Shrinkage, compressive and bond strengths of alkali activated/cement powder for alternative coating applications

This paper reports the properties of a novel coating material produced from alkali-activated/cement powder (AACP), including setting time, strength development, drying and autogenous shrinkages, and bond strength of one-part AACP paste-coated reinforcing steel bars in concrete. The AACP paste was prepared by activating a mixture of dry geopolymer powder (GPP), Portland cement (PC), and silica fume (SF) with tap water and 2 M sodium hydroxide solution. The effect of PC replacement, sodium silicate-to-sodium hydroxide solution (SS-toSH) ratio, and pre-curing temperature in the production of GPP on the properties of AACP paste were also investigated. Test results showed that the incorporation of FA and PC activated with an SS-to-SH ratio of 2.0 for the production of GPP decreased their setting time of fresh one-part AACP pastes, whereas their strength development marginally increased. Furthermore, the increasing PC content and SS-to-SH ratio had an adverse effect on drying and autogenous shrinkages. However, the pre-curing temperature had a marginal effect on their shrinkages. In addition, one-part AACP paste-coated reinforcing steel bars positively affected the bond strength of reinforced concrete, especially for the GPP produced by FA without PC. The increased reaction products at the contact zone could assist in improving their bond strength. It can be recommended that the use of FA without PC activated with a low SS-to-SH ratio in the production of GPP would be beneficial in improving shrinkage and bond strength while providing high equivalent substrate stiffness (ks).