Behavior Of Concrete Research Articles

Increasing the Length of Concrete Pavement Slabs Using Shrinkage Reducing Admixture and Polypropylene Fiber

Pavement engineers frequently employ concrete pavements because of their benefits such as extended lifetime, superior performance and durability, and so on. However, there are some disadvantages of these pavements such as shrinkage which may lead to cracking, warping, and limiting the length of the concrete pavement slabs. Shrinkage reducing admixture (SRA) and polypropylene fibers can be employed to prevent or control shrinkage cracking. In this study, increasing the length of concrete pavement slabs using shrinkage reducing admixture and polypropylene fiber was investigated. For mix compositions, two water–cement ratios of 0.35 and 0.4 were employed, and the percentages of SRA and polypropylene fiber utilized in mixes were 2% and 1% by weight of cement, respectively. Slump, compressive strength, third point flexural strength, electrical resistance, free and restrained shrinkage tests were carried out as the experimental programming to investigate the effect of these materials on concrete behavior and evaluate the amount of concrete pavement design parameters. Statistical analysis and RSM were used to determine the significance of each parameter and their interactions on concrete properties. It was observed that the use of SRA had no influence on workability; however, polypropylene fibers reduced the slump flow of concrete. Also, the use of SRA resulted in a decrease in mechanical properties. In addition, the use of polypropylene fibers considerably enhanced the energy absorption of concrete. Furthermore, on concrete containing SRA and polypropylene fiber, the magnitude of free and restrained shrinkage and crack width were reduced. Finally, the length and thickness of concrete pavement slabs were evaluated using the experimental results on the Tehran-Shomal freeway as a case study. The slab length could be increased by about 20% without any significant change in the slab thickness using SRA and polypropylene fiber in concrete mix composition. This can lead to an increase in construction speed, improve the durability of pavement and generally increase the quality of the concrete pavement.

Mechanical behavior of recycled lump concrete containing mixed demolished concrete lumps with different sizes or/and shapes

This study explored the utilization of mixed demolished concrete lumps (DCLs) to develop recycled lump concrete (RLC) fabricated using high-strength fresh concrete. With 100 mm spherical DCLs as a benchmark, the impacts of mixed spherical DCLs of different sizes (50, 67, 100, or 133 mm), mixed 100 mm DCLs of various shapes (oblate, spherical, or slender), and mixed DCLs of both various sizes and shapes, on the compressive, flexural, and direct shear behaviors of RLC were examined. Test results show that the mixed DCLs with various sizes or diverse shapes insignificantly affects the compressive strength and elastic modulus of RLC, but reduces the flexural strength by 6%–12%. Besides, mixed-size spherical DCLs allow RLC to achieve similar direct shear strength to that of benchmark RLC, while mixed-shape 100 mm DCLs and a single shape (oblate or slender) 100 mm DCLs make RLC exhibit about 10% higher direct shear strength than that of benchmark RLC. Further investigations show that using mixed DCLs with both different sizes and various shapes has a negligible impact on the compressive, flexural, and direct shear behaviors of RLC, which manifests the great potential of simplifying the production of RLC in practical engineering. Finally, the applicability of the previously proposed prediction formulas for the strength and elastic modulus of RLC containing single shape and single size DCLs to the RLC with mixed DCLs was discussed.

Failure investigation of steel and brick aggregate concrete composite construction with angle and channel shear connectors

ABSTRACT This investigation focuses mainly on the failure behaviour and performance of angle and channel shear connectors in composite structures made with steel and brick aggregate concrete. It was observed that both angle and channel shear connectors did not fail themselves. However, in some specimens, localised connector yielding was observed in channel shear connectors. In both cases, concrete strata failed as either concrete crushing and shearing, combined splitting and bending, or complete splitting mode of failure. Crushing and shearing failure was noticed in specimens having smaller web and flange and were brittle in nature as compared to the failure of specimens with larger web and flange. Other parameters, such as shear resistance, energy absorption, and load-slip behaviour, were also investigated. Web height and flange width of both connectors significantly affected the ultimate shear capacity and slip of the brick aggregate concrete specimen. Channel connectors were found more flexible and carried more shear than angle connectors. Channel connectors had an average of 32.41% and 116.17% more ultimate load and slip capacity than the angle connectors in brick aggregate concrete, respectively. The load-carrying capacity, slip, and failure behaviour of the brick aggregate concrete were found similar to those of stone aggregate concrete.

Theoretical Model for the Stress–Strain Curve of CNT-Reinforced Concrete under Uniaxial Compression

The incorporation of carbon nanotubes (CNTs) can enhance the mechanical properties of concrete. The stress–strain curves of CNT-reinforced concrete under uniaxial compression are investigated through an experimental program with different CNT and steel fiber proportions considered. The test results demonstrate that CNTs can increase both peak stress and peak strain, and steel fibers can further enhance the effect of CNTs. Additionally, steel fibers can effectively enhance both the strength and ductility. Theoretical models for the peak strain, initial elastic modulus, toughness index and relative absorbed energy are established. A theoretical model for the uniaxial compressive constitutive relationship of CNT-reinforced concrete considering CNT and steel fiber content is developed. Finite element (FE) modelling is developed to simulate the axial compression behavior of CNT-reinforced concrete.

Laboratory Evaluation of Tensile Creep Behavior of Concrete at Early Ages

Short-term uniaxial tensile creep tests were conducted for early-age concrete at different ages in an effort to characterize early-age concrete as an aging viscoelastic material. Based on the test results, the viscoelastic material properties of the test concrete were characterized in terms of the Dirichlet series creep compliance and relaxation modulus functions. Applications of the model to the numerical analysis of the test samples showed a good agreement between the tests and computational results for the samples tested at different ages. This paper presents the test procedures and data analysis with a brief introduction of theoretical background.

Effect of different surface preparation techniques on the bond behavior of normal and fiber-reinforced geopolymer concrete

Fiber-reinforced geopolymer concrete offers a sustainable alternative to conventional concrete; however, its application to repair and strengthen existing concrete structures is inadequately understood. The effectiveness of repairing and strengthening system depends upon the bond characteristics of existing and overlay concrete. Therefore, the present study aims to assess the bond performance of normal (old) concrete and fiber-reinforced geopolymer (new) concrete (FRGC) using different bond tests such as split tensile, bi-surface shear, and slant shear tests. The performance of four interface preparation techniques has been compared: wire brushing, epoxy, carbon fiber reinforced polymer (CFRP), and glass fiber-reinforced polymer (GFRP). Moreover, the effect of various sizes of groove width on the bond characteristics of old and new concrete interfaces is also investigated. CFRP and GFRP, as surface preparation techniques over plain old concrete surfaces, showed the highest split tensile, bi-surface shear, and slant shear strength. Additionally, the interface prepared with grooves of 40 mm width and 10 mm depth with epoxy represented a 113.5% enhancement in slant shear strength compared to the ungrooved one because of the additional mechanical interlocking provided by the defined shape of the grooves. The composite prepared with FRGC as new concrete performed equivalently and even better in some cases than new normal concrete due to the increased interfacial adhesion and dense transition zone created by PVA fiber. Thus, FRGC, being sustainable, has the tendency to replace conventional concrete as an effective and efficient repairing and strengthening concrete. Finally, the obtained experimental results have been compared with the predicted interfacial shear capacity using different design code models, and amongst them, Eurocode 2 predictions are closest to the experimental results.

Influence of pre-existing cracks and concrete cover on service life of reinforced concrete and mechanical behaviour of corroded rebars

PurposeIncorporating pre-existing crack in service life prediction of reinforced concrete structures subjected to corrosion is crucial for accurate assessment, realistic modelling and effective decision-making in terms of maintenance and repair strategies.Design/methodology/approachAn accelerated corrosion test was conducted by using impressed current method on cylindrical specimens with varying cover thickness and crack width. Mechanical properties of the specimens were evaluated by tensile tests.FindingsThe results show that, the pre-cracked samples exhibited shorter concrete cover cracking times, particularly with wider cracks when compared to the uncracked samples. Moreover, the load-bearing capacity of the reinforcement bars decreased owing to the pre-cracks, causing structural deflection and a shortened yield plateau. However, the ductility index remained consistent across all sample types, implying that the concrete had good overall ductility. Comparing the results of the non-corroded rebar and corroded rebar samples, the maximum reduction in the yield load was 25.22%, whereas the maximum reduction in the ultimate load was 26.23%. The simple mathematical model proposed in this study provides a reliable method for predicting the chloride ion diffusion coefficient in cracked concrete of existing reinforced concrete structures.Originality/valueA simple mathematical model was proposed for evaluation of the equivalent chloride ion diffusion coefficient considering crack width, average crack spacing and crack extending lengths for cracked reinforced concrete structures, which is used to incorporate existing crack in service life prediction models.

Effect of partial sand replacement with PVC and glass mix on flexural behavior of concrete

Waste in millions of tons is produced in the world each year and most of it is not recyclable. Furthermore, recycling waste consumes energy and produces pollution. In addition, the accumulation of waste in suburbs and disposal of waste is dangerous for the environment. Using waste material in concrete production is an appropriate method for achieving two goals i.e. eliminating waste and adding positive properties in concrete. Since the green concrete industry is expanding, it is necessary to evaluate concrete that contains waste from all aspects to determine its capability. This research consists of analyzing the use of waste as a partial substitute for sand. Leading waste material that has been used as substitutes is highlighted and the characteristic of the resulting concrete is evaluated in this research. Among other findings, rubber was found to have improved fire resistance and ductility in concrete, and agricultural and Polyethylene terephthalate (PET) wastes were successfully used in non-structural concrete, while glass helped to improve thermal stability. In this research aggregate and sand is replaced by waste materials of Polyvinyl Chloride (PVC) and Glass to check their effect on the mechanical properties. Lab tests were performed to analyze the flexural behavior of concrete samples having waste material. The results show how partial replacement of sand affects the behavior of concrete and based on that specify the conditions where it can be used. The results show that Young’s modulus, maximum bending stress, and bending deflection varies with the percentage composition of PVC and glass. Bedding stress and bending deflection decrease with PVC and glass composition up to 35%. Although Young’s modulus is fluctuating bending deflection will decrease.

Compressive behavior of FRP-confined normal concrete or seawater sea-sand concrete containing FRP-bar recycled coarse aggregates

Fiber-reinforced polymer (FRP) waste has become an environmental concern owing to the non-biodegradable nature and widespread use of FRP composites. Cutting the disposed waste of FRP bars into small pieces (referred to as FRP-bar recycled aggregate or FRP-RA) and replacing natural coarse aggregate in concrete with these pieces is considered a promising solution for recycling FRP waste. Owing to its excellent corrosion resistance, FRP-RA can be used as a raw material for the production of seawater sea-sand concrete (SSC). This study investigated the axial compressive behavior of FRP-confined normal concrete (NC) or SSC containing FRP-RA. The FRP-RA was cut from glass FRP (GFRP) bars of different diameters. Axial compression tests were conducted on 96 specimens. The specimens were designed with the following parameters: the type of concrete (NC and SSC), natural coarse aggregate replacement ratio (0%, 33%, 66%, and 100% by volume), thickness (1-layer and 2-layer), and type (carbon FRP and GFRP) of the FRP jacket. The test results indicated that the presence of the FRP-RA reduced the compressive strength and elastic modulus of the concrete. FRP confinement significantly enhanced the compressive strength and ultimate axial strain of the concrete with FRP-RA. No discernible difference was observed between SSC and NC with respect to FRP-RA. Finally, a widely adopted stress-strain model for FRP-confined NC was first evaluated using the test results, and a modified stress-strain model was then proposed for more accurate predictions.

A comprehensive review of ultra-high performance concrete (UHPC) behaviour under blast loads

Blasts resulted from industrial/residential accidents and deliberate attacks can impose extremely hazardous loading conditions upon nearby structures. The repercussions of these blasts encompass not only direct effects such as blast overpressure and fragments but also indirect outcomes like progressive collapse of structures. In the pursuit of enhanced protection for concrete structures, substantial endeavors have been directed towards developing innovative construction materials with outstanding properties, among which the ultra-high performance concrete (UHPC) has emerged as a notable representative. Drawing from existing experimental, numerical and theoretical studies, this paper presents an inclusive overview of recent progress in UHPC structural members (slabs, beams and columns) and UHPC-based composite structures (mesh reinforced UHPC, UHPC-filled steel tube and UHPC strengthening of normal reinforced concrete (NRC) structures) in their ability to withstand blast loads. While discussing the exceptional material and structural dynamic performance of UHPC, recommendations are offered for the further research directions in utilising UHPC structures to resist blast loads, which include exploring eco-friendly UHPC, integrating 3D printing technology and employing machine learning analytical methods.

Effect of accelerated carbonation of fully recycled aggregates on fracture behaviour of concrete

Accelerated carbonation of recycled aggregates (RAs) enables fast carbon sequestration while improving engineering properties of prepared concrete. This paper presents a systematic experimental study on the fracture behaviour of concrete with carbonated recycled coarse and fine aggregates (RCA and RFA), in terms of fracture parameters and fracture process zone (FPZ). The relevant influencing mechanism was investigated by relating the macroscopic fracture responses to microstructural features. Results indicate that carbonated RFA mainly enhanced the initial fracture toughness of concrete, while carbonated RCA primarily increased its unstable fracture toughness. The enhancement of fracture energy was closely associated with carbonated RCA and RFA. The utilization of RFA resulted in the looseness and higher porosity of mortar matrix, which reduced the crack initiation resistance of concrete, mainly affecting its initial cracking stage. The incorporation of RCA reduced crack bifurcation and deflection of concrete, leading to a smaller width of FPZ, which made the initial descending segment of the tension softening curve (TSC) steeper and its tail segment shorter. The carbonation treatment of RAs improved the densification of the adhered old mortar and reduced the porosity of prepared concrete, rising the cracking resistance and inducing a wider FPZ. As a result, the initial descending segment of TSC became flatter and its tail segment tended to be longer.

Effects of eccentric loading on performance of concrete columns reinforced with glass fiber-reinforced polymer bars.

Glass fiber-reinforced polymer (GFRP) reinforcements are superior to traditional steel bars in concrete structures, particularly in vertical elements like columns, and offer significant advantages over conventional steel bars when subjected to axial and eccentric loadings. However, there is limited experimental and numerical research on the behavior of GFRP-reinforced concrete (RC) columns under eccentric loading having different spacing of stirrups. In this study, six specimens were cast under three different values of eccentricities (25mm, 50mm, and 75mm) with two groups of stirrups spacing (50mm and 100mm). The experimental results showed that by increasing the eccentricity value, there was a reduction in the load-carrying capacityof the specimens. The finite element ABAQUS software was used forthe numerical investigation of this study.The results from the finite element analysis (FEA) were close to the experimental results and within the acceptable range. The maximum difference between theexperimental and FEA resultswas 3.61% for the axial load and 12.06% for the deformation.

Cohesive element-based chemo-thermo-mechanical multi-field coupled cracking simulation of early-age concrete

Due to the intense exothermic hydration process, early-age concrete undergoes restrained shrinkage deformation, which can easily lead to cracks in concrete structures during construction. In order to accurately predict the adverse effects of early-age concrete cracking behavior, a cohesive element-based chemo-thermo-mechanical multi-field coupled cracking model of early-age concrete is proposed in this study. Parametric analysis shows that by selecting appropriate gap conductance, constitutive thickness, mesh size, and viscosity coefficient for the cohesive elements, the multi-field coupled cracking model can successfully simulate the entire cracking process of early-age concrete, and it has the ability to obtain crack development behavior based on the real displacement field jumps, coordinates, and damage of cohesive elements. The validation of the numerical examples reveals the competing mechanisms between thermal expansion and autogenous shrinkage in early-age concrete and accurately predicts the cracking strain, region, time, and width (within an order of magnitude) as reported in the literature.

Mechanism of Influence of Sawtooth Interface Parameters on Shear Behavior of New and Old Concrete

Mechanism of Influence of Sawtooth Interface Parameters on Shear Behavior of New and Old Concrete

Current trends and biotechnology infused cleaner production of biomaterials for the construction industry: A critical review

Abstract Over the last few decades, there has been a significant awareness established to accept the idea of biotechnology in the field of construction. This growth in awareness has occurred tremendously. In today's world, the development of new building materials and processes that make use of biobased components, such as microorganisms and materials that are mediated by microbes, is an example of developing scientific technology. In general, building materials that are produced through the use of biotechnology, such as cement and grout, are seen as being environmentally benign, affordable, and sustainable. In contrast to traditional cementitious materials, bio-based cementitious materials has the potential to considerably contribute to a large role in reducing the negative impact that the building sector has on the surrounding environment. The purpose of this review work is to present a contemporary evaluation of biotechnology and biobased materials to assess existing developments and suggest new prospective routes for the advancement of construction biotechnology. Based on this study, it was observed that the inclusion of biotechnology can significantly increase the engineering behaviour of cement concrete and weak foundation soil. Hence, its was recommened to implement the idea of biotechnology as effectively in the building industry to obtain the major environmental and economic benefits it offers.

Flexural behavior of ultra-high performance concrete (UHPC) shaped thin-plate ribbed staircases: an experimental and numerical study

Flexural behavior of ultra-high performance concrete (UHPC) shaped thin-plate ribbed staircases: an experimental and numerical study

Experimental and analytical investigation of a model towards predicting the compressive stress–strain behavior of Graded Glass Fiber Reinforced Concrete (GGFRC) using fiber reinforcing index

AbstractThe stress–strain behavior of graded glass fiber reinforced concrete (GGFRC) is a crucial factor in its performance and appropriateness for diverse applications. In the present study, experimental and analytical methods were used to develop a model for the stress–strain behavior of GGFRC under uniaxial loading. The experimental program is designed to investigate the impact of mono glass fibers (3, 6, 12, and 20 mm) with varying volume fractions (0.1%–0.5%) and graded glass fibers (combinations of 3 + 6 + 12 + 20 mm) on the behavior of concrete of M50 grade. By grading glass fiber lengths in the concrete, GGFRC's pre‐peak strength and post‐peak deformation have increased, allowing the composite to control the various scales of cracking. A uniaxial compressive stress–strain model has been developed utilizing the fiber reinforcing index to predict the stress–strain curves of GGFRC in compression. The fiber reinforcing index, which is a measure of the quantity of fiber reinforcement in the material, is used as a variable in the current model to observe how it impacts the material's behavior. This would help evaluate the material's behavior under uniaxial compressive loading conditions and then use that data to develop a mathematical model that can predict the material's response under other conditions. Finally, it can be concluded that there is a significant correlation between the experimental results and the proposed analytical model.

Simulation of four-point bending tests for the viscoelastic fracture properties of concrete

Understanding the fracture properties of concrete, such as crack propagation behavior and fracture energy, is crucial for designing and evaluating concrete structures. Experimental results are insufficient and cannot be directly employed for a comprehensive analysis of the fracture behavior of concrete structures under load, particularly when considering concrete as viscoelastic with the presence of cracks. Recognizing the time and cost constraints of traditional experimental testing, this research leverages numerical simulations as a cost-effective alternative to determine viscoelastic material parameters. Thus, the critical evaluation of concrete fracture properties, fundamental for the design and assessment of concrete structures, is addressed. Employing a finite element method for four-point bending tests, the study systematically investigates parameters such as initial crack depth, displacement acceleration, and time step. The material properties of concrete are described using viscoelastic models. The findings provide valuable insights into crack propagation behavior and deformation characteristics, emphasizing the significant influence of the modulus of elasticity on both maximum load values and displacement. These findings contribute to a deeper understanding of the structure's response and underscore the importance of considering these parameters in similar simulations. The study highlights the importance of considering these parameters in simulations to enhance the understanding of concrete fracture behavior. The paper's contributions can extend to optimizing concrete mixtures, formulating repair strategies, and improving structural assessments. Further research is suggested to improve the accuracy of simulations and investigate material properties under various conditions.

Inter-school collaboration leaders’ behaviors and underlying leadership styles: The case of China

There has been a sizable increase in studies of leadership in inter-school collaboration (ISC) over the past years. But few studies have focused on leaders’ concrete behavior in ISC settings. Drawing on the Leadership for Learning (LfL) theory, this research explored ISC leaders’ behaviors and then surmised underlying leadership styles. A mixed-method design was used to collect data from China. The results showed that the behaviors of high-rated leaders partly revealed that they adopted a caring-oriented leadership style, which focused on situations, needs, and concerns of members. The behaviors of low-rated leaders somewhat presented a control-oriented leadership style, which emphasized dominating the operation of the organization. This research adds to the growing knowledge body of research on leadership in ISC. It not only has important implications for future research but also provides useful implications for ISC leaders’ practice and policy-making.

Cracking and thermal resistance in concrete: Coupled thermo-mechanics and phase-field modeling

Modeling damage and fracture in concrete accurately is crucial for a comprehensive analysis of structures under concurrent thermal and mechanical actions. This paper presents a novel coupled thermo-mechanical phase field model for concrete at high temperatures. Derived from principles of thermodynamics and unified phase field theory, the model integrates temperature-dependent thermal and mechanical properties, accounting for thermal expansion and transient creep. Mechanical damage, represented by the crack phase field, is augmented by a temperature-dependent thermal damage variable for heat-induced degradation. Addressing the impact of cracks on heat conduction and stress redistributions, the model introduces a novel approach to depict thermal resistance, seamlessly integrating mechanics, heat transfer, and crack propagation. Governing equations for damage evolution are derived, and the numerical implementation is detailed. Numerical illustrations showcase the model's ability to simulate diverse thermo-mechanical cracking patterns without explicit fracture path tracking or assumed criteria. Moreover, the model captures the influence of thermal actions on concrete cracking behavior and mechanical performance. This research is significant for predicting multi-field coupling damage in concrete and structures exposed to elevated temperatures.