| In many cases concrete infrastructure is currently suffering from the expansive and degrading affects of alkali silica reactive gel. Alkali silica reactivity in concrete is recognized as the production of an expansive gel caused by a reaction between aggregates containing certain forms of silica, alkalis, and hydroxides in cement paste. Current alkali silica gel mitigating technologies have recently been found to fail both in the field and laboratory. The use of nano silica is a novel approach to minimze the formation of the alkali silica reactive gel and resist the catastrophic stresses caused by the expansion. The modes by which the nano silica optimizes the hydrated cement matrix of concrete include breaching the pessimum where the alkali silica reactive gel can thrive, increasing the production of calcium-silicate-hydrates, and reducing the amount of residual bulk water in the cement matrix of the concrete composite. The use of nano silica in an alkaline solution is an advanced additive that increases both the strength and durability of cement composites and concrete. In the proposed work the behavior of the cement composite and the expansion of the alkali silica reactive gel was studied. Thermogravimetric analysis, scanning electron microscopy, and compressive strength tests were used to determine that while at higher dosages the smallest nano silica particles were less effective; at a lower dosage for the smallest nano silica particle the compressive strength increased and the amount of calcium hydroxide decreased. A chemical shrinkage analysis was used to discern how the size of nano silica impacts the change in volume of hydrated products. Mortar beams and pats with reactive aggregate and nano silica were soaked in a heated alkaline bath in order to measure the formation and expansion of the alkali silica reactive gel. The results of this dissertation support the use of nano silica as a means to increase the strength and resistance of cement composite samples and concrete to degradation due to the affects of the alkali silica reactive gel. |
