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.

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On Engineered Cementitious Composites (ECC)

The author details the reactions of various concretes on steel reinforcement. Although portland cements, slag cements and high alumina cements are all hydraulic binders, each possess special properties which are examined. The discussion of causes and methods of preventing the corrosion of steel reinforcement covers such aspects as galvanised steel reinforcement, effects of concrete composition, corrosion of steel reinforcments in concrete and prestressed reinforcement. It is concluded that the most significant influences on the corrosion of prestressing wire in concrete are: the presence of chloride; the presence of nitrates; the composition of the concrete; the degree of carbonation of the concrete; concrete compaction and, chlorides and sulphates should be used as far as possible when steel is embedded. (TRRL)

Corrosion of steel by concrete

Concrete is very sensitive to crack formation. As wide cracks endanger the durability, repair may be required. However, these repair works raise the life-cycle cost of concrete as they are labor intensive and because the structure becomes in disuse during repair. In 1994, C. Dry was the first who proposed the intentional introduction of self-healing properties in concrete. In the following years, several researchers started to investigate this topic. The goal of this review is to provide an in-depth comparison of the different self-healing approaches which are available today. Among these approaches, some are aimed at improving the natural mechanism of autogenous crack healing, while others are aimed at modifying concrete by embedding capsules with suitable healing agents so that cracks heal in a completely autonomous way after they appear. In this review, special attention is paid to the types of healing agents and capsules used. In addition, the various methodologies have been evaluated based on the trigger mechanism used and attention has been paid to the properties regained due to self-healing.

https://biblio.ugent.be/publication/4144354/file/4144368.pdf

Self-Healing in Cementitious Materials—A Review

A review : Self-healing in cementitious materials and engineered cementitious composite as a self-healing material

Environmental sustainability considerations are taken into account in this report on high-performance fiber-reinforced cementitious composite (HPFRCC) development. Featuring high tensile ductility with high volumes of fly ash (HVFA) replacement of cement (up to 85% by weight), unique HPFRCC members are engineered cementitious composites (ECC). While the material design process sees application of micromechanics in many of its aspects, this study emphasizes how fly ash content alters material microstructure and mechanical properties. While they incorporate high recycled fly ash volumes, HVFA ECCs are shown in experimental results to be able to retain an approximately 2 to 3% long-term tensile ductility. Significantly, there is reduction in both free drying shrinkage and crack width with a fly ash amount increase, though which HVFA ECC structures' long term durability may benefit. That HVFA ECCs' fiber/matrix interface frictional bond increase is responsible for tight crack width is indicated through micromechanics analysis. Use of industrial waste stream material instead of cement reduces environmental impact and achieves more saturated multiple cracking, meaning a robustness improvement is shown in HVFA ECCs.

Use of High Volumes of Fly Ash to Improve ECC Mechanical Properties and Material Greenness

This paper presents the results of an experimental investigation on the chloride transport properties of engineered cementitious composites (ECC) under combined mechanical and environmental loads. ECC is a newly developed, high-performance, fiber-reinforced cementitious composite with substantial benefit in both high ductility and improved durability due to tight crack width. By employing micromechanics-based material design, maximum ductility in excess of 3% under uniaxial tensile loading can be attained with only 2% fiber content by volume, and the typical single crack fracture behavior commonly observed in normal concrete or mortar is converted to multiple microcracking in ECC. In this study, immersion and salt ponding tests were conducted to determine chloride ion transport properties. Under high imposed bending deformation, the preloaded ECC beam specimens reveal microcracks less than 50 μm and an effective diffusion coefficient significantly lower than that of the similarly preloaded reinforced mortar beam because of the tight crack width control in ECC. In contrast, cracks larger than 150 μm are easily produced under the same imposed deformation and have significant effects on effective diffusion coefficient of reinforced mortar. Moreover, through the formation of microcracks, a significant amount of self-healing was observed within the ECC cracks subjected to NaCl solution exposure.

Transport Properties of Engineered Cementitious Composites under Chloride Exposure

The capability of processing robust Engineered Cementitious Composites (ECC) materials with consistent mechanical properties is crucial for gaining acceptance of this new construction material in various structural applications. ECC’s tensile strain-hardening behavior and magnitude of tensile strain capacity are closely associated with fiber dispersion uniformity, which determines the fiber bridging strength, complementary energy, critical flaw size and degree of multiple-crack saturation. This study investigates the correlation between the rheological parameters of ECC mortar before adding PVA fibers, dispersion of PVA fibers, and ECC composite tensile properties. The correlation between Marsh cone flow rate and plastic viscosity was established for ECC mortar, justifying the use of the Marsh cone as a simple rheology measurement and control method before fibers are added. An optimal range of Marsh cone flow rate was found that led to improved fiber dispersion uniformity and more consistent tensile strain capacity in the composite. When coupled with the micromechanics based ingredient-tailoring methodology, this rheological control approach serves as an effective ECC fresh property design guide for achieving robust ECC composite hardening properties.

Rheology, fiber dispersion, and robust properties of Engineered Cementitious Composites

The lack of durability in concrete structures worldwide demands fast and durable repairs. To address this need, high-early-strength engineered cementitious composites (HES-ECC) were recently developed for concrete repair applications in which minimum operations disruption is desired. A detailed characterization of HES-ECC’s compressive, tensile, flexural, and shrinkage properties at different ages is reported in this paper. HES-ECC achieves a compressive strength of 23.59 ± 1.40 MPa (3422.16 ± 203.33 psi) in 4 hours and 55.59 ± 2.17 MPa (8062.90 ± 315.03 psi) in 28 days. Under uniaxial tension, HES-ECC exhibits tensile strain-hardening behavior with a strain capacity greater than 2.5%. Its flexural strength exceeds twice that of concrete with similar compressive strength. Under restrained shrinkage conditions, HES-ECC forms microcracks with a self-controlled crack width below 50 μm (0.002 in.). The combination of these properties suggests HES-ECC material is highly suitable for fast and durable concrete repairs with shortened downtime and improved longterm durability.

High-Early-Strength Engineered Cementitious Composites for Fast, Durable Concrete Repair—Material Properties

Engineered cementitious composite’s (ECC) tensile ductility and microcracking behavior are essential for achieving structural durability (for example, corrosion resistance). This paper investigated ECC’s durability in terms of maintaining its unique tensile characteristics under combined mechanical loading and aggressive chloride conditions. ECC specimens were preloaded to 0.5, 1.0, and 1.5% tensile strain levels; immersed in chloride solution for 30, 60, and 90 days; and reloaded until failure. This study revealed that the reloaded specimens retained multiple microcracking behavior and tensile strain capacity greater than 2.5%, while the average crack width increased from 50 μm to 100 μm. Self-healing in ECC under chloride exposure is evident in terms of recovery of initial material stiffness and tensile strain capacity. Subsequent studies at the microstructure scale explained the macroscopic composite behavior. These results indicated that under severe marine environmental conditions, ECC remains durable and provides reliable tensile ductility and crack-controlling capability to prevent the localized cracking failure often observed in concrete structures.

Cracking and Healing of Engineered Cementitious Composites under Chloride Environment

Concrete cracking and deterioration can potentially be addressed by innovative self-healing cementitious materials, which can autogenously regain transport properties and mechanical characteristics after the damage self-healing process For the development of such materials, it is crucial, but challenging, to precisely characterize the extent and quality of self-healing due to a variety of factors This study adopted x-ray computed microtomography (μCT) to derive threedimensional morphological data on microcracks before and after healing in engineered cementitious composite (ECC) Scanning electron microscope and energy dispersive x-ray spectroscopy were also used to morphologically and chemically analyze the healing products This work showed that the evolution of the microcrack 3D structure due to self-healing in cementitious materials can be directly and quantitatively characterized by μCT A detailed description of the μCT image analysis method applied to ECC self-healing was presented The results revealed that the self-healing extent and rate strongly depended on initial surface crack width, with smaller crack width favoring fast and robust self-healing We also found that the selfhealing mechanism in cementitious materials is dependent on crack depth The region of a crack close to the surface (from 0 to around 50–150 μm below the surface) can be sealed quickly with crystalline precipitates However, at greater depths the healing process inside the crack takes a significantly longer time to occur, with healing products more likely resulting from continued hydration and pozzolanic reactions Finally, the μCT method was compared with other selfhealing characterization methods, with discussions on its importance in generating new scientific knowledge for the development of robust self-healing cementitious materials

https://iopscience.iop.org/article/10.1088/0964-1726/24/1/015021/pdf

Mo Li

Papers

Transport Properties of Engineered Cementitious Composites under Chloride Exposure

Rheology, fiber dispersion, and robust properties of Engineered Cementitious Composites

High-Early-Strength Engineered Cementitious Composites for Fast, Durable Concrete Repair—Material Properties

Cracking and Healing of Engineered Cementitious Composites under Chloride Environment

X-ray computed microtomography of three-dimensional microcracks and self-healing in engineered cementitious composites