Development of Rapid and Reliable Pozzolanic Reactivity Test Method

With the potential decline in supplies of today's most widely used supplementary cementitious materials (SCMs) such as fly ash and slag, there is growing interest in the use of natural pozzolans (for example, pumice, volcanic ash), processed pozzolans (for example, calcined clays and shales), and manufactured pozzolans (for example, ground glass). Establishing the pozzolanic reactivity of these materials is an essential part of the evaluation process. Currently, pozzolans are assessed using ASTM C618 and C311, with the strength activity test being the only real performance indicator. Unfortunately, it is not possible to accurately determine the contribution of the pozzolanic reactivity to the strength in this test. This paper presents the development of a new pozzolanic reactivity test method based on the previous strength-activity-with-lime test but modified to increase the rate of the pozzolanic reaction. In this test, the solution-to-binder ratio is kept constant with workability adjusted using chemical admixtures. A range of mixing solutions containing combinations of KOH, NaOH, and K2SO4 and various curing regimes were investigated. The outcome of the test is compared with results from the current ASTM C311 and CSA A3004-E1 test methods for a wide range of pozzolanic (and inert) materials.