Direct Tensile Research Articles

Mesoscale modelling of SFRC based on 3D RBSM considering the effects of fiber shape and orientation

In this study, a mesoscale model of steel fiber reinforced concrete (SFRC) based on 3D RBSM (rigid body spring model), was proposed to take the fiber shapes (straight and hook end) and orientation into account in concrete. The steel fibers were distributed into the Voronoi mesh system of RBSM, and a zero-size spring was assigned at the interface of Voronoi mesh crossed by discrete fiber, to transfer the fiber pullout load to the nearest nodes of RBSM. The straight steel fiber was modeled based on proposed local bond-slip relationship and the mechanical hook action was proposed additionally to model the hook end fiber. The model can predict the macroscopic response and cracking of SFRC made with straight and hook end fibers under direct tensile and bending loads. The analysis results found the mechanical hook action as the governing parameter for hook end fiber then the bond-slip properties for straight fiber. The fiber orientation and matrix spalling due to friction induced pullout load component, were found prominent for steel fiber. The anisotropy induced by fiber shapes and orientations was headed by hook end fiber with superior macroscopic load capacity by delaying the crack propagation and transformation.

A Direct Tensile Strength Testing Method for Concrete from Existing Structures

Tensile strength is a crucial property for the function, safety and durability of all concrete structures. The general procedure to assess the tensile properties of concrete from existing structures is to perform indirect tests and predict the tensile strength based on established empirical relationships. In this study, the direct tensile strength of concrete was investigated using cylindrical specimens. The aim of the study was to propose, test and evaluate a general method for direct tensile tests of concrete from existing structures. A total of 16 specimens were tested under deformation-controlled tensile-loading until failure. The concrete samples were prepared with 10 or 15 mm grooves at mid-height to obtain cracking in the groove region, where the crack-opening sensors were installed. The load and corresponding deformation were recorded continuously during the test to obtain the load–crack-width relationship of the concrete. The tests showed that the method can be used to assess the tensile properties of concrete from existing structures. The study provides important insights regarding the assessment of direct tensile strength of concrete and the results can be used to improve the structural health monitoring of existing structures and thereby ensure their safety and durability.

Experimental investigation and micromechanics-based damage modeling of tensile failure of polymer concrete reinforced with recycled PET bottles

Epoxy-based polymer concretes (PCs) behave in a quasi-brittle manner and suffer from low tensile strength. Adding different kinds of fillers has been widely used to improve the ductility of these materials and change the failure mechanisms. In this study, we used polyethylene terephthalate (PET) fillers from recycled bottles to enhance the tensile strength and ductility of PCs and prevent sudden brittle failure. Two different sizes of fillers (i.e., fine and coarse) are considered and the Brazilian disk configuration is used to measure the indirect tensile strength of reinforced PCs. Experimental results showed that the addition of coarse PET fillers to the PC has more significant effects on tensile strength and failure mechanism than fine PET fillers. Then, micromechanical damage analyses are conducted via finite element simulations of two-dimensional representative volume elements. The effects of void content and recycled PET fillers on the tensile strength and ductility of reinforced PCs were studied in the micromechanical simulations. Since the Brazilian disk examines the indirect tensile behavior, a relationship was proposed between the direct micromechanical tensile strength and the indirect macro mechanical tensile strength. The new procedure is experimentally validated for the prediction of the tensile strength of both reinforced and unreinforced PCs.

Analysis of Low-Temperature Rheological and Mechanical Properties of Steel Slag Asphalt Mixture Based on Direct Tensile Test

Due to the high resource requirements for specimen preparation and testing equipment, the direct tensile test method is seldom used to study the cracking behavior of asphalt mixture at low temperatures. In this study, three asphalt mixtures were prepared in which all of the basalt or part of the basalt and basalt aggregate was replaced by steel slag. Through the direct tensile creep test and direct tensile relaxation tests including the measurement of creep rate, cumulative strain change rate, and relaxation time, the variation law of rheological properties of low-temperature steel slag asphalt mixture was analyzed and the variation law of viscoelastic properties was explored. Meanwhile, based on the traditional viscoelastic constitutive model, the creep compliance and relaxation modulus were fitted. The mechanical response of the transformation from creep compliance to relaxation modulus of steel slag asphalt mixture was analyzed by a numerical method. The results show that, with the decrease of temperature, the creep rate εs and cumulative strain change rate of the three asphalt mixtures gradually decline, and the relaxation time gradually increases. In particular, when the temperature was reduced from −20°C to −30°C, the cumulative strain change rate of all three asphalt mixtures reached the minimum, which was less than 10%. Moreover, none of them relax to 75% σ0 within 3,600 s at −30°C. The mixture specimens with steel slag replacing all basalt exhibited the best low-temperature deformation adaptation performance under different temperature conditions. Mixture specimens with basalt as aggregate have the worst low-temperature deformation adaptation performance. The relaxation modulus obtained by the measurement of creep compliance is similar to that obtained by testing, and the relaxation modulus calculated through the direct tensile test is more accurate.

A Framework for Determining Direct Tensile Properties of Ultra-High-Performance Concrete

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Dynamic mechanical behavior of strain-hardening cementitious composites under drop weight impact loading

Dynamic mechanical behavior of strain-hardening cementitious composites (SHCC) incorporated with different fly ash content at various curing ages was investigated using drop weight impact test. Direct tensile, compressive and bending tests were conducted on SHCC incorporated with various fly ash content. Two-parameter Weibull distribution was performed to analyze the variation of the results of SHCC after drop weight impact test under various curing ages from the perspective of reliability function. The cracking area ratio and fractal dimension were used to quantificationally investigate the failure characteristics of SHCC after the drop weight impact loading. Results indicate that the tensile, compressive, flexural strength and impact energy absorption capacity of SHCC decrease as the increasing of fly ash content. Impact ductility decreases slightly with the curing age. Single impact energy has an obvious effect on the impact resistance of SHCC, and it has a greater influence on the crack width at the initial cracking of SHCC than the crack width at failure. The two-parameter Weibull distribution can estimate the impact properties of SHCC by calculating the impact times at initial cracking and failure of SHCC. Cracking area ratio and fractal dimension can intuitively assess the impact failure characteristics of SHCC. Scanning electron microscopy images show that fibrillation and uneven scratches appear on the surface of the fibers, and the wavy texture can be observed in the axial direction of the fiber, indicating fiber pull-out is a typical failure pattern of the fiber under dynamic loading.

Influence of Fiber Type and Dosage on Tensile Property of Asphalt Mixture Using Direct Tensile Test.

In engineering practice, fiber addition is a frequently used method to improve the tensile property of asphalt mixture. However, the optimum fiber type and dosage have not been determined by direct tensile tests. In this paper, monotonic tensile tests were conducted on three kinds of stone mastic asphalt (SMA13) mixtures, that is, granular-lignin-fiber-reinforced SMA (GFSMA), flocculent-lignin-fiber-reinforced SMA (FFSMA), and basalt-fiber-reinforced SMA (BFSMA) at different fiber dosages to probe the influence of fiber dosage on their tensile mechanical indexes (tensile strength, ultimate strain, elastic modulus, and strain energy density) and to determine the optimum dosage of each kind of fiber. The results showed that with the elevation of fiber dosage, the tensile strength, elastic modulus, and strain energy density of all three kinds of asphalt mixtures increased first and then decreased, while the ultimate strain increased constantly. The optimum dosage was 0.50 wt%, 0.45 wt%, and 0.50 wt% for granular lignin fiber, flocculent lignin fiber, and basalt fiber, respectively. On this basis, strain-controlled direct tensile fatigue tests were conducted on the three kinds of asphalt mixtures at the corresponding optimum fiber dosage. The results indicated that asphalt mixture reinforced with 0.50 wt% granular lignin fiber exhibited ideal direct tensile fatigue performance with respect to fatigue life and accumulative dissipated energy. Therefore, granular lignin fiber is recommended as the favorable fiber type, and its optimum dosage is 0.50 wt%. Moreover, scanning electron microscopy (SEM) demonstrated that the essence of the impact of fiber dosage and type on the tensile property of SMA is whether the reinforcement effect on the mixture matrix outweighs the negative effect of the defects between fiber and mixture matrix, or whether the reverse applies.

Mechanical Properties of Giomer After Immersion in Carbonated Drinks


 Introduction: Giomer is a resin-based restorative material consisting of prereacted glass ionomer (PRG) filler which can release fluoride. Carbonated beverages, popular beverages which contain acids that rich in H+ ions, can diffuse into the resin-based restoration and cause high solubility. Objective: To analyze the effect of immersion in carbonated drinks on water absorption and diametral tensile strength of giomer. Methods: Giomer was packed into a stainless-steel mold to obtain sample with diameter of 6.0±0.03mm and height of 3.0±0.09mm. The samples were divided into 2 groups for water absorption test and 3 groups for diametrical tensile strength test. Ten samples of giomer were soaked in artificial saliva for 4 days as a control group, 10 giomer samples were immersed in carbonated drinks for 6 hours, then replaced with artificial saliva for 18 hours and repeated for 4 days as a treatment group, and 10 samples of giomer were used as immediate group for direct diametral tensile strength test. Samples were incubated at 37°C. Results: Mann-Whitney test showed no significant difference (p>0.05) in giomer absorption between the control group (0.99±0.54%) and the treatment group (2.37±2.62%). One Way ANOVA test showed significant difference (p<0.05) in giomer diametral tensile strength among the immediate group (29.6±3.7MPa), the control group (51.1±3.9MPa) and the treatment group (44.8±5.3MPa). Conclusion: Immersion in carbonated beverages did not show significant difference with artificial saliva for the water absorption ability of giomer. However, the diametral tensile strength of giomer decreased after immersion in carbonated beverages for 24 hours.

Full-scale and laboratory investigations on the performance of asphalt mixture containing recycled aggregate with low viscosity binder

The proposed research aims to evaluate the practical application of the reclaimed asphalt pavement (RAP) mixture fabricated from recycled aggregate with the low-viscosity extracted binder. To cope with this objective, the combined effects of extracted binder’s absolute viscosity and nominal maximum aggregate size (NMAS) of recycled aggregate on the performance of the RAP mixture were investigated in the research. Various mix designs and laboratory experiments were then developed to examine the characteristics of RAP specimens including Indirect Tensile Strength, Direct Tensile Cyclic, Dynamic Modulus, and Hamburg Wheel Tracking tests. Afterward, the full-scale testbed accompanied by Heavy Vehicle Simulator was performed in the field to verify the practical application of the best RAP mixture. Regards to the improvement method, the low-viscosity binder (700 Poise) techniques were added to the mixture to enhance the performance of the RAP. In general, the test results reveal that the absolute viscosity of extracted binder of recycled aggregate should be controlled at lower than 40,000 Poise to ensure proper durability. Meanwhile, the application of 80,000 Poise recycled aggregate may result in a critical drop in cracking and permanent deformation resistance. Further, the NMAS of 13 mm of recycled aggregate is suggested to be applied in the RAP mixture instead of the 10 mm type to enhance the bearing capacity of the recycled mix. The results also suggest the slight contribution of the proposed measure to partly restore the capacity of the RAP mixture while the field test result confirmed equivalent rutting results between the controlled and RAP section.

Evaluation of Engineered Cementitious Composites (ECC) containing Polyvinyl Alcohol (PVA) fibers under compressive, direct tensile, and drop-weight test

Evaluation of Engineered Cementitious Composites (ECC) containing Polyvinyl Alcohol (PVA) fibers under compressive, direct tensile, and drop-weight test

Research on strength and fatigue properties of asphalt mixture with different gradation curves

The gradation design has an essential influence on the mechanical properties of asphalt mixture. Strength and fatigue are two critical mechanical properties of asphalt pavement structure. The purpose of this paper is to reveal the strength and fatigue properties of asphalt mixture with four gradation curves within the range of AC-16, namely Types A, B, C, and D. Strength and fatigue tests were conducted under indirect tensile, direct tensile, and unconfined compressive loading modes. The strength of asphalt mixture with various gradation curves shows a power function relationship with the loading rate. The fatigue performance of asphalt mixture with different gradation curves was first analyzed based on the conventional S-N fatigue model. Then, the unified fatigue models under three different loading modes were established based on the fatigue stress strength ratio, which reduced the difference of S-N fatigue equation parameters. Furthermore, the unified fatigue equations achieved the unity of strength failure and primary fatigue failure. The analysis results indicate that the mixture with Type D gradation curve realizes the highest strength and most extended fatigue life. This research contributes to the gradation design of asphalt mixture. And the unified fatigue equation provides a reference for the durability design of pavement.

Impact of Glass Waste on the Flexural, Compressive, and Direct Tension Bonding Strengths of Masonry Bricks

The waste material problem in today's world has become a major topic affecting all sectors of human life. Researchers are interested in providing solutions for each kind of waste material. Waste glass is one of the waste materials whose amounts increase daily. This article deals with two types of modified cement mortar with glass granular in the masonry wall to find their effect on the wall's property (direct tensile, flexural, and compressive bond strength). Seven different mixes were prepared according to the used glass granular ratio (three mixes contained white glass with 15, 20, and 25% while three of them contained green glass granular 5, 10, and 15%, and the last mix was a controlled mix which contains no glass granular).Based on the obtained result, the used white glass granular provides optimum compression and direct tensile bond strength when 20% of sand is replaced with white glass granular; optimum direct tensile bond value was obtained, which increased by 1.4% and increased compressive strength by 13.08% compared to control mortar. Green glass granular provides optimum compression and direct tensile bond strength when 10% of sand is replaced, direct tensile strength by 1.02%, and increased compressive strength by 3.7% compared to control mortar. The increase of the used waste glass granular in the mortar decreases flexural bond strength, and the amount of decrease depends on the chemical glass compositions.

EFFECT OF WASTE GLASS ADDITION AS A REPLACEMENT OF SAND ON PROPERTIES OF ECO-FRIENDLY POLYMER MORTAR

Polymer concrete is a fine aggregate bound with a polymer binder instead of cement as in conventional concrete. The main aim of this research is investigation some properties (compressive strength, direct tensile strength, dry density) of epoxy polymer mortar with recycled glass as partial replacements of normal sand. According to the findings of this study, waste glass was substituted for 5%, 10%, 15%, and 20% of the sand in polymer mortar, respectively. When using waste glass as an alternative to natural sand, a decrease in dry density is observed when compared to the reference mixture by 2.14%, 2.23%, 2.32% at 7 days, 14 days and 28 days, respectively. Addition of 5%, 10%, 15% and 20% of waste glass as a partial substitute for natural sand leads to improvement the mechanical properties (direct tensile and compressive strength) of eco friendly polymer mortar. The results showed that recycled glass with 20% replacement ratio has given best results when compared with reference mix and other ratios. Finally, a regression analysis is used to establish the link between tensile strength and compressive strength.

Experimental study on factors influencing ERC-NSC interface bonding performance

The short-term behavior and long-term durability of materials for structural strengthening are significantly affected by their bond properties and compatibility with the existing substrate. In this study, the bonding performance between a normal strength concrete (NSC) substrate and an epoxy resin concrete (ERC) layer was investigated by applying direct tensile, splitting tensile, bi-shear, and slant shear tests, and the interfacial bond strength and corresponding failure modes were explored. Several factors that may affect the interfacial bond strength, including the ERC age, substrate moisture degree, and interface inclination angle, were examined to explore their influences. The results reveal that the increase in ERC age resulted in various degrees of increment for the bond strength among the four tests. The saturated surface dry (SSD) preparation method slightly increased the bond strength by 3 % in the splitting tensile tests. However, moisture at the substrate interface reduced the bond values by 25.5 %, 29.67 %, and 16.9 % in the direct tensile, bi-shear, and slant shear tests, respectively. As the inclination angle increased, the bonding strength of the slant shear test increased, while a larger inclination angle reduced the likelihood of interfacial failure. Furthermore, the minimum cohesion and shear friction coefficients were determined to be 2.26 MPa and 1.68 for air surface dry preparation and 1.62 MPa and 1.48 for SSD preparation.

Mechanical Responses of Granite Under Confined Direct Tensile Testing: Fracture, Strength, Energy Conversion and Mechanism

Mechanical Responses of Granite Under Confined Direct Tensile Testing: Fracture, Strength, Energy Conversion and Mechanism

Uniform fatigue characterization of high modulus asphalt mixtures under three-dimensional stress state

To improve the durability of asphalt pavement, high modulus asphalt mixtures were developed and widely utilized to construct heavy trafficked pavements to resist rutting. Except for rutting, serving under repeated heavy loads, pavements with high modulus asphalt mixtures are also vulnerable to fatigue cracking. To prevent fatigue cracking, the fatigue resistance of high modulus asphalt mixtures is a crucial indicator for pavement structural design and checking computations, which is generally obtained by laboratory tests. However, the current test methods are generally based on maximum tensile stress or strain theory and neglecting the effects of loading velocities, so the fatigue resistance obtained cannot match that under actual pavement serving conditions. Moreover, the fatigue performance of high modulus asphalt mixtures obtained by different test methods are quite different, which caused random and disunity when selecting fatigue parameters for pavement structural design. Therefore, the objective of this paper is to accurately and uniformly characterize the fatigue resistance of high modulus asphalt mixtures. To this end, the indirect tensile, direct tensile, unconfined compressive strength and fatigue tests of high modulus asphalt mixtures were implemented under distinct loading velocities. Based on the Desai yield criterion, the strength yield surfaces under diverse loading velocities and the fatigue path of high modulus asphalt mixtures in three-dimensional stress state were established. Finally, the fatigue life values of high modulus asphalt mixtures obtained under distinct test methods and loading velocities were uniformly characterized by the relationship between fatigue life and equivalent stress ratioΔ, which wasNf=Δ-5.42. With the uniform characterizing model, the disunity of fatigue parameters can be eliminated, and the fatigue resistances of high modulus asphalt mixtures under three-dimensional stress states and different loading velocities can be evaluated.

Prediction of Direct Tensile Strength of Bamboo Fiber Reinforced Concrete Using Artificial Neural Network

Bamboo is among the most economically-significant non-timber forest products in the Philippines, and its fiber can be used for concrete reinforcement, known as bamboo fiber reinforced concrete (BFRC). However, BFRC needs further exploration, and its direct tensile strength is an essential factor that needs to be studied. The present study assessed the direct tensile strength of BFRC utilizing finite element modeling (FEM) and Artificial Neural Network (ANN). A positive correlation was found between compressive and direct tensile strength of the BFRC. The optimum ANN model was obtained from the trial-error approach. This model has 5-5-1 (input-hidden neurons-output) network topology and uses the tan sigmoid transfer function for both input-hidden and hidden-output layer which brought the most accurate prediction. The Levenberg–Marquardt (LM) provided the best optimization performance among other algorithms. The best model has a mean squared error (MSE) of 0.0000287 and r values of 0.98619, 0.99936, 0.99516, and 0.98565 for training, testing, validating, and overall. Sensitivity Analysis shows that compressive can significantly change the system’s performance even with a small change in its parameter value.

Calibrating a New Compressive-to-Tensile Load-Transferring Device for Determining the Direct Tensile Strength of Granite

Calibrating a New Compressive-to-Tensile Load-Transferring Device for Determining the Direct Tensile Strength of Granite

Studying Tensile Strength of the Recycled Coarse Aggregate Concrete Using Double-Punch Test

Using the recycled materials can be considered as a suitable solution for resolving environmental issues. The recycled coarse aggregates (RCA) can be utilized effectively in manufacturing structural concretes. Due to hardness and errors of direct tensile and splitting tensile tests, double -punch test (DPT) can be regarded as a reliable test method for evaluation of tensile strength.In this study, application of DPT was investigated as a less known method for RCA concretes considering effective factors, such as water–to-cement ratio (0.4, 0.5, and 0.6), maximum nominal size of RCA (10 and 19 mm), curing conditions (wet and dry), and replacement level of RCA (0, 50, and 100%) and the results were validated by direct tensile and splitting tensile test results. A statistical analysis was performed to indicate significance of each variable in DPT results of RCA concretes. Also, compressive strength and modulus of elasticity were assessed and their relationships with tensile strength of the specimens were studied.The maximum RCA size, replacement level of RCA, and mechanical properties were diminished in mixtures by increasing water-to-cement ratio. Generally, DPT results showed remarkable proximity to direct tensile test results with a slight increase. In wet curing condition, mean values of splitting tensile, DPT, and direct tensile tests in the specimens containing 19mm of RCA were 11.61, 10.06, and 9.44% higher than those containing 10mm of RCA, respectively. Moreover, results of statistical analysis showed that the studied factors had significant effects on the results and they must be regarded in evaluation of DPT.

Effect of alkali treatment on physical–chemical properties of sisal fibers and adhesion towards cement-based matrices

This work aims to evaluate the effect of alkali treatment on sisal fibers to improve the fiber properties and the effectiveness of their use as reinforcement in cement-based matrices. Alkaline solution concentration (1, 5 and 10 wt% NaOH) and post-treatment protocol (use of distilled water or acetic acid) influence were evaluated. The physical, chemical, thermal, wettability and surface characteristics were analyzed. Also, single-fiber direct tensile and pullout tests were performed. Results showed an increase in cellulose proportion with a reduction in hemicellulose and lignin content upon alkali treatment. Consequently, enhanced thermal stability and a decrease on the water uptake tendency were reached. Additionally, improved tensile properties, as well as an enhanced bond with the cementitious matrix, were found for alkali-treated fibers. Also, fibers became more stable when subjected to alkaline aggressive conditions. Thus, the alkali-treated sisal fiber seems to be an adequate and sustainable alternative as reinforcement for cement-based matrices.