The pseudo strain-hardening behavior of ECC (Engineered Cementitious Composites) is a desirable characteristic for it to substitute for concrete in applications where brittle failure is likely to occur. The widespread use of ECC in the industry is, however, limited by its high cost. In order to maximize the performance over cost, partial application of ECC in locations subjected to severe loading is proposed. In this thesis, layered concrete-ECC components subjected to both static and cyclic loadings were investigated. In parallel to the investigation of mechanical performance, the mix proportion of ECC is also studied to identify compositions that will produce the most desirable multiple cracking and deformation behavior....[ Read more ]

The pseudo strain-hardening behavior of ECC (Engineered Cementitious Composites) is a desirable characteristic for it to substitute for concrete in applications where brittle failure is likely to occur. The widespread use of ECC in the industry is, however, limited by its high cost. In order to maximize the performance over cost, partial application of ECC in locations subjected to severe loading is proposed. In this thesis, layered concrete-ECC components subjected to both static and cyclic loadings were investigated. In parallel to the investigation of mechanical performance, the mix proportion of ECC is also studied to identify compositions that will produce the most desirable multiple cracking and deformation behavior.

In the study of mix design, various ECC compositions were tried with the use of different admixtures. Based on our test results, although the use of HPMC can improve the rheology of ECC, it will also increase the porosity of the mix. Therefore, HPMC is not recommended for the making of ECC. To find a mix that can provide a good combination of flow property and mechanical performance, the size distribution of various constituents of the mix were first obtained. The constituents are then combined in a proportion that will best approximate the Fuller's curve. The final weight ratio was found to be cement: water: fine sand: fly ash: PVA fibers (by volume) = 1: 0.44: 0.5: 0.12: 1.7/2%. For beams made with this mix ratio, four point bending tests give very satisfactory results with failure associated with a large number of multiple cracks.

To study the mechanical performance of layered ECC beams, specimens cast with different ECC thicknesses (25mm, 50mm, 100mm) were investigated through the conducting of four-point bending tests. Results showed that the application of the ECC layer helped to increase both the flexural strength and ductility of the failed beams. In addition, a semi-analytical crack propagation model was developed to predict the flexural behavior of the layered ECC beam. Reasonably good predictions of the strength and deformation behavior of the layered beam were obtained.

Layered ECC beams with the same ECC thicknesses as mentioned above were tested under four-point cyclic bending and their fatigue lifetimes were recorded. The ECC layer gave rise to a great improvement in the fatigue lifetime of the beam. For example, under 90% stress level, with the application of a 25mm ECC layer, the fatigue lifetime increases by two orders of magnitude in comparison to concrete; and the application of a 50mm ECC layer led to three orders of magnitude increase in the lifetime. Such a great improvement in fatigue performance was attributed to the effectiveness of fibers in controlling the growth of small cracks. The experimental findings reflect the potential for ECC to be employed in locations where fatigue cracks are likely to initiate and grow.