Polyvinyl Alcohol-engineered Cementitious Composite Research Articles

Shear cracking behavior of pre-damaged PVA-aggregate mixed ECC beams: Direct observation using DIC

Normal polyvinyl alcohol-engineered cementitious composites (PVA-ECC) exhibit high mechanical performance but are susceptible to shear cracking. It has been recently found that the shear resistance can be largely improved by including coarse aggregates. However, under complex stress conditions, the mechanism of shear movement and the contribution from coarse aggregate remain unclear. This paper presents an experimental investigation of the shear cracking behavior in pre-damaged PVA-ECC beams with a mixture that includes coarse aggregate. Symmetric and antisymmetric loading tests were carried out to examine the effects of coarse aggregate under different stress rotation fields. To clarify the shear cracking mechanism, digital image correlation (DIC) was applied to observe crack development and strain localization in the shear span of the PVA-ECC beams. The results obtained from DIC and conventional measurements showed good agreement, confirming the reliability of monitoring complex fracture processes using the DIC technique. The shear cracking mechanism of the PVA-ECC beam under complex stress conditions was analyzed. The collaboration of coarse aggregate was observed from the orientation of secondary cracks, which showed less dependence on the presence of precracks. Crack opening and sliding were significantly limited due to the reduced anisotropic effect of the predamage. Therefore, using the DIC technique, the positive effect of coarse aggregates was verified, and the shear cracking mechanism of pre-damaged PVA-ECC beams was revealed through direct observations.

Numerical Modeling and Design Method for Reinforced Polyvinyl-Alcohol-Engineered Cementitious Composite Beams in Bending

The polyvinyl-alcohol-engineered cementitious composite (PVA-ECC) is a superior cementitious material when used for tension and flexural loading. The utilization of PVA-ECC in the tension zone can prevent the development of wide cracks and increase the flexural resistance of reinforced PVA-ECC members. In this paper, a nonlinear finite element model is established to simulate the behavior of PVA-ECC beams in bending. In the model, the constitutive models for PVA-ECC in compression and tension are employed by simplifying them as piece-wise linear models, and the bond between the reinforcing bar and PVA-ECC is also considered. The load–deflection curve and failure mode of beams can be obtained from the finite element model. Comparisons between numerical and experimental results show that the developed numerical model can estimate the ultimate load and failure mode of beams with reasonably good accuracy. After evaluating the accuracy of the finite element model, parameter analysis is conducted to investigate the effects of the reinforcement ratio, steel strength grade, and mechanical properties of PVA-ECC on the flexural behavior of reinforced PVA-ECC beams. The numerical results conclude that the effects of reinforcement ratio on the peak load, stiffness, and deflection are obvious while the influence of steel grade is mainly on the peak load. The tensile localization strain of PVA-ECC mainly affects the ductility of the beam. Furthermore, a design method is proposed based on the plane-section assumption to calculate the ultimate load of reinforced PVA-ECC beams, in which the contribution of PVA-ECC to the moment resistance of beam sections is considered. Comparisons between existing design methods and the proposed method indicate that the ultimate load of beams can be predicted more accurately by considering the tensile strength of PVA-ECC in the tension zone.

Multifunctional engineered cementitious composites modified with nanomaterials and their applications: An overview

Abstract Due to their advantages such as high tensile strength, low cost of production, easy manufacturing methods, and ease of use, cementitious materials are extensively utilized in the construction industry. The applications of nanomaterials in cementitious materials have been found to enhance their properties. It allows molecular changes to improve the material behaviour and the performance of civil infrastructure structures, including buildings and highways. Owing to the high ductility of polyvinyl alcohol-engineered cementitious composites (ECCs), it was suggested to be used in steel-reinforced structural elements to enhance the strength and ductility of the components. The presence of hybrid fibres provided increased shattering resistance with decreased scabbing, spalling, destruction, and damage zone and better absorption of energy through distributed microcracking. The presence of nanomaterials in ECCs modifies its atomic macroscopic scales, enhancing its mechanical and microstructural properties. The versatile properties of nanomaterials offer immense potential to cementitious composite for structural applications.

Experimental study on compressive behavior of PE-ECC under impact load

Compared with polyvinyl alcohol-engineered cementitious composites (PVA-ECC), engineered cementitious composites containing polyethylene fibers (PE-ECC) has captured the attention of researchers because of lower cost. Nevertheless, there is a limited amount of research that focuses on their dynamic behavior. Thus, specimens with different water binder ratios were tested by split Hopkinson pressure bar (SHPB) to unveil the dynamic compressive behavior of PE-ECC. The dynamic behaviors were analyzed based on the tests, including dynamic failure modes, dynamic stress-strain curves, dynamic compressive strength, dynamic peak strain, and dynamic toughness. The result shows the PE-ECC has excellent compressive ductility, and a long post-peak descending part in the stress-strain relations. Furthermore, the sensitivity analysis reveals that the strain rate is the most crucial factor that directly affects the dynamic compressive strength, dynamic peak strain, and dynamic toughness in a monotonic fashion.

The Impact of Carbonation Curing on the Fatigue Behavior of Polyvinyl Alcohol Engineered Cementitious Composites (PVA-ECC)

The Impact of Carbonation Curing on the Fatigue Behavior of Polyvinyl Alcohol Engineered Cementitious Composites (PVA-ECC)

Effect of low temperature and moisture on bond properties of PVA fibres and engineered cementitious composite matrix

The chemical debonding energy, initial interfacial frictional bond strength and slip-hardening coefficient between polyvinyl alcohol (PVA) fibres and an engineered cementitious composite (ECC) matrix were obtained by means of single PVA fibre pull-out tests. The effect of three moisture states (fully saturated, semi-saturated and fully dry) on the bonding properties between the PVA fibre and ECC matrix at three target temperatures (25°C, 0°C and −20°C) was investigated. It was found that, at 25°C, the bonding properties decreased with an increase in moisture content. At 0°C and −20°C, the bonding properties increased with an increase in moisture content. At −20°C in the fully saturated state, the bonding load was too large to cause fibre rupture. The bonding properties were found to increase with decreasing temperature in the fully saturated and semi-saturated states and decrease with decreasing temperature in the fully dry state. This study of the effect of low temperature and moisture state on the bonding properties between PVA fibres and ECCs provides theoretical support for how to ensure good ductility when ECCs are in service at low temperature.

Mechanical and shrinkage performance of 3D-printed rubberised engineered cementitious composites

Taking the advantages of 3D concrete printing (3DCP) and tackling the environmental issues related to the waste tires, current paper evaluates the material behaviour of rubberised engineered cementitious composites (ECC) using waste crumb rubber (CR) aggregates and polyvinyl alcohol (PVA) fibres, manufactured through 3DCP. To elaborate on the role of PVA fibres on the material properties, two different control mix designs were prepared through conventional mould-casting method, including control mix design without PVA fibres and ECC with PVA fibres equal to 1.75 vol% of binder. Thereafter, using the control ECC mix design, four mix designs containing 5, 10, 15, and 20% CR aggregates as replacement of fly ash, were prepared to assess the effect of CR on the mechanical performance of ECC. The prepared mix designs were subjected to compressive and flexural strengths, and shrinkage tests, and the rubberised ECC containing 5% CR was selected for 3DCP as it revealed superior compressive, flexural and shrinkage behaviour. Results obtained for 3D-printed specimens confirmed the dominant role of anisotropy on the material performance, which was very pronounced for flexural behaviour of printed elements. Comparing to the samples loaded in perpendicular direction, loading in the parallel direction to the fibre orientation (X direction) led to 3 and 4% higher 7- and 28-day compressive strengths, and loading parallel to the fibre alignment along the longitudinal axis of the specimen (Z direction) resulted in 104% and 47% increase in the 7- and 28-day flexural strengths, respectively. Moreover, printed specimens in the fibre-parallel direction showed 37% less drying shrinkage comparing to those printed in the perpendicular direction. Additionally, 3D-printed elements represent superior performance in terms of compressive strength, ductile characteristics, flexural behaviour, and shrinkage performance over the mould-casted ones.

Effect of solid waste ceramic on uniaxial tensile properties and thin plate bending properties of polyvinyl alcohol engineered cementitious composite

As a kind of non degradable waste, solid waste ceramics has caused serious negative impact on land resources and ecological environment. Therefore, the reasonable recycling of solid waste ceramics is of great significance to the sustainable development of society. In this study, solid waste ceramic powder (CP) was taken as a supplementary cementing material to replace cement (Cement) partly in polyvinyl alcohol-engineered cementitious composites (PVA-ECC) materials. Twelve groups of PVA-ECC materials were designed, with a CP substitution rate of 10%, 15%, 20% (proportion in the mass of cementing materials) respectively. The uniaxial tensile properties and thin plate bending properties of PVA-ECC with different substitution rate solid waste CP were compared and analyzed. The theoretical calculation model of uniaxial tensile stress-strain is established. The results show that recycling of solid waste CP is helpful to clean production of PVA-ECC materials. PVA-ECC with solid waste CP shows good tensile strain and bending toughness. Therefore, CP was taken as a supplementary cement material is feasible. When the content of fly ash (FA) is 70%, the content of Cement is 10%, and the content of solid waste CP is 20%, the uniaxial tensile strain of the material is the largest, which is 4.94%; at the same time, the ultimate bending toughness index of the material is the largest, which is 352.21. Therefore, the mix proportion of this group of specimen is the optimal mix proportion. Compared with the uniaxial tensile test results, the accuracy of the model established in this study is verified. It can effectively predict the uniaxial tensile constitutive model of PVA-ECC material with any substitution rate when the substitution rate of solid waste CP is 10%–20%. This study can play a certain role in promoting the resource utilization of solid waste CP.

Experimental investigation of engineered cementitious composites (ECC) retrofitted masonry structures

Earthquake has proven the most damaging natural hazard in the world. So, structures in the earthquake-prone areas are need to be retrofitted prior and post of the calamity. It has been observed that most of the research solutions available focus upon reinforced concrete and steel constructions. Engineered cementitious composites (ECC) developed for economical utilization of fibres in retrofitting of masonry structures have been focused herein. The performance of beam-like masonry specimens subjected to their out-of-plane forces are experimentally and numerically investigated in this paper. Twelve beam-like specimens were cast and retrofitted with polyvinyl alcohol engineered cementitious composites (PVA-ECC) for the purpose. The casting of the retrofitting layer was done by varying percentages of PVA fibres that are 1%, 1.5% and 2% addition by the total volume of mortar. The performance of out-of-plane direction is investigated trough static two-point loading. The specimens were tested at a constant load increment of 0.1 mm per second. Work was conducted to simulate the ultimate cracking loads, maximum tension/deflection and load to deflection relationships of retrofitted and non-retrofitted specimens. Preliminary experimental data were used for numerically modelling the specimens in finite element package. Numerical results for deflection and strength were finally compared with experimental results. Experimental results revealed that the maximum load-carrying capacity with retrofitted samples increased by 11.8, 10.15 and 11.13% for 1%, 1.5% and 2% fibre addition, respectively. Simultaneously, deflection before complete collapse increases 5, 8 and 10% for 1%, 1.5% and 2% fibre additions. It can be finally said that utilization PVA-ECC as retrofitting material is an economical and easy method available.

Strength enhancement of high strength steel beams by engineered cementitious composites encasement

This study proposes a method of using Polyvinyl Alcohol Engineered Cementitious Composites (PVA-ECC) encasement to provide continuous restraints along the compression flange of High Strength Steel (HSS) section so that it will reach its sectional plastic moment resistance under bending without lateral restraint. In order to demonstrate the effectiveness of the proposed method, experimental and numerical investigations were carried out to study the flexural strength of the ECC encased HSS beams (ECC-HSS beams). Six simply supported beams fabricated with identical HSS sections but with different encasement configurations were tested until failure. Flexural resistance and failure modes of the ECC-HSS beams were compared with similar bare HSS and normal concrete (NC) encased HSS beams (NC-HSS beams). It was found that when compared with the bare HSS and NC-HSS beams, a significant enhancement in flexural resistance was achieved for the ECC-HSS beams. More importantly, this study confirmed that the compressive ECC layers was crushed after the compression flanges were yielded and therefore successfully prevented the onset of lateral torsional buckling. Besides the flexural responses, the interfacial slip behaviours along the compression flange of the HSS section were also studied. Finally, a finite element (FE) model was developed and validated against the experimental results.

Flexural fatigue properties of a polyvinyl alcohol-engineered cementitious composite

The flexural fatigue properties of a recently developed polyvinyl alcohol-engineered cementitious composite (PVA-ECC) using local dune sand were investigated. Fatigue flexural tests were conducted under a four-point bending setup. Normal concrete beams were also tested as a benchmark. To determine the stress range versus fatigue life relationship, five and four stress ranges were applied to the PVA-ECC and the normal concrete specimens, respectively. It was found that, compared with normal concrete specimens, the PVA-ECC specimens showed much superior flexural fatigue performance in terms of fatigue strength and deformation capacity, with a more ductile failure mode. Furthermore, typical fatigue performance indicators of the PVA-ECC specimens, including evolution of the midspan deflection, total crack mouth opening displacement, crack width and crack depth of the critical crack that led to final failure, with number of cycles as well as total dissipated energy, were recorded and compared with those of normal concrete specimens. It was observed that the PVA-ECC specimens tested under a stress range of 3 MPa (32% of the flexural strength) did not fail by fatigue after 5·6 million cycles; subsequent static tests demonstrated that they still had good residual flexural properties, including residual flexural strength, deformation capacity, stiffness and energy absorption capacity.

Mechanical behaviour of polyvinyl alcohol-engineered cementitious composites (PVA-ECC) tunnel linings subjected to vertical load

Polyvinyl alcohol-engineered cementitious composites (PVA-ECC) have been attracted considerable attention due to the high toughness, excellent crack resistance, remarkable strain hardening and good durability. However, PVA-ECC application in tunnel lining is far from advanced. To evaluate the adaptability of PVA-ECC lining in mountain tunnels, a series of 1/5-scale tunnel lining specimens were tested to investigate the mechanical behaviour of traditional reinforced concrete (RC), PVA-ECC and steel-reinforced ECC (R/ECC) linings under vertical loading. The influence of subgrade stiffness on the mechanical behaviour of ECC linings was analysed. Experimental results showed that the ECC and R/ECC lining specimens exhibited multiple crack distributions and excellent cracking control capability, which showed better ductility and toughness compared to the traditional RC lining specimen. The PVA-ECC and R/ECC linings are flexible supports with initial stiffness values less than that of the traditional RC lining. Smaller subgrade stiffness may induce lager tensile stress distribution range of the linings, where the toughness of ECC could be fully utilized.

Flexural behaviour of engineered cementitious composite encased high strength steel composite beam

ABSTRACTIn this paper, the flexural performance of a new type of composite beam comprised of High Strength Steel (HSS) section encased by polyvinyl alcohol‐engineered cementitious composite (PVA‐ECC) and lightweight concrete (LWC) is studied. An experimental investigation on the flexural performance of HSS beams encased by different thickness of ECC is conducted and their performances are compared with bare HSS beam and normal strength concrete (NSC) encased HSS beam. Four‐point bending tests are carried out on simply supported beams including one bare HSS beam, one NSC encased HSS (NSC‐HSS) beam and two ECC‐LWC encased HSS (ECC‐HSS) beams. For ECC‐HSS beams, both top and bottom flanges of the HSS sections are encased with PVA‐ECC while the web was encased by LWC. The test results showed a significant improvement in load‐carrying capacity, ductility and failure modes for ECC‐HSS beams when comparing with bare HSS and NSC‐HSS beam.

Flexural fatigue behaviour of steel reinforced PVA-ECC beams

This paper presents an experimental investigation of the flexural fatigue behaviour of steel reinforced polyvinyl alcohol-engineered cementitious composite (PVA-ECC) beams. The influence of the PVA-ECC matrix and stirrups on the fatigue strength of steel reinforced beams was studied. Eleven beams, including three steel reinforced normal concrete beams (RC beams), four reinforced PVA-ECC beams with stirrups (RECC beams) and four reinforced PVA-ECC beams without stirrups (RECC-NS beams), were tested under a constant amplitude cyclic loading. The minimum load of each cycle was set at 20% of the static strength of the corresponding beam while the maximum loads ranged from 60% to 90%. Experimental results showed that the RC and RECC beams exhibited flexural failure with fracture of tensile reinforcement bars. By contrast, RECC-NS beams tested under 20–90%, 20–70% and 20–60% load ranges were respectively failed by shear, combined of shear and flexural, and flexural with tensile reinforcement bars yielded. The test results showed that the RECC beams generally had shorter fatigue life than the RC beams when tested under relatively high load ranges. This could be due to greater stiffness degradation which eventually led to a higher stress increasing rate in tensile reinforcement bars of the RECC beams.

Flexural and bond-slip behaviours of engineered cementitious composites encased steel composite beams

This paper studies the flexural and bond-slip behaviour of composite beams fabricated by encasing universal steel beams with Polyvinyl Alcohol-Engineered Cementitious Composite (PVA-ECC) and Light Weight Concrete (LWC). Four-point bending tests were conducted on one bare steel and four composite beams with different ECC and LWC encasement configurations. Test results showed that the ECC and LWC encasements could enhance the flexural strength and ductility of bare steel beams significantly. Furthermore, it was found that the weight of the encased beams could be further reduced by either replacing the bottom ECC layer with LWC or even only encasing the compression flange of the steel section without reducing the flexural strength of the beam significantly. The bond-slip behaviour between the ECC matrix and the steel section was also investigated. The experimental study is complemented by a non-linear finite element (FE) model which was validated against the test results. A small scale parametric study was then conducted by using the validated FE model to investigate the performances of beams formed by the steel sections with yield strengths ranging from 350 MPa to 960 MPa.

Flexural performance of concrete beams containing engineered cementitious composites

Engineered Cementitious Composites (ECC) considers a type of ultra-ductile cementitious composites with fiber reinforcement. It is developed for applications for economic purpose in the construction industry. ECC characterizes by strain hardening and multiple cracking. This paper experimentally investigates the performance of ECC concrete beams reinforced with conventional reinforcement bars. Advanced Polyvinyl Alcohol Engineered Cementitious Composite (PVA-ECC) fibers were selected in this purpose. Twelve RC beams were poured and tested to study flexure behavior under four-point loading test. Two different longitudinal reinforcement percentages, variable volume ratios of (PVA) and polypropylene fibers (PP) were used. optimizing the usage of PVA material trails to put it in the lower layer of the section at point of maximum tension with variable thicknesses was conducted. Initial flexure cracking load, ultimate load, the ductility and the load-to-deflection relationship at various stages of loading were evaluated. Experimental outcomes revealed that the enhancement in maximum capacity is more significant in the case of using PVA rather than PP. The maximum load increases by 20% and 34% for 1.0% and 2.0% of PVA contents in total section respectively. The relative ductility factor increases by 30% and 45% for 1.0% and 2.0% of PVA content. Results also depicted that a reasonable considerable increasing in the load capacity when used limited layer thickness of PVA concrete. Nonlinear Finite Element Analysis (NLFEA) was conducted for the purpose of simulating the behavior of experimentally tested beams, regarding crack behavior and load-deflection response. Reasonable agreement was achieved between the experimental results and NLFEA results.

Flexural and shear behaviours of plain and reinforced polyvinyl alcohol-engineered cementitious composite beams

In this paper, the results of an experimental investigation on the flexural and shear behaviours of plain and reinforced polyvinyl alcohol-engineered cementitious composite (PVA-ECC) beams are presented. The PVA-ECC employed in this study, which has a tensile strain capability up to 1%, has been recently developed by the authors using local sand to reduce cost. The aim of this study is to investigate the effects of PVA-ECC matrix, transverse reinforcement (stirrups) and longitudinal reinforcement bars on the flexural and shear structural performances of reinforced PVA-ECC beams. Four-point bending tests were conducted and normal steel reinforced concrete beams were tested for comparison. Digital Image Correlation technique was used to monitor single crack development and was validated by LVDT measurements. Experimental results show that PVA-ECC beams present significantly improved flexural behaviour compared with normal concrete beams. Furthermore, PVA-ECC beams without stirrups eventually fail in flexure rather than in shear, and exhibit similar load-deflection, moment-curvature relationships and crack development history when compared with PVA-ECC beams with stirrups.

Effects of High Temperature on Mechanical Properties of Polyvinyl Alcohol Engineered Cementitious Composites (PVA-ECC)

The influence of elevated temperatures on the mechanical properties of polyvinyl alcohol engineered cementitious composites (PVA-ECCs) was investigated in this study. A comparison of the compressive strength, flexural strength, compressive strain capacity, and modulus of elasticity of specimens with/without PVA fiber (volume dosage of PVA fiber: 2%) was conducted. The microstructure of PVA-ECC exposed to different high temperatures was studied using scanning electron microscopy (SEM). Based on previous thermal analysis tests of PVA fibers, all specimens were subjected to 20, 100, 200, 300, and 400 °C for 6 h. The experimental results showed that the compressive strength, flexural strength, and modulus of elasticity decreased as the temperature increased, whereas the compressive strain capacity increased with temperature. PVA incorporation significantly increased the flexural strength initially but accelerated the rate of strength reduction at high temperatures. The investigation of the PVA-ECC microstructure provides a fundamental reason for the decrease in the macro-mechanical properties. These findings provide guidance for the engineering applications of PVA-ECC to resist high temperatures.

PVA-ECC에 의해 피복 보강된 RC보의 비틀림 거동에 대한 연구

The need to consider torsion in the design of members of a structure has recently been increasing; therefore, many studies on torsion have been carried out. Recent research was focused on the torsional performance of concrete according to the reinforcing materials used. Of particular interest, are torsion studies of beams made of SFRC(steel fiber reinforced concrete), and there has been increasing use of SFRC at construction sites. In contrast, research on the composite PVA-ECC (polyvinyl alcohol-engineered cementitious composite) has only covered its mechanical performance, though it exhibits excellent tensile-strain performance (better than SFRC). Therefore, research on the torsion of concrete beams retrofitted using PVA-ECC is lacking. In this study, the behavior characteristics and performance of reinforced-concrete beams retrofitted by PVA-ECC was investigated experimentally. The experimental results show that the resistance to torsional cracking is increased by PVA-ECC. In addition, the strain on the rebar of the specimen was found to be reduced.

Study on mechanical properties of cost-effective polyvinyl alcohol engineered cementitious composites (PVA-ECC)

Engineered cementitious composites (ECC) which shows prominent tensile ductility and toughness, and fine multiple cracking, meets the high requirements of safety and durability in developing sustainable infrastructures. Currently, the cost of oiled polyvinyl alcohol (PVA) fiber widely used in ECC is very high. The price of regular unoiled PVA fiber is relatively lower, however, the tensile ductility of unoiled PVA-ECC may be limited. Based upon the micromechanics model, the feasibility of use of unoiled PVA fibers and hybrid PVA fibers in ECC were studied, and the mix proportion was redesigned through parametric analysis. The four-point bending test, uniaxial tensile test and uniaxial compressive test were carried out to characterize the mechanical behavior of ECC with 21 mix proportions. According to the cost and performance of PVA-ECC, three typical mixes were proposed: M7 with low cost, relatively low tensile ductility and reinforced by unoiled PVA fibers, M17 with moderate cost, relatively high tensile ductility and reinforced by hybrid PVA fibers and M21 with high cost, high tensile ductility and reinforced by oiled PVA fibers. In practical applications, the determination of mix depends on the structural performance requirements.