Direct Tensile Research Articles

Evaluation on tension-compression anisotropic behavior of recycled asphalt mixture

The utilization of recycled asphalt pavement (RAP) is the effective way to improve resource conservation and reduce energy consumption. The asphalt mixture is a kind of typical anisotropic pavement materials due to its heterogeneity in composition and microstructure. This could lead to the differences of mechanical response between the tensile and compressive direction. However, there are limited researches to study the effect of RAP on the tension-compression anisotropic behavior of asphalt mixture. The strength, modulus and fatigue resistance tests are carried out and different loading modes are adopted. The results show that the tension-compression anisotropic behavior is more prominent with the increase of RAP content. The regenerant served as a kind of typical additive could alleviate this effect. In addition, the result of dynamic modulus test shows that the tension-compression anisotropic behavior has an increasing trend with the decrease of frequency and the increment of temperature. The ranking of fatigue life is opposite for the direct tensile and compressive loading mode, and the fatigue life ratio of compression to tension also show positive relation with the RAP content. Due to the difference in the stress mode, the fatigue life between the indirect tensile loading and four-point bending loading also show opposite trend, and the indirect tensile fatigue life has a larger discreteness.

Evaluating the impact of specimen and punch sizes on the tensile strength of UHPC through double punch testing

Many studies have shown that direct tensile tests are fraught with numerous challenges. The Double Punch Test (DPT) is considered a more reliable alternative for evaluating tensile properties among the indirect tensile methods. While DPT is efficient and reliable, its size effect should not be overlooked. Previous studies on DPT size effects have primarily focused on specimen size, with little discussion on the impact of punch size variations. Additionally, with the evolution of construction materials, the applicability of the generalized DPT formula to new materials, such as Ultra-High-Performance Concrete (UHPC), with its exceptional strength, toughness, durability, and crack resistance, needs to be evaluated. This study conducts experimental research on UHPC, focusing on the relationship between specimen and punch sizes and their impact on tensile strength measurements. By designing experiments with 12 different specimen sizes and punch ratios, we explore the differences between actual experimental results and simplified formula calculations. Bažant's theoretical methods are also applied to analyze the size effects of specimen and punch dimensions on DPT. The results indicate that, with appropriate specimen size and punch ratio, DPT can provide tensile strength measurements closer to those of Direct Tensile Tests (DTT). It was also found that tensile strength, strain, and toughness decrease with increasing specimen size. When the ratio of UHPC specimen to punch size (d/D) is 1/3, the results align well with the predictions of the simplified formula. This indicates that the optimal punch ratio is not fixed for different specimen sizes. These findings offer valuable references for designing related experiments and improving quality control and structural performance in various engineering fields.

Parameter determination of Johnson–Holmquist–Cook constitutive model and calibration for Indiana Limestone

In this study, a comprehensive parameter determination procedure for the Johnson–Holmquist–Cook (JHC) constitutive model is introduced, including calibration and validation processes for Indiana Limestone rocks. The procedure is conducted utilizing the existing physical and mechanical properties of Indiana Limestone. To obtain an accurate set of parameters for the JHC model for Indiana Limestone, an extensive dataset comprising mechanical and physical properties of Indiana Limestone rocks was initially compiled. The static mechanical tests incorporated uniaxial compression, triaxial compression, direct tensile, and uniaxial strain data, while the dynamic mechanical test data was primarily derived from the Split Hopkinson Pressure Bar experiments. Subsequently, the JHC constitutive model parameters were determined using existing literature data, employing statistical analysis, theoretical derivation, and numerical back analysis techniques. One of the damage parameters was determined through numerical post-peak behavior calibration of triaxial compression strength test results on experimental data. Finally, the accuracy of the determined parameters was validated by comparing the numerical and experimental results of both static and dynamic tests. This study effectively addresses the challenges associated with the numerical method using the JHC material model, such as the complex parameter determination process and the costly required tests, thereby preserving the efficiency and applicability of the numerical method.

Study on fatigue parameters of high modulus asphalt pavement

High Modulus Asphalt Mixtures (HMAM) have gained widespread utilization in asphalt pavement construction. It is great critical to study the fatigue characteristics of HMAM. At present, various fatigue test methods are employed in indoor testing to assess HMAM under different mechanical states. Therefore, there is a critical problem that the value of fatigue parameters is not unique in the structural design of HMAM. In this study, three fatigue testing methods were initially used to address the above issues: direct tensile testing, indirect tensile testing, and uniaxial compression testing. These tests help to determine the strength yield surface states at different loading rates. And to reveal the effect of loading rate on the mechanical behavior of HMAM. The results show a power function fit and a good correlation between strength and loading rate. The relationship models of strength with speed for indirect tensile, direct tensile and uniaxial compression tests are SI=3.22(v)0.14, SD=3.22(v)0.15 and SU=3.22(v)0.12, respectively.The higher the loading rate for the three fatigue test results, the greater the expansion of the strength yield surface.The fatigue life (Nf) of HMAM underwent testing, yielding its fatigue effective stress ratio. The relationship between the two was and then established. It is found that the point (1, 1) appears on the backextension line, thus effectively complementing the conventional S-N equation. In addition, the fatigue equations for various fatigue test methods were unified based on effective stress strength ratio and the fatigue life. This paper introduces a novel method for the antifatigue design of HMAM.

Tensile and bond properties at elevated temperatures of a PBO-FRCM composite system for strengthening concrete elements: Experimental and analytical investigations

This paper presents experimental and analytical investigations on the tensile and bond behaviour at elevated temperature of a polypara-phenylene-benzo-bisthiazole (PBO) fabric reinforced cementitious matrix (FRCM) system for strengthening concrete elements. Direct tensile (DT) and single lap direct shear tests (DS) were performed under steady-state conditions at the following temperatures: 20 °C, 85 °C, 150 °C, 230 °C and 300 °C. The results obtained were evaluated in terms of strength, stiffness, ultimate strain, load vs. slip response at the interface PBO FRCM/concrete and failure modes. Overall, the tensile and bond properties were significantly affected by the temperature increase. These results are mainly associated with the reductions of mechanical properties of the FRCM constituent materials as well as the degradation of the interaction between the fibres and the inorganic matrix at elevated temperatures. The experimental results were then used (i) to evaluate the suitability of the Aveston–Cooper–Kelly (ACK) model in describing the tensile response of FRCM at elevated temperatures and (ii) to calibrate temperature-dependent local shear bond stress vs. slip laws for the FRCM-concrete interaction.

Experimental and analytical investigation of the tensile mechanism of textile-reinforced mortar (TRM) composites and fabric grids in elevated temperatures

The textile-reinforced mortar (TRM) combines high-strength fabric textiles with cementitious mortar matrix to enhance mechanical behaviour and durability, especially at high temperatures. The current study investigated how basalt, carbon, and glass textile grids and TRM composites respond under direct tensile and thermal loading up to 800 ℃. Changes in microstructure were analyzed using scan electron microscopy (SEM), thermo-gravimetric analysis (TGA), and ultrasonic pulse velocity (UPV). The results indicated that temperature significantly affected the coating material and cementitious mortar, weakening the grids and composite specimens. Carbon and glass fibre grids proved more resilient, and the carbon and glass TRM reduced 50% of their ultimate stress at 500 ℃, while for basalt TRM is 200 ℃. A slight gain of strength was observed for all TRM specimens at 300 ℃, and SEM analysis revealed critical changes in the mortar matrix and interfacial transition region. The results were further utilized to calibrate the Gibson model considering humidity and early-stage coating material changes, and yielding results consistent with experimental data.

Investigating the role of steel and polypropylene fibers for enhancing mechanical properties and microstructural performance in mitigating conversion effects in calcium aluminate cement

Fiber reinforcement is widely employed in numerous industries due to its exceptional mechanical properties; however, its specific role in enhancing the strength of calcium aluminate cement (CAC) composites remains inadequately understood. This study investigates the influence of fiber addition on the mechanical characteristics of CAC composites during curing. Two types of fibers, steel and polypropylene, were incorporated into CAC composites, and their mechanical properties, chemical composition, and microstructural performance were evaluated using various methods. Assessments including flowability, bulk density, volume of permeable voids, water absorption, and mechanical strength tests were conducted, alongside X-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA), and Field Emission Scanning Electron Microscopy (FESEM) analysis. Results reveal a significant enhancement in mechanical strengths with the inclusion of fibers in CAC composites. The addition of 1% fibers to the composites resulted in significant improvements. Steel fibers (SF) led to notable enhancements of approximately 19.7%, 68%, and 26.4% in compressive, direct tensile, and flexural strengths, respectively, while polypropylene fibers (PF) resulted in enhancements of 1.9%, 20%, and 16.7%, respectively. Microstructural analysis revealed that SF and PF contribute to pore refinement, enhancing strength and durability. Findings suggest that SF addition effectively mitigates strength loss induced by the conversion effects of stable phase C3AH6 in CAC, thereby fostering the development of an environmentally friendly, quick-setting, high-performance concrete system. This research offers valuable insights for the design and potential enhancement of CAC-based composites to improve performance and durability under severe conditions.

Tensile, flexural, and mode-I cracking behavior of interpenetrating phase composites (IPC), developed using additively manufactured PLA-based structures with different infill densities and epoxy resin polymer as matrix

Interpenetrating phase composites (IPC) materials are designed to combine the advantages of made-from materials or develop an intended behavior. Recently, the use of 3D printed structures has received attention due to advantages, such as the rapid and cheap prototyping techniques of complex structures. However, most materials, such as polylactic acid (PLA) used for conventional 3D printing, have low strength and insignificant durability. To overcome these issues, the excellent characteristics of polymer adhesives, such as epoxy resin, can be used to increase their strength and durability. In this paper, PLA-based 3D printed samples and epoxy resin adhesive were merged to develop an interpenetrating phase composite. The samples were printed with 25, 50, 75, and 100 infill percentages and tested in direct tensile, bending, and mode-I fracture. From the results, it can be seen that reducing the infill percentage to 75, 50, and 25 % reduces the tensile strength to 16, 9, and 3 MPa (−40 %, −66 %, and −90 % compared to the sample with 100 % infill with 26 MPa strength), adding epoxy resin to develop an IPC, results in 24, 29 and 32 MPa tensile strength. Compared to 3D-printed parts with the same infill percentages, the IPCs have 150, 320, and 1140 % higher tensile strengths, respectively. Also, the failed samples were reviewed by scanning electron microscope.

Effects of freeze-thaw cycles on the tensile properties of geogrids and shear behavior of geogrid-soil interface

The tensile strength of geogrids and the shear strength of the reinforced soil interface are critical technical indicators for designing reinforced soil structures. This study developed a temperature-controlled apparatus to examine the tensile properties of geogrids subjected to freeze-thaw cycles within the soil, and the effect of interface temperature and freeze-thaw cycles on the shear behavior of the geogrid-soil interface. Eight and four groups of direct shear and tensile tests were conducted on the geogrid-soil interface and geogrids, respectively, under varying conditions. The peak tensile strength of geogrids remained similar to that of non-freeze-thaw samples after experiencing freeze–thaw cycles within the soil. tensile properties of geogrids were independent of the number of freeze–thaw cycles. At constant water content (w=6%), the peak shear stress at the geogrid-soil interface decreased by 24% (7 freeze-thaw cycles) compared to the non-freeze-thaw group. The cohesion and friction angle of the geogrid-soil interface decreased with increasing freeze-thaw cycles but tended to stabilize after 4 freeze-thaw cycles. The reinforcement provided by the geogrid enhanced with decrease in the interface temperature. The shear stress was higher at interface temperature under 0 °C, whereas in a non-frozen state, the interface exhibited lower shear stress with a consistent stable value.

Experimental verification of innovative spatial reinforcement of ultra-high performance concrete with mesh tubes

The article presents the concept of innovative spatial concrete reinforcement, consisting of a new, patented reinforcement system with mesh tubes. The concept of spatial reinforcement is a proposal for homogenization of composite concrete structures, which in a unique and very effective way allows the use of reinforcing material in the form of an ordered structure of glass fibres. A comparative analysis was carried of the test results of concrete composite samples reinforced with mesh tubes made of high-strength glass fibre, with the results on concrete samples without reinforcement and on fibre concrete samples containing an equivalent amount of glass fibres of two different lengths, made of the same type of glass fibre as the mesh tubes. Base concrete with ultra-high performance properties was used for the tests. Experimental tests concerned the strength and deformation properties of the composites, i.e. compressive strength, direct tensile strength and splitting tensile strength, and secant modulus of elasticity in compression. Beam models were also tested in a four-point bending test, which made it possible to determine the load-carrying capacity, flexural strength and analyse the cracking and failure mechanism. Comparative analysis of the experimental results showed the high effectiveness of the proposed spatial reinforcement of concrete with glass fibre mesh tubes. The use of spatial reinforcement resulted in an increase in compressive strength, direct tensile and splitting tensile strength by 5 %, 29 %, 27 % respectively, compared to fibre concrete. However, the load-carrying capacity of the spatially reinforced beam was 85 % higher compared to the fibre concrete beam.

Investigating the effect of steel micro‐ and macro‐fibers on the bond behavior of steel rebar embedded in ultra‐high performance concrete

AbstractIn recent years, the use of ultra‐high performance concrete (UHPC) has been widely considered in special structures and retrofitting of existing structures. Since most of the relations proposed by the regulations are based on the behavior of concrete with normal strength concrete, it is necessary to conduct more experimental studies to predict the behavior of UHPC. One of these notable behaviors is the bond and cohesion between rebar and UHPC, which plays a critical role in the design and seismic behavior of structures. In the present study, a series of experimental tests of uniaxial compressive strength, splitting (Brazilian) tensile strength, elastic modulus, and pull‐out of ribbed steel bars from ultra‐high performance fiber‐reinforced concrete (UHPFRC) were performed. The tests were done considering the four‐volume fractions of hooked‐end steel macro‐fibers, straight steel micro‐fibers, a hybrid combination of these two fibers, three different diameters of ribbed steel bars, and several embedded lengths. Moreover, direct tensile and compressive stress–strain curves, Young's modulus, bonding properties of rebar with UHPFRC, and fracture mechanisms were considered. The results indicated that applying micro‐fibers may enhance the bond stress between rebar and UHPC better than macro‐fibers. Also applying hybrid fibers resulted in the concurrent enhancement of bond stress and the optimum point slip of UHPC in the stress–slip diagram. This finding maybe attributed to the satisfactory performance of micro‐fibers in reducing the growth speed of micro‐level cracks and the suitable effect of macro‐fibers in decreasing the progression speed of macro‐level cracks. Furthermore, it was revealed that the increase in rebar diameter and embedding length leads to the reduction of maximum bond stress in UHPFRC.

Recent studies on the mechanical properties of Engineered Cementitious Composite

Engineered Cementitious Composite (ECC) is a type of High-Performance Fiber-Reinforced Cementitious Composite (HPFRCC) that has emerged as a promising material for use in construction and engineering. ECC is designed based on micromechanical theory, resulting in a remarkable tensile strain capacity of over 6%, while maintaining a low fiber volume fraction of no more than 2%. The material’s high flexibility enables it to be molded into various shapes, and it exhibits excellent mechanical properties, making it suitable for field applications such as the construction of joint-less deck slabs, link slabs, and retrofitting of critical structures like dams and tunnels. However, the accurate characterization of ECC’s properties requires the use of appropriate testing methods, particularly regarding its mechanical characteristics, including compressive strength, flexural strength, and direct and indirect tensile strength. This review highlights the significance of understanding ECC’s mechanical properties and emphasizes the importance of using appropriate testing techniques to evaluate the material’s properties and structural behavior.

Role of fiber-reinforced chip seal interlayers in asphalt pavement bonding strength

ABSTRACT This study investigates the influence of seal coat parameters – rubber-modified asphalt content, fiber content, fiber length, and chip content – on the bonding characteristics of asphalt pavement layers. Employing a full factorial experiment and utilizing direct shear and tensile tests, the research identified the optimal material composition for improving interlayer bonding. The results showed that fiber content notably enhanced shear strength, whereas rubber-modified asphalt content significantly influenced tensile strength. The inclusion of fibers in the seal coat notably increased bonding strengths by up to 45.6% and 61.5% in shear and tensile strengths, respectively, demonstrating considerable performance enhancements at room temperature. In addition, the study explored the economic advantages of fiber-reinforced chip seal treatments, revealing substantial improvements in interlayer strength, particularly under diverse temperature conditions. This research contributes valuable insights into optimizing reinforced bituminous interfaces for asphalt pavements, offering a promising avenue for enhancing pavement durability and performance.

Interlayer mechanical performance of 3D-printed cementitious systems: A comprehensive study on operational and material parameters

This study delves into the interlayer mechanical performance of 3D-printed cementitious materials, exploring a variety of operational and material parameters to understand the practical effects on the performance of printed structures. To achieve this, a comprehensive battery of tests, encompassing compression, triplet shear, direct tensile, and diagonal tension tests, was conducted. Within the scope of this investigation, the anisotropic performance in perpendicular, lateral, and parallel directions was examined, along with varying printing time intervals (0, 15, 30, and 60 min between consecutive layers), material aging times (0, 30, and 60 min), and different manufacturing methodologies, including cast, horizontal-printed, and vertical-printed specimens. The research findings indicate that well-established mechanical tests, commonly utilized for evaluating masonry structures, can be effectively transferred and applied to assess 3D printed structures. A noteworthy discovery is the anisotropic behavior observed in compressive strength, characterized by diminishing results from perpendicular to parallel and parallel to lateral loading directions. Extended printing time intervals have an adverse impact on the interlayer mechanical performance of cementitious systems. Material aging time also significantly influences bond strength, particularly in mixtures aged for 60 min. In conclusion, it is evident that material aging exerts a more substantial influence on bond strength compared to printing time intervals in cementitious systems. Additionally, it was observed that vertically printed specimens replicate the mechanical performance and fracture mechanism of cast specimens, while horizontally printed specimens exhibit slightly lower performance with distinct fracture patterns.

Properties of Cement Mortars Made With Local Steel Slag

As a way to reduce the impact of the cement industry and reduce its production cost, researchers have studied to use by product materials such as fly ash, silica fume and slag as a partial replacement for Portland cement in the making of concrete. In this study, the effect of partial cement replacement with Libyan electric arc furnace steel slag in different substitution levels (0, 10, 20 and 30% by weight) were investigated using cement mortars. Slag of 350 m2/kg Blaine fineness was used in this study. The mortar specimens were tested for compressive, flexural and direct tensile strengths at the ages of 3, 7, 28, 56 and 90 days. The effect of slag content on mortar workability was studied. Setting times and soundness of cement paste were also investigated.The experimental results showed that replacement of cement by slag causes delay in cement setting times. Setting times increases as the slag content increases. The results also showed that compressive, direct tensile and flexural strength of mortar improves with time and the development in strengths is influenced by the slag content. The addition of 10% electrical arc furnace slag (EAFS) has positive effect on compressive, tensile and flexural strengths of mortar at late age.

Improvement of the Cracking Moment-Based Asphalt Mixture Splitting Test Method and Splitting Strength Research

The asphalt mixture splitting test is one of the most important methods for measuring asphalt’s tensile properties. To characterize the limitations of the traditional splitting test and the influence of the specimen size and loading conditions on the accuracy of the test, the factors affecting the strength of the splitting test were analyzed to reveal the splitting failure state and establish a unified representation model between the splitting and direct tensile tests. Initially, the moment of specimen cracking was taken as a key indicator, combined with image processing technology, to establish a set of criteria to judge the splitting test. Subsequently, standardized splitting tests were conducted and compared to tests of different specimen sizes and loading methods. Based on the octahedral strength theory, the stress points before and after the improved test were compared to the existing failure criteria. Direct tensile and splitting tests were conducted at different rates, and a unified strength–rate function model was established, realizing the unified representation of direct tensile and splitting tests. The research results indicate that the standardized splitting test is prone to the phenomenon wherein the specimen end face cracks before the center, affecting the accuracy of the test and potentially leading to redundant material strength evaluations. Using a loading method with a “35 mm specimen thickness” and a “0.3 mm rubber gasket + 12.7 mm arc-shaped batten” can essentially achieve the test hypothesis of “cracking at the center first”, resulting in less discrete outcomes and closer alignment to the three-dimensional stress failure state. The tensile and splitting strengths are both power function relationships with the rate as the independent variable, establishing a unified function model of the tensile and failure strengths. The research provides a more reliable testing method and calculation model for asphalt pavement structure design, and it also provides an effective basis for the improvement of splitting tests on materials such as concrete and rock.

Sample Size Requirements of a Pharmaceutical Material Library: A Case in Predicting Direct Compression Tablet Tensile Strength by Latent Variable Modeling.

The material library is an emerging, new data-driven approach for developing pharmaceutical process models. How many materials or samples should be involved in a particular application scenario is unclear, and the impact of sample size on process modeling is worth discussing. In this work, the direct compression process was taken as the research object, and the effects of different sample sizes of material libraries on partial least squares (PLS) modeling in the prediction of tablet tensile strength were investigated. A primary material library comprising 45 materials was built. Then, material subsets containing 5 × i (i = 1, 2, 3, …, 8) materials were sampled from the primary material library. Each subset underwent sampling 1000 times to analyze variations in model fitting performance. Both hierarchical sampling and random sampling were employed and compared, with hierarchical sampling implemented with the help of the tabletability classification index d. For each subset, modeling data were organized, incorporating 18 physical properties and tableting pressure as the independent variables and tablet tensile strength as the dependent variable. A series of chemometric indicators was used to assess model performance and find important materials for model training. It was found that the minimum R2 and RMSE values reached their maximum, and the corresponding values were kept almost unchanged when the sample sizes varied from 20 to 45. When the sample size was smaller than 15, the hierarchical sampling method was more reliable in avoiding low-quality few-shot PLS models than the random sampling method. Two important materials were identified as useful for building an initial material library. Overall, this work demonstrated that as the number of materials increased, the model's reliability improved. It also highlighted the potential for effective few-shot modeling on a small material library by controlling its information richness.

Research on Acoustic Emission Characteristics and Crack Evolution during Rock Failure under Tensile and Tensile- and Compressive-Shear Stress States

Tensile, compressive-shear, and tensile-shear failure are three typical failure modes of rock- and lining-support structural materials in underground engineering. Comparative studies of the acoustic emission (AE) evolution characteristics of specimens of the same shape and size under different stress states are of great significance in determining universal disaster warning guidelines. Based on a self-developed multi-functional test system, direct tensile, compressive-shear, and tensile-shear tests were conducted on intact and jointed rock-like specimens, comparing AE amplitude and peak frequency parameters under different failure modes from the perspectives of crack scale and crack type evolution. All failure tests were monitored with microcrack propagation at an early stage until ultimate rupture occurred at the peak-load moment. As a result, the “quiet-period” could only be observed from the compressive-shear test. The AE signals distributed in three bands can be used as an indicator of failure identifications. Tensile and shear cracks can be identified by strong and weak amplitudes of low- and high-frequency signals. These results enhance the knowledge of the failure modes of rock mechanics for more applications in monitoring disasters in rock engineering.

Effect of Filler to Bitumen Weight Ratio on Low-temperature Cracking Performance of Asphalt Mixture

The effect of mineral filler weight ratio on the low-temperature performance of hot asphalt mixtures with continuous gradation has been a subject of significant interest in the field of pavement engineering. This study focused on testing mastic, which is a bitumen mixture with mineral filler passing through a No. 200 sieve, using various tests, such as the bending beam rheometer test (BBR), direct tensile (DT) test, Infrared spectroscopy test (FTIR), X-ray diffraction (XRD) test, and semi-circular bending (SCB) test. Different weight ratios of mineral filler to useful bitumen ranging from 0.4 to 1.6 were investigated for PG 70-16 bitumen. According to the SHRP-A-407 standard, the weight ratio of mineral filler to useful bitumen plays a crucial role in determining the low-temperature performance of asphalt mixtures. The research findings confirm this fact, indicating that the weight ratio of mineral filler to bitumen plays a crucial role in determining the low-temperature performance of asphalt mixtures. As the filler-to-bitumen ratio increased, the stiffness of the bituminous mastic increased, leading to reduced fracture strain and decreased low-temperature cracking life. The optimal filler-to-bitumen ratio was recommended to be a maximum of 0.8 to balance performance and control low-temperature behavior. The results of this study underscore the importance of considering the rheological properties of bitumen mastic in addition to bitumen and asphalt mix when evaluating lowtemperature performance. Keywords: Asphalt mixing, Filler-to-bitumen ratio, Cracking performance, Lowtemperature, cracking.

Direct and Indirect Tensile Behavior of Cement-Zeolite-amended Sand Reinforced with Kenaf Fiber

Direct and Indirect Tensile Behavior of Cement-Zeolite-amended Sand Reinforced with Kenaf Fiber