Concrete Spalling Research Articles

Precast segmental beams made of fibre-reinforced geopolymer concrete and FRP tendons against impact loads

In the open literature, there is no investigation into the impact behaviour of prefabricated segmental concrete beams (PSCBs) cast with low CO2-emission fibre-reinforced geopolymer concrete (GPC), reinforced with non-corrodible basalt fibre-reinforced polymer (BFRP) reinforcement, and post-tensioned with carbon FRP (CFRP) tendons. This research, hence, aims to close this existing gap of knowledge. The primary goals are to investigate the effect of dispersed fibres on the impact response of PSCBs and to compare the performance of CFRP versus steel tendons. The experimental results reveal that the PSCBs fail due to excessive joint openings that lead to concrete spalling and flying concrete debris. The inclusion of dispersed fibres in the concrete postpones crack development, reduces reinforcement strain, and effectively mitigates concrete spalling and stiffness degradation of the beams. While fibres show limited influence on the deflection response of PSCBs, as the deformation of segmental beams is predominantly governed by joint openings with no fibres bridging across the joints, they play a crucial role in preventing severe damage during impact events. The impact response of beams post-tensioned with CFRP tendons is analogous to those with steel tendons. Notably, both the CFRP tendon and BFRP reinforcement remain intact even when the beam fails under impact loads. This implies that CFRP tendons and BFRP reinforcement can be successfully employed in constructing durable and sustainable segmental GPC beams capable of withstanding impact loading. A high-fidelity numerical model of PSCBs made of GPC and FRP tendons and reinforcement subjected to impact loads is also developed, for the first time, to supplement the discussions of experimental findings.

Modelling of long-term performance of RC beams under coupling steel corrosion and bond deterioration

The steel-to-concrete bond deterioration due to corrosion in the reinforced concrete (RC) structures still needs more investigation because the existing models were established based on pull-out tests, which do not represent the real RC beams owing to the flexural cracks. This paper presents a new approach that discusses the bond deterioration of corroded steel bars embedded in RC beams. The study presents simulations for an experimental database of existing corroded RC beams from previous papers using a nonlinear finite element model. The simulated specimens were divided into two categories: accelerated and long-term (after 14,23, and 28 years) corroded beams to identify the key corrosion parameters in these two conditions. The results indicated that the behavior of the RC beams, which corroded via the accelerated method, failed by concrete crushing after steel yielding, and it could be simulated considering the reduction of both steel area and bond strength only. On the other hand, the spalling pressure is a key parameter to simulate the long-term corroded RC beams because it controls the ultimate deflection, and the failure is governed by concrete cover spalling due to concrete deterioration. As an innovative result, a novel bond-slip model was proposed to predict bond deterioration due to corrosion in the RC beams, and it showed excellent accuracy compared to the existing models.

Investigation on the impact of elevated temperature on sustainable geopolymer composite

Geopolymer concrete (GPC) is an eco-friendly, sustainable, cementless and green concrete. It could be an alternative to the conventional concrete. In alkaline circumstances, the alumina and silica concentration in geopolymer concrete creates the geopolymer bond, while regular concrete creates C-S-H (calcium silicate hydrate bond). The final result of the geopolymer bond does not include any water. At elevated temperatures, geopolymer concrete would thus be more stable. Due to its greater strength and durability quality, geopolymer concrete may be the ideal replacement for ordinary portland cement (OPC) concrete. This research intends to examine how specimens of geopolymer concrete and regular concrete respond to exposure to increased temperatures between 100°C and 800°C. Mass loss, ultrasonic pulse velocity, compressive strength, X-ray diffraction, thermogravimetric analysis and derivative thermogravimetric analysis were all examined throughout the experimental examination. Both concrete specimens lose mass or weight as the exposure temperature rises; OPC concrete samples spalls at 600°C, while GPC sample fail at 800°C. GPC specimens lose around 12% of their original mass after being exposed to temperatures of 800°C, while OPC specimens lose about 7%. The GPC specimens maintained 60% of their initial compressive strength after being exposed to a temperature of 700°C, but the OPC concrete specimens only kept 52%. With each increase in exposure to extreme temperatures, the peaks of quartz and cristobalite are lowered. Only the form or structure of the mineral oxide would change; the chemical linkages would remain. The GPC samples subjected to temperatures of 100°C exhibit effective thermal stability than all other specimens exposed to extreme temperatures. As the exposure temperature rises, the GPC specimens become more thermally stable. According to the experimental findings, the GPC specimens’ bonding structure makes them more resistant to high temperatures than regular concrete specimens. Micropores are present in the voids of the geopolymer matrix, while mesopores and micropores are present in the voids of the OPC matrix. While OPC bonding is C-S-H formed by the hydration of lime and silica contained in the cement, the geopolymer bonding did not include the water content in the final or end result of geopolymerisation for strengthening.

Load bearing behavior of concrete encased composite columns with high‐performance materials

AbstractThe use of steel‐concrete composite columns, such as concrete‐encased steel columns have increased in the construction of high‐rise buildings and longspan structures. In particular, the use of high‐performance materials in composite columns is expanding, enabling optimisation of the column dimensions, theultimate load capacity, improve economic design and resource efficiency. However, high‐strength concrete shows a more brittle behaviour compared to normal concrete compression strength classes that may limit the development of plastic strains in the encased steel section. In addition concrete spalling is a serious issue that may become decisive for the determination of the ultimate resistance. Therefore, to extend the design methods for composite columns using high‐performance materials, the ideitified knowledge gaps need to be filled. For this reason an experimental campaign has been performed consisting of nine concrete‐encased steel composite column test specimens; five specimens with circular and four with rectangular cross‐sections. The testing campaign was carried out in a 20 MN servo‐hydraulic universal testing machine at the Ruhr‐Universität Bochum.Abaqus® FEM software has been used to develop numerical models able to reproduce the behavior of the tested specimens. The comparisons of the experimental and numerical results show a very good correlation. The numerical analysis enable more detailed understanding of the tests results and behavior of the columns.

Meso-scale simulation of thermal fracture in concrete based on the coupled thermal–mechanical phase-field model

Temperature-induced concrete fracture is a multi-field coupled process and the propagation of crack is complex because of the nonhomogeneity of materials. In this paper, the mesoscale concrete containing aggregate, interfacial transition zone (ITZ), and mortar is established using the random generation algorithm. The governing equations of the coupled thermal–mechanical phase-field model are established, and the finite element method is implemented to solve these equations. Several representative numerical samples are solved by the proposed coupled model, such as concrete under tension after high temperature, concrete spalling caused by high temperature, concrete cracking caused by the temperature rise of a circular hole, and cracking of confined concrete. Numerical results have shown that concrete cracks first appear at the ITZs and eventually develop into one or more major cracks. Most numerical results indicate that the influence of the length scale in the proposed phase-field model on crack propagation is little. It has shown that the application of the phase-field model to simulate mesoscale concrete fracture problems under multi-field coupling is feasible.

Parametric study on lateral behavior of totally precast RC shear wall with horizontal bolted connection

Dry-type connections have gained considerable popularity worldwide due to their superior construction efficiency and quality. However, a significant drawback of most conventional dry-type connections is the direct embedding of connectors in the concrete wall panel, consequently causing stress concentration in the connections and leading to extensive spalling of concrete. This study introduces an innovative high-strength bolted connection as a solution to address the problem of stress concentration in concrete. To evaluate the seismic performance of the high-strength bolted connection, monotonic lateral loading tests were conducted. In this study, a finite element (FE) model was developed using ABAQUS software, and validated through experimental results. Furthermore, a parametric study was conducted using the FE model to assess the influence of several key design parameters on the lateral response and anti-slip capacity of the bolted connection in the precast shear wall. These parameters include bolt specifications, anti-slip coefficient, flange thickness of the H-connector, widths of the initial gap, axial compression ratio, and connection arrangement. The results indicate that the anti-slip capacity is not significantly influenced by the flange thickness of H-connectors and initial gap width, but it increases with an increase in bolt specification, slip coefficient, and axial compression ratio. Additionally, the ultimate bearing capacity of the precast shear wall remains unaffected by both the anti-slip coefficient and the initial gap width. Moreover, the high-stress area of the H-connector is concentrated at the ends. Finally, the design parameters are recommended according to the numerical analysis results.

Assessment of repaired reinforced concrete dapped-end beams exhibiting bond deterioration under static and cyclic loading

An experimental investigation has been conducted to scrutinize the behavior of reinforced concrete dapped end beams repaired with different configuration of CFRP sheet under static and cyclic loading due to induced cracks from previous examination. The static load was adopted to determine the amplitude of cyclic loading at an increment of 15% until failure. It was demonstrated that retrofitting increased load capacity and ductility significantly; approximately 28% increase in capacity and 1.5 times higher ductility over the un-retrofitted beam under static loading, and approximately 80% higher capacity with three times increase in ductility and a change in crack orientation under cyclic loading. Nonetheless, the reentrant corner's significant concrete spalling is a major concern. It is thus essential to focus on the dapped section for monitoring and maintenance of this beam.

Quasi-static Cyclic Tests and Paramatric Analysis on the Seismic Performance of Partial Precast Bridge Columns

Partial precast bridge column (PPBC) is an innovative column composed of upper precast segments and cast-in-place (CIP) base. The CIP base and precast segments are connected by unbonded posttensioned tendons. It is expected to achieve self-centering capacity as well as energy dissipating capacity during earthquakes. However, the research about damage mechanism and seismic performance of PPBC are still scarce. To investigate the seismic performance, quasi-static cyclic tests of one PPBC and a referenced CIP column are conducted in this study. Unlike CIP column, the PPBC shows excessive joint opening and obvious rocking characteristics during cyclic loadings. Slight concrete cracking in CIP base and severe concrete spalling at upper joints implies limited ductility of PPBC. Moreover, PPBC indicates smaller horizontal force, minor residual drifts and lower energy dissipation when compare with CIP columns. Based on damage distribution and deformable modes, increased prestress force, elevated CIP base and enlarged prestress ratios are analyzed to improve the anti-seismic behavior of PPBC. With cautious simulations and comprehensive comparisons, elevated CIP base and enlarged prestress ratios are validated to enhance the energy-dissipating capacity of PPBC.

Application of Steel Slag as an Aggregate in Concrete Production: A Review.

Steel slag is a solid waste produced in crude steel smelting, and a typical management option is stockpiling in slag disposal yards. Over the years, the massive production of steel slags and the continuous use of residue yards have led to vast occupation of land resources and caused severe environmental concerns. Steel slag particles can potentially be used as aggregates in concrete production. However, the volume stability of steel slag is poor, and the direct use of untreated steel slag aggregate (SSA) may cause cracking and spalling of concrete. The present research summarizes, analyzes, and compares the chemical, physical, and mechanical properties of steel slags. The mechanism and treatment methods of volume expansion are introduced, and the advantages, disadvantages, and applicable targets of these methods are discussed. Then, the latest research progress of steel slag aggregate concrete (SSAC) is reviewed. Using SSA leads to an increase in the density of concrete and a decrease in workability, but the mechanical properties and durability of SSAC are superior to natural aggregate concrete (NAC). Finally, future research in this field is proposed to motivate further studies and guide decision-making.

Rapid Prestressed Concrete Retrofit with Prestressed Mechanically-Fastened Fiber-Reinforced Polymer: Field Performance and Observation for a Deteriorated Prestressed Concrete Bridge

This paper presents repairs to rural bridges in North Carolina that deteriorated as a result variously of aging, overweight traffic, and exposure to salts and sulfates. The prestressed concrete C-channel superstructures exhibited prestressing strand loss and displayed significant concrete spalling, with one structure having to be closed to traffic after a routine inspection. Analysis conducted using the American Association of State Highway and Transportations Officials (AASHTO) bridge load rating criteria concluded that repair techniques which strengthen deteriorated flexural elements without also restoring lost prestressing forces are insufficient to maintain load ratings in C-channel structures with heavily damaged prestressing tendons. A prestressed mechanically-fastened fiber-reinforced polymer (MF-FRP) retrofit solution was developed and successfully installed on three structures by the authors and North Carolina Department of Transportation maintenance crews. The most extensive of these three repairs is presented here in detail. The field applications and associated analysis show the temporary MF-FRP repair system is capable of restoring lost prestressing forces, allowing original inventory and operating ratings to remain in place until a permanent superstructure replacement can be scheduled. The most heavily repaired bridge remains in service after 23 months, its performance demonstrated by long-term monitoring data. As currently implemented, the MF-FRP repair is a viable temporary solution for maintaining traffic on a degraded structure while a replacement structure is designed, programmed, and implemented. Efforts to expand the MF-FRP repair into a longer-term solution are underway.

Concrete spalling behavior and damage evaluation of concrete members with different cross-sectional properties under contact explosion

Concrete members such as columns, beams, slabs, and walls exhibit different damage modes under contact explosion due to their different cross-sectional properties, potentially posing distinct levels of threat to structural safety. Understanding the effect of cross-sectional properties on damage to concrete members is fundamental for accurately predicting blast response and rapidly assessing damage degrees of engineering structures. In this paper, FE models for concrete members under contact explosion were established and validated. Based on the FE models, parameter analyses were conducted to investigate the concrete spalling behavior of concrete members with varying cross-sectional thickness and width under contact explosions, and the stress wave propagation character was investigated to reveal the damage mechanics of concrete members and the effects of cross-sectional properties. It is found that, on the whole, the increase of both cross-sectional thickness and width reduces the concrete spalling damage on back surface, and the increase of cross-sectional width instead of thickness reduces the concrete spalling damage on side surfaces. Both the relation between spalling angle on the back surface and cross-sectional thickness and relation between spalling angle on the side surface and cross-sectional width are linear. Increasing the cross-sectional dimension restrains the concrete damage on the side surface more effectively compared to that on the back surface. According to the concrete spalling character, a damage index and a damage classification method were proposed, and based on the numerical results, a rapid damage evaluation approach was developed for concrete members with different cross-sectional properties under contact explosion.

Flexural Behavior of Slabs with Different Anchorage Locations of Longitudinal Reinforcing Bars in a Composite Basement Wall Junction

Although the anchorage location of longitudinal reinforcing bars is a significant design element for flexural behavior, the conventional anchorage method of using longitudinal reinforcing bars has limited applications in new types of structures, such as composite structures. Therefore, this study examined the effect of the anchorage location of longitudinal reinforcing bars on the flexural behavior of slabs at the junctions of developed composite basement walls (SCBW) under monotonic loads at the top free end of the slab. The test results showed that the slab with longitudinal reinforcing bars anchored to the cast-in-place pile (CIP) in the composite basement wall exhibited ductile behavior accompanied by the yielding of the longitudinal reinforcing bars, a relatively wide area of vertical cracks propagating along the slab length, and a plastic plateau flow in the load–deflection relationships. In particular, the slab with longitudinal reinforcing bars anchored to the basement wall experienced severe crack concentration localized at the junction of the composite basement walls and concrete spalling in the basement walls, which resulted in no yielding of the longitudinal reinforcing bars and no cracks in the slab. Consequently, in a slab, it is recommended that longitudinal reinforcing bars be anchored into the CIP by penetrating the steel plate.

Research on the resilience model of a new prefabricated shear wall structure

Based on high-strength bolts, steel plates and other components to achieve the advantages of prefabricated shear wall assembly connection “dry connection” operation advantages, a new type of assembled shear wall with friction energy consumption function was proposed. Using a combination of model tests and numerical simulations, three shear wall specimens with a scaling ratio of 1:1.54 were designed and the corresponding seismic performance tests were carried out. The effects of axial compression ratio and longitudinal reinforcement rate of edge members on the damage mode, hysteresis performance, load carrying capacity, deformation performance, stiffness degradation and energy dissipation capacity of specimens are systematically analyzed. The test results showed that the final failure modes of the three specimens were similar, which was the bending-shear failure from the development of the oblique cracks in the wall to the concrete spalling in the compression zone; The reduction of the axial compression ratio or the reinforcement rate of the longitudinal reinforcement of the edge members will lead to the reduction of the bearing capacity of the shear wall and the increase of the ultimate displacement has a negative impact on the seismic performance of the new assembled shear wall, which is manifested by the weakening of the hysteresis performance and the reduction of the ultimate bearing capacity. Combined with the finite element simulation results, the five-fold skeleton model and restoring force model of the new assembled shear wall were established, and then the calculation formulae of unloading stiffness and loading stiffness of the hysteresis curve were obtained by regression fitting. The restoring force model proposed in this paper is in good agreement with the test results, which can provide a reference for the elastic–plastic seismic response analysis of the new fabricated shear wall structure.

Use of Continuous Wavelet Transform to Generate Endurance Time Excitation Functions for Nonlinear Seismic Analysis of Structures

This paper presents the use of continuous wavelet transform (CWT) to capture the frequency contents, spectra of dominant frequencies and associated time durations of real earthquakes for generating artificial excitations to perform endurance time analysis (ETA) of structures. Applying CWT to three sets of forty earthquakes, the 90 percentile frequencies that span the ranges 0.08–18.41 Hz, 0.61–12.73 Hz, and 0.56–15.53 Hz; with associated time durations of 20, 15 and 16 s, respectively, for these earthquake sets are extracted. Artificial excitations that contain these ground motion characteristics are generated, progressively scaled up and applied to the target structure until failure. The scaling used is a block-shaped envelope that increases in size by a factor of 3/2 over time. Nonlinear seismic analyses of a steel frame and a concrete bridge bent using these artificial excitations have shown that the method not only successfully predicts the base shear–roof displacement responses of these structures, it also correctly identifies behavior such as weak story, concrete spalling, and core cracking. When compared with the increment dynamic analysis and time history analysis using multiple earthquakes, the proposed method is capable of producing comparable results with a significant reduction in computational time and a much smaller output file size.

Shaking table test of fully assembled precast concrete shear wall substructure with tooth groove connection and vertical reinforcement lapping in reserved hole

In this paper, an innovative fully assembled precast concrete shear wall structural system with tooth groove connection and vertical reinforcement lapping in reserved hole was proposed, and the constructional requirements and joint assembly process were elaborated in detail. Based on the similarity theory, a 1/2 scaled fully assembled precast shear wall substructure was designed and manufactured. The damage mode, dynamic characteristics, acceleration response, displacement response, seismic action response, inter-storey shear response and strain response of the fully assembled precast concrete shear wall substructure with tooth groove connection and vertical reinforcement lapping in reserved hole under the different earthquake excitations were comprehensively analyzed by shaking table test, and the connection performance and seismic performance of the substructure in high intensity areas were investigated. The research results showed that the cracks at the horizontal joint of the 1st floor were completely penetrated, accompanied by slight concrete spalling, the 1st floor shear wall perpendicular to the input direction of seismic excitation was slightly uplifted, and there was no obvious damage in other parts. Overall, the tooth groove connection and vertical reinforcement lapping in reserved hole was reliable. Besides, the dynamic characteristics and seismic response of the substructure were consistent with the three-stage test phenomena. The acceleration amplification factor, storey displacement, seismic action increased with the increase of the height of the substructure and the excitation of PGA. When the excitation of PGA = 0.638 g, the maximum inter-storey drift was 1/213, which was in line with the plastic limit of 1/120. On the whole, the integrity of the substructure remained good and there was no danger of collapse. Finally, a comprehensive seismic performance evaluation method suitable for fully assembled precast concrete shear wall substructure with tooth groove connection and vertical reinforcement lapping in reserved hole was proposed with inter-storey drift and damage index as quantitative indicators.

Structural behaviour of steel fibre-reinforced concrete floor system for modular construction

Steel fibre-reinforced concrete (SFRC) slabs are ideal for modular construction owing to the shorter span of slab in standardised modules. To investigate the structural behaviours of SFRC floor system designed for modular construction, nine full-scale slab specimens were tested both at ambient temperature and under fire conditions. The crack pattern, failure mode, concrete spalling phenomenon, deformation capacity, load-carrying capacity and fire resistance time of the SFRC slabs are reported and compared with those of conventional steel rebar-reinforced concrete slabs. The experimental results showed that SFRC slabs achieved sufficient load carrying-capacity and fire resistance time for the application in modular buildings. A fibre-element model is proposed for computing the temperature distribution and cross-sectional moment resistance of SFRC slabs under fire conditions. Based on the experimental findings, design recommendations are provided to determine the fire resistance of SFRC floor system in modular construction.

A review of test Methods, issues and challenges of Large-Scale fire testing of concrete tunnel linings

This article provides a summary of substantial aspects pertaining to the design of concrete tunnel linings subjected to serious fire exposure. Compared to building fires, the air temperature rise of tunnel fires is more significant within a few minutes due to the confined space. This is of concern to tunnel designers as rapid temperature rise has shown to be a dominant factor in relation to concrete spalling. The dramatic European tunnel fires that occurred in 1999 and 2001 led to the development of new regulations and recommendations, including new guidelines recommended by the European Federation of National Associations Representing producers and applicators of specialist building products for Concrete (EFNARC 132F r3:2006) and Efectis R0695:2020. These regulations were intended to offer tunnel designers some scope on how to test for concrete spalling with particular focus on explosive spalling of concrete given that, in general, tunnels are at greater risk than other structures. This is principally due to the high heating rate and the high initial moisture content present. To date, full scale experimental works have been limited and not as extensive as those of small to medium scale unloaded specimens exposed to elevated temperatures. This paper summarizes recent research on large scale concrete tunnel lining tests exposed to fire conditions. The methodologies, questions, and challenges regarding large-scale fire tests on tunnel lining concrete and the current design guidelines are highlighted. First, this review examines published large-scale testing including unloaded and loaded applications. Secondly, a discussion surrounding the issues faced in testing, including the effects of loading, size reduction, boundary conditions, inclusion of polypyrene fibers and steel reinforcement is presented. Finally, current design guidelines for tunnel fire safety are reviewed and recommendations for future structural fire testing of full-scale tunnel elements was presented.

Comparative response of tiled finishes and bonded fire resistive coatings for normal weight concrete tunnel liners under high-intensity one-sided heating

Experimental tests were performed to examine the relative fire resistance provided by several bonded coatings for normal weight concrete (NWC) panels that emulate a tunnel liner: ceramic tiling on mortar, spray-applied fire resistive material (SFRM), and intumescent paint (IP). Sixteen panel specimens (150-mm [6-in.] thick, 457-mm [18-in.] wide, and 610-mm [24-in.] tall) were subjected to one-sided heating using a gas-fired radiant panel, which can apply heat flux at intensities similar to hydrocarbon fuel fire. All specimens were cast from a single batch of NWC (approx. 40 MPa compressive strength) with a single curtain of steel reinforcing bars at 38-mm (1.5-in.) cover to the heated face. All specimens were vertically loaded to a service level of compressive uniaxial stress (approx. 14% of ambient specified compressive strength), which remained relatively constant during each test. Four bare concrete panel specimens were tested as a control group, and a ceramic tile finish was installed on six specimens in accordance with a current state department of transportation specification. The other six specimens were coated with fire resistive material (three each with SFRM and IP) at thicknesses corresponding to a 1-hr fire resistance rating per manufacturer specifications. Thermally-induced explosive concrete spalling was observed in 3 of 4 control specimens, 4 of 6 tiled specimens, and none of the 6 SFRM/IP coated specimens. The tiled finishes delaminated and eventually became fully detached from the concrete surface, thus providing negligible fire resistance compared to that provided by the SFRM or IP. Temperature time histories recorded within the outer 25-mm (1.0-in.) thickness of the heated concrete were used to evaluate the relative thermal resistance of each surface finish, as well as to validate a simplified thermal numerical model used for a brief parametric study. Post-fire removal of the surface finishes is also demonstrated.

Experimental and numerical investigation on the shear behavior and damage mechanism of segmental joint under compression-shear load

The segment dislocation at circumferential joints severely impacts on the structural safety of shield tunnels during construction and operation. Especially for the underwater tunnel with a super-large cross-section, the circumferential joint usually consists of oblique bolts and distributed mortises and tenons to control the dislocation. Given this, a series of full-scale loading tests of the circumferential joint is carried out based on Jinan Yellow River Tunnel, and a three-dimensional refined numerical model with concrete damage plastic (CDP) constitutive is also established to reveal the condition of stress and damage. The deformation process of joints, the stress of bolts, and the damage characteristics of mortises and tenons are investigated through the full-scale tests and numerical simulation. Moreover, the mechanical behavior and damage evolution of circumferential joint has been revealed under compression-shear loads. Besides, the influence of mortises and tenons, bolts on the shear resistance of joints is unraveled. The results show that the deformation process of the circumferential joint can be divided into three stages under the ordinal shearing loading scenario (OSLS) and reverse shearing loading scenario (RSLS). The bolt plays an important bearing role under OSLS and the bolt is in an unstressed state under RSLS, which makes the shear stiffness and shear capacity of the joint under OSLS larger than that under RSLS. The tenon and bolt hole damage presents local concrete crushing, while the damage of mortise occurred with concrete spalling. Compared with bolts, the mortises and tenons can significantly improve the shear stiffness and the ultimate bearing capacity of circumferential joints.

Early residual splitting tensile strength of concrete at elevated temperature

Assessment of the fire-induced spalling of high-strength concrete in concrete structures requires knowledge of the tensile strength of concrete at an elevated temperature. However, previous research has mainly focused on determining residual tensile strength, measured at the post-fire stage after cooling the specimens to ambient temperature. However, such residual tensile strength is only applicable to concrete after fire exposure and not during the fire event, which is usually more critical. In this study, the early residual splitting tensile strength of concrete at high temperature is determined experimentally. The test results indicate that early residual splitting tensile strength decreases with temperature. To understand this phenomenon, temperature distribution is examined. Compared to residual tensile strength, loss of early residual splitting tensile strength is found to be faster due to the elevated temperature effect. Lastly, in order to reproduce early residual splitting tensile strength, a numerical model is developed and empirical expressions are proposed for engineering application.