SIGNIFICANCE OF AND ASSESSMENT APPROACHES TO INTERPHASES IN CEMENTITIOUS COMPOSITES

摘要

The cement grains undergo size-segregation when deposited and packed in the fresh state around the densely packed particles of the aggregate. A spatial network of such interphases (called Interfacial Transition Zones -ITZs- in concrete technology) is formed as a result. A computer-simulation approach on microlevel to the structural features of ITZ is presented. Density and bonding gradients in the ITZ are visualised as a function of water cement ratio and cement fineness. On mesolevel the fracture surface is the result of debonding (interphase cracking) and crack coalescence along a supposedly flat dividing plane. This serves as a model for determination of the fracture surface roughness. The analytical solution is derived in this paper. Damage evolution in cementitious materials is a process starting in general with interphase debonding (microcracking), followed by crack coalescence with near neighbours, finally concentrating in a so-called fracture process zone in which ultimately crack concentration leads to the formation of the macrocrack. This process can be recorded in sections. The methodological aspects of obtaining unbiased 3-D macroscopic (global) information on the damage structure is presented.