Interaction between Steel Reinforcement and Engineered Cementitious Composites

Engineered Cementitious Composite (ECC) is a special type of HPFRCC designed using micromechanics concepts which take into account the mechanical interactions between fiber, matrix and interface in deformation processes under load. While the properties of ECC have been extensively investigated, the interaction between ECC and steel reinforcement has not been studied. This interaction is important for predicting reinforced “concrete” structural response when the concrete is replaced by ECC. This paper reports preliminary experimental findings of the interaction of a steel re-bar embedded in a rectangular block of ECC loaded in tension. A typical tension-stiffening experiment reveals that the tension-stiffening effect for ECC extends well beyond the steel yielding range (3-4 %) when the control test with regular concrete shows negligible contribution of the concrete to load carrying capacity. While the concrete cracks and eventually becomes rigid blocks carrying little load, the ECC maintains load carry capacity even when strained to several percent due to its strain-hardening property. Thus for the ECC specimen, the steel and ECC maintains deformation compatibility by each acting as an elastic-“plastic” material. In addition, the readings from the strain gauges embedded inside the diametrically split rebar show significant difference between the R/ECC specimens and the control R/C specimens. In the latter, strain jumps are observed in gauges close to the large cracks in the concrete at the load level when these cracks occurred. For the R/ECC specimens, all the strain gauges maintain smooth increase in strain up to one percent. These observations have significant implications in structural response of R/ECC structures, especially when large deformations are imposed as during earthquake loadings.