Properties of modified metakaolin-based geopolymer concrete with crumbed rubber waste from damaged car tires

Abstract

Waste rubber tires are materials that have a negative impact on the environment. Therefore, it is essential to use waste rubber recycled from damaged tires (CRWA) in geopolymer concrete (GPC) by different partial volumetric replacements to natural coarse aggregate (0, 10, 20, 25%) after preparation to a gradation similar to that for natural coarse aggregate. Calcium oxide and silica fume were substituted in metakaolin (MK) at 5 wt%. The GPC mix consisted of MK after modification, coarse aggregate, fine aggregate sodium hydroxide solution, sodium silicate solution, superplasticizer, and extra water, with quantities of 372, 911, 83, 192, 4, and 52 kg/m3, respectively. It is clear from the experimental results that the mechanical properties of geopolymer concrete decreased with the increase in the content of the crumbed rubber waste aggregate. The compressive, splitting tensile, and flexural strengths decreased by approximately 38.6, 44.6, and 52.6%; 10.6, 15.2 and 21.2%; and 6.25, 12.75, and 16.5% when the crumbed rubber aggregate was 10, 20 and 25%, respectively. In addition to recycling the rubber waste from damaged tires, desirable properties can be obtained, starting from not using water in curing GPC and rapid strength development at early ages. There is a clear improvement in the thermal properties and weight of GPC containing CRWA by reducing the thermal conductivity and dry density by including 10, 20, and 25% CRWA compared with the reference GPC without this waste material.