The Influence of Limestone and Al2O3 Content in the Slag on the Performance of the Composite Cements

In the present contribution, the interaction between limestone and slag is investigated by a multi-method approach using chemical shrinkage, thermogravimetry, scanning electron microscopy (SEM) techniques and compressive strength measurements. The impact of limestone was investigated in blends containing synthetic slags of different alumina content. The results are correlated with the thermodynamic modelling in order to gain further insights into the physical and chemical processes governing the interaction between limestone, slag and Portland cement.Beyond 28 days of hydration, slag composites exhibit higher compressive strength values than their equivalent with quartz. Increasing the Al2O3 content from 8 to 12% in slag influenced compressive strengths positively at all hydration times. Further increase of alumina in slag to 16% has no positive effect on strength. Addition of limestone, results positively only on early compressive strengths. After 28 days and longer effect of limestone is either slightly negative or neutral. Only in the case of the slag containing 16% of alumina, limestone has positive impact on the late compressive strength. The effect of limestone has two main components: physical, so called filler effect and chemical that depends on the slag composition.