Analysis of probable consequences of cement composite frost destruction

Abstract

The article presents an analysis of variations in the internal resistance of standard and fiberreinforced cement composites under non-stationary low-temperature and humidity effects. Various aspects of the response kinetics of prismatic samples in the monotonous compression mode are considered. The sample set included control samples and those subjected to cyclic freezing and thawing according to their standard frost resistance. Test samples (100 × 100 × 400 mm) were made of conventional (B series) and fiber-reinforced (FB, polypropylene fibers df = 0.8 mm, lf = 40 mm, µf = 1.5 vol%) concrete with a component ratio of cement: sand: crushed stone: water = 1:1.42:3.57:0.55. The accepted base of T-W cycles corresponded to the standard concrete grade in terms of frost resistance, established in control tests (F200). Static tests of composites were preceded by low-temperature exposures according to an accelerated method for assessing frost resistance with a temperature decrease down to minus 35℃ and thawing in a 5% NaCl solution. Samples were automatically loaded (Instron 5989 test complex) according to a special program with a constant deformation rate of 5·10-5 mm/s and continuous recording of deformations. Significant differences were observed in the strength kinetics, magnitude and structure of deformations, along with a high sensitivity and quantitative informativeness of the significant parameters of the strength kinetic concept for solid bodies. The expediency of a differentiated approach to the selection of calculation models and criteria for the temperature and humidity transformations of cement-matrix composites, which takes operational requirements into account, is substantiated.