Abstract—Brick masonry plays an important role in the field of construction, signifying the need to study the nature of behaviour of masonry in different conditions and compositions. In this paper, studies on the experimental investigation of material properties, compressive and shear behaviour of brick masonry with different mortar ratios are presented. The material properties are evaluated from compression testing of brick units, mortar cubes and cylinders. Bricks are tested in dry and wet conditions in order to make a comparative study of the material behaviour along all three axes. Compression and shear tests on brick prism triplets with different mortar ratios are performed to evaluate and compare their compressive strength, bond strength and interface behaviour. The results obtained from the compression and shear tests are then evaluated and contrasted. The research carried out would facilitate to evaluate the behavior of unreinforced brick masonry using numerical simulations under shear and compression loading. Keywords—Brick masonry, Material properties, Mortar ratios, Shear

I. INTRODUCTION N the history of construction, brick masonry contributes the major portion in the development of eminent historical

masonry structures. Since then, this most economical and suitable method of construction gained more importance and huge structures started to emerge all over the world. The materials required for construction of brick masonry were easily available in the ancient period.

In later years, Introduction of new technologies in the field of construction made a great impact in the history of construction. Advanced construction practices were adopted using new materials to increase the strength and stability of the structures. However, this affected the economical factor since huge investment was required to implement this new method of construction. New research and developments in this concern have improved the accuracy and hence the developed

1 – Final year Civil Engineering, Bannari Amman Institute of Technology, Sathyamangalam, India.

2 – Principal Scientist, CSIR-Structural Engineering Research Centre, Chennai, India.

3 – Assistant Professor, Department of Civil Engineering, Bannari Amman Institute of Technology, Sathyamangalam, India.

*– Corresponding Author. E-mail address: ntp1393@gmail.com

countries started to fund for the implementation of new construction methodologies into practice. Tremendous improvement was found due to the implementation of these technologies and this overtook the importance of brick masonry. Still, masonry buildings were in practice in many places around the world as this could only satisfy the economical method of construction of the basic requirements of the people.

But, many ancient masonry structures failed due to their inadequate design against structural durability and strength. This facilitates the importance to study on the brick masonry in order to predict their behaviour and properties. Many researches have been carried out in the past to stipulate the nature of brick masonry and their constituent materials under different circumstances. But, there are no proper results published or standard specifications that could meet the requirements of the engineers. Further research in this field is necessary to understand their heterogeneous material properties and to gain an in depth knowledge about their behaviour.

The present paper deals with the experimental investigations of the constituent material properties of the brick masonry for different mortar ratios. Burnt clay bricks of standard size are used to determine their individual properties. Brick triplet prisms were cast with different mortar ratios to identify their composite material properties. The stress-strain curve is plotted from the experimental data. The flexural strength of unit brick is found using flexural testing based on the Indian standard code [1]. The shear bond strength of triplet brick prisms is also calculated based on the experimental maximum shear load withstand by the specimen.

The strength of masonry structure mainly depends on the strength of bonding between the bricks. Interface between the mortar and brick plays a vital role in enhancing the strength of masonry. Hence, the interface behaviour of masonry is also discussed in this paper. Further studies are also proposed to identify the interface model and bond-slip relation of brick triplet prism for different mortar ratio based on the experimental results which is useful for numerical studies on brick masonry.

As a result of the literature study, few important observations are listed as follows. Palanisamy and Premalatha

Experimental Approach to Investigate the Behaviour of Brick Masonry for Different

Mortar Ratios Thanikasalapradeep Nagarajan1*, Selvakumar Viswanathan1, Sinthiya Ravi1, V.Srinivas2, and

Premavathi Narayanan3

I

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[2] studied on the experimental investigation of masonry infill material properties. Masonry infill walls were constructed using different types of structural blocks to investigate their behaviour. Experiments were carried out using fly ash and clay brick prisms of CM1:4, CM1:5 and CM1:6 for 7 days and 28 days curing period. The stress-strain curve is plotted based on the experimental results. The fly ash brick prism achieved maximum strength compared to the clay brick prism.

Nowfer [3] carried out uniaxial compressive test to determine the mechanical properties of unreinforced masonry constituent materials. Based on the results, the stress-strain relationship is defined and a simple numerical model is also formulated to estimate the elastic modulus. The values are used as the input for the numerical modeling of masonry which is used for nonlinear finite element analysis.

Christy et al. [4] studied the bond strength of brick masonry triplet and found that it varies with difference in the mortar or masonry unit combination. The bond strength of triplet clay and fly ash brick prism was determined using mortar with and without pozzolanas. The result showed that the presence of fly ash increased the bond strength.

Meghashree and Satish [5] deals with the experimental identification of shear strength of brick masonry by 100% replacement of pond ash in place of cement mortar. Experiments are carried on brick triplets and masonry wall panels for determining the shear bond strength and diagonal split tension respectively. The author has recommended further studies by using pond ash to increase the strength of masonry.

II. PROPERTIES OF MATERIAL

A. General Brick masonry exhibits heterogeneous property due to

different constituent materials. Hence, it is important to identify the individual properties of brick and mortar to understand the overall behaviour of masonry. Experiments were carried out using the compression testing machine and the compressive strength is determined. The maximum strain values for individual material are also tabulated from the experimental results.

B. Brick The bricks used in the research are the handmade burnt clay

bricks of uniform shape and size. The dimension of the bricks is measured using measuring scale. The average dimension was found to be 220mmx100mmx75mm. The quality of brick is ensured by its appearance and the good bricks are selected from the brick stack as per the requirements.

C. Cement The 53 grade ordinary Portland cement is used in this

research to cast mortar cubes and cylinders. The cement mortar is prepared using this OPC and fine aggregate with suitable water-cement ratio which is further used to cast triplet brick prisms.

D. Sand The river sand is used to prepare the cement mortar as per

the mix proportion. The sand is sieved using 1.2mm sieve to prepare a fine mix of the cement mortar.

III. TEST ON BRICK UNIT

A. General Tests on individual brick units include the determination of

water absorption capacity and compressive strength. Since, the burnt clay bricks are porous in nature, the absorption capacity is found using the water absorption test as per IS 3495 (Part 2): 1992 [6].

Totally three brick specimens are weighed and their individual weight is noted (M1). These specimens are immersed in water for 24 hours. After 24 hours the specimens are removed from water and wiped to determine their weight (M2). The water absorption after 24 hours immersed in water is given by the formula (1),

M2 – M1 × 100 (1) M1

The water absorption values of bricks used in the present study are given in Table I from which the water absorption of the bricks is found to be around 14%.

TABLE I WATER ABSORPTION

Specimen No

Brick Dimension (mm)

Water Absorption (%)

1 220×100×74 10.71

2 220×100×75 13.33

3 220×105×75 18.52

B. Compression Test on Brick Units The maximum load that the burnt clay brick can withstand is

determined using the compressive strength test as per IS 3495 (Part 2): 1992 [6]. Compressive strength of brick depends upon the composition of clay, method of brick manufacturing and degree of firing [4]. The bricks are tested along three axes both in wet and dry conditions as shown in Fig 1. The test is carried out using the compression testing machine of maximum 300 tonnes capacity. The test is progressed with a constant rate of loading of 50 N/s. The frog of the brick is filled with mortar and the level of bed surface is also ensured before testing.

Compressive Strength = in N/mm2 (2)

The load at which the brick fails in (N) is noted and the maximum compressive strength of individual brick is

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evaluated by the above mentioned equation (2) and the values are given in Table II. The average compressive strength of bricks used is found to be 3.57MPa in the x-axis direction.

TABLE II

COMPRESSIVE STRENGTH OF BRICK UNIT S.No

Axis of Testing

(Refer Fig.1)

No of Specimens

Average Compressive

Strength of Brick ( N/mm2 )

Dry Brick

Wet Brick

Dry Brick

Wet Brick

1 X-Axis 3 3 3.93 3.57 2 Y-Axis 3 3 2.67 2.49 3 Z-Axis 3 3 1.64 1.27

From the experimental data, the stress-strain graphs are

plotted for dry and wet bricks for the three different axes of testing. A comparative study is made by plotting the combined stress-strain graph for the dry and wet bricks for each axis as shown in Fig 2-4.

(a) (b)

(c)

Fig 1 Compression Test on Brick Unit (a) Along X-axis,

(b) Along Y-axis and (c) Along Z-axis

Fig 2 Stress-Strain Curve for Dry and Wet Brick along X-axis

Fig 3 Stress-Strain Curve for Dry and Wet Brick along Y-axis

Fig 4 Stress-Strain Curve for Dry and Wet Brick along Z-axis

Dry bricks are found to be giving more compressive

strength than the wet bricks. The value of young’s modulus obtained from the stress-strain curve plotted from the experimental results of the compression testing on brick is found to be 3070MPa.

C. Flexural Strength Test on Brick Unit The flexural strength of brick is obtained experimentally as

shown in Fig 5 based on the Indian standard code IS: 4860-1968[1]. The flexural breaking load (P) for individual brick is noted for three different specimens. The flexural strength of brick specimen with breadth (B) and depth (D) is calculated using the formula,

Where, (L) is the intermediate span between the supports.

Fig 5 Flexural Test on Brick Unit

x

y

z

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The value of flexural strength of brick is given in Table III. The average flexural strength of brick is found to be 1.12MPa.

TABLE III FLEXURAL STRENGTH OF BRICK UNIT

Specimen No Failure Load (kN) Flexural Strength (N/mm2)

1 2.72 1.137

2 2.62 1.095

3 2.70 1.128

IV. TEST ON CEMENT MORTAR

A. General The cement mortar plays a vital role in the construction of

brick masonry as its property greatly influences the strength of masonry. The strength of masonry bond depends on the type of mortar used and the thickness of mortar joint between the brick units [7]. Hence, this specifies the importance of cement mortar and their properties. In order to know their behaviour and properties, cubes and cylinders were cast using standard moulds for different mortar proportions of 1:2, 1:3 and 1:4 to determine their strength experimentally. The moulds are removed after 24 hours and the cubes are allowed for curing for a period of 15 days.

B. Determination of compressive strength of mortar cubes and cylinders

The cement mortar cubes and cylinders of standard size were cast for 1:2, 1:3 and 1:4 mix proportions and cured for 15 days. Totally twelve cubes are tested using the compression testing machine as shown in Fig 6 to calculate the maximum compressive strength as stipulated by IS 2250-1981 [8] and the values of compressive strength are given in Table IV . From the experimental data, stress-strain curve is plotted as shown in Fig 7 and the Young’s modulus of cement mortar obtained is given in Table V. The compressive stress obtained from the test on cubes and cylinders is compared and is shown in Fig 8.

(a) (b)

(c)

Fig 6 Compressive Strength Test (a) CM Curing (b) CM Cube and (c) CM Cylinder

TABLE IV COMPRESSIVE STRENGTH OF CEMENT MORTAR CUBE

S.No Mortar Proportion

Average Compressive Strength (N/mm2)

1 1:2 18.19

2 1:3 15.47

3 1:4 11.81

Fig 7 Stress-Strain Curve for Mortar Cube for Different Mortar

Proportions

TABLE V MODULUS OF ELASTICITY AND MAXIMUM STRAIN VALUES OF MORTAR

S.No Mortar Ratio

Modulus of Elasticity

(MPa)

Maximum Compressive Strain (mm)

1 1:2 5385 0.0083 2 1:3 4075 0.0078 3 1:4 3600 0.0076

Fig 8 Comparison of Cube and Cylinder Strength for Different

Mortar Proportions

V. TEST ON TRIPLET BRICK PRISM

A. General Along with the individual properties of the constituent

materials of brick masonry, the composite behaviour is also

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studied by different experimental tests on triplet brick prism [9]-[16]. The behaviour of constituent materials of brick masonry varies in individual and composite state. In order to understand their behaviour, a total of 24 brick triplet prisms were cast for different mortar mix proportions to identify their compressive strength, shear bond strength and their interface behaviour. Based on the experiment results, the values obtained are used as the input to numerical models for finite element analysis of the same in order to establish a comparitive study.

B. Determination of compressive strength of triplet brick prism

Ganapathi, et al [11] found that the compressive strength of brick prisms vary based on the failure pattern, Water absorption, mortar proportion and individual compressive strength of bricks. In this research, triplet brick prisms were cast using different cement mortar proportions 1:2, 1:3 and 1:4 with bond thickness of 10mm and cured for 15 days. The compressive strength of brick prisms are obtained from the test as shown in Fig 9 and the average of three test specimen results for respective mortar proportions are given in Table VI. Corresponding stress-strain curves is shown in Fig 10 and the values of elastic modulus are identified as given in Table VII for further analysis.

(a) (b)

Fig 9 Compression Test on Triplet Brick Prism (a) During Test and (b) At Failure

TABLE VI

MAXIMUM COMPRESSIVE STRENGTH OF BRICK PRISM

S.No

Mortar Ratio

Mortar Thickness

(mm)

Compressive Strength of

Prism (MPa) 1 1:2 10 2.43 2 1:3 10 2.03 3 1:4 10 1.92

From the results, the average compressive strength of triplet

brick prism is found to be around 2.15MPa. The brick prism with mortar ratio of 1:2 exhibits higher strength than other two mortar ratios. This shows that the mortar ratio plays important role in the strength of the brick masonry. The average modulus of elasticity of the masonry is found to be 3570, 3155 and 3125 MPa for three mortar ratios of 1:2, 1:3 and 1:4 respectively at almost the same compressive strain values.

Fig 10 Stress-Strain Curve for Brick Prism for Different Mortar

Proportions

TABLE VII MODULUS OF ELASTICITY AND MAXIMUM STRAIN VALUES OF

BRICK PRISM

C. Calculation of Shear Bond Strength of Triplet Brick Prism

Masonry is a combination of brick and cement mortar which need to exhibit homogeneous material property. The homogeneity of masonry depends on the level of bond strength. But, in most of the cases this is not applicable due to variation in the property of the materials [17]-[22]. The bond strength between brick units is greatly influenced by the characteristics of cement mortar. Sometimes, the property of brick also affects the bonding due to high water absorption capacity. Kishi et al. [19] carried out shear strength tests with triplet brick prisms to obtain the shear strength of interface between brick and mortar by immersing them in water for 24 hours before casting the prisms. Samarasinghe and Lawrence [20] performed shear tests on masonry triplets and found that the shear bond strength of brick prisms cast with pre-wetted bricks is high compared to dry bricks. There are no proper code specifications for testing shear bond strength. Hence, a setup is made as shown in Fig 12 particularly to test the shear bond strength of triplet brick prisms according to the required setup as shown in Fig 11. The shear bond strength of triplet clay brick prisms cast using 1:2, 1:3 and 1:4 cement mortar proportions are experimentally determined. The average bond strength values of triplet brick prism is shown in Table VIII.

S.No

Mortar Ratio Modulus of

Elasticity (MPa)

Maximum Compressive Strain (mm)

1 1:2 3570 0.00098

2 1:3 3155 0.00088

3 1:4 3125 0.00085

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Fig 11 Shear Test Setup for Triplet Brick Prism

Fig 12 Experiment Setup for Shear Testing

TABLE 8 SHEAR BOND STRENGTH OF TRIPLET BRICK PRISM

S.No Mortar Ratio Average Shear Bond Strength (MPa)

1 1:2 0.139

2 1:3 0.087

3 1:4 0.072

Fig 13 Comparison of Shear Stress and Displacement of Triplet Brick Prism for Different Mortar Ratio

From the experimental data, a graph is plotted between the shear bond strength and displacement as shown in Fig 13. The average bond strength of brick triplet is found to be 0.139MPa, 0.087MPa and 0.072MPa for CM1:2, CM1:3 and CM 1:4 respectively as shown in Table VIII.

D. Interface Behaviour of Brick Masonry Interface is a thin layer between the brick and mortar which

greatly influences the strength of bonding [23]. In order to understand their behaviour, an interface model is derived and the experimental results are compared with the proposed model. Based on the experimental results of this paper, various studies are to be carried out in the future to propose an interface model which predicts the exact failure mode of brick masonry.

VI. CONCLUSION The experimental research work carried out to investigate

the material properties of brick masonry constituent helps in gaining an in depth knowledge about the difference in individual and composite behaviour of masonry.

1. The Young’s Modulus and the Stress-Strain values of the constituent materials of brick masonry are determined under compressive load.

2. The flexural strength of brick is also identified from the experimental result which is used as an input for finite element analysis.

3. The shear bond strength of triplet brick prism for different mortar proportions is experimentally found and future studies are recommended to identify the bond slip relation and interface model.

This research paper can also be used as a reference for numerical modeling and analysis. Using the prescribed Young’s modulus value of different materials of brick masonry, the finite element model can be created and analyzed.

ACKNOWLEDGMENT This paper is being published with kind permission of the

Director, CSIR-SERC, Chennai. The Scientists, Project Assistants of Bridge Engineering Division, Technical Staff of Structural Testing Laboratory are highly acknowledged for their kind support in this research work. We thank the Dean, Head of Department and faculty members of Civil Engineering department of Bannari Amman Institute of Technology for their support and encouragement.

REFERENCES [1] Indian Standard code of practice [IS: 4860 – 1968, Reaffirmed 2001]

Specification for Acid resistant bricks. [2] M. Palanisamy and J. Premalatha, “Experimental study on Masonry

Infill Material Properties”, International Journal of Scientific & Engineering Research, Volume 3, Issue 7, July-2012.

[3] T.C. Nwofor, “Experimental Determination of the Mechanical Properties of Clay Brick Masonry”, Canadian Journal on Environmental, Construction and Civil Engineering, Vol. 3, No. 3, March 2012.

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[4] C.F. Christy, R.M. Shanthi and D. Tensing, “Bond Strength of the Brick Masonry”, International Journal of Civil Engineering and Technology (IJCIET), Vol-3, pp. 380-386.

[5] M.Meghashree and G A Sathish, “Shear Strength of Pond Ash Mortar Brick Masonry”, International Journal of Engineering Research & Technology (IJERT), ISSN: 2278-0181, Vol. 2 Issue 9, September – 2013.

[6] Indian Standard code of practice [IS 3495 (Parts 1- 4) : 1992, Reaffirmed 2002] Methods of tests of Burnt clay building bricks

[7] R. H. Brown, Principal Investigator, Georgia Institute of Technology, “Compressive Tests of Brick Units to Predict the Strength of Brick Masonry”, Submitted to the National Science Foundation under Grant GK-32648.

[8] Indian Standard code of practice [IS : 2250 – 1981, Reaffirmed 2000] For Preparation and use of masonry mortars (First revision)

[9] Md. M. Hossain, Sk. S. Ali and M. A. Rahman, “Properties of Masonry Constituents”, Journal of Civil Engineering, The Institution of Engineers, Bangladesh, Vol CE 25, No.2, 1997.

[10] D.J. Heath, E.F. Gad and J.L. Wilson, “Experimental Testing Techniques to Determine Unreinforced Masonry Material Properties”, The University of Melbourne.

[11] S. C. Ganapathi, A.R.C. Murthy, N. R. Iyer, N. Lakshmanan and N. G. Bhagavan, “Experimental and Numerical Study on In-Plane Behavior of Brick Masonry Wall Panels”, International Journal of Structural Stability and Dynamics, Vol. 11, No. 3 (2011) 431-450. http://dx.doi.org/10.1142/S0219455411004208

[12] R. Lumantarna, D. T. Biggs and J. M. Ingham, “Compressive, Flexural Bond and Shear Bond Strengths of In-Situ New Zealand Unreinforced Clay Brick Masonry Constructed using Lime Mortar between the 1880s And 1940s”, Journal of Materials in Civil Engineering, 10.1061/ (ASCE) MT.1943-5533.0000685.

[13] T.C. Nwofor, “Numerical Evaluation of the Elastic Properties of Brick-Mortar Prisms: The Effect of Varying Thickness of Mortar Joint”, International Journal of Engineering and Technology Volume 2 No. 6, June, 2012.

[14] S P Narayanan and M Sirajuddin, “Properties of Brick Masonry for FE modeling”, American Journal of Engineering Research (AJER) e-ISSN: 2320-0847 P-ISSN: 2320-0936 Volume-1 pp-06-11.

[15] Q. Ali, Y. I. Badrashi, N. Ahmad, B. Alam, Shahzad Rehman and Farhat Ali Shah Banori, “Experimental Investigation on the Characterization of Solid Clay Brick Masonry for Lateral Shear Strength Evaluation”, International Journals of Earth Sciences and Engineering, ISSN 0974-5904, Volume 05, No. 04.

[16] F. C. C, Tensing D and Mercy Shanthi R, “Experimental Study on Axial Compressive Strength and Elastic Modulus of the Clay and Fly Ash Brick Masonry”, Journal of Civil Engineering and Construction Technology, 10.5897/JCECT12.089, Vol. 4(4), pp. 134-141, April, 2013.

[17] B. Ghiassi, Daniel V. Oliveira, Paulo B. Lourenco and Giancarlo Marcari, “Numerical study of the role of mortar joints in the bond behavior of FRP-strengthened masonry”, ISISE, University of Minho.

[18] B. Blackard, B. Kim, C. Citto, K. Willam & S. Mettupalayam, “Failure issues of brick masonry”, CEAE Department, University of Colorado-Boulder.

[19] Y. Kishi, T. Kitahara, K. Nozaka & K. Izuno, “Experimental Evaluations for Peeling and Shear Strength of Masonry Arch Bridges”, 15 WCEE, Lisboa 2012.

[20] W Samarasinghe and S. J. Lawrence, "Effect of high suction rate in low strength bricks on brick mortar bond", The 4th International Seminar on Structural Masonry for Developing Countries, Madras, India, December, 43-50.

[21] R.Capozucca, “Shear Behaviour of Historic Masonry Made of Clay Bricks”, the Open Construction and Building Technology Journal, 2011, 5, (Suppl 1-M6) 89-96.

[22] P.B. Lourenco, J.O. Barros, J.T. Oliveira, “Shear testing of stack bonded masonry”, Construction and Building Materials 18 (2004) 125–132. http://dx.doi.org/10.1016/j.conbuildmat.2003.08.018

[23] L. Macorini and B. A. Izzuddin, “A Non-linear Interface Element for 3D Mesoscale Analysis of Brick-Masonry Structures”, International Journal for Numerical Methods in Engineering, Published online 28 October 2010 in Wiley Online Library.

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