DR. K. RAMAMURTHY, FBMS (Professor) and R. MANIKANDAN (Research Scholar)

Building Technology and Construction Management Division, Department of Civil Engineering, Indian Institute of Technology Madras, Chennai-600 036, India


This study is focused on the use of fly ash in mortar as an addition to and a replacement of an equivalent volume of cement. For each mix, the water content required for achieving a flow value of 135%, was first determined. The water requirement for each mix increases as the addition and replacement level of fly ash increases. Based on this water content, the 7, 28 and 90-day compressive strengths were determined. Irrespective of the age of each mix, compressive strength decreases as the addition level of fly ash increases for mixes 1:3 and 1:4 and almost remains constant for 1:5. An increase in strength is observed for up to a 100% addition level for mixes 1:6 and 1:7. Replacement of cement causes reduction in compressive strength at all ages. For a given cement content, the addition of fly ash results in a reduction in compressive strength for the 1:3 mix and an increase in strength for 1:4 and 1:5 mixes. The compressive strength obtained at all addition and replacement levels of fly ash satisfies code specified minimum compressive strengths.