Figure 3.3 Photograph of laser extensometer during testing: (a) the complete experimental set-up and (b) exaggerated view of AAC cubic specimen with reflective tape strip and laser beam
sample was calculated by dividing the peak load with the area of the specimen surface normal to the load.
Figure 3.4 The experimental setup for compression test of AAC: (a) photograph and (b) schematic drawing of loading condition
3.3.2 Experiment setup for tensile test of AAC block
The tensile strength of AAC block was tested using AAC cylindrical specimens of size 75 mm diameter and 150 mm length as per ASTM C 1006-07. A compressive load was applied along the length of the specimen and on the diametrically opposite side of the cylindrical surface that causes lateral tensile stresses. Two plywood strips of 200 mm length and 3 mm thick were kept in between the test specimen and upper/lower crosshead of universal testing machine as shown in Figure 3.5. The purpose of plywood strip is to uniformly distribute the applied compressive load in the lines, which further causes the uniform lateral tensile stress in the test specimen. The tensile strength of AAC cylindrical specimen was calculated using the theory of isotropic elasticity.
Figure 3.5 The tensile test set-up of AAC cylindrical specimen: (a) photograph of test set-up and (b) schematic diagram of loading condition
3.3.3 Experiment setup for compression test of AAC masonry
Compressive strength is the most important parameter to quantify the characteristics of masonry. The compressive strength of masonry is primarily evaluated using a masonry prism. The prism is a small masonry wall built of one or two bricks in length and three or more bricks in height and is tested under compressive load perpendicular to the bed joint. In this study, AAC masonry prisms have been prepared using one block length and five blocks height assembled using mortar layers in between. Since the friction between bearing faces of the prism and loading platens restrains significantly the transverse deformation of the prism, higher aspect ratio or height-to-thickness (h/t) ratio of prism specimen has been used. The lower aspect ratio overestimates the compressive strength of the prism. IS: 1905 suggests a height-to-thickness (h/t) ratio between 25 and a minimum height of 40 cm.
Francis et al. (2017) reported that prisms with a height of five to six brick units can be considered to be free from effects of end platen during testing. Therefore, in this study the higher aspect ratio of 3.62 has been considered to eliminate the platen effect. The testing was carried out with help of a universal testing machine of 1000 kN capacity at a loading rate of 1 kN/s. During the test, the specimen was put between upper and lower platens of UTM and clamped properly. The experimental test setup for compressive strength of AAC masonry is presented in Figure 3.6.
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Figure 3.6 Experiment test set-up for compressive strength of AAC masonry: (a) photograph of compression test set-up and (b) schematic diagram of loading condition
3.3.4 Experiment setup for shear bond strength test of AAC masonry
The shear bond strength of the AAC brick masonry can be evaluated through testing of the AAC triplets. Three block units and two mortar layers (1012 mm thickness) were used to prepare the triplet specimen. A uniform vertical (without pre-compression) load was applied on the middle block using 20 mm thick mild steel plate and two rollers of 12 mm diameter, as illustrated in Figure 3.7. In order to reduce the eccentricity, the two side blocks were supported by mild steel roller at a location close to the mortar joint. The displacement controlled loading rate of 0.01 mm/s, corresponding to a strain rate of the order of 5105 s1, was applied with help of a 250 kN servo hydraulic actuator. A photograph and schematic drawing of front view of the triplet test setup are shown in Fig. 3.7. Vertical compressive load on the middle brick is applied until the failing of bond between brick and mortar. The shear bond strength is calculated using the obtained peak load at failure during the test. The procedure mentioned by a number of researchers such as Alecci et al. (2013) and Singh and Munjal (2017) was followed to carry out the shear bond strength test for AAC masonry.
Figure 3.7 The triplet test setup: (a) a photograph (b) front view
3.3.5 Experiment setup for tensile bond strength test of AAC masonry
The resistance of masonry to tensile stress when subjected to out-of-plane loading is an important aspect for the safe design of masonry wall system. The tensile strength of masonry is primarily governed by the bond strength of brick mortar interface and is therefore called tensile bond strength (Crisafulli, 1997). In this work, the tensile bond strength of AAC block and mortar interface was determined using a cross-couplet test, which is a direct method of testing. The specimens were prepared using AAC block and mortar bed joint. It measures direct tensile strength of the bond between the mortar and AAC block unit.
The displacement controlled loading rate of 0.01 mm/s was applied with help of a 250 kN servo hydraulic actuator, which provides a strain rate of order of 103 s1 during the test.
Although the piston of the testing machine moves downwards at a controlled rate during testing, two specially made platens are used so as the compressive load applied n platen will be transferred to the specimen as tensile load. Specimen was placed on lower platen with lower surface of the upper block touching bars of the lower platen. Second platen was gently placed on lower block with its bars touching the upper surface of the lower block. There exists some gap between lower block and lower platen and also between upper platen and upper block. The whole setup is clearly depicted in Figure 3.8. The specimen preparation and the testing procedure were carried as per the guideline mentioned in ASTM C 952 (ASTM 1991). The tensile bond strength was calculated corresponding to the peak load at failure divided by block-mortar interface contact area.
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Figure 3.8 Experimental set-up for tensile bond strength test (a) photograph, (b) the loading condition and (c) top view of the cross-couplet test setup