With the development of society, the demand for cement-based composites is increasing day by day. Cement production significantly increases CO₂ emissions. These emissions are reduced when high volumes of cement are replaced. The consideration of sustainable development has prompted people to search for new cement substitutes. The lignocellulosic biomass ash obtained from burning lignocellulosic biomass contains a large number of active oxides. If lignocellulosic biomass ash is used as a partial cement substitute, it can effectively solve the high emissions problem of cement-based composites. This review summarizes the physicochemical properties of lignocellulosic biomass ashes and discusses their effects on the workability, mechanical properties, and durability (water absorption, acid resistance, etc.) of cement-based composites. It is found that appropriate treatments on lignocellulosic biomass ashes are beneficial to their application in cement-based composites. Meanwhile, the issues with their application are also pointed out.

With the aim to systematically analyze the ambient relative humidity on the shrinkage strain of Engineered Geopolymer Composites (EGCs), this paper studied four variables (fly ash to ground granulated blast furnace slag mass ratio, alkali content, water–binder ratio, and fiber volume content) though orthogonal experimental design and three different relative humidity values (30%, 60%, and 100% RH). The results indicated that, for EGC specimens under 30% RH and 60% RH, the decrease in slag content and increase in alkali content both resulted in greater drying shrinkage. The addition of fibers effectively reduced the shrinkage strain, while a minor impact on shrinkage was presented by the W/B ratio. The first and second key factors affecting the drying shrinkage strain were the FA/GGBS ratio and the alkali content. The optimal ratio of FA/GGBS, alkali content, and fiber volume fraction were 0/100, 4%, and 1.5%, respectively. Dring shrinkage strain was decreased with the increase in ambient relative humidity. Compared with the shrinkage strain under 30% RH, the reduction in shrinkage strain under 60% RH and 100%RH was up to 46.1% and 107.5%, respectively. At last, a relationship between shrinkage strain and curing age under 30% and 60% RH was established with a fitting degree from 0.9492 to 0.9987, while no clear relationship was presented under 100% RH. The results in this paper provide a practical method for solving the shrinkage problem of EGCs.