Compressive strength is one of the important properties of concrete as it influences the durability requirements of concrete. This work presents the effects of varying size of aggregate on the strength of concrete. The coarse aggregates used for this study were 10mm, 12.5mm and 19mm uncrushed gravel with river sand as fine aggregate. Sieve analysis was carried out on the aggregates. A nominal mix of 1:2:4 was adopted for the mix and the mix proportions were calculated by weight. The concrete test cubes used were made in batches with each batch containing just one coarse aggregate size. Two test cubes each were made respectively for each batch making a total of 18 cubes and cur ed for 7, 21, and 28 days respectively.

1. http://www.iaeme.com/IJCIET/index.asp 233 editor@iaeme.com
International Journal of Civil Engineering and Technology (IJCIET)
Volume 7, Issue 3, May–June 2016, pp. 233–240, Article ID: IJCIET_07_03_023
Available online at
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=7&IType=3
Journal Impact Factor (2016): 9.7820 (Calculated by GISI) www.jifactor.com
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication
APPRAISAL ON THE STRENGTH OF
CONCRETE PRODUCED WITH VARYING
AGGREGATE SIZE
T.C. Nwofor and D.B. Eme
Department of Civil Engineering,
University of Port Harcourt, P.M.B 5323 Port Harcourt,
Rivers State, Nigeria
ABSTRACT
Compressive strength is one of the important properties of concrete as it
influences the durability requirements of concrete. This work presents the
effects of varying size of aggregate on the strength of concrete. The coarse
aggregates used for this study were 10mm, 12.5mm and 19mm uncrushed
gravel with river sand as fine aggregate. Sieve analysis was carried out on the
aggregates. A nominal mix of 1:2:4 was adopted for the mix and the mix
proportions were calculated by weight. The concrete test cubes used were
made in batches with each batch containing just one coarse aggregate size.
Two test cubes each were made respectively for each batch making a total of
18 cubes and cured for 7, 21, and 28 days respectively. Compressive strength
tests were carried out on all 18 test cubes and their compressive strength
values were recorded. The compressive strength was found to increase with
increase in coarse aggregate size with19mm gravel having as much as
36.31N/mm2
.
Cite this Article: T.C. Nwofor and D.B. Eme, Appraisal on The Strength of
Concrete Produced with Varying Aggregate Size, International Journal of
Civil Engineering and Technology, 7(3), 2016, pp. 233–240.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=7&IType=3
1. INTRODUCTION
Coarse aggregates are relatively inert material fillers which when combined with
cement and water forms a stone-like material called concrete (1-2]. Coarse aggregates
predominantly range from particle sizes of 5 mm to an average of 20 mm size and
most be properly graded to form dense concrete [3-7]. The coarse aggregate mainly
provides the necessary weight to the concrete, hence improving the volume stability
and durability of the concrete, thereby affecting the plastic and hardened state of
concrete through its physical characteristics [1, 8].

2. T.C. Nwofor and D.B. Eme
http://www.iaeme.com/IJCIET/index.asp 234 editor@iaeme.com
Bayasi and Zhou [9] and Ruiz [10] reported that the compressive strength of
concrete increases with an increase in coarse aggregate content up to an optimum
proportion after which there is a marginal decrease and this strength property of
concrete is an important parameter in the design of structures [11-15]. The effect of
increase aggregate sizes as it affects the water-cement ratio have been studied [16].
The study suggested that increasing the maximum aggregate size reduced the total
surface area of the aggregate, thus reducing the mixing water requirements. However,
even with the reduction in water, a larger aggregate produced concrete with low
compressive strengths compared to concrete containing smaller aggregate.
This paper aims at investigating the effects of varying aggregate sizes on the
strength properties of concrete noting that other characteristics of concrete such
impermeability, durability and volume stability may be very important, the
compressive strength is considered the most viable property.
2. MATERIALS AND METHOD
The fine aggregate used in this study was natural river sand obtained from Imo River
in Oyigbo Local Government area of Rivers State, Nigeria. It was washed and air-
dried for two weeks before it was used for concrete work. The granite aggregates
were milled from crushed rock in Rivers State. The aggregates were thoroughly
washed and air-dried for a period of three weeks to remove dirt and later surface dried
before usage. The sizes of uncrushed gravel were 12.5mm, 19mm and 10mm
respectively. The brand of ordinary portland cement used as binder in this study. They
were brought to the laboratory in bags, carefully arranged and contact with moisture
was avoided. The water used for this study was colourless, odourless, tasteless and
fresh. The particle size distribution of fine and coarse aggregates was also carried out
in accordance with the requirements of BS 812, 1985.
2.1. Concrete Mix Design
For the purpose of uniformity and ease in evaluating the effect of coarse aggregate
size on concrete compressive strength, a nominal concrete mix of 1:2:4 was adopted
for each concrete mix containing the different coarse aggregate sizes with water-
cement ratio of 0.6 in compliance with BS 5328: part 1. The result obtained from mix
design is shown in Table 1.
Table 1 Concrete Constituents Mix Proportions
3. RESULTS AND ANALYSIS
The values of compressive strength obtained for different aggregate sizes at varying
curing age of concrete are displayed in Table 2 to 10.
Mix Ratio Batch No. Quantities of Mix Constituents (g)
Cement Sand Gravel
1:2:4 1 1157.28 2314.56 4629.12

3. Appraisal on The Strength of Concrete Produced with Varying Aggregate Size
http://www.iaeme.com/IJCIET/index.asp 235 editor@iaeme.com
Table 2 Compressive Strength Result at 7 Days for 10mm Coarse Aggregate Size
Cube Size
(mm)
Weight of
Specimen
(g)
Density of
Specimen
(kg/m3
)
Age in
(Days)
Load
(KN)
Stress
(N/mm2
)
Material &
Identification Mark
(g) (kg/m3
)
150x150x150
7995 2370 7 398 17.69 10mm aggregate size
150x150x150 7983 2370 7 508 22.58 "
AVERAGE 7989 2370 7 453 20.13
Table 3 Compressive Strength Result at 21 Days for 10mm Coarse Aggregate Size
Cube Size
(mm)
Weight of
Specimen
(g)
Density of
Specimen
(kg/m3
)
Age in
(Days)
Load
(KN)
Stress
(N/mm2
)
Material &
Identification Mark
(g) (kg/m3
)
150x150x150 8211 2430 21 673 29.91 10mm aggregate size
150x150x150 8119 2410 21 652 28.98 "
AVERAGE 8165 2420 21 663 29.44
Table 4 Compressive Strength Result at 28 Days for 10mm Coarse Aggregate Size
Cube Size
(mm)
Weight of
Specimen
(g)
Density of
Specimen
(kg/m3
)
Age in
(Days)
Load
(KN)
Stress
(N/mm2
)
Material &
Identification Mark
(g) (kg/m3
)
150x150x150 8110 2400 28 398 31.02 10mm aggregate size
150x150x150 8124 2410 28 508 31.47 "
AVERAGE 8117 2405 28 703 31.24
Table 5 Compressive Strength Result at 7 Days for 12.5mm Coarse Aggregate Size
Cube Size
(mm)
Weight of
Specimen
(g)
Density of
Specimen
(kg/m3
)
Age in
(Days)
Load
(KN)
Stress
(N/mm2
)
Material &
Identification Mark
150x150x150 8042 2380 7 521 23.26
12.5mm aggregate
size
150x150x150 8074 2390 7 540 24.00 "
AVERAGE 8058 2385 7 531 23.58
Table 6 Compressive Strength Result at 21 Days for 12.5mm Coarse Aggregate Size
Cube Size
(mm)
Weight of
Specimen
(g)
Density of
Specimen
(kg/m3
)
Age in
(Days)
Load
(KN)
Stress
(N/mm2
)
Material &
Identification Mark
150x150x150 7895 2340 21 760 33.78 12.5mm aggregate size
150x150x150 7798 2310 21 748 33.24 "
AVERAGE 7847 2325 21 754 33.51

4. T.C. Nwofor and D.B. Eme
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Table 7 Compressive Strength Result at 28 Days for 12.5mm Coarse Aggregate Size
Cube Size
(mm)
Weight of
Specimen
(g)
Density of
Specimen
(kg/m3
)
Age in
(Days)
Load
(KN)
Stress
(N/mm2
)
Material &
Identification Mark
150x150x150 7998 2370 28 800 35.56
12.5mm aggregate
size
150x150x150 7860 2340 28 782 34.76 "
AVERAGE 7937 2355 28 791 35.16
Table 8 Compressive Strength Result at 7 Days for 19mm Coarse Aggregate Size
Cube Size
(mm)
Weight of
Specimen
(g)
Density of
Specimen
(kg/m3
)
Age in
(Days)
Load
(KN)
Stress
(N/mm2
)
Material &
Identification Mark
150x150x150 8323 2470 7 537 23.87 19mm aggregate size
150x150x150 8287 2460 7 553 24.58 "
AVERAGE 8305 2465 7 545 24.22
Table 9 Compressive Strength Result at 21 Days for 19mm Coarse Aggregate Size
Cube Size
(mm)
Weight of
Specimen
(g)
Density of
Specimen
(kg/m3
)
Age in
(Days)
Load
(KN)
Stress
(N/mm2
)
Material &
Identification Mark
150x150x150 8199 2430 21 794 35.29 19mm aggregate size
150x150x150 8203 2430 21 776 34.49 "
AVERAGE 8201 2430 21 785 34.89
Table 10 Compressive Strength Result at 28 Days for 19mm Coarse Aggregate Size
Cube Size
(mm)
Weight of
Specimen
(g)
Density of
Specimen
(kg/m3
)
Age in
(Days)
Load
(KN)
Stress
(N/mm2
)
Material &
Identification Mark
150x150x150 8224 2440 28 810 36.00 19mm aggregate size
150x150x150 8276 2450 28 824 36.62 "
AVERAGE 8250 2445 28 817 36.31
The compressive strength cuf was determined using:
A
P
fcu 
Where:
P Maximum load on the cube at failure
A Cross-sectional area of the concrete cube specimen

5. Appraisal on The Strength of Concrete Produced with Varying Aggregate Size
http://www.iaeme.com/IJCIET/index.asp 237 editor@iaeme.com
Table 11 Average Compressive Strength Values for Each Concrete Batch
Batch No.
7-Day
Strength
(N/mm2
)
21-Day
Strength
(N/mm2
)
28-Day
Strength
(N/mm2
)
Coarse Aggregate Size
(mm)/ Batch
1 20.13 29.44 31.24 10 (batch 1)
2 23.58 33.51 35.16 12.5 (batch 2)
3 24.22 34.89 36.31 19 (batch 3)
A summary of average compressive strength development in concrete at different
curing age for the different aggregate sizes is shown in Table 11 and plotted in Figure
1.
Figure 1 Strength Development of the Concrete Test Cubes at varying Aggregate Size
For batch 1 concrete cubes made with 10mm coarse aggregate size, about 65%
strength was gained after 7 days while for batch 2 and batch 3 concrete cubes made
with 12.5mm and 19mm coarse aggregate sizes respectively, about 67% each of the
total strength had been reached after 7 days.
The bar chart below shows clearly the effect of the coarse aggregate size on the
compressive strength of the different batches of concrete cubes casted using only the
values for 28th
day strength.
0
5
10
15
20
25
30
35
40
7 days 21 days 28 days
compressivestrength(N/mm2)
batch 1
batch 2
batch 3

6. T.C. Nwofor and D.B. Eme
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Figure 2. 28th
day Compressive Strength for the Concrete Cubes made with different Coarse
Aggregate Size.
From Figure 2, it can be observed that as aggregate size increases, the
compressive strength increases generally. Thus compressive strength and aggregate
size can be related as shown in Figure 3, using only the values for 28th
day strength.
Figure 3 Relationship between Aggregate Size and Compressive Strength at 28th
Day
Compressive strength values for 7-day strength and 28-day strength for all
concrete mix batches agree favorably with Table 12 of BS 12 for concrete made with
Portland cement and strength class of 32.5N (C30 grade).
28
30
32
34
36
38
40
28-daycompressivestrength(N/mm2)
10mm
12.5mm
19mm
30
31
32
33
34
35
36
37
10 12.5 19
28-daycompressivestrength(N/mm2)
Coarse aggregate size (mm)

7. Appraisal on The Strength of Concrete Produced with Varying Aggregate Size
http://www.iaeme.com/IJCIET/index.asp 239 editor@iaeme.com
Table 12 Compressive Strength Requirements for Concrete made with Portland Cement
according to BS 12
Class of
Strength
Early Strength Standard Strength
2 days 7 days 28 days
(N/mm2
) (N/mm2
) (N/mm2
) (N/mm2
)
G32.5 - ≥16
≥32.5 ≤52.5
G32.5 ≥10 -
G42.5 ≥10 -
≥42.5 ≤62.5
G42.5 ≥20 -
G52.5 ≥20 - ≥52.5 ≤72.5
G62.5 ≥20 - ≥62.5 -
In compliance with Table 1 of BS 5328: part 4 shown above, the 28-day
compressive strength for the concrete cubes made for all batches exceeds the
characteristic strength (30N/mm2
) by at least 1N/mm2
, thereby satisfying the
requirements in the code. Therefore, the compressive test results are within acceptable
limits.
4. CONCLUSSION
From the study, the following conclusions are made.
 After 7 days, strength had developed in the concrete cubes to approximately two-
thirds of the 28-day strength which is within acceptable limits.
 The results of this work show that for an increase in coarse aggregate size from
10mm to 19mm at constant water content, the compressive strength increased by
about 16.2 percent.
 The slump value for the mix batch 3containing 19mm uncrushed gravel was higher
than that of mix batch 2 containing 12.5mm uncrushed gravel. This indicates that
water content was increased for mix batch 3 due to a poor level of workmanship.
 The results of this work agree with Ruiz [10] who after their investigations on the
effect of aggregate size on compressive strength stated that strength increases with
increase in aggregate size by about 10 percent.
 The result of this work then tends to disagree with Bloem [16] and Walker [20], who
all concluded that compressive strength decreases with increase in aggregate size by
about 10 percent.
4.1. Recommendation
 The compressive strength of concrete produced with aggregates size beyond 19 mm
is recommended to be considered.
 Further research work considering other attributes of aggregates such as type and
texture is recommended
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