Drying shrinkage of alkali-activated concrete -State-of-the-art

Abstract

Alkali-activated concrete (AAC) has emerged as an environmentally friendly alternative to conventional concrete, as It is a cement-free concrete made by activating precursors (mainly low-cost, low-CO2 industrial by-products) with alkalis. AAC has demonstrated some remarkable mechanical properties and long-term performance (e.g., high strength, chemical durability, and fire resistance). However, high drying shrinkage in AAC, causing cracks degrading the long-term durability of AAC, is one of the obstacles that must be overcome before it can be widely applied in the construction field.
This study investigates the mechanisms of drying shrinkage, provides a survey and evaluation of the influencing factors, and accordingly proposes an integral solution to mitigate drying shrinkage in AAC. This was done through a qualitative approach based on literary research.
The investigation showed that the main driving forces of drying shrinkage are surface, disjoining, and capillary tension forces, and they are related to relative humidity (RH) and meniscus radius. Further, different reaction products' characteristics can be attributed to different drying shrinkage mechanisms, as they have a critical role in determining AAC properties. Furthermore, poor mechanical properties of AAC often lead to a higher drying shrinkage rate. Surveying the influencing factors of drying shrinkage of AAC, in terms of raw materials, mix designs, and curing conditions showed their significant effect on drying shrinkage magnitude and mechanical properties. These factors were accordingly evaluated and systematized. Therefore, based on the survey and evaluation, a strategy was proposed to mitigate drying shrinkage in AAC.