Investigation of chemical processes, mechanical behaviors and durability of high performance concrete subjected to stress corrosion.

Stress corrosion of concrete is a new research field which was first initiated 1984 by Schneider and co-workers, who investigated the effect with Portland cement mortar and ordinary concrete. The behavior of high strength concrete under chemical corrosion and stress corrosion was studied in the thesis. The concrete specimens were immersed into a variety of chemical solutions e.g. 5%, 2.5%, 0.5%, 0.1% and 0.05% ammonium sulfate solutions, 10%, 5%, 1% and 0.1% ammonium nitrate solutions, under different flexural loads with load levels of 30%, 40% and 50% of their initial flexural strength, respectively. The effect of stress corrosion under the flexural loads was observed during the immersion in the solutions. The strength development, the weight changes of the specimens and the fracture energy of concrete immersed in ammonium sulfate and ammonium nitrate solutions were measured. The depth of penetration of the attacking ammonium nitrate ion was determined too. The corresponding behavior of specimens immersed in water saturated with Ca(OH)2 was determined as a reference. The influences of the initial strength, load level, concentration of the aggressive solutions, temperature and the surface coatings on the behavior of the high performance concrete were extensively investigated. The fracture probability (Bi) and the life -time coefficient (L i) were defined in order to evaluate the experimental results obtained. As well, the chemomechanical effect, the mechanochemical effect and the synergetic effect factor S(t) were defined and determined. The mechanisms of the stress corrosion of the cementitious materials were interpreted in terms of the experimental effects and a theoretical model. Several relations, namely, the relation between the strength and the weight loss, the relation between the strength and the penetration depth, the relation between the life-time and the concrete quality, the relation between the life- time and the load level as well as the relation between the life-time and the concentration of solution were determined and discussed. Consequently, a strength model for the cementitious materials was developed, and furthermore, new equations for chemical corrosion and stress corrosion of high performance concrete, i.e., strength-time-curve for HPC under corrosion, are proposed in this report.