Interfacial transition zone in cementitious materials

Subjected to interfacial transition zone (ITZ) examinations were concretes made from gravel and dolomite aggregates in a natural state, and concretes made from the same aggregates coated with paraffin, and also concretes made from the same aggregates with a silica fume admixture. In the case of the gravel concrete, silica fume was added only on the aggregate side, i.e., by taking off 10% of sand in relation to the cement mass and substituting it with silica fume. In the case of the dolomite concrete, silica fume was added on the aggregate side, and also on the cement side. Fracture toughness tests were carried out according to Mode I (tension at bending) following the RILEM Draft Recommendations [Determination of fracture parameters (K-Ic(S) and CTODC) of plain concrete using three-point bend tests, RILEM Draft Recommendations, TC 89-FMT, Fracture Mechanics of Concrete-Test Methods, Materials and Structures, 23 (1990) 457-460]. The critical values of stress intensity factors, K-Ic(S), and the critical values of crack tip opening displacement, CTODc, have been determined. The paraffination of coarse aggregate grains, eliminating the adhesion at the aggregate-cement paste interface, caused significant drops in the values of critical stress intensity factor, K-Ic(S), as well as those of the critical crack tip opening displacement, CTOD,. This indicates a predominant effect of that layer on the mechanical properties of concretes, and also a high sensitivity of the fracture mechanics parameters to changes within the structure of the aggregate-cement paste transition zone. (C) 2000 Elsevier Science Ltd. All rights reserved.