Hydration heat comparison of portland cement blends with commonly available supplementary cementitious materials (SCMs) by isothermal calorimetry

This study presents a systematic evaluation of early-age hydration behavior of portland cement blended with ten (10) widely used supplementary cementitious materials (SCMs) using isothermal calorimetry. The SCMs included metakaolin (MK), calcined clay (CC), Class C fly ash (CFA), Class F fly ash (FFA), blast furnace slag (BFS), silica fume (SF), sugarcane bagasse ash (SBA), natural clinoptilolite zeolite (NCZ), eggshell powder (ESP), and limestone powder (LSP). Each SCM replaced PC at 0–20 % by mass, and hydration heat was monitored over 60 h at 25 °C with a water-to-cementitious ratio of 0.45. Results revealed distinct effects on early-age hydration: FFA and BFS reduced cumulative heat by 50–65 %, CFA, CC, SF, and LSP caused moderate reductions of 20–40 %, while MK and ESP increased normalized cumulative heat by up to 10–15 %. C₃S peaks decreased by 10–45 %, whereas C₃A peaks increased by 15–20 % for MK and ESP but decreased by up to 20 % for NCZ. Dormancy periods were largely unaffected, with minor extensions of 1–6 h for CFA, FFA, BFS, and SF. These findings provide practical guidance for selecting SCM types and replacement levels to optimize early-age hydration, with implications for potential strength development and mixture optimization in sustainable, low-carbon cementitious systems relevant to real-world construction applications.