Mechanical Behavior Of Concrete Research Articles

Fracture and mechanical performance of Two-Lift Concrete Pavements made of Roller Compacted Concrete and Polypropylene Fibers

The present study has examined the two-lift concrete pavement (2LCP) fracture and mechanical behavior by casting the Roller Compacted Concrete (RCC) as the bottom lift and the conventional or fibrous Portland cement concrete (PCC, FPCC) as the top lift. To this end, the three-point bending test was carried out on notched beams by considering different thicknesses for both layers. Results showed that fibers had no positive effects on the compressive and flexural strength, but improved the post cracking behavior considerably. Compared to full-depth RCC/PCC, 2LCP specimens had similar flexural strengths, but an increase in the FPCC top-layer thickness increased the fracture energy noticeably.

Numerical modeling of the interaction between reinforcement and concrete at early age—A comparison between glass fiber reinforced polymer and steel rebars

AbstractThis study has been undertaken for the assessment of steel/glass fiber reinforced polymer (GFRP) reinforced concrete mechanical behavior at an early stage. We developed a numerical model to describe the hydration process by using a chemo‐thermo‐mechanical scheme in ABAQUS finite element software. Mechanical properties of early age concrete versus hydration degree were determined using De Shutter's laws. The thermal and the autogenous strains are numerically implanted. Mazars elastic model was used to describe the concrete cracking. In addition, experimental validation of the established numerical model was performed and compared to the available literature. These data are selected for both plain and steel reinforced early age high‐strength concrete (HSC). Moreover, two mechanical boundary conditions were taken into account in accordance with the numerical simulations. Thermal conditions were considered in isothermal (20°C) and semiadiabatic conditions. Steel rebars were substituted by the GFRP under the same reinforcement percentages and configurations. The Interface between the steel and the GFRP reinforcement, and HSC was considered a perfect surface condition. Numerical predictions of the GFRP reinforcement were compared to those of steel reinforcement. Our results prove that the GFRP rebars restrain the concrete strains more than steel rebars. The GFRP rebar postpones concrete cracking compared to steel reinforcements. Furthermore, the concrete stress in the GFRP reinforced element is lower than the concrete stress in the RC steel.

Experimental investigation of ASR-affected concrete – The influence of uniaxial loading on the evolution of mechanical properties, expansion and damage indices

The alkali silica reaction (ASR) in concrete causes internal localized swelling and micro cracking, which result in expansion and correlated deterioration of the concrete material. The stress state of the concrete is known to affect expansion due to ASR, with an anisotropic stress state giving rise to anisotropic expansion. Similarly, the orientation and extent of micro cracking have a directional effect on the concrete mechanical behaviour. This research studied the effect of sustained uniaxial compressive stress on the evolution of the mechanical behaviour of concrete in compression. Concrete cubes of 230 mm side length were uniaxially restrained and stored in accelerated conditions, with cores drilled in two directions for mechanical tests: a cyclic test in compression, i.e. a stiffness damage test (SDT) and a complete stress-strain test. A clear directional dependency of the mechanical characteristics was found. Furthermore, the results indicate that reduction in modulus of elasticity is well correlated with the expansion in the test direction. On the other hand, the damage indices obtained from the SDT merely relate to the expansion, which puts in question the SDT’s ability to predict ASR expansion in stressed concrete and therefore in concrete structures.

Rheological and Mechanical Properties of Heavy Density Concrete Including Barite Powder

Heavy weight concretes (HWCs) or heavy density concretes are commonly used for radiation shielding in nuclear plant to ensure protection against X-rays and Gamma rays. It can also be required in other structures where a large mass is needed. This experimental study was effected to design a HWC, which can be used in bentonite-bored piles concreting in order to remove as much as possible the amount of mud that resides in the pile. In this study, barite is used as fine aggregate mixed with Portland cement to design HWC. Different barite concrete mixes were designed, where barite is used once as an addition while maintaining constant the amount of cement (400 kg/m3) and as a substituent, with different percentage (38, 46, 53 and 57%) to reach different concrete densities. The effect of barite on rheological, heat hydration and mechanical behavior of concrete was investigated. The use of barite as an addition leads to an increase in viscosity and yield stress of concrete; however, when barite is used as a cement substituent, a viscosity decrease is recorded. Barite concrete has shown a lower heat of hydration generation in comparison with a standard mix, which is correlated with compressive strength results.

Assessment of GFRP bond behaviour for the design of sustainable reinforced seawater concrete structures

Freshwater is an increasingly scarce resource. Its use in the production of concrete is one important contributor to its fast depletion. Alternatively, the use of seawater for reinforced concrete production, combined with the use of glass fibre reinforced polymers (GFRP) as reinforcement, may represent an interesting solution to increase concrete sustainability. The objective of this paper is to explore this promising solution through the development of concrete compositions with seawater. Additionally, it is also an objective to assess the bond behaviour between GFRP rods and concrete, in a design perspective. The influence of concrete age, rod diameter and anchorage length were also investigated. An analytical model capable of determining the local bond stress-slip laws was used. Results demonstrated that the use of seawater had no relevant effects on neither concrete mechanical properties nor bond behaviour.

Validation and Investigation on the Mechanical Behavior of Concrete Using a Novel 3D Mesoscale Method.

The mechanical performance of concrete is strongly influenced by the geometry and properties of its components (namely aggregate, mortar, and Interfacial Transitional Zone (ITZ)) from the mesoscale viewpoint, and analyzing the material at that level should be a powerful tool for understanding macroscopic behavior. In this paper, a simple and highly efficient method is proposed for constructing realistic mesostructures of concrete. A shrinking process based on 3D Voronoi tessellation was employed to generate aggregates with random polyhedron and grading size, and reversely, an extending procedure was applied for ITZ generation. 3D mesoscale numerical simulation was conducted under a quasi-static load using an implicit solver which demonstrated the good robustness and feasibility of the presented model. The simulated results resembled favorably the corresponding experiments both in stress–strain curves and failure modes. Damage evolution analysis showed that the ITZ phase has profound influence on the damage behavior of concrete as damage initially develops from here and propagates to mortar. In addition, it was found that tensile damage is the principal factor of mortar failure while compressive damage is the principal factor of ITZ failure under compression.

Destructive and non-destructive experimental investigation of polypropylene fibre reinforced concrete subjected to high temperature

Concrete is an inherently fire-resistant material, which in most cases requires no additional fire protection. However, a long-term exposure to high temperature results in the change in both strength properties and mechanical behaviour of concrete. Most of the experimental studies conducted so far investigated the fire resistance of concrete composites after the fire exposure. Whereas the aim of this paper was to focus on the performance of selected concrete composites, particularly plain concrete and fibre reinforced concrete with polypropylene fibres, exactly at the elevated-temperature state. Namely it concerns reference plain concrete and polypropylene fibre reinforced concrete tested up to 800 °C. Standard destructive tests and non-destructive tests were conducted on cylindrical specimens at hot state immediately after heating-up by using a specific heat treatment. The system used for the heat treatment was composed of ceramic pads, thermocouples the Mannings HTC 70 kW heating and control machine, which provided and regulated the heat transferred to the pads. The main objective of the experimental study was to observe actual material strength during fire situation as well as the reliability of the Schmidt's rebound hammer test when used for testing concrete at elevated temperature. The obtained results are in good agreement with the existing result database of polypropylene fibre reinforced concrete and plain concrete subjected to elevated temperature. The results obtained by the two different testing methods also show good agreement in a certain range of temperatures. As a consequence, in scientific manner, it seems that conducting the Schmidt's rebound hammer test on hot specimen with subsequent standard destructive compression test on the identical specimens cooled down to ambient temperature enable the observation of the compressive strength at hot state and the residual compressive strength after fire exposure on the same specimen. The investigation also demonstrates the benefit of the polypropylene fibres when added to a concrete composite subjected to elevated temperatures. Their presence in a mixture improves concrete spalling resistance and ensures a stable environment with low pore pressure in the concrete microstructure when subjected to elevated temperature and as a consequence the deviation in concrete compressive strength is small. The upcoming experimental investigation will focus on the effect of fibre content on the strength properties of concrete under elevated temperature.

Improved method to measure the strength and elastic modulus of single aggregate particles

The standard methods used to determine the mechanical properties of single aggregate particles have shortcomings. Indeed, methods that are commonly used to measure the strength of irregular particles do not provide their elastic modulus and are also only semi-quantitative. The aim of this work is to determine more accurately both the tensile strength and the elastic modulus of single coarse aggregate particles using the point load test fitted with tungsten carbide semi-spheres and coupled with a linear transducer. In the experiment, the poles of the particles are made flat and parallel at the points of contact with the semi-spheres of the apparatus, allowing to estimate the elastic modulus of aggregates in accordance to Hertz contact theory. Glass particles of different shapes (spheres, cubes, and prisms) were used as reference material to validate the experimental method and establish the optimal conditions to conduct the test. These conditions consisted of a deformation rate of 0.2 mm/min, a blunt 4.0-mm diameter cylinder piston for spherical particles, while two 14.0-mm diameter semi-spheres in the case of rectangular particles (cubes/prisms). It is also hereby proposed to measure the tensile strength of irregularly-shaped particles by a modified version of Hiramatsu and Oka’s formula using the equivalent core diameter. The proposed method was then applied to measure the strength and modulus of coarse granite aggregate particles (25.0 to 9.5 mm). It demonstrated that the variability of the elastic modulus and tensile strengths of the individual aggregate particles was quite significant, confirming the importance of using the proposed improved method to qualify materials for structural (high strength) concrete, or to simulate/predict the mechanical behavior of concrete.

Mechanical behavior of concrete using seawater and sea‐sand with recycled coarse aggregates

AbstractAdopting locally available seawater and sea‐sand to produce concrete in marine and coastal projects is considered sustainable in concrete industry. This paper studies the mechanical behavior of seawater sea‐sand concrete (SSC) and explores the feasibility of mixing SSC with recycled coarse aggregate (RCA). The early‐age cracking and mechanical behaviors of SSC with or without the addition of RCA are experimentally studied. The results demonstrate that, compared with conventional concrete, the compressive strength of SSC with natural coarse aggregate (SSNAC) at 7 days increases by 36–76%, and the compressive strength at 28 days is similar while the compressive strength at 180 days decreases by 3.7–10.2%. The addition of seawater and sea‐sand improves the mechanical behavior of recycled aggregate concrete, but deteriorates the early‐age cracking behavior. Furthermore, the stress–strain relationship of SSNAC is analyzed, and applicability of the existing model is evaluated.

Fracture Behavior and Energy Analysis of 3D Concrete Mesostructure under Uniaxial Compression.

In order to investigate the fracture behavior of concrete mesostructure and reveal the inner failure mechanisms which are hard to obtain from experiments, we develop a 3D numerical model based on the Voronoi tessellation and cohesive elements. Specifically, the Voronoi tessellation is used to generate the aggregates, and the cohesive elements are applied to the interface transition zone (ITZ) and the potential fracture surfaces in the cement matrix. Meanwhile, the mechanical behavior of the fracture surfaces is described by a modified constitutive which considers the slips and friction between fracture surfaces. Through comparing with the experiments, the simulated results show that our model can accurately characterize the fracture pattern, fracture propagation path, and mechanical behaviors of concrete. In addition, we found that the friction on the loading surfaces has a significant effect on the fracture pattern and the strength of concrete. The specimens with low-friction loading surfaces are crushed into separate fragments whereas those with high-friction loading surfaces still remain relatively complete. Also, the strength of concrete decreases with the increase of the specimen height in the high friction-loading surfaces condition. Further, the energy analysis was applied to estimate the restraint impact of loading surfaces restraint on the compressive strength of concrete. It shows that the proportion of the friction work increases with the increase of the restraint degree of loading surfaces, which finally causes a higher compressive strength. Generally, based on the proposed model, we can characterize the complicated fracture behavior of concrete mesostructure, and estimate the inner fracture mode through extracting and analyzing the energies inside the cohesive elements.

Effect of Glass Fibres on the Mechanical Behaviour of Concrete with Recycled Concrete Aggregates (RCAs)

This paper presents an experimental study on the influence of glass fibres on the mechanical behaviour of concrete with recycled concrete aggregates (RCAs). In the test programme, four concrete mixtures with coarse RCAs and glass fibres are manufactured. The used fibres are the CEM-FIL Minibars™ with a fibre content of 5 kg/m3, 10 kg/m3 and 15 kg/m3, respectively. The investigated properties are the compressive strength, the splitting tensile strength, the modulus of elasticity as well as the flexural behaviour. The latter is determined by the three-point bending test on concrete beams according to the standard EN 14651: 2005+A1:2007 – Test methodfor metallic fibre concrete: Measuring the flexural tensile strength (limit of proportionality (LOP), residual). Based on the test observations, it seems that the used glass fibres are able to improve the mechanical behaviour of recycled aggregate concrete (RAC).

Concrete fracture toughness increase by embedding self-healing capsules using an integrated experimental approach

An alternative solution to repair cracks in concrete has been recently established, namely autonomous healing by embedding repair agent into concrete during casting. The agent is included into small-size capsules that break as cracks form. As the agent is released into the crack void, it solidifies fast permitting crack sealing and mechanical restoration. Most of literature studies focus on the healing system design and the repair efficiency assessment. However, limited knowledge exists on the effect of the macro-capsules themselves on concrete mechanical behaviour. This is a crucial subject as the healing mechanism should not compromise the material mechanical properties. The paper investigates the effect of capsules on damage resistance by considering fracture constitutive models. Fracture toughness of samples with capsules increases up to 35% compared to the reference. Acoustic emission is applied to assess the capsules effect on fracture processes. Events localization indicates fracture process zone expansion by 40%. It is proven that the capsules beneficially contribute as local reinforcement perturbating the crack path and forming multiple microcracks (additionally verified by Digital Image Correlation). In summary, an integrated experimental protocol is developed to highlight the concrete toughness enhancement by adding capsules.

Thermal and Mechanical Behaviors of Concrete with Incorporation of Strontium-Based Phase Change Material (PCM)

In this study, phase change material (PCM) was used to control the heat of hydration of mass concrete, and the study aimed to evaluate the resulting fundamental and thermal properties of mass concrete with PCM. To evaluate the feasibility of adding PCM to concrete with various binder conditions for mitigating the hydration heat of mass concrete, mechanical and adiabatic temperature rise tests were conducted. The test results showed that the use of PCM did not significantly influence air content, while it slightly reduced flowability. For initial setting properties of concrete, it was found that the initial and final time were delayed when PCM was added. Even though compressive strength was slightly reduced when PCM was added into concrete, the strength development properties of concrete were more closely associated with the strength development properties of the binder. The adiabatic temperature rise test results showed that the addition of PCM resulted in an approximately 15–21% decrease in temperature rise of concrete. From the thermal analysis results, it is noted that thermal cracking probability could be decreased by adding PCM into concrete mix.

Semi-Flexible Material: A Solution for High-Performance Pavement Infrastructures

Asphalt pavement technology has been widely adopted due its good mechanical performance, its excellent surface properties, the ease of construction and driving comfort. Nevertheless, asphalt pavements, commonly also known as “flexible pavements” have demonstrated to present high moisture susceptibility, low resistance to several chemical agents and poor long-term performance. Moreover, both high and low temperatures can produce different damages in flexible pavement such as rutting and cracking. On the other hand, rigid pavements have been losing popularity mainly due to the presence of transversal joints, required to consider the expansion of concrete slabs that produce a reduction of user-comfort and safety. In addition, Concrete pavement need longer construction procedure and a curing time before opening to traffic. Hence, a new technology has been developed in the last years in order to gather the essential properties that characterize rigid and flexible pavements. This technology, usually called semi-flexible pavements, or grouted macadam, consist in producing a highly open porous asphalt mix (voids around 25-30%) and filling the voids with selected cementitious grout. Thus, the ease and speed of construction of flexible pavement, joint with the optimal surface properties is combined with the concrete good mechanical behaviour, resistance to chemical agents and limited temperature susceptibility. The final product is a high performance pavement material, particularly indicated to high traffic volume roads, airports, ports, and industrial areas. However, the fact that this type of pavement is still innovative compared to rigid and flexible pavement has made that there is no standard procedure to produce this type of mixture. For this reason, the characteristics of the mixtures vary with authors and in the different real scale applications. In this manner, this paper aims at studying the most significant advances in the area of semi-flexible pavements, describing, comparing and statistically analysing the different investigation and practical experiences. Mix-design details, i.e., asphalt binder characteristics, aggregate properties and cementitious grout composition are deeply investigated, as well as mixing and compaction procedures, lab testing and real application performance of this innovative and promising pavement material.

Effect of new mixing method of glass powder as cement replacement on mechanical behavior of concrete

This study investigates the effects of using local wastes of Glass Powder (produced from crushing the glass waste) as replacement of cement in fresh and hardened concrete. Four percentages of Glass Powder (GP) were used: 0%, 10%, 20%, and 30%. Two mixing methods were used in the study. First, the conventional mixing method, where the glass powder was added with the cement and aggregates. Second, the glass powder was dissolved in water before adding it to cement and aggregates. The slump increased as the glass powder replacement increased in the concrete due to the presence of more free water in the structure, which leaded to have lower density and higher water absorption. As a result, the compressive strength of conventional mixes method decreased as the glass powder increased at early age. Later, after 90 days, the highest compressive strength was obtained for the 20% GP. The new mixing method showed higher compressive strength than the conventional mixing method. Using 10% GP in the new mixing method gave a significant increase, around 130% of the compressive strength of the control mix. This increase can be related to the hydrolysis of the glass powder into free ions of SiO2, CaO and Na2O in the water which formed more CSH. The relative index proves the rise of the glass powder reactivity as the amount of glass powder increases.

Influence of plastic pour-in form on mechanical behavior of concrete

The behavior of slender concrete columns encased in a thin, flexible plastic pour-in form under increasing axial load was evaluated experimentally, by testing two groups of columns. Group one included seven unconfined concrete specimens and group two included nine steel-fibered concrete specimens with or without the plastic pour-in form. Different end-restraint conditions were used at the top and bottom ends of the columns. The main variables of the research included plastic tube geometry, slenderness ratios, steel fiber, and the rotation of the loading platen, and their effect on the ultimate strength and lateral deformations were investigated. Results show an increase in strength of 42% to 71% for specimens with pour-in form over plain concrete columns. The experimental results were compared with the calculated results showing good agreement.

Analysis of pullout behavior of single steel fibers embedded in concrete using phase‐field modeling

AbstractIn this contribution, a constitutive framework of elasto‐plastic phase‐field model for fracture is applied to simulation of pullout test of single steel fiber embedded in concretes and compare it to the experimental results. For the description of the mechanical behavior the Drucker‐Prager plasticity model is used. The aim is to examine the pullout behavior of a single steel fiber and its influence on the overall material behavior. Therefore, the mechanical behavior of concrete is studied in experimental single fiber pullout test. The predictive capability of the above mentioned model is analyzed in detail by simulating a single fiber pullout test and compared against the experimental data.

Study of Portland Cement Based Materials with Addiction from Cactus Opuntia Ficus-indica

Reinforcing Steel bars corrosion is one of the most common causes of reinforced concrete structures deterioration. Steel rebars are protected against corrosion by both chemical and physical mechanisms. The chemical protection is provided by the concrete high pH (12–13), which promotes the formation of a passive film on the steel surface. On the other hand, concrete acts as a physical barrier, hindering the access of aggressive agents. With the main aim of extending useful life of the structures and reducing the corrosive process in concrete, currently many investigations focus on the use of organic materials to analyze the electrochemical and mechanical behavior of concrete. For centuries, the use of cactus (Nopal) and its properties had special relevance in the economic, social and religious life of ancient civilizations. Currently, the mixture of cactus mucilage and lime is used as a layer to protect or repair historic buildings in Mexico.The main aim of this work is to analyze the electrochemical and mechanical behavior of Portland cement mixtures with cactus mucilage as a substitute for water. Three concentrations of cactus mucilage, 1:1, 1:2 and 1:3 ratios in cactus-water by weight were obtained. Concrete mixture was designed with a characteristic strength of f'c = 250 kg/cm2, Portland cement CPC 30R, coarse aggregate with a maximum size of 20 mm and river sand as fine aggregate. The proportions of mixtures were designed for a mucilage/cement ratio of 0.45. Each specimen contained three corrugated steel bars grade 42 of 3/8 inch. Samples were placed in a 3% sodium chloride solution after 28 days simulating an aggressive environment such as seawater and there were evaluated for 245 days through different electrochemical techniques. Half-cell potential is one of the most used techniques to analyze corrosion in concrete. Noble potential values were obtained for all samples with cactus mucilage compared to the control sample; calomel saturated electrode (CSE) was used. The electrochemical noise (EN) technique was performed using three nominally identical steel electrodes; noise resistance values and localization index for each sample were obtained. Linear polarization resistance (LPR) is a non-destructive technique, which provides information about the kinetics of corrosion in concrete. The samples with cactus mucilage after 245 days maintained values of corrosion rate close to 0.1 μA/cm2, remaining in the negligible corrosion rate interval while the control sample reached a value of 0.5 μA/cm2 close to the high corrosion rate interval. The compression strength technique was performed after 28 days of concrete curing. The samples with 1:3 concentration of cactus mucilage reached a resistance of 97.6% with respect to the control sample.

The effect of steel slag as a coarse aggregate and Sinabung volcanic ash a filler on high strength concrete

The Development of concrete technology is continues to grow. The requisite for efficient constructions that are often viewed in terms of concrete mechanical behavior, application on the field, and cost estimation of implementation increasingly require engineers to optimize construction materials, especially for concrete materials. Various types of concrete have now been developed according to their needs, such as high strength concrete. On high strength concrete design, it is necessary to consider several factors that will affect the reach of the quality strength, Those are cement, water cement ratio (w/c), aggregates, and proper admixture. In the use of natural mineral, it is important for an engineer to keep an eye on the natural conditions that have been explored. So the selection of aggregates as possible is a material that is not causing nature destruction. On this experiment the use of steel slag from PT.Growth Sumatra Industry as a substitute of coarse and fine aggregate, and volcanic ash of mount Sinabung as microsilka in concrete mixture substituted to create high strength concrete that is harmless for the environment. The use of mount sinabung volcanic ash as microsilika coupled with the use of Master Glenium Sky 8614 superplasticizer. This experiment intend to compare high strength concrete based slag steel as the main constituent aggregates and high strength concrete with a conventional mixture. The research result for 28 days old concrete shows that conventional concrete compressive strength is 67.567 MPa, slag concrete 75.958 Mpa, conventional tensile strength 5.435 Mpa while slag concrete 5.053 Mpa, conventional concrete bending strength 44064.96 kgcm while concrete slag 51473.94 kgcm and modulus of conventional concrete fracture 124.978 kg / cm2 while slag concrete 145.956 kg / cm2. Both concrete slump values shows similar results due to the use of superplasticizer.

Damage Evolution of Steel‐Polypropylene Hybrid Fiber Reinforced Concrete: Experimental and Numerical Investigation

This paper presents an experimental investigation on the stress‐strain behavior and damage evolution of steel‐polypropylene hybrid fiber reinforced concrete (HFRC) with different fiber types, volume fractions, and aspect ratios. The damage evolution laws of HFRC were obtained using uniaxial cyclic compression and tension tests. The results show that the addition of hybrid fiber has a significant synergetic effect on the mechanical behavior of concrete. The peak strength, peak strain, toughness, and postpeak ductility of HFRC under both tension and compression are improved, and the damage accumulation and stiffness degradation are alleviated by increasing volume fractions of SF and PF, as well as aspect ratios of SF. Moreover, the steel fiber volume fraction shows a more pronounced effect than that of other considered factors on the enhancement of cyclic mechanical parameters of HFRC. Based on the unloading stiffness degradation process, analytical equations were, respectively, proposed to generalize the damage progression of HFRC under compression and tension, with the effects of hybrid fiber taken into consideration. Finally, the proposed uniaxial damage evolution equations combined with the calibrated concrete damaged plasticity (CDP) model in ABAQUS were used to predict the responses of HFRC materials and structural members subjected to shear and seismic loads. The comparisons between the numerical predictions and experimental results show a good agreement.