AbstractThe suitability of the rapid, relevant, and reliable (R3) heat of hydration and bound water tests for measuring the reactivity of various supplementary cementitious materials (SCMs) and their blends with calcium hydroxide (CH) was investigated in this study. These tests have been recently standardized in current standards. The test was carried out on pastes of fly ash (FA), slag (S), kaolinitic calcined clay (K), limestone (LS), and their blends. A detailed analysis of the heat of hydration and bound water measurements specified according to the R3 test was carried out. A good correlation was found between the two types of test results and also between the reactivity test results versus strength activity index measured using cement mortar compressive strength. The formation of hydration products in the R3 test paste specimens was also studied using X-ray diffraction (XRD). The hydration products for SCMs formed in the test were similar to those reported in cement systems. It was seen that the interactions in the blended SCMs with CH were also similar to those reported in cement pastes. Further, the microstructure of the specimen was studied using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analysis, and the overall hydration of various SCMs was studied. The influence of the proportions of the SCMs in the blended SCMs and that of fineness were also investigated. The applicability and limitations of this test method for SCMs and their blends were discussed.