the area of the two faces of heater, A
= 100×100×2; ΔT: is the difference of temp between the two
faces of specimen, DT = (T2 + T3/2) − (T1 + T4/2) at steady
state; T₁,T₂, T₃, and T₄: are the temperatures on the four faces
of the two concrete specimens; T: is the thickness of concrete
specimen, t = 30 mm.
Equation (1) is finally put in the form:
K = 2.055 × 10−4
× V2
/DT (2)
As illustrated in Figure 10 (c), the coefficient of thermal
conductivity (K) decreases with the increase of slag aggre-
gate at all percentages. It decreased from 2.113 W/m.K for
H0 to 1.632 W/m.K for H4, i.e. increasing the steel slag per-
centage from 0% (H0) to 100% (H4) decreases the thermal
conductivity of concrete by 22.75%. The reason for decreas-
ing concrete conductivity with the increase of steel slag
aggregate, is that steel slag aggregate contains some air
voids in its texture. This makes the steel slag aggregate
Figure 8. Effect of cement content and mineral materials on compressive
strength at 28 days.
10 R. T. ABD EL-HAKIM ET AL.
12. concrete less thermal conductive if compared with the
ordinary aggregate concrete.
4.9. Statistical analysis of testing results
The above testing was conducted on three replicate samples for
each test. The Minitab software was used to perform a one-way
analysis of variance (ANOVA) with the null hypothesis that all
mean values for each of the laboratory measured property in
the current study are equal, while the alternate hypothesis
assumes that at least one mean is different. The ANOVA
analysis was conducted at 5% level of significance. The results
of the ANOVA test represented in Table 6 show that all the
null hypothesis is rejected for all of the tested properties at a
level of significance of 5% except the modulus of elasticity
for two studies (the effect of EAFSS as coarse aggregate repla-
cement and the effect of mineral material content and type),
and Coefficient of Thermal Conductivity for three studies
(the effect of mineral material content and type at all cement
contents). This means that the use of EAFSS has a significant
influence on the majority of the mechanical properties of con-
crete at a 5% level of significance.
5. Field performance prediction using
AASHTOWare Pavement ME design
Performance prediction of pavements is a key element in the
design/analysis process. Thus, AASHTOWare Pavement ME
Designs oft ware was used to predict the performance of
Jointed Plain Concrete Pavements (JPCP) using the properties
of the concrete mixes tested in this research. The AASHTO-
Ware predicts distresses in terms of mean joint faulting and
International Roughness Index (IRI)in addition to transverse
cracking (% slabs cracked). Continuously reinforced concrete
pavement (CRCP)can develop many of the same distresses as
JPCP (Jeffrey Stempihar 2020). Computer simulation runs
using the AASHTOWare were conducted for 50 years of ser-
vice life. The inputs of the AASHTOWare are divided into:
Traffic inputs, Climatic inputs, Material inputs, and design cri-
teria. Average Annual Daily Traffic (AADT) of 15000 vehicles
per day with a growth rate of 5%, which is equivalent to about
122 million Equivalent Single Axle Loads (ESALS) at the end
of the 50 years design life was used for all runs. The simulation
runs were conducted using one climatic weather station simi-
lar to the weather in upper Egypt with a Mean Annual Air
Temperature of 25.6°C (78.04o
F). The investigated cross sec-
tion shown in Figure 11 is composed of three layers (30 cm
JPCP over 30 cm unbound granular base layer over a subgrade
foundation) with a fixed ground water table depth of 2.0 m.
The required concrete properties (30 cm JPCP) used for the
AASHTOWare runs are summarised in Table 7 which were
obtained from the testing results of this study. The Coefficient
of Thermal Expansion (CTE) input values were obtained from
pervious literature studies (Kim 2012; Ley, Hajibabaee et al.
2013). The literature refers that the CTE can be either esti-
mated or measured in the laboratory (Tanesi, Kutay et al.
Figure 9. Effect of steel slag percentage on splitting tensile strength, flexural strength, and modulus of elasticity (a) Splitting Tensile Strength (b) Flexural Strength (c)
Modulus of Elasticity.
INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING 11
13. 2007). When different PCC CTE values for different materials
were used to evaluate the rigid pavement performance using
older version of the AASHTOWare ME (back then it was
called Mechanistic–Empirical Pavement Design Guide;
MEPDG), it was found that the effect of PCC CTE is more pro-
nounced on the cracking than on mean joint faulting (Mallela,
Abbas et al. 2005). Research concerning the impact of CTE
variability on JPCP sections indicated that, irrespective of
the input level, CTE values had very little influence on the
amount of joint faulting predicted (McCarthy, Gudimettla
et al. 2015). It was also found that the effect of greater CTE
values is more evident on continuously reinforced concrete
pavements (CRCP).
A typical 30 cm unbounded granular base course material
(GB) which is A-1-b according to the American Association
of State Highway and Transportation Officials (AASHTO)
classification system was used for all runs. The subgrade
(SG) is A-4 which is the typical subgrade in some regions in
Egypt. The unbound GB material properties and subgrade
soils are summarised also in Table 7.
The software predicts the pavement distresses at the
specified reliability over the whole pavement age spectrum.
All runs were conducted at 95% reliability. The relationships
between age (in years) and the predicted distresses are plotted
to get the maximum age of the pavement at failure Figure 12.
From the curves, the final age of the pavement was obtained at
the intersection between the predefined failure limit and the
distress-age curve. At this intersection the pavement is
assumed to be failed. The failure limit (design criteria) for
mean joint faulting is taken as 2.34 mm (0.12 in), 15% for
transverse cracking and 2.72 m/km (172 in/mile) for terminal
IRI which are the default values in the software.
From such curves the deduced final ages at failure limit for
all mixes were used to plot a bar chart which shows the pave-
ment final ages for mixtures with different EAFSS contents due
to distresses as shown in Figures 13(a–c).
Figures 14(a and b) show the relationship between the pre-
dicted distresses and age for the mixes containing different
proportions of pozzolanic materials. Figure 14(c) shows the
effect of the filler material type and content on faulting and IRI.
Figure 10. Manually assembled device and concrete samples and the effect of EAFSS% on thermal conductivity after 28 days (a) Manually Assembled Device (b)
Concrete Samples (c) Effect of EAFSS % on Thermal Conductivity after 28-Days.
12 R. T. ABD EL-HAKIM ET AL.
15. The predicted performance did not show any significant
amount of transverse cracking for all investigated concrete
mixes. Moreover, the faulting criterion yielded slightly shorter
pavement lives compared to the IRI which is predicted as a
function of faulting and transverse cracking among other par-
ameters (MEPDG 2008). Faulting is a function of strains due
to curling of slabs, which in turn is a function of coefficient of
thermal expansion, percent subgrade material passing #200
sieve, and average annual number of wet days. All mixes con-
taining steel slag showed pavement age longer than the control
mix (H0). From an economic perspective, using 100% EAFSS
coarse aggregate, reduces the cost due to the fact that steel
slag aggregate is relatively cheaper than the natural aggregates.
The use of 100% EAFSS (H4 with cement content of 500 kg/
m3
) resulted in a relatively longer pavement life of 24.5, and
27.7 years based on faulting and IRI, respectively, compared
to 22.9, and 26.3 years for H0. This gain in pavement life is in
addition to the lower construction cost and the environmental
benefits. This improved performance is in fact due to the higher
compressive strength, modulus of elasticity, and flexure strength
of the EAFSS mixes. From the strength and pavement life per-
spective, H2 with 50% EAFSS achieved the longest pavement life
compared to all other mixtures with pavement life of 25.9, and
29.5 years for faulting and IRI, respectively which is consistent
with the experimental work results. Using 20% SF resulted in
longer pavement life (25.9 and 29.3 years) for faulting and IRI
respectively, compared to 10% SF +10% SSP (24.8, 28.1 years),
and 20% SSP (23.8 and 27.0 years). This could be imputed to
the better pozzolanic action of SF than that of SSP. These results
encourage the use of EAFSS aggregates as a cheaper and sustain-
able road construction material in addition to all other advan-
tages. It is imperative to indicate that the AASHTOWare,
does not consider the volume instability which is a major con-
cern of several types of steel slag. The suitability criterion
Figure 11. Pavement system used for the AASHTOWare Pavement ME design
runs.
Table 7. AASHTOW are inputs for different pavement layers.
Concrete properties
Mix
Thermal properties
Cement content (Kg/m³) w/c Ratio
Concrete strength parameters at 28 days
Unit weight (t/m3
) K (W/m⋅K) CTE (μɛ/°C) Flexural strength (MPa) Modulus of elasticity (GPa)
H0 2.48 2.113 8.68 500 0.30 13.25 39.73
H1 2.61 1.857 8.80 500 0.30 14.06 40.37
H2 2.68 1.774 8.93 500 0.30 14.47 40.99
H3 2.76 1.713 9.05 500 0.30 14.35 40.78
H4 2.80 1.632 9.18 500 0.30 13.49 39.94
H5 2.72 1.741 8.93 400 0.30 11.32 38.2
H6 2.75 1.904 8.93 600 0.30 16.85 43.78
H7 2.72 1.710 8.93 400 0.30 10.53 37.07
H8 2.74 1.732 8.93 500 0.30 13.23 39.94
H9 2.76 1.862 8.93 600 0.30 15.8 42.61
H10 2.74 1.604 8.93 400 0.30 10.24 36.37
H11 2.75 1.665 8.93 500 0.30 12.64 38.65
H12 2.77 1.771 8.93 600 0.30 13.25 41.24
Unbounded Granular Material and Subgrade Properties
Material Granular Base Subgrade
Material Type According to AASHTO Classification A-1-b A-4
Thickness, cm (in) 30.48 (12) Semi-infinite
Poisson’s ratio 0.35 0.35
CBR (%) 73 10
Passing #200 Sieve (%) 16.6 79.1
Passing #100 Sieve (%) 17.2 —
Passing #80 Sieve (%) —- 84.9
Passing #50 Sieve (%) 20 —
Passing #40 Sieve (%) 22.7 88.8
Passing #30 Sieve (%) 28.2 —
Passing #16 Sieve (%) 30.4 —
Passing #10 Sieve (%) — 93
Passing #8 Sieve (%) 31.8 —
Passing #4 Sieve (%) 41.9 94.9
Passing 3/8 inch Sieve (%) 45.3 96.9
Passing ½ inch Sieve (%) 46.8 97.5
Passing ¾ inch Sieve (%) 51.1 98.3
Passing 1-inch Sieve (%) 57.6 98.8
Passing 1 1/2-inch Sieve (%) 84.3 99.3
Passing 2-inch Sieve (%) 100 100
Specific gravity 2.70 2.7
Liquid Limit, % 25 51
Plasticity Index, % 3.6 30
MDD, t/m3
(pcf) 1.92 (120) 1.6 (100)
Resilient Modulus, MPa (psi) 291 (42205) 76.9 (11153)
14 R. T. ABD EL-HAKIM ET AL.
16. suggested by (Wang 2016) should be followed first in order to
assess expansion issues of the steel slag before using it in con-
crete or HMA mixes.
6. Summary and conclusions
The present study investigated the feasibility of using EAFSS as
a sustainable eco-friendly pavement construction material.
Figure 13. Effect of EAFS content on pavement distresses and age at failure (a) Mean Joint Faulting (b) International Roughness Index (c) Effect of % EAFSS on
Pavement Ages at Failure.
Figure 12. Relationship between pavement age and predicted distresses for all mixtures (a) Mean Joint Faulting (b) International Roughness Index.
INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING 15
17. High strength concrete was manufactured by replacing natural
coarse aggregates with different percentages of steel slag aggre-
gates (0,25%, 50%, and 100%). In addition to that, the effect of
replacing 20% of filler materials by SF or SSP or both was
investigated. An extensive laboratory testing programme
along with the AASHTOWare Pavement ME design software
were used to predict the field performance of a typical JPCP
system based on the investigated concrete mixes. Based on
the experimental testing results and the performance predic-
tion, the following conclusions can be drawn:
. Because of its higher specific gravity, the EAFSS concrete
showed higher density compared to the concrete containing
only conventional dolomite aggregate. As the percentage of
EAFSS increases, the concrete density also increases.
. A linear decrease in concrete workability was found with an
increase in the EAFSS replacement percentage.
. Even though all replacement ratios of the natural coarse
aggregate by EAFSS showed better mechanical properties
compared to the control mix, the optimum percentage of
EAFSS was found to be 50% by weight of coarse aggregate.
. The compressive strength of mixes with EAFSS after 28
days well exceeded 60 MPa which confirms the feasibility
of EAFSS aggregate to produce high performance high
strength concrete.
. With the addition of steel slag coarse aggregate, the com-
pressive strength, tensile split strength, flexural strength,
and modulus of elasticity improved by about 9.0%, 46.5%,
9.2%, and 3.2%, respectively, compared to the control
mix. The improvement in the mechanical properties is
due to the higher density, better angularity, and surface
roughness of the EAFSS as well as the lower interconnected
voids causing increased bond between aggregates and
cement paste.
. Using the SSP powder with or instead of SF was found to
slightly reduce the compressive strength at all ages,
although it is still higher than the control mix.
. The ANOVA statistical analysis confirmed that, incorporat-
ing the EAFSS to replace part of the conventional coarse
aggregate showed a significant impact on investigated
mechanical, physical, and thermal properties of the tested
concrete at a 5% level of significance. Only, the effect on
the modulus of elasticity was not found significant at the
5% level.
. As an application of steel slag in rigid pavements, with the
addition of steel slag coarse aggregate, there is a relative
Figure 14. Effect of Pozzolanic materials content on pavement distresses and age at failure (a) Mean Joint Faulting (b) International Roughness Index (c) Effect of
Pozzolanic Materials Content on Pavement Ages at Failure.
16 R. T. ABD EL-HAKIM ET AL.
18. improvement in pavement service life, with the possibility
of 100% natural aggregate replacement by EAFSS to main-
tain the maximum degree of economy without decline in
pavement performance in terms of thermal cracking, fault-
ing, and roughness.
. The use of steel slag represents a cheaper and sustainable
aggregate in HPC not only saves the natural stone aggre-
gates but also increases the strength of concrete, which con-
tributes to better pavement performance, longer service life,
energy savings, and reduction in greenhouse emissions.
. The extended pavement life will postpone and consequently
reduce the reconstruction and /or rehabilitation processes
which consume natural resources and energy and cause
air pollution resulting from querying operation, and
material transportation.
7. Limitations and recommendations for future
studies
The generalizability of current research findings is limited due
to the lack of free CaO and free MgO contents measurements
after weathering of steel slag and their exact effect on HPC
concrete mixtures expansion. The precise mechanism and
magnitude of expansion in steel slag HPC mixes remains to
be elucidated.
. Further research is required to account for the varying
microstructural development in HPC made with EAFSS.
. An additional study could assess the very long-term dura-
bility behaviour of HPC slag mixes.
. A further study with more focus on life cycle cost analysis of
rigid pavement using EAFSS coarse aggregate is therefore
suggested.
. Future studies on the life cycle assessment of high-perform-
ance concrete using EAFSS coarse aggregate are
recommended
Disclosure statement
No potential conflict of interest was reported by the author(s).
ORCID
Ragaa T. Abd El-Hakim http://orcid.org/0000-0003-4148-6855
Sherif M. El-Badawy http://orcid.org/0000-0001-8348-1580
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