INNOVATIONS FORUM : Engineered Cementitious Composites for Structural Applications

Abstract

IntroductionIn the last several decades, concrete with increasingly high compressive strength have been used for structural applications. However, most of these materials remain brittle. In some cases, the brittleness as measured by the brittleness number (Hillerborg, 1983) actually increases as the compressive strength goes up. This poses potential danger and limitations of high strength concrete in structural applications. In certain locations, such as where steel and concrete come into contact (e.g. steel anchors in concrete at column base) or in connections of steel/concrete hybrid structures, the high stress concentration created can lead to fracture failure of the concrete. In seismic elements, high ductility in the concrete can make a significant difference in the seismic response of the overall structure. These and other examples discussed below point to the need to develop costeffective high ductility cementitious materials suitable for structural applications. In the last several years, the University of Michigan has been investigating a composite material known as Engineered Cementitious Composites, or ECC for short. In many respects, this material has characteristics similar to medium to high strength concrete. However, the 2 tensile strain capacity generally exceeds 1% with the most ductile composite in the 6-8% range. This article briefly reviews these emerging materials, and also reports on some ongoing developmental application studies. What is ECC?In terms of material constituents, ECC utilizes similar ingredients as fiber reinforced concrete (FRC). It contains water, cement, sand, fiber, and some common chemical additives. Coarse aggregates are not used as they tend to adversely affect the unique ductile behavior of the composite. A typical composition employs w/c ratio and sand/cement ratio of 0.5 or lower. Unlike some high performance FRC, ECC does not utilize large amounts of fiber. In general 2% or less by volume of discontinuous fiber is adequate, even though the composite is designed for structural applications. Because of the relatively small amount of fibers, and its chopped nature, the mixing process of ECC is similar to those employed in mixing normal concrete. Also by deliberately limiting the amount of fibers, a number of proprietary studies have concluded economic feasibility of ECC in specific structural applications. Various fiber types can be used in ECC, but the detail composition must obey certain rules imposed by micromechanics considerations (Li, 1998;Kanda and Li, 1998). This means that the fiber, cementitious matrix, and the interface (mechanical and geometric) properties must be of a correct combination in order to attain the unique behavior of ECCs. Thus ECC designs are guided by micromechanical principles. Most data so far has been collected on PVA-ECC (reinforced with PolyVinyl Alcohol fibers) and PE-ECC (reinforced with high modulus polyethylene fibers). 3The most fundamental mechanical property difference between ECC and FRC is that ECC strain-hardens rather than tens...

Behavior of channel shear connectors, Part I: Experimental study

“…PVA-REC15 fibers were used at fixed volume fraction of 2% in the ECC specimens. Coarse aggregates are not used in preparing ECC [10,11]. Properties of fibers and mix properties of different concrete materials used in this study are presented in Tables 1 and 2 respectively.…”

“…A number of recent studies have indicated that engineered cementitious composites (ECC), a unique type of highperformance fiber-reinforced cementitious composite, shows promise in overcoming the stress concentration problems [10]. ECC is a portland cement-based mortar matrix with a small volume fraction of polyvinyl alcohol (PVA) or polyethylene (PE) fibers (typically 2%).…”

Cement-based composites reinforced with localized and magnetically oriented Al2O3 microplatelets

“…Likewise, improvements in the mechanical performance of cement-based materials would also help to reduce their carbon footprint by enhancing their lifetime and durability. State-of-the-art methods to effectively reinforce concrete rely on precise micro-mechanical design in so-called Engineered Cementitious Composites (ECCs) [1,2]. Usually, ECCs are prepared with 10-30 mm long stainless steel fibers, with diameters from several hundreds of microns to a few millimeters.…”

Rate dependence of ultra high toughness cementitious composite under direct tension

“…UHTCC is often referred to as engineered cementitious composite (ECC) (Li and Kanda, 1998) or strain hardening cement-based composite (SHCC) (Boshoff and van Zijl, 2007). This type of material was developed to overcome the weaknesses of concrete, which include brittleness, low tensile deformability, low tensile strength, vulnerability to cracking, and the tendency of fine cracks to develop into wide cracks.…”