Strength and crack-resistance of concrete with fibre fillers and modifying nano-additives

The article dwells on a comprehensive method for determining concrete strength and crack-resistance in sample testing with varying loading rate. The method allows for receiving simultaneously kinetic parameters of the microstructure defects and length and rate of the main crack growth. The authors consider the impact of effective involved volume on the formation and growth of minor structural defects in cement gel with their eventual phased transition to larger defects. It facilitates increased stress concentration and the development of main cracks at the matrix-aggregate interface. Control over the development of the main crack allows for determining the time till destruction for concrete (longevity). The suggested method and the obtained formula helped applying a wide range of loading rates for determining the critical length of the main crack in concrete. The testing results were used to identify the coefficients of dynamic strengthening for the sample sets with and without an artificially created main crack. These coefficients were applied for calculating the main crack critical length. The article presents the results of experiments aimed at development of concrete compositions comprising fibre fillings and modifying additives including nano-additives followed by determination of their strength and crack-resistance as per the presented comprehensive method. The found values of efficient involving volume, activation energy characterise the microstructure parameters and critical length of the main crack in concrete. The resulting conclusion was that the main crack length in all of the developed concrete compositions exceeded the half of the section in the sample where it developed. Comprehensive assessment of concrete strength and crack-resistance and accumulation of experimental data improve the reliability of scientific research due to the emerging integrated approach to determining quantitative parameters of crack-resistance and longevity of the developed concrete compositions with forecasted properties.