Performance Of Concrete Structures Research Articles

Autogenous deformation and coefficient of thermal expansion of early-age concrete: Initial outcomes of a study using a newly-developed Temperature Stress Testing Machine

Thermal and autogenous deformations of high-performance concrete at early ages have significant impact on the performance, serviceability, and durability of concrete structures. While substantial past research has significantly improved our fundamental understanding of the autogenous shrinkage and of the coefficient of thermal expansion (CTE) of cement paste and mortar, such understanding for concrete, especially modern types of high-performance concrete at early ages, remains inadequate. Accordingly, a new Temperature Stress Testing Machine (TSTM) capable of generating reliable data on autogenous shrinkage and CTE of concrete from very early ages has been built. After a review of relevant major aspects, key features of the newly-built TSTM are reported, with a focus on advanced thermal regulation and deformation capturing systems. The outcomes of a study using the newly-developed TSTM on autogenous deformation and CTE of early-age concrete (two mixtures with water-to-binder ratio of 0.35 and 0.42) subject to different curing temperatures (23, 35 and 45 °C) are then presented. Higher curing temperatures significantly accelerate the development of autogenous shrinkage at very early ages, whereas after the initial period, the magnitude of autogenous shrinkage cured at the intermediate temperature of 35 °C gradually becomes the largest. Despite this cross-over, the maturity concept appears appropriate to approximate the effect of curing temperature on autogenous shrinkage of concrete at early ages. The linear CTE of early-age concrete, obtained using stepped temperature profiles, follows a clear rising trend after setting. Based on the newly-measured CTE, an attempt was made to separate thermal strain and self-desiccation shrinkage, in which the presence of non-negligible delayed thermal strain became evident.

Seismic performance assessment of tunnel form concrete structures under earthquake sequences using endurance time analysis

A low-computational cost method is developed for seismic performance assessment of tunnel-form concrete structures under earthquake sequences. Using incremental dynamic analysis (IDA), a structure already damaged under a code spectrum-compatible mainshock is subjected to a set of aftershock events. The seismic reliability of the structure under successive earthquakes is then evaluated by comparing the fragility curves of the intact and the damaged structures. To achieve this, the newly developed endurance time approach is used to obtain the residual capacity of the structures to withstand aftershocks. The efficiency of the proposed method is demonstrated by using 5 and 10-storey 3D tunnel-form concrete structures as case study examples. It is shown that using endurance time method for seismic performance evaluation under mainshock-aftershock sequences generally leads to accurate results (less than 15% error), while it can significantly reduce (up to 90%) the computational costs of the conventional IDA method. The results also indicate that the application of the code design basis earthquake as the mainshock has no significant effect on the seismic performance of the tunnel form concrete structures under aftershocks, especially for the shorter systems. This highlights the excellent seismic resistance of tunnel-form structures under earthquake sequences.

Cyclic Behavior of Beam-Column Connections in Precast Structures

The performance of precast concrete structures is greatly influenced by the response of beam–to-column connections. In this study, a new moment resisting precast concrete beam-column connection detail with post-tensioning bolts, made out of high yield strength spring steel, has been experimentally investigated as an alternative to the conventional precast moment resisting connections. Precast specimens and an aseismic monolithic reference specimen have been tested under reverse cycling loads. The contribution of the mild steel in the connection region to the flexural moment capacity, and to the initial pre-stressing force on post-tensioning bolt have been the main test variables. The moment capacity, stiffness, energy dissipation capacity and the residual displacement performance of the precast connections have been compared with those of the aseismically detailed monolithic connection. The conducted tests reveal that the connection detail with steel corbel along with the post-tensioning bolt and mild steel has superior performance properties as compared to the companion precast specimens.

Finite Element Analysis-Based Damage Metric for Airtightness Performance Evaluation of Concrete Tube Structures

The super speed tube transport (SSTT) system is considered as a strong candidate for next-generation long-distance transport systems because of its anticipated highly efficient performance. Several studies have been conducted on infrastructure systems using concrete to improve the construction and economic feasibility of SSTTs. However, most of these only focused on the applicability of concrete in maintaining its airtightness; the effects of concrete cracks on the airtightness performance have not been investigated. Accordingly, this paper proposes a method using the finite element analysis (FEA) for evaluating the structural damage associated with the airtightness performance of concrete tube structures. An experimental work was conducted to measure this performance by subjecting a concrete tube structure to four stages of displacements at the midspan. Thereafter, to analytically measure the structural damage, the FEA was conducted and the results were compared with the experimental values. It is found that the structural damage expressed in terms of the eroded volume fraction (VF) calculated at each stage is closely correlated with the corresponding airtightness performance obtained from the experiment. These results show that FEA can be efficiently used for conducting experiments in the SSTT design phase to verify the concrete tube’s airtightness performance under many load cases.

Modeling Constitutive Relationship of Steel Bar Removed from Corroded PC Beams after Fatigue Considering Spatial Location Effect

AbstractFatigue changes the mechanical behavior of reinforcing bars, significantly reducing the performance of aging concrete structures. This study performed a fatigue loading test on post-tension...

Impact response of fibre reinforced geopolymer concrete beams with BFRP bars and stirrups

Increased number of studies of the performances of geopolymer concrete (GPC) structures reinforced with fibre reinforced polymer (FRP) under static loadings have been reported recently, aiming at developing an alternative of the traditional constructions with ordinary Portland concrete (OPC) and steel reinforcement because GPC is a sustainable construction material and FRP is corrosion resistant. Study of the dynamic performance of GPC structures reinforced with FRP is, however, very limited. This study experimentally investigates the impact response of ambient cured GPC beams reinforced with different types of fibres and basalt fibre reinforced polymer (BFRP) bars. Four GPC beams reinforced with steel fibres or synthetic fibres and two control beams made of GPC and OPC without fibre reinforcement were cast and cured under ambient conditions. The volume fraction of fibres varied from 0 to 0.5% were used in concrete mix and BFRP bars and stirrups were used for longitudinal and transverse reinforcements respectively. All the beams were tested under drop-weight impact and after impact tests, the damaged beams were monotonically loaded under three-point bending tests to obtain the residual strength. The experimental results demonstrate that the presence of fibres reduced damages in the crushing zone and mitigated the concrete cover spalling at the bottom of the beams. Also, increasing the volume fraction of fibres shifted the crack patterns and failure modes of the beams from shear-flexure to flexural dominance. However, adding fibres had insignificant effects on the peak impact force, reaction forces, and mid-span displacement. The findings from the residual strength tests indicate that the beams with higher fibre dosage which failed in flexural dominance mode under impact loading have smaller residual strength, different from the expected performance observed in the fibre reinforced concrete beams under static load. Discussions are provided to explain these observations.

Structural Behavior of Reinforced Concrete Slabs Containing Fine Waste Aggregates of Polyvinyl Chloride

In several areas worldwide, the high cost and shortage of natural resources have encouraged researchers and engineers to explore the serviceability and feasibility of using recycled aggregates in concrete mixtures, substituting a normal aggregate percentage. This technique has advantages for the environment by reducing the accumulation of waste materials, while it impacts the fresh and hardened concrete performances, reducing workability, flexural strength, compressive strength, and tensile strength. However, most studies have investigated the influence of replacing normal aggregates with waste aggregates on the concrete mechanical properties without examining the impact of using waste materials on concrete structural performance. The aim of this research is to investigate the effect of replacing 75% of sand volume with polyvinyl chloride (PVC) fine waste aggregates on the performance of reinforced concrete slabs. Different thicknesses of the concrete layer (0%, 25%, 50%, and 100% of slab thickness) containing PVC fine waste aggregates are investigated. Based on the reductions in the toughness and flexural strength capacity due to incorporating 75% PVC fine aggregate dosage, two approaches are used to strengthen the slabs with 75% PVC fine aggregates. The first approach is adding polyvinyl alcohol (PVA) to the PVC fine aggregate concrete mix to improve the mechanical properties of the concrete. The PVA increases the water viscosity in the concrete, which reduces the dry out phenomenon. With that said, the PVA modified fresh concrete does enable the use of the limits of the PVC fine aggregate dosage for high dosage plastic aggregate concrete. The second approach uses two fiber wire mesh layers as an additional reinforcement in the tested slab. Results show that the PVC-30 slab exhibits an 8% decrease in total area toughness compared to the control (Con) slab, while for PVC-60 slab toughness, the total area shows 26% less. Additionally, the inclusion of PVA in the concrete with 75% PVC plastic waste fine aggregate replacement greatly influences the pre-and post-cracking ductile performance among other slabs, representing that using PVA with higher contents might increase the flexural performance. Therefore, due to the substantial effect of PVA material on the concrete flexural performance, it is proposed to utilize PVA with an optimum PCV fine aggregate dosage in the concrete mix.

Evidence for pore water composition controlling carbonate morphology in concrete and the further effect of gamma radiation

Radiation, heat and carbonation can all affect the performance of concrete structures. This study applies either a1.5 MGy gamma radiation dose or thermal treatment at 60°C, followed by an accelerated carbonation period. In comparison to a control sample, irradiation and heat treatment lead to an increase in the carbonation depth which correlates with an increase in crack depth induced by restrained drying-induced shrinkage. When compared to thermally treated samples, there is greater variability in the crack depth of irradiated samples which we ascribe to a radiation-induced change in the mechanical properties of the cement paste. X-ray diffraction is used to identify the calcium carbonate polymorphs that form as result of carbonation. The dominant phase in the control sample is vaterite whereas the dominant phase in both the irradiated and thermally treated samples is calcite. Gamma irradiation leads to a greater calcite:vaterite ratio than thermal treatment. The sequential application of gamma radiation/heat treatment followed by a carbonation period rules out radiolytically producedalcium peroxide octahydrate as the cause of the polymorph switch as it is too short-lived. A new mechanism is hypothesised, where elemental substitution into the calcium carbonate lattice results in deformation and so alters the morphology of the calcium carbonate, leading to the formation of a different polymorph.

Effects of dowel bars misalignment in jointed plain concrete pavements – A numerical analysis considering thermal differentials and bonded slab-base interface

Abstract Joints in concrete pavements are built to allow slab volumetric variations avoiding random cracks. Moreover, as they are discontinuities, the use of dowel bars prevents loss of load transfer across joints. During bars installation or even concrete casting, misalignments and misallocations of those devices may occur, affecting the concrete pavement structural performance. This study explores the effects of such non-conformities in the positioning of dowel bars through numerical modeling, using the 3D finite element program EverFE2.25. For, numerical simulations, bending stresses in concrete slabs of a typical bus corridor were ascertained, varying misalignments types and magnitudes (vertical tilt and horizontal skew), base type (cemented and asphalt), slab/base interface bond conditions and concrete thermal differential. Results disclosed the contribution of using bonded base in reducing stresses, even when the dowels were severely misaligned while slabs were subjected to high thermal differentials.

Experimental Analysis of Influence of Pouring Interval on Fracture Performance of Concrete Structures with Cold Joints

Experimental Analysis of Influence of Pouring Interval on Fracture Performance of Concrete Structures with Cold Joints

Study on the Weakening Performance of Fiber Concrete under the Action of Acid Rain-sewage Coupling Erosion

Unfavorable environments such as acid rain corrosion and sewage erosion will have a great impact on the mechanical properties and durability of concrete structures. In order to further explore the weakening performance of concrete structures in harsh environments such as acid rain and sewage, plain concrete, basalt concrete with 0.08%, 0.1%, and 0.12% fiber content were adopted for comparative analysis. The weakening of compressive and flexural strength of concrete with different fiber content under sewage erosion and acid rain corrosion were investigated. The results of this paper can provide reference value for further research on the deterioration performance and life prediction of structures under long service life.

Analytical models to estimate efficiency of capsule-based self-healing cementitious materials considering effect of capsule shell thickness

Capsule-based self-healing materials are a promising solution for maintaining the mechanical properties and durability performance of concrete structures. To assess the efficiency of capsule-based self-healing cementitious material, analytical models considering the effect of the capsule shell thickness were derived for three common capsule shapes: sphere (SPH), cylinder (CYL), and a cylinder with spherical tips (CST). A numerical simulation method was used to validate the proposed analytical models. A parametric study was conducted to investigate the effect of the capsule diameter, aspect ratio, and shell thickness on the self-healing efficiency. Simplified analytical models were derived to calculate the capsule diameter, aspect ratio, and shell thickness for the shape design and manufacturing of the capsule. The results of this study show that: (1) the self-healing efficiency is proportional to the diameter of the capsule; (2) the self-healing efficiency increases approximately linearly with an increase in the aspect ratio for CYL and CST capsules; (3) the self-healing efficiency may be greatly over-estimated without considering the shell thickness, especially for spherical capsules.

An influence of pozzolanic materials with hybrid fibers on structural performance of concrete: A review

Abstract Concrete is the major building material which has been used in Construction. Concrete is poor in tension and good in compression so to overcome this, fibers are adding in concrete to increase the strength and also the structural integrity. By using the hybrid fibers, it can improve the Structural performance of concrete. In Addition of two or more fibers is called Hybrid fibers. The objective of this paper presents the investigation on types of fibers and pozzolanic materials along with, how they influence and how they improve the Properties of Concrete. Actually, Pozzolanic materials are one of the major partial replacement of the cement like Rice husk, Silica flume, Fly ash, Brick powder these materials are produced in Steel plants, Power plants and Industries. It is by product of Industrial wastes. In these replacement of cement with pozzolanic materials which reduce the environmental pollution and also improves the workability of concrete. Finally, the combination of both pozzolanic materials and Hybrid fibers and how the Temperature impact on Concrete with these materials is also discussed.

The Investigation of The Different Types of the Ground Rebar Spacers with Proposing New Design Rebar Space Mixed of Concrete Palstic

The reinforcing spacers are commonly prepared from cementitious material, plastic or metals. These spacers are prepared to provide the reinforcing steel with ensuring that the requested concrete cover thickness is attained to guard surrounded steel from corrosion. Also, they pretend a vital role in the concrete structure performance. The toughness of reinforced concrete buildings remains extremely reliant on the features of the protection of concrete to be strong with thickness. A disappointment in finding cover thickness is considered the main impact on early deterioration within the steel, whichever in chance is a chief weaken method in reinforced concrete constructions. The specified study offerings a review study on the investigation of the advantages and disadvantages of six factors in various types concerning the ground rebar spacers studies. As a result, different types of ground rebar spacers have been compared and the new rebar spacer has been designed mixed of concrete_ plastic material

Thermal behavior of Concrete subjected to elevated temperature: Case Studies

Fire presents a significant danger to the survival of the building and inhabitants, adverse effects at the structural level. In view of this, several researchers have measured the fire efficiency and behavioural characteristics of concrete under varying temperatures. Using indirect measures such, water permeability, as chloride ion permeability absorption and sorptivity, the resilience of concrete after fire exposure is assessed. In most previous literature, residual mechanical properties mentioned may be overvalued, where cooling was typically employed. Proper assessment of concrete fire resistance requires more experimental data found under different cooling environments, such as water spraying or water quenching. Design considerations and analytical methods are provided to determine the reaction of reinforced concrete structures to elevated-temperature settings. Related studies in which reinforced concrete structural components have being exposed to cyclic loading. The purpose of this review is to provide a description of the elevated temperature characteristics of the performance of concrete ingredients and structures. The impacts of high temperatures on high-strength concrete materials are observed and their quality is compared to standard concrete strength.

Characteristics of Interfacial Shear Bonding Between Basalt Fiber and Mortar Matrix.

Basalt fibers have been adopted as reinforcements to improve mechanical performance of concrete materials and structures due to their excellent corrosion resistance, affordable cost, and environmental-friendly nature. While the reinforcing efficiency is significantly dependent on fiber–matrix interfacial properties, there is a lack of studies focusing on the bonding behavior of basalt fibers in the mortar matrix. In this paper, a series of experiments were carried out to investigate the characteristics of single basalt fiber pulled out from the mortar matrix. Three embedment lengths and three types of mortar strength were considered. As references, the pull-out behavior of single polyvinyl alcohol (PVA) fiber and glass fiber in mortar matrix were also tested for comparison. Results from the pull-out test revealed that the average bonding strength is more effective than the equivalent shear bonding strength to illustrate the interfacial bond behavior of single basalt fiber in mortar matrix, which can be improved by either longer embedment length or the stronger mortar matrix. Finally, the tensile and compressive strengths of basalt/PVA/glass fiber-reinforced concrete (FRC) were measured to investigate the influence of interfacial shear bonding strengths. It was shown that, while PVA fiber developed the highest shear bonding strength with mortar, the basalt fiber exhibited the best reinforcing efficiency of FRC.

Effect of Silica Fume & Steel Slag on Nano-silica based High-Performance Concrete

This study presents strength behaviour of concrete based composites including three different ternary binders namely Nano-Silica (NS), Silica Fume (SF) & Steel Slag (SS). NS as fragmental substitution of cement, SF as the fragmental substitution for the fine aggregates and SS as fragmental substitution of coarse aggregates has been used. The study has been conducted at an optimized content of NS (2%) and by varying the content of SF (10-15%) and SS (10-30%). Cement concrete having M60 grade strength at fixed W/C (0.35) has been explored for the strength behaviour. The studies have revealed that the optimized content of NS, SF and SS can be used as a partial substitute of cement, fine aggregates and coarse aggregates respectively to obtain increased strength. Thus, NS, SF and SS can be used to obtain high performance and eco-friendly concrete structures.

Effects of unbonded steel layout on seismic behavior of post-tensioned precast concrete shear walls

Unbonded post-tensioned precast connections have been studied widely in various applications and shown to be promising seismic resisting systems with superior seismic performance including exceptional self-centering capability and minimized structural damage. In this paper, effects of unbonded post-tensioned steel layout of precast concrete shear walls on seismic performance of a typical five-story precast concrete parking garage structure with the walls being the only lateral load resisting system is studied. The seismic behavior of the walls is determined using static nonlinear push-over, cyclic, and nonlinear time-history dynamic analyses under both the design and survival level ground motions. Three prototype unbonded post-tensioned precast concrete shear walls are designed with different unbonded post-tensioning steel tendon layout. Roof drift, post-tensioning force, and base shear and normal forces at the wall-foundation horizontal joint are monitored, and the demand for the coefficient of shear friction along the horizontal joint is calculated. The results show that seismic behavior of unbonded post-tensioned precast shear walls, in particular, maximum building drift, permanent losses in post-tensioning steel force, and coefficient of shear friction, is significantly influenced by layout of unbonded post-tensioned steel. The results and findings presented are valuable to improve design guidelines and provide a useful reference for practical applications of unbonded post-tensioned precast concrete connections in seismic applications.

Lightweight dense polymer concrete exposed to chemical condition and various temperatures: An experimental investigation

Throughout the last years, Polymer concrete (PC) has been using to enhance the performance of concrete structures. Manufacturing lightweight construction material aims to reduce the weight of structures and utilize lightweight polymer concrete (LPC) to combine with ordinary cement concrete (OCC). The purpose of this paper is to determine the mechanical and durability properties of LPC using destructive and non-destructive test methods. The mixtures were prepared with five polyester resin ratios (15%, 18%, 21%, 24%, and 27%) and two types of aggregates, lightweight expanded clay aggregate (LECA) and natural river sand. Specimens were investigated under compression, flexural and tensile tests after 1, 7 and 28 days of curing for mechanical tests. Water absorption, chemical resistance and heating test at 23 ᵒC, 100 ᵒC, 150 ᵒC, 200 ᵒC, 250 ᵒC, 300 ᵒC, and 400 ᵒC was used for assessing the durability of LPC. Outcomes were compared to the OCC in similar condition. Results demonstrate that an increase in the polymer ratio led to improve the strength in compression, flexural, and tensile, which is attributed to coat all aggregates and fill the pores. Despite increases in the polymer content, excess resin ratio (27%), has no significant influence on the properties of LPC. As for durability tests, LPC represents an excellent behavior against the chemical situation, while by raising the temperature, an intense reduction in the PCs properties is observed. Finally, the most favorable mix proportion that provides higher performance is obtained for polymer content of 24%.

Review on electromagnetic wave absorbing capacity improvement of cementitious material

The ever increasing electromagnetic energy and multiple reflections of electromagnetic wave (EMW) impair human health and information security. The EMW absorbing cementitious material paves an innovative way to improve EMW absorbing performance of concrete structures. This study will elaborate on the EMW absorbing mechanism including energy exhaustion and impedance matching. A comprehensive review on the raw absorbent cementitious materials and the relevant preparation methods to be integrated into EMW absorbing concrete. Two new theoretical models are proposed including optimization zone model and equivalent electromagnetic parameter model to improve the current transform line model. Subsequently, the measurement and evaluation methodologies for EMW absorbing performance of cementitious materials are summarized. The expected research topics and applications of EMW absorbing cementitious materials are suggested. Through this critical review on the research status of EMW absorbing concrete, suggestions for optimizing the performance and workability of cementitious material are made to promote large-scale 3D printing technology.