Alkali activated slag (AAS) has gained huge attention in recent years due to its ability to replace ordinary Portland cement (OPC) as a binder in concrete. A need to replace OPC is imminent due to the high carbon dioxide emitted into the environment during its production. However, the use of this type of binder did not eliminate the huge strain placed on the deposit of natural resources. With the demand for concrete predicted to rise significantly in coming years, this means there will be a consequential increase in the amount of natural deposits of aggregates exploited, as aggregates make up about 80% by the volume of concrete. Therefore, in order to meet this forthcoming demand of sustainable concrete, and reduce the excessive strain on the use of natural aggregates, it is essential to find alternative materials that can be used as aggregate in concrete using AAS as a binder. This paper summarizes experimental results from various studies on the use of waste materials on aggregate. The fresh and hardened properties, alongside the cost and sustainability indications, are explored. It was drawn from this review that more reduction in carbon dioxide emission and cost could be achieved with the use of waste materials as aggregate in concrete. In addition, concrete made with AAS as a binder and incorporating waste as aggregate showed similar/higher properties with those made with natural aggregate. However, proper selection of types of wastes and replacement levels of these waste materials used as aggregate is still required to achieve enhanced properties.
Thermodynamic modelling of phase evolution in alkali-activated slag cements exposed to carbon dioxide
