Use Of Engineered Cementitious Composites Research Articles

Smart Cement Composites for Durable and Intelligent Infrastructure

The self-healing and self-sensing performances of Engineered Cementitious Composite (ECC) mixtures developed recently at Heriot-Watt University are presented. In the first series of experiments, fifteen dog-bone shaped ECC samples were preloaded to known strains and then left to heal outdoors under a natural environment. Ultrasonic pulse velocity measurements were then undertaken periodically to determine the rate and extent of healing in these samples. It was found that the samples were able to heal micro-cracks and show a recovery in UPV after two loading events over a six month outdoor exposure. In another series of experiments, the effectiveness of incorporating milled carbon (MC) fibers into an ECC mix, with the aim of enhancing the self-sensing functionality of ECC, is demonstrated for the first time. The MC-ECC mix exhibited equivalent tensile response compared to the control ECC mix and displayed a strong relationship between tensile strain and the fractional change in resistivity. The inclusion of MC fibers at 0.75% by volume was found to exhibit high sensitivity to micro-cracks formation, with gauge factor two orders of magnitude larger than that of an ordinary strain gauge, albeit less than that of the control mix. It is envisaged that the use of ECC can create an intelligent infrastructure able to sense and repair damage and monitor the recovery extent.

Development of engineered cementitious composites with limestone powder and blast furnace slag

Nowadays limestone powder and blast furnace slag (BFS) are widely used in concrete as blended materials in cement. The replacement of Portland cement by limestone powder and BFS can lower the cost and enhance the greenness of concrete, since the production of these two materials needs less energy and causes less CO2 emission than Portland cement. Moreover, the use of limestone powder and BFS improves the properties of fresh and hardened concrete, such as workability and durability. Engineered cementitious composites (ECC) is a class of ultra ductile fiber reinforced cementitious composites, characterized by high ductility, tight crack width control and relatively low fiber content. The limestone powder and BFS are used to produce ECC in this research. The mix proportion is designed experimentally by adjusting the amount of limestone powder and BFS, accompanied by four-point bending test and uniaxial tensile test. This study results in an ECC mix proportion with the Portland cement content as low as 15% of powder by weight. This mixture, at 28 days, exhibits a high tensile strain capacity of 3.3%, a tight crack width of 57 μm and a moderate compressive strength of 38 MPa. In order to promote a wide use of ECC, it was tried to simplify the mixing of ECC with only two matrix materials, i.e. BFS cement and limestone powder, instead of three matrix materials. By replacing Portland cement and BFS in the aforementioned ECC mixture with BFS cement, the ECC with BFS cement and limestone powder exhibits a tensile strain capacity of 3.1%, a crack width of 76 μm and a compressive strength of 40 MPa after 28 days of curing.

Fatigue enhancement of concrete beam with ECC layer

The pseudo strain-hardening behavior of Engineered Cementitious Composites (ECC) is a desirable characteristic for it to replace concrete to suppress brittle failure. This widespread use of ECC in the industry is, however, limited by its high cost. To achieve higher performance/cost, ECC can be strategically applied in parts of a structure that is under relatively high stress and strain. In this paper, layered ECC-concrete beams subjected to static and fatigue flexural loads were investigated by experiments. The static test results showed that the application of a layer of ECC on the tensile side of a flexural beam increased its flexural strength and the degree of improvement increased with the thickness of ECC applied. In addition, the layer of ECC enhanced the ductility of the beam and the failure mode changed from brittle to ductile. Under four-point cyclic loading, the ECC layer significantly improved the fatigue life of the beam. Moreover, in comparison to plain concrete beams, layered ECC beams could sustain fatigue loading at a larger deflection without failure. The great improvement in fatigue performance was attributed to the effectiveness of ECC in controlling the growth of small cracks. The experimental findings reflect the feasibility of using ECC strategically in critical locations for the control of fatigue crack growth.

Partial Use of Pseudo-Ductile Cementitious Composites in Concrete Components to Resist Concentrated Stress

The high pseudo-ductility of Engineered Cementitious Composites (ECC) makes it a particularly effective material to resist the propagation of cracks. In applications where failure is due to cracking initiated by localized stresses, the application of ECC around the stress concentrated region should result in significant improvement in the ultimate failure load. In this investigation, we will study the use of ECC in (i) the anchorage zone of post-tensioned concrete members, and (ii) the region around embedded anchor bolts in concrete blocks. For the first application, the replacement of concrete with ECC at the anchorage zone is found to be very effective in increasing the load capacity under concentrated compression. Based on our test results, ECC can actually replace all or part of the conventional steel stirrups in resisting splitting failure at the anchorage zone. For embedded anchor bolts, the placement of a small ECC disc above the steel bolt can effectively delay the propagation of cone-shape failure and increase the pull-out force. Through the present experimental program, we have illustrated the advantage of strategically applying ECC in critical region of structural components, to improve performance without significant increasing the material cost.

Flexural performance of layered ECC-concrete composite beam

The pseudo strain-hardening behavior of fiber reinforced engineered cementitious composites (ECC) is a desirable characteristic for it to act as a substitute for concrete to suppress brittle failure. The use of ECC in the industry is, however, limited by its high cost. To achieve higher cost/performance ratio, ECC can be strategically applied in parts of a structure that is under relatively high stress. In this paper, layered ECC-concrete beams subjected to flexural load are investigated from both theoretical and experimental aspects. Four-point bending tests are performed on beam members with ECC layer at its tensile side. The application of ECC layer leads to increase in both the flexural strength and ductility, and the degree of improvement is found to increase with the ECC thickness. A semi-analytical approach for modeling the flexure behavior of layered ECC-concrete beams is also developed. In the model, the stress–crack width relation of both concrete and ECC are employed as fundamental constitutive relationships. The model and experimental results are found to be in good agreement with one another. Simulation with the model shows that when the ECC thickness goes beyond a certain critical value, both the flexural strength and ductility (reflected by crack mouth opening and crack length at ultimate load) will significantly increase. The critical ECC thickness is hence an important design parameter, and it can be determined with the theoretical approach developed in the present work.

Innovative Materials For Bridge Seismic Design

Shape memory alloys (SMAs) are unique alloys that have the ability to undergo large deformation, but can recover deformations fully after the loads. The primary objective of this study was to investigate the seismic performance of RC columns with SMA longitudinal reinforcement in the plastic hinge area. Another target was to evaluate seismic performance and damage in a repaired SMAreinforced column using engineered cementitious composites (ECC). Two quarter-scale spiral RC columns with SMA longitudinal reinforcement in the plastic hinge area were designed and constructed for shake table testing at the Large Scale Structure Laboratory of the University of Nevada, Reno. The shake table data showed that SMA RC columns were able to recover nearly all of the post-yield deformation and that the use of ECC reduced the concrete damage substantially, thus requiring minimal repair even after very large earthquakes.

Engineered cementitious composites for effective FRP-strengthening of RC beams

This paper presents the results of an experimental program designed to evaluate the performance of FRP-strengthened RC beams incorporating engineered cementitious composites (ECC) as a ductile layer around the main flexural reinforcement (ECC layered beams). The load-carrying and deflection capacities as well as the maximum FRP strain at failure are used as criteria to evaluate the performance. Further, 2-D numerical simulation is performed to verify the experimental results. The results have shown that ECC can indeed be used to delay debonding of the FRP resulting in effective use of the FRP material. These positive results warrant further studies on the use of ECC in combination with FRP to repair and strengthen deteriorating RC structures, particularly those where deteriorated concrete has to be replaced with a new repair material.

On Engineered Cementitious Composites (ECC)

This article surveys the research and development of Engineered Cementitious Composites (ECC) over the last decade since its invention in the early 1990's. The importance of micromechanics in the materials design strategy is emphasized. Observations of unique characteristics of ECC based on a broad range of theoretical and experimental research are examined. The advantageous use of ECC in certain categories of structural, and repair and retrofit applications is reviewed. While reflecting on past advances, future challenges for continued development and deployment of ECC are noted. This article is based on a keynote address given at the International Workshop on Ductile Fiber Reinforced Cementitious Composites (DFRCC) - Applications and Evaluations, sponsored by the Japan Concrete Institute, and held in October 2002 at Takayama, Japan.

INNOVATIONS FORUM : Engineered Cementitious Composites for Structural Applications

In the last several years, the University of Michigan has been investigating a composite material known as Engineered Cementitious Composites (ECC). In many respects, this material has characteristics similar to medium- to high-strength concrete. However, the 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. The relatively small amount of fibers (less than or equal to 2%) utilized ensures economic feasibility in practical applications, whether in precast elements or on-site constructions. Results of the studies provide confidence in the widening use of ECC in a broad range of new and retrofitted concrete structures.