Study On Physical-mechanical Properties And Durability Of Cementitous Materials With The Addition Of Nano Metakaolin Clay

The material and mechanical properties of concrete are decreased due to the corrosion of reinforced steel and debonding behavior between concrete and reinforced steel under the multiple aggressive environment, which results in the deterioration of durability of reinforced concrete structures and the failure of constructions prior to the estimated service life. Nowadays, the deterioration of durability and mechanical properties of concrete structures is attracting more and more attention in civil engineering. Based on the recent research, the failure of concrete structures stems from the failure of concrete elements; the failure of concrete elements stems from the failure of concrete material. Therefore, the new-type high-durability concrete is crucial to enhance the durability of concrete structures, which need to be deeply considered in the further research.This research is based on the investigation of the durability of reinforced concrete structures and the application of nano-materials in civil engineering, and funded by the National Natural Science Foundation of China (Grant No.51178069) and the Program for New Century Excellent Talents in University (Grant No.NCET-11-0860). This paper focuses on the physical and mechanical properties, corrosion resistance, conductivities and bonding behavior of nano-metakaolin cementitious materials, including the modification mechanisms of nano-metakaolin cementitious materials under micro-scale, meso-scale and macro-scale analysis. The principal research work is listed as follows:1. Dispersity of nano-metakaolin cementitious materials. Based on the microstructures and pore analysis of nano-metakaolin cement paste, the effect of dispersing methods and time on dispersity of nano-metakaolin cementitious materials was obtained. An optimized dispersion process of nano-metakaolin in cementitious materials was proposed.2. Modification mechanism of cement hydration process with nano-metakaolin. Based on the Differential Scanning Calorimetry (DSC) and X-ray diffraction, the influences of nano-metakaolin in cement hydration, Calcium Silicate Hydrate (C-S-H) and hydrated product such as Ca(OH)2 were discussed. The improve effect of nano-metakaolin on the microstructure of cement paste under micro-scale was analyzed.3. Physical and mechanical properties of nano-metakaolin cementitious materials. This chapter studied the influences of nano-metakaolin in flexural properties, compressive strength and drying shrinkage of early-age cement paste, and revealed the improve effect of nano-metakaolin on mechanical properties of cement paste at early-age.4. Durability of nano-metakaolin cementitious materials under aggressive environment. This chapter studied the deterioration of physical and mechanical properties of cementitious materials under chlorine salts, acid rain and freeze throwing environment, such as structures, mass, relative dynamic modulus of elasticity, pore structures, compressive strength, permeability and resistivity. The modification mechanisms of nano-metakaolin cementitious materials under micro-scale and meso-scale were obtained. An accumulated damage model of durability of nano-metakaolin concrete was built. An evaluation method of nano-metakaolin concrete based on resistivity was proposed.5. Bond-slip properties between reinforced steel and nano-metakaolin concrete. This chapter studied the delayed effect of corrosion in reinforced nano-metakaolin concrete. The test revealed that the bond-slip relationships between the reinforced steel bar and nano-metakaolin concrete, including the bonding eigenvalues such as bonding strength, slip value and bonding stiffness. The bond-slip constitutive relationships between reinforced steel and nano-metakaolin concrete were built.6. A new weight calculation model of durability of nano-metakaolin concrete based on the Copula function. Combined with Gumble Copula function and Kendall coefficient, the failure matrix of correlation coefficient was proposed based on the nonlinear transition function of failure mode. The calculation model of durability of concrete with failure correlation was built.