Sulfate performance of calcined illitic shales

Abstract

In the past, calcined pozzolans were largely used in massive concrete, and nowadays, they appear as an excellent alternative to reduce the clinker factor in general use cement. The pozzolanic activity of two calcined illitic shales (CIS) is verified using different standards, indicating the importance of the water requirement for these pozzolans. The sulfate performance of blended cement containing 0, 20, and 40% of CIS was studied with high and low C3A cement using the ASTM C1012 test. Results show that highly reactive CIS is necessary to control the expansion of high C3A-cement at constant w/cm. For low-C3A cement, the highly reactive CIS provides high-sulfate resistant cement with low CIS-replacement, while the water requirement of the other CIS is the main shortcoming to obtain this property. CIS contributes to sulfate resistance due to the CH-consumption and reduction of ions ingress that impedes ettringite and gypsum formation.