Non-aging basic creep of alkali-activated slag concrete: Multiscale characterization and modeling

Abstract

This study focuses on a multiscale characterization of basic creep behavior of two AAS creep mixes with high (hS) and low (lS) slag content, loaded at 28 days. Nano-indentation tests are performed to investigate creep properties of individual phases and classical creep tests to analyze the creep behavior of concrete. An analytical multiscale micromechanics-based model is applied to downscale creep properties of the reaction product foam at nano-scale to compare it with results from nano-indentation. The creep at nanoscale of reaction product foam is modeled with a compliance function considering only deviatoric component consisting of Kelvin–Voigt chain for short term behavior and logarithmic function to account for long-term behavior. Comparing downscaled compliance with creep modulus measured from nano-indentation it is concluded that nano-indentation captures long-term behavior of reaction product foam. In terms of two mix tested, while at nano-scale mix hS has a higher creep modulus, presence of more capillary porosity and micro-cracks counteracts this and as a result concrete with mix hS shows higher creep. The creep modulus of AAS product foam obtained from nano-indentation is significantly lower compared to the OPC products. Additionally, higher amount of gel water and fewer crystalline secondary products could explain higher creep observed for AAS concrete compared to OPC concrete.