Research progress on macroscopic properties of concrete based on microporous structure and exploration of fracture models

Concrete is a typical multiphase composite material, and its fracture failure essentially involves a multi-scale nonlinear fracture of heterogeneous and discontinuous materials. The pore structure of concrete is divided into three scales: macroscopic, mesoscopic, and microscopic. The microscopic pore structure of concrete has a significant influence on its macroscopic performance. This study classifies concrete pores into four types: gel pores, transition pores, capillary pores, and macropores. These four types of pores are recognized as harmless pores, minimally harmful pores, harmful pores, and multi-harmful pores, respectively. This study summarizes the advantages and disadvantages of three common methods for testing pore structures. The relationship models between microporous structure and macroscopic strength, as well as fracture performance, are discussed. The results showed that the lower the porosity of concrete is, the higher the compressive strength and fracture toughness of concrete are. The prediction results of the model that considers multiple factors, such as porosity and pore size, are superior to those of the model that considers only porosity. The fracture model of multi-scale FPZ is proposed, and the sensitive aperture parameter is introduced. Finally, the research progress of the mesoscopic numerical analysis of pore structure is presented, and prospects for research on the microscopic pore structure and fracture performance of concrete are outlined.