Metakaolin and demolition wastes in eco-based sand consolidated concrete

This study was undertaken to valorize naturally occurring silica sand in the synthesis of new consolidated concrete materials. The mixtures of silica sand, calcium sulphate, com-mercial metakaolin, demolition materials were designed to propose sulphate and sodium silicate/NaOH activate concretes and geopolymers, respectively. Three raw silica sand sam-ples were collected from various locations in Tunisia. The obtained new materials were characterized by SEM and mechanical properties were investigated. The calcium sulphate-based concretes displayed good technological properties with a compressive strength close to 15 MPa and 40-56% of water adsorption. When, metakaolin and demolition reject were added the mechanical resistance decreased due to the lower pozzolanic properties of these materials. Concerning the geopolymer-based sand concrete, lower compressive strength values were registered. Moreover, by incorporating demolition materials, the mechanical resistance decreased in all consolidated products. The effect of the metakaolin reactivity is more sig-nificant when it is activated with a alkaline solution. However, the sodium silicate/NaOH activation of metakaolin governs the reaction when it is highly reactive. Finally raw silica sand from Tunisia provided good consolidated concrete materials in the presence of calcium sulphate. As well, the silica sand provided good geopolymers in the presence of metakaolin and alkaline solution. Published by Elsevier Espana, S.L.U. on behalf of SECV. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This research utilized silica sand from Tunisia to synthesize new consolidated concrete materials. By adding different materials, the study investigated the effects on concrete properties and the impact of activation with sulphate and alkaline solutions.