1. TENSILE CHARACTERISTICS OF NO
AGGREGATE CONCRETE
Abstract - This paper considers the tensile characteristics
of no aggregate concrete and its practical usability in
construction activities. In the present context most of the value
engineers look for modification in the conventional concrete to
enhance the performances and also to make construction
activities more feasible. Since this is a newly introduced
material it is essential to identify the major strength
characteristics of the material and the behavior in practical
situations. Therefore this paper has identified the basic
properties of the No Aggregate Concrete and the behavioral
patterns with various mixing proportions. At the same time it
has identified probable practical difficulties in real time
scenarios and suggestions to minimize those effects. Specimens
were tested for 7, 14 and 28 days and compared the results
obtained with conventional concrete.
Keywords – No Aggregate Concrete; Tensile characteristics;
Properties of No Aggregate Concrete; Elastic Modulus
INTRODUCTION
Concrete can be identified as the most commonly used
construction material on earth in the present context. With
the increasing demand for the natural resources in the
developing world construction industry finds it difficult to
acquire adequate composites to manufacture traditional
concrete. Therefore manufacturing durable concrete using
industry waste products will be beneficial and provide
solutions to the trending issues in the industry. When fine
and coarse aggregates are replaced completely in concrete
then it is called no aggregate concrete.
Since all the aggregates have been replaced with fly ash,
the density of NAC is lesser than the conventional concrete.
According to past research data density of a similar kind
concrete is around 1850 – 2000 kg/m3
[1]. This will address
many present construction issues which are mainly related
weight and durability. Also there could be considerable
savings in structural design and inputs. When aggregates are
not available in concrete it devoid the transition zone and
many durability issues would be addressed in one stroke [2].
Even the inert fly ash particles develop cohesive bond with
cement matrix making the ultimate NAC matrix close to
monolithic [3]. Based on previous experimental research
some beneficial effects have been reported that fly ash was
able to enhance the compressive strength when used as a
replacement material with low water cement ratio [4].
The main objective of this research is to identify tensile
characteristics of NAC. Therefore the paper focuses mainly
on how the tensile characteristics varies of this
unaccustomed material based on time and different mix
proportions. Though concrete has very low tensile capacity
compared to compression capacity it is difficult to isolate
concrete members from dynamic tensile stresses. This is a
crucial design parameter especially in structures such as
concrete dams, airfield runways, concrete roads and
pavements and other slabs. Therefore good understanding
about the tensile characteristics and tensile capacity will give
a broad insight on the load at which the concrete members
may crack. Cracking is a form of tension failure. Also the
elastic modulus for this material has also been identified so
complex numerical models can be developed using the
results.
Identifying the material used for the research and their
mechanical and physical properties have identified in the
Section 2. Section 3 explains the methodologies followed in
order to achieve the final objectives of the research. Section
4 discusses the results ascertained from the experiments and
a brief analysis on each result. Section 5 concludes the paper
while summarising all the results observed and suggesting
probable further developments to the research topic.
MATERIAL DESCRIPTION
Cement
OPC (grade 42.5) was used. It is manufactured in
compliance with Sri Lankan Standard SLS 107:2008 and
British Standard CEM I 42.5N of BS EN 197-1:2000.
Physical and chemical compositions of cement.
Density 3.15 g/cm3
Fineness 340 m2
/kg
Soundness 0.32 mm
Setting time (Initials) 125 min
Comp. strength at 2 days 30.8 MPa
at 28 days 58 MPa
Chemical compositions
CaO 64.5%
SiO2 20.5%
Al2O 3 5.7%
Fe2O 3 2.9%
MgO 1.27%
SO3 2.15%
Cl-
0.009%
Loss of ignition 3.0
D.D Nakandala (110379D)
Department of Civil Engineering
University of Moratuwa
Moratuwa, Sri Lanka
dulannakandala@gmail.com

2. Fine aggregate
Local river sand with a 5mm maximum size was used. It
conforms to BS 882.
Coarse aggregate
Crushed rock aggregate of 20mm nominal size were used.
It met the requirements of BS 882
Fly ash
Class F fly was used for the study and met requirements
of ASTM C 618
Properties and chemical compositions of fly ash
Density 2.16 g/cm3
Blaine fineness 3310 cm2/g
pH 4.6
Loss of ignition 4.0%
Chemical compositions
SiO2 62.4%
Al2O3 3.3%
Fe2O3 3.19%
K2O 1.38%
CaO 0.98%
MgO 0.55%
SO3 0.24%
Na2O 0.19%
Superplasticizer
A commercially available fourth generation
superplasticizer formulated specifically to give high range
water reduction with retarding effect for hot weather
construction was used. It conforms to the requirement of
ASTM C4g4 Type G, BS 5075 and SS320: 1987
METHODOLOGY
Material proportions for NAC
For normal concrete, BRE mix design procedure were
adopted to identify the mix proportions needed to gain grade
30 strength. Since no standard method is available for mix
design of NAC, the procedure followed was preparing
several trial mixes. This was done by assuming a density
initially and varying mix proportions (keeping the cement
quantity constant) till the mix get the assumed density. After
several trial mixes the appropriate mix proportions were
found as shown in table 1 and used it for test batch
preparations.
Table 1 Mix Proportions of Different Mixes
Mixing procedure
The normal concrete batch was mixed following the
general procedure where coarse aggregates were added first
and cement was added last. Then it was mixed till it form a
good paste. However this procedure was quite different when
it came to NAC mixing. In that mix, cement and fly ash was
mixed together first using shovel. Supercrete (Plasticizer)
was mixed with the measured water quantity. After mixing
fly ash and cement in the drum mixer without any
interruptions for few minutes 90% of the liquid mixture
(water and plasticizer) was added completely. Mixing was
continued till it form a good paste and the remaining liquid
mixture was added appropriately.
Specimen details
For this research four different batches were produced.
Those batches were namely normal concrete, NAC, 10%
cement increased NAC and 10% fly-ash increased NAC.
Variations in mix proportions were done in order to identify
the strength behavior in NAC. All those batches were tested
for 7, 14 and 28 days. Since splitting tensile strength were
tested it was used 150 mm x 300 mm cylinders for testing
purposes. To reduce the error margin 3 cylinders were casted
for each test and took the average. The mix designs of the
concretes are shown in the table 1.
Splitting tensile test
The present study mainly focuses on tensile properties
observed from splitting tensile test. The tests were performed
as shown in figure 1 at the ages outlined previously to
determine the relationships with tensile properties. This test
method consists of applying a diametral compressive force
along the length of cylindrical concrete at a prescribed rate
until failure occurs. ASTM standards [5] were followed as
stated during the testing period. Tensile strength of the
specimen (T) can be estimated from equation (1).
T = 2P/πld (1)
Where P is the applied load in kN, l is the length of the
specimen in meters and d is the diameter of the specimen in
meters.
Figure 1: Performing splitting tensile test
Normal
Concrete
(1 m3)
NAC (Mix 1)
1 m3
NAC (Mix
2)
10%
cement
increased
1 m3
NAC (Mix
3)
10% fly
ash
increased
1 m3
Cement 350 kg 350 kg 385 kg 315 kg
Coarse
Aggregates
1075 kg - - -
Fine
Aggregates
875 kg - - -
Fly Ash - 1400 kg 1365 kg 1540 kg
Supercrete 5.25 l 8.6 l 8.5 l 8.5 l
Water 300 l 300 l 328 l 335 l

3. Determining static modulus of elasticity
Since this is novel material it is essential to identify the
basic properties of the material. This will help for further
studies and to develop numerical models. In order to identify
static modulus of elasticity test procedure given in ASTM
C469 was followed. The cylindrical compressive strength
was calculated using ASTM Designation: C 39 before the
test. The cylindrical compressive strength value obtained
was 20.53 N/mm2
. Loads and readings of the dial gauge were
recorded as specified in the standard. Following equation (2)
was used to determine the static modulus of elasticity.
E =
(s2 – s1)
(ε2 – 0.000050)
(2)
E = Chord modulus of elasticity
s2 = Stress corresponding to 40% of the estimated ultimate
load or ultimate stress, based upon previously tested
specimens in accordance with ASTM Designation: C 39
s1 = Stress corresponding to a longitudinal strain of 0.000050
ε2 = Longitudinal strain corresponding to the s2 stress
ε1 = Strain 0.000050 and, therefore, does not appear in the
formula for E.
TEST RESULTS AND DISCUSSION
Tensile strength comparison between normal grade 30
concrete and NAC
From figure 2 and it is clear that the Normal grade 30
concrete is having higher tensile capacity compared to the
NAC which had same cement content. Both concrete types
showed an increase in strength with time but at the end of 28
days normal concrete gave a tensile strength of 3.07 MPa
where NAC gave only 2.36 MPa. The values obtained is an
average value of 3 specimens.
This difference may be due to the high brittle nature of NAC.
Brittleness is one of the governing factors in determining
tensile strength.
Variability of tensile strength with changes in mix
proportions in NAC
Since this is a novel material strength behavior is
unknown. To identify the strength behavior, different mix
proportions were tested. Keeping the original mix
proportions for NAC as the yardstick, percentage increase in
materials was done to the other two batches. However all
three batches showed lesser tensile capacities than the
normal concrete. In the second batch where 10% cement was
increased gave the highest tensile capacity with a strength of
2.45 MPa in 28days. In the third batch where 10% fly ash
was increased had very low tensile capacities where only
1.98 MPa gained after 28 days. All the 3 batches showed
increase in strength with time and this variation is visible in
figure 3. This strength increase in NAC with time can be
explained by referring to the improved microstructure in the
concrete. Use of finer particles for the aggregate leads to
densification of matrix and secondary reaction between fly
ash and CH in the transition zone also improves the
microstructure of the concrete.
This variation in strength with different mix proportions
is probably due to the level of unreacted fly ash content
available in the final concrete mix. In the second batch when
the cement was increased more fly ash might have reacted
with cement and gave better tensile capacity.
Reason for increase in strength with time can be explained
by the amount of CH and rate of reaction of fly ash with CH.
This is represented by cementing efficiency factor of fly ash
at the age.
Density variation in normal concrete and NAC
In the figure 4 it is clear that normal concrete has much
higher density compared to NAC. The density of normal
concrete was around 2400 kg/m3
where NAC had only a
density of 2100–2000 kg/m3
. This may be due to the
replacement of aggregates which have higher specific
gravity than fly ash. Densities of different batches in NAC
also had slight variations. Where NAC (batch 1) had much
higher density and NAC (batch 3) had the lowest density.
Densities reduce with time in all the scenarios and this is
probably due to moisture loss in concrete with time.
Figure 2: Tensile strength variation in normal concrete & NAC
Figure 3: Tensile Strength variation of different NACs
Figure 4: Density variation with time

4. Relationship with compressive strength and tensile
strength in NAC
Generally in concrete tensile strength is known to be
around 10% of the compressive strength. In this research
compressive strength of normal concrete was around 36.7
MPa and the tensile capacity was around 3.07 MPa which is
9% of compressive strength obtained. However this is
different when it comes to NAC. Because from the values
obtained tensile strength of no aggregate concrete was only
about 5%-6% of compressive strength of NAC. So compared
to normal concrete there is a considerable reduction in tensile
strength in NAC. This variation is illustrated in figure 5.
In NAC because of the fly ash substitution micro structure
of the material was enhanced. Because of this compressive
strengths increased. Also there is a better compaction in this
material which gives favorable results in compression.
However due to high brittleness of the material it has very
low tensile capacity compared to normal concrete. Since
there are no any aggregates the surface friction is also lesser
in NAC which might has led to low tensile capacity. Due to
these reasons ratio between tensile strength and compressive
strength of NAC is much lower than the value obtained in
normal concrete.
Properties of NAC
Some mechanical properties of NAC was identified
which will be helpful in future experiments and other
modelling activities. Using ASTM C469 it was found that
elastic modulus (E) of NAC is around 11.58 GPa. In normal
concrete (G30) this value was around 26 GPa. Also from the
results stress strain graph was developed as shown in figure
6.
Also from the obtained test results and visual
observations it was identified that the material is highly
brittle.
CONCLUSION
The present study aimed to obtain the tensile properties
of NAC. This paper describes splitting tensile strength and
Young’s modulus of NAC and also some behavioral patterns
in tensile strength of NAC under various conditions.
 Tensile capacity of NAC is lesser than the tensile
capacity of normal concrete which has the same
cement content.
 Tensile capacity of NAC can be increased by replacing
some amount of the fly ash with cement in the original
mix. If the tensile capacity has to be decreased then
cement should be replaced with fly ash.
 Density of NAC is lower than the density of normal
concrete. Also the density values reduce with time.
 Ratio between tensile strength and compressive
strength is lesser in NAC compared to normal
concrete. In NAC tensile strength is around 6% of
compressive strength but in normal concrete this value
is around 10%.
 Young’s modulus of NAC (11 GPa) is lower than the
Young’s modulus of normal concrete (26 GPa).
 Brittleness of NAC is higher than the brittleness of
normal concrete.
 Workability and the setting time in NAC is higher than
the normal concrete.
 Surface condition of NAC is better than normal concrete
and has a very smooth surface.
 As a final note it is not recommended to use 100%
aggregate replaced concrete. However viable solution
would be partial replacement of fine aggregates.
REFERENCES
[1] Fahrizal Zulkarnain, Mahyuddin Ramli. Durability
performance of lightweight aggregate concrete for
housing construction. 2008.
[2] Clarke, J.L. (1993) Structural Lightweight
Aggregate Concrete (First Edition). Glasgow,
Blackie Academic & Professional, an imprint of
Chapman & Hall, Wester Cleddens Road, Bishop
Briggs.
[3] Bhanumathidas N & Kalidas N(2010). Irrational
concrete with rational performance. The institute of
solid waste research and ecological balance,
Vishakhapatnam.
[4] Hossain AB, Islam S, Copeland KD. Influence of
ultrafine fly ash on the shrinkage and cracking
tendency of concrete and the implications for bridge
decks.
[5] Standard test method for splitting tensile strength of
cylindrical concrete specimen. ASTM (C496)
Figure 5: Comparison between Compressive strength & Tensile
strength
Figure 6: Stress vs Strain graph