Influence of the composition of alkali-activated lime-metakaolin mortars on compressive strength, cost, and CO2 emission

Abstract

The environmental impact associated with Portland cement production makes it necessary to explore alternatives that minimize the polluting effects of this industrial activity. A promising approach is the development of alkali-activated mortars composed of lime and pozzolan. Therefore, the objective of this study was to analyze the influence of components on the compressive strength of alkali-activated lime-metakaolin mortars. The mortar composition was defined in three ways: the first way followed the guidelines of the Brazilian standard NBR 5751 and used the specific masses of the materials; the second was based on the CaO/SiO2 mass ratio, analyzing the reasons for 0.40 and 0.75 and the third followed the guidelines of NBR 7215 standard and ratio of 0.75. In this last composition, the alkaline activator (NaOH) was incorporated in proportions of 1.5%, 3%, 4.5%, and 6%. The results indicated that the lime: metakaolin ratio has a significant impact on strength, with a 34% decrease in compressive strength when the lime-pozzolan ratio was reduced from 3.35 to 1.77. Furthermore, it was observed that the addition of an alkaline activator improved mechanical resistance. Therefore, these mortars proved to be viable for several non-structural applications, highlighting their environmental advantages in comparison with Portland cement mortars.