Effect of gypsum content on the compressive strength of LC3 cement

ABSTRACT The cement industry has been required to minimize the CO2 emissions caused by the Portland cement manufacturing process. The use of supplementary cementitious materials (MCS's) replacing part of the clinker is one of the most viable options to reduce the emission of this pollutant. LC3 cement is a new type of cement that uses high MCS contents, counting on the synergistic reaction between calcined clay and limestone to obtain mechanical strength similar to that of traditional cements. This research intends to investigate the influence of the gypsum content on the compressive strength of a LC3 cement at 1, 3, 7, 28 and 91 days, considering that the effects of the gypsite content on the mechanical resistance of the LC3 cement are little understood. For the accomplishment of this study six mortars were produced. In three of them the reference cement (clinker + gypsum) was produced with 3.5% gypsum, without additions. In three mortars an LC3 cement with 45% clinker replacement (30% calcined clay and 15% limestone) was used. The proportion of gypsum in these cements was 3, 5 and 7% in relation to the total mass. The properties in the fresh state were evaluated by means of the spreading test, taking into account the superplasticizer content used in each mortar. For the hardened state analysis, the compressive strengths were compared at the ages of 1, 3, 7, 28 and 91 days. A statistical analysis (ANOVA and DUNCAN test) was performed on the results. From the results obtained it was possible to verify that the gypsite content influences the compressive strength of the LC³ cement. In the early ages, from 1 to 7 days, the greatest results of compressive strength were obtained by cements with gypsum contents of 5%. At these three ages the 5% gypsum LC3 cement had comparable results with the reference cements. At 28 and 91 days LC3 cements with 7% gypsum led to the highest values of compressive strength, and the highest value at 91 days was 40.0 MPa, comparable to the reference cements.