Effects of slag and alkaline solution contents on bonding strength of geopolymer-concrete composites

Geopolymer has received widespread attention due to their excellent mechanical properties and more environmentally friendly characteristics. Studying the bonding performance between geopolymer and concrete is of great significance for the development of a building material for repairing damaged concrete. The paper studied the effects of slag and alkaline solution contents on bonding strength of geopolymer-concrete composites (GCC). Firstly, 15 groups of geopolymer concrete mix proportions with 5 groups slag contents and 3 groups alkaline solution contents were designed. GCC specimens were prepared by casting geopolymer concrete on cement concrete substrates. Secondly, the splitting tensile test was conducted on GCC specimens. The strain field during the testing process of GCC specimens was analyzed based on the digital image correlation (DIC) technique. Thirdly, the effects of slag and alkaline solution contents on the splitting tensile strength of GCC specimens were discussed. Finally, the optimal mix proportion of geopolymer concrete which has the highest bonding strength with cement concrete was proposed. The results show that the splitting tensile strength of GCC specimens increases first and then decreases as the slag content increases. The splitting tensile strength of GCC specimens decreases linearly as the alkaline solution content increases. In addition, the crack growth rate of GCC specimens increases with the increase of slag content during the splitting processing. The geopolymer concrete with 50.0 % slag content and 0.7 alkaline solution-binder ratio shows the highest bonding strength with cement concrete, which is recommended for the potential application in the pavement repair works.