Mechanical Properties Of Engineered Cementitious Composites Research Articles

Optimal Design of Micro-expanded ECC and Its Interfacial Bonding Property with Steel Tube

The large shrinkage strain of Engineered Cementitious Composites (ECC) seriously affects its combined application with steel tube in engineering. In order to reduce the shrinkage of ECC and realize the effective bonding between ECC and steel tube, this paper studied the effects of single or multiple doped of expansive and internal curing agent on the shrinkage and mechanical properties of ECC, and tested the interfacial bond strength between ECC and steel tube. CaO and MgO compound expansive agent (CME), calcium sulfoaluminate expansive agent (HCSA), super water-absorbing polymer (SAP) internal curing agent are chosen for test. The results show that ECC mixed with 10% CME expansive agent and 0.2% SAP shows a slight expansion under the condition of sprinkling water curing. Moreover, the push-out test shows that the bond strength between micro-expanded ECC and steel tube reaches 1.27 MPa, which is nearly 2 times higher than that of the ordinary ECC, and higher than the bond strength of C50 filled steel tube. This paper provides the test and theoretical basis for the joint application of ECC with steel tube.

Preparation of low-cost green engineered cementitious composites (ECC) using gold tailings and unoiled PVA fiber

The current study aims to establish low-cost green engineered cementitious composites (ECC) using gold tailings, unoiled PVA fiber and large-volume fly ash. Through compression test, four-point bending test, direct tensile test, matrix fracture toughness test and single-crack tensile test, the mechanical properties of ECC were explored. It is found that incorporation of gold tailings leads to the enhanced compressive strength and reduced ductility. When quartz sand was fully replaced by gold tailings, the compressive strength increased by 19.5%, the strain capacity decreased by 22.3%, the deflection decreased by 15.8% but no obvious change occurred in first crack stress as well as tensile strength. A rougher surface of unoiled PVA leads to reduced slip hardening response. At micro-scale, replacement of the quartz sand using gold tailings leads to higher complementary energy (Jb’) available for strain hardening during the crack development and reduced matrix fracture energy (Jtip) for crack initiation. This contributes to the increased pseudo strain-hardening PSHE (=Jb’/Jtip) index and ductility. When fiber content is 2.0%, the values of PSHS (=σ0/σfc) index reached 1.2, which ensures the saturated multi-joint cracking behavior.

Engineered cementitious composites (ECC) with manufactured sand (M-sand) for pavement applications

Nowadays, Engineered Cementitious Composites (ECC) are highly regarded for use in pavement applications due to their exceptional deformability. Nonetheless, these composites' high cost and limited practicality restrict their use in pavements and overlays. Few studies are available using river sand substituting micro silica sand (MSS) to produce economic ECC, but the depletion of river sand and increased cost limit the large-scale applications. To address these aforementioned challenges, the present study aimed to explore the feasibility of replacing natural sand with manufactured sand (M-sand). The present article discussed the optimization of superplasticizer dosage subjected to desired rheological properties. Further, the influence of M-sand gradation (coarse/fine) on the mechanical properties of ECC is presented. The results revealed that using M-sand slightly increased the compressive (10–30%) and tensile strength and showed a noticeable decrease (22–35%) in the tensile strain capacity. Moreover, the gradation of M-sand considerably influenced the tensile strain capacity, with a decrease of 17% in coarser gradation mixtures. These preliminary results provide valuable insights into the development and utilization of M-sand in the matrix tailoring of ECC.

Compressive properties and microscopic analysis of engineered cementitious composites after salt freezing

In order to study the compressive properties of Engineered Cementitious Composites (ECC) after salt freezing, the failure, compressive strength, and deformation capacity of cubic concrete specimens subjected to single-side freezing–thawing cycles considering the number of cycles, aggregate type Maowusu or Tengger Desert sands (MDS and TDS, respectively) and river sand (RS), and salt medium (NaCl or NaCl + Na2SO4). The results showed, In the presence of salt, the compression failure modes of all samples involved the formation of vertical cracks in the stress direction, but MDSECC and TDSECC showed better integrity than C30 concrete. With increasing freeze–thaw cycles, the strengths, slopes of the stress–strain curves, peak stress, and curve area of the desert sand specimens decreased, but the residual stress and ductility increased. Through regression analysis of the strength loss rate, the ECC lifetime was predicted, and using X-ray diffractometry and scanning electron microscopy, the effects of salt freezing on the mechanical properties of ECC were revealed.

Mechanical property and durability of engineered cementitious composites (ECC) with nano-material and superabsorbent polymers

To improve the tensile capacity and control crack width, engineered cementitious composites (ECC) are considered as a promising strategy for structural reinforcement. However, the shrinkage deformation of ECC threatens the structural integrity and durability of the concrete structure. In this study, a novel ECC with low shrinkage and high ductility is designed by utilizing the synergistic effect of nano-materials and superabsorbent polymers (SAPs). Compared with plain ECC, the application of SAP decreases the compressive strength and ultimate tensile strength of ECC, whereas it increases the strain capacity by 56.0%–81.3%. Meanwhile, the nano-enhanced ECC mixed with SAP exhibits lower autogenous shrinkage and drying shrinkage in comparison with plain ECC, especially for small-sized SAP. Although the incorporation of SAP reduces the mechanical properties and impermeability of ECC due to the coarsening of the pore structure, further application of an appropriate amount of nano-SiO 2 (NS) can effectively increase the content of hydration products in the matrix, thereby improving the mechanical properties and durability of ECC mixed with SAP. However, as NS is more likely to agglomerate on the surface of large-sized SAP, the incorporation of excessive amount of NS leads to a decrease in the mechanical properties and impermeability of ECC. A low-shrinkage, high-toughness nano-engineered ECC developed in this study provides a theoretical basis and guidance for the application of ECC in practical engineering. • The mechanical properties of ECC containing nano-material and SAP are investigated. • The internal curing effect of SAP effectively reduces the shrinkage deformation of ECC. • The incorporation of SAP effectively improves the tensile strain capacity of ECC. • An appropriate amount of nano-SiO 2 improves the strength reduction of ECC caused by SAP.

Microstructure and mechanical behaviors of engineered cementitious composites with high-volume fly ash

To study the effects of fly ash, polyvinyl alcohol (PVA) fibers and curing schemes on the microstructure and mechanical behaviors of Engineered Cementitious Composites (ECC) with high-volume fly ash, two kinds of fly ash and two PVA fibers were used in ECC. Besides, two curing schemes were adopted. The microstructure and mechanical properties of ECC were investigated by mercury intrusion porosimetry (MIP), scanning electron microscope (SEM), uniaxial compression test and three-point bending test. The results show that curing schemes and adding PVA fibers have a great influence on the differential curves of the pore size distribution of ECC and matrix in the range of 0–100 nm. There is a positive relationship between the deflection capacity or ultimate tensile strain of ECC and its macro pore volume fraction. Number of cracks increases with increasing the capillary pore volume fraction. On the contrary, the deflection capacity, ultimate tensile strain and number of cracks decrease when the transitional pore volume percent in ECC increases.

Durability and self-healing of engineered cementitious composites exposed to simulated sewage environments

Corrosion factors including microbiologically induced corrosion accelerate cracking and deteriorations in a sewer concrete pipe especially in regions close to the pipe crown and that near the waterline. Engineered cementitious composites (ECC) is a novel class of ductile cement-based composites and possesses autogenously tight cracks and robust self-healing conducive to sewage environments resistance. This paper presents an experimental study on the durability of ECC exposed to sewage environments simulated by treatments including sulfuric acid exposure and physical erosion. The physical and mechanical properties of ECC were examined in relation to those of fiber-free mortar specimens as control. The objective of this research is to establish fundamental knowledge on the behavior of ECC under aggressive sewage environments. Results showed that the permeable voids increased, and the strength decreased for both ECC and mortar. However, the residual compressive and tensile strength of ECC were 30–65% and 300–370% higher than those of the mortar group after 12 corrosion cycles, respectively. After corrosion cycles, the length change ratio of ECC was about 20% of that of the control, which indicates that ECC has better dimensional stability under the corrosive conditions. Further, self-healing of microcrack damage was observed in ECC under all exposure conditions in this study. It is concluded that ductile ECC has significant advantages in mechanical and durability performance over conventional brittle mortar/concrete under the simulated environments unique in sewage lines. This research generates new data that establish ECC as a durable material for sewer pipeline construction and rehabilitation.

Effects of different mixing ratio parameters on mechanical properties of cost-effective green engineered cementitious composites (ECC)

ECC is an advanced construction material with tensile strain hardening characteristics and multiple cracking behavior, which is very attractive to the construction industry. However, the oiled polyvinyl alcohol (PVA) fibers and fine silica sand widely used in traditional ECC lead to high cost, and high cement content will lead to high carbon footprint. In order to reduce the cost and severe environmental concern, the paper develops a low-cost green ECC. The means adopted is to replace oiled PVA fibers and fine silica sand with hybrid local fibers (unoiled PVA fibers and basalt fibers) and river sand, respectively and thus decreases the ECC cost, and replace the cement with the high-volume fly ash and silica fume and thus improve the green. And then the influences of river sand particle size, sand-binder ratio, water-binder ratio and fiber content on mechanical properties of ECC are studies by some macro experiments. Furthermore, a new method which can comprehensively evaluate the flexural toughness of ECC from two aspects of energy and strength is proposed. In addition, the microstructure of the samples was studied by scanning electron microscopy. Test results showed that the low-cost green ECC can be developed by using local materials, but the grain size of river sand should not exceed 0.85 mm, the sand-binder ratio should not exceed 0.5, and the water-binder ratio should not be less than 0.3. Although the basalt fiber can effectively reduce the average crack width, the strength of basalt fiber decreases according to the fiber orientation, resulting in its low contribution to flexural toughness.

Experimental in-plane seismic strengthening of masonry infilled reinforced concrete frames by engineered cementitious composites (ECC)

The present study aimed to evaluate the performance of engineered cementitious composites (ECC) retrofit technique for unreinforced hollow clay brick masonry infill wall in non-ductile reinforced concrete (RC) frames subjected to in-plane cyclic loading (quasi-static loading). To this aim, the mechanical properties of ECC and masonry elements were tested. Then, four 1/3-scale, one-story, single-bay RC frames were fabricated. Among these specimens, one frame was tested without infill wall (BF), one frame with unretrofitted infill wall (IF-E0), and specimens IF-SF-E20 and IF-DF-E20-2 were retrofitted by using an overlay ECC on the masonry infill wall on one side and both sides, respectively. The retrofitted specimens provided higher lateral load capacity, stiffness, and energy dissipation capacity up to 215%, 32%, and 102%, respectively, compared to the unretrofitted specimen. Further, the proposed strengthening technique prevented brittle premature failure in the masonry infill walls and partially maintained the integrity of unreinforced infill walls. Also, the obtained backbone curves of specimens were idealized. Based on the results, the displacement ductility factor of the retrofitted specimens decreased up to 50%, but also the force reduction factor and the overstrength factor of them increased up to 19 and 68%, respectively. At the end of the paper, a simplified analytical method is proposed to calculate the peak strength of retrofitted masonry infilled RC frames. The results obtained from this method were close to the experimental results.

Effect of curing relative humidity on mechanical properties of engineered cementitious composites at multiple scales

In recent years, broad interests in ductile Engineered Cementitious Composites (ECC) have been accompanied by increasing amount of laboratory investigations of this material. Both wet and air curing have been applied in the preparation of specimens. However, the effect of curing condition on mechanical properties of ECC has yet to be elucidated. This research attempts to fill this knowledge gap. Specifically, experiments were conducted to investigate property changes at different length scales under three curing relative humidity (RH) levels. Macroscopic properties including composite first crack strength, ultimate tensile strength and strain capacity, and crack pattern of ECC reinforced with PVA fibers were recorded. As well, matrix fracture toughness and fiber/matrix interface properties were measured. Correlation of macro-properties and micromechanical parameters was interpreted using a previously developed micromechanical model. The changes of tensile properties and crack pattern were found traceable to RH effects on the matrix and fiber/matrix interface properties. The findings of this study reveal the underlying mechanisms of property differences in specimens cured under different RH. The knowledge gained provides a better understanding of the effects of curing conditions on ECC specimens used in property characterization, and is particularly relevant to maintaining consistency in standardized testing of ECC.

Test research on mechanical properties of engineered cementitious composites

Taking engineered cementitious composites(ECC) as the research object, the effects of sand particle size(A), total fiber volume content(B) and fiber types(C)(single, double or triple blending)on the flexural strength, compressive strength and tensile strength of ECC were studied by orthogonal test. The results show that the total fiber volume content has the greatest influence on the three mechanical properties of ECC, and the three mechanical properties are improved with the increase of total fiber volume content. Followed by the influence of fiber types, the flexural and compressive strength of single doped PVA is higher than single doped PP and the two mixed, steel fiber can improve the flexural and tensile strength. The influence of sand particle size on the three mechanical properties of ECC is the least. After comprehensive consideration, in the range considered in this study, the optimal scheme is 600 μm grain size, 2% fiber volume content and triple blending(PP0.5%+PVA1%+S0.5%).

Effect of sub-elevated temperature on mechanical properties of ECC with different fly ash contents

In this paper, the mechanical properties of Engineered Cementitious Composites (ECC) with two different fly ash contents after sub-elevated temperature exposure were investigated systematically at multiple scales. At composite level, uniaxial compressive and tensile tests were performed on specimens underwent 20 °C, 50 °C, 100 °C, and 200 °C exposure. The results indicate that, as temperature rise from 20 °C to 200 °C, the compressive strength of both ECC mixtures increased due to the refinement of the matrix pore structure. In term of tensile properties, after exposed to 100 °C and 200 °C, ECC M1 with relatively lower fly ash content shows a substantial reduction in strain capacity, but still retaining strain-hardening behavior, whereas ECC M2 with higher fly ash content exhibits a comparable or even enhanced tensile strength and strain capacity. At micro-scale, ECC matrix toughness was increased and PVA fiber strength was degraded under 200 °C exposure, which deteriorates the tensile properties of ECCs. However, the above negative effects are diminished due to the reduced fiber/matrix interfacial bond. Furthermore, the rather low matrix toughness and fiber/matrix interfacial bond associated with high fly ash content are the main reasons for the highly remained ductility in ECC M2 after sub-elevated temperature exposure.

ECC Design Based on Uniform Design Test Method and Alternating Conditional Expectation

Engineered cementitious composites (ECC) have higher ultimate tensile strains than normal concrete. The mechanical properties of ECC strongly depend on raw materials and the mix proportions. The uniform design test method and alternating conditional expectation, which is a nonparametric regression analysis method, were used to design the ECC mix proportion. According to the regression analysis, the optimized W/B, S/B, and F/B ranges could be obtained as 0.35–0.42, 0.25–0.3, and 0.02, respectively. The tested proportions for validation were randomly adopted within the range of W/B, S/B, and F/B. The uniaxial compression, tension, and four-point bending tests were conducted to verify the material behaviour of the designed ECC. Results showed that all the specimens had large ultimate tensile strains and high fracture energy capacities, and strain hardening was also observed. The fibers were found to be uniformly distributed in the specimens by using a scanning electron microscope. This paper may provide theoretical and practical guidance for the ECC and other cement-based material mix proportion design.

Investigation of the Mechanical Properties of Engineered Cementitious Composites with Low Fiber Content and with Crumb Rubber and High Fly Ash Content

Engineered cementitious composites (ECCs) are a type of micromechanically-designed cementitious composite reinforced with a moderate volume fraction of short fiber, typically 2% by volume. ECCs form steady-state multiple cracking that considerably improves the tensile strength and ductility of traditional concrete. In this study, the properties of matrix and the interface of ECCs were tailored through the use of crumb rubber, different types of sand, and different replacement levels of cement with fly ash. The study examined the effect of sand replacement with crumb rubber (20% by volume), two types of river sands (coarse and fine), increasing the content of class F fly ash (up to 75% cement replacement), and low fiber content (1.75%) on the mechanical properties of ECCs. Compressive strength, uniaxial tensile, and third-point bending tests were performed to characterize the properties of ECC mixes. Experimental results demonstrated that increasing fly ash content and using crumb rubber favored ductility of the composites. However, higher fly ash contents and a low water-to-binder (W/B) ratio produced lower strengths as these limited the pozzolanic reaction of fly ash making it act partially as a filler. While incorporation of crumb rubber showed adverse effects on the tensile strength of ECC materials (up to 26% decrease), the tensile ductility of ECC materials improved significantly (up to 434% improvement). Moreover, the implementation of different types of sand produced minor effects on the mechanical properties of ECCs. Overall, a tradeoff between the strength and ductility of the composites was detected, which highlights the implications of matrix/interface tailoring in the overall performance of ECC.

Effect of fineness and calcium content of fly ash on the mechanical properties of Engineered Cementitious Composites (ECC)

Abstract As a new green material, ECC has received extensive attention all over the world because of its potent ability of crack width controlling, excellent behavior of flexural toughness, and fatigue durability. The use of high volume fly ash as a partial replacement of cement reduces environmental pollution and conserves natural resources. This paper presents the experimental results to find out the effect of fineness and calcium content of fly ash on the mechanical properties of ECC. Four different types of fly ash were used and a series of mechanical tests, including cube compressive strength, uniaxial direct tensile, three-point bending and single-crack tension tensile were conducted in this paper. The results indicate that between tensile strain properties and fly ash fineness, there is not just a simply linear relationship. Fineness is not the determining factor for ECC’s compression performance, but the activity of fly ash. Fly ash with the higher calcium content did not make the tensile properties of ECCs greater at all ages, but make compressive performance better.

Coupled effects of limestone powder and high-volume fly ash on mechanical properties of ECC

Owing to its exceptional strain capacity, which can reach hundreds of times that of normal concrete, and its reduced crack width, engineered cementitious composites (ECC) are a very promising solution for mitigating many of the problems that generate colossal backlogs of deteriorated concrete structures worldwide. However, research is needed to develop more sustainable ECC with flexible formulation that uses local materials. This paper investigates the coupled effects of using limestone powder in ECC as partial or total replacement for silica sand aggregate, coupled with using high-volume fly ash as a binder. The compressive and flexural strengths and fracture toughness for the formulated ECCs were examined at 3, 28 and 90 days. The results of this study demonstrate that sustainable ECC for resilient structural applications can be produced. It is aimed that more flexible formulations of ECC using local materials with lower environmental footprint could emerge and contribute to more durable and sustainable civil infrastructure.

Effect of Water-Curing Time on the Mechanical Properties of Engineered Cementitious Composites

AbstractThe influence of initial water-curing time on the mechanical properties of engineered cementitious composites (ECCs) was investigated by employing a four-point bending test, compressive strength, and flexural strength. Five different curing regimes were applied to the specimens, which were in continuous room-air storage, curing in the laboratory room air after submersion in water for 3, 7, 14, and 28 days, respectively. The experimental results show that the deflection and the toughness index of ECC under water-curing conditions decrease gradually as water-curing time is prolonged. First cracking load, peak load, compressive strength, and flexural strength increase as water-curing time increases and total curing age is extended. The higher volume of fly ash is beneficial in lowering the adverse effect of water-curing time on the mechanical properties of ECCs. The cement of ECCs replaced by 80% fly ash by weight exhibited good ductility and mechanical properties whenwater curing time was 7 days. Ot...

Effect of limestone powder on the rheological, mechanical and durability properties of ECC

This paper presents the results of an investigation on the influence of a replacement of limestone powder (LSP) by silica sand (SS) on properties of engineered cementitious composites (ECC). For this purpose, five different ECC mixtures were adopted: ECC mixture with only SS (M1) for control purposes and four ECC mixtures in which SS is partially replaced by four levels of replacements (25, 50, 75 and 100% by weight of total SS) of LSP. The mechanical properties of ECC were investigated for 3, 28 and 90 days, while the durability tests were performed for 90 days. It was concluded that increase in LSP content resulted in a decrease in fluidity of ECC mixtures indicating longer flow times. Increase in the LSP content had a positive effect on the performance of the compressive strength, fracture toughness and flexural strength at the ages of 3 and 28 days, while this was not valid at the age of 90 days when compared to the reference mixture M1. Moreover, it can be said that the use of LSP instead of SS in ECC mixtures had the positive effect on ductility and good dispersion of fibres due to its fine particle structure compared to SS. On the other hand, the mass loss due to acid attack and the sorptivity coefficient of ECC specimens decreased, while the carbonation resistance increased in all ECC mixes compared to the reference mixture M1 with only SS when LSP content in ECC mixtures increased.

Correlation between the viscoelastic properties and cracking potential of engineered cementitious composites

Although Engineered Cementitious Composites (ECC) offer a number of advantages over ordinary and fiber reinforced concrete in many respects, it is not cost-effective to build a whole structure with ECC, currently. Thus, ECC can potentially be used in repair systems or in bi-material systems which require it to be used together with a dimensionally stable material. High shrinkage, together with the restraining effect brings about cracking a critical phenomenon for ECC. In this study, along with the mechanical properties of ECC, viscoelastic properties like autogenous shrinkage, drying shrinkage and tensile creep which were used to calculate ECC’s cracking potential were studied. At the same time, the tendency of ECC mixtures to crack under restrained shrinkage conditions was also investigated using restrained shrinkage rings. It was concluded that creep, elastic properties, and shrinkage data should be together used to evaluate the dimensional compatibility.

Mechanical Properties and Applications of Engineered Cementitious Composites (ECC)

Engineered Cementitious Composite (ECC) is a fiber reinforced cement based composite material, which systematically designed on the basis of micromechanics and engineered to achieve high ductility under tensile and shear load. The article introduced the development of ECC as advanced construction material, shown different mechanical properties of ECC, tensile strength, compressive strength, bending strength, shear strength. And in light of recent and future full-scale field applications of ECC were also summarized.