Strain Hardening Cementitious Composite Material Research Articles

Ductility Variation and Improvement of Strain-Hardening Cementitious Composites in Structural Utilization.

Strain-hardening cementitious composite (SHCC) has the obvious advantages of excellent material properties such as its high tensile and compressive strengths, high tensile strain capacity, and excellent durability against multi-cracking performance with very fine crack widths. In particular, the multi-cracking performance of SHCC during structural utilization is obviously reduced compared to that of SHCC in uniaxial tension tests using dumbbell-shaped specimens of small size. The corresponding tensile strain capacity of SHCC during structural utilization is, thus, significantly decreased compared to that of SHCC in uniaxial tension tests. However, the reduction in the ductility of SHCC during structural utilization has not been sufficiently understood, and further study is required. This paper presents an experimental investigation into the ductility variation of flexural-failed and shear-failed SHCC members as well as the ductility improvement of SHCC members with steel reinforcement compared with that of SHCC in uniaxial tension tests using small-sized specimens. This study focuses on not only the decrease in the crack elongation performance of the SHCC material during structural utilization but also the increase in the crack elongation performance of SHCC members with steel reinforcement. The results demonstrate that the crack elongation performance of flexural-failed and shear-failed SHCC members is significantly reduced compared to that of SHCC in the uniaxial tension tests. Moreover, it was confirmed that steel reinforcement can effectively improve the SHCC member, increasing the strain-hardening capacity and multi-cracking performance. The load-carrying capacity of the flexural-failed SHCC member with steel reinforcement seemed to increase linearly with an increase in the reinforcement ratio, accompanied by an increase in the distribution of multiple fine cracks in the flexural-failed SHCC member with steel reinforcement.

Strain-hardening cementitious composites ultra-thin whitetopping (SHCC-PUTW) for rapid asphalt pavement rehabilitation

Whitetopping is the concrete overlay used to upgrade distressed asphalt road surface, where the distressed asphalt is milled off and concrete is cast on top as the new wearing course. However, it requires road closure for multiple days, which is not accepted in many urban constructions. Precast concrete pavement (PCP) is the technology that shortens the construction period. However, it is associated with complicated construction procedures due to the brittleness of conventional concrete. In this paper, a brand-new PCP design, i.e., ultra-thin whitetopping (PUTW) is studied and applied in a demonstration project in Singapore. The PUTW is enabled by employing strain-hardening cementitious composites (SHCC) with significantly higher ductility than conventional concrete. The current work includes four parts. First, the desirable combinations of SHCC’s tensile and compressive uniaxial behaviors are identified in the analytical model and experimental study to enhance its flexural strength for pavement application. Second, the slab-to-slab joint efficiency in the PUTW, the critical mechanism in the structural design, is examined and validated with a full-scale cyclic wheel test. Third, the structural performance of the entire SHCC-PUTW is examined in a new finite element (FE) model validated against the wheel test. Based on the FE model, parametric studies on the SHCC material properties and PUTW slab dimensions are conducted to optimize the structural design. Fourth, a small-scale field project on the Jurong Island of Singapore, which involves the fabrication and installation of 11 SHCC-PUTW slabs, is reported to assess the feasibility of this new structural design.

Performance Review of Strain-Hardening Cementitious Composites in Structural Applications.

Strain-hardening cementitious composites (SHCC) are an attractive construction material with obvious advantages of large strain capacity and high strength, as well as excellent workability and easy processing using conventional equipment. Moreover, SHCC can be designed with varied mix proportions in order to satisfy various requirements and expectations to overcome the shortages of existing construction materials. However, the behavior of SHCC in the structural application is varied from that of SHCC material, which is reviewed and presented in this paper, focusing on the flexural and shear behavior of the SHCC member and the SHCC layer used for strengthening reinforced concrete (RC). The reviewed results demonstrate that both the zero-span tensile behavior of the stress concentration and the uniaxial tensile behavior of the bending effect can influence the crack propagation patterns of multiple fine cracks in the SHCC strengthening layer, in which the crack distribution within the SHCC layer is limited near the existing crack in the RC substrate member in the zero-span tensile behavior. Moreover, the crack propagation patterns of the SHCC strengthening layer are changed with varied layer thicknesses, and the SHCC strengthening layer, even with a small thickness, can significantly increase the shear load carrying capacity of the shear strengthened RC member. This work provides the foundations for promoting SHCC material in the structural application of repairing or retrofitting concrete structures.

A Unified Model for Fibers With Divergent Pullout Behaviors in Strain Hardening Cementitious Composites (SHCC)

Strain Hardening Cementitious Composites (SHCC) are materials exhibiting high tensile ductility with the formation of multiple cracks. Since the mechanical properties of SHCC members are governed by the interfacial characteristics between fibers and matrix, understanding the mechanism of single fiber pullout behavior is crucial for SHCC material design. Existing model was set up based on Polyvinyl Alcohol (PVA) fibers, making it inapplicable to other kinds of synthetic fibers those exhibit divergent pullout behaviors. As a result, the simulated curves cannot agree well with the tested results of SHCC made with other fibers or hybrid fibers. In this study, a unified single fiber pullout model was proposed to take divergent kinds of fiber pullout behavior into account. Five parameters were defined to describe the single fiber pullout behavior, where the frictional strength during the pullout stage and the blocking length of fiber under pulley force were for the first time introduced. For verification purpose, fiber-pullout samples with Polyethylene terephthalate (PET) and PVA fibers were tested and the results agree well with the simulated curves from proposed model. The stochasticity of each parameters were then analyzed and described by normal distribution, through which fibers with various random pullout behaviors can be incorporated into a larger scale modelling. Therefore, the fiber-bridging constitutive law for a single crack was calculated and compared with the single crack test results, which confirmed again the validity of the proposed model.

Retrofitting of shear-damaged RC T-beams using U-shaped SHCC jacket

Strengthening of Reinforced Concrete (RC) beams using Strain-Hardening Cementitious Composites (SHCC) material became a worldwide practice. Previous investigations showed significant improvement in the shear resistance of SHCC-strengthened (undamaged) beams. However, a little effort has been devoted to study the ability of SHCC material in retrofitting shear-damaged RC beams. Thus, the current study aims to evaluate the shear response of shear-damaged RC beams repaired with SHCC material. In this context, eleven RC beams were prepared and configured to be failed in shear. One beam was considered as control specimen; while, four beams were strengthened with 20 mm thick U-shaped SHCC jackets having four different transversal reinforcement ratios (0, 0.65, 0.86 and 1.08%). The remaining six beams were pre-cracked (preloaded) with three different preloading levels (0.75, 0.85 and 0.95% of the ultimate capacity), then, three differently preloaded beams were repaired with SHCC jackets, whereas, for the remaining three beams, the developed shear cracks were injected by epoxy prior to the application of SHCC jackets. All beams were tested under four point loading scheme with shear span-to-depth ratio of 2.5. The test results showed that the strength, post-peak deformability and shear-crack response of the repaired beams were improved compared to those of the control beams. In addition, the use of epoxy injection prior to the application of the SHCC jacket showed its ability to restore a significant value of the lost strength gain due to preloading. However, the repairing technique was not able to restore the initial stiffness of the uncracked beams. Finally, based on analytical analysis, the design equations of JSCE code underestimated the ultimate shear capacity of the strengthened/repaired beams with average safety margin of about 27%.

Strengthening of shear-deficient RC beams using near surface embedded precast cement-based composite plates (PCBCPs)

Precast cement-based composite plates (PCBCPs) have been prepared, cured and then used to strengthen shear-deficient reinforced concrete (RC) beams. The used PCBCPs have rectangular cross-sections of 100 mm width and 20 mm thickness made of strain-hardening cementitious composite (SHCC) material and reinforced with mild steel plates of 1 mm thickness having variant reinforcement ratios (1.4, 2.8, and 4.2%). The motivation of using such reinforced composite plates is to make use of the mutual benefits between the used materials where the internal steel plate alleviates the cracks localization manifested by plain SHCC material after cracking, while the SHCC material protects the steel plates against corrosion. Experimental test results showed that the use of PCBCPs significantly increased the ultimate shear capacity of the strengthened beams. Besides, inclined configuration of the PCBCPs showed higher shear performance compared to that exhibited by the vertical configuration from both the ultimate capacity and shear cracks characteristics viewpoints. Beam B3-56-100-45 strengthened by inclined PCBCPs showed the best performance among all tested beams. It exhibited about 126% increases in the ultimate capacity compared to that of the control un-strengthened beam. On the other hand, the corresponding increase of counterpart beam reinforced with vertical plates was about 88%.

Tensile Performance of SHCC Road-Bridge Link Slabs in Fully Jointless Bridges

Deformation of the main girder is absorbed by a continuously reinforced concrete pavement (CRCP) with microcracks in fully jointless bridges. The conventional fully jointless bridge has been challenged by durability and reliability issues because the CRCP is vulnerable to crack and hard to control the crack width when it suffers temperature variation. In this paper, a new type of fully jointless bridge with the road-bridge link slabs using strain-hardening cementitious composite (SHCC) material is investigated. First, an experiment was carried out to study the material properties of SHCC material for a preliminary assessment of road-bridge link slab performance using this material. Results found that SHCC is adequate for link slabs for its high tensile ductility and fine cracks development. Second, an SHCC slab model tensile test was carried out to study the absorptive capacity and the crack distribution of the SHCC slab. Results verified the high absorptive deformation capacity of the SHCC slabs. When the longitudinal deformation reaches 10 mm, the surface cracks in the SHCC slab are fine and dense, the crack width is kept in 80 μm, and the internal force is small. Third, by comparing the tensile test results with a conventional CRCP slab with same length, it is found that an SHCC slab has higher absorption capacity, better crack distribution, and smaller internal force than a CRCP slab. Finally, through ABAQUS finite element modelling, the stress performance of SHCC road-bridge link slabs is simulated using a trilinear constitutive model. The calculated results are consistent with the experimental results.

Experimentally based parameters applied to concrete damage plasticity model for strain hardening cementitious composite in sandwich pipes

Sandwich pipes (SPs) composed of two concentrically steel tubes with a strain hardening cementitious composite (SHCC) filling core is a new concept designed for oil and gas transportation in deep waters. In this concept, the SHCC core is the most critical component that should withstand the combined loading of high hydrostatic pressure and bending moment. This paper proposes a particular concrete damage plasticity (CDP) model for the SHCC core based both on experimental data and on the continuum damage mechanics theory. The basic fundamentals of the CDP model can be divided into three major issues, namely, damage evolution, yield criterion, and plastic flow rule. For the damage evolution, two models of damage variables, under tension and compression, respectively, were built based on uniaxial experimental data available and the fracture energy theory. For the yield criterion, the parameters for the Lubliner model were fitted according to available experimental data from uniaxial and biaxial compressive tests. For the plastic flow rule, the dilation angle was deduced from the results of triaxial compressive tests combined with the Drucker-Prager type plastic flow rule. Finally, four-point bending tests were carried out on SHCC specimens and collapse tests were conducted on SP models to allow a correlation study between experimental data and results obtained from numerical simulations incorporating the proposed CDP model. The correlation between numerical and experimental results showed good agreement, demonstrating that the proposed CDP model can accurately reproduce the mechanical behavior and damage distribution experienced by an SHCC material.

Scaling up modeling of Strain-Hardening Cementitious Composites based on beam theory: From single fiber to composite

The behavior of Strain-Hardening Cementitious Composites (SHCC) is often studied at different scales, from single fiber to single crack and further to the composite material. Establishing a model that can link SHCC behavior at different scales is crucial for the design of SHCC through the proper selection or tuning of properties at the microscale. In this paper, the entire scaling up modeling process is presented. Different from existing models that treat the fibers as strings, the fundamental of the model in this study is to treat the fibers as beams so their bending stiffness is taken into account. To verify the model directly, experiments for SHCC were conducted at various scales. Meanwhile, a novel digital image processing method was developed to extract the opening of a single crack from photographs taken during testing. Through the comparison, the ‘beam’ model was found to give a better prediction for SHCC material.

Punching shear resistance of strengthened reinforced concrete interior slab–column connections using ultra-high-performance strain-hardening cementitious composite material

The main target of this article is to find out the most applicable strengthening technique to change the brittle punching shear failure of slab–column connection to a ductile one. The considered strengthening technique uses the combined effect of the internal single-leg stirrups and a thin layer of ultra-high-performance strain hardening cementitious composite material provided in either tension or compression side. Thus, 12 slab specimens divided into four groups were prepared and configured. It was found that the slab provided with properly anchored single-leg stirrups with a cross-shaped thin layer of ultra-high-performance strain hardening cementitious composite material at the compression side proved the most efficient technique among all the considered configurations. This technique enabled the slab to sustain a punching load of about 2.38 times that of the control unstrengthened slab. In addition, it exhibited ductile failure showing strain hardening and softening plateaus. Finally, the experimental shear resistances of all the strengthened slabs were compared against the design resistances stipulated by different design standards such as the ECP 203-2007, ACI 318-14, DIN 1045-1, and EC2-2004 codes. It can be concluded that the failure characteristics stipulated by the DIN 1045-1 code showed the most rational results compared with those of the experimental findings.

Study of steel corrosion in strain-hardening cementitious composites (SHCC) via electrochemical techniques

This paper investigates corrosion of steel bar in reinforced strain-hardening cementitious composites (R/SHCC) through electrochemical techniques. Linear polarization resistance is engaged to determine corrosion rate of steel bar while electrochemical impedance spectroscopy is employed to study corrosion kinetics by probing the electrode and interface reactions. An equivalent circuit model is used to quantitatively interpret the impedance data of steel corrosion. Results show that polarization resistance Rp of R/SHCC is much higher than that of R/M and thus corrosion rate of steel bar in R/SHCC is much reduced. The Rp of R/SHCC is about two orders of magnitude higher while the corrosion rate of R/SHCC can be two orders of magnitude lower than that of R/M after 137 h accelerated corrosion. Rp of specimen is dominated by the charge transfer resistance Rct before cover cracking and governed by both Rct and cover resistance Rc after cover cracking. R/SHCC specimen possesses a much higher Rct and Rc than R/M due to high tensile ductility and damage tolerance of SHCC material together with tight crack with in SHCC cover.

Shear strengthening of damaged reinforced concrete beams with Hybrid Composite Plates

This paper aims to evaluate experimentally the potentialities of Hybrid Composite Plates (HCPs) technique for the shear strengthening and repairing of reinforced concrete (RC) beams. HCP is a thin plate of Strain Hardening Cementitious Composite (SHCC) reinforced with Carbon Fiber Reinforced Polymer (CFRP) laminates. For this purpose, an experimental program composed of four Rectangular and five T-cross section beams was executed to assess the strengthening efficiency of HCPs technique. There were two control beams without any type of shear reinforcement, and seven beams strengthened with HCPs. The HCPs were applied to the lateral faces of the beams by using a combination of epoxy adhesive and mechanical anchors. The bolts were applied with a certain torque in order to increase the concrete confinement. To have a better understanding of the shear behavior of SHCC material, Iosipescu shear tests were carried out, and the results were used to derive their fracture mode II parameters.To further explore the potentialities of the HCPs technique for the shear strengthening, the experimental tests were simulated numerically by a FEM-based computer program considering the material properties obtained experimentally. After demonstration of the good predictive performance of the numerical model, a parametric study was executed to investigate the influence of some parameters on the load carrying capacity of the strengthened beams, namely: i) Use a mortar instead of the SHCC; ii) application of different applied torque level to the mechanical anchors; iii) different bond condition between HCPs and concrete substrate.

Cyclic constitutive model for strain-hardening cementitious composites

A uniaxial cyclic constitutive model for strain-hardening cementitious composites (SHCCs) is proposed based on the response of the material at the stress–strain level under different loading regimes. The ascending branch of the compressive envelope curve was developed using the form of a parabolic curve, while the descending branch adopted the bilinear form. The full tensile stress–strain curve was approximately simulated by a trilinear form comprising ascending, strain-hardening and descending branches. Using the method of setting a reference point, the characteristics of the unloading and reloading process were determined, with consideration of the partial unloading–reloading scheme. Furthermore, the transition between tension and compression was taken into account in the model development. The proposed cyclic constitutive model was coded into the OpenSees platform and applied to simulate the responses of specimens at material and member levels. The simulation results indicate that the proposed model is reasonably accurate in simulating the mechanical properties of SHCC material and the cyclic behaviour of SHCC flexural elements.

Shear Properties of the Strain Hardening Cementitious Composite Material

AbstractRecently, strain hardening cementitious composite (SHCC) material has been used for the shear strengthening and the structural rehabilitation of reinforced concrete structures. However, the shear behavior of this material has not been yet fully understood due to lack of an appropriate and accurate direct shear test method. This paper aims to investigate the shear properties of the SHCC material. For this purpose, Iosipescu shear test was selected, where loads are applied in antisymmetric four-point bending, assuring a pure shear section at the center of the specimen. A special geometry for the specimen was adopted in order to assure a uniform shear stress distribution in the pure shear section. This experimental test can characterize the shear behavior of SHCC material. The experimental test was simulated by the finite element method (FEM)-based computer program, FEMIX. To predict the average shear stress–sliding response, the shear crack softening diagram, available in the multidirectional fixed ...

수축저감제의 종류 및 혼입률에 따른 변형경화형 시멘트복합체의 역학적 특성

본 연구는 두 종류의 수축저감제를 혼입한 변형경화형 시멘트 복합체(SHCC)의 압축, 인장 및 휨 특성을 평가하기 위하여 계획되었으며, 재령과 수축저감제의 종류 및 혼입률을 변수로 진행되었다. SHCC는 설계기준압축강도 50 MPa이며, 섬유는 PVA 섬유를 2.2% 혼입하였다. 배합에 혼입된 수축저감제는 상변이 물질로 수화현상으로 발생되는 열을 흡수 또는 방출하여 급격한 수축 및 팽창을 제어하는 물질이다. 수축저감제의 혼입에 대한 영향은 선변형 길이변화 실험과 압축, 인장 및 휨 성능의 측면에서 평가되었으며, 수축저감제를 혼입할 경우 초기 재령에서의 수축량이 감소되었다. 또한 수축저감제를 혼입함에 따라 균열 분산 성능과 인장 및 휨 성능이 개선되었다.

고강도 철근과 변형경화형 시멘트복합체를 사용한 보의 균열거동 및 휨 성능

This paper describes the effect of strain hardening cement composite (SHCC) material on structure performance of reinforced concrete (RC) beams with high-strength reinforcing bar. Also, this paper explores the structure application of SHCC in order to mitigation cracking damage and improve the ductility of flexural RC members. The prediction model for flexural strength of doubly reinforced SHCC beams are investigated in this study. To achieve the these objectives, a total of 6 rectangular beam specimens were tested under four point monotonic loading condition. The main parameters included the types of cement composite and reinforcing bar. Test results indicated that reinforced beam specimens with SHCC material were improved the structure performances and damage characteristics. Specifically, replacement of conventional high-strength concrete with SHCC materials has the potential of high-strength steel bar as flexural reinforcement on RC members. It is remarkable that suggested method of reinforced SHCC beams with high-strength reinforcing bar could be used usefully to the structure design.

Tensile and Cracking Behaviors of Strain-Hardening Cement Composite (SHCC) with Fluosilicate Based Shrinkage-Reducing Agent (SRA)

This paper provides the results of direct tensile tests for strain-hardening cement composite (SHCC) to investigate the influence of fluosilicate based shrinkage-reducing agent (SRA) on the tensile and cracking behaviors of SHCC material under direct tension. The specified compressive strength of the SHCC material is 50MPa. The adding ratio of fluosilicate based SRA for SHCC material is 2.5 and 5.0%. Two mixitures of SHCC with 2.2% polyvinyl alcohol (PVA) fibers at the volume fraction were mixed; two mixtures with SRA and one mixture of conventional SHCC material. To evaluate the tensile and cracking behaviors of SHCC materials, two dumbbell-shaped tensile specimens for each mixture were manufactured and tested in direct tension. Test results show that the addition of fluosilicate based SRA improved direct tensile and cracking behaviors of SHCC materials with rich mixture. This phenomenon is noticeable for SHCC with higher volume of SRA.

Effects of Shrinkage Reducing Admixture (SRA) on the Tensile Behavior of Strain-Hardening Cement Composite (SHCC)

This research investigates the influence of shrinkage reducing admixture (SRA) on the tensile behavior of strain-hardening cement composite (SHCC). SHCC materials with specified compressive strength of 50MPa were mixed and tested. All SHCC mixes with different dosage of shrinkage reducing admixtures were reinforced with 2.2 % polyvinyl alcohol (PVA) fibers at the volume fraction. A special SRA, i.e. strontium (Sr)-based SRA, used in this study was based on a phase change material (PCM) that has the ability to absorb or release the hydration heat of cement composite. This paper focuses on the tensile behavior and cracking characteristics of SHCC materials under direct tension. The effect of a special SRA on the fresh properties, such as flow and air content, and hardened properties of SHCC materials was investigated. Test results showed that SRA reduces the air content of SHCC material. The SRA can also improve the tensile strength of SHCC material.

Influence of Shrinkage Compensation in Cement Matrix on the Tension Stiffening of Reinforced Strain-Hardening Cement Composite (SHCC) Tension Ties

This paper investigates the interaction of structural deformed bar reinforcement and strain hardening cement composite (SHCC). The SHCC shows excellent mechanical properties such as multiple cracks and strain-hardening. Generally, SHCC material consists of cement, silica sand and fibers and is rich mixture without aggregate. Rich mixture leads to much shrinkage strain of SHCC material. In this research, the replacement of a part of cement by expansive admixture (EXA) is considered as an alternative to compensate the shrinkage strain of SHCC material. This paper presents the experimental results of tests on tension stiffening and cracking behavior of reinforced conventional and shrinkage-compensating SHCC ties in monotonic and cyclic tension. Each tie specimen had a square cross-section dimension of 100 x 100mm and length of 1,500mm. A 16mm diameter deformed bar was embedded centrally and mixed with 1.5% hybrid fibers composed of Polyethylene(PE) and Steel core(SC). The test results indicated that the shrinkage compensation of cement matrix in SHCC improve the tension stiffening and cracking behavior of reinforced SHCC ties in monotonic and cyclic tension loading.

Effect of Cement Composite’s Ductility on the Flexural and Cracking Behavior of Reinforced Cement Composite Beams

Abstract. Fiber-reinforced strain-hardening cement composite (SHCC) shows multiple cracking, higher tensile strain capacity and tensile strength than conventional concrete and fiber-reinforced cement composite (FRCC). These characteristics of SHCC materials improve crack-damage mitigation. Current application of SHCC materials includes bridge decks, building dampers, retaining wall, and irrigation channels. During SHCC’s hardening, higher shrinkage occurred because SHCC’s mixture is richer than conventional cement composite. In this study, an expansive admixture was utilized for SHCC mixture to control the shrinkage of SHCC materials. The objective of the study is to investigate the effect of cement composite’s ductility and shrinkage on the flexural and cracking behaviors of reinforced cement composite beams. Test result indicates that cement matrix’s ductility has a significant effect on the flexural and cracking behavior of reinforced cement composite beams and the phenomenon is remarkable for a beam with shrinkage-compensating SHCC replaced a part of cement by expansive admixture.