Quantifying the swelling properties of alkali-silica reaction (ASR) gels as a function of their composition

Synthetic alkali-silica reaction (ASR) gels were produced and tested to investigate the effects of chemical composition (Ca/Si, Na/Si, and K/Si atomic ratios) on the gels’ free swelling strain (ε_g,fr) and restrained swelling pressure (P_rs). The gels were cast into disk-shape molds and exposed to distilled water after curing. Each gel's ε_g,fr was recorded over a period of 28 days, followed by measuring P_rs, defined as the pressure required to fully reverse and eliminate the gel's free swelling under a drained configuration. Regression models were developed linking gels compositions to their swelling properties. The outcomes show that Na/Si and K/Si monotonically increase ε_g,fr. Increasing Ca/Si up to 0.23 drastically reduces ε_g,fr; higher Ca/Si has modest effect on free swelling. P_rs increases by increasing calcium up to a pessimum Ca/Si level; P_rs decreases for higher Ca/Si. The value of (Ca/Si)_pess is related to the alkali content of the gel. P_rs also increases by increasing the gel's alkali content, while a (Na/Si)_pess exists in the range 0.85-0.95. These observations are linked with the roles of alkalis and calcium in modifying the silica gel network.