High-performance Fiber-reinforced Cementitious Composites Research Articles

Mechanical Characteristics of Self-Healing, Deflection-Hardening, High-Performance Fiber-Reinforced Cementitious Composites Using Coarse Aggregates

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Cyclic behavior of high-performance fiber-reinforced cementitious composite corner joints

In moment frames, beam-column joints are critical elements that ensure the structural integrity of the frames. During earthquakes, beam-column joints can withstand large shear forces transmitted from nearby columns and beams. In old reinforced-concrete (RC) moment frame buildings, beam-column joints had little joint transverse reinforcement, which are susceptible to significant damage during large earthquakes. Their corner joints could experience a more severe seismic loading environment than other joints because they are subjected to bidirectional lateral loadings during earthquakes. The objective of this study was to improve the cyclic behavior of corner joints by using high-performance fiber-reinforced cementitious composite (HPFRCC). For this purpose, seven corner joint specimens were made and tested under unidirectional and bidirectional cyclic loadings. The application of HPFRCC improved the cyclic behavior of corner joint specimens. The contribution of HPFRCC outweighed that of the minimum joint transverse reinforcement. The minimum joint transverse reinforcement moderately affected the cyclic behavior of the specimens. The shear strength and drift capacity of unidirectional HPFRCC specimen without the joint transverse reinforcement had 13% and 24% larger than those of unidirectional RC specimens with the joint transverse reinforcement, respectively. Similar observations were made for bidirectional specimens. Particularly, the failure mode of the specimens was changed by using HPFRCC from brittle joint shear failure and axial failure to beam flexural failure followed by joint shear failure.

Impact of fiber distribution and cyclic loading on the bond behavior of steel-reinforced UHPC

Ultra-high performance concrete (UHPC) is a class of concrete materials that exhibits high compressive strength (over 150 MPa) and is seeing increasing applications around the world. Current reinforced UHPC (R/UHPC) bond studies mostly adopt non-flexural setups, i.e., pull-out tests and tension-lap-splice tests. The bond behavior of R/UHPC in flexure remains largely unknown, which is a fundamental aspect of designing R/UHPC flexural elements. Additionally, the impact of fiber distribution and cyclic loading on R/UHPC bond is little understood, which is important for guiding the casting and design of R/UHPC structures especially in earthquake zones. This study experimentally investigates the impact of fiber volume, cast flow direction, and cyclic loading on R/UHPC bond behavior under a simulated flexural stress state. Results from twenty-five beam-end tests are discussed. Specimens cast with flow perpendicular to the bar exhibited a 9%–26% higher bond strength than specimens cast with the flow parallel to the bar due to the resulting higher fiber-bridging capacity across the splitting crack plane. Compared to the monotonically-loaded specimens, cyclic loading minimally impacts R/UHPC bond strength and accelerates bond-degradation after bond softening occurs. Current R/UHPC bond strength prediction methods are evaluated on the test results from this study and the literature. An energy-based R/UHPC bond-slip model is developed. This model captures the cyclic bond degradation of R/UHPC and other types of high-performance fiber-reinforced cementitious composites (HPFRCC) with a mean absolute error under 13%.

Damage characteristics of high-performance fiber-reinforced cement composites panels subjected to projectile impact

The authors examined both experimental and numerical studies on the structural response of high-performance fiber-reinforced cement composite (HPFRCC) panels with a matrix strength of 180 MPa and a high fiber content from 1.0 to 3.0% subjected to projectile impact. The failure mechanism, such as penetration and scabbing, of HPFRCC panels was experimentally investigated according to volume fractions, the thickness of specimens, and impact velocities. The effect of fiber volume fraction and thickness on the compressive and tensile performance of HPFRCCs was also assessed through a comparison with empirical equations. In addition, a finite element model was established by using LS-DYNA to predict the impact behavior of the panels with calibration of a concrete material model based on previous experimental data. The numerical simulations of HPFRCC panels subjected to impact were verified through comparisons with the experimental results. Based on the verified FE model, a parametric study was also conducted and discussed to better understand the mechanical characteristics of HPFRCC panels under impact loading.

Photocatalytic high-performance fiber-reinforced cement composites with white Portland cement, titanium dioxide, and surface treated polyethylene fibers

In this study, titanium dioxide (TiO2) and polyethylene (PE) fibers were employed to develop photocatalytic high-performance fiber-reinforced cement composites (HPFRCCs). To achieve high NOx removal capacity, it was necessary to confirm the dispersion of the TiO2 powder. For this purpose, various amounts of viscosity-modifying agent (VMA), ranging from 0% to 1% by weight to cement, were considered along with two types of white Portland cement: Union and Aalborg. Additionally, the PE fiber surface was modified via cold gas plasma and chromic acid treatment to improve the tensile performance of the HPFRCCs. The experimental results indicated that the plastic viscosity of the mortar increases with the addition of VMA. Optimum NOx removal capacities of 5.72 and 8.10 μmol were respectively achieved for the Aalborg and Union cement types in the mortar at a VMA content of 0.5%. The compressive strength of the tested photocatalytic HPFRCC was approximately 72.7–91.8 MPa. In the case of the hybrid argon (Ar) and oxygen (O2) gases being subjected to plasma treatment, optimum tensile performance—in terms of tensile strength, strain capacity, and g-value—was achieved, whereas the samples subjected to chromic acid treatment exhibited poorer tensile performance. Moreover, the single Ar–or O2-gas-based plasma treatment yielded an intermediate tensile performance. The cracking behavior showed trends similar to those of the g-value: the hybrid plasma treatment produced the most microcracks because of its high fiber bridging capacity.

Evaluation of Impact-Critical RC Beams Strengthened with a Bottom Layer of HPFRCC

One of the most hazardous consequences of impacts on concrete structures is the high tendency to develop shear or punching failures, with debris generation and associated flying fragments split out. In order to reduce such hazards, concrete structures can be strengthened with a thin bottom layer of high performance fiber-reinforced cement composites (HPFRCCs). As strengthening and anti-spalling layers, the most demanding application is for shear-critical elements, where extensive diagonal cracking leads to multiple fragments, besides concrete cover spalling typical of bending-critical members. An experimental campaign has been carried out on 21 beams to investigate their failure mode. Different configurations were studied for the HPFRCC to determine the influence of the fiber amount (2-4%) and the introduction of embedded steel bars in the strengthening layer. Specimens were subjected to drop weight tests and quasi-static reference tests. The tests have shown that a membrane-type resisting mechanism can be activated by the HPFRCC layer, which can retain potentially falling generated fragments and improve the carrying capacity. Embedding steel bars in the strengthening layers can avoid HPFRCC rupture. Moreover, members strengthened using tensile strain-hardening HPFRCC mixes have shown enhanced strength compared with unstrengthened members, while mixes without strain-hardening did not.

High-strength high-ductility Engineered/Strain-Hardening Cementitious Composites (ECC/SHCC) incorporating geopolymer fine aggregates

In this study, Engineered/Strain-Hardening Cementitious Composites (ECC/SHCC) incorporating geopolymer fine aggregates were successfully developed with high strength and high ductility. A multi-scale investigation was conducted to gain an in-depth understanding of the microstructure and ductility enhancement mechanism of geopolymer aggregate ECC (GPA-ECC). The use of geopolymer fine aggregates enabled the high-strength ECC to achieve higher tensile ductility and finer crack width compared to existing ones with similar compressive strength in the literature. It was found that the GPA reacted with the cementitious matrix, and the width of the GPA/matrix interfacial transition zone (ITZ) was larger than that of the silica sand/matrix ITZ. Moreover, the GPA achieved a strong bond with the cementitious matrix and could behave as “additional flaws” in high-strength matrix, resulting in saturated multiple cracking and excellent tensile ductility of ECC. This study provides a new avenue for developing high-performance fiber-reinforced cementitious composites based on artificial geopolymer aggregates.

Mechanical and Antibacterial Behavior of Photocatalytic Lightweight Engineered Cementitious Composites

In recent years, there has been increasing interest in using cementitious materials as a catalyst-supporting media such as air-purifying paving block, self-cleaning exterior wall, and photocatalytic ceiling panel. Despite many works on photocatalytic cementitious materials, most of them were focused on the application of TiO2-based cement mortars. Little work has been done on the development of photocatalytic functionalities on highperformance fiber-reinforced cementitious composite (HPFRC). Engineered cementitious composites (ECCs), a class of HPFRC, have been used in a wide range of full-scale applications, from sprayed ECC for dam retrofitting to lightweight building facade and bridge deck pavement. In this work, titanium dioxide (TiO2) was incorporated into lightweight ECC. The influence of TiO2 and different lightweight ingredient materials on mechanical properties and antibacterial behavior based on Escherichia coli (E. coli) was investigated. Two types of lightweight aggregates were evaluated: fly ash cenospheres (FACs) and glass bubbles K-1. Furthermore, an air-entraining agent (AEA) was also evaluated to induce air bubbles to achieve lightweight ECC. The use of a glass bubble is preferable to achieve lightweight ECC with a density of around 890 kg/m3 (60% lower than normal ECC) while maintaining a tensile strain capacity of more than 3% with moderate tensile strength. At the same time, lightweight ECC using glass bubbles show the smallest number of viable bacteria after 240 min of ultraviolet (UV)/visible light exposure. The smallest number of viable bacteria indicates it has the highest antibacterial activity among lightweight ECC materials. The use of glass bubble significantly alters the pore structure of lightweight ECC, which improves the access to irradiate TiO2 particle. The incident photon could pass along the pore to activate more TiO2 particles for the photocatalytic process.

Experimental evaluation of flexural behavior of HPFRCC beams reinforced with hybrid steel and GFRP bars

In this paper, seven beams were reinforced with the steel and Glass Fiber Reinforced Polymer (GFRP) bars in a hybrid system and the experimental behavior of beams was investigated. Three groups of beams were reinforced, including only-GFRP, only-steel, and hybrid steel-GFRP rebar subjected to four-point bending tests, respectively. To enhance the ductility of beams, conventional concrete was substituted with the High Performance Fiber Reinforced Cementitious Composites (HPFRCC). The beams of the first and second group were separately constructed by conventional concrete and HPFRCC; however, the third group was only consisted of HPFRCC. Moreover, the beams were reinforced in proportion to the percentages of the balanced ratio of longitudinal rebar. The results indicated that HPFRCC concrete positively influenced on the strength, ductility, and energy absorption of reinforced beams using composite and hybrid bars. The flexural capacity of hybrid reinforced concrete beams was between 86 and 115% of only-GFRPs and between 47 and 63% of only-steel beams and their ductility was between 88 and 235% compared to only-steel fiber reinforced concrete beams. Energy absorption in only-GFRP and only-steel samples were 50 and 34% compared to the hybrid beams. In hybrid beams, the higher ratios of effective (ρsf,f) was, the greater energy absorption was observed.

Gradual Crushing of Steel Reinforced HPFRCC Beams: Experiments and Simulations

While the tensile performance of high-performance fiber-reinforced cementitious composites (HPFRCC) has been extensively studied, the crushing behavior is less understood. Notably, crushing is an important load-reduction mechanism for reinforced HPFRCC flexural members that fail in a ductile mode, i.e., failure after gradual strain hardening of the steel reinforcement accompanied by gradual HPFRCC crushing. This study first investigates the crushing behavior of HPFRCC flexural members through experimental testing of two reinforced HPFRCC beams. The experimental program includes two types of HPFRCC materials: engineered cementitious composites (ECC) and ultra-high performance concrete (UHPC). The test results show that both ECC and UHPC gradually soften in compression after the initiation of crushing, which is in contrast to the more brittle crushing behavior typically observed in conventional concrete. In addition to the experimental investigation, a new HPFRCC compression model is implemented in a two-dimensional finite-element analysis to simulate the gradual compression softening behavior in reinforced HPFRCC flexural members. Different modeling strategies are compared and evaluated. Results show that the proposed model with an initial material flaw, the new compression model, and a hybrid-rotating/fixed-crack model best predict the reinforced HPFRCC structural performance, especially the failure mode and drift capacity.

Experimental evaluation of flexural behavior of High-Performance Fiber Reinforced Concrete Beams using GFRP and High Strength Steel Bars

Substitution of only steel rebar with fiber-reinforced polymer (FRP) or in combination with steel rebar has been recommended to reduce corrosion effects in steel rebar. This paper has pursued the impact of hybrid concrete beams reinforced with High Strength Steel Bars (HSS) and Glass Fiber-Reinforced Polymer Bars (GFRP) manufactured employing High-Performance Fiber-Reinforced Cementitious Composites (HPFRCC) instead of conventional concrete through experimental tests. Seven concrete beams including conventional concrete and HPFRCC in three separate groups, having identical compressive strengths and longitudinal steel reinforcement ratios, have been tested following respected codes and regulations to supply sufficient development lengths using GFRP headed bars, under four-point loading tests. The first and second groups, each represented one conventional concrete beam and an HPFRCC model with GRFP or HSS; the third group included three HPFRCC beams using GRFP and Steel rebar to assess flexural behavior of beams under different reinforcement ratios. Experimental results indicated that HPFRCC beams demonstrated improvements in their load capacity, flexural strength, bending stiffness, ductility, and energy absorption compared to similar conventional concrete beams. Also, in hybrid beams compared to steel reinforced concrete beams both cast with HPFRCC, the more the effective reinforcement ratio of both single and hybrid bars increased, the more ductility was improved between 37 and 88 percent. Displacement ductility of hybrid beams having effective reinforcement ratios up to 1.35 and 1.25 times more than the balance ratio was increased 23 and 37.5 percent, respectively. Energy absorption for HPFRCC beams reinforced only with GFRP or steel rebar was increased 31 and 250 percent compared to identical conventional concrete beams, respectively. In hybrid compared to GFRP reinforced beams both cast with HPFRCC, the more effective reinforcement ratio increased, the more energy absorption was increased in a range of 51 up to 174 percent. Therefore, it can be concluded that using the hybrid of GFRP and HSS bars result in up to 30 percent improvement in flexural strength because of the effective performance of GFRP after steel rebar yielding and ductility increase due to HSSs yielding.

Automatic identification and quantification of dense microcracks in high-performance fiber-reinforced cementitious composites through deep learning-based computer vision

High-performance fiber-reinforced cementitious composites (HPFRCCs) feature high mechanical strengths, crack resistance, and durability. Under excessive loading, HPFRCCs demonstrate dense microcracks that are difficult to identify using existing methods. This study presents a computer vision method for identification, quantification, and visualization of microcracks in HPFRCCs based on deep learning. The presented method integrates multiple deep learning models and computer vision techniques in a hierarchical architecture. The crack pattern (e.g., number, width, and spacing of cracks) are automatically determined from pictures without human intervention. This study shows that the presented method achieves an accuracy of 0.992 for crack detection and an accuracy finer than 50 μm (R2 > 0.984) for quantification of crack width when deep learning models are trained using only 200 pictures of HPFRCCs and 200 pictures of conventional concrete with incorporation of data augmentation. The presented method is expected to be also applicable to other materials featuring complex cracks.

Predicting Mechanical Properties of High-Performance Fiber-Reinforced Cementitious Composites by Integrating Micromechanics and Machine Learning.

Current development of high-performance fiber-reinforced cementitious composites (HPFRCC) mainly relies on intensive experiments. The main purpose of this study is to develop a machine learning method for effective and efficient discovery and development of HPFRCC. Specifically, this research develops machine learning models to predict the mechanical properties of HPFRCC through innovative incorporation of micromechanics, aiming to increase the prediction accuracy and generalization performance by enriching and improving the datasets through data cleaning, principal component analysis (PCA), and K-fold cross-validation. This study considers a total of 14 different mix design variables and predicts the ductility of HPFRCC for the first time, in addition to the compressive and tensile strengths. Different types of machine learning methods are investigated and compared, including artificial neural network (ANN), support vector regression (SVR), classification and regression tree (CART), and extreme gradient boosting tree (XGBoost). The results show that the developed machine learning models can reasonably predict the concerned mechanical properties and can be applied to perform parametric studies for the effects of different mix design variables on the mechanical properties. This study is expected to greatly promote efficient discovery and development of HPFRCC.

Review of using glass in high-performance fiber-reinforced cementitious composites

As an increasing amounts of waste glass are produced annually, recycling glass in manufacturing concrete shows economic and environmental benefits. Recently, glass has been used as one of the ingredients to prepare high-performance fiber-reinforced cementitious composites (HPFRCCs), like strain-hardening cementitious composite and ultra-high-performance concrete, featuring high mechanical properties and long-term durability. While the application of glass particles may reduce the material cost, however, fundamental knowledge of the effects of using glass to replace concrete components on the key properties (e.g., mechanical properties, fresh properties, durability) and the underlying mechanisms is still lacking. This study aims to reveal the roles of waste glass particles on the key properties, clarify the fundamental mechanisms, and point out viable strategies to enhance the key properties of HPFRCCs incorporating glass. To this end, the paper reviews existing studies on using glass in preparing HPFRCCs and discusses possible methods to develop HPFRCCs with glass particles. While there are different types of glass, this review focuses on soda-lime glass, which is representative among all types of glass. At last, life cycle analysis is conducted to assess the effect of using glass particles on reducing the cost, CO2 emission, and energy consumption. This review aims to enhance the fundamental knowledge of HPFRCC and propose further research of HPFRCCs incorporating glass.

Residual Tensile Properties and Explosive Spalling of High-Performance Fiber-Reinforced Cementitious Composites Exposed to Thermal Damage.

This study examined the effect of adding synthetic fibers, that is, polypropylene (PP) and nylon (Ny), on explosive spalling and residual tensile mechanical properties of high-performance fiber-reinforced cementitious composites (HPFRCCs). Three different matrix strengths (100 MPa, 140 MPa, and 180 MPa), four different volume contents of the synthetic fibers (0%, 0.2%, 0.4%, and 0.6%), and three different exposure time (1 h, 2 h, and 3 h) based on the Internatinoal Organization for Standardization (ISO) fire curve were adopted as variables for this experiment. The experimental results revealed that the addition of synthetic fibers improved the resistance to explosive spalling induced by high-temperature, especially when PP and Ny were mixed together. For a higher matrix strength, greater volume content of the synthetic fibers was required to prevent explosive spalling, and higher residual strengths were obtained after the fire tests. An increase in the volume fraction of the synthetic fibers clearly prevented explosive spalling but did not affect the residual tensile strength. In the case of a higher matrix strength, a reduction in the strength ratio was observed with increased exposure time.

Application of HPFRCC in beam–column joints to reduce transverse reinforcements

In this paper, in order to prevent the congestion of transverse reinforcements in beam-column joints of reinforced concrete frames which meet special seismic regulations, high-performance fiber reinforced cement composites (HPFRCC) with a combination of double hooked-end steel fibers and steel microfibers were used.For this purpose, four external beam-column joints were constructed to a scale of 1/2 and the specimens were tested under cyclic loading.The tested specimens include a normal concrete one meeting special seismic regulations as the control specimen and three HPFRCC ones made by reducing the transverse reinforcement in the beam and column. Hysteresis behavior, load-carrying capacity, energy dissipation and cracking patterns were analyzed and compared with the cyclic response of the control specimen for all experimental specimens. The test results indicate that the HPFRCC specimens, in comparison with the control specimen, have higher stiffness, load-carrying capacity and energy dissipation. Moreover, HPFRCC joints show a better damage tolerance capacity than the control specimen at higher drifts. Furthermore, the results of this study indicate that the use of HPFRCC in joint can be a proper strategy for increasing shear capacity and reducing the amount of beam and column transverse reinforcements.

Blast Response Simulation of the Alfred Murrah Building Reinforced by Use of HPFRCC

Structural behavior against the blast load is evaluated for a structure reinforced by high-performance fiber-reinforced cementitious composites (HPFRCC). The Alfred P. Murrah Federal Building, which experienced a terrorist attack in 1995 is taken into consideration for the blast analysis using the finite element method. The continuous surface cap model (CSCM) is used to simulate the behavior of normal concrete and HPFRCC. By reinforcing normal concrete with HPFRCC, damage, and deformation of the structure are significantly reduced. This study presents an efficient reinforcement method by performing an explosion simulation on the structure using HPFRCC and evaluating the behavior according to various reinforcement methods. Specific reinforcements according to the types of members are required to enhance the efficiency of reinforcement. With the optimized reinforcement using high-performance fiber-reinforced cementitious composites (HPFRCC), the resistance to blast load is significantly improved.

Relationship between Three-Dimensional Steel Fiber Statistics and Electromagnetic Shielding Effectiveness of High-Performance, Fiber-Reinforced Cementitious Composites.

This study aims to investigate the relationship between the steel fibers and the electromagnetic wave shielding effectiveness of a high-performance fiber-reinforced cementitious composite (HPFRCC). The distribution characteristics of the steel fibers and the variation of the electrical conductivity of HPFRCC as a function of the fiber content were quantified based on micro computed tomography (CT) and impedance measurements to determine their correlations with the electromagnetic shielding effectiveness. The impedance results showed that no electrical network was formed in the composite by the steel fibers and it is difficult to manufacture HPFRCC with high-electrical conductivity using steel fibers alone without CNTs or other carbon-based materials. For the steel fiber content of greater than 0.5%, the number of contact points between the steel fibers increased significantly, and the relationship between the fiber content and the number of contact points was observed. Despite the improvement of the electrical conductivity owing to the presence of the steel fibers and to the increase in the contact points between the steel fibers, the shielding effectiveness did not increase further for the steel fiber contents equal or above 1.5%. Consequently, it was found that the factor that controls the shielding effectiveness of HPFRCC is not the electrical network of the steel fibers, but the degree of the dispersion of the individual steel fibers.

Influence of carbon fiber on the electromagnetic shielding effectiveness of high-performance fiber-reinforced cementitious composites

The significance of electromagnetic interference shielding is being increasingly emphasized in the construction field due to information security violation. This study investigated the mechanical performance, electrical conductivity, and electromagnetic shielding effectiveness of high-performance fiber-reinforced cementitious composite (HPFRCC) produced by incorporating carbon fibers. The carbon fibers were added to the HPFRCC at 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4 vol %. The electrical resistivity of the HPFRCC was measured by alternating current (AC) and direct current (DC) methods and the shielding effectiveness was measured in the shielding room in accordance with MIL-STD-188-125. The test results showed that the AC resistivity of the HPFRCC mixed with carbon fibers was strongly associated with the applied voltage. For measuring the real resistivity of the HPFRCC, the applied voltage should be more than the minimum voltage required for the current to pass through the electrical path in the cement matrix if the carbon fiber content exceeds the percolation thread (greater than 0.8% here). The compressive strength decreased with increase in the carbon fiber content owing to the reduced slump flow and resultant less compaction effect of HPFRCC. The relative permittivity results indicates that the shielding mechanism of the HPFRCC is likely to be electromagnetic reflection rather than electromagnetic absorption by the carbon fibers. It also clearly showed that the dominant factor affecting electromagnetic shielding of the HPFRCC is the amount of carbon fibers rather than the electrical conductivity resulting from continuous connection of carbon fibers.

Dynamic tensile behavior of SIFRCCs at high strain rates

Reinforced concrete (RC) does not provide sufficient resistance against impacts and blast loads, and the brittle structure of RC fails to protect against fractures due to the lack of shock absorption. Investigations on improving its resistance against explosion and impact have been actively conducted on high-performance fiber-reinforced cementitious composites (HPFRCCs), such as fiber-reinforced concrete and ultra-high-performance concrete. For these HPFRCCs, however, tensile strength and toughness are still significantly lower compared to compressive strength due to their limited fiber volume fraction. Therefore, in this study, the tensile behavior of slurry-infiltrated fiber-reinforced cementitious composites (SIFRCCs), which can accommodate a large number of steel fibers, was analyzed under static and dynamic loading to improve the shortcomings of RC and to enhance its explosion and impact resistance. The fiber volume fractions of SIFRCCs were set to 4%, 5%, and 6%, and three strain rate levels (maximum strain rate: 250 s-1) were applied. As a result, the tensile strength exceeded 15 MPa under static load, and the dynamic tensile strength reached a maximum of 40 MPa. In addition, tensile characteristics, such as tensile strength, deformation capacity, and energy absorption capacity, were improved as the fiber volume fraction and strain rate increased.