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The widespread use of carpets in residential and commercial buildings and their relatively short life span result in large volumes of carpet being landfilled. A potential solution to this problem is the use of post-consumer carpet fibers in concrete. To this end, this paper systematically identifies the common fiber types in a typical post-consumer carpet fiber bale and evaluates their durability under exposure to varying levels of alkalinity. The tensile strengths and toughness of the fibers belonging to the nylon and polyethylene terephthalate (PET) families (the dominant fibers in most post-consumer carpets) are reduced by up to 50% following exposure to extreme alkalinity, the reasons for which are determined using spectroscopic and microscopic evaluations. The chloride ion transport resistance of concretes (~40 MPa strength) containing 2.5% carpet fibers by volume (~25 kg of fibers per cubic meter of concrete) is comparable to that of the control mixture, while mortar mixtures containing the same volume fraction of carpet fibers demonstrate negligible enhancement in expansion and loss of strength when exposed to 1 N NaOH. This study shows that moderate-strength concretes (~40 MPa) for conventional building and infrastructure applications can be proportioned using the chosen volume of carpet fibers without an appreciable loss of performance. Consideration of low volume fractions of carpet fibers in low-to-moderate-strength concretes thus provides a sustainable avenue for the use of these otherwise landfilled materials in construction applications. [ABSTRACT FROM AUTHOR]

The increasing demands of sustainable design and construction with economical sections, reduced cover, and more efficient time schedule require more flexibility in the design methodologies. The development of ultra‐high performance concrete (UHPC) have gained increasing interests as an attractive option for structural members with lightweight and superior performances. Concrete members reinforced with steel bars and fibers, generally known as hybrid reinforced concrete (HRC), offer a feasible solution in terms of reducing reinforcing materials and achieving desired structural performance. This paper proposes an analytical model to predict the flexural behavior of hybrid reinforced UHPC with steel reinforcements. Moment–curvature solutions are derived for reinforced sections based on parameterized tension‐compression constitutive models. The approach is applicable to customized cross section and derivation of T‐section is demonstrated. The moment–curvature response is further simplified as a tri‐linear model, which is used for the development of full‐range displacement solutions in analytical form. The proposed model is validated with the experimental data from literature covering a range of materials and member sizes. The full‐range solutions may provide insights into the serviceability design approach based on the criterion of maximum crack width or allowable deflection. [ABSTRACT FROM AUTHOR]

A constitutive model consisting of a tri-linear tensile stress-strain with residual strength was applied in characterization and prediction of long term flexural behavior of several cement-based composite materials. Flexural test results were back-calculated to obtain material parameters and establish their relationship with aging. The material behavior is described by tensile stress-strain parameters consisting of elastic modulus, first cracking strain, post cracking stiffness, ultimate strain, and a residual strength parameter. The relationships between the material parameters and age were established by studying the time dependent flexural performance of various composites with glass and natural fibers as reported by Litherland et al. (1981), Marikunte et al. (1997), Bartos et al. (1996), and natural fibers reported by Toledo-Filho et al. (2000). An analytical model for prediction of rate and extent of damage as a function of time and temperature is proposed for degradation of flexural behavior of strain softening and hardening fiber reinforced concrete subjected to aging. This model is applicable to long-term durability of different classes of materials subject to accelerated aging under different environmental conditions. [ABSTRACT FROM AUTHOR]

Textile-reinforced concrete (TRC) is used widely in thin-walled structures due to its unique construction characteristics and superior mechanical properties. However, previous studies of the dynamic flexural properties of alkali resistant (AR)-glass TRC thin plates did not consider the influence of exposure to high temperature. In this study, the effect of impact velocity (range from 1.29 to 4.04 m/s) on AR-glass TRC after exposure to elevated temperatures up to 400°C was investigated experimentally using a drop-tower impact system. AR-glass TRC specimens were heated to target temperatures (100°C, 200°C, 300°C, and 400°C) in a furnace and then tested at room temperature. The effects of exposure to high temperature and the strain rate of loading (impact velocity) on the flexural mechanical properties were measured, and the microstructure and damage evolution of the composites was evaluated. Results show that the strain rate had a direct effect on the flexural properties of AR-glass TRC composite under impact after exposure to high temperatures. Furthermore, the weakening effect of high temperature in AR-glass TRC material could equal or even exceed the hardening effect due to the strain rate. The results were evaluated by comparing dynamic flexural stress and toughness features. Finally, the high-temperature deterioration mechanism of AR-glass TRC material was determined by comparing the changes in the matrix–textile interface and the textile fracture after exposure to different temperatures. [ABSTRACT FROM AUTHOR]

Structural applications of hybrid reinforced concrete (HRC) involve a composite system with a fiber-reinforced concrete (FRC) matrix in conjunction with conventional reinforcement. The system offers economic benefits by reducing the number of rebars, minimizing labor costs, and shortening the construction schedule. This paper presents the generalized approach to evaluating closed-form moment–curvature relationships from constitutive models with multilinear equations. The interaction of various moment–curvature solutions is by sequential switching from one mode to the other to form an envelope curve as the minimum moment among all available options. Results lead to explaining the interaction of material and geometrical parameters as well as the interaction of various failure modes. Furthermore, the model can be used for both the ultimate limit state (ULS) and serviceability limit state (SLS) since the strain history is the primary independent variable. These lead to parametric design charts for adjusting material parameters, reinforcement amount and location, and section geometry within the bounds of ρmin and ρbal is applicable for HRC, RC, and FRC sections. Analytical equations show that as the concrete flexural crack extends in a hybrid section, the bridging effect of fibers delays the stress accumulation into the rebar and its subsequent yielding. The efficiency of the volume of concrete that is under tensile loads is significantly improved, extending the serviceability range and increasing the stiffness of cracked concrete. The extension of the serviceability limit range is also associated with potential improvements in durability since the HRC model predicts smaller apparent strains and crack widths at a given load. The proposed solutions are validated by simulating the load-deflection responses of various full-scale flexural tests published in the literature. [ABSTRACT FROM AUTHOR]

• A parametric moment-curvature section analysis using piecewise linear properties of elastic-plastic-hardening materials and metals. • Closed-form solutions generated for all specific sets of input parameters before the interaction of failure modes are addressed. • Results are extended for efficient computation of load-deflection response of determinate beams or non-linear structural analysis. • Applications to Textile Reinforced Concrete (TRC) and structural steel W-sections with several case studies. • Potential applications to limit state serviceability or ultimate state design using curvature, strain, deflection, or load criteria. A piecewise linear parametric constitutive model of elastic-plastic-hardening in tension and elastic-plastic in compression is used to develop closed-form solutions for flexural moment-curvature of generalized sections. Brittle matrix composite such as Textile Reinforced Concrete (TRC) is homogenized using three zones of elastic, distributed cracking, and tension stiffening up to the maximum tensile strength. Linear segments of the tensile and compressive constitutive responses are integrated for various states of strain and extended to geometrical structural shapes such as steel W-, T-, and C- sections. The closed-form moment-curvature response is obtained using two independent variables of strain distribution and neutral axis location and extended to obtain the stress distribution, curvature, rotation, and deflection profile of statically determinate load cases using an input strain. The solutions for serviceability-based criteria and limit state parameters such as curvature, rotation, and deflection distribution as a function of the applied load can be obtained. The generalized parametric solutions are applied to the elastic-plastic flexural response of quasi-brittle or ductile beams of structural steel with unique cross-sectional geometries. Case studies of the correlation of tensile and flexural tests of TRC with variables such as types and direction of the weave, number of textile layers, and section geometry are validated. The parametric nature of the formulation offers computational efficiency for applications that address material and shape optimization, as well as serviceability-based flexural design using different limit states. [ABSTRACT FROM AUTHOR]

• Evaluation of critical fiber length (L c) is a key to optimal performance of FRAC. • Shear bond strength (τ) can be measured using fiber pullout test to evaluate the L c. • The τ is a time-dependent property and depends on the asphalt matrix modulus. • A relationship was developed between the τ and the modulus using viscoelastic theory. • The relationship was used to estimate the L c in AC at different temperatures/rates. The interfacial shear bond strength (τ) between fibers and matrix is typically measured by fiber pullout test to determine the critical fiber length (Lc) in fiber reinforced composites. In fiber reinforced asphalt concrete (FRAC), the τ is a time-dependent property and it is affected by asphalt modulus. The main objective of this study was to establish a relationship between the τ and modulus of asphalt mastic and asphalt concrete (AC), from which the Lc in AC was determined. Results from direct tension test, performed to validate the analytical framework, suggested that the use of longer fibers (38-mm vs 19-mm) showed higher reinforcement efficiency in FRAC. [ABSTRACT FROM AUTHOR]

Hybrid reinforced concrete (HRC) is referred to as a structural member that combines continuous reinforcement with randomly distributed chopped fibers in the matrix. An analytical model for predicting flexural behavior of HRC which is applicable to conventional and fiber reinforced concrete (FRC) is presented. Equations to determine the moment–curvature relationship, ultimate moment capacity, and minimum flexural reinforcement ratio are explicitly derived. Parametric studies of the effect of residual tensile strength and reinforcement ratio are conducted and results confirm that the use of discrete fibers increases residual tensile strength and enhances moment capacity marginally. However improvements in post-crack stiffness and deformation under load is substantial in comparison to conventional steel reinforcement. Quantitative measures of the effect of fiber reinforcement on the stiffness retention and reduction of curvature at a given applied moment are obtained. The approach can also be presented in a form of a design chart, representing normalized moment capacity as a function of residual tensile strength and reinforcement ratio. Numerical simulations are conducted on the steel fiber reinforced concrete (SFRC) and HRC beam tests from published literature and the analytical solutions predict the experimental flexural responses quite favorably. [ABSTRACT FROM AUTHOR]

The tensile stress–strain response of a fiber reinforced concrete dominates the performance under many loading conditions and applications. To represent this property as an average equivalent response, a back-calculation process from flexural testing is employed. The procedure is performed by model fitting of the three-point and four-point bending load deflection data on two types of macro synthetic polymeric fibers, one type of steel fiber and one type of Alkali Resistant (AR) glass fiber. A strain softening tensile model is used to simulate the behavior of different FRC types and obtain the experimental flexural response. The stress–strain model for each age, fiber type and dosage rate is simulated by means of the inverse analysis procedure, using closed-form moment–curvature relationship and load–deflection response of the piecewise-linear material. The method of approach is further applied to one external data set for High Performance Fiber Reinforced Concrete (HPFRC) with two different types of steel fibers and validated by tensile test results reported. Results of back-calculation of stress–strain responses by tri-linear tensile model for all mixtures are compared and correlated with the corresponding standard method parameters used for post crack behavior characterization and a regression analysis for comparative evaluation of test data is presented. [ABSTRACT FROM AUTHOR]

This papers addresses the disparities that exist in measuring the constitutive properties of thin section cement composites using a combination of tensile and flexural tests. It is shown that when the test results are analyzed using a simplified linear analysis, the variability between the results of tensile and flexural strength can be as high as 200-300%. Experimental results of tension and flexural tests of laminated Textile Reinforced Concrete (TRC) composites with alkali resistant (AR) glass, carbon, aramid, polypropylene textile fabrics, and a hybrid reinforcing system with aramid and polypropylene are presented. Correlation of material properties is studied analytically using a parametric model for simulation of flexural behavior using a closed form solution based on tensile stress-strain constitutive relation. The flexural load carrying capacity of TRC composites is computed using a back-calculation approach, and parameters for a strain hardening material model are obtained using the closed form equations. While the parametric model over predicts the simulated tensile response for carbon and polypropylene TRCs, predictions are however consistent with experimental trends for aramid and glass TRCs. Detailed discussion of the differences between backcalculated and experimental tensile properties is presented. Results can be implemented as average moment-curvature relationship in the structural design and analysis of cement composites. [ABSTRACT FROM AUTHOR]

Abstract: Woven fabrics are used in many applications, including ballistic armors, propulsion engine containment systems and fabric reinforced composites. In order to facilitate the design and improvement of such applications, this paper investigates the stress–strain response in warp and fill directions, the apparent Poisson’s ratio, and the in-plane shear response of Kevlar 49 fabric including the possible effects of specimen size and pre-loading on the mechanical responses of the fabric. Full-field image analysis of the fabric under shear deformation is used to better understand the mechanisms related to in-plane shear. The experimental results show that the fabric exhibits non-linear and orthogonal behavior in tension, and can deform up to 20% before complete failure. It has identical Young’s modulus (pre-peak elastic stiffness) in warp and fill directions, but has different crimp strain, tensile strength and ultimate strain. The apparent Poisson’s ratio is a nonlinear function of strain and dependent upon the levels of pre-loading. It increases with strain quickly at the beginning and decreases gradually until the fabric fails. The shear response is highly nonlinear and has four distinct regions: linear elastic rotation region, dissipative rotation region, yarn compression region and shear locking region, and it is not dependent upon specimen size after normalization. [Copyright &y& Elsevier]

Abstract: This paper presents the development of a test procedure and application of non-contacting strain measurement for cement-based composites under moderately high strain rate tensile tests. The strain time histories of test specimens measured by a laser extensometer in high speed mode were derived by a phase-shift technique based on zero-crossing method. The accuracy of the linear variable differential transformer (LVDT) of the actuator in a servo-hydraulic high rate testing machine was verified by image analysis using sisal fiber reinforced cement composite at a strain rate of 25s−1. The same procedure was then applied to Alkaline Resistant (AR) glass fabric reinforced cement composite tested at an average strain rate of 17s−1. Comparison between the strain values measured by the laser extensometer and the LVDT shows a good agreement between these two measurement techniques. The test results show that the Young’s modulus, tensile strength, maximum strain, and toughness of the AR-glass fabric–cement composite increase with increasing strain rate. However, under both static and dynamic loadings the composite has similar behavior: multi-crack development and one dominant crack leading to final failure. In order to ensure the accuracy of dynamic tensile test procedures, non-contacting devices and techniques should be used as an independent means of verification of test results. The accuracy required in quantifying relative improvements in mechanical properties necessitates the various methods of measuring the displacement and strain rate properties. [Copyright &y& Elsevier]

Dynamic tensile tests are conducted on aluminum alloy (AA) 6061-T6 using a high-speed servohydraulic machine at intermediate strain rates to validate the testing technique and to investigate the strain-rate effect on the material's stress-strain behavior and failure mode. We present the experimental procedures and results discussing the constitutive response of the alloy at strain rates up to approximately 200 s-1. The predominant frequencies of the high-speed testing machine were characterized by modal analysis, and we analyzed the effect from vibration of the system and loading rate on flow stress by using a single degree-of-freedom (SDOF) spring-mass-damper model. We tested two different specimen sizes at a wide range of actuator velocities to achieve the desired strain rates. Results show that the yield strength, ultimate strength, and failure strain were dependent on strain rate. We fitted the data to the Johnson-Cook (JC) constitutive model, and the resulting parameters are comparable to published results in the literature. The fracture surface of specimens tested at different strain rates obtained by scanning electron microscopy (SEM) showed that the ductile failure mode was dominant for the alloy, and strain rates within the range examined affected the fracture morphology. [ABSTRACT FROM AUTHOR]

Abstract: An experimental investigation was performed to understand the pull-out behavior of sisal fibers from a cement matrix. The effect of curing age and fiber embedment length on the fiber–matrix interface was studied. Sisal fiber presents irregular cross-section with different shapes that may be beneficial for the bond strength. A scanning electron microscope coupled with image analysis was used to measure the cross-section area of individual tested fibers and to determine and classify their morphology. The results were correlated to the fiber morphology. Direct tension tests were performed on composites reinforced by 10% in volume of continuous aligned sisal fiber. A finite difference model developed earlier by authors was used to determine the bond strength versus slip constitutive relation from experimental data and to predict the composite tensile behavior and crack spacing. It was found that the sisal fiber morphology plays an important role in the bond strength. Average adhesional bond strength as high as 0.92MPa were reported for the fiber shape that promoted the best interfacial performance. [Copyright &y& Elsevier]

Measurement of deformation history during a high-speed mechanical test plays an important role in establishing the dynamic behavior of materials. Traditional strain measuring techniques such as extensometers and strain gauges have limitations such as frequency response and range of strain. Kevlar 49 fabrics were tested in tension within a strain-rate range of 25 to 170 s-1 using a high-speed servohydraulic testing system. Results show that the dynamic material properties in terms of Young's modulus, tensile strength, maximum strain, and toughness increase with increasing strain rate. The woven nature of Kevlar 49 fabric results in large displacements and shape changes during tests. Noncontacting strain measuring technique is therefore highly preferred. A technique was developed using image analysis to obtain the deformation of Kevlar 49 fabrics at the tested strain rates. Using image analysis results, the stress-strain curves of Kevlar 49 fabrics at different strain rates were constructed and compared with those based on stroke measurement. Good agreement was obtained between these two methods. [ABSTRACT FROM AUTHOR]

Abstract: The tensile fatigue behavior of long aligned sisal fiber reinforced cement composites was investigated. The fatigue behavior was examined in terms of the stress versus cycles and stress–strain hysteresis behavior of the composites. Composites were tested at stress levels ranging between 4 and 9.8MPa which represent approximately 30–80% of the monotonic ultimate tensile strength. The composites did not fail in fatigue below a maximum fatigue level of 6MPa up to 106 cycles. Monotonic tensile testing was performed for composites that survived 106 tests to determine the residual strength. Crack spacing was measured by image analysis technique. There was no observed loss in strength, but a decrease in Young''s modulus and an increase in first crack strength was observed with increasing fatigue stress. Fluorescent optical microscopy was used to investigate the micro-crack formation in composites subject to fatigue loading. [Copyright &y& Elsevier]

The laboratory testing of concrete has shown that elevated temperatures cause air permeability index (API) increase and elastic modulus E decrease. Indeed, the API response typically spans several orders of magnitude making it a sensitive indicator of elastic modulus reduction. However, the API versus E data has been historically assumed to be both event and concrete composition specific, thus limiting its applicability for predictive or modeling purposes. In response, a theoretical model is developed here by (1) establishing that the API is equivalent to the Darcy permeability; (2) developing a microcrack flow model accounting for tortuosity, crack density, and microcrack geometry; and (3) interpreting the Giordano and Colombo elastic modulus damage formulas in terms of the corresponding increase in permeability. The resulting general model depends on stress conditions (plane stress versus plane strain) and a single microcrack flow parameter. For materials with small Poisson’s ratios, however, the model becomes independent of stress condition and both equations converge on the same simple solution. The model is verified with both field and laboratory data of concrete response to typical fire elevated temperatures and shown to be comparable in accuracy to previous empirical approaches requiring many more degrees of freedom. Moreover, the data on fire damaged concrete were found to collapse to a single curve suggesting that the microcrack flow parameter is sensitive to elevated temperature but insensitive to concrete composition. The success of the model implies certain limits to microcrack geometry and airflow turbulence in damaged concrete, both of which are discussed. [ABSTRACT FROM AUTHOR]

Concrete is the most widely used material in construction industries. Therefore, it is necessary to understand and when possible, improve the efficiency of a concrete production process. Statistical process control is generally applied to gain information about variation in the manufacturing process. Control charts can be implemented to monitor the various processes involved in the production, the delivery and construction of concrete. When historical data are available on various projects, better insight into operational procedures can be obtained through the use of control charts. This paper studies a series of statistical analysis procedures to analyze the compressive strength of concrete. The proposed method is based on combining the cumulative sum (CUSUM) control chart and a run chart (CUSUM-run chart) for early detection of shifts in the process mean. The combined charts address both the consumers’ and the producers’ perspectives. The CUSUM-run chart can aid the consumer in making decisions about accepting or rejecting a strength test. In addition, the producers (concrete manufacturers) can use the chart to determine if the monitored process is out-of-control and subsequently attempt to identify the possible causes for the out-of-control situation. By identifying assignable causes of the out-of-control process, the producer can then improve the manufacturing process by reducing product variation, unnecessary waste, or over-designed concrete mixtures. The CUSUM-run chart is also beneficial in that it can often indicate when the strength of mixture is less than the minimum acceptable level very quickly. The delay in detecting an unacceptable strength can result in more penalties, project delays and increased associated costs. [ABSTRACT FROM AUTHOR]

Abstract: Fiber reinforced cement composite laminates with long sisal fibers were manufactured using a cast hand lay up technique. A matrix with partial cement replacement by metakaolin and calcined waste crushed clay brick was used in order to improve the durability aspects. Mechanical response was measured under tension and bending tests while crack formation was investigated using a high resolution image capturing procedure. Crack spacing was measured using image analysis and correlated with the applied strain under both the tensile and bending response. Various stages of loading corresponding to initiation, propagation, distribution, opening, and localization of a crack system in the specimen are discussed. The effect of flexural cracking on the location of neutral axis during the bending tests was measured using strain-gages. [Copyright &y& Elsevier]

Abstract: This work concerns the tensile properties of cement-based hybrid composites manufactured as: (i) sandwich composites that combine different layers of single fabric types; and (ii) hybrid composites, made from several yarn types within the same fabric. Hybrid combinations of low-modulus fabrics of polyethylene (PE) or polypropylene (PP) and high-modulus AR glass or aramid fabrics were prepared by the pultrusion process and tested in tension. Influence of pultrusion direction on the results was one of the parameters studied. It was found that hybrid composites made from PE and AR glass sustain strains better than 100% AR glass composites, and are stronger than a single PE fabric composite. A hybrid fabric composites made with combination of high strength–high cost aramid and low stiffness–low cost PP yarns performed better than a single aramid fabric composite relative to their reinforcing volume contents. Results show that making hybrid composites is an attractive option for cement-based elements. The performance of hybrid fabric composites is also influenced by the arrangement of fabric layers in the laminates. Composites with brittle and relatively strong fabrics (glass) at the mid-section and ductile fabrics (PE) near the surfaces of the composite performed better in tension than composites with the opposite arrangement. [Copyright &y& Elsevier]

Abstract: Closed form equations for generating moment–curvature response of a rectangular beam of fiber reinforced concrete are presented. These equations can be used in conjunction with crack localization rules to predict flexural response of a beam under four point bending test. Parametric studies simulated the behavior of two classes of fiber reinforced concrete: strain softening and strain hardening materials. The simulation revealed that the direct use of uniaxial tension and compression responses under-predicted the flexural response for strain softening material while a good prediction for strain hardening material was obtained. The importance of strain softening range on the flexural response is discussed using non-dimensional post-peak parameters. Results imply that the brittleness and size effect are more pronounced in the flexural response of brittle materials, while more accurate predictions are obtained with ductile materials. It is also demonstrated that correlations of tensile and flexural results can be established using normalized uniaxial tension and compression models with a single scaling factor. [Copyright &y& Elsevier]

Abstract: A model simulating the tensile behavior of fabric–cement composites is presented to relate the properties of the matrix, fabric, interface and the damage parameters to the overall mechanical response of the composites. Crack spacing parameters measured during tensile tests are used to define the damage parameters, and related to the stiffness degradation as a function of the applied strain. This procedure is integrated in composite laminate theory using an incremental approach to model the uniaxial tensile response. Two approaches of linear and nonlinear fabric bridging models are used. The model is capable of using interface parameters for different fabrics, matrix properties, and processing parameters. Simulation results are studied by means of parametric simulation and a validation of a variety of experimental observations which vary the matrix formulation with flyash, changes in pressure after casting, and fabric type. [Copyright &y& Elsevier]

A chemomechanical mathematical model is presented to simulate the response of concrete exposed to external sulfate solutions. The model is based on the diffusion-reaction approach, and several mechanisms for the reaction of calcium aluminates with sulfates to form expansive ettringite are considered. Fick’s second law is assumed for diffusion of the sulfate ions. A second-order chemical reaction between reacting calcium aluminates and ingressing sulfates depletes the sulfate concentration. The products of the second-order reaction between the aluminates and sulfates are chosen among several competing mechanisms, and a rule-of-mixtures approach is used to relate the expansive nature of the products with the prescribed specific gravity of the compounds. It is furthermore assumed that the crystallization pressure of products of reaction results in a bulk expansion of the solid. The constitutive response of the matrix and the expansive stresses are calculated from the imposed volumetric strain. Microcracks are initiated when the strength of the matrix is reached, leading to changes in the diffusivity and a reduction in the elastic properties of the matrix. The variation of diffusivity is linked to the scalar damage parameter due to cracking of the matrix. Due to the changes in the diffusivity, the problem is treated as a moving boundary problem, and a methodology is proposed to adapt the solution of the 1D case to the 2D problem of a prismatic specimen. Theoretical expansion-time responses are obtained and compared with a variety of data available in the literature. [ABSTRACT FROM AUTHOR]

A study is presented to predict the degradation of cement-based materials due to external sulfate attack. Parameters of the model are chosen based on the mix design parameters, degree of hydration, and exposure conditions of concrete. A solution of the diffusion equation with a term for a second-order chemical reaction is proposed to determine the sulfate concentration and calcium aluminate profile as a function of time and space. The crystallization pressure of hydration products such as ettringite can lead to internal stresses. Using the volumetric information, the model predicts the generation of internal stresses, evolution of damage, reduction in stiffness, and thus expansion of a matrix phase. The theoretical expansion-time responses are obtained and compared with a variety of available data in the literature. The most important parameters are the w/c ratio, internal porosity, diffusivity of the cracked and uncracked material, and available calcium aluminates. The importance of controlling the pH of the test solution is clearly observed. Model simulations indicate a reasonable agreement with experimental expansion-time data available in the literature. [ABSTRACT FROM AUTHOR]

The nature of cracking in flexural specimens made using ultra-high-performance concrete (UHPC) is studied in the context of mechanisms of enhanced strength and ductility. The effect of fibers on the suppression of cracking and the attendant toughening mechanisms are addressed at two different fiber contents to elucidate the strain-softening and strain-hardening responses. Results indicate that the first crack strength is directly related to the fiber content, with fibers extending the stable crack growth region at high fiber contents such that flexural strengths as high as 20 MPa are obtained. Fiber bridging results in resistance to crack growth, stabilization, as well as multiple crack formation, all of which contribute to toughening. Using a combination of experimental results, digital image correlation (DIC) measurements of crack extension, and an analytical model for the flexural response, the stress and strain distributions across the depth of the specimens are determined, leading to stress-crack width relationships, and consequently, the relationship between tensile and flexural stresses in fiber-reinforced UHPCs. The results are also used to determine the tensile and compressive strain and stress distributions. Using back-calculated tensile properties from the flexural response and the 3-D DIC results, crack width profile and the stress-crack width relationship in tension are obtained for UHPCs, leading to a comprehensive understanding required for the structural design using such high-ductility materials. [ABSTRACT FROM AUTHOR]

Evaluates the crack propagation properties of asphalt mixes at two temperature levels. Fracture mechanisms; R-Curve approach as measure for fatigue behavior; Linear elastic fracture mechanisms; Link of asphalt curve and binder control.

Abstract Ultra-high performance concrete (UHPC) mixtures demonstrating more than 150 MPa compressive strength and 20 MPa flexural strength are proportioned with commonly available cement replacement materials (30% or 50%, mass-based replacement levels) and steel fibers using a recently developed combined binder and aggregate optimization approach. The compressive (axial) stress-strain responses of the unreinforced and fiber-reinforced UHPC mixtures, along with the calculated volumetric strains, are used to define two critical stress states – viz., crack initiation and crack damage stresses. The crack damage stress, being the threshold value at which unstable crack propagation begins, is suggested to be used as the true strength of UHPC in structural design. The influence of matrix composition and fiber volume on these parameters is brought out, to better elucidate the influence of material design on properties. Digital image correlation (DIC) on unnotched beams under flexure is used to show the fundamental differences in the matrix properties that lead to differences in strain localization. The beneficial influence of fibers on strain localization in UHPC mixtures is also brought out. [ABSTRACT FROM AUTHOR]

This paper addresses the effects of loading rate and notch-to-depth ratio on flexural properties of ultra-high-performance concrete (UHPC) notched beam specimens, in order to enable use of standardized laboratory test data to predict flexural properties of UHPC structures that have different dimensions and are subjected to a range of loading rates. UHPC notched beams were tested in three-point bending to study the effects of three notch-to-depth ratios of 1/6, 1/3, and 1/2 at five loading rates of 0.05, 0.50, 1.25, 2.50, and 5.00 mm/min on flexural performance. Test results indicate that loading rate and notch-to-depth ratio have significant effects on flexural properties of the UHPC notched beams. The flexural strength is shown to increase with the loading rate and the notch-to-depth ratio. The fracture energy increases with the loading rate but decreases with the notch-to-depth ratio. The changes of flexural properties with the loading rate are also dependent on the notch-to-depth ratio. Regression analyses to correlate flexural properties associated with the loading rate and notch-to-depth ratio were conducted to obtain parameters for UHPC structures. [ABSTRACT FROM AUTHOR]

The fracture behavior of a novel structural binder developed using carbonation of metallic iron powder is investigated using notched beams under three-point bending. The iron-based binder demonstrates significantly higher fracture energies compared to conventional ordinary Portland cement binders in both unreinforced and glass fiber-reinforced states. The influence of metallic iron particle inclusions and the carbonate binder on the strain energy release rates ( R ) and width of the fracture process zone (FPZ; which is the zone of strain localization at the tip of the crack) are evaluated and compared to that of Portland cement-based binders. Tensile constitutive response of these binders is extracted using a crack-face bridging model. The control and fiber-reinforced iron-based binders demonstrate higher tensile strength and ultimate strain capacity as compared to conventional cementitious binders. [ABSTRACT FROM AUTHOR]

Numerical and empirical models addressing the drying shrinkage cracking behavior of joint-free steel-fiber-reinforced concrete (SFRC) slabs are presented. Effect of water--cement ratio, admixtures, and free shrinkage are considered. Mechanical restrictions including base friction, fiber dosage, and interfacial bond properties restrain the growth of microcracks into main cracks and also reduce crack opening. A model based on a finite-difference equilibrium solution of a one-dimensional (1D) slab on frictional ground simulates the formation and subsequent opening of cracks in the slab. Results are compared with an empirical predictive tool for crack opening. A sensitivity study shows that correlation of predicted crack opening reduced by increasing fiber volume, base friction, and interfacial bond strength. Case studies are conducted on three slabs in service at different occasions and both models are used to predict the crack opening. While these models are developed based on different methodologies, they are related to a great extent by addressing the same mechanical characteristics. A simple method to estimate the slab curl is proposed and a parametric study has been conducted. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a material model suitable for simulating the behavior of dry fabrics subjected to ballistic impact. The developed material model is implemented in a commercial explicit finite element (FE) software LS-DYNA through a user defined material subroutine (UMAT). The constitutive model is developed using data from uniaxial quasi-static and high strain rate tension tests, picture frame tests and friction tests. Different finite element modeling schemes using shell finite elements are used to study efficiency and accuracy issues. First, single FE layer (SL) and multiple FE layers (ML) were used to simulate the ballistic tests conducted at NASA Glenn Research Center (NASA-GRC). Second, in the multiple layer configuration, a new modeling approach called Spiral Modeling Scheme (SMS) was tried and compared to the existing Concentric Modeling Scheme (CMS). Regression analyses were used to fill missing experimental data – the shear properties of the fabric, damping coefficient and the parameters used in Cowper-Symonds (CS) model which account for strain rate effect on material properties, in order to achieve close match between FE simulations and experimental data. The difference in absorbed energy by the fabric after impact, displacement of fabric near point of impact, and extent of damage were used as metrics for evaluating the material model. In addition, the ballistic limits of the multi-layer fabrics for various configurations were also determined. [Copyright &y& Elsevier]

Abstract: Dynamic tensile tests were conducted using a high speed servo-hydraulic testing machine on three types of fabric reinforced cement composites. The high speed testing procedure and data processing method are presented. Quasi-static tests were also conducted on the composites. Effects of strain rate on the mechanical properties of fabric–cement composites are noted. A good correlation was found between the properties of the fabrics and the composites, with the carbon fabric exhibiting the highest strength and ductility performance in high speed tensile tests. The differences in tensile behavior of the various composites were correlated with the differences in the role of the fabric materials. Composites tested under high speed loading exhibited different responses as compared to similar composites tested under quasi-static condition. [ABSTRACT FROM AUTHOR]

Abstract: The experimental behavior of sisal fiber reinforced cement composites subjected to high speed tension load was studied. High strain rates were achieved by using a high rate servo-hydraulic testing machine. A state-of-the-art high speed Phantom camera was also used to take images from the specimen during the test. The images were used in a digital image correlation model to determine the displacement fields and to calculate crack spacing. The effect of strain rate was investigated by comparing static and dynamic tensile tests which were performed at strain rates ranging from 5.5×10−6 to 24.6s−1, respectively. A numerical tension stiffening model based on nonlinear finite difference method was used to simulate tensile cracking behavior of sisal fiber cementitious composites. The composite presented strain rate sensitivity for ultimate tensile strength and strain capacity with a dynamic amplification factor of 1.26. [Copyright &y& Elsevier]

Abstract: Fabric–cement composites developed using the pultrusion production process have demonstrated impressive tensile and flexural properties. For instance fabric reinforced composites with bonded Alkali Resistant (AR) glass fabrics exhibit strain-hardening behavior, tensile strength in the range of 20–25MPa, and strain capacity of the order of 2–5% under static conditions. Properties of these composite systems were investigated under three point bending conditions using an instrumented drop weight impact system. Samples were studied from the viewpoint of the variations of impact load, deflection response, acceleration and absorbed energy. Development of the testing system in terms of components and acceleration response are discussed in detail. Methods of the impact load measurement using three different ways of acceleration response, piezoelectric load washer and conventional strain gage based load cell are discussed. Cement composites with two different fabric contents and four different drop heights of hammer (dropping mass) were tested. Experimental results indicate that for the same drop height, the stiffer beam type specimens have a lower ultimate deflection but a higher load carrying capacity than the plate type specimens. The maximum flexural stress and absorbed energy of composites increase with drop height. In beam specimens, complete fracture does not take place as cracks form and close due to rebound and significant microcracking in the form of radial fan cracking is observed, whereas interlaminar shear is the dominant failure mode in the plate specimens. [Copyright &y& Elsevier]

Abstract: This paper compares the effects on the bond between fabric and cement matrix of three different processing methods: casting, pultrusion and vacuum condition. The fabrics included bonded glass mesh, woven polyvinylalcohol, and warp knitted weft insertion polypropylene. Pullout tests were performed to examine the bond between fabric and cement matrix. A microstructural analysis was conducted and correlated with pullout data. Improved bonding was obtained for fabric–cement composites produced with the pultrusion process, particularly for fabrics composed of multifilament yarns that have open junction points and no sizing to seal individual yarns. This improved bonding results from the impregnation of the fabric in the cement chamber during the pultrusion process, which filled the spaces between the filaments of the multifilament yarns. [Copyright &y& Elsevier]

• Linking nanomechanical response and qualitative chemical maps for ultra-high performance binders. • 30–50% replacement of cement by mass. • HD C-S-H and UHS phases determined to have similar mean Ca and Si intensities. • Mean Ca/(Si + Al) intensity ratio lower for the UHS phase, with a higher Al incorporation. • Al incorporation in UHP binders more dependent on Ca/Si ratios than the Al content. Ultra-high performance (UHP) cement pastes with 30–50% of cement (by mass) replaced by multiple cement replacement materials are evaluated in this study through concise nanomechanical investigations and qualitative chemical intensity mapping. Nanomechanical clustering identifies high density (HD) C-S-H and an ultra-high stiffness (UHS) phase as the major reaction products in very low w/b UHP pastes. Chemical mapping revealed HD C-S-H and UHS phases to have similar mean Ca and Si intensities. The indentation modulus (M) - hardness (H) relationships for the C-S-H phases in the UHP pastes are similar irrespective of their starting compositions. The mean Ca/(Si + Al) intensity ratio is found to be lower for the UHS phase, and the Al incorporation is noted to be higher. The Al incorporation in the C-A-S-H gel is seen to depend more on the Ca/Si ratio of the gel rather than on the amount of Al in the starting materials. The normalized chemical intensities and ratios of Ca, Si, and Al species, along with the mechanical property description provided by nanoindentation, allows for further insights into the microstructure of complex, heterogeneous systems such as UHPC pastes. [ABSTRACT FROM AUTHOR]

• Nanomechanical response of highly heterogeneous ultra-high performance cement pastes. • Elucidates the influence of very low w/b and high volume of cement replacement materials on the nanoscale response. • Explains the reasoning for an ultra-high stiffness phase in UHPC pastes. • Models to upscale elastic modulus from nanoscale measurements and their applicability. The nanomechanical signature of highly heterogeneous ultra-high performance (UHP) cement pastes are explored in this paper. The UHP pastes are proportioned using 30% or 50% (by mass) of commonly available cement replacement materials including fly ash, microsilica, and fine limestone. Nanoindentation experiments coupled with a Bayesian information criterion-based statistical approach is used to develop modulus-hardness (M−H) clusters for the UHP pastes. While typical low-density (LD) and high-density (HD) C-S-H phases are present in early-age UHP pastes, it is shown that an ultra-high stiffness (UHS) phase, which is a composite of HD C-S-H and nanoscale CH, is predominant at later ages. Nanoindentation data points to the presence of significantly higher proportions of mixed phases in the UHP pastes, comprising of cement hydrates/pozzolanic reaction products and unreacted phases including fine limestone and microsilica acting as micro-aggregates to enhance the stiffness of the paste. The presence of such mixed phases complicates upscaling of the elastic modulus using multi-scale homogenization models, which is to be carefully accounted for in such highly heterogeneous systems. [ABSTRACT FROM AUTHOR]

Present research brings a broad analysis on the influence of steel fibers on quasi-static and fatigue rebar pull out loading. The analysis covers the impact of fiber addition on diverse mechanical parameters, such as peak bond strength, stiffness and bond degradation under fatigue. A model previously developed for single fiber pull out in the literature was modified in order to study the bond response through analytical equations. The fiber reinforcement is responsible for providing post-crack resistance to the composite, raising the confinement around the interface and significantly increasing the peak bond strength. Moreover, by enhancing the bond strength, the addition of steel fibers could successfully increase fatigue life of cyclic pull out tests. Finally, the proposed model for rebar pull out from steel fiber reinforced concrete matrices successfully fitted the bond-slip behavior observed the experimental data. The model divided the bond-slip response in three distinct stages: elastic, nonlinear and dynamic. • Positive influence of the fiber addition on the bond-slip mechanical response. • Analytical model divided into three major stages: elastic, nonlinear and dynamic. • Analytical model successfully fitted the studied experimental results. • The fiber addition successfully enhanced bond-slip behavior under fatigue loading. [ABSTRACT FROM AUTHOR]

Present research brings a novel methodology to estimate FRC mechanical degradation throughout closed-form solutions for FRC beams. The first step consisted on deriving the constitutive relations for tension and compression. While a quad-linear model was used for tension, an elastic perfectly plastic model was applied for compression aiming to reach the moment-curvature with the closed-form solutions. Crack opening is, subsequently, verified using the characteristic length and the evaluated tensile strains, which allows to evaluate crack increase under quasi-static loading. With the complete composite quasi-static mechanical characterization, the next step is to evaluate CMOD increase under fatigue loading with the proposed power law equation and the material S-N curve. Finally, the CMOD evolution under fatigue is estimated and the back-calculations bring the evolution of the other mechanical parameters along the cycles. The methodology was applied for three distinct concrete compositions in the literature and the results correctly fitted the observed CMOD evolution along the cycles. • A novel model for CMOD evolution under fatigue is proposed. • CMOD evolution under fatigue calibrated based on published literature. • Closed-form solutions applied to verify the mechanical degradation along the cycles. • Deformation and crack length evolution under fatigue estimated analytically. [ABSTRACT FROM AUTHOR]

Abstract The pullout behavior of single filament jute fibers and yarns from a low calcium hydroxide cement matrix were studied. Pullout tests were performed in the micro and meso scales. In the micro scale, the tests were conducted inside an environmental SEM. The fibers were treated with styrene butadiene polymer to improve the fiber-matrix bond and a double-sided pullout configuration was used for the meso scale tests. An analytical model was used to calculate the parameters related to adhesional, frictional, and dynamic bond slip mechanisms between jute fiber and matrix. Results showed that the polymer coating increased the bond up to 130%. The fiber matrix bond at the meso scale also yielded higher values for the polymer-coated fibers. The analytical model is observed to fit the experimental results with the parameters of the maximum shear and frictional stresses that correlate well with the nominal interface strength. [ABSTRACT FROM AUTHOR]

A standard approach is presented to obtain analytical solutions for deflection field of determinate beams subjected to conventional loading patterns. The solutions are based on a trilinear moment–curvature response using a deflection hardening behavior characterized by flexural crack initiation, inelastic response due to crack extension, and full plastic hinge formation. Methodology for full span deflection and rotation distributions are presented for multiple cases that include three‐ and four‐point bending, uniform load, concentrated moment, and cantilever beams. The proposed approach provides analytical expressions for the curvature, rotation, and deflection at any point along the beam, and correlated to stress or strain distribution. The procedure can therefore be integrated into a serviceability‐based design approach. A parametric study of the effects of model parameters on the stages of the response is addressed. Several case studies involving steel fiber reinforced concrete (SFRC), textile reinforced concrete (TRC) and ultra‐high performance concrete (UHPC) are conducted and the simulated load‐deflection responses are verified against the experimental data from several published experiments. Size effect on the serviceability limits of beams with spans ranging from 0.22 to 8.6 m is studied by tracking the full‐range moment–curvature and load‐deflection responses. [ABSTRACT FROM AUTHOR]

Precast tunnel lining segments manufactured with synthetic macro-fibers and steel fibers as the primary reinforcement were tested under flexural and edge compression loading. Since steel fibers are usually prescribed as the primary reinforcement of tunnel sections, the dosage of synthetic fibers was determined by matching their residual flexural strength. The performance of tunnel segments was verified using the extensive data collected from instrumented deflection, crack growth, quantitative DIC, and strain gauge results and correlated with the load vs. deformation response. Results show that synthetic fibers can meet the design load requirements specified for the steel fibers reinforcement. Flexural test results indicate a 16% increase in macro-fiber content from 0.80% to 0.93% by weight resulting in a 32% increase in the residual strength of standard beam samples and a 41% increase in the residual strength of full sections. Compared to the steel fiber samples, samples with polymeric macro-fiber had a 6.5% higher average toughness. The full-scale load-deflection results were within 7% of the average values in each category of samples which is almost half the variation in the flexural ASTM C1609 results. The edge compression tests indicated that the mode of failure under concentrated jack forces is governed and dominated by the tensile lateral bursting stresses resulting from inefficient distribution of the load to the supporting edge. [ABSTRACT FROM AUTHOR]

Abstract The fracture response of cementitious composites containing compliant microencapsulated inclusions and its influence on the fracture process zone (FPZ) are reported. The incorporation of small amounts of phase change material (PCM) microcapsules (replacing up to 10% by volume of sand) is found to slightly improve the strength, fracture toughness, critical crack tip opening displacement (CTOD c), and the strain energy release rates. Digital image correlation is used to examine the FPZ at the tip of the advancing crack, to better explain the influences of compliant microscale inclusions on energy dissipation. The FPZ widths are found to slightly increase with PCM dosage but its lengths remain unchanged. The increase in FPZ width is linearly related to the CTOD c , showing that inelastic deformations of the crack-tip in the direction of crack opening are indeed influenced by microscale inclusions. It is shown that cementitious systems containing microencapsulated PCMs can be designed to demonstrate mechanical performance (including fracture) equivalent to or even better than their PCM-free counterparts, in addition to the well-described thermal performance. [ABSTRACT FROM AUTHOR]

This paper reports synthesis routes and microstructural and performance characterization of a family of economical, multifunctional porous ceramics developed through geopolymerization of an abundant volcanic tuff (aluminosilicate mineral) as the primary source material. Metakaolin, silica fume, alumina powder, and pure silicon powder are also used as additional ingredients when necessary, and activated by potassium-based alkaline agents. The composition and heat treatment regimes are modified to provide the desired pore structure features for percolation, contaminant retention, and thermal conductivity. The treatment temperatures used are lower than those used in conventional porous ceramics synthesis. Extensive microstructural characterization using different techniques to examine the morphology and to quantify the pore volumes, sizes, and connectivity, which are important in dictating the performance characteristics, are reported. Measurements of flow rates and thermal conductivity demonstrate the multifunctionality of the synthesized matrices, which demonstrate adequate strengths for a number of buildings-related applications. [ABSTRACT FROM AUTHOR]

This paper reports strategies to design the binder phase of ultra-high performance concretes (UHPC) from commonly available cement replacement (fly ash, slag, microsilica, metakaolin) and fine filler (limestone) materials. A packing algorithm is used to extract the number density, mean centroidal distance, and coordination number of the microstructure. Similarly, rheological studies on the pastes provide yield stress, plastic viscosity, and min-slump spread. The selection criteria involves using the three microstructural and three rheological parameters individually or in combination to define packing and flow coefficients. The selection criteria is flexible enough to allow users modify the constraints depending on the application. In this study, only ternary and quaternary blends, with a total cement replacement of 30% by mass are selected for further characterization. The highly efficient microstructural packing in these mixtures and better workability that facilitated dispersion of particles to enhance the reactivity results in beneficial pore structure and mechanical properties. [ABSTRACT FROM AUTHOR]

This study proposes a comprehensive analysis on the structural performance of reinforced Recycled Aggregate Concrete members. Particularly, it summarizes the results of an experimental investigation aimed at analyzing the tension stiffening behavior of normal and high strength class concretes produced with Recycled Concrete Aggregates (RCAs). The mixtures were proportioned in order to achieve 25 and 65 MPa of compressive strength and, moreover, several recycled-to-natural coarse aggregates replacement ratios were considered: 0%, 25% and 50%. The results derived from this type of test furnish a comprehensive analysis on both the steel-to-matrix interaction and the crack formation and propagation on concrete elements as well as distributed cracking mechanisms. Using a finite difference numerical model, the experimental results are used to back-calculate and identify the steel-to-concrete bond slip law. Also, it is an alternative mean of developing the stress-crack-width law for concrete in tension. The results showed that the use of recycled concrete aggregate does not affect the resulting concrete performance and, therefore, the RCAs can be successfully employed, up to the levels analyzed herein, for the production of structural elements made with normal and high strength class concrete mix. [ABSTRACT FROM AUTHOR]

The work in hand presents results of an experimental and numerical research on the post-heating residual strength of a basalt textile refractory composite submitted to tensile loading. The tensile tests were performed after a preheating process at temperatures ranging from 25 to 1000 °C. The mechanical performance and cracking mechanisms were discussed and compared to that obtained at room temperature. Image analysis by means of digital image correlation method was used to obtain the evolution of crack width which was subsequently correlated with the stress response for all target temperatures. Scanning electron microscopy was used to investigate the damage processes in the fiber–matrix interfaces after exposure to high temperatures. A finite difference model was used to simulate the tension stiffening behavior of TRC (Textile Reinforced Concrete) systems predicting their crack spacing and stress vs. strain responses. The obtained results indicated that due to the coating decomposition the reliability of basalt TRC can only be guaranteed from room temperature to 150 °C. [ABSTRACT FROM AUTHOR]

High-strength fabrics are ideal materials for use in structural and aerospace systems where high-performance and lightweight structures are demanded. Mechanical characterization of this class of materials under dynamic loading is of great importance considering extreme conditions such as explosion, impact, and ballistic loading. The strain-rate effect on the tensile behaviors of unidirectional glass, basalt, carbon, and plain-woven aramid fabrics were evaluated under various strain rates (25, 50, and 100 s-1) using a servohydraulic high-rate testing system. The stress-strain responses and failure modes of these fabrics at the investigated strain rates were studied. Quasi-static tests were also performed as a comparison. The results showed that as the strain rate increased from 25 to 100 s-1, the average tensile strength of basalt, carbon, glass, and aramid fabrics increased from 1,095 to 1,743, 1,516 to 1,974, 1,072 to 1,462, and 1,530 to 1,897MPa, respectively. Toughness and maximum strain were also found to be increased. The significance of strain-rate effect on the material properties of different fabrics was statistically tested using ANOVA. The P-values of tensile strength, toughness, maximum strain, and Young's modulus of all materials were less than 0.05, except for the maximum strain of basalt (P-value of 0.3134) and the toughness (P-value of 0.1832) and Young's modulus (P-value of 0.0662) of aramid. [ABSTRACT FROM AUTHOR]

Plastic shrinkage cracking in restrained cement pastes reinforced with wollastonite particles of micro and submicron sizes was studied using a quantitative two-dimensional (2D) cracking experiment. A series of blended paste mixes with portland cement and different grades of wollastonite fibers were developed and tested under low vacuum conditions. Testing parameters included four grades of wollastonite with aspect ratio in the range of 3:1-20:1 and average particle size ranging from 33 to 2,000 µm at 15% cement replacement. Wollastonite beneficially altered the shrinkage cracking morphology by arresting crack growth, wherein crack lengths and widths were reduced by a factor of two, and the area by a factor of three when compared with the control specimens. However, the initial evaporation rate, early age diffusivity, and cumulative moisture loss increased. Influence of the microfibers in controlling early age drying were related to the porosity of the microstructure using mercury intrusion porosimetry (MIP). [ABSTRACT FROM AUTHOR]

Unidirectional carbon fiber reinforced polymer (CFRP) composites fabricated by Vacuum Assisted Resin Transfer Molding (VARTM) are tested at four initial strain rates (25, 50, 100 and 200 s −1 ) and six temperatures (−25, 0, 25, 50, 75 and 100 °C) on a servo-hydraulic high-rate testing system to investigate the effects of strain rate and temperature on their tensile properties and failure behaviors. A high speed digital camera is used to capture the deformation and failure behavior of the CFRP composites at a sampling rate of 20,000 fps with resolution of 256 × 256 pixels. In order to illuminate corresponding strain rate effect mechanism, carbon yarn samples are complementally tested under dynamic tensile loading at four different strain rates (40, 80, 120 and 160 s −1 ) utilizing an Instron drop-weight impact system. The stress–strain responses at these strain rates are discussed. A Weibull statistics model is used to quantify the degree of variability in tensile strength and to obtain Weibull parameters for engineering applications. The non-uniform strain and displacement fields as well as the damage process are characterized by digital image correlation (DIC) method. [ABSTRACT FROM AUTHOR]