Journal of Minerals & Materials Characterization & Engineering, Vol. 10, No.7, pp.609-615, 2011
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609
Evaluation of the Compressive Strength of Hybrid Clay Bricks
O. Azeez
1
, O. Ogundare
1
*, T.E. Oshodin
1
, O.A. Olasupo
2
, and B.A. Olunlade
1
1
Engineering Materials Development Institute P.M.B. 611 Akure Nigeria.
2
National Agency for Science and Engineering Infrastructure P.M.B. 391 Garki Abuja
Nigeria.
*Corresponding Author: [e-mail]
ABSTRACT
This work has presented the evaluation of the compressive strength of hybrid clay bricks from
interlocking brick making machine. The mixture of clay and cement at varying proportions
was loaded into the mould compartment, mechanically rammed and hydraulically controlled.
The raw clay was sourced from Ilesa and Akure in the south-western part of Nigeria. The
results showed that when the cement content was 6%, the highest compressive load and
energy at break were obtained in hybrid bricks from both Ilesa and Akure samples. However,
the optimum service performance under compressive loading was attained at 6% cement in
Ilesa hybrid bricks. Ilesa hybrid bricks possess better reliability and workability under
loading than the Akure bricks.
Keywords: Hybrid bricks, compressive strength, clay, cement, interlocking machine.
1. INTRODUCTION
Clay based material is one of the materials that has been widely used in construction
materials instead of wood, sand, concrete and other waste materials. This material is a major
compound in clay brick, clay tiles and clay roofing tiles due to its wide-ranging properties,
high resistance to atmospheric condition, geochemical purity, and easy access to its deposits
near the earth’s surface and low price. Fired clay brick (FCB) can be categorized as one of
the demolition wastes as most of the unwanted FCB from buildings or houses renovation are
being illegally disposed off in most places. The utilization of this type of clay based waste
materials would replace the natural aggregates in concrete mixture [1]. Studies related to
ancient clay bricks alone deal mainly with physical, chemical, and mineralogical composition
[2,3,4], durability and deterioration agents [5] and deterioration modelling [6,7,8] neglecting
the mechanical properties.

610 O. Azeez, O. Ogundare, T.E. Oshodin, O.A. Olasupo, and B.A. Olunlade Vol.10, No.7
The compressive strength is a mechanical property used in brick specifications, which has
assumed great importance for two reasons. Firstly, with a higher compressive strength, other
properties like flexure, resistance to abrasion, etc., also improve. Secondly, while other
properties are relatively difficult to evaluate, the compressive strength is easy to determine
[9]. Generally, compressive strength decreases with increasing porosity but strength is also
influenced by clay composition and firing.
Compression testing is a method for assessing the ability of a material to withstand
compressive loads. This test is commonly used as a simple measure of workability of
material in service. Materials behave differently in compression than they do in tension so it
may be important to perform mechanical tests which simulate the condition the material will
experience in actual use. Compression testing is typically carried out on the following
materials; Plastics, Foams, Rock, Concrete and Asphalt. It is rarely used to test metals [10].
Compressive strength of Blocks and Bricks is a critical parameter for determining the quality
of these materials. The loads and forces acting on these materials while in service are
compressive in nature and their ability to withstand such loads and forces without failure is a
measure of their reliability [11].
The tasks of inspection and diagnosis of ancient buildings require obtaining a certain number
of parameters, which provide information about the properties of the materials, the structural
behaviour, or possible defects. Mechanical characterization is a fundamental task for the
structural works and safety assessment, where the compression strength is a key parameter in
the case of masonry structures. In fact, the compressive strength of masonry in the direction
normal to the bed joints has been traditionally regarded as the sole relevant structural material
property, at least until the recent introduction of advanced numerical methods for masonry
structures [12].
The aim of this research is to evaluate the compressive strength of hybrid bricks from 8-
mould interlocking brick making machine.
2. MATERIALS AND METHODS
2.1 Materials
The samples were collected from certain locations in Ilesa and Akure in South western part of
Nigeria. The Ordinary Portland Cement (OPC) was obtained commercially.
2.2 Method
The clay sample was mixed with water to desired consistency. Ordinary Portland Cement
(OPC) was added in different percentages ranging from 0% – 14% putting into consideration
the volume of each mould. The OPC was thoroughly mixed with the clay sample for even
distribution and homogeneity. The aggregate was loaded into the eight moulds of the
interlocking machine. After sometime, the hydrid bricks were hydraulically lifted out of the

Vol.10, No.7 Evaluation of the Compressive Strength of Hybrid Clay Bricks 611
moulds. The interlocking machine used for this research was the 8- Mould Interlocking Earth
Brick Making Machine which was designed, developed and fabricated at Engineering
Materials Development Institute Akure Nigeria. Each sample was left for the first 28 days for
proper curing and sufficient strength before compression testing was carried out.
2.3 Compression Testing Procedure
For the compression test, the specimens were cut from the bricks to be tested in the direction
of the moulding or perpendicular to bed joints (see Fig.1), which is the usual loading
direction in building elements (e.g., walls and vaults) subjected to dead load. Generally, very
small specimens were obtained, with typical cross sections of 30mm x 30 mm and 30mm of
height. All specimens were ground using a rectifying machine, so that the loading faces were
properly aligned. The test setup for the compression tests was carried out on Instron
Universal Tester model 3369 available at the Engineering Materials Development Institute
Akure Nigeria. Its steel frame was equipped with a compression load cell with a maximum
capacity of 50 kN and connected to a software- driven computer system. The steel platens
were rectified in order to provide a flat surface. The lower platen has a spherical seat made of
tempered steel that allows the initial alignment and accommodation of the specimen, thus
facilitating the alignment of the applied load with the centre of the specimen as well as
preventing any other unfavourable effect due to geometrical imperfection of the specimen.
The Instron software was programmed to capture all data during the course of the test.
Fig. 1 Schematics showing how specimens were cut from bricks and direction of compression
tests
3. RESULTS AND DISCUSSION
Figure 2 shows the bar chart of compressive load at break of hybrid bricks made from Ilesa
samples. The mixing of Ordinary Portland Cement (OPC) in different percentages has
revealed the different compressive strengths. It was observed that when no cement (0%
cement content) was mixed, a compressive strength of 727.91 N was obtained. This shows
the fact that the virgin clay sample possesses a reasonable compressive strength. With 4%
cement mixed with the clay sample, a compressive load at break (crushing strength) of
481.03 N was obtained. It was observed that when 6% cement was mixed with the clay
sample before loading into the interlocking machine, the highest compressive load at break of
2,537 N was obtained. This shows that 6% hybrid bricks will be able to withstand 2537 N
before failure under loading. This is because at this percentage, the cement elements were

612 O. Azeez, O. Ogundare, T.E. Oshodin, O.A. Olasupo, and B.A. Olunlade Vol.10, No.7
able to penetrate most into the matrix of the clay resulting in strong interlinking and bonding
network of the hybrid brick. This means that in service, 6% hybrid bricks will be used under
compressive loading up to 2,537 N.
Fig. 2 Compressive Load at break of hybrid bricks from Ilesa samples
Figure 3 shows compressive load at break of hybrid bricks from Akure samples. It was
observed that the highest compressive load was obtained at 8% cement ratio and followed by
14% cement ratio. This was closely followed by 6% cement ratio. This is because the cement
elements were able to intertwine the network of the clay elements at the highest capacity at
8% cement ratio. This resulted in formation of strong matrix of the hybrid bricks with the
same compressive stress values of 1.12 MPa and 1.11 MPa at 6% and 14% cement ratio
respectively as shown in figure 4 below.
Fig. 3 Compressive Load at break of hybrid bricks from Akure samples
0
500
1000
1500
2000
2500
3000
Compressive Load at break of Hybrid bricks from
ILESA samples
0% Cement
4% Cement
6% Cement
8% Cement
10% Cement
12% Cement
14% Cement
Compressive Load at break (N)
% OPC in clay
0
200
400
600
800
1000
1200
0% Cement
4% Cement
6% Cement
8% Cement
10% Cement
12% Cement
14% Cement
Compressive Load at break (N)
% OPC in clay
Compressive Load at break of Hybrid bricks from AKURE samples

Vol.10, No.7 Evaluation of the Compressive Strength of Hybrid Clay Bricks 613
Fig.4 Comparative Compressive Loads at break of hybrid bricks from Ilesa and Akure
samples
The comparative compressive loads at break of hybrid bricks from both Ilesa and Akure
samples are presented in figure 4 above. At a glance, it can be observed that at 0%, 6%, 10%
and 12% cement ratios, the compressive resistance of Ilesa Hybrid bricks are better than that
of Akure. This may be due to geographical and environmental factors on the virgin clay since
that same ordinary Portland cement was mixed
.
Fig.5 Energy at break of hybrid bricks from Ilesa samples
0
500
1000
1500
2000
2500
3000
1
2
3
4
5
6
7
Compressive load at
break of AKURE
samples
Compressive load at
break of ILESA
samples
Comparative Compressive Load at break of Hybrid bricks
from AKURE and ILESA samples
Compressive Load at break (N)
% OPC in clay
Key
1 - 0% Cement
2-4% Cement
3 - 6% Cement
4 - 8% Cement
5 - 10% Cement
6 - 12% Cement
7 - 14% Cement
0
10
20
30
40
50
60
70
80
% OPC in clay
0% Cement
4% Cement
6% Cement
8% Cement
10% Cement
12% Cement
14% Cement
Energy at break (J)
Energy at break of Hybrid bricks from ILESA samples

614 O. Azeez, O. Ogundare, T.E. Oshodin, O.A. Olasupo, and B.A. Olunlade Vol.10, No.7
Fig. 6 Energy at break of hybrid bricks from Akure samples
Figure 5 is a bar chart of energy at break of hybrid bricks from Ilesa samples. It shows that
energy absorbed (71 J) before failure is greatest at 6% cement ratio. This is to support the
highest compressive load at break that also occurred at 6% cement ratio (see Fig. 2 above). In
other words, the energy absorbed is directly proportional to the compressive strength
characteristics. This is due to high adhesive property between the clay and the cement
particles resulting in high resistance to dislocation stress.
Figure 6 is a bar chart of energy at break of hybrid bricks from Akure samples. It can be
observed that the highest energy absorbed before break of 16 J was at 6% cement ratio.
4. CONCLUSION
On the strength of the results presented above, it can be concluded that
1. The optimum service performance under compressive loading was attained at 6%
cement in Ilesa hybrid bricks.
2. Ilesa hybrid bricks possess better reliability and workability under loading than the
Akure bricks.
3. Ilesa clay has better binding characteristics and quality than the Akure species.
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