Structural applications of engineered cementitious composites (ECC): Fid-Bau Portal

Structural applications of engineered cementitious composites (ECC)

Fischer, Gregor

This paper describes the basic material properties and unique features of Engineered Cementitious Composites (ECC) pertaining to structural applications and explores the effect of substituting brittle concrete in conventional reinforced concrete structural members with a ductile, strain hardening cement-based composite. Based on the deformation characteristics of ECC, the interaction with structural reinforcement is characterized by compatible deformations of the structural reinforcement and the ECC matrix in the elastic and inelastic deformation regime. The benefits of using ECC in place of conventional concrete with respect to structural response, design, and economic feasibility of seismic resistant structures as well as thin, prefabricated structural components are described. Particularly, the combination of reinforcement and matrix material with elastic/plastic stress-strain behavior results in a composite where both materials are deforming compatibly in the inelastic deformation regime. Consequently, damage induced by local slip and excessive interfacial bond stress between reinforcement and matrix is prevented. The ECC matrix stiffens the specimen at uncracked sections and also strengthens it at cracked sections. Hence, the composite load-deformation response is significantly improved in terms of axial load-carrying capacity as well as ductility. In order to maintain this composite action at relatively large inelastic deformations, strain hardening and multiple cracking of the ECC matrix are essential. It should be emphasized that the resulting composite behavior is not primarily achieved by enhanced material resistance in terms of matrix tensile strength, confinement effect or interfacial bond strength but rather by reducing internal stresses which would necessitate such resistance. Compatible deformation between ECC and steel reinforcement implies that bond strength in R/ECC is not as significant as in R/C for enhanced structural performance. For seismic resistant structures, important findings include the extremely ductile response of steel reinforced ECC members subjected to reversed cyclic deformations at a simultaneous reduction of transverse reinforcement requirements as well as reduced structural damage after experiencing relatively large deformation reversals. The application of Engineered Cementitious Composites (ECC) in thin, prefabricated structural members was found to eliminate some technological constraints and lead to the development of innovative floor panel elements.