Ductility Of Engineered Cementitious Composites Research Articles

Fresh, Compressive and Direct-Tensile characterization of Engineered Cementitious Composite

A new category of high-performance fiber-reinforced composite broadly known as Engineered Cementitious Composite (ECC) has gained rapid attention in the construction industry in recent years. The exceptional behaviour of ECC, therefore high ductility, toughness, and durability, make it a promising material for various structural applications such as tunnel inner lining, dam and bridge deck slab construction. This investigation aims to study the fresh and mechanical characteristics of ECC, including workability, compressive, and direct tensile strength. A total of 15 ECC mixes are prepared with varying superplasticiser-binder ratio (0.200, 0.225, 0.250, 0.275 and 0.300 %), sand-binder ratio (0.35, 0.40 and 0.45) and a constant water-binder ratio (0.27). The mini-slump cone test was performed to examine the workability of the fresh ECC mixtures. The results showed that using a higher content of the superplasticiser resulted in an upsurge in both the workability of the fresh ECC mixtures and the mechanical strength of ECC, particularly the tensile strength. Apart from this, both the mechanical tests are performed at the 7 and 28 days. As per the results, both the compressive strength and direct tensile strength of ECC are found to be comparatively higher than that of the conventional mix. In conclusion, ECC is an efficient construction material for various structural applications, especially for the latest 3D printing construction techniques. The uniform dispersion of fibers significantly improves the tensile strength and ductility of ECC, making it a suitable material for seismic-resistant structures.

Study on Mechanical and Rheological Properties of Solid Waste-Based ECC

As one of the main raw materials of engineered cementitious composite (ECC), fly ash exerts the “ball effect” and “pozzolanic effect” in concrete, which improves the working performance of concrete and enhances the strength of the concrete matrix. Polyvinyl alcohol (PVA) fiber has been widely used in the preparation of ECC, while ground fly ash can be used to enhance the performance of ECC as a kind of high-activity admixture. In this paper, the compressive strength, flexural strength and flexural toughness of ECC prepared from different types of fly ash (raw fly ash, sorted fly ash and ground fly ash) are compared, and the rheological properties of the ECC are analyzed by studying the two parameters of yield stress and plastic viscosity. The results show that the smaller the particle size of fly ash is, the more sufficient it reacts with Ca(OH)2 produced by cement hydration, and the more it can improve the compressive strength and flexural strength of the matrix. In addition, the smaller the particle size of fly ash, the higher the yield stress and plastic viscosity of ECC; therefore, the distribution of PVA fiber in ECC is more uniform, thereby improving the flexural toughness and ductility of ECC.

Size effect on compressive behavior of FRP-confined engineered cementitious composites (ECC)

• A first-ever experimental study on the size effect of GFRP- and LRS FRP-confined ECC columns was conducted. • The influences of specimen size, FRP confinement level, and FRP type were examined. • A new size-dependent ultimate stress model of FRP-confined ECC was established. The reliable design of the high-performance column made of fiber reinforced polymer (FRP)-confined engineered cementitious composites (ECC) necessitates a clear understanding of the size effect under axial compression. This paper presents the compressive behaviors of glass FRP (GFRP) and large rupture strain (LRS) polyethylene terephthalate (PET) FRP-confined ECC columns. The specimen size, confinement level, and FRP type were the variables. Five diameters of 100, 200, 300, 400, and 500 mm were designed to cover a wide size range. Results showed that both the compressive strength and ductility of ECC were substantially improved with FRP confinement. Compared with GFRP-confined ECC, PET FRP-confined ECC exhibited higher ductility. The key stresses, namely initial peak stress, post-peak ravine stress, and ultimate stress decreased with increasing specimen size. Nevertheless, the specimen size had a marginal influence on the key strains and dilation behavior. After evaluating the existing size-dependent ultimate strength models of FRP-confined concrete, a new expression for predicting the ultimate strength of FRP-confined ECC was introduced, which was shown to fit well with the test results.

Mechanical and Impact Properties of Engineered Cementitious Composites Reinforced with PP Fibers at Elevated Temperatures

The repeated impact performance of engineered cementitious composites (ECCs) is not well explored yet, especially after exposure to severe conditions, such as accidental fires. An experimental study was conducted to evaluate the degradation of strength and repeated impact capacity of ECCs reinforced with Polypropylene fibers after high temperature exposure. Compressive strength and flexural strength were tested using cube and beam specimens, while disk specimens were used to conduct repeated impact tests according to the ACI 544-2R procedure. Reference specimens were tested at room temperature, while three other groups were tested after heating to 200 °C, 400 °C and 600 °C and naturally cooled to room temperature. The test results indicated that the reference ECC specimens exhibited a much higher failure impact resistance compared to normal concrete specimens, which was associated with a ductile failure showing a central surface fracture zone and fine surface multi-cracking under repeated impacts. This behavior was also recorded for specimens subjected to 200 °C, while the exposure to 400 °C and 600 °C significantly deteriorated the impact resistance and ductility of ECCs. The recorded failure impact numbers decreased from 259 before heating to 257, 24 and 10 after exposure to 200 °C, 400 °C and 600 °C, respectively. However, after exposure to all temperature levels, the failure impact records of ECCs kept at least four times higher than their corresponding normal concrete ones.

Optimal design of bridge columns constructed with engineered cementitious composites and Cu-Al-Mn superelastic alloys

Recent major earthquakes have shown that conventional bridge columns are susceptible to large residual deformations and considerable damage to the plastic hinge region under seismic loading. The use of high-performance materials such as high-performance fiber reinforced concrete (HPFRC) and superelastic alloys (SEA) has attracted attention in the recent years to address these issues. Unique properties of engineered cementitious composites (ECC), as a special type of HPFRC, including superior ductility and durability compared to conventional concrete and non-localized multiple fine cracking under cyclic tensile loading have been shown to improve the damage tolerance of bridge columns. Moreover, the ability of SEAs to recover large inelastic deformations, when replaced with traditional steel reinforcement, significantly reduces the permanent deformations in bridge columns subjected to ground shaking. The objective of this study is to identify the optimal geometry and material distribution of an innovative bridge column concept that has recently been demonstrated to be effective in addressing these issues, i.e., damage tolerance and post-earthquake functionality. A numerical parametric study of high-fidelity full-scale bridge column models incorporating ECC and Cu-Al-Mn (CAM) SEA bars has been performed. The material properties of ECC, the thickness of the hollow reinforced ECC (RECC) column cross-section, the number of CAM SEA bars in the plastic hinge region, and the effect of a concrete core have been investigated as the variables of the parametric study. It was found that the ductility of ECC in tension had little influence on the global behavior of the columns, the hollow columns up to a hollow ratio of 35% performed equally well as the solid ones, and there was an optimal replacement ratio of approximately 65% of the steel reinforcement with CAM SEAs that would yield a compromise between energy absorption and self-centering capacity.

Effect of Specimen Shapes on Compressive Strength of Engineered Cementitious Composites (ECCs) with Different Values of Water-to-Binder Ratio and PVA Fiber

This paper presents experimental investigation on the effect of specimen shapes of engineered cementitious composites (ECCs). In various types of cement concrete, cubic specimens have shown to have higher compressive strength than cylindrical specimens. However, no research has been conducted yet to study the effect of specimen shapes (cube or cylinder) on the compressive strength of new cementitious materials like ECC. In this study, cylinders and cubic specimens were prepared to study the effect on the compressive strength and elastic modulus of the ECCs. In addition, the effects of water-to-binder ratio (w / b) and polyvinyl alcohol (PVA) fiber on the compressive strength and the modulus of elasticity of ECC were investigated. Two categories of ECC were considered, with PVA fibers (PVA-ECC or shortly PE) and without PVA fibers (NO-PVA-ECC or simply NE). Three different w / b ratios were used for each material category. The results revealed that PVA fiber has a significant effect on ductility of ECCs but with minor effect on compressive strength for both the specimen shapes. As expected, the cubic specimens of ECC exhibit higher strengths than the cylindrical counterparts after 28 days. Based on the measurement data, new generalized correlation models were proposed via linear regression analysis showing the relation between the cylindrical and cubic shapes for ECC at 14 and 28 days of age. Another interesting models are proposed to establish the correlations between the compressive strength as well as the moduli of elasticity of ECCs with and without PVA fiber, for both specimen shapes.

Nonlinear FE modelling and parametric study on flexural performance of ECC beams

Engineered Cementitious Composite (ECC) is a special class of the new generation of high performance fiber reinforced cementitious composites (HPFRCC) featuring high ductility with relatively low fiber content. In this research, the mechanical performance of ECC beams will be investigated with respect to the effect of slag and aggregate size and amount, by employing nonlinear finite element method. The validity of the models was verified with the experimental results of the ECC beams under monotonic loading. Based on the numerical analysis method, nonlinear parametric study was then conducted to evaluate the influence of the ECC aggregate content (AC), ECC compressive strength (fECC), maximum aggregate size (Dmax) and slag amount (ϕ) parameters on the flexural stress, deflection, load and strain of ECC beams. The simulation results indicated that when increase the slag and aggregate size and content no definite trend in flexural strength is observed and the ductility of ECC is negatively influenced by the increase of slag and aggregate size and content. Also, the ECC beams revealed enhancement in terms of flexural stress, strain, and midspan deflection when compared with the reference beam (microsilica MSC), where, the average improvement percentage of the specimens were 61.55%, 725%, and 879%, respectively. These results are quite similar to that of the experimental results, which provides that the finite element model is in accordance with the desirable flexural behaviour of the ECC beams. Furthermore, the proposed models can be used to predict the flexural behaviour of ECC beams with great accuracy.

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.

Combined Effect of Aggregate and Mineral Admixtures on Tensile Ductility of Engineered Cementitious Composites

The mixture proportions of engineered cementitious composites (ECCs) are optimized through micromechanics-based material design theory to attain high tensile ductility. Therefore, ECC ingredients with inappropriate characteristics (such as type and amount of mineral admixture and size and amount of aggregate) from different sources can negatively influence the microstructure of the composite and the tensile ductility of the ECC. In this study, an experimental program is performed to understand the dependence of the composite properties on its mixture composition governed by mineral admixture types and replacement level, and maximum aggregate size and amount. The test results reveal that increasing the size and amount of aggregates does not negatively influence the ductility of ECC when combined with an appropriate mineral admixture type and amount. Instead, an increase in the age of restrained shrinkage cracking and a significant decrease in the drying shrinkage are accomplished.

Internal curing of engineered cementitious composites for prevention of early age autogenous shrinkage cracking

This investigation was carried out to study the effects of using a replacement percentage of saturated lightweight fine aggregate (LWA) as an internal curing agent on the shrinkage and mechanical behavior of Engineered Cementitious Composites (ECC). ECC is a micromechanically-based, designed high-performance, fiber-reinforced cementitious composite with high ductility and improved durability due to tight crack width. Standard ECC mixtures are typically produced with micro-silica sand (200 µm maximum aggregate size). Two replacement levels of silica sand with saturated LWA (fraction 0.59–4.76 mm) were adopted: the investigation used 10 and 20% by weight of total silica sand content, respectively. For each LWA replacement level, two different ECC mixtures with a fly ash-to-Portland cement ratio (FA/PC) of 1.2 and 2.2 were cast. In a control test series, two types of standard ECC mixtures with only silica sand were also studied. To investigate the effect of replacing a portion of the silica sand with saturated LWA on the mechanical properties of ECC, the study compared the results of uniaxial tensile, flexure and compressive strength tests, crack development, autogenous shrinkage and drying shrinkage. The test results showed that the autogenous shrinkage strains of the control ECCs with a low water-to-cementitious material ratio (W/CM) (0.27) and high volume FA developed rapidly, even at early ages. The results also showed that up to a 20% replacement of normal-weight silica sand with saturated LWA was very effective in reducing the autogenous shrinkage and drying shrinkage of ECC. On the other hand, the partial replacement of silica sand with saturated LWA with a nominal maximum aggregate size of 4.76 mm is shown to have a negative effect, especially on the ductility and strength properties of ECC. The test results also confirm that the autogenous shrinkage and drying shrinkage of ECC significantly decreases with increasing FA content. Moreover, increasing FA content is shown to have a positive effect on the ductility of ECC.