Strain Hardening Cementitious Composites Research Articles

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.

Assessment of shrinkage and bond behaviour of high performance cement-based composites as a repair mortar

There is a need to develop innovative repair materials which can overcome the challenges of cement-based repair mortars being relatively prone to shrinkage effects. In practice, free shrinkage of repair mortar is often considered as an indicator for potential cracking and delamination of applied repair mortars due to restrained shrinkage effects. As it is hard to measure restrained shrinkage directly, a restraint factor (R) can be used to correlate both. This study investigates the shrinkage characteristics of strain-hardening cementitious composites (SHCC), making use of polyvinyl-alcohol (PVA), high-density poly-ethylene (HDPE), or short glass fibres, for the repair and strengthening of existing concrete structures. Along with drying shrinkage and autogenous shrinkage, restrained shrinkage has been characterized with respect to the concrete substrate. Furthermore, pull-off tests were performed to assess the bond properties of these repair mortars. The results show around 65% higher autogenous shrinkage in high strength SHCC mixes while there was a decrease in drying shrinkage compared to the reference mix. In contradiction to what was initially expected, an increase in fibre content from 1.5 to 2.0 vol% resulted in a significant increase in autogenous shrinkage, especially in the high strength SHCC mixes. The restraint factor for all repair mortars was determined and was found to be in the range of 0.82–0.94. The pull-off tests showed an overall excellent bond behaviour of all studied mortars.

A new fiber-bridging constitutive model for quantifying the matrix carbonation and fiber-to-matrix interface healing in PVA fiber-reinforced SHCC

Predicting fiber-bridging constitutive law is conducive to the rational design of strain-hardening cementitious composites (SHCCs). However, non-uniform carbonation along depths and fiber-to-matrix interface debonding and healing may significantly affect fiber-bridging behavior, which is seldom considered in current models. Therefore, a new micromechanics-based analytical model quantifying the carbonation-induced depth dependency and the healing-induced interfacial enhancement is developed. Particularly, to quantify the carbonation effect, the quantitative relationships between the interfacial properties (Gd, τ0, and β) and depth y are characterized by Fick’s Law of diffusion. To quantify the interface debonding and healing, the debonding crack lengths are calculated based on preloading level; new interfacial properties (Gd’, τ0′, and β’) are assigned to the debonded-and-healed interface segment; complex two-way fiber pullout scenarios during reloading are determined based on thorough classification. This new model is validated by the tensile test results of SHCCs with pristine and SiO2-coated PVA fibers under monotonic loading and reloading. The modeling results can reflect the multiple peculiar phenomena in SHCCs service, i.e., the overestimation of fiber-bridging strength of partially carbonated MgO cementitious matrix, the healing-induced fiber-bridging tensile strength enhancement, and the coating-induced higher PVA fiber-bridging recovery.

Enhancing Punching Shear Capacity of Flat Slabs with Hidden Capitals made of Strain Hardening Cementitious composite (SHCC)

Enhancing Punching Shear Capacity of Flat Slabs with Hidden Capitals made of Strain Hardening Cementitious composite (SHCC)

Ultra-thin Strain Hardening Cementitious Composite (SHCC) layer in reinforced concrete cover zone for crack width control

In the current study, experiments and numerical simulations were carried out to investigate the cracking behavior of reinforced concrete beams consisting of a very thin layer (i.e., 1 cm in thickness) of SHCC in the concrete cover, tension zone. A novel type of SHCC/concrete interface that features a weakened chemical adhesion but an enhanced mechanical interlock bonding was developed to facilitate the activation of SHCC. The study involved testing hybrid SHCC/concrete beams that have various types of interfaces. The results were compared to the control reinforced concrete beams that do not have SHCC in the cover. Four-point bending tests were performed with the beams and Digital Image Correlation (DIC) was utilized to track the development of crack pattern and crack width. Results show that hybrid beams possessed similar load bearing capacity but exhibited a significantly improved cracking behavior as compared to the control beam. With a 1-cm-thick layer of SHCC, the maximum crack width of the best performing hybrid beam exceeded 0.3 mm at 53.3 kN load, whereas in the control beam the largest crack exceeded 0.3 mm at 32.5 kN load. The hybrid beam with the proposed new interface formed 10 times more cracks in SHCC than the hybrid beam with a simple smooth interface and had an average crack width less than 0.1 mm throughout the loading. The lattice model has successfully showcased its ability to predict and offer valuable insights into the fracture behavior of hybrid systems. The simulation results indicate that the presence of a weak interface bond, coupled with mechanical interlocking, can effectively facilitate the activation of SHCC, resulting in the formation of more cracks and a delayed progression towards the maximum crack width. As the volume ratio of SHCC used in the hybrid beams is only 6%, the current study highlights the strategic use of minimum amount of SHCC in the critical region to efficiently enhance the performance of hybrid structures.

Lattice discrete particle modeling of the cycling behavior of strain-hardening cementitious composites with and without fiber reinforced polymer grid reinforcement

Strain-hardening cementitious composites (SHCC) has become increasingly prevalent in structural design. Compared to ordinary concrete, SHCC exhibits ultra-high tensile ductility, significant strain-hardening behavior, very fine multi-point cracking, high energy dissipation, and good durability. One robust model for simulating reinforced concrete behavior is the so-called Lattice Discrete Particle Model (LDPM), and specifically LDPM-F which includes the effect of fiber reinforcement. The present cycling constitutive law implemented in LDPM and the cycling fiber-bridging law in LDPM-F though cannot accurately capture the residual tensile plastic strain, loading–unloading path, and energy dissipation of SHCC during cyclic tension. To solve these concerns, the cycling tension–compression constitutive law and the nonlinear cycling fiber-bridging law were reformulated. Further, the new model was used to simulate the cycling tensile behavior of plain concrete, SHCC, and Fiber-Reinforced Polymer (FRP) grid reinforced SHCC (FRP-SHCC). Simulation results show that the multi-point cracking, crack widths, and ultra-high ductility properties are correctly captured by LDPM-F. In addition, LDPM-F with the modified cycling constitutive model can effectively simulate the cycling tension–compression behavior, accurately reproducing the stress–strain relationship, residual plastic strain, and overall dissipated energy. Finally, the simulated failure modes agree well with the actual fracture planes of these materials under cyclic tension.

Strain hardening geopolymer composites with hybrid POM and UHMWPE fibers: Analysis of static mechanical properties, economic benefits, and environmental impact

With unique ultra-high toughness, strain-hardening cementitious composite (SHCC) has attracted considerable attention. However, environmental and economic concerns have hindered its engineering application due to the high consumption of Portland cement and expensive high-performance fibers. To address this issue, geopolymer concrete and polyoxymethylene (POM) fibers are adopted to replace Portland cement and ultrahigh molecular weight polyethylene (UHMWPE) fibers, respectively, to prepare strain-hardening geopolymer composite with hybrid POM and UHMWPE fibers (POM/PE-SHGC). Static mechanical properties, economic benefits, and environmental impact of POM/PE-SHGC with different POM fiber replacement ratios are investigated. Axial compression and tensile tests on POM/PE-SHGC with different POM fiber replacement ratios (0%, 25%, 50%, 75%, 100%) are conducted to investigate the effect of different POM fiber replacement ratios on the static failure mode, tensile crack development, compression behavior, and strain-hardening behavior of POM/PE-SHGC. In addition, Carbon emissions and energy consumption of POM/PE-SHGC were estimated and compared with SHCC. An evaluation method that comprehensively considers environmental and economic benefits and mechanical properties is proposed. The results indicated that under the condition of a total fiber volume fraction of 2%, POM/PE-SHGC with a POM fiber replacement ratios under 75% exhibited good strain-hardening behavior. The compressive strength, ultimate compressive strain, and ultimate tensile strain of POM/PE-SHGC reached a maximum at a POM replacement ratios of 50%, except for a decrease in its tensile strength. Furthermore, the cost, carbon emissions and energy consumption of POM/PE-SHGC was significantly lower than that of SHCC. This study verified the feasibility of producing green, high-performance SHGC and promoted the engineering application of this material.

Novel application of Chilean natural pozzolan for sustainable strain-hardening cementitious composite

This study aims to develop a novel solution to improve the sustainability and resiliency of the infrastructure in Chile. Due to the country's unique geographic situation of the coastal environment and high seismicity, the key is to design a low-carbon strain-hardening cementitious composite (SHCC) by replacing ordinary portland cement (OPC) with an abundant Chilean natural pozzolan (NP). The results indicate that the optimal replacement level is 30%. The newly developed NP-based SHCC shows a tensile strength of 6 MPa, a tensile strain capacity of 2.5%, and micro-cracks of <100 µm. In addition, this study also quantifies the environmental impact of the NP-based SHCC using a ‘cradle-to-gate’ life-cycle analysis. By replacing OPC with the NP, the CO2 emission of NP-based SHCC reduces by 23%. The excellent tensile properties and cracking control suggest that NP-based SHCC could contribute to developing sustainable and resilient Chilean infrastructure.

Piezoresistive properties of strain-hardening cement composite with liquid-type multi-walled carbon nanotubes dispersed by ultrasonicator

Multi-walled carbon nanotubes (MWCNTs) are a new type of nanomaterial with superior performance. They are frequently used in cement matrices to increase electrical conductivity and as a sensor for monitoring the health of building structures. However, MWCNTs agglomerate easily and are difficult to disperse, which makes their homogeneous dispersion in the matrix material the focus of exploration. In this study, the dispersion method of MWCNTs in strain-hardening cement composites (SHCCs) with corresponding piezoresistance is investigated along with the effects of dispersed and nondispersed MWCNTs on the resistive sensitivity of the composites under monotonic loading. The experimental results indicate that MWCNTs in cement matrix composites can be effectively dispersed by applying ultrasonic energy. In addition, they can significantly increase the piezoresistive sensitivity of the composite.

Electrical Properties of Strain-Hardening Cement Composite (SHCC) with Multi-Walled Carbon Nanotubes Exposed to High temperature up to 900 °C

Cement-based sensors mixed with carbon nanotube (CNTs) for structural health monitoring were studied to detect changes in electrical resistance under the influence of temperature, pressure, and mass. Strain-hardening concrete composite mixed with CNT was heated to 900 °C to analyze the electrical resistance characteristics at high temperatures. The temperature and electrical resistance were measured using a thermocouple and an LCR meter during the heating and cooling processes. The resistance trend changed between 300 and 400 °C during the heating process, after which the resistance change rate with respect to temperature decreased. At 700 °C or higher, the resistance became larger as the initial resistance increases. In the cooling process, when the temperature dropped below 700 °C, a rapid change in resistance was observed, and the resistance began to drop sharply between 500 °C and 600 °C to become negative resistance. Following this, self-sensing ability decreased owing to changes in the resistance with respect to temperature. Multi-walled carbon nanotubes could not be distinguished by scanning electron microscope imaging after heating.

Electromagnetic interference shielding effectiveness of multi-cracked strain-hardening cementitious composites (SHCC)

Electromagnetic interference shielding effectiveness of multi-cracked strain-hardening cementitious composites (SHCC)

Shear-bond behavior of nanocellulose-modified SHCC composite slabs: Translating material-level capacity into improved structural performance

Owing to their exceptional tensile properties, strain-hardening cementitious composites (SHCC) are indispensable for building and maintaining sustainable and resilient civil infrastructure. As such, to propel the structural implementation of SHCC, it is critical that their intriguing tensile characteristics be effectively translated into improved structural performance. Herein, we capitalize on the intrinsic pseudo-ductility of a novel SHCC—incorporating nanocellulose fibers and post-consumption glass powder (hereafter referred to as “nSHCC-GP”)—to mitigate shear-bond failure caused by the relative slip between steel and concrete in composite deck slabs. Twelve full-scale composite deck slabs, six with conventional high-performance concrete (HPC) incorporating steel mesh and six steel-mesh-free nSHCC-GP slabs, were subjected to monotonic bending. With the concrete for both slab sets designed for similar compressive strengths, the influence of concrete type (HPC or nSHCC-GP), decking profile (trapezoidal or reentrant), and shear span (520–770 mm) on the flexural capacity and shear-bond resistance was examined. The use of nSHCC-GP as a concrete topping improved the flexural capacity of composite slabs by >50 % and the shear-bond resistance by up to 40 %. Thus, the strain-hardening characteristics of nSHCC-GP were effectively translated into the structural scale, providing steel-mesh-free, high-performance composite deck slabs.

A novel strategy to assess healing induced recovery of mechanical properties(HIRMP) of strain hardening/engineering cementitious composites(SHCCs/ECCs) in autogenous healing

The crack-bridging effect of fibers in strain-hardening cementitious composites (SHCCs) restricts the crack width to a very small value, which promotes autogenous self-healing. The healing should lead to a noticeable recovery of mechanical properties. To ensure healing-induced recovery of mechanical properties (HIRMP) is relied upon in the built environment, a novel strategy for in-situ assessment of HIRMP is developed. HIRMP causes the stress-strain response of healed specimen to be ‘close’ to that of the pre-damaged state. It was derived that the ratio of areas(ROA) under the stress-strain response between ‘healed’ and ‘undamaged’ state appropriately measures the ‘closeness’ between these stress-strain curves. Exploiting the fact, acoustic emission (AE) signals are associated with fracture energy (thus also with the area under stress-strain curve). We design novel damage parameters to statistically represent random-stochastic fracture processes in self-healed SHCCs. The ratio of these parameters was then utilized to estimate HIRMP. This strategy was then studied experimentally on self-healed SHCCs with a different healing environment, fiber content, and pre-damage level. The results computed from this strategy are more consistent and comprehensive as compared to the conventional technique. The predicted HIRMP matches well with the expectation over a long range of recoveries.

Development of novel self-healing strain-hardening cementitious composites (SH2CC) for dynamic cyclic loading conditions using mineral and polymer admixtures

Dynamic cyclic loading commonly encountered in engineering practice can pose great threat to the integrity and durability of concrete infrastructures. Ductile materials with enhanced self-healing performance could provide a promising solution under such conditions. This study proposes and investigates, for the first time, as self-healing SHCC (SH2CC) for dynamic reversed-cyclic (DRC) applications through incorporating a mineral substitute (MS) comprising of reactive MgO and quicklime and triethanolamine (TEA) additive in a high-volume-fly-ash matrix. Different DRC preloads were considered. Results indicated that applying 5% MS combined with 1.5% TEA additive showed optimal crack width control below 12 μm under up to 5 cycles of DRC preloading and the highest potential for mechanical strengthening of modulus of rupture, first cracking strength and flexural stiffness reaching up to 160%, 137% and 210% respectively after healing. Moreover the highest crack sealing efficiency was observed up to 88% under 14d water immersion. Microstructural analysis revealed that MS produced additional hydrates and promoted more carbonates to form in cracks during healing, while TEA effectively paused hydration under air curing but resumed the process upon water contact for massively enhancing crack healing (especially mechanical strengthening). Combining MS and TEA in SH2CC produced complementary healing products both in cracks and fibre-matrix interfaces indicating better filling and bridging of the cracks and demonstrating great potential for enhancing healing performance under aggressive loading conditions.

Enhancing the behavior of R.C. Continuous-Defected Slabs Using Strain-Hardening Cementitious Composites (SHCC)

Enhancing the behavior of R.C. Continuous-Defected Slabs Using Strain-Hardening Cementitious Composites (SHCC)

Predicting the life cycle durability and ecological performance of cementitious coatings with a fuzzy‐stochastics–based approach

AbstractCementitious coating effectively prevents chloride‐induced corrosion in offshore reinforced concrete (RC) structures. Strain hardening cementitious composites (SHCC) is a class of advanced cementitious composites with superior ductility and durability. Due to the lack of long‐term test data, the current probability‐based design guidelines may not be applicable to SHCC coating. This paper develops a fuzzy‐stochastic–based approach to assess the durability performance of coatings using cement mortar and engineered cementitious composites (ECC), a specific type of SHCC. The age factor and the mean of chloride diffusion coefficient are modeled as fuzzy variables, and the chloride diffusion coefficient follows Gaussian distribution. Based on limited test data and subjective opinion, membership functions are proposed for the mean of initial chloride diffusion coefficient and the age factor of cement and ECC. To achieve equivalent durability performance of cement mortar coating, the amount of uncracked and cracked ECC coating are estimated to be around 33% and 25%, respectively. Based on equivalent durability performance, life cycle assessment (LCA) is conducted to compare the ecological performance of the two coatings. A case study, based on a 25‐m‐long simply supported box girder in Shenzhen Bay, is given to elaborate the proposed approach and the evaluation results of durability performance and ecological impacts.

Fiber orientation distribution in strain hardening cementitious composites (SHCC): Experimental investigation and consideration of processing effect

Tensile performance of strain hardening cementitious composites (SHCC) is determined from uniaxial tensile specimens, in which the fiber orientation can vary with sample size and processing method. However, when interpreting the laboratory-determined tensile behaviors, synthetic fibers in SHCC are usually assumed to be randomly oriented without experimental validation. In this study, an automatic image processing workflow for obtaining accurate fiber orientation distribution over a whole section is proposed. The experimentally obtained fiber orientation distributions in PVA-SHCC tensile samples form a clear peak at around 20 degrees relative to the tensile direction, which is not revealed by any existing model on fiber distribution. A modified fiber orientation analysis considering the sample processing effect (flattening effect) is presented to derive the distribution, with parameters obtained by computational fluid dynamics simulations. The measured or derived orientation distribution can be used to replace random distributions in fiber bridging models to reduce systematic simulation errors.

A novel seismic strengthening method for RC frames: Precast ultra-high performance concrete braces

A novel bracing method to strengthen the seismic behavior of reinforced concrete (RC) frames was developed in the study. The brace was made using steel reinforced ultra-high performance concrete (UHPC). UHPC is a class of tensile strain-hardening cementitious composites and has ultra-high compressive strength of greater than 120 MPa. To utilize the capacity of the UHPC brace prior to the onset of major inelastic response of the RC frame, a design method for the UHPC brace was established. In the developed strengthening method, the in-situ construction process was simplified by conveniently installing the precast UHPC brace using the UHPC connections that was constructed in-situ to link the UHPC brace to the frame. The performance of the UHPC bracing method was evaluated using cyclic loading tests on two frame specimens, i.e., a bare RC frame and a UHPC brace-strengthened RC frame. The test results showed that the UHPC brace effectively enhanced the initial stiffness, peak strength, and energy dissipation capacity of the original frame. Moreover, it successfully preserved the capacity of the columns when the UHPC brace was active without magnifying the shear demand in the columns. As a result, the strengthening method allowed the original columns to utilize their full force resisting capacity after the capacity of the UHPC brace was depleted. In addition to the experimental study, an analytical model, which was derived based on equilibrium, compatibility, and suitable material constitutive laws, was developed to reasonably evaluate the load-displacement response of RC frames strengthened with UHPC braces.

In-situ microtomography image segmentation for characterizing strain-hardening cementitious composites under tension using machine learning

The application of machine learning and computer vision in microtomography provides new opportunities to directly analyze the microstructural evolutions of strain-hardening cementitious composites (SHCC) under tensile load, especially the strain-hardening process. For the first time, a state-of-the-art machine-learning pipeline combined with digital volume correlation for automated microtomography segmentation analysis (MSA) was developed to separate different components and quantify the in-situ 3D morphological properties of the fibers and pore networks imaged with in-situ synchrotron X-ray computed microtomography. Strain localization and crack initiation were observed around the interconnected pores where strain localized instead of the weakest cross-section defined by the fiber distribution and porosity. Fibers reinforced the crack planes through fiber debonding, bridging, bending, stretching, and orientation redistribution, which contributed to the crack width control and ductility of SHCC in the experiment. This work is essential to understand the progressive damage mechanisms of SHCC and help refine the characterization, modeling, and design of the composite using a bottom-up approach.

Effects of fiber volume fraction, fiber length, water-binder ratio, and nanoclay addition on the 3D printability of strain-hardening cementitious composites (SHCC)

Strain-Hardening Cementitious Composites (SHCC) exhibit superior mechanical performance and show potential in 3D printing applications. However, the formation of fiber agglomerates causes significant challenges during pumping and 3D printing. This study explores the 3D printability of SHCC, using a progressive cavity pump. Various situations are found: Some SHCC mixtures could be 3D printed smoothly with a continuous and non-fractured filament; Some show fractured filaments; Some cause the pump automatically stopped. For these failed extrusion cases, fiber agglomerates are found in the nozzle resulting in fractured filaments, or in the pump screw resulting in automatic cessation of the pump. Effects of fiber volume fraction, fiber length, water-binder ratio, and nanoclay addition on the 3D printability of SHCC are explored. Analysis based on the contact percolation packing fraction of flexible fibers is performed to explore the formation of fiber agglomerates and its impact on 3D printability. The significance of fiber deflection is also highlighted.