CHAPTER 5 COMPRESSIVE STRENGTH AND MODULUS OF ELASTICITY OF MASONRY PRISMS

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1 68 CHAPTER 5 COMPRESSIVE STRENGTH AND MODULUS OF ELASTICITY OF MASONRY PRISMS In this chapter, after many trials, the mix ratio of metakaolin based geopolymer brick to attain a compressive strength of 5.5 N/mm 2 was designed to be used in masonry construction. Properties of wire cut clay bricks and metakaolin based geopolymer bricks were tested in accordance with IS 3495 and compared for its suitability in masonry construction. The behaviour of metakaolin brick masonry prisms and clay brick masonry prisms of different aspect ratio constructed in 1:3 cement mortar is studied. 5.1 Metakaolin Based Geopolymer Brick The demand for ordinary clay bricks leads to a search for alternate bricks to meet the escalating demand of the construction sector. Production of clay brick involves usage of natural resources in large quantity and there is nonuniformity in compressive strength of bricks of different regions. In order to produce bricks of uniform strength, factory production is resorted to using materials of known strength. Geopolymer bricks require no firing like clay brick or curing like commercially available flyash and cement bricks. In this study, different mix ratios with flyash and metakaolin were studied with sand as fine aggregate in 1:5 and 1:6 ratios. The proportions of various mix ratios of MK modified GP brick studied is presented in Table % replacement of flyash with metakaolin in 1:6 ratio with liquid to solid ratio of 1 was selected to produce 1000 bricks of size mm and an average compressive strength of 5.5 N/mm 2.

2 69 Table 5.1 Mix proportion for Metakaolin Geopolymer brick MIX 1:5 by mass in kg 1:6 by mass in kg FA MK SAND LIQUID FA MK SAND LIQUID MK MK MK MK The minimum compressive strength required for the bricks to be used for the structural purpose is 5.5 N/mm 2 according to IS Metakaolin 1 was chosen for the casting of bricks as it has lower silica and high alumina and results in the inferior quality of bricks. Two mix ratios of 1:5 and 1:6 by mass of MK+FA and sand were identified for Metakaolin based geopolymer bricks and in each mix ratio, the percentage of MK is varied from 0-75, and the remaining FA was used. Using trial mixes, the average mass of material required for a mould of mm was estimated as 3.2 kg. The solidliquid ratio was maintained at 1. Eight different mixes were cast and tested. 12M NaOH solution and sodium silicate solution with 3.2 moduli (mass of Na 2 O/SiO 2 =3.2) was used. The ratio between two liquids was maintained as 2.5. Eight different types of bricks of mix MK0, MK25, M50, M75 with 1:5 and 1:6 ratio of alumina silicate precursor (FA+MK) and sand mm size and 40 number of bricks were hand moulded using steel moulds. The stacking of trial GP brick is shown in Figure 5.1

3 70 Figure 5.1 Stacking of Trial Bricks 5.2 Clay Bricks In this study, locally available clay bricks were used. They were chosen to be wire cut bricks to have uniform size and to have consistent properties with average size of the brick as 220 mm 90 mm 70 mm bricks were procured for use and broken bricks were rejected. 5.3 Tests on Bricks The properties of bricks were tested in accordance with IS 3495 (1-4) The compressive strength of metakaolin based geopolymer bricks and clay bricks were tested in compression testing machine of 400 kn capacity. Load at failure was taken as the ultimate compressive load. Percentage of water absorption was calculated after immersing the bricks in water for 24 hours. Efflorescence was calculated by immersing clay bricks and metakaolin based geopolymer bricks on their ends in a square tray of 18 cm and depth of 60 cm. It is ensured that the minimum depth of immersion was 25 cm. The entire setup was closed with a lid to prevent evaporation of water to the atmosphere. When water is completely absorbed, a similar quantity of water is placed in the tray for evaporation. Bricks were examined for efflorescence after second evaporation.

4 71 Table 5.2 Properties of clay brick and MK-Based GP brick S.No Property Clay brick MK geopolymer brick 1 Size mm mm 2 Compressive strength 9.5 N/mm N/mm 2 3 Weight 3 kg 2.9 kg 4 Efflorescence Slight nil 5 Initial Rate of Absorption 0.8 Kg/m 2 /min 0.5 Kg/m 2 /min 6 Water absorption 10-15% 3-5% 7 Static E of brick 3155 MPa 2340 MPa 8 Dynamic E of brick 3210 MPa 2490 MPa 9 µ of brick Poisson's ratio (µ) is calculated using a quasi-static method of testing of bricks in compression. Brick specimen in a vertical direction is tested in UTM of 2000 kn capacity. Dial gauges of Baker make with least count of 0.01mm and maximum of 25 mm are fixed in three directions and for every increment of load dial gauge reading is noted. Thin glass pieces are inserted at places of contact of the dial gauge and brick. As bricks in masonry are subjected to uniaxial stress or biaxial plane stress, the deformations in lengthwise (220 mm) and widthwise (70 mm) are considered for calculating Poisson's ratio. Lateral and longitudinal deformations are noted till 1/3 of the failure load. Three brick specimens are tested and the average of the values is recorded. Poisson's ratio (µ) = Lateral strain Longitudinal strain (5.1)

5 72 Dynamic modulus of elasticity of clay brick and metakaolin based geopolymer brick was calculated by performing Ultrasonic Pulse Velocity test. Portable Ultrasonic Non- Destructive Digital Indicating Tester (PUNDIT) unit of model Telsonic ultrasonix UX 4600 pulse velocity was used with a transducer of 60 khz of natural frequency. Testing of dynamic modulus of elasticity using PUNDIT is presented in Figure 5.2. Direct, indirect and surface transmission methods of testing can be chosen on the basis of the viability in field conditions. In this study, the direct transmission method was followed to assess the Dynamic Young's modulus of bricks. The test was conducted in accordance with IS (1992) Method of Non-destructive testing of concrete, Part 1: Ultrasonic pulse velocity. Figure 5.2 Dynamic Young s Modulus using PUNDIT Time taken to travel the path length was digitally displayed. Velocity of the pulse was calculated using V = L/T (5.2) V-Velocity of the pulse in m/s L-Length of the path travelled in m T-Time taken in seconds Taking µ from quasi-static method, dynamic modulus of elasticity is calculated using

6 73 E = ρ (1+µ) (1-2µ) V (1-µ) (5.3) E = Dynamic Young s Modulus of elasticity in MPa ρ = density in kg/m 3 and V = pulse velocity in m/s. The properties of clay brick and MK based metakaolin brick is tabulated in Table Tests on Mortar Cement mortars of 1:3 ratio by volume were used for the construction of clay brick masonry and metakaolin based geopolymer bricks. OPC was used for mortar preparation and sand used was in accordance with IS 2116(1980). Mortar Cubes of size 150 mm side were cast with water cement ratio of 0.6 in accordance to IS 2250(1981) Code of practice for preparation and use of masonry mortars. The compressive strength of mortar cubes was tested after 28 days of water curing in compression testing machine. Cylinders of 150 mm diameter and 300 mm height were cast with the mortar used and tested for Young s modulus using compressometer. The test setup used for finding Young's modulus of Elasticity is shown in Figure 5.3. The compressometer is fitted with a dial gauge of 25mm as largest deformation and a least count of 0.01mm.

7 74 Figure 5.3 Test setup for Young s Modulus of Mortar Mortar cylinders were loaded up to 1/3 of the ultimate load and deformations were noted for equal increments of the load. Secant modulus of elasticity of the mortar was calculated using a slope between 5 to 33 percentage of ultimate strength in stress-strain graph in accordance with ACI Building code requirements for masonry structures. 5.5 Masonry Prisms Masonry is an assemblage of building units bonded together by mortar. It is non-homogenous, orthotropic leading to complex mechanical behaviour. In this study, prisms in axial compression are studied as in most situations brick masonry experiences axial compression. The performance of metakaolin modified geopolymer bricks in combination with cement mortar require investigation as the question about the compatibility of the two is aroused in the minds. Study of the mechanical behaviour of masonry structures with metakaolin modified geopolymer bricks gives confidence for the practising Engineers to use these bricks in construction.

8 75 Laboratory investigation of masonry prisms was done in accordance with IS Indian Standard Brick works-code of practice. Prisms were constructed with a minimum height of 40cm with a height to thickness ratio of at least 2 but not more than 5. Correction factors were applied for prisms with h/t between 2 and Clay brick masonry prism Clay bricks were soaked in water for 30 minutes before being placed in position and used in the construction of prisms in surface dry condition. 10mm mortar thickness was maintained in joints and beddings. Details of the size, type of bonding and number of clay prisms used in this study are given in Table 5.3. As it is customary to test stacked five brick prisms, three prisms of mm in stretcher bond with an aspect ratio of 4.33 were constructed. English bond is in practice in the construction field and it is relevant to test the prisms in this bond. Nine prisms in English bond with h/t ratio of 2, 2.77, and 3.8 were constructed. Photograph of clay brick prisms used in this research is presented in Figure 5.4. Clay brick masonry was cured for 28 days with water and tested for compressive strength. Table 5.3 Dimension of Clay Brick Masonry Prism S. No Size in mm h/t ratio Bonding No. of prisms Stretcher English English English 3

9 76 Figure 5.4 Clay Brick Masonry Prism Testing of brick masonry prisms was done by Loading frame of 500 kn capacity and a hydraulic jack of 250 kn. The hydraulic jack was fitted with a load cell of 250 kn capacity. Deformation in the masonry was measured using Linearly Varying Displacement Transducer (LVDT) with maximum deformation that could be measured as 10cm. LVDT was attached to the prism by means of two L-shaped angles. Angles were attached to the prisms by steel paste. The surface of the prism was smoothened by emery sheet to ensure perfect adhesion. Angles were pasted on to the prisms near the place where maximum deformation was expected. LVDT and load cell were connected to a data acquisition system which recorded the data in the computer connected to it.

10 77 Figure 5.5 Test setup for MK Based GP Masonry Prism Metakaolin Based Geopolymer Brick Prisms Metakaolin based geopolymer bricks prisms were constructed with 1:3 C.M. with h/t ratio as given in Table 5.4. The experimental setup used testing of MK based GP masonry prism is presented in Figure 5.5. The thickness of mortar joints and bedding were maintained at 10 mm. Curing of metakaolin modified geopolymer brick prisms with water was required for 28 days as cement mortar in the masonry needs curing. A 10 mm steel sheet was laid on the top of the prisms before testing for even distribution of load. Masonry was loaded till it displaces LVDT from its position and then LVDT was removed. Masonry was continued to load till it fails. Prism types and bonding adopted are listed in Table 5.4. MK based GP brick prisms used in this study is represented in Figure 5.6.

11 78 Table 5.4 Dimensions of MK-Based GP Brick Prism S.No Size in mm h/t ratio Bonding type No. of Prisms Stretcher English English English 3 Figure 5.6 MK-based GP Brick Prism