•Drop-weight impact tests were performed on steel or GFRP bars RC slabs.•Effects of bar type, reinforcement ratio and arrangement were investigated.•Effects of concrete strength and slab thickness ...were also investigated.•Singly RC slab with higher tensile bars than doubly RC slab perform better.•The results obtained from experiment and numerical simulation are in good agreement.
Reinforced concrete slabs are common structural elements that could be exposed to impact loading. Although use of reinforced concrete slabs and utilization of Fiber Reinforced Polymer (FRP) as alternative to traditional steel reinforcement slabs are growing, but the influence of various parameters on their response under impact loads is not properly evaluated. This study investigated the effect of rebar’s material, amount and arrangement of reinforcements, concrete strength and slab thickness on dynamic behavior of reinforced concrete slabs using both laboratory experiments and numerical simulations. Performance of fifteen 1000 × 1000 mm concrete slabs, including two 75 mm thick plain slabs, five 75 mm thick steel reinforced concrete slabs, six 75 mm thick reinforced concrete slabs with Glass Fiber Reinforced Polymer (GFRP) bars and two 100 mm thick steel reinforced concrete slabs under drop weight impact loads was experimentally investigated. Failure mode, crack development, displacement-time, strain-time, and acceleration-time responses were studied and compared between various slabs. Finite element analyses and simulation of specimens were conducted using LS-DYNA explicit software. The results obtained from experiments and numerical models are in good agreement, and they indicate that increasing the reinforcement ratio or the slab thickness enhance the behavior of RC slabs under impact loads. By adjusting the amount and arrangement of GFRP, better performance in GFRP slabs than steel reinforced slabs can be achieved, which considering the corrosion resistance of this material, can make it an appropriate selection of reinforcement material.
•Using the linear polarization resistance (LPR) method to test the steel bars embedded in the CAC prismatic specimen and obtain the corrosion rate of them.•The anti-corrosion performances of ...different reinforcements in CAC were compared and ranked via corrosion rate measured by LPR method.•The surface free chloride content of steel bar in CAC was obtained through the two-dimensional chloride diffusion model.•The critical chloride content of different steel bars in CAC were determined based on the statistical relationship between surface free chloride content and corrosion rate of them.
Chloride threshold is a significant index to judge the initial corrosion of rebar in concrete structures, and a key parameter for durability analysis and service life design of reinforced concrete structures. In the present wok, the corrosion rate of rebar embedded in coral aggregate concrete and the chloride ion diffusion law of coral aggregate concrete was studied by the linear polarization resistance method and two-dimensional chloride diffusion model, respectively. Depending on the relationship between the surface free chloride content of rebar and its corrosion rate, the chloride threshold values of different rebar in coral aggregate concrete were finally determined. The results indicate that the corrosion rate of rebar in coral aggregate concrete gradually decreases with the increase of concrete strength grade and cover thickness, and the order of anti-corrosion performance of reinforcements from high to low is: epoxy resin coated steel, 2205 duplex stainless steel, 316 L stainless steel, organic coated steel and ordinary steel. The chloride threshold values (% by weight of concrete) of these reinforcements in coral aggregate concrete were determined and ranked from small to large as follows: ordinary steel (＜0.15%), organic coated steel (＜ 0.21%), 316 L stainless steel (0.33% ∼0.41%), 2205 duplex stainless steel (＞0.46%) and epoxy resin coated steel (＞0.49%). Additionally, there is a remarkable regression relation of corrosion rate between surface free chloride contents and cover thickness of reinforcement, which has a great significance of the research of steel corrosion in coral aggregate concrete.
Concrete‐encased concrete‐filled steel tubes (CFST) has extensive applications in the world. According to previous researches, if the CFST is placed in the compression zone, the confinement ...increases, and the compressive capacity of the concrete is completely used. The prestressed strands also increase the core concrete confinement and eliminate tension cracks. Therefore, in this paper, to achieve the benefits of CFST and prestressed strand, for the first time, a novel concept called prestressed concrete‐encased CFST (PCE‐CFST) beams were introduced. The main objective of the combination of steel tube and pre‐stressed strands is to increase the core concrete compressive strength and control the concrete crack in the tension zone. Six beams were constructed using self‐compacting concrete to investigate the influence of variations in the pre‐stressing force level of the pre‐stressed strands, the pre‐stressed strands eccentricity, and the steel tubes diameter‐to‐thickness ratio on the structural performance of these members. The specimens were tested under four‐point loading. The results showed that the pre‐stressed strands increased the confinement effect on the core concrete and improved the bearing capacity, ductility, and bending stiffness. The steel tubes improved the bearing capacity, ductility, and energy absorption, while they did not significantly affect the bending stiffness. Finally, it was shown that the pre‐stressed strands increased the bearing capacity, energy absorption, and bending stiffness in reinforced concrete beams.
•The first study on the creep behavior and microstructure of recycled aggregate concrete (RAC) containing high-strength recycled aggregates is presented.•Long-term compressive strength, elastic ...modulus, splitting tensile strength, workability, drying shrinkage, and creep of RACs are studied.•Parent concrete strength of recycled aggregates significantly affects the time-dependent and long-term behavior of RACs.•High-strength RACs containing 110-MPa recycled aggregates exhibit long-term properties that are similar to or better than those of companion conventional concrete.•SEM and EDX analyses were performed to explain the mechanisms behind the mechanical test results.
It is now accepted that replacement of natural aggregates in concrete with recycled concrete aggregates obtained from construction and demolition waste is a promising technology to conserve natural resources and reduce the environmental impact of concrete. This paper presents a study on long-term properties of concretes manufactured with recycled aggregates of different parent concrete strengths. A total of six batches of recycled aggregate concretes (RACs) were manufactured. Tests were undertaken to establish the long-term compressive strength, elastic modulus, splitting tensile strength, workability, drying shrinkage, and creep of each batch. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) characterizations were performed to explain the mechanisms behind the observed time-dependent and mechanical properties of RACs. Test parameters comprised the replacement ratio and parent concrete strength of the recycled aggregates used in the preparation of the new concrete mixes. The results indicate that the parent concrete strength of the recycled aggregates significantly affects the time-dependent and long-term mechanical properties of RACs. It is shown that concrete mixes containing lower strength recycled concrete aggregates develop lower mechanical properties and higher shrinkage strain and creep deformation compared to mixes prepared with higher strength recycled concrete aggregates. Normal-strength RAC mixes containing higher strength recycled concrete aggregates develop slightly lower splitting tensile strength at all curing ages but similar compressive strength and elastic modulus in longer term (i.e. over 90 days) compared to those of the control mix. It is also shown that high-strength RACs, prepared with full replacement of natural aggregates with recycled concrete aggregates having a higher parent concrete strength, exhibit time-dependent and long-term mechanical properties that are similar to or better than those of companion natural aggregate concretes.
•Green concrete utilizes waste materials as SCM and aggregates in concrete.•It promotes effective waste management, GHG reduction and resource conservation.•Benefits: improved strength, workability, ...durability, pumpability, reduced cracking.•Benefits: reduction of construction & maintenance costs and increased service life.•More R & D, standards and large-scale demonstration projects are required.
Utilization of green concrete in construction is increasingly adopted by the construction industry owing to the drawbacks of conventional concrete and the numerous inherent benefits of green concrete. The increasing demand for green concrete has been spurred by demand for high quality concrete products, desire of nations to reduce green-house gas emission, need for conservation of natural resources and limited landfill spaces. Green concrete comes in various forms such as high-volume fly ash concrete, ultra-high performance concrete, geopolymer concrete, lightweight concrete to mention a few. Green concrete offers numerous environmental, technical benefits and economic benefits such as high strength, increased durability, improved workability and pumpability, reduced permeability, controlled bleeding, superior resistance to acid attack, and reduction of plastic shrinkage cracking. These characteristics promotes faster concrete production, reduction of curing waiting time, reduction of construction costs, early project completion, reduction of maintenance costs and increased service life of construction projects. Green concrete promotes sustainable and innovative use of waste materials and unconventional alternative materials in concrete. Suitable standards, more demonstration projects, as well asadequate training, public awareness, cross-disciplinary collaborations and further research and developments are required to promote global adoption of green concrete in large-scale infrastructure projects.
Sulphate corrosion of concrete is a complex chemical and physical process that leads to the destruction of construction elements. Degradation of concrete results from the transportation of sulphate ...compounds through the pores of exposed elements and their chemical reactions with cementitious material. Sulphate corrosion can develop in all kind of structures exposed to the corrosive environment. The mechanism of the chemical reactions of sulphate ions with concrete compounds is well known and described. Furthermore, the dependence of the compressive strength of standard cubic samples on the duration of their exposure in the sulphate corrosion environment has been described. However, strength tests on standard samples presented in the scientific literature do not provide an answer to the question regarding the measurement methodology and actual distribution of compressive strength in cross-section of reinforced concrete structures exposed to sulphate ions. Since it is difficult to find any description of this type of test in the literature, the authors undertook to conduct them. The ultrasonic method using exponential heads with spot surface of contact with the material was chosen for the measurements of concrete strength in close cross-sections parallel to the corroded surface. The test was performed on samples taken from compartments of a reinforced concrete tank after five years of operation in a corrosive environment. Test measurements showed heterogeneity of strength across the entire thickness of the tested elements. It was determined that the strength of the elements in internal cross-sections of the structure was up to 80% higher than the initial strength. A drop in the mechanical properties of concrete was observed only in the close zone near the exposed surface.
The use of ultra‐high‐performance fiber reinforced concrete (UHPFRC) to repair or rehabilitate old concrete structures has been shown to be appropriate due to its properties, such as higher ...compressive strength, ductility, and durability than conventional concretes. One of the studied strengthening techniques is the reinforced concrete columns jacketing by UHPFRC. Some recent research evaluated some parameters, such as the repair thickness and the volumetric ratio of stirrups. However, other important parameters, such as UHPFRC jacketing thickness in different column cross‐sections and the concrete core compressive strength, need to be addressed. In addition, the analytical models presented in the literature are restricted to only one concrete grade. The present study aims to evaluate the behavior of short reinforced concrete columns strengthened with UHPFRC subjected to centered compression. Numerical analyses of three‐dimensional models were performed using the finite element method, validated, and calibrated using experimental results. The influence of the concrete core compressive strength, the UHPFRC jacketing thickness, and the shape of the cross‐section were evaluated. Numerical simulations concluded that the lower concrete core compressive strength columns showed the best relative increase performance. Moreover, the concrete core strength was inversely proportional to the resistance capacity of the repair system. In addition, the increase in repair thickness contributes to the axial strength of the column. Furthermore, the cross‐section influences the distribution of stresses and strains, showing the best performance for circular sections. Finally, regardless of cross‐section type, the proposed equations accurately predicted the numerical results.
Comprehensive coverage of durability of concrete at both material and structural levels, with design related issues Links two active fields in materials science and structural engineering: the ...durability processes of concrete materials and design methods of concrete structures Facilitates communication between the two communities, helping to implement life-cycle concepts into future design methods of concrete structures Presents state-of-the-art information on the deterioration mechanism and performance evolution of structural concrete under environmental actions and the design methods for durability of concrete structures Provides efficient support and practical tools for life-cycle oriented structural design which has been widely recognized as a new generation of design philosophy for engineering structures The author has long experience working with the topic and the materials presented have been part of the author's current teaching course of Durability and Assessment of Engineering Structures for graduate students at Tsinghua University The design methods and approaches for durability of concrete structures are developed from newly finished high level research projects and have been employed as recommended provisions in design code including Chinese Code and Eurocode 2
•Eight full-scale high strength steel fiber reinforced concrete (SFRC) columns were tested.•High strength material were used. (f′c = 70 MPa, fy = 685 MPa and fyt = 785 MPa).•The applied axial loading ...level ranged from 0.1 to 0.4 Agf′c.•The effects of fiber volume fraction and axial loading level on shear behavior of SFRC columns were investigated.
The ties configuration in accordance with every requirement of ACI 318-14 or newer for confinement and shear strength in a reinforced concrete (RC) column is strong required so that the RC column can dissipate seismic energy through flexural mechanism. In addition, according to ACI 318, the amount of confinement may increase as axial loading level increases. The increase of amount of confinement may lead to construction difficulties, particularly in column with small cross-section size; meanwhile, according to ACI 318, there is an upper limit for the transverse reinforcement in an RC column. An alternative material that has feasibility in substituting and reducing the traditional transverse reinforcement while maintaining shear strength and ductility is required. Application of short and discontinuous steel fibers to concrete element can be an alternative, since previous experimental results showed the improvement of shear strength, ductility, and toughness after adding steel fibers. However, no comprehensive experimental study of shear behavior of steel fiber reinforced concrete (SFRC) column with high strength concrete and steel reinforcing bars under different axial compression ratios subjected to lateral displacement reversals were available. In this study, large-scale double curvature SFRC columns with concrete strength design, yield strength for longitudinal reinforcement, and yield strength for transverse reinforcement, respectively of 70 MPa, 685 MPa (SD685), and 785 MPa (SD785) were prepared and tested.
This book was proposed and organized as a means to present recent developments in the field of testing of materials and elements in civil engineering. For this reason, the articles highlighted in ...this editorial relate to different aspects of testing of different materials and elements in civil engineering, from building materials to building structures. The current trend in the development of testing of materials and elements in civil engineering is mainly concerned with the detection of flaws and defects in concrete elements and structures, and acoustic methods predominate in this field. As in medicine, the trend is towards designing test equipment that allows one to obtain a picture of the inside of the tested element and materials. Interesting results with significance for building practices were obtained.
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