6.4 Results and Discussion
6.4.4 Cost comparison
The cost incurred for the preparation and deployment of mortar used in AAC wall is estimated for the wall size of 18001000200 mm3. The detailed cost analysis is shown in Table 6.4. The wall considered has 3 blocks along length and 5 blocks along height and constitutes a total volume of 36107 mm3. A total of 15 AAC blocks of size 600200200 mm3 and the 29 mortar joints (17 bed joints and 12 head joints) have been used for the wall assembly as shown in Figure 6.7. The volume occupied by the mortar layers in the wall system has been calculated by considering the bed joint and head joints separately. The bed area of the wall is considered to be 1800200 mm2.
Figure 6.7 The schematic view of the AAC wall system: (a) front view, (b) side view and (c) top view
The joint thickness using sand-cement mortar and polymer modified (PMM) mortar is 12 mm and 3 mm, respectively. However, in case of combination of cement slurry coating and mortar, the total joint thickness is slightly increased from 12 mm to about 13.5 mm due to the addition of extra two coating layers.
The densities of mortars SCM1, SCM2, SCM3 and PMM are 2221 kg/m3, 2159 kg/m3, 1998 kg/m3 and 1700 kg/m3, respectively. Using the length of block as 600 mm, width as 200 mm, joint thickness as 12 mm, number of head joints as 12 and number of bed joints as 17, the total volume of sand-cement mortar occupied in the wall comes out to be 3107 mm3. A total volume of 3.3107 mm3 was calculated to be occupied by the combination of cement slurry coating and sand-cement mortar. Since the density of the individual sand- cement mortar is different, the total mass of the mortar SCM1, SCM2 and SCM3 consumed
in the wall is 66.63 kg, 64.77 kg and 59.94 kg, respectively as shown in Table 6.4.
In case of combination of slurry coating with sand-cement mortar, the extra mass of cement (1.14 kg) consumed during the coating is added. During the study, a total of 30 gm cement was consumed by one block of surface area 600200 mm2 in the form of cement slurry coating. Similar to the sand-cement mortar, using same block, joint thickness as 3 mm, number of head joints as 12 and number of bed joints as 17, the total volume of PMM mortar occupied in the wall is calculated to be 0.7107 mm3. The total mass of the PMM mortar consumed in the wall is found to be 11.90 kg. The sand-cement mortar joints contribute 8.3%
of the total wall volume, while the PMM mortar contributes only 2% of the total wall volume.
The price of sand, cement and PMM powder were collected from the local market (Guwahati, Assam, India). The prices for 50 kg bag of cement, 1500 kg of sand and 30 kg bag of PMM powder are $ 6.10, $ 29.05 and $ 10.89, respectively.
Further, the labour cost incurred for the mortar preparation using all the joint materials was also considered. In India, in general practice, one mason and one helper are required to construct a complete AAC wall of 1 m3 in 8 hours of working day. The daily wages of mason and helper is $ 6.97 and $ 4.88, respectively (CPWD 2014). In this analysis, one mason and one helper have been considered to construct the AAC wall using the mortar SCM1, SCM2, SCM3 and PMM, respectively. However, one extra helper is required to construct the wall using a combination of cement slurry coating and ordinary sand-cement mortar. From Table 4, it can be observed that using the SCM3 mortar, the total cost incurred is the least while the CSCM1 mortar costs the highest. Comparing the cost and strength of various mortars from Table 6.4, Table 6.3 and Table 6.2, the mortar CSCM3 is found to be the best choice in the building wall construction using AAC blocks.
Table 6.4 The mortar cost analysis for the AAC wall of size 18001000200 mm3 Mortar
types
Sand (kg)
Cement (kg)
PMM (kg)
Cement in coating (kg)
Total mortar consumed (kg)
Mortar cost ($)
Labour cost ($)
Overall cost ($)
SCM1 44.42 22.21 Nil Nil 66.63 3.58 4.27 7.85
SCM2 51.82 12.95 Nil Nil 64.77 2.59 4.27 6.86
SCM3 51.37 8.56 Nil Nil 59.94 2.04 4.27 6.31
CSCM1 44.42 22.21 Nil 1.14 67.77 3.72 6.02 9.74
CSCM2 51.82 12.95 Nil 1.14 65.91 2.73 6.02 8.75
CSCM3 51.37 8.56 Nil 1.14 61.08 2.18 6.02 8.20
PMM Nil Nil 11.90 Nil 11.90 4.33 4.27 8.60
The mortar CSCM1, CSCM2 and PMM can be compared with CSCM3. The total cost of using CSCM3 is the least when compared with CSCM1, CSCM2 and PMM. Although the shear and tensile bond strengths of masonry using CSCM1 and CSCM2 mortars are higher than CSCM3, but their total costs are higher. An equal average shear bond strength and higher tensile bond strength as compared to the CSCM3 is observed in case of using the PMM mortar. However, during the bond strength test, the complete block failure occurred rather than the interface or mortar failure in most of the masonries made of CSCM1, CSCM2 and PMM. This indicates that these masonries provide more bond strength than the required bond strength. On the other hand, the interface or mortar failure was observed in the masonry using CSCM3 mortar; however, the bond strength was still significantly higher than that of SCM1, SCM2 and SCM3. Moreover, the availability of CSCM3 mortar is not a problem.
Thus, considering cost, supply chain aspect and bond strength, CSCM3 is an optimal choice.
PMM mortar is also a good choice because the overall cost of wall-construction using PMM is only slightly more than that using CSCM3; however, its availability may be a problem in some cases. PMM mortar provides extra bond strength but overall cost of constructing a wall is lower than that by using CSCM1 and CSCM2 mortars.