Fracture Properties Of Concrete Research Articles

Elevated temperature inversion phenomenon in fracture properties of concrete and its application to maturity model

The effect of elevated curing temperature on the fracture properties of concrete was investigated. Fracture experiments were carried out on wedge splitting specimens exposed to temperatures ranging from 5 to 60 °C. A new maturity model was then proposed for describing the combined influence of the temperature and aging on the fracture properties of concrete. The results show that the fracture energy of concrete subjected to high temperature is high at early ages; however, the effect of curing temperature on the fracture energy was reversed after 14 days, with greater later-age fracture energy corresponding to lower temperature and vice-versa. The effective fracture toughness of concrete also exhibited the same temperature inversion phenomenon. The optimum curing temperature was found to be approximately 40 °C for development of concrete fracture properties. The value of activation energy changed with fracture properties, temperature ranges and the development stage of a given fracture property. The proposed model accurately predicts the fracture properties of concrete and significantly simplifies the calculation process of the maturity index relative to the existing maturity method.

Fracture Properties of Concrete Reinforced with Steel Fibers

Background: Concrete is a material strong in compression but exhibits low tensile strength, low strain capacity in tension and low cracking & fracture resistance due to presence of defects like voids, cracks, air pockets. Hence to improve fracture resistance of concrete, different types of discrete short fibers are added in concrete at the time of casting. Objectives: To evaluate the various fracture properties such as fracture energy, toughness (KIC) and Critical Tip Opening Displacements (CTODC ) of normal strength concrete reinforced with Steel Fiber (SF) (0, 0.25, 0.5, 0.75 & 1% by volume of concrete). Methods: Authors have studied the effect of addition of steel fibers on various fracture properties of concrete. Normal strength concrete was cast by using water to cement ratio as 0.38 and a total of five mixtures were prepared by using steel fibers (0.25, 0.5, 0.75 & 1% by volume of concrete) into those concretes. Notched beam specimen was used to conduct three-point bending test to study fracture properties such as fracture energy, fracture toughness (KIC) and CTODC of different concrete mixes. Findings: Test results showed an improvement in tensile strength and fracture properties of steel fiber reinforced concrete mixes when compared with control mix. Fracture energy was enhanced by 243 % & 208 % with addition of 0.75% and 1% steel fibers. Fracture toughness was also enhanced by 95% & 94 % with addition of 0.75% and 1% steel fibers. However inclusion of steel fibers resulted in reduction in the workability of concrete mixture with increasing fiber contents. Novelty/Improvements: For the novel material containing steel fibers, fracture properties of concrete are enhanced to a great extent and thus brittle and sudden failure of concrete can be avoided and material undergoes a more ductile failure which in turn improves the performance of structure in terms of durability and serviceability. Keywords: Critical Tip Opening Displacement, Fracture Energy, Fracture Toughness, Steel Fibers

Effect of curing humidity on the fracture properties of concrete

This study investigates the influence of curing humidity on concrete fracture properties. Concrete fracture energy, effective fracture toughness, and characteristic length were tested at five different ages using wedge splitting specimens exposed to four different relative humidity values (30%, 50%, 70% and 98%). Four environmental chambers capable of automatically controlling temperature and relative humidity were constructed. A data averaging method for companion specimens was introduced. The test results show that at the early age, fracture energy, effective fracture toughness, and characteristic length remained almost constant during drying. As time elapsed, however, the influence of curing humidity on the concrete fracture properties became increasingly pronounced; larger values of fracture energy, effective fracture toughness, and characteristic length were measured by concrete specimens kept at high humidity. The concrete fracture mode also gradually changed from ductile to brittle with curing humidity decreasing and hydration time elapsing.

A novel approach to estimate the evolution of fracture energy and tensile softening curve of concrete from very early age

Concrete fracture properties and their evolution over time are critical inputs for numerous engineering aspects. Despite substantial efforts invested, there exists a crucial need to establish a comprehensive model for reliable estimation of such evolution. In this paper, combining reliable experimental data and in-depth analysis, a novel approach for proper estimation of the evolution of fracture energy and tensile softening curve of concrete from early age is proposed. Fundamentally, the approach relies on three key criteria related to (i) tensile strength, (ii) tensile strength-fracture energy correlation and especially, (iii) centroid coordinates of the area under the stress-crack opening curve. The capability and reliability of the proposed approach are clearly demonstrated through a detailed assessment of these criteria and examples of practical applications.

Investigation on the Relationship between Microstructure and Fracture Properties of Self-Compacting Concrete (SCC)

Abstract Self-compacting concrete (SCC) is a high-performance concrete that is increasingly replacing conventional concrete because of its many advantages. SCC is prepared with chemical and mineral admixtures to achieve increased flowability. These admixtures modify the microstructural characteristics of SCC, which in turn affect the mechanical and fracture properties of concrete. In this study, an attempt has been made to establish the relationship between the microstructure and fracture properties of SCC mixes. The fracture properties are studied by using the RILEM work of fracture method, Bazant’s size effect, and the Wittman boundary effect models. Microstructural characterization has been carried out using X-ray diffraction, scanning electron microscopy (SEM), and microindentation techniques. It is revealed that the presence of mineral admixtures alter the microstructural skeleton of SCC, which in turn increase its brittleness. However, it is also found that the reason for brittleness is not because of cracking through aggregates as is reported in many literature regarding high-strength concrete; on the contrary, the cracks are passing through the interfacial transition zone or matrix in all SCC mixes, as is revealed by SEM images. Furthermore, it is found that the mechanical properties of the aggregate used have a significant influence on the fracture properties of the mixes.

Modeling the dynamic fracture in concrete: an eigensoftening meshfree approach

The objective of this work is twofold. First, we develop an eigensoftening algorithm to capture the gradual process of failure in materials with a softening behavior as an extension of the eigenerosion approach. Both methods are validated against the physical measurements in three-point bending tests of concrete with a drop-weight device, including impact and reaction forces, loading-line displacements as well as strain histories from gauges. The comparison shows that the eigenerosion algorithm significantly overestimates the tensile stresses and the strain peaks, while it captures the forces and crack pattern accurately. Predictions made by the proposed eigensoftening algorithm agree very well with experimental results in all aspects. Second, the energy evolution and partition in the beam predicted by the eigensoftening algorithm at various impact rates is analyzed to quantify the rate dependent fracture properties of concrete. It is demonstrated that, at impact loading conditions, the area below the reaction-deflection curve is much larger than the dissipated fracture energy.

Influence of recycled coarse aggregates incorporation on the fracture properties of concrete

This paper presents the mechanical and fracture properties of a structural concrete incorporating coarse recycled aggregate. Four mixes were designed according to the standard EN 206-1 to achieve S4 consistence class and C35/45 class of strength. Concrete specimens were prepared with different recycled gravel content of 0%, 30%, 65% and 100% by volume of the total coarse gravel.Three points bending tests were performed on 10×10×40cm pre-notched samples in order to determine the flexural strength and fracture properties according to the RILEM recommendations. From experimental Force-CMOD curves, the intrinsic fracture properties were obtained by an inverse analysis using an analytical model and a power law strain-softening relationship. The strain-softening law is described by two parameters being respectively the power n and the critical crack opening displacement wc. It was found that the difference between the calculated fracture energy, GF, and the RILEM fracture energy, GFRILEM, is more pronounced for recycled aggregate concrete.The evolution of n and wc, the parameters of the power strain-softening law, was also studied. It appeared that the power, n, depends on the compressive strength, the aggregate size and the water to binder ratio. For the same class of compressive strength, it remains substantially unchanged when the recycled aggregates content increases. For the critical crack opening wc, it decreases when the substitution ratio increases. Finally, the relationship between fracture properties and the tensile strength has been established.

A coupled diffusion-mechanical model with boundary element method to predict concrete cover cracking due to steel corrosion

Concrete cracking caused by steel corrosion is one of the most important durability issues for reinforced concrete structures. A coupled diffusion-mechanical model has been developed in this study to predict the crack propagation in concrete during the steel corrosion process. The spatial and time distribution of corrosion depth around the steel cross section during the corrosion process is first calculated from the chloride diffusion analysis in the corrosion module. In the mechanical module, for each time moment corresponding to a certain degree of corrosion, the non-uniform corrosion distribution obtained from the corrosion module is adopted as geometric input, and governing equations based on boundary element methods are set up to calculate the extent of cracking in the concrete. Based on two indirect boundary element methods, the fictitious stress method and displacement discontinuity method, the mechanical problem of the concrete/rust/steel composite under rust expansion is formulated. Different concrete fracture properties and rust properties are employed as input in the model to examine their effects on the crack width evolution in concrete. A slab with steel reinforcements of different diameters but at the same concrete cover is analyzed as an example to illustrate the applicability of the developed model in predicting crack width in the concrete cover. The delaying effect of rust penetrating into concrete cracks on the crack width evolution is also simulated with the present model. The developed boundary element model coupling the diffusion and mechanical processes shows the potential for realistic prediction of service life of structures suffering from steel corrosion by taking into account of the interaction effects during the corrosion and concrete cracking processes.

Molecular dynamics simulation of the nonlinear behavior of the CNT-reinforced calcium silicate hydrate (C–S–H) composite

Calcium–Silicate–Hydrate (C–S–H), which is the major constituent of the cement at the nanoscale, is responsible for the strength and fracture properties of concrete. This research is dedicated to the numerical study of enhanced mechanical properties of C–S–H reinforced by embedding carbon nanotube (CNT) in its molecular structure. Series of molecular dynamics (MD) simulations indicate that the tensile strength of CNT-reinforced C–S–H is substantially enhanced along the direction of CNT as compared to the pure C–S–H. The results of tensile loading reveal that CNT can efficiently bridge the two sides of cracked C–S–H. In addition, CNTs can severely intensify the “transversely isotropic” response of the CNT-reinforced C–S–H. Furthermore, the pull-out behavior of CNT reveals that the force-displacement response can be estimated by a bilinear model, which can later be used for simulation of cohesive crack propagation and multiscale simulation of crack bridging at macro scale specimen of CNT-reinforced cement.

Influence of waste rubber utilization on the fracture and steel–concrete bond strength properties of concrete

Mechanical and fracture properties of concretes in which the natural aggregate was replaced with two types, crumb rubber and/or tire chips, of waste scrap tire rubber were experimentally investigated. The concrete mixtures were produced at a constant water-to-cement ratio of 0.40 and with a cement content of 450kg/m3. A total of 19 concrete mixtures were designed by replacing the fine and coarse aggregates with crumb rubber and tire chips, respectively, at designated replacement levels of 0%, 5%, 10%, 15%, 20%, 25% and 30% by total aggregate volume. The concrete samples were tested for compressive and splitting tensile strengths, modulus of elasticity, fracture energy, characteristic length, and steel–concrete bond strength. Test results indicated that utilization of rubber significantly affected the mechanical and fracture properties of concretes. Compressive strength and modulus of elasticity of the concretes decreased while the ductility increased as the rubber had been used. Besides, the effect of rubber appeared to be more pronounced at higher rubber content and bigger size.

EFFECT OF MILLED ELECTRICAL CABLE WASTE ON MECHANICAL PROPERTIES OF CONCRETE

The article focuses on investigation of mechanical and fracture properties of concrete containing electrical cable waste as well as some microstructural features of such concrete. Added to concrete, electrical cable waste reduces the overall concrete bulk density. Compressive, flexural, tensile splitting strengths and elastic modulus decreased when electrical cable waste was admixed to conventional and polymer modified concretes. The best mechanical properties of concrete samples containing electrical cable waste were identified in polymer modified concrete containing 5% of electrical cable waste. Electrical cable waste particles increase the deformability of polymer modified concretes and have almost no influence on normal concrete. Consequently, the optimal amount of electrical cable waste particles can provide concrete with desirable strength that is required for different applications.

Effect of Cement Dosage on Selected Mechanical Fracture Parameters of Concretes

Mechanical fracture parameters obtained from three-point bending tests on concrete specimens with a central edge notch are introduced in this paper. A total of four sets of specimens were tested. The concrete used in each set differed in cement dosage, which ranged from 250 to 455 kg per m3 of fresh concrete. Three specimens in each set were tested at the age of 28 days. Increasing the dosage of cement influences the mechanical fracture properties of concretes in both positive and negative ways.

Effect of Cement Replacement by Zeolite on the Basic Mechanical Fracture Properties of Concrete: A Parametric Study

This paper introduces the results of fracture experiments on concrete specimens of different composition modified by zeolite (7.5 to 30 % by weight of cement dosage). It presents the determination and comparison of basic mechanical/fracture parameter values such as volume density, compressive strength, elasticity modulus, effective fracture toughness and fracture energy.

Flexural Capacity of Full-Depth and Two-Lift Concrete Slabs with Recycled Aggregates

Full-depth and two-lift concrete slabs were cast with fractionated reclaimed asphalt pavement and recycled concrete aggregate as partial and full replacements of the coarse aggregate in a ternary blend concrete containing cement, slag, and fly ash. These large-scale slabs were monotonically loaded at the edge to quantify the effect of recycled aggregates on the slab's flexural capacity. Although the introduction of these recycled aggregates into the concrete reduced the compressive, split tensile, and flexural strengths as well as the elastic modulus of the concrete relative to virgin aggregate concrete, fracture testing demonstrated that recycled concrete aggregate can have fracture properties statistically similar to those of virgin aggregate concrete. Testing of the flexural capacity of the slabs revealed that concrete with recycled aggregates had peak loads at failure similar to or greater than those of virgin aggregate concrete despite a significant difference in beam flexural strength. The calculated tensile stress in the slab at flexural failure was underpredicted by the beam flexural strength by a factor of 1.5 for virgin aggregate concrete and 1.9 to 2.7 for concrete with recycled aggregates; these findings demonstrate that the beam flexural strength results are not always reliable predictors of slab capacity, especially with recycled aggregates. Because of lower beam flexural strengths with recycled aggregates, pavement engineers should compare the fracture properties of concrete containing recycled aggregate with those of typical virgin aggregate concrete before deciding whether to increase the required concrete slab thickness.

Fracture Properties of Roller-Compacted Concrete with Virgin and Recycled Aggregates

Roller-compacted concrete (RCC) pavement has renewed interest among designers as a sustainable pavement option with the potential to lower total cement content, incorporate recycled aggregates, reduce road closure time, and decrease total project costs. One main design challenge is whether RCC can achieve the same performance life as conventional portland cement concrete (PCC) pavement with similar slab thickness. This research investigated the strength and fracture properties of RCC containing virgin aggregates and fractionated reclaimed asphalt pavement (FRAP) relative to conventional PCC to address this design challenge. The compressive and split tensile strengths of the RCC mixes showed similar strengths to the same constituents in PCC. RCC containing FRAP had lower strengths than did RCC with virgin aggregates. The critical stress intensity factor and the initial and total fracture energies were not statistically different between the RCC mixes containing virgin and FRAP aggregates. Overall, the RCC fracture properties were found to be significantly higher than those of conventional PCC. At lower stress ratios, RCC fatigue data from laboratory beam tests predict lower fatigue life relative to PCC; this result translates to a thicker RCC pavement. Large-scale testing has shown that the flexural capacity of PCC slabs is strongly related to the concrete fracture properties despite differences in beam flexural strength. Because these RCC fracture properties were shown to be higher than similar constituents used in conventional paving concrete, RCC designs could employ similar PCC fatigue curves for certain conditions, such as when the RCC fracture properties are equivalent to or greater than those of conventional PCC.

Fracture Properties of Polypropylene Fiber Reinforced Concrete Containing Fly Ash and Silica Fume

A parametric experimental study has been conducted to investigate the effect of polypropylene fiber on the fracture properties of concrete containing fly ash and silica fume, with five fiber volume fraction (0.04, 0.06, 0.08, 0.1 and 0.12%) used. The results indicate that the addition of polypropylene fiber has greatly improved the fracture parameters of concrete composite containing 15% fly ash and 6% silica fume, such as fracture toughness, fracture energy, effective crack length, maximum mid-span deflection, the critical crack opening displacement and the maximum crack opening displacement of the three-point bending beam specimens. When the fiber volume fraction increases from 0 to 0.12%, the fracture parameters increase gradually with the increase of fiber volume fraction. The variation rules of the fracture parameters indicate that the capability of polypropylene fiber to resist crack propagation of concrete composite containing 15% fly ash and 6% silica fume is becoming stronger and stronger with the increase of fiber volume fraction with the fiber volume fraction not beyond 0.12%.

Experimental Study on Fracture Properties of Hybrid Fiber Reinforced Concrete

Though fracture test on the fifteen specimens with notch of hybrid fiber reinforced concrete with the size of 100mm×100mm×400mm, this paper explores the hybrid effect between steel fiber and polypropylene fiber and impact on the fracture properties, such as critical effective crack length, critical crack tip opening displacement, effective stress intensity factors and fracture energy. The test results indicate that the addition of fiber is helpful to improve the fracture properties of concrete. Synergistic effect of two kinds of fibers is good, the steel fiber with high elastic module can restrain the cracking of concrete when the crack displacement is small, polypropylene macro-fiber with high ductility is more beneficial to increase the fracture properties of concrete than steel fiber when the crack displacement is big. The best fiber compounding can be gotten when the volume fractions of steel fiber and polypropylene fiber is respectively 0.5％and 1.0％in this experiment.

Experimental Study on Fracture Properties of Hybrid Fiber Reinforced Concrete

Though fracture test on the fifteen specimens with notch of hybrid fiber reinforced concrete with the size of 100mm×100mm×400mm, this paper explores the hybrid effect between steel fiber and polypropylene fiber and impact on the fracture properties, such as critical effective crack length, critical crack tip opening displacement, effective stress intensity factors and fracture energy. The test results indicate that the addition of fiber is helpful to improve the fracture properties of concrete. Synergistic effect of two kinds of fibers is good, the steel fiber with high elastic module can restrain the cracking of concrete when the crack displacement is small, polypropylene macro-fiber with high ductility is more beneficial to increase the fracture properties of concrete than steel fiber when the crack displacement is big. The best fiber compounding can be gotten when the volume fractions of steel fiber and polypropylene fiber is respectively 0.5％and 1.0％in this experiment.

Influence of particle packing on fracture properties of concrete

Particle packing on meso-level has a significant influence on workability of fresh concrete and also on the mechanical and durability properties of the matured material. It was demonstrated earlier that shape exerts but a marginal influence on the elastic properties of concrete provided being packed to the same density, which is not necessarily the case with different types of aggregate. Hence, elastic properties of concrete can be treated as approximately structure-insensitive parameters. However, fracture behaviour can be expected structure-sensitive. This is supported by the present study based on discrete element method (DEM) simulated three-phase concrete, namely aggregate, matrix and interfacial transition zones (ITZs). Fracture properties are assessed with the aid of a finite element method (FEM) based on the damage materials model. Effects on tensile strength due to grain shape and packing density are investigated. Shape differences are shown to have only modest influence. Significant effects are exerted by packing density and physical-mechanical properties of the phases, whereby the ITZ takes up a major position.

Effect of Calcium Dissolution on the Fracture Properties of Concrete Exposed to Nitric Acid Environment

The effect of calcium leaching by nitric acid on fracture properties of concrete was experimentally studied. The double-K fracture parameters were investigated using three-point bending beams, and the deterioration regularity of fracture properties of concrete chronically attacked by nitric acid was gotten on basis of these results. The load-crack mouth opening displacement curves under different nitric attack periods were obtained by pasting some strain gauges onto the pre-crack tip. On basis of the double-K criterion, the unstable fracture toughness as well as the initial fracture toughness was calculated according to the critical crack mouth opening displacement, the unstable fracture load and initial cracking load which can be obtained from the test. The experimental results indicated that the ratio of the initial fracture toughness to the unstable fracture toughness varied between 0.47 and 0.61 approximately. Both of the unstable fracture toughness and the initial fracture toughness decrease with attack period especially during the early 60 days, then drop to a stable trend gradually. In addition, the initial fracture toughness is less sensitive to acid attack compared with the unstable fracture toughness.