Effect Of Al³⁺ On The Expansibility Of Alkali-Silica Gel

Alkali-Silica reaction （ASR） can lead to crack in concrete structure, and crackpropagation causes the collapse of the structure finally. When ASR is happening, but itdoes not yet cause serious damage of concrete structure，taking the remedial measuresfor the ASR expansion can improve the durability of concrete structure, and hasimportant theoretical significance and engineering value.According to ASTM C1260, the rapid method of mortar bar was used to test theeffect of Al³⁺on inhibiting expansion caused by ASR. The effect of Al³⁺concentrationand the time when Al³⁺was infiltrated to the specimens was studied. The results showthat the expansion caused by ASR was inhibited by Al³⁺obviously, and the Al³⁺concentration and the time when Al³⁺was infiltrated to the specimens had obvious effecton inhibiting expansion. There was a proper Al³⁺concentration in which the expansionwas inhibited best. It was better to infiltrate Al³⁺to the specimens when ASR hadhappened than ASR had not happened.Alkali-Silica gel with different ratio of Ca/Si and Al/Si was prepared by chemicalmethod, and an apparatus used to measure the expansion of alkali-silica gel was made byus, and the expansion of alkali-silica gel was tested. It was found that pure alkali-silicagel （N-S-H） did not expand almost. However, when Ca²⁺existed, alkali-silica gelappeared to expand. It was also found that the expansion of alkali-silica gel could besuppressed by Al³⁺.The morphology and composition of ASR gel was observed and analyzed bySEM/EDS and XRD, and the polymerization degree of Si and the coordination of Al wasanalyzed by NMR. The mechanism of Al³⁺inhibiting ASR expansion was discussed. Al³⁺can enter the structure of alkali-silica gel and form-Si-O-Al-chain, which increases thepolymerization of-Si-O-. Under the action of Al³⁺on polymerization, the N-S-H gel withexpansibility changes to N-A-S-H gel without expansibility, and the amorphous N-S-Hgel changes to crystal matters, such as zeolite-like minerals.