A thermodynamic correlation between damage and fracture as applied to concrete fatigue

Fatigue damage in concrete is characterized by the simultaneous presence of micro and macrocracics. The theory of fracture mechanics conveniently handles the propagation of macrocracks, whereas damage mechanics precisely describes the state of microcracking. This paper provides a platform to correlate fracture mechanics and damage mechanics theories through an energy equivalence within a thermodynamic framework by equating the energy dissipated according to each theory. Through this correlation, damage corresponding to a given crack length could be obtained, and alternatively a discrete crack could be transformed into an equivalent damage zone. The results are validated using available experimental data on concrete fatigue including stiffness degradation and acoustic emission. (C) 2015 Elsevier Ltd. All rights reserved.

Micromechanical analysis of self compacting concrete

The micro-level properties of different self compacting concrete (SCC) mixes with and without mineral admixures are studied. The study considers SCC as a two phase material consisting of matrix and aggregate. Micro indentation technique is employed to obtain the hardness of individual phases and to compute the micro-property (modulus of elasticity). Using a self consistent homogenization procedure, the micro-property is scaled-up to obtain the macro-property which is shown to agree with the experimentally obtained macro values. It is seen that there exists a smaller interfacial transition zone at different ages of curing across all the mixes due to the presence of more fines in SCC. Also, there is no significant change in the property of the SCC having no fly ash or silica fume beyond 28 days whereas a substantial change in the micro and macro properties are seen in the SCC having fly ash and silica fume.

Measurement of existing prestressing force in concrete structures through an embedded vibrating beam strain gauge

A steel frame is designed to measure the existing prestressing force in the concrete beams and slabs when embedded inside the concrete members. The steel frame is designed to work on the principles of a vibrating wire strain gauge and in the present study is referred to as a vibrating beam strain gauge (VBSG). The existing strain in the VBSG is evaluated using both frequency data on the stretched member and static strain corresponding to a fixed static load, measured using electrical strain gauges. The evaluated strain in the VBSG corresponds to the existing stain in the concrete surrounding the prestressing strands. The crack reopening load method is used to compute the existing prestressing force in the concrete members and is then compared with the existing prestressing force obtained from the VBSG at that section. Digital image correlation based surface deformation and change in neutral axis monitored by putting electrical strain gauges across the cross section, are used to compute the crack reopening load accurately. (C) 2016 Elsevier Ltd. All rights reserved.