The effect of lime and silica fume contents on the physical and mechanical properties of high volume fly ash mortars

Abstract

Using fly ash to partially or totally replace Portland cement in making mortar and concrete have been attracting more attention in academic researches and practical applications due to its advantages in both physical and mechanical properties, environmental friendliness of the material. However, with high fly ash content, the setting time of the mortar is prolonged, the strength development the construction progress were delayed, and the applicability of the mortar is limited. In this study, the effect of the addition of lime (5÷30 %) or silica fume (2÷10 %) on some properties of mortar, such as the consistency, setting time, and strength development over time (3÷90 days old) of mortars, in which Nghi Son PC40 cement was replaced by 60, 70 and 80 % Duyen Hai fly ash by weight, was investigated and compared with the control group (100 % PC40). Experimental results showed that the optimal lime addition content to achieve early age strength properties (3 and 7 days) and improve setting time was 5 %; 10 %; 15 % corresponding to mortars using fly ash of 60 %; 70 % and 80 %, respectively. Meanwhile, the reasonable rate of silica fume addition is 6 % in all mixes.