Reduction of concrete expansion by ettringite using crystallization inhibition techniques

Many researchers have proposed that secondary or delayed ettringite is responsible for serious, premature deterioration of concrete highways. The current research project was designed to determine experimentally if secondary ettringite formation in concrete can be reduced by treating the concrete with commercial crystallization-inhibitor chemicals. The hypothesis is that if ettringite is reduced, a concomitant reduction of concrete expansion and cracking will occur. If ettringite formation and concrete deterioration are simultaneously reduced, then the case for ettringite-induced expansion/cracking is strengthened. Our experiments used four commercial inhibitors-two phosphonates, a polyacrylic acid, and a phosphate ester. Concrete blocks were subjected to continuous-immersion, wet/dry cycling, and freeze/thaw cycling in sodium sulfate solutions and in sulfate solutions containing an inhibitor. The two phosphonate inhibitors were effective in reducing ettringite nucleation and growth in the concrete. Two other non-phosphonate inhibitors were somewhat effective, although less so than the two phosphonates. Reduction of new ettringite formation in concrete blocks also reduced expansion and cracking of the blocks. This relationship clearly links concrete expansion with ettringite formation. Secondary ettringite nucleation and growth must cause concrete expansion, because the only effect of these inhibitor chemicals is to reduce crystal nucleation and growth. These inhibitors cannot be responsible in any other way for reduction in expansion.