Incidence of recycled aggregates and ternary cements on the compressive strength and durability of ecological mortars

Abstract

This research presents the effect of substituting natural aggregates by recycled aggregates and cement blended with limestone by coal ashes on the compressive strength and durability properties of an ecological mortar. Firstly, the industrial wastes (recycled aggregate from concrete and coal ash) were characterized using physical, chemical, and mineralogical techniques such as x-ray diffraction (DRX), particle size distribution (PSD), and electronic scanning microscopy (SEM). Secondly, the maximum substitution of blended cement for coal ash was defined based on the compressive strength in order to obtain a ternary cement. Subsequently, the mortars with ternary cement and different dosages of recycled aggregate were made, these mortars were evaluated through compressive strength and sulfate attack resistance (durability). The results found show that the inclusion of these by-products improved mechanical properties due to the chemical affinity between the recycled aggregates and the ashes. The contents of old adhered mortar in recycled aggregates made more susceptible mixtures to be attacked by the magnesium sulfates. This phenomenon was studied through SEM and sulfate attack test. Finally, the expansion exhibited by the samples manufactured with recycled aggregate and coal ash did not reach the limits for the initial degradation of the material. That is, ternary cements, such as those used in this research, when mixed with recycled aggregates, allow the production of ecological concretes and mortars with excellent mechanical behavior and resistance to sulfate attack.