Wave full-element based compressive strength calculation method and discrete element simulation of concrete considering coarse aggregate volume fraction and Weibull distribution

To quantitatively characterize the influence of coarse aggregate volume content on the uniaxial compressive performance of concrete and improve the theoretical calculation system of concrete compressive strength, cubic compressive tests were carried out with seven volume fractions of coarse aggregate ranging from 0% to 70% and five water-cement ratios from 0.3 to 0.5, using grade 42.5 ordinary Portland cement and natural limestone coarse aggregate as raw materials. Firstly, the coupling mechanism of coarse aggregate volume content and water-cement ratio on concrete compressive strength was analyzed. Two paste thickness indicators of coarse aggregate were defined based on stereology, a mechanical calculation model for the clear distance between adjacent coarse aggregates was established, and force transfer equations between aggregates were modified by introducing a clear distance adjustment coefficient. Secondly, two types of mesoscopic spring failure element models were constructed according to the relative stiffness of coarse aggregate and interfacial transition zone. The fitting errors of Weibull, Gamma, Normal and other probability distributions were compared, and Weibull distribution was selected to describe the evolution relationship between aggregate clear distance and compressive strength. A prediction model of concrete compressive strength considering coarse aggregate volume fraction was proposed. Finally, based on the parallel-bond model of particle discrete element method (DEM), the Weibull stochastic damage function was embedded into the numerical program. The effects of key DEM parameters on mechanical response and failure pattern of concrete were systematically investigated, and the model was verified by experimental data. The results show that the compressive strength of concrete increases first and then decreases with the growth of coarse aggregate volume content under all water-cement ratios, and the optimal volume fraction of coarse aggregate is 45%. The effective range for coarse aggregate to improve mortar strength narrows with the increase of water-cement ratio. The theoretically calculated reasonable clear distance of coarse aggregates derived in this paper is highly consistent with the measured paste thickness. The correlation coefficients of the proposed Weibull-based compressive strength model are all higher than 0.96, indicating excellent prediction accuracy. The DEM model embedded with Weibull stochastic damage can accurately reproduce the evolution law of concrete compressive strength under load, which effectively remedies the defects of traditional discrete element simulation. The research results can provide theoretical basis and simulation method for skeleton mechanism analysis, mix proportion optimization and mesoscopic numerical simulation of concrete.