Engineered Cementitious Composites Mixtures Research Articles

Nano-modification to improve the ductility of cementitious composites

Effect of nano-sized mineral additions on ductility of engineered cementitious composites (ECC) containing high volumes of fly ash was investigated at different hydration degrees. Various properties of ECC mixtures with different mineral additions were compared in terms of microstructural properties of matrix, fiber-matrix interface, and fiber surface to assess improvements in ductility. Microstructural characterization was made by measuring pore size distributions through mercury intrusion porosimetry (MIP). Hydration characteristics were assessed using thermogravimetric analysis/differential thermal analysis (TGA/DTA), and fiber-matrix interface and fiber surface characteristics were assessed using scanning electron microscopy (SEM) through a period of 90days. Moreover, compressive and flexural strength developments were monitored for the same period. Test results confirmed that mineral additions could significantly improve both flexural strength and ductility of ECC, especially at early ages. Cheaper Nano-CaCO3 was more effective compared to nano-silica. However, the crystal structure of CaCO3 played a very important role in the range of expected improvements.

Evaluation of reinforced concrete and reinforced engineered cementitious composite (ECC) members and structures using small-scale testing

The behavior of reinforced concrete (RC) and reinforced engineered cementitious composites (ECC) was comparatively investigated at the component and system levels through a small-scale (1/8 scale factor) experimental program. The logistical and financial advantages of small-scale testing were utilized to investigate a range of parameters, including the effect of reinforcement ratio and material properties, on the response of reinforced concrete and reinforced ECC structures. The procedures pertaining to material preparation, specimen construction, and input motion development that were critical for enhancing the similarity between the scales are provided. Engineered cementitious composite mixtures with different cost and sustainability indices were evaluated. Under cyclic loading, the stiffness, strength, ductility, and energy absorption capacity of columns made of different ECC mixtures were found to be 110, 65, 45, and 100% higher, respectively, than those of the RC columns. The system level investigation through hybrid simulation showed that the ECC structures sustain less deformation under earthquake excitation due to high energy absorption capacity of the material. The differences in cost, sustainability, and structural performance of different ECC mixtures suggest that a careful selection of materials is required for optimal performance.

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.

Measurement and correlation of ductility and compressive strength for engineered cementitious composites (ECC) produced by binary and ternary systems of binder materials: Fly ash, slag, silica fume and cement

The purpose of this paper is to investigate the mechanical properties of engineered cementitious composites (ECC) produced by high volume mineral admixtures which are fly ash, slag and silica fume. Emphasis of this study is placed on building the correlation between compressive strength and the parameters obtained in load–deflection curves of 12 different ECC mixtures. The results indicate that the compressive strength has an inverse relationship with deflection, toughness index and fracture energy, respectively; but the compressive strength have an direct proportional relation with flexural strength, first cracking load, and peaking load, respectively. Additionally, in the binary system of binder materials, the ductility of ECC can be obviously improved by introducing high volume fly ash and slag replacing the cement, respectively. However, the compressive strength of ECC with fly ash and slag can reduce 40% and 14%, respectively. For the ternary system of binder materials with replacement 70% of cement, the combination of fly ash and slag can keep not only the excellent ductility of ECC, but also enough stronger matrix strength. Meanwhile, the combination of fly ash and silica fume only increase the compressive strength, but weaken the toughness of ECC. Therefore, based on comprehensively considering both compressive strength and fracture energy, the optimal range of ECC mixture proportion can be properly selected to satisfy the demands in practical engineering applications.

Investigating mechanical properties and self-healing behavior of micro-cracked ECC with different volume of fly ash

In this paper, the mechanical properties and self-healing behavior of Engineered Cementitious Composite (ECC) are investigated. Three ECC mix proportions with different volume of fly ash are used in this research. The mechanical properties of ECC are revealed via compressive strength, deflection capacity and cracking behavior. Meanwhile, the self-healing behavior of ECCs is investigated by sorptivity test and rapid chloride penetration test (RCPT). Specimens are pre-loaded first to produce micro-cracks, followed by sorptivity and RCPT tests. It is found that both compressive strength and crack width decrease with increasing volume of fly ash, while deflection capacity shows the opposite trend. Micro-cracks produced by pre-loading heal themselves after cured in water, thus decrease sorptivity and charge passed of micro-cracked specimen. Subsequent Environment Scanning Electron Microscope (ESEM) observations also confirm the above findings. The sorptivity test result suggests that ECC mixture with fly ash/cement ratios of 4.0 by weight reveals best self-healing behavior. Therefore, with excellent capacity of crack width control, deformability and self-healing behavior, ECC can be an ideal material for durable concrete infrastructure.

Specimen size effect on the residual properties of engineered cementitious composites subjected to high temperatures

In this study, size effect on the residual properties of Engineered Cementitious Composites (ECC) was investigated on the specimens exposed to high temperatures up to 800°C. Cylindrical specimens having different sizes were produced with a standard ECC mixture. Changes in pore structure, residual compressive strength and stress–strain curves due to high temperatures were determined after air cooling. Experimental results indicate that despite the increase of specimen size, no explosive spalling occurred in any of the specimens during the high temperature exposure. Increasing the specimen size and exposure temperature decreased the compressive strength and stiffness. Percent reduction in compressive strength and stiffness due to high temperature was similar for all specimen sizes.

Investigation of the Bond between Concrete Substrate and ECC Overlays

AbstractRigid concrete overlays have been used for smoothing damaged surfaces and/or restoring or improving the mechanical capacity of bridge decks for many years. However, engineered cementitious composites (ECCs), which demonstrate superior ductility with high strength and improved durability characteristics, are an attractive alternative to conventional overlay materials if a strong mechanical bond is formed between the overlay and the substrate material. An experimental study was performed to evaluate the bond strength between ECC overlay and an ordinary concrete substrate with smooth and rough surface textures. Microsilica concrete (MSC), generally used as an overlay material, was also prepared as a control mixture. ECC and MSC overlay mixtures were cast over the concrete substrate to determine bonding performance. Slant shear and splitting prism tests were performed with MSC and two ECC mixtures. The experimental results show that when ECC is used as an overlay material, bond strength is significant...

The mechanical properties of engineered cementitious composites containing limestone powder replaced by microsilica sand

In this study, an experimental program is conducted to understand the effect of the limestone powder (LSP) content replaced by silica sand on the composite properties. For this purpose, five different engineered cementitious composite (ECC) mixtures were adopted: ECC mixture with only silica sand (SS) 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 properties of ECC mixtures produced were investigated for the ages of 3, 28, and 90 days. It was concluded that the mechanical properties of the ECC mixtures with LSP were in general higher than the reference mixture with only SS for all curing ages. 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. Also, the ductility of the ECC beams strongly depends on the LSP content and specimen age.

Effect of Microcracking on Frost Durability of High-Volume- Fly-Ash- and Slag-Incorporated Engineered Cementitious Composites

This paper reports the durability performance of high-volume-fly-ash (FA)- and slag (S)-incorporated engineered cementitious composites (ECCs) when subjected to mechanical loading and freezing-and-thawing cycles. Composites containing two different contents of FA and slag as a replacement of cement (55 and 70% by weight of total cementitious materials) are examined. To find out the effect of mechanical preloading on the frost durability of ECCs, prism specimens were preloaded up to a certain deformation level under four-point bending loading to generate microcracks. Then, the preloaded and pristine (sound) specimens were subjected to the freezing-and-thawing test in accordance with ASTM C666/C666M. Experimental tests consisted of measuring the change in mass and ultrasonic pulse velocity (UPV) and residual flexural properties of ECC specimens exposed to the freezing-and-thawing cycles up to 300. Test results revealed that the frost resistance of ECCs was significantly influenced by the mineral admixture type and amount and preloading deformation. The deterioration with an increasing number of freezing-and-thawing cycles was relatively more for ECC mixtures with FA than for slag mixtures at the same replacement level. In addition, an increase in the FA replacement rate was observed to exacerbate the deterioration caused by freezing-and-thawing cycles. Apart from some reduction in flexural properties and UPV and an increase in mass loss and residual crack width, the results presented in this study, however, confirm the durability performance of ECC material under freezing-and-thawing cycles, even in cases where the material experiences mechanical loading that deforms it into the strain hardening stage prior to exposure. It is important to note that this durability of ECCs under freezing and thawing was achieved without deliberate air entrainment, and contrary to conventional concrete, no relationship of frost resistance was found to the air-void structure of the ECC mixtures.

Shrinkage Characteristics of Green Engineered Cementitious Composites with Varying Palm Oil Fuel Ash Contents and Water-Binder Ratios

The present paper is a part of an extensive study on green palm oil fuel ash engineered cementitious composites conducted at Universiti Sains Malaysia. It specifically investigates the effects of waterbinder ratio (w/b) and palm oil fuel ash (POFA) on the drying shrinkage of engineered cementitious composites (ECCs). W/b values of 0.33, 0.36, and 0.38 were selected. ECC mixes were proportioned to have various ratios of POFA ranging from 0 to 1.2 from the mass of cement. The drying shrinkage measurements were taken at 4, 11, 18, 25, 57, and 90 days. The experimental results show that w/b has a significant effect on the drying shrinkage of the ECC mixtures. Drying shrinkage is remarkably reduced with a decrease in the w/b. The results also showed that drying shrinkage of the composites is considerably reduced when POFA is used in the matrix. The measured drying shrinkage strain at 90 days is only 920×10-6 µε to 1216×10-6 µε for ECC mixtures with high POFA content. The shrinkage strain of the ECC mixtures without POFA at 90 days is nearly 1597×10-6 µε to 1910×10-6 µε.

Mechanical Properties of Engineered Cementitious Composite with Palm Oil Fuel Ash as a Supplementary Binder

Palm oil fuel ash (POFA) was used to produce engineered cementitious composite (ECC) in this research where ECC mixtures containing different volume of POFA (up to 55% by weight) of cement, were prepared. Mechanical properties of the resulting ECC mixtures were assessed using the compression, flexural and uniaxial tensile tests. The findings of the study show that the use of POFA improves the mechanical properties of the ECCs. The ECC mix with 1.2 POFA/cement ratio achieved a compressive strength of 30 MPa at 28 days, which is within the normal range of concrete strength for many applications. Moreover, the results portray that the use of POFA should be helpful for achieving strain-hardening behaviour. The increase in the POFA content concomitantly increased the flexural deflection and tensile strain capacities of the POFA-ECC. Furthermore, crack width of the ECC was significantly decreased with an increase of POFA content. In addition, the resulting POFA-ECC is expected to enhance the material greenness and durability.

Improving the workability and rheological properties of Engineered Cementitious Composites using factorial experimental design

In the development of Engineered Cementitious Composites (ECC), micromechanics-based design theory is adopted to properly select the matrix constituents, fiber, and fiber–matrix interface properties to exhibit strain hardening and multiple cracking behaviors. Despite the micromechanics design constraints, practical applications show that the workability and rheological properties of matrix can affect the fiber dispersion uniformity, which have also direct concerns on composite mechanical properties. For this reason, in this research, parameters of micromechanics-based optimized ECC mixture design, which most possibly affecting the workability and rheological properties, are investigated. An experimental program that contains 36 different ECC mixtures was undertaken to quantitatively evaluate the combined effects of the following factors on workability and rheological properties: water-binder (w/b), sand-binder (s/b), superplasticizer-binder (SP/b) ratios and maximum aggregate size (Dmax). A mini-slump cone, a Marsh cone and a rotational viscometer were used to evaluate the workability and rheological properties of ECC mixtures. Compressive strength and four point bending tests were used for mechanical characteristics of ECC mixtures at 28days. The effects of studied parameters (w/b, s/b, SP/b and Dmax) were characterized and analyzed using regression models, which can identify the primary factors and their interactions on the measured properties. Statistically significant regression models were developed for all tested parameters as function of w/b, s/b, SP/b and Dmax. To find out the best possible ECC mixture under the range of parameters investigated for the desired workability and mechanical characteristics, a multi-objective optimization problem was defined and solved based on the developed regression models. Test results indicate that w/b, s/b and SP/b parameters affect the rheological and workability properties. On the other hand, for the range of studied aggregate sizes, Dmax is found to be statistically insignificant on the rheological and workability properties of ECC.

Flexural performance of green engineered cementitious composites containing high volume of palm oil fuel ash

The flexural performance of green engineered cementitious composites (ECCs) containing high volume of palm oil fuel ash (POFA) has been investigated. Three sets of ECC mixtures with water–binder ratios of 0.33, 0.36, and 0.38 were prepared, and for each set, the ECC mixtures were proportioned to have varying POFA contents of 0, 0.4, 0.8, and 1.2 from the mass of cement. The flexural performance was assessed after 3, 28, and 90days of curing using the four-point bending test. The results suggest that there is a corresponding reduction in the first cracking strength and flexural strength of the ECC beams with the increase of water–binder ratios and POFA content. Nonetheless, higher water–binder ratio and higher POFA content was found to concomitantly improve the flexural deflection capacity, which indicates a superior deflection hardening behaviour. Furthermore, number of cracks was increased and crack width of the ECC was significantly reduced with an increase of POFA content. In addition, there are good correlations between flexural deflection capacity from the four-point bending test and tensile strain capacity from the uniaxial tensile test.

Self-healing capability of cementitious composites incorporating different supplementary cementitious materials

The presence of deleterious substances and their transport are among the most important factors controlling the durability of cementitious composites . The present paper studies the relationship among the applied mechanical deterioration in terms of splitting tensile deformation , curing conditions and chloride ion permeability of Engineered Cementitious Composites (ECCs) that contain different supplementary cementitious materials (SCMs). Three SCMs, representing a wide range of compositions, were used in the study. The splitting tensile deformations are introduced to generate microcracks in ECC specimens, where cylindrical specimens were pre-loaded to different deformation levels. After that, the mechanically pre-cracked and pristine ECC specimens were exposed to three different curing conditions (continuous wet, continuous air, and freeze–thaw cycle) for up to 2 months. Rapid chloride permeability test (RCPT), microscopic observation and microstructural analysis were used to assess the rate and extent of self-healing. Test results indicate that the SCM type greatly affects the self-healing capability of cementitious composites as measured by chloride ion permeability. Although ECC samples with fly ash have more unhydrated cementitious materials , and therefore, expectedly, a higher capacity for self-healing, more evident self-healing product was observed from the ECC mixture incorporating slag. Therefore, in addition to the crack width distribution and curing condition, the reaction products associated with SCMs have a great impact on the self-healing capability of cementitious composites.

Use of slag to improve mechanical properties of engineered cementitious composites (ECCs) with high volumes of fly ash

Fly ash (FA) has been a necessary ingredient for engineered cementitious composites (ECCs) with excellent tensile strain capacity and multiple cracking. However, ECC with high volumes of FA has lower matrix strength, especially at early age. The purpose of this paper is to develop a kind of green ECC with high tensile ductility and strong enough matrix strength, especially at early age. A series of investigations has carried out to evaluate mechanical properties and drying shrinkage of ECC with 70% combination mineral admixtures of FA and ground granulated blast furnace slag (SL). The experimental results show that ECC with combination mineral admixtures can achieve strain hardening behavior, tensile capacity of ECC can be more than 2.5% at 90days. Meanwhile, compared to ECC only with FA, SL and FA can effectively increase compressive strength of ECC, especially at early age. Incorporating SL into matrix can slightly increase drying shrinkage of ECC. However, among four ECC mixtures, ECC with 30% SL and 40% FA presents the lowest drying shrinkage at later ages.

Frost resistance and microstructure of Engineered Cementitious Composites: Influence of fly ash and micro poly-vinyl-alcohol fiber

Abstract One of the most damaging environmental conditions to concrete structure is cyclic freezing and thawing. This paper discusses the influence of the high volumes of fly ash (FA) and micro poly-vinyl-alcohol (PVA) fibers on the cyclic freeze–thaw resistance and microstructure of the Engineered Cementitious Composites (ECC). ECC mixtures with two different FA–cement (FA/C) ratios (1.2 and 2.2 by weight), and at constant water-cementitious materials (fly ash and cement) ratio of 0.27 are prepared. To compare the behavior of ECC with ECC matrix, all of the preceding properties are also investigated for ECC matrix mixtures of same composition without PVA fiber. For frost resistance, mixtures are exposed to the freeze and thaw cycles up to 300 cycles in accordance with ASTM C666, Procedure A. Experimental tests consist of measuring the residual mechanical properties (flexural strength, mid-span beam deflection and flexural stress – deflection curve), ultrasonic pulse velocity and mass loss. The roles of PVA fibers and FA are discussed through the analysis of microstructure and fiber–matrix interactions as function of frost exposure. The microstructural characterization by measuring pore size distributions is examined before and after exposure to frost deterioration by using mercury intrusion porosimetry (MIP). The air-void characteristics of mixtures are also studied using linear transverse method. Test results confirm that both ECC mixtures with high volumes of FA remain durable, and show a tensile strain capacity of more than 2% even after 300 freezing and thawing cycles. On the other hand, before completing 300 freezing and thawing cycles, matrix (ECC without fiber) specimens have severely deteriorated, requiring removal from the freeze–thaw machine. Therefore, results indicate that the addition of micro PVA fiber to the ECC matrix substantially improved the frost resistance. The results of freeze–thaw tests also indicated that the reduction of residual physical and mechanical properties with increasing number of freeze–thaw cycles is relatively more for ECC mixture with FA/C ratio of 2.2 than for ECC mixture with FA/C ratio of 1.2.

Incorporation superabsorbent polymer (SAP) particles as controlling pre-existing flaws to improve the performance of engineered cementitious composites (ECC)

This paper concerns a new concept for introducing superabsorbent polymer (SAP) particles as pre-existing flaws into matrix to improve tensile property, flexural property, drying shrinkage and restrained shrinkage of engineered cementitious composites (ECC). The experimental results show that all ECC mixtures exhibit excellent ductility, more than 1.5%. Incorporating SAP particles in ECC matrix can apparently improve tensile strain capacity and toughness of ECC specimens. Compared to control specimens, tensile capacity and deflection of ECC with SAP particles can increase 92% and 77%, respectively. Moreover, SAP particles have an apparent effect on ECC with 50% fly ash (FA) compared with ECC with 70% FA. Meanwhile, introducing SAP in matrix is effective in reducing drying shrinkage and restrained shrinkage of ECC specimens, due to water-entrained capacity of SAP particles. However, SAP particles can reduce compressive strength of 5–15% compared to control specimens. In addition, increasing FA content can also increase tensile capacity and decrease drying shrinkage and restrained shrinkage of ECC specimens.

Effect of Fly Ash and PVA Fiber on Microstructural Damage and Residual Properties of Engineered Cementitious Composites Exposed to High Temperatures

This paper discusses the influence of high volumes of fly ash and micro polyvinyl alcohol (PVA) fibers on the fire resistance and microstructure of engineered cementitious composites (ECC). Composites containing two different contents of fly ash as a replacement for cement (55 and 70% by weight of total cementitious materials) are examined. To determine the effects of microfibers and ultrahigh ductility of ECC, ECC matrix mixtures of similar composition except PVA fiber are also produced and tested for the fire resistance. The mixtures are exposed to temperatures up to 800°C for one hour. Fire resistances of the mixtures are then quantified in terms of the residual mechanical properties (strength, stress-strain curve, deflection, and stiffness) and mass loss. The role of PVA fibers and fly ash is discussed through the analysis of microstructure and fiber-matrix interactions as a function of heat treatment. The microstructural characterization is examined before and after exposure to fire deterioration by using scanning electron microscopy and the pore size distribution is obtained by mercury intrusion porosimetry. Results indicate that adding micro PVA fiber to the ECC matrix substantially improves the fire resistance and eliminates the explosive spalling behaviors of the ECC matrix. Fire resistance of ECC mixtures is further improved with the increase of fly ash content.

Assessing Mechanical Properties and Microstructure of Fire-Damaged Engineered Cementitious Composites

In recent years, a number of investigations of engineered cementitious composites (ECC) have been carried out, and the mechanical behavior and durability characteristics of this type of composite are now increasingly better understood. The fire-resistant behavior of this specialized concrete, however, has not yet been studied as extensively. This investigation develops important data on the mechanical properties and microstructure of ECC exposed to temperatures up to 800°C (1472°F). In this study, the mechanical properties (residual compressive strength, stress-strain curve, and stiffness) and mass loss were determined after air cooling, subsequent to temperature exposure. Changes in the microstructure, porosity, and pore size distribution of the fire-deteriorated ECC specimens were identified using scanning electron microscopy and mercury intrusion porosimetry techniques. Test results revealed no significant changes in the mechanical properties for tested specimens exposed to temperatures up to 400°C (752°F) for 1 hour. Microstructural analysis showed the creation of supplementary pores and channels in the matrix due to polyvinyl alcohol (PVA) fibers melting in the 200-400°C (392-752°F) temperature range. After a 1-hour exposure to temperatures of 600 and 800°C (1112 and 1472°F), the mechanical performance of fire-deteriorated ECC mixture is similar to or better than that of conventional concrete incorporating polypropylene or steel fibers, despite a significant reduction in compressive strength and stiffness. Moreover, no explosive spalling occurred in any specimens during the fire test. The promising performance of ECC under fire exposure may be due to the presence of PVA fibers and high-volume fly ash. The beneficial influence of fly ash can be ascribed to the pozzolanic reaction consuming calcium hydroxide in the hydrates. PVA fiber is also beneficial in that it prevents explosive spalling. This introduces additional channels for vaporized moisture in ECC to escape without creating high internal pressure in the material.

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.