A transition towards circular economy with the utilisation of recycled fly ash and waste materials in clay, concrete and fly ash bricks: A review

Coal burning in power plants is considered an energy-intensive process that increases carbon emissions and generates numerous tonnes of fly ash materials. Incorporating fly ash disposal into bricks is regarded as an effective approach for achieving net-zero goals in 2050. This recycling approach can mitigate the waste stockpiling and conserve millions of tonnes of resources annually. Researchers have conducted numerous studies about fly ash in bricks and evaluated particle size, curing days, w/c ratio, firing temperature followed by different testing methods such as compressive strength, tensile strength, water absorption and workability, however, a systematic review of bricks containing fly ash is yet to be published. This review presents a comprehensive analysis of studies on incorporating fly ash in clay-fired bricks, fly ash in unfired bricks and blending fly ash with waste materials in concrete bricks. The conventional bricks can be prepared by using the fired method and the unfired method. High temperature firing was employed by brick manufacturers in developing countries especially for its long-term performance and is associated with major constraints. On the other side, unfired bricks made using clay or concrete can be substituted with recycling materials such as sludge, gypsum, quarry dust and lime have gained attention in the last few decades which contributes to overall environmental benefit owing to reduced carbon emissions. In addition, it was found that fly ash-based bricks can be an essential product in the construction industry because of their high performance, reduced carbon emissions low material cost and can be an ideal replacement for conventional bricks. Furthermore, this review highlights the benefits of fly ash and its potential industrial utilisation including agricultural applications across the globe.