Flexural Tensile Tests Research Articles

Direct tensile tests on steel fiber reinforced concrete with focus on wall effect and fiber orientation

Adding steel fibers to concrete essentially improves its post-crack tensile properties. To determine this experimentally, indirect methods, such as flexural tensile tests, are generally used, which allow only indirect conclusions about the material´s tensile properties. In contrast, direct tensile tests provide the desired result immediately, but are difficult to realize. A key parameter affecting the performance of the SRFC is the orientation of the fibers, which is mainly influenced by the manufacturing process. Typically, when the concrete is cast, the steel fibers align with the edges of the formwork. This is commonly called the wall effect. We address these issues, presenting the setup and results of direct tensile tests on bone shaped specimens with three different steel fiber contents. For each content, a series of specimens with a three-sided formwork (i.e. three-sided wall effect and strong influence on the fiber orientation) and a series with cut-out bones (i.e. one-sided wall effect and less influence on fiber orientation) were fabricated and tested. After these tests, the fiber orientation was determined using an opto-analytical method to quantify the influence of the manufacturing methods on the fiber orientation. Comparing the stress-crack-opening relationships shows that the cut specimens at 0.5 mm crack openings have only about 80% of the tensile strength of three-sided formwork specimens. This effect decreases with larger crack openings and vanishes at about 3 mm crack opening. Finally, a new fiber reinforcement index is defined to correlate observed stress in direct tensile tests to fiber content and orientation in direct tensile tests.

Boosting mortar performance: use of recycled brick sand for enhanced mechanical properties

The construction industry is constantly seeking ways to become more sustainable. One area of exploration is mortar technology, where researchers are looking at replacing traditional components with alternative materials and adding a superplasticizer to improve mechanical strength and reduce the use of natural resources. The present study focuses on substituting brick waste sand in mortar at different replacement ratios of 0%, 10%, 30%, and 50%. The main objective is to investigate the effect of this substitution material on the properties of the mortar. The researchers have conducted compression and flexural tensile tests on prismatic specimens (4 x 4 x 16 cm³) at various curing periods (2, 7, and 28 days). The results showed that replacing 50% of sand with brick wastes significantly improved mortar properties. However, replacing more than 50% of the sand hurt the workability of the mortar. This study highlights the potential of using brick waste sand as an alternative to sand in mortar production, promoting resource conservation and sustainable construction. The findings suggest that while a 50% replacement ratio is beneficial, it is essential to carefully consider the mix design to maintain workability and overall performance.

Tensile properties of steel fiber reinforced recycled concrete under bending and uniaxial tensile tests

It is important to study the tensile behavior of steel fiber reinforced recycled concrete (SFRRC) for the reliability of structural design. This paper investigates the effects of different mixture systems, including full-NA, full-RCA, full-RFA, full-RA, and full-RA+10%RP, on the tensile behavior of recycled concrete through uniaxial tensile and three-point bending tests. In addition, the effects of the volume content of steel fiber on tensile behavior are investigated. The uniaxial tensile strength and stress-strain curves of SFRRC were tested and the load-deflection, P-CMOD, double K fracture parameter and fracture energy under flexural tensile load were measured. The results show that the incorporation of recycled materials may negatively affect the tensile strength of recycled concrete. Compared with natural concrete, the uniaxial tensile strength decreased by 28.4%–50.2 % and the flexural tensile strength decreased by 17%–42.52 %. In addition, tensile properties, such as initial crack stress, peak strain, double K fracture toughness, and fracture energy, will also decline. The effect of the volume content of steel fibers on the tensile properties of recycled concrete with different mixed systems is analyzed. The steel fiber changes the tensile cracking mode of recycled concrete. When the content of steel fiber exceeds 1 %, the SFRRC of different mixed systems has the phenomenon of deflection hardening. When the fiber content is 2 %, the uniaxial tensile strength is increased by 13.83%–69.07 %. Contrasting with the control group, the recycled concrete group containing 2 % steel fiber showed enhanced fracture energy, which was increased by 15–23 times with different mixture systems. Uniaxial tensile constitutive models of SFRRC have been established under different mixture systems. The tensile stress-strain response of SFRRC was obtained indirectly by inverse analysis. It has been found that flexural tensile tests overestimate the post-crack properties of materials, and this phenomenon is more obvious in recycled concrete. This research is of great significance for the structural design of SFRRC.

Mechanical Properties and Stress-Strain Relationship of PVA-Fiber-Reinforced Engineered Geopolymer Composite.

In this study, seven Engineering Geopolymer Composite (EGC) groups with varying proportions were prepared. Rheological, compressive, flexural, and axial tensile tests of the EGC were conducted to study the effects of the water/binder ratio, the cement/sand ratio, and fiber type on its properties. Additionally, a uniaxial tension constitutive model was established. The results indicate that the EGC exhibits early strength characteristics, with the 7-day compressive strength reaching 80% to 92% of the 28-day compressive strength. The EGC demonstrates high compressive strength and tensile ductility, achieving up to 70 MPa and 4%, respectively. The mechanical properties of the EGC improved with an increase in the sand/binder ratio and decreased with an increase in the water/binder ratio. The stress-strain curve of the EGC resembles that of the ECC, displaying a strain-hardening state that can be divided into two stages: before cracking, the matrix primarily bears the stress; after cracking, the slope decreases, and the fiber predominantly bears the stress.

Effect of Hybridization of Carbon Fibers on Mechanical Properties of Cellulose Fiber–Cement Composites: A Response Surface Methodology Study

Fiber-reinforced cement composites, particularly those incorporating natural fibers like cellulose, have gained attention for their potential towards more sustainable construction. However, natural fibers present inherent deficiencies in mechanical properties and can benefit from hybridization with carbon fibers. This study focuses on the incorporation of cellulose and carbon fibers, in varying contents, into fibrocement composites, employing a Response Surface Methodology (RSM) to optimize the material characteristics. The methodology involves testing, encompassing flexural tensile, compression, and fracture toughness tests. The results indicate an increasing trend in flexural strength for higher carbon fiber content, peaking near 5%. A plateau in flexural strength is observed between 1.2% and 3.6% carbon fiber content, suggesting a range where mechanical properties stabilize. Compressive strength shows a plateau between 1.2 and 3.6% and reaches its highest value (≈33 MPa) at a carbon fiber content greater than 4.8%, and fracture toughness above 320 MPa·m1/2 is achieved with carbon fiber content above 3.6%. This study offers insights into optimizing the synergistic effects of cellulose and carbon fibers in fibrocement composites.

The Effect of Adding Coconut Coir Fiber on Compressive Strength, Tensile Strength, and Concrete Flexural Strength in Eco-Friendly Tetrapod Planning in Coastal Areas of IKN Supporting Cities

Beaches often experience erosion or abrasion problems caused by various factors, such as climate change which triggers rising sea levels, high waves, human activities such as beach reclamation, and infrastructure construction that is not environmentally friendly, triggering erosion on the coast. In the coastal area of the city that supports IKN, which is located in the Balikpapan area, Manggar Beach, also experiences abrasion which causes land to narrow in that area. The abrasion that occurs erodes the coastal area around 7-8 meters every year. To produce environmentally friendly infrastructure, this research carried out the addition of coconut fiber waste components to tetrapod concrete used for breakwater construction. In this research, variations in the addition of coir used were 0%, 1%, 2%, 3%, 4% and 5%. The aim was to find out how much influence the addition of coconut coir waste to the concrete mixture had on the compressive strength, tensile strength and flexural strength of the concrete in tetrapods. and produce concrete that uses coconut fiber waste as an alternative material for tetrapod concrete as breakwater armor. Based on the analysis results, the quality of the concrete was 23 Mpa. This value was determined based on wave generation analysis. In addition, it is known that variations in coconut fiber affect the slump, compressive strength, flexural and split tensile test values of concrete. Based on the slump test results, it was found that the greater the variation of coconut fiber in the concrete, the lower the resulting slump test value. In testing the compressive, flexural and split tensile strength, it was found that the optimal composition for adding coconut fiber was 3%, in this composition the amount of coconut fiber fiber was able to improve the mechanical properties of tetrapod concrete compared to other compositions.

Ecological cement: replacement of sugarcane bagasse ash derived from the sugar and alcohol industry

Untreated sugarcane bagasse ash (CBCA) from two plants was investigated as a partial replacement for Portland cement (CP) with the aim of reducing environmental problems arising from clinker production by evaluating the feasibility of use as a supplementary cementitious material with pozzolanic reactivity. Mortars and pastes were produced with replacement rates of 25%, 30% and 35% of CBCA, with cures of 7, 14, 28, 90 and 180 days. The mortars were characterized in a fresh state through workability testing and in a hardened state through mechanical performance through compression and flexural tensile tests, water absorption and void index. The chemical composition, mineralogical composition, thermal analysis and formation of hydrate phases were carried out on the pastes and both ash. The ash tests showed that the CBCA-CM presented an amorphous halo and that it consumed portlandite in the process of forming the paste hydrates at 28 and 90 days. Mechanical performance tests showed that the ash has lower resistance at short ages and surpassed the control sample at long ages.

Mechanical Behavior of Compression-Compacted Dry Concrete Paver Blocks Making Use of Sea Sand and Seawater

Dry concrete is a kind of concrete whose fresh mixture has almost no flowability and is widely used in the production of small-size unreinforced compression-compacted concrete blocks in plants. Considering the shortage of natural river sand and freshwater for concrete production, this study proposes that sea sand and seawater can be directly used in the manufacture of compression-compacted dry concrete paver blocks. The idea was verified in the laboratory to find suitable mix proportions and forming pressure, which are two key parameters for the production of paver blocks. Furthermore, the effect of sea sand replacement ratio and seawater replacement ratio is investigated, where compression and flexural tensile tests were conducted on lab-made paver blocks at different ages. The experimental results reveal that both the compressive and flexural tensile strengths of paver blocks increased when sea sand and seawater were adopted. It is finally suggested that sea sand and seawater are suitable for the production of unreinforced paver blocks with enhanced mechanical performance.

Reduce the cost and embodied carbon of ultrahigh performance concrete using waste clay

Recent research has recognized limestone calcined clay cement (LC3) a promising sustainable cementitious material. While LC3 could be used in a wide range of applications, it is important to explore its feasibility in developing (ultra-)high performance concrete. In this paper we attempt to produce ultrahigh performance LC3 concrete (UHP-LC3). With 20%, 30%, and 40% OPC replaced by coal gangue waste calcined clay and limestone (LC2), the mechanical, hydration, and microstructural properties were extensively studied. The mechanical properties were investigated by compressive and flexural tensile tests. The hydration behavior of UHP-LC3 was evaluated by thermogravimetric analysis (TGA), quantitative X-ray powder diffraction (QXRD) analysis, 29Si nuclear magnetic resonance (NMR) spectroscopy, and scanning electron microscope (SEM). Finally, the microstructure of UHP-LC3 was studied by mercury intrusion porosimetry (MIP). Results show that the substitution of LC2 improve the early strength by quickly pozzolanic reaction to form denser hydration products as well as the synergistic interaction between silica fume and limestone/calcined clay in the system. However, the long-term strength would drop as LC3 caused insufficient hydration reaction due to the high water-demand of calcined clay that reduced the amount of free water. Also, there are abundant unreacted calcined clay particles in the hydrated system. Meanwhile, LC3 substitution of OPC seems to improve the polymerization of C-A-S-H gel and densify the pore structure, thus display excellent carbonation resistance. This paper explores new options to prepare more sustainable and cost-effective UHPC.

Effect of microcrystalline and nano-fibrillated cellulose on the mechanical behavior and microstructure of cement pastes

When nanomaterials are added to cementitious materials, their microstructure and mechanical properties are affected. The most targeted effect of their use is the improvement of the composites’ mechanical performance. The present investigation brings the characterization of a cement paste reinforced with two different cellulosic inclusions: microcrystalline cellulose (MCC) and nanofibrillated cellulose (NFC), added in the contents of 0.050%, 0.075%, and 0.100%, in relation to cement weight. First, the morphology, crystallinity, surface area, and thermal decomposition of MCC and NFC were analyzed. Then, the composites’ microstructure was characterized by thermogravimetric analysis, X-ray diffraction, and porosity measurements. This analysis was made considering the development of hydration between 3 and 28 days. Furthermore, their mechanical performance was investigated by compressive, flexural, and direct tensile tests at 28 days of hydration. Despite the differences regarding the morphologies and physical aspects between MCC and NFC, their inclusions resulted in positive effects on the flexural and tensile strengths. The cement pastes reinforced with 0.075% of MCC and NFC had their tensile strength enhanced by over 70% compared to the reference. Nevertheless, TGA and XRD analyses showed that the addition of MCC and NFC decreased the formation of all hydration products, except the calcium carbonate. Therefore, the combination of mechanical and microstructure analyses indicates that the tensile strength improvement obtained with the MCC and NFC addition was most likely due to their reinforcing capability.

Comparisons of flexural, split tensile, double punch, and direct tension tests on high-performance concrete reinforced with different fiber types

The study investigates the variation of tensile strength of high-performance concrete (HPC) based on various tensile tests, such as the flexural test, splitting tensile test, double punch test, and direct tension test, conducted on dog bone specimens. The test samples were HPC concrete reinforced with three different fibers in a fraction ratio ranging from 0 % to 2 %. The three kinds of fibers utilized in this investigation are those most frequently employed in Vietnam, including straight steel fibers with copper plating, polypropylene (PP), and hook steel fibers. The study additionally investigates the similarities between the results of tensile strength experiments on HPC concrete by examining the average tensile strengths, tensile failure modes, and material behavior graphs of tensile stress versus recorded specimen displacement. Overall, The average tensile strength results of bending and splitting tensile tests were significantly higher than those of the direct tensile and double punch tests. All tests could capture the behavior of HPFRC in the working periods. Splitting and flexural tensile test results followed a normal distribution. However, direct and double punch test results did not. The results of this study show that double punch tests can be used instead of direct tensile tests to measure the tensile strength of fiber concrete.

THE EFFECT OF ADHESIVE TYPE AND REINFORCEMENT TYPE ON FLEXURAL DEFORMATION OF BENDING LVL

In this study, the effect of reinforcement type and glue type on the amount of flexural deformation of reinforced bending LVLs was investigated. Within the scope of the study, 2.2mm peeled poplar veneer and 1.5mm peeled alder veneer were used as wood material. Glass fiber and basalt fabric (200g/m²) were used as reinforcement. Alder veneer was used on the lower and upper surfaces, and poplar veneer was used on the middle layers. Reinforcement material was applied to the convex surface of the bending LVL. A total of 7 different combinations of bending LVLs in the form of chair leg-armrest were produced. Flexural test, tensile test and ANSYS analysis were performed on the produced LVLs. According to the test results, it was determined that there was a decrease in flexural deformation with the use of reinforcement. It was determined that the best results were obtained with the use of glass fiber and epoxy. In addition, ANSYS results and real test results were found to be similar.

Exploration of mechanical properties of hemp fiber/flax fiber reinforced composites based on biopolymer and epoxy resin

Recently natural fiber-reinforced polymer composite materials are highly growing both in the relationship of their manufacturing industries applications such as automobile, lightweight biosensor chips, and microfluid and fundamental research as they are renewable, low, eco-friendly, biodegradable and completely recyclable. The hemp and flax solutions have not only met the technical requirements of prepared composite but also reduced environmental impacts. The present study involves the investigation on mechanical behavior such as flexural strength, flexural modulus along with moisture absorption performance of flax and hemp fiber composite is reinforced with the natural resin and epoxy resin. The biodegradable composite by the help of synthesis of natural acids such as citric acid (CA) and maleic anhydride (MA). In additional acrylic acid (AA) and glycerol (GL) were used for synthesis of natural resin to be more reactive by condensation method. The laminate has been prepared by flax and hemp fiber reinforced with the epoxy resin. The prepared laminate has been used study the flexural and tensile studies by ASTM standard procedure. The mechanical properties of flexural test and tensile test has been studied by hemp fiber/flax fiber reinforced composites. The obtain results were compared with the natural fiber reinforced by natural resin and epoxy resin. Hence, this kind of light weight biocomposite materials has been utilized for many industrial applications.

Influence and Mechanism of Curing Methods on Mechanical Properties of Manufactured Sand UHPC.

The mechanical properties of ultra-high performance concrete (UHPC) made of manufactured sand (MS) under four curing methods (steam, standard, sprinkler and saturated Ca(OH)2) were investigated via compressive, flexural and uniaxial tensile tests, and the bond strength of steel fiber and manufactured sand UHPC (MSUHPC) matrix. Based on the analysis of the microstructure, the influence mechanism of curing methods on the mechanical properties of materials was explored. The results showed that the early compressive strength of MSUHPC under steam curing (SM) is much higher than that of the other three curing methods, but the difference gradually decreases with the increase of age. The compressive strength of MSUHPC under SM is higher than that of river sand UHPC (RSUHPC). The bending strength and compressive strength of MSUHPC under different curing methods are similar, and the bending strength of 28 days steam cured samples is the highest. The uniaxial tensile properties of MSUHPC did not show significant difference under standard curing (SD), sprinkler curing (SP) and saturated Ca(OH)2 curing (CH), and the uniaxial tensile properties of MSUHPC under SM are slightly better than RSUHPC. The ultimate bond strength and fiber pullout energy of steel fiber and MSUHPC increase with the development of age. The bond strength and fiber pullout work of SM is higher than those of the other three curing methods, but there are lower increases in the later stage than that of the other three curing methods.

Mechanical test and constitutive model of recycled plastic fiber reinforced recycled concrete

• The uniaxial compression test, quasi-triaxial compression test and flexural tensile test of RPFRRC are carried out. • The compressive and flexural tensile strength of the RAC can be improved by adding recycled plastic fibers. • The confining pressure and the fiber volume ratio have obvious effects on the stress-strain curve of RPFRRC. • A three-dimensional constitutive model of RPFRRC is proposed. • The rationality of the improved model is verified by the experimental data of quasi-triaxial compression test. The use of the Recycled Plastic Fiber Reinforced Recycled Concrete (RPFRRC) can not only improve the mechanical properties of concrete, but it also can reuse the waste. The uniaxial compression test, quasi-triaxial compression test and bending-tension test of RPFRRC are carried out. Experimental results show that the compressive and flexural tensile strength of the RPFRRC can be improved by adding an appropriate content of recycled plastic fibers. For constant fiber content, the fiber length has a great influence on the compressive strength and flexural tensile strength of the RPFRRC. The confining pressure and the fiber volume ratio have a relatively large influence on the stress-strain curve of RPFRRC specimens. Considering the shortcomings of the Ottosen model, a three-dimensional constitutive model which is suitable for describing the triaxial compressive stress-strain relationship of RPFRRC is proposed. This model uses the improved equation as the equivalent uniaxial equation for the three-dimensional stress state of fiber reinforced concrete. The quasi-triaxial compression test data of the RPFRRC shows that the improved model is more consistent with the test results than the Ottosen model. The experimental data of other fiber reinforced concrete also verify that the improved model proposed in this paper is reasonable.

MECHANICAL PERFORMANCE OF POLYPROPYLENE FIBRE REINFORCED MORTAR INCORPORATING PALM OIL FUEL ASH

The performance of Fibre Reinforced Mortar (FRM) mixed with microfine size Palm Oil Fuel Ash was investigated in this study (POFA). The ideal volume of POFA and fibre in the mixed mortar is calculated in order to generate a cost-effective high-strength mortar with increased ductility. In this experimental investigation the polypropylene fibre used ranged from 0 kg/m3 to 20 kg/m3 and the replacement of cement with microfine POFA content of 0% and 40% (optimum) was studied. The mechanical properties of fibre reinforced masonry in the presence of the POFA was tested using compressive strength, flexural and split tensile tests. The surface morphology of the fibre reinforced mortar was studied using scanning electron microscopy (SEM) which showed the good fibre-mortar bond in the morphology of the samples at 7 and 28 days. From the compressive strength results, FRM tester contains 40% microfine POFA as a replacement against cement mixed with 10 kg/m3 of polypropylene fibre is optimum and achieved compressive strength up to 79.5 MPa at the 56th day of curing. Ductility ratio up to 13.3 was achieved from the flexural test for FRM sample with 15 kg/m3 polypropylene fibres. The high strength FRM with inclusion of POFA as supplementary cementitious material had the potential to become a new sustainable material in construction.

Experimental Study on the Interfacial Bonding Performance of a New Steel Bridge Deck Interface-Bonding Agent

The construction of steel deck pavements is still considered difficult worldwide, and interfacial bonding is a major factor influencing this construction. With the recent developments in the field of pavement materials, high-performance cement-based concrete is used to construct steel bridge deck pavements. However, ensuring adequate interface-bonding strength remains particularly complex and difficult. In this study, with the aim of striking the right balance between rigidity and flexibility, an interface-bonding material was formed using modified epoxy resin, cement, and rubber powder. Polymer lattice porous concrete was used as the paving material, and the interface-bonding effect was studied experimentally by employing three methods using the material: pull-off, dual-interface shear, and flexural tensile tests. The results showed that (1) the interface pull-off strength was higher than 4 MPa, that is, higher than twice that of epoxy asphalt pavements used currently on steel bridge decks, and the failure surface was located on the pavement material rather than on the bonding interface; (2) the interface flexural strength and tensile strength were significantly higher than those of epoxy asphalt at room temperature and those of the ordinary epoxy resin; (3) the dual-interface shear strength was nearly four times higher than that of epoxy asphalt. Therefore, the modified epoxy resin composite interface-bonding material suggested in this study is an excellent bonding material that can serve as a reference for interface-bonding of steel bridge deck pavements.

A new performance test to evaluate the sulfate resistance of concrete by tensile strength measurements

Concrete structures without sufficient durability can be damaged by sulfates in groundwater and from surrounding rock layers. To evaluate the performance of a concrete mixture, precise and performance-oriented test methods are a must. Therefore, a new a performance oriented concrete test procedure based on tensile strength measurements was developed considering experiences reported in international literature and recommendations of state-of-the-art reports. A vast parameter study with approx. 3850 tensile tests on ASTM briquets, 1900 flexural tensile tests on standard prisms and 2100 expansion tests on mortar flat prisms of different ages and with different storage conditions was statistically assessed. Based on the results a performance-oriented test method could be defined which considers not only the chemical, but also the physical resistance of a concrete against sulfate attack. The method was verified by 23 concretes with different cements or cement fly ash combinations and additional field tests. It could clearly be demonstrated that the results represent the performance of a practical concrete in case of sulfate attack. Furthermore, it leads much faster to an evaluation of the sulfate resistance compared to the most other practical oriented methods.

Damage Evolution of Steel Fibre-Reinforced High-Performance Concrete in Low-Cycle Flexural Fatigue: Numerical Modeling and Experimental Validation.

This contribution aims to analyze the deterioration behaviour of steel fibre-reinforced high-performance concrete (HPC) in both experiments as well as numerical simulations. For this purpose, flexural tensile tests are carried out on beams with different fibre contents and suitable damage indicators are established to describe and calibrate the damage behaviour numerically using a phase-field model approach. In addition to conventional measurement methods, the tests are equipped with acoustic emission sensors in order to obtain a more precise picture of crack evolution by observing acoustic events. It is shown that, in addition to classical damage indicators, such as stiffness degradation and absorbed energy, various acoustic indicators, such as the acoustic energy of individual crack events, can also provide information about the damage progress. For the efficient numerical analysis of the overall material behaviour of fibre-reinforced HPC, a phenomenological material model is developed. The data obtained in the experiments are used to calibrate and validate the numerical model for the simulation of three-point bending beam tests. To verify the efficiency of the presented numerical model, the numerical results are compared with the experimental data, e.g., load-CMOD curves and the degradation of residual stiffness.

Incorporation of graphene in slag-fly ash-based alkali-activated concrete

The use of an alkali-activated binder as a replacement for ordinary Portland cement (OPC) for the manufacturing of concrete would help in reducing CO2 emissions in the environment. In this study, different percentages of graphene nano-platelets (by weight of aluminosilicate materials) were added in slag-fly ash-based ambient cured alkali-activated concrete. The slump, compressive, flexural, splitting tensile, pulse velocity and direct tensile tests were performed. It has been observed that the addition of 0.5% graphene by weight of aluminosilicate materials improved the compressive, splitting tensile, flexural and direct tensile strengths of slag-fly ash-based ambient cured alkali-activated concrete.