Cracks are among the most common flaws in civil engineering structures and, considering the cyclic nature of the variable loading patterns, it is evident that the evaluation of the structure safety factor should consider the stability of cracks when fatigue loading occurs.In the present paper, the behaviour of cracked concrete subjected to cyclic loading is experimentally investigated by means of direct tension tests. In particular, the experiments concern cycles that stay below the critical concrete softening curve.The results show that, depending on the maximum load, damage could occur and that the cyclic envelope curve is very close to the monotonic quasi-static curve. On the basis of the experimental results, an empirical model for subcritical crack growth for cracked concrete under low-cycle fatigue loading is proposed.
NOMENCLATURECOD, w = crack opening displacement dwSup/dn = crack opening rate at the upper cyclic load f,* = concrete tensile strength G, = specific fracture energy N,, = maximum number of inner loops to reach the envelope curve P~ = lower cyclic load P-= maximum tensile load Psup = upper cyclic load wsUp = crack opening at the upper load during cyclic loading w, = crack opening at the envelope curve S, =maximum displacement across the notch in cyclic tests +a = maximum aggregate size u,, = residual tensile stress after cracking = maximum value of cyclic load on the envelope curve w,,, w, = initial and critical crack opening during cyclic loading respectively
Abstract. The phisyco-mechanical processes triggering concrete explosive spalling are related to the heat-induced micro-and meso-structural changes. To have new information on concrete properties at the microstructural level, as well as on how concrete spalling sensitivity is affected by polypropylene and steel fibers, and by aggregate type, ordinary and high-performance concretes are investigated in this research project, after being heated to different temperatures. The focus is on the relationship among porosity, vapor permeability, pore pressure and microcracking inside the cementitious matrix. Polypropylene fibers are shown to increase the total porosity, to favor microcracking and to reduce significantly pore pressure, to the advantage of concrete resistance to explosive spalling, whose risk is markedly reduced -or even zeroed.
Heat-exposed High-Performance Concrete (HPC) has been the subject of relatively few studies focused on the relationship between the chemo-physical processes occurring in concrete constituents (microscopic level) and concrete mechanical properties (macroscopic level). In order to investigate the correlation between the intrinsic damage and the mechanical damage induced by heat exposure, eleven concrete mixes have been investigated, differing for: compressive strength (fcm,cube ≥ 45, 70, 95 MPa), aggregate type, fiber type (polymeric and metallic) and fiber content. The microstructural and mechanical characterization was carried out on concrete specimens before and after being exposed to 105, 250, 500 and 750°C. The results show that using different experimental techniques at the microstructural level allows to monitor the development of microcracks, whose size is similar to that of macropores. This behavior at the nano, micro-level is reflected by the post-peak branch of the stress-strain curve at the macro-level. This extensive investigation allows to understand concrete mechanical decay due to heating on the basis of microstructural observations, paving the way to mix optimization for high temperature and fire.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.