Research On Meso-scale Dynamic Constitutive Relation Of Concrete Under Sulfate Attack

Sulfates widely exist in atmosphere, soil and water. Sulfate attack is one ofthe major durability problems of concrete structures, which is manifested byexpansion failure and mechanical performance degradation. At meso-scale level,concrete can be regarded as a three-phase composite material consisted by mortarmatrix, coarse aggregate and interfacial transition zone. With regarding tounderstand the dynamic mechanical properties degradation and its evolution ofsulfate attacked concrete, it is significant to build a meso-scale numerical model,which can consider the actual geometric and distribution characteristics of coarseaggregates in concrete. Meanwhile, experimental investigations on diffusion ruleof sulfate ion in concrete and degradation evaluation of sulfate attacked cementare indispensable.The improved barium sulfate weight method was used to evaluate the sulfateion concentration of concrete and cement with different sulfate attacked ages.Then the diffusion law of sulfate ion in mortar and concrete was analyzed. Thedynamic compressive and bending tests were carried out to study the influence ofsulfate attack on the dynamic properties of cement and concrete. It is shown thatthe diffusion speed of sulfate ion gradually slows down with the increasingattacked time. The compressive strength of attacked mortar is increased with theincreasing strain rate and the strain rate effect of attacked mortar will experience asignificant variation with the growth of attacked time.The image processing technology of MATLAB was employed to evaluate theboundary conditions of aggregates and polygon fitting was used to obtain themorphology of aggregate. Firstly, the aggregate vertex coordinates was determined,then geometric characters were analyzed statistically based on the date of polygonfitting. The statistical results show that the distribution of the edge number, thesize irregular degrees and the shape irregular degrees conform to Gaussdistribution, while the areas and the equivalent radiuses conform to Lognormaldistribution.，Finally, two-dimensional concrete meso-scale numerical model wasestablished based on the analysis results.The random circular aggregate model and polygonal aggregate model were established respectively, using Monte Carlo method and polygon fitting analysisresults in ABAQUS software. A comparative analysis between above two modelswas also conducted to discuss their advantages and disadvantages. The resultsshow that the polygonal aggregate model is more accurate than circular aggregatemodel. In addition, the dynamic compression test and tensile splitting test werenumerical simulated. The numerical results show that the rate effect ofcompressive strength and splitting tensile strength could be better simulated by themeso-scale numerical model. In the end, a relation between sulfate ionconcentration and mortar compression strength was established, and themechanical performance degradation law of sulfate attacked concrete wasforecasted using meso-scale numerical model.