Creep behaviour of alkali activated slag and fly ash concrete: effects of hypothetical thickness, aggregates, and loading age

Although alkali activated materials have been researched intensively over the last few decades, their time dependent properties such as creep and shrinkage remain less understood. This paper investigates the influence of major factors affecting the basic and total creep behaviour of Alkali Activated Slag and Fly ash concrete (AASF), focusing on loading age, sizes of exposed surface and aggregate size and content. Creep tests were performed for a period of 180 days. The variation in the mechanical properties, including the compressive strength and elastic modulus of both AASF and OPC concrete over time was also measured. The experimental results indicate that AASF concrete exhibits an upward trajectory in creep in log-time, while the rate of creep of OPC concrete with similar mix proportion diminishes in log-time, tending to a level of stability. The study also demonstrates that creep strain of AASF concrete decreases as the exposed surface area and the age of loading increase, albeit at different rates than OPC, as was demonstrated through comparison with prediction models calibrated for OPC concrete. The experimental program also includes basic and total creep testing of mortar specimens, which provides insights into the effect of aggregates. A preliminary meso-scale finite element model was used and validated against the test results to predict the creep response of AASF concrete from the mortar. Additionally, parametric studies regarding the effect of aggregate size and content were conducted. The results show that an approximately linear relationship was observed between the content of aggregate and total creep strain while aggregate size has little impact on the total creep of AASF concrete.