Effect of coarse aggregate on the interfacial transition zone of concrete based on grey correlation

In order to investigate quantitatively the influence of multiple aggregate factors on the interfacial transition zone (ITZ) and to determine the major and minor factors, it is necessary to adopt a mathematic model. A mathematic model of the interface influence factor (K_I) is proposed, based on a previous formula of the volume fraction of the ITZ and combined with microhardness test results. Using the model, the positive and negative influences on the ITZ of coarse aggregate of different types, volume fractions and grading can be quantitatively assessed. Furthermore, the grey correlation degree between the coarse aggregate and K_I is analysed. The results show that, for normal weight aggregate (NWA), the aggregate grading is the major influencing factor and, for lightweight aggregate (LWA), water absorption is the major influencing factor; both of these factors have the highest correlation degree with K_I. Therefore, to improve the microstructure of the ITZ in concrete, NWA with a large average particle size and LWA with a high water absorption should be used to prepare the concrete, on the premise of meeting the necessary workability and mechanical properties of the concrete. The grey correlation model can be successfully applied to sensitivity analysis of the influence of coarse aggregate with various factors on the ITZ.