Pozzolanic Reactivity Test of Supplementary Cementitious Materials

The reactions of supplementary cementitious materials (SCMs) in concrete can be pozzolanic, hydraulic, or a combination of both. This paper focuses on the pozzolanic reactivity test (PRT) for SCMs that are blends of reactive aluminous and siliceous phases. The PRT quantifies reactivity by measuring heat release (Q) and calcium hydroxide (CH) consumption, which are interpreted using thermodynamic modeling. The robustness of the PRT is examined by experimentally varying the CH-to-SCM ratio, solution-to-solid ratio, sulfate content, alkali type (Na versus K), and alkali content. This paper also assesses similarities and differences between the PRT and the R3 test (ASTM C1897). It was found that sulfates, which are used in the R3 test, did not impact the siliceous reactions; however, they led to the preferential reaction with aluminous phases to form monosulfoaluminates and ettringite. A generalized relationship for the degree of reactivity is proposed as a function of Q and CH consumption.