혼합시멘트 수화모델을 이용한 콘크리트의 초기 특성과 내구성 예측에 관한 연구

Abstract

Fly ash from the combustion of coal, silica fume from certain metallurgical operations, and granulated slag from both ferrous and nonferrous metal industries, are among the industrial by-products that are widely used as mineral admixtures in Portland cement concrete to improve durability and produce high strength and high performance concrete. In addition, due to energy-saving and resource-conservation, both ecological and economical benefit can be achieved by using blended Portland cement. Compared with Portland cement, the hydration of cement incorporating supplementary cementing materials (SCM), such as fly ash, slag, and silica fume, is much more complex due to the coexisting of cement hydration and the reaction of mineral admixtures. To model the hydration of blended concrete, it is a general idea to treat the hydration reactions of cement and blended mineral admixtures respectively. In this paper, a numerical model is proposed to simulate the hydration of concrete containing silica fume, fly ash and slag. By considering the producing of calcium hydroxide in cement hydration and the consumption of it in the reaction of mineral admixtures, the reaction of mineral admixtures is separated from the cement hydration. The fit parameters do not change from one mix to another, and depend only on chemical characteristic of the mineral admixtures. The model of the effect of applied hydrostatic pressure on cement hydration is also proposed. Based on the degree of hydration of cement and mineral admixtures, the early-age properties of hardening concrete, such as the evolution of calcium hydroxide, the chemically bound water and porosity, the hydration heat evolution, the autogeneous shrinkage and drying shrinkage, the development of compressive strength and elastic modulus, the temperature distribution under a semi-adiabatic condition, and early-age viscoelasticity behavior (basic creep), are predicted. The prediction procedures are verified with the experimental results from literatures. Based on the hydration model, the evaluation of porosity, chemical composition of hydration products, saturation of pore and other properties can be obtained. As the durability relates closely with microstructure of concrete, it is possible to evaluate the durability aspects through hydration model. In this paper, the carbonation of blended concrete, the chloride attack into concrete, and the corrosion of steel rebar in concrete are modeled by introducing the hydration model. The prediction procedures are verified with the experimental results from literatures. The thesis includes six chapters. The first chapter is the introduction part. In this part, the background and motivation of this research, and objectives and organization of the thesis are shown. The second chapter is the investigations of literatures. A review on the existing hydration model is shown. The third chapter is the derivation of the hydration model. The basic idea of the proposed model is separated the reactions of mineral admixtures from Portland cement. The properties of concrete relate with the degree of hydration of cement and reaction degree of mineral admixtures. The model of the effect of applied hydrostatic pressure on cement hydration is also proposed. The fourth chapter is the prediction of early-age properties of concrete. The development of properties, such as short-term mechanical properties, visco-elastic and fracture properties can be determined as functions of degree of hydration. This part can be regarded as a hydration-based integrated program to evaluate the early-age crack of concrete. The effect of released heat from hydration, shrinkage, and creep on crack are considered. A thermo-chemo-mechanical finite element program will be made to evaluate the potential of crack in the near further. The fifth part is the evaluation the durability properties of concrete. Based on the hydration model, the evaluation of porosity, chemical composition of hydration products, saturation of pore and other properties can be obtained. As the durability relates closely with microstructure of concrete, it is possible to evaluate the durability aspects through hydration model. In this part, the carbonation of blended concrete and the chloride attack into concrete in concrete are modeled by introducing the hydration model. The sixth part is the conclusion and discussion part. The conclusion is summarized. The advantage and disadvantage of proposed model are discussed, and the further researches on hydration model are highlighted.