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In the saline environment, chloride ions diffusion depth in concrete is very important for predicting the service life of concrete structures. Moreover, concrete structures are not always crack-free. Cracks with different widths and depths will reduce the cover thickness and accelerate the migration of chloride ions. So, it’s significant to develop a model to predict the chloride diffusion depth in cracked concrete. In this research, the whole chloride diffusion process was divided into two parts: chloride diffusion in sound concrete and in crack. The solution concentration gradient existed in the crack obviously, and it changed the chloride concentration along the crack surface continually. Considering four factors that will influence the chloride diffusion in sound concrete, the diffusion model based on Fick’s second law was modified. And a FEM analysis on chloride diffusion in cracked concrete was performed with the new model in ANSYS. A good agreement can be found in comparison the numerical solution with test results. It proves that the new mathematic model is within a good accuracy in predicting the chloride diffusion depth in cracked concrete.

The research described in this paper is based on the theory of linear elastic fracture mechanics (LFEM) using the standard three-point notched bending beam for the double-K model. In this model, the value of initial fracture toughness and unstable fracture toughness are taken as the two key parameters to analyze the fracture process of concrete. These two parameters were obtained from the three-point bending tests employing the beams with initial notch to depth ratio of 0.3 at the ages of 1d, 3d, 7d and 28d. The results gotten from the test and analysis indicate that these two parameters of fly ash concrete are slightly lower than those of pure cement concrete. The two parameters of concrete with two kinds of mixture proportions increase observably as the age increases. The influence of fly ash on the initial fracture toughness and unstable fracture toughness are not such obvious as that on the compressive and tensile strength. The research results can provide a valuable reference in construction engineering.

A new concept of polymer modification on cementitious materials was proposed. Cement mortars were modified using polyacrylate (PA) emulsion. Mixtures with polymer—cement ratios of 0, 5, and 10 wt.% were investigated in compressive strength and fracture properties at 0.5d, 0.75d, 1d, 3d, 7d and 28d. Compressive tests indicated a remarkable change of PA emulsion modified mortars from the early age to 28d. PA emulsion modification also gained considerable improvement in fracture properties. However, the test results revealed that the mechanical properties growth had not linear relationship with the PA emulsion addition. The mercury intrusion porosimetry (MIP) test proved that the optimization of PA emulsion addition should be emphasized in considering the pore introduction due to the emulsifier in PA emulsion. The principle of the PA emulsion modification was provided in a view of the microstructure of the mortars obtained from scanning electronic microscope (SEM) test and thermogravimetric (TG) analysis.