Reuse of fly ash and bottom ash in mortars with improved thermal conductivity performance for buildings

An approach towards effective utilization of fly ash and bottom ash in the construction of energy efficient buildings has been presented in this paper. Two masonry mortar grades MM3 and MM5 were considered for trial mix. Portland pozzolana cement with substitution of sand by fly ash and bottom ash separately in different substitution ratios (SR) were adopted for preparation of test samples. Fly ash and bottom ash with lime dust and marble dust combinations were also tested as sand free mortars. 28 days compressive strength, apparent porosity, bulk density and thermal conductivity parameters were evaluated for all such samples. By analysing the test results, it was observed that all the SR combinations satisfied the minimum masonry mortar grade MM0.7, as per IS 2250. Both the MM3 and MM5 grade mortars could be produced at 60% SR by fly ash, and corresponding reductions in thermal conductivity values were 69%, and 54% respectively, while compared with conventional mortar. Sand less mortar for both the grades resulted around 57% reductions in corresponding thermal conductivity values. Overall heat transfer co-efficient (U-value) for both side plastered and rendered brick masonry wall panel was found to be reduced by 15.58%, while comparison made between conventional mix of MM5 grade and corresponding 50% fly ash substituted mix. Thus such ash blended mortar mix appears to be advantageous in building envelop application for lowering the overall cooling/heating demand of building, besides utilizing the coal ash up to largest extent and saving natural mineral sand from depletion.