Drying Shrinkage of Alkali-Activated Concrete
摘要
The large shrinkage of alkali-activated concrete (AAC) still represents one of its main limitations to scale it up for real life applications as it may lead to the formation of cracks, compromising its long-term durability. This chapter is specifically focused on the drying shrinkage behaviour of AAC, which is the volume reduction of concrete due to the loss of internal water to the external environment through evaporation. It summarises the main parameters that can affect the drying shrinkage of AAC, including the characteristics of the activator solution (ionic species present, activator modulus), the curing conditions (temperature, relative humidity, curing time), the specific surface area of the selected precursors and the effect of incorporating either fibres or additives such as Ca(OH)2, nano-TiO2, MgO, or shrinkage reducing admixtures to mitigate the drying shrinkage amplitude. General trends are given as function of the specific aluminosilicate precursor used (either ground granulated blast furnace slag, fly ash or metakaolin) and combinations thereof besides other non-traditional precursors, as they tend to develop different matrices and pore structures, which greatly determine the shrinkage behaviour of AAC. The chapter also includes a brief description of the existing standards to measure the drying shrinkage and the advances done on adopting the existing models to predict the drying shrinkage of Portland cement concrete to AAC, before some general conclusions are outlined.