The use of thermodynamic analysis in assessing alkali contribution by alkaline minerals in concrete

Using a thermodynamic method, the decomposition reactions of alkaline minerals in alkaline solution were studied, and the theoretical alkali contribution by alkaline minerals was analyzed also. It was indicated that the theoretical maximum alkali released from alkaline minerals in order was dawsonite > leucite > nepheline > dehydration analcime > paragonite > muscovite > jadeite > Na-feldspar > K-feldspar in alkaline solution with pH > 13. With the increasing of pH in alkaline solution, the maximum amounts of alkali released from alkaline minerals increase excluded nepheline. Furthermore, the maximum alkali contribution by alkaline minerals to concrete was calculated based on an aggregate content of 1850 kg/m3. It was found that the maximum alkali contribution by alkaline minerals was affected mainly by the pore solution/aggregate ratio, then the pH level of pore solution. These results also suggest that using low water-to-cement ratio and preventing water from permeating into concrete could effectively restrain alkali released from aggregate.