Drying shrinkage properties of alkali-activated metakaolin-blast furnace slag inorganic adhesive for FRP-based structural rehabilitation

This paper presents a novel alkali-activated metakaolin (MK)-blast furnace slag (BFS) inorganic adhesive for FRP-based structural rehabilitation, and the effects of different parameters, such as MK-to-BFS ratio, water-to-binder ratio, water glass modulus and Na₂O content, on drying shrinkage behaviors, pore size characteristics, internal reactions and microscopic morphologies of MK-BFS inorganic adhesive are systematically investigated. A range of macroscopic and microscopic characterization techniques are used to elucidate mechanism by which these parameters affect drying shrinkage. The results reveal that as MK-to-BFS ratio or water glass modulus increases, drying shrinkage of 7d specimen increases and then decreases, and it reaches the maximum when MK-to-BFS ratio and water glass modulus are 1/9 and 1.4, respectively. Increasing water-to-binder ratio or decreasing Na₂O content increases drying shrinkage of 7d specimen. The mass loss of 7d specimen gradually increases as MK-to-BFS ratio, water-to-binder ratio or water glass modulus increases, while it decreases as Na₂O content increases. The differences in drying shrinkage behavior are largely attributed to the inconsistent effects of various parameters on the development of reaction equilibrium, medium transfer, reaction evolution, reaction degree and pore connectivity in the system. Additionally, smaller pores generally impede the escape of water but increase drying shrinkage, whereas larger pores facilitate water evaporation but are detrimental to compressive strength.