Splitting Tension Tests Research Articles

Modeling of the fracture behaviors of concrete using 3D discrete element method with softening effect

Understanding the fracture mechanism of concrete is very important for the safety design of concrete structures. We develop a 3D discrete element model with softening effect to study the fracture behaviors of quasi-brittle materials. The basic ideas of our model inspired from the flat-joint concept and the cohesive crack model are implemented in the framework of MUSEN, which is an open source discrete element software with CPU–GPU accelerating computation. The placement-package-compaction method is proposed together with laser scanning technology to construct the meso-scale geometric model of concrete. The meso-parameters of 3D discrete element model developed are calibrated by uniaxial compression and splitting tension tests of concrete. The validation of the present model is verified by the laboratory test of concrete. Compared with the results predicted by the flat-joint model, the F-CMOD curves and fracture parameters simulated by our model are in good agreement with that of the laboratory tests of concrete. Finally, it is concluded that the fracture strain of bond significantly affects the fracture behavior but the softening mode does not. It is found that the linear one is better choice among three softening modes in the present model.

Experimental investigations on tensile strength and fracture toughness of a polyoxymethylene fiber reinforced concrete

The crack resistance performance of concrete materials, characterized by tensile strength and fracture toughness, is vital for the durability and structural functionality of concrete components. In this study, polyoxymethylene (POM) fibers were added into concrete to enhance the crack resistance. Firstly, three-point-bending (3-p-b) tests and splitting tension tests were performed on notched beam and cubic specimens of plain concrete and POM fiber reinforced concrete. Then, considering the heterogeneity of concrete, the 3-p-b and splitting tension test results were analyzed to reveal the failure behaviors of plain concrete and POM fiber reinforced concrete materials. It was found that the addition of POM fibers was beneficial for improving the fracture resistance of concrete. The Boundary Effect Model (BEM) was used to estimate the tensile strength and fracture toughness of plain concrete and POM fiber reinforced concrete materials from the 3-p-b test results, which correlated well with those obtained from the splitting tension tests and the conventional method. Moreover, the influence of POM fiber length and volume fraction on fracture resistance was evaluated. Findings revealed that increasing fiber length and volume fraction effectively enhanced the tensile strength and fracture toughness of concrete material.

Characteristics study of concrete strength using periwinkle seashell as cement partial replacement

Due to global population growth and improving economic conditions, infrastructure development in the form of residential homes and commercial structures is increasing yearly. The rising real estate market draws middle-class buyers to upscale apartments and opulent homes at steep discounts. On the other hand the availability of traditional construction materials are reducing. As a result, the idea of partial replacement is a good substitute. The current effort attempts to substitute periwinkle shells gathered from Chennai, the coastal metropolis, for traditional coarse aggregate. Through the compaction factor, slump cone, and flow tests in the fresh condition and the 14-day and 28-day compression tests, flexure tests, and split tension tests in the hardened state, an effort is made to assess the workability and strength of the partially replaced concrete in the laboratory. In addition to the aforementioned, tests are done on the periwinkle shell's influence value, breaking down value, specific gravity, absorption of water, and particle size distribution in order to evaluate the properties with those of conventional coarse aggregate in order to confirm the effectiveness of the former. A notional percentage is deduced through comparison analysis after partial replacement of periwinkle shells with gravel in various percentages of 0%, 20%, 30%, and 40% is carried out. This study reveals an understanding of the characteristics of building materials mixed with periwinkle shells and helps todetermine the ideal combined mixture percentage which can be recommended as an appropriate replacement construction material in the construction of elegant villas and luxury apartments.

An inverse analysis method for determining tensile softening relationship of concrete considering local response

This study presents an inverse analysis algorithm for deriving the softening relationship of concrete. The algorithm can not only reproduce the influence of local response on the σ-w curve by introducing additional load criteria but also reduce the dependence of optimization results on the initial guesses by combining global best-fitting with the automatic parameter updating technique, improving the prediction accuracy and lowing the possibility of obtaining pseudo-solutions. Then, the fracture tests were carried out on the wedge splitting specimens. The validity and versatility of the algorithm were verified using experimental data. The findings show that the simulation responses agree well with the test ones in all regions of the load-CMOD curve, and the values of fracture energy determined by the load-CMOD and σ-w curves are consistent. The derived σ-w curve is independent of the initial guesses of parameters. The widely used bi-linear σ-w curve tends to overestimate the load in the post-peak of load-CMOD, and the tri-linear model is recommended after considering the accuracy, computation time, and convergence. The tensile strength evaluated by the inverse analysis method is 75% of the splitting tension test and 91% of the fracture theory method. Further, the proposed algorithm exhibits outstanding versatility, applying to various concrete materials and specimen configurations.

Evaluation of strength of self-compacting concrete having dolomite powder as partial replacement for cement

Now a day, the utilization of self-compacting concrete (SCC) has become popular in creating RC structures. Apart from self-compaction, SCC has got many advantages such as excellent flow ability, filling ability, smooth finish of surface, ease of work etc. The use of waste material in concrete is the area of having scope for researchers for many years. Use of waste material reduces the consumption of cement by construction sector. In this present experimental work, dolomite powder is used as fractional replacement material for cement. The cement in the SCC is replaced by dolomite at fractions of 10%, 20%, 30%, 40%, 50%, 60%, and 70%. Fly ash is also added to the mix at constant fraction of 18% of the cement. The strength of SCC is assessed by performing compression test, splitting tension test and bending test. The test results showed that the use of dolomite powder in SCC is advantageous up to 20% replacement fraction. It is also observed that the strength of DC40 mix (i.e the mix having Dolomite at 40% of cement) is almost equal to the strength of normal SCC. Even at 70% replacement level, the strength of SCC having dolomite achieved is 25 MPa. SEM images are analyzed to identify the spread of hydrated products.

Study on Mechanical Properties and Mesoscopic Numerical Simulation of Recycled Concrete

To obtain the mechanical properties of recycled concrete (RC) under different replacement rates (RRs) of recycled coarse aggregate (RCA), a quasi-static uniaxial compression test, a uniaxial splitting tension test and a uniaxial dynamic compression test of RC with replacement rates (RRs) of 0%, 20%, 40%, 60%, 80% and 100% were carried out. ABAQUS was used to investigate the cracking and failure of RC. The results showed that, when the RR was less than 60%, the uniaxial compressive and tensile strengths of RC decreased with the increase in RR, but slightly increased when RR was greater than 80%. Under impact load, the dynamic compressive strength of RC increased linearly with the increase in the strain rate, showing an obvious strain rate effect. With the increase in RR, the strain rate sensitivity of RC gradually decreased. The concrete damage plastic (CDP) model can describe the mechanical behavior of RC well. The damage and failure of RC occurred first at the old interface transition zone (ITZ) and old mortar. As the strain rate increases, the damage and failure rate of the specimens is intensified. Research on the mechanical properties of RC can provide a basis for the application and promotion of RC technology.

Experimental methods for the analysis of the tensile behavior of concrete joints

AbstractAdhesion plays an important role in the evaluation of hydraulic structures with unreinforced concrete joints. The experimental determination of joint tensile strength as a quantifiable parameter is not standardized, resulting in a variety of test setups found in literature. The present paper highlights advantages and disadvantages of three of the most common tension tests for plain concrete and concrete joints through both theoretical and laboratory experimental analysis on specimens with artificial joints. Splitting tension tests were found to be inexpensive but tend to overestimate the adhesive strength of weak joints. Direct tension tests require an elaborate test setup but may yield information on the tension softening behavior. Pull‐off tests stand out for their ability to yield in‐situ results but deliver inconclusive results.

High-strain rate tension behavior of Fiber-Reinforced Rubberized Concrete

This paper investigates for the first time the high-strain rate splitting tension behavior of Fiber-Reinforced Rubberized Concrete (FRRC). Splitting tension tests were performed on Φ100-mm specimens. Quasi-static tests were carried out using conventional quasi-static loading with a compressive testing machine and dynamic high-strain rate tests with a Φ80-mm Split Hopkinson Pressure Bar (SHPB) for strain rates up to 10s−1. The experimental program comprises the characterization of Plain Concrete (PC), Fiber Reinforced Concrete (FRC), Rubberized Concrete (RuC), and FRRC with a full test matrix (a total of 240 specimens) covering fiber contents up to 1.5% and rubber volume substitution ratios up to 30%. A high-speed camera was used to capture the cracking development processes together with Digital Image Correlation (DIC). The addition of fibers enhances the deformation capacity with a marked increase in the tensile strength both for quasi-static and dynamic conditions while the substitution with rubber aggregates significantly reduces the tensile strength with a similar enhancement of the deformation capacity. For FRRC, a combination of the two effects was observed. FRC, RuC, and FRRC are characterized by marked strain rate dependency within the considered test range. Furthermore, data-driven models for compression and tension strength reduction factor (SRFc and SRFt) and tension Dynamic Increase Factor (DIF) are proposed for different types of FRRC. Finally, a discussion on the image-based damage development processes is provided based on the high-speed camera videos. This study indicates that FRRC has an excellent high-strain rate tension behavior reducing and controlling the crack propagation.

Investigation of the mechanical and shrinkage properties of plastic-rubber compound modified cement mortar with recycled tire steel fiber

To facilitate the recycling of waste solids in cement-based materials, plastic-rubber (PR) compound modified mortar (PRM) samples and recycled steel fiber (RSF)-reinforced plastic-rubber modified mortar (PRSRM) samples were prepared and tested to evaluate their mechanical and drying shrinkage properties. PR compound particles, with a mesh size of #8, replaced the natural aggregates with four volume percentages: 2%, 5%, 7.5%, and 10%. The fiber was added with a constant volume fraction of 0.2%. Accordingly, control mortar, PRM mortar with different PR replacement ratios, and PRSRM mortar with RSF were prepared and tested. A numerical splitting tension test model was also established based on the two-dimensional Distinct Element Method (DEM) to investigate the crack initiation and propagation mechanism of the PRM samples. The mechanical test results indicated that the addition of RSF enlarged the compressive strength by 14–27% PRM samples. Meanwhile, both PR and RSF improved mortar flexural behavior by increasing the fracture energy. The SEM image of a fracture surface and DEM simulation showed the crack propagation path was changed by PR particles due to its lower stiffness. Meanwhile, the 7-days drying shrinkage length change was reduced by about 25% due to the PR’s porous structure and water-retaining ability. Overall, the sustainable material design with the combination of PR and RSF would promote the full-recycling of waste tires in cement-based materials.

Investigation on the dynamic tensile behaviour of rubberized mortar using the Brazilian disc method

The use of tire rubber particles as a partial substitute for fine aggregate in cement-based materials has been proven to potentially have both environmental and economic benefits. Although the studies on the physical and mechanical properties of rubberized mortar are abundant, those related to the dynamic tensile behaviour are scarce. In this study, rubber powders with three sizes (0.125 mm, 0.180 mm, and 0.425 mm) are used to fabricate the Brazilian disc rubberized mortar specimen, with rubber volume percentages up to 40%. A 50 mm-diameter split Hopkinson pressure bar (SHPB) apparatus is then adopted to conduct the dynamic split tension tests, and the static tensile tests are also conducted for comparison purposes. Experimental results show that the dynamic split tensile strength of the rubberized mortar linearly increases with increasing the loading rate, whereas decreases with the increase of the rubber volume percentage. The mortars with smaller rubber powder at the same percentage exhibit more significant dynamic strength loss. As compared with the static tests, the reduction ratio of the dynamic split tensile strength of mortar with different rubber content is much smaller. The dynamic increase factors of the rubberized mortar are more sensitive to the loading rate, and positively correlated to both the rubber volume and the powder size. Besides, the occurring time of the primary crack initiation gradually decreases with increasing the loading rate and rubber size, whereas increases with increasing the rubber volume percentage. In addition, the dissipated energy density of the rubberized mortar is positively correlated with the rubber volume percentage, and the addition of the smaller rubber powder can enhance the dynamic energy absorption capacity.

Low strength concrete: Stress-strain curve, modulus of elasticity and tensile strength

Material characterization of low strength concrete has significant importance for structural/ seismic performance assessments of existing low-quality structures. The main objectives of this study are to characterize the compressive and tensile behaviors of low strength concrete (LSC). For this purpose, an extensive experimental database is formed by collecting available test results and by conducting new tests. The database combines the compression or splitting tension test results of 165 standard concrete cylinders with the compressive strengths ranging from 3.9 to 20.3 MPa. Firstly, the test results are presented by plotting compressive stress-axial strain curves and by calculating moduli of elasticity, axial strains at peak stresses, ultimate axial strains, and tensile strengths. Secondly, the predictive capabilities of available expressions are demonstrated by comparing them with the corresponding experimental results. Thirdly, simple regression analyses are conducted to define the compressive stress-axial strain curves, and the relationships between compressive, tensile strengths, and elastic modulus. Finally, the prediction capabilities of the proposed expressions are evaluated considering the tests, which were not used to establish the proposed expressions and conducted by other researchers. The comparisons show that the proposed expressions can predict the low strength concrete characteristics with good accuracy.

Mathematical Models for Tensile Resistance Capacities of Concrete

Although the uniaxial tensile strength (ft) of concrete is one of the most essential properties in designing and analyzing the tensile performance of a concrete member, a rational consensus to assess it is still lacking because of experimental difficulties. The objective of the present study is to generalize ft through mathematical analysis based on the plasticity of concrete. The principle of equivalent resultant tensile forces at failure planes is introduced to straightforwardly determine the splitting tensile strength (fsp) and modulus of rupture (fr) from ft. The accuracy and reliability of the proposed equations are confirmed at different ranges of the compressive strength and unit weight of concrete by comparing with test data, including 219, 674, and 242 data sets for uniaxial tension tests, splitting tension tests, and flexural tests, respectively. Thus, the present mathematical approaches proved the significance of considering the concrete unit weight and maximum aggregate size in predicting the tensile resistance capacities of the concrete. However, with the variations of the compressive strength and unit weight of concrete, the empirical equations recommended in previous studies and code provisions are insufficient.

Dynamic properties of granite rock employed as coarse aggregate in high-strength concrete

The dynamic properties of a granite rock employed in crushed form as coarse aggregate in high-strength concrete, were experimentally characterised, and the average values obtained were assumed to be representative of the properties of the coarse aggregate. Cylindrical specimens were core-drilled from the granite rock, then cut into various lengths for different tests, i.e. static and dynamic uniaxial compression, as well as static and dynamic splitting tension (Brazilian tests). From the data obtained, the effects of strain rate on the mechanical properties (e.g. stress-strain relationship, tensile and compressive strengths) were analysed. Significant rate dependence was observed for both tensile and compressive responses, and this was quantified via a dynamic increase factor (DIF, the ratio between the dynamic and static strength). For compression, the DIF follows the CEB-FIP 2010 equation frequently used to describe the rate sensitivity of normal-strength concrete. The tensile response shows a stronger rate dependence than the compressive response, and its DIF deviates from predictions based on the CEB-FIP equation, which underestimates the tensile DIF, and defines a much higher strain rate at which transition from a gradual to a rapid increase in the DIF occurs. An empirical DIF formula, derived from fitting of experimental data, is proposed to describe the tensile rate sensitivity. Apart from experimental characterisation, efforts were also directed at identifying a constitutive model to describe the dynamic behaviour of the granite coarse aggregate, and the Johnson-Holmquist 2 (JH-2) model, commonly used to capture the impact response of brittle materials (e.g. rock, ceramic) was chosen. The dynamic tensile and compressive properties obtained from experiments, were employed to determine the material parameters in the JH-2 model. Finite element modelling of the dynamic compression and splitting tension tests was performed, using the JH-2 model and the material constants derived, to describe the behaviour of the granite specimen. The simulation results correlate well with experimental measurements.

An isotropic elasto-damage-plastic micromechanical framework of innovative pothole patching materials featuring high-toughness, low-viscosity nanomolecular resin

In a recent companion paper, a three-dimensional isotropic elastic micromechanical framework was developed to predict the mechanical behaviors of the innovative asphalt patching materials reinforced with a high-toughness, low-viscosity nanomolecular resin, dicyclopentadiene (DCPD), under the splitting tension test (ASTM D6931). By taking advantage of the previously proposed isotropic elastic-damage framework and considering the plastic behaviors of asphalt mastic, a class of elasto-damage-plastic model, based on a continuum thermodynamic framework, is proposed within an initial elastic strain energy-based formulation to predict the behaviors of the innovative materials more accurately. Specifically, the governing damage evolution is characterized through the effective stress concept in conjunction with the hypothesis of strain equivalence; the plastic flow is introduced by means of an additive split of the stress tensor. Corresponding computational algorithms are implemented into three-dimensional finite elements numerical simulations, and the outcomes are systemically compared with suitably designed experimental results.

Study on mechanical properties of steel fiber reinforced nano-concrete (SFRNC) after elevated temperature

This paper presented 180 specimens to investigate mechanical properties of steel fiber reinforced Nano-concrete (SFRNC) after elevated temperature through the method of compression test, splitting tension test and flexure test. The test parameters effects of different elevated temperature and different content of steel fiber on mechanical properties including compressive strength, splitting tensile strength and flexural strength of SFRNC were analyzed in this paper. The integrity of Nano-concrete after elevated temperature could be improved because of the mixing of steel fiber, which could be observed from the failure process of SFRNC. Furthermore, mixing of steel fiber can change failure mode of Nano-concrete and improve the ductility of concrete greatly. It could be summarized that the elevated temperature had negative effects on compressive strength, splitting tensile strength and flexural strength of SFRNC. And it also could be found that Nano-concrete mixed with steel fiber can improve residual compressive strength, splitting tensile strength and flexural strength of these specimens after high temperature.

A micromechanical model of elastic-damage properties of innovative pothole patching materials featuring high-toughness, low-viscosity nanomolecular resin

Innovative pothole patching materials reinforced with a high-toughness, low-viscosity nanomolecular resin, dicyclopentadiene (DCPD, C10H12), have been experimentally proven to be effective in repairing cracked asphalt pavements and can significantly enhance their durability and service life. In this paper, a three-dimensional micromechanical framework is proposed based on the micromechanics and continuum damage mechanics to predict the effective elastic-damage behaviors of this innovative pothole patching material under the splitting tension test (ASTM D6931). In this micromechanical model, irregular coarse aggregates are approximated and simulated by randomly allocated multi-layer-coated spherical particles in certain representative sizes. Fine aggregates, asphalt binder (PG64-10), cured DCPD (p-DCPD), and air voids are formulated into an isotropic elastic asphalt mastic matrix based on the multilevel homogenization approach. The theoretical micromechanical elastic-damage predictions are then systemically compared with properly designed laboratory experiments as well as three-dimensional finite elements numerical simulations for the innovative pothole patching materials.

Mechanical Properties of Self-Compacting Rubberised Concrete (SCRC) Containing Polyethylene Terephthalate (PET) Fibres

This study focuses on the development and assessment of greener and sustainable mix of self-compacting rubberised concrete (SCRC) utilising commonly available waste materials such as fly ash, worn tires, and polyethylene terephthalate (PET) drinking bottles as fibres. Ten mixes containing ground tire rubber and PET fibres were investigated under compression, split tension, and flexure. In 05 out of 10 mixes, SCRC contained 35% fly ash by mass substitution of cement and ground tire rubber to substitute 0, 5, 10, 15, and 20% masses of fine aggregates. The remaining 05 mixes of SCRC contained a fixed 2% volume fraction of PET fibres measured by the volume of concrete. The compression, split tension, and flexure tests were performed at 28 days to assess the effects of ground tire rubber and PET fibres on the strengths, compressive stress–strain behaviour, and load–deformation behaviour. The results indicated that the replacement of 15% mass of fine aggregates with ground tire rubber is optimum without impairing the strengths of concrete. The PET fibres played a role in stabilising and improving the post-peak response in the compression and the flexure. Overall, the use of ground tire rubber as fine aggregates and PET fibres as reinforcement in concrete improved the response of concrete in compression and flexure.

Properties of Steel Fiber Reinforced Concrete Using Either Industrial or Recycled Fibers from Waste Tires

Currently, more than 2.5 million tires are discarded each year in Bogota, Colombia, and 1.2 million of them are not properly disposed, producing a huge environmental problem. As a possible solution, previous studies have assessed the performance of steel fibers recovered from recycled post-consumer tires as reinforcement of concrete. However, engineers in Colombia are still uncertain to use this type of recycled material, since the concrete and the dosages used in reported studies were obtained mostly from different construction practices and materials in countries other than Colombia. The aim of this paper is to show and discuss the results of a research intended at evaluating the mechanical response of concrete reinforced using recycled steel fibers from waste tires in Bogota, Colombia. The testing campaign of the study comprised 45 axial compression and splitting tension tests on cylinders, and 14 bending tests on concrete slabs reinforced using nominal fiber dosages of 15, 30 and 60 kg/m3 of steel fibers obtained from used tires. For comparative purposes, the study included also the test on 21 cylinders and 12 beams made of concrete reinforced using industrial steel fibers, with the same nominal dosages used for the recycled steel fibers. Based on measured response, preliminary design equations are proposed to estimate the mechanical properties of concrete reinforced using recycled steel fibers. It is also checked whether the obtained results fulfil the requirements specified by ACI-318 and NSR-10 building codes when steel fibers are used as minimum shear reinforcement of concrete beams.

Effects of Partial Replacement of Coarse Aggregates with Reclaimed Rubber on the Mechanical Properties of Hardened Concrete

<p>The replacement of conventional aggregates with alternate materials like Reclaimed Rubber (RR) results in reduction of self-weight and compressive strength of concrete. This reduction in self-weight further decreases the dead load which contributes towards contraction in size of concrete members and reinforcement requirements. This diminution in compressive strength is compensated by replacing cement with supplementary materials like Silica Fume, Fly Ash or GGBS. This research focuses on the effects of partial replacement of cement and coarse aggregates with Silica Fume (SF) and Reclaimed Rubber (RR) respectively in the concrete mix. Concrete mix was prepared for M20 grade by replacing cement and coarse aggregates with SF and RR respectively for cube and cylinder samples. A base study has been carried out through compression and split tension tests by partially replacing cement with SF in 3 percent increments up to 24 percent. Maximum compressive strength of 19.6N/mm<sup>2</sup>, 24.2N/mm<sup>2</sup> and 32.5N/mm<sup>2</sup> was obtained at 12% replacement of cement with SF by weight while testing specimens after 7, 14 and 28 days of curing. Maximum strength of 2.4N/mm<sup>2</sup>, 2.9N/mm<sup>2</sup> and 3.1N/mm<sup>2</sup> was obtained during split tension tests conducted after 7, 14 and 28 days of curing period. Further compression and tension tests were conducted replacing cement with 12%SF along with various proportions of RR replacing coarse aggregates after different curing periods. Experiments reveal that a combination of 12%SF and 9%RR replacement produces maximum compressive strength of 19.2N/mm<sup>2</sup>, 23.1N/mm<sup>2</sup> and 29.4N/mm<sup>2</sup> after curing the samples for 7, 14 and 28 days respectively. The tensile strength decreases as the rubber content is increased in the concrete mix along with optimum SF when compared with normal mix.</p>

Mechanical characterization of structural lightweight aggregate concrete made with sintered fly ash aggregates and synthetic fibres

This study explores the development of fibre reinforced structural lightweight aggregate concrete (SLWAC) using sintered fly ash aggregate (SFA) as coarse aggregate. SFA is manufactured from fly ash, an industrial by-product, thus making SLWAC a sustainable building material. SLWAC of density 1800 kg/m3 is developed with and without the addition of synthetic polyolefin (macro and micro) fibres to achieve a target compressive strength of 40 MPa. The main objective of this study is to understand the mechanical properties of SLWAC made of SFA and the influence of fibres in improving mechanical properties of SLWAC. The effect of monofilament macro-synthetic fibre dosages of 0.2%, 0.4%, and 0.6%, as well as the fibrillated micro fibres of 0.02% on the mechanical properties of SLWAC is studied. Tests were carried out for understanding the stress-strain behaviour under compression, split tensile strength, and fracture behaviour under flexure. Digital image correlation technique is used to study the crack propagation in fracture and splitting tension tests. A significant improvement in flexural strength, splitting tensile strength and toughness of SLWAC is observed due to the addition of synthetic fibres. Fibres significantly contributed to load resistance by arresting both micro and macro cracks. Thus, with the help of synthetic fibres addition in SLWAC, the desirable mechanical properties for structural applications such as strength and ductility can be achieved at reduced density.