Durability Of Low-Calcium Alkali-Activated Gelling Materials In Chloride And Sulfuric Acid Environments

The environmental problems caused by the production and application of silicate cement are increasing,and alkali-activated materials are being widely studied as a new green building material.This paper explores durability of low-calcium alkali-activated gelling materials in chloride and sulfuric acid environments,and provides a theoretical basis for the establishment of durability models and the improvement of test specifications for alkali-activated materials.First,the ability of alkali-activated metakaolin-slag slurry(AAMS)to cure chloride ions was investigated by means of isothermal adsorption equilibrium method and XRD analysis to examine the effects of slag dosage,activator modulus and activator concentration.The results showed that AAMS has a certain ability to bind chloride ions,which is mainly derived from the physical adsorption of chloride ions by C/N-A-S-H and C-S-H gels.The chloride binding ability of alkali-activated metakaolin is poorer than that of net cement paste(PC),but the slag incorporation makes AAMS have a stronger ability to bind chloride ions than alkali-activated metakaolin.the relationship between free and bound chloride ions after binding by AAMS is better fitted by Langmuir isotherm.the binding effect of AAMS on chloride ions in NaCl solution is affected by the NaCl solution concentration,and the adsorption was more significant for high concentration(>1.0 M)NaCl solutions.The effect of activator modulus on the binding effect of chloride ions is less,when the activator modulus is higher,the binding ability of AAMS on chloride ions is poor,and the amount of chloride ions bound by AAMS with lower activator modulus keeps increasing with the increase of slag dosage.The activator concentration has a greater effect on the binding effect of chloride ions,and the low concentration of the activator has a better ability to bind chloride ions for AAMS.In addition,the erosive effect of sulfuric acid on alkali-activated fly ash was investigated from the aspects of mechanical properties,corrosion condition and erosion mechanism,and the erosive effect of SO42-was examined as a comparison with that of hydrochloric acid on alkaliactivated fly ash to provide a theoretical basis for the application of alkali-activated fly ash in sulfuric acid environment.The results show that alkali-activated fly ash has excellent resistance to sulfuric acid erosion compared with silicate cement.The increase of exciter modulus has a better effect on the anti-sulfuric acid erosion performance of alkali-activated fly ash.Silica fume incorporation reduced the sulfuric acid erosion resistance of alkali-activated fly ash.With the incorporation of slag,the strength and structural denseness of the alkali-activated fly ash were enhanced,but the sulfuric acid attack resistance of the alkali-activated fly ash with slag was significantly lower than that of the alkali-activated fly ash.The alkali-activated fly ash without slag has better resistance to sulfuric acid attack than to hydrochloric acid attack,while the alkaliactivated fly ash with slag is the opposite.