| The understanding of the expansion mechanisms resulting from the alkali-silica reaction allows the identification of the truly important factors, the assessment of the susceptibility of a concrete structure to deterioration by these processes, and the planning and implementation of preventive measures. The mechanisms of deterioration of concrete due to the alkali-aggregate reaction are investigated in this dissertation. A theoretical model is proposed to explain the volume change behavior of the reaction product gels formed in concrete containing a reactive aggregate. ASTM C 1260 test results in combination with semi-quantitative chemical analysis (EDS) of the reaction product gels are used to validate the proposed model. The osmotic swelling of the reaction product gels is attributed to double-layer repulsion forces. For a given colloidal system, the double-layer theory indicates that the larger the valence of the ions in the double layer, or the larger the concentration of ions, the smaller the double-layer thickness and repulsion forces that may be generated in the presence of water. Experimental results available in the literature support the double-layer model. According to these results, the expansion of mortar bars in the ASTM C 1260 test is related to the composition of the reaction product gels. The reaction product gels containing larger amounts of equivalent sodium oxide (Na{dollar}sb2rm Osb e{dollar}) and smaller CaO/Na{dollar}sb2rm Osb e{dollar} causes larger expansions in the mortar bars.; The ability of several chemical additives to interfere with the alkali-silica reaction and the resulting expansion in mortar bars is also investigated in this dissertation. Hydroxides and chloride salts were added to the mixing water at initial molar concentrations of 1 or 2. The following salts and hydroxides were evaluated: NaOH, KOH, LiOH, NaCl, KCl, LiCl, CaCl{dollar}sb2{dollar}, MgCl{dollar}sb2{dollar}, and AlCl{dollar}sb3{dollar}. After the mortar bars were subjected to ASTM C 1260 tests, samples were prepared and examined in a scanning electron microscope with EDS capabilities. The expansion test results indicate that the chloride salts with monovalent cations are the most damaging, followed by those with divalent and trivalent cations.; Finally, a method is proposed for interpretation of immersion test results and prediction of service life of concrete structures exposed to chloride ions. Once the chloride-content profiles are obtained after the immersion test, a realization of the diffusion coefficient is obtained at each point for which there is a measurement of the chloride content. These realizations are used to determine the probability density function of the diffusion coefficient. A reliability analysis is subsequently performed for ten different lightweight high-strength concrete mixtures. A reinforced concrete element is considered to have failed when corrosion initiates at the reinforcement bar, i.e., when a certain chloride-concentration threshold is reached at the reinforcement. The probability of corrosion initiation in time is calculated for the ten concrete mixtures investigated. |
