Degradation Mechanism Of Concrete Due To Calcium Dissolution

Calcium dissolution is a usual erosion behavior affecting the durability of concrete. It would lead to the loss of calcium and then a great change ofmicrostructure and macroscopic mechanical properties of concrete. In this paper, the deterioration mechanism of concrete due to calcium leaching as well as the concrete strength prediction model was studied with consider of two different types of calcium dissolution. To reveal the damage mechanism, some macro experiments were carried out to measure the erosion depth, compressive strength, splitting tensile strength, fracture properties and the quality of the concrete after different erosion ages; some microscopic tests were developed to analyze the hydrate, pores, and calcium contents in the damaged materials. The macro tests show that the erosion depth increases linearly with the square root of erosion time, and that the growth rate oferosion depth in nitric acid is greater than that in soft water. The compressive strengths, splitting tensile strengths and weights decrease gradually with the erosion ages, but the splitting tensile strengths are more sensitative to the leaching level than the axial compressive strength. The deterioration degree of concrete eroded by nitric acidis greater than the concrete in the same erosion age in soft water. The fracture toughness of concrete decreases with the erosion age and the decipline is more remarkable in the early stage of erosion period. In addition, the fracture toughness of concrete shows a good linear relationship with the axial compressive strength. The micro-tests show that the porosity and the micro-crack size in concrete increases with the dissolving of CH and CSH. Therefore, the original defects in concrete are aggravated, and this phenomenon is more serious in nitric acid. The micro-test analyses reveal the essential change mechanism of macro-mechanical properties of damaged concrete, and give a reference to the strength prediction. In terms of the stress distribution in concrete underspilting tension, a double crack model was established on basis of the micro-cracks changes caused by leaching. The relationship between the relative length of cracks and the splitting tensile strength of concrete was studied on the basis of micromechanics and fracture mechanics. By using the existing porosity model and the empirical formula of crack size, the crack lengths of concretes with different erosion depths were calculated, and then the splitting tensile strength of concrete with different erosion depth were predicted by this model, which results show a good agreement with experimental values. To predict the axial compressive strengths of leached concretes, the composite material mechanics and damage mechanics were used in the analysis. On basis of the test results and the damage constitutive relations of the concrete, considering the chemical damage by leaching, a compressive strength prediction model was established. The comparison results between prediction results and tested values show that this model can make a good prediction on the strength of eroded concrete.