Concrete Surface Research Articles

Bond behaviour of CFRP-to-concrete bonded joints with a GFRP interlayer: An experimental study

This paper presents an experimental investigation into the improvement of efficiency in carbon fibre reinforced polymer (CFRP)-to-concrete bonded joints by an introduction of a glass fibre reinforced polymer (GFRP) interlayer. By introducing a ±45° biaxial GFRP interlayer between the CFRP and concrete, applied force on the CFRP laminate was distributed over a larger area of concrete surface, thereby increasing the load carrying capacity of the bonded joint. A total of 18 single-shear pull test specimens were prepared and tested to investigate the effect of CFRP width (varying from 25 mm to 50 mm) and GFRP/CFRP width ratio (ranging from 2 to 4) on the behaviour of the CFRP-to-concrete bonded joints with a GFRP interlayer. Addition of the GFRP interlayer was found to increase both ultimate load capacity and the deformation capacity significantly. Increase in the GFRP interlayer width, while keeping the CFRP width the same, increased the ultimate load of the bonded joint. Increasing the GFRP width while keeping the GFRP/CFRP width ratio the same also increased the ultimate load of the bonded joint but had little effect on the bond strength. An idealized mechanism was presented to explain the behaviour of the CFRP-to-concrete bonded joints with a GFRP interlayer. It was shown that due to 2D stress transfer of the newly proposed bonded joints, underlying mechanisms may be different to the conventional FRP-to-concrete bonded joints. Therefore, design theories developed for conventional FRP-to-concrete bonded joints may not be directly applicable to the CFRP-to-concrete bonded joints with a GFRP interlayer. Much more investigations are necessary to better understand the behaviour of the newly proposed bonded joints.

Effect of corrosion on bond slipping between steel and concrete in SRC structures

Corrosion critically impacts bond performance in steel-reinforced concrete (SRC) structures. In this study, we investigate the impact of corrosion on bond-slipping between steel components and concrete within SRC structures. Initially, SRC specimens were subjected to electrochemical corrosion tests to induce varying corrosion rates. Then, pull-out tests were conducted to study the specimens' failure modes, bond stress–slip curves, and displacement distribution. The experimental results indicate that lower corrosion rates can increase bond strength due to enhanced steel surface roughness. As the corrosion rate increased from 0% to 5%, the initial bond stress, peak bond stress, and residual bond stress increased by 133%, 101%, and 102%, respectively. However, when the corrosion rate increased from 5% to 15%, these stresses decreased by 57.1%, 49.6%, and 49.6%, respectively. Furthermore, with an increase in corrosion rate from 15% to 20%, the initial, peak, and residual bond stresses decreased by 100%, 67.6%, and 69.0%, respectively. Corrosion considerably affected the initial and peak slipping observed between the steel components and the concrete, yet its impact on residual slip was relatively minor. In addition, a nonlinear finite element model for characterising the corrosion and pull-out tests was developed and validated according to the experimental results. The numerical results showed that the four shear transfer mechanisms, including chemical bonding, micromechanical interlocking, macromechanical interlocking, and rust interface bonding, exhibited distinct behaviours at different loading stages. Finally, a parametric study was conducted using a finite element model. With variations in corrosion rates, four modes of cracking patterns on the concrete surface were observed.

Research on the performance of foamed concrete based on superhydrophobic bulk modification

Foamed concrete is a kind of lightweight insulation material formed by the uniform mixture of foam and cement slurry. The superhydrophobic bulk modification of foamed concrete can reduce its high water absorption and prolong its service life. In this paper, the compatibility of three hydrophobic agents named polydimethylsiloxane (PDMS), isoctyltriethoxysilane (ICTS) and SBT®-TIA with foams was studied, and the reasons of incompatibility were revealed. Then, the superhydrophobic bulk foamed concrete system was constructed by physical foaming method, adding polydimethylsiloxane (PDMS), calcium stearate (CS), nano-silica (NS) and covering the surface of the specimen with 200-mesh wire mesh. The results show that the maximum contact angles of the meshed surface and the internal polished surface of superhydrophobic foamed concrete were 162.7° and 153.5°, respectively. At the same time, the water absorption rate of the modified specimen was significantly reduced, and the reduction rate was up to 90 %. In addition, the deterioration degree of thermal insulation performance after soaking and the dry shrinkage rate were significantly reduced compared with ordinary foamed concrete. Scanning electron microscopy (SEM) revealed that increasing the multi-scale roughness could improve the hydrophobic properties of foamed concrete. Fourier infrared spectroscopy (FT-IR) also confirmed that low surface energy groups such as -CH2 and -CH3 in PDMS bonded to the cement hydration products, indicating the successful preparation of superhydrophobic bulk foamed concrete.

Advanced image stitching method and evaluation for underwater structure inspection utilizing planar array cameras

The inspection of underwater structural health is crucial for comprehensive bridge health assessments. In underwater structure imaging, traditional methods include single-camera and binocular camera inspection. However, due to water turbidity and long working distances with a small field-of-view, obtaining clear and high-quality detection images with these methods takes much work. To address this problem, this paper presents a method for planar array image stitching based on Harris corner point extraction, utilizing the advantages of planar array cameras characterized by short working distances and wide field-of-view. The core contribution of this paper is the introduction of an innovative image sequence stitching algorithm utilizing Harris corner point extraction and the combination of the first proposed planar array cameras with the image sequence stitching algorithm, which solves the problem of long distance and small field-of-view during the underwater inspection. The image stitching method involves calibrating camera parameters with a checkerboard and stitching underwater images from planar array cameras to reveal underwater structural features. Furthermore, five quantitative evaluation metrics and the method for calculating the field-of-view loss rate are presented to evaluate and analyze the stitched images. A series of experiments were performed on concrete surfaces, aquatic and underwater, with a total field-of-view of the underwater image after stitching of 358.86 mm × 319.24 mm at a working distance of 160 mm. Five evaluation methods were used to quantitatively evaluate the quality of the stitched images and calculate the field-of-view loss rate of the images. The results indicate that the proposed method improves the ability to inspect underwater. The stitched images achieve notable metrics: an entropy of approximately 6.7, an average gradient of about 1.7, a spatial frequency of around 3.5, an edge strength of about 17, mutual information of approximately 1.2, and a field-of-view loss rate of <0.1, facilitating more effective underwater structure inspection.

Study on impermeability of reinforced concrete wall with horizontal construction joints

The reinforced concrete (RC) water retaining tank walls with horizontal construction joints are prone to experiencing seepage under high hydrostatic pressure, which can affect the structural integrity and functionality. To evaluate the impermeability of construction joints with different improvement measures, the permeability test of concrete with and without horizontal construction joints was conducted. The test results show that the addition of Polypropylene fibers (PP fiber) and Cementitious Capillary Crystalline Waterproofing materials (CCCW) can improve the self-waterproofing ability of concrete. The impermeability at the construction joint is much lower than that of single-casting concrete. Moreover, applying CCCW to the water-facing surface of the construction joint can significantly enhance its impermeability. Then, two 1:2 scaled RC tank wall specimens were manufactured, with one wall of conventional concrete and the other wall of modified concrete. The impermeability tests of the typical single-casting and double-layer casting parts of the two wall specimens were carried out respectively. The experimental results show the RC tank wall with construction joint is prone to generate initial defects and seepage, making it difficult to achieve the design watertight requirements. The use of modified concrete materials and surface treatment in the relevant part can effectively improve the impermeability performance of the construction joint. Finally, the BP neural network was used to establish a prediction model between the impermeability of concrete and its material parameters and construction technology.

Proportioning Study for Low-carbon Sulfate-resistant Concrete by Microbial Corrosion Testing

In addition to water absorption and chloride permeability measurement, sulfate resistance testing by microbial corrosion was conducted on low-W/B concretes made using large amounts of supplementary cementitious materials, including GGBF slag, for use as sewage pipes. The corrosion testing was conducted in a corrosion chamber at 30°C with a H2S concentration of 100 ppm, in which specimens were exposed to the environment under two conditions: one group in the gas and the other partially submerged in circulating sewage water. After exposure for one year, the corrosion rate in the partially submerged phase tended to be 1.3 to 2.9 times higher than in the gas phase. Also, the amount of corrosion was compared, with the corrosion products being examined by EPMA. Exposure to the gas phase and partially submerged phase was thus found to represent the stage of forming monosulfates and dihydrate gypsum and ettringite, respectively. Deterioration was found to proceed at a higher rate as the pH value on the concrete surfaces decreased. Within the range of this study, the addition of silica fume and small-size GGBF slag led to no appreciable effect.

Effects of carbonation modification on shear performance of recycled aggregate concrete beams: Test and mechanism analysis

The effective use of recycled aggregates (RAs) in construction significantly contributes to environmental preservation and the conservation of non-renewable natural resources. However, RAs typically exhibit inferior performance relative to natural aggregates (NAs). To improve the quality of RAs, carbonation modification has been introduced as an eco-friendly and practical method. This study explores the shear performance of concrete beams that incorporate various replacement ratios (30 %, 50 %, 70 %, and 100 %) of carbonated recycled aggregates (CRAs). The experiment employed Digital image correlation (DIC) system to evaluate the stress distribution on the concrete surface within the shear span section. The evaluation of shear performance was conducted through comprehensive analysis includes load-deflection curve, steel strain, the width of the primary diagonal crack, average principal tensile strain, orientation of principal directions, average shear strain, and shear deflection. A practical approach was adopted to separate the shear strength contributions of transverse steel (Vs) and concrete (Vc), based on transverse steel strains along the primary diagonal crack. Results indicate that carbonated recycled aggregate concrete (CRAC) beams demonstrate enhanced shear performance in comparison to recycled aggregate concrete beams. Shear strength significantly decreases with replacement rates exceeding 70 %. Furthermore, the experimental results were compared against shear strength with the design codes, and shear deflection with existing models.

The Potential Risk of Nanoparticulate Release from Photocatalytic Pavement Concrete Surface Due to a Simulated Abrasion Load-An Experimental Study.

The risk of the releasing of nanometric particles from construction materials with nanometric components might be one of the biggest threats to further development of them. One of the possible ingress routes to human organisms is the respiratory system. Therefore, it is crucial to determine the risk of emission of nanometric particles during material usage. In the presented paper, abrasion of mortar samples with nanometric TiO2 was investigated. A special abrasion test setup was developed to reflect everyday abrasion of the concrete surface of pavements. In the study, three TiO2-modifed mortar series (and respective reference series) underwent the developed test protocol and the grains were mobilized from their surface due to the applied load analyzed (granulation, morphology, and chemical composition). For a comparative analysis, an abrasion parameter was developed. Based on the obtained results, the modification of cementitious composites with nanometric TiO2 contributed to a reduction in the emission of aerosols and, therefore, confirmed the compatibility between TiO2 and cement matrix.

Analytical model for evaluating bond strength of steel rebar in cracked concrete considering confinement effect

This study delves into the intricate relationship between concrete cracking and bond strength, a critical factor in transferring forces between concrete and steel rebars. While previous research has often overlooked the impact of concrete cracking on bond strength and overestimated the beneficial effects of external confinement, this study aims to fill these gaps. A new failure criterion is introduced to predict bond strength of steel rebar in cracked concrete, considering the influence of concrete crack roughness and steel rebar surface features on force transfer at their interface. This criterion incorporates an interlock capacity coefficient that considers crack kinematics and the mentioned factors, enhancing the evaluation of effective compressive strength of cracked concrete in the limit analysis. Leveraging the Mohr-Coulomb failure criterion, an adaptable failure criterion accounts for crack kinematics, concrete damage, and confinement level to assess force transfer at the concrete/steel rebar interface. The developed criterion offers a practical calculation method to estimate bond strength in cracked reinforced concrete (RC) members with various confinement setups. Validation of this criterion and approach involved comparison against experimental results from 127 specimens, confirming its effectiveness and reliability in predicting bond strength in real-world scenarios.

Structural performance of steel reinforced concrete L-shaped columns in high temperature

This paper presented structural performance of steel reinforced concrete (SRC) L-shaped columns under high temperature and axial load coupling effects. Considering the influence of the axial load ratio (0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8), eccentricity (25, 50, 75 and 100 mm), concrete strength (40, 50, 60 and 70 MPa), calculation length (500, 1000, 1500 and 2000 mm), the SRC L-shaped columns were tested and analyzed in high temperature conditions. The results demonstrated that: (1) Concrete surface of all specimens was grayish white with many cracks. With the increasing axial load ratio, the number of cracks decreased and crack width increased. (2) The fire resistance decreased by 1.3–15.1 %, 6.1–14.9 %, and 3.8–7.1 % respectively, with increasing axial load ratio, eccentricity, calculation length; the fire resistance increased by 0.7–5.3 % with increasing concrete strength. (3) Axial displacement trend first increased gradually because of the thermal expansion of concrete, and decreased gradually after reaching the maximum axial expansion deformation. With increasing axial load ratio, the maximum axial expansion deformation decreased by 42.4–60.2 %, the time of displacement to reach the maximum expansion deformation decreased by 29.7–57.0 %, and the time of displacement to reach 0 mm decreased by 272.7–366.2 %. Finally, the calculation method for displacement and maximum bearing capacity in high temperature was proposed according to principle of virtual work, which served as a guide for fire evaluation of SRC L-shaped columns.

Experimental determination of deposition velocity of CsOH aerosols on CaCO3 at temperature range 170 - 290 °C

A field assessment at the Fukushima-Daiichi Nuclear Power Station revealed high radioactivity on the concrete shield plugs, which is estimated above 20 PBq for Cs-137 at units 2 and 3. This leads to significant interest in the retention of Cs on concrete during severe accidents (SA). However, the interaction of CsOH, as one of the main Cs forms released in SA, with concrete surfaces at elevated temperatures remains poorly researched. In this study, we have experimentally investigated the deposition behavior of CsOH on CaCO3, which is the primary phase existing on the surface of concrete, under humid atmosphere. As a result, the chemical reaction enhanced deposition rate (N), and increased linearly with CsOH concentration (Cg), as following expression:N(µg/cm2.s)=vdCg, where vd is temperature-dependent deposition velocity as given by lnvd(cm/s) = -3785.8/T + 3.766, for T in the range of 170 and 290 °C.This empirical model can be integrated into severe accident codes to quantify the chemical trapping of cesium on concrete surfaces during ex-vessel release. Moreover, it can contribute to understanding the reasons behind the high dose rate on concrete shield plugs at the Fukushima Daiichi Nuclear power stations and aid in developing effective decommissioning practices for concrete structures.

Recognition and Classification of Concrete Surface Cracks with an Inception Quantum Convolutional Neural Network Algorithm

Recognition and Classification of Concrete Surface Cracks with an Inception Quantum Convolutional Neural Network Algorithm

Cracks monitoring in reinforced concrete structure with optical fibers patch

In the context of the necessity to monitor civil engineering structures in order to prevent incidents, this paper presents the performance of an innovative optical fibers patch sensor. The patch comprises a tissue containing an optical fiber network. The sensor is attached to the concrete surface and capable of detecting opening cracks in the order of 0.01 mm with good precision, thus satisfying the regulatory limits. The sensor is capable of precisely following the evolution of the crack, including cyclic changes in crack width. The procedure presented in this paper includes a preliminary investigation into the influence of the fibers’ diameter and the density of fibers in the patch, as well as the method of attachment to the concrete’s surface with the objective of identifying an optimal sensor configuration. Subsequently, a series of laboratory tests were conducted on reinforced concrete samples of varying dimensions. Comparisons and verifications of measurements of optical fiber patch sensors are conducted via Digital Image Correlation process. The conclusions of this paper permit the consideration of the use of this novel sensor on and within real reinforced concrete structures.

Research on improving the frost resistance and self-repair performance of limestone calcined clay cement concrete by microcapsules

Limestone calcined clay cement (LC3) concrete has emerged as a pivotal construction material aimed at mitigating carbon emissions and bolstering sustainability. However, LC3 concrete confronts durability challenges in frigid regions attributable to freeze-thaw cycles. Microcapsule self-repair technology, as an innovative paradigm, presents a promising avenue to augment the freeze-thaw resistance and self-repair attributes of LC3 concrete. Within this inquiry, microcapsules containing isophorone diisocyanate (IPDI) and encapsulated with microcrystalline wax, ceresine wax, and CaCO3 were synthesized and effectively integrated into LC3 concrete matrices. Freeze-thaw cycle investigations were conducted to juxtapose LC3 concrete specimens with and without microcapsules. The findings evinced that LC3 concrete augmented with microcapsules demonstrated enhanced resistance to freeze-thaw cycles, thereby mitigating mass loss and compressive strength degradation. Microscopic structural analyses, pore size distribution assessments, mechanical property evaluations, impermeability, and ultrasonic waveform analyses of LC3 concrete samples featuring microcapsules corroborated the heightened freeze-thaw resistance, thus fortifying its applicability in rigorous environments. Moreover, deliberate pre-cracking of the concrete surface unveiled the self-repair efficacy of microcapsules, with empirical observations underscoring the prompt crack remediation capabilities of the implemented technology.

Thermal responses of a concrete slab under hydrogen fuel cell vehicle fires in a semi-open car park

This work aims to investigate the thermal behaviors of the concrete ceiling slab of a semi-open car park exposed to localized fire in hydrogen fuel cell vehicles. For this purpose, a numerical simulation of the hydrogen fuel cell vehicle fire was performed in the Fluid Dynamic Simulator and then coupled with a subsequent thermal analysis of concrete structure carried out in ANSYS Mechanical APDL. In particular, an automatic procedure was used to extract the output of the fire simulation and apply them as boundary conditions of the thermal model. The one-way coupling procedure involving fire simulation and transient thermal analysis has been validated by comparing it with concrete temperatures of a previous test study. Then, two parameters, the diameter of thermal pressure relief devices (1 mm, 2 mm, 3 mm, and 4 mm) and fire spread time between vehicles (0 min, 20 min, and 30 min), are taken into account to study the thermal properties of concrete. The analysis revealed that an increase in the nozzle diameter of the thermal pressure relief device leads to a rise in the maximum concrete surface temperature. The simulation results also showed that the maximum value of the heat release rate increases with a higher value of the nozzle diameter of the thermal pressure relief device and a shorter fire spread time between vehicles.

The impact of seawater ions on urea decomposition and calcium carbonate precipitation in the MICP process

As an environmentally friendly biotechnology, the microbial induced calcium carbonate precipitation (MICP) provides a new approach to repair concrete cracks. Most existing studies focused on finding a suitable environment for bacteria to induce as much calcium carbonate as possible, but the effect of actual concrete service environment on the repair of concrete cracks was usually ignored. This work compared the repair quality of cracked specimens via MICP with the original Sporosarcina (Sp.) pasteurii strain and salt-tolerant Sp. pasteurii strain in the deionized water and simulated seawater. Then the adverse effects of seawater ions on the MICP process was investigated. The results showed that the permeability coefficient of repaired specimens was 175.7 % higher, and the bond strength between the calcium carbonate and concrete surface was lower in the simulated seawater as compared with the deionized water environment. The high concentration of sodium, chloride, magnesium, and sulfate ions in the seawater led to the decrease of the urea decomposition rate and calcium carbonate yield rate, which further induced the decreased super-saturation of calcium carbonate and the conversion of the calcium carbonate crystal form from calcite to vaterite. Besides, the salt-tolerant strain with a high salt adaptability showed a higher repair ability in the simulated seawater as compared with the original strain.

Aggregate interlock and effective strain of FRP-strengthened flanged RC members subjected to torsion: Experimental evaluation and analytical modeling

The effective strain of externally bonded FRP strengthening systems and the loss of concrete aggregate interlock are critical factors for predicting strength and developing design models for structural strengthening. Current research on FRP strengthening of reinforced concrete (RC) members primarily focuses on flexural, shear, and axial loading, neglecting torsional systems. This study introduces an innovative analytical-experimental model/formulation predicting FRP effective strain and concrete strain, based on Digital Image Correlation (DIC) analysis outcomes of an experimental study on RC beams strengthened with FRP sheets under torsion. Eight flanged RC beams, strengthened with various FRP ratios, configurations, and installation methods were also systematically tested. The findings emphasize the need for reevaluation of strain limits in existing guidelines. It points out that the shear integrity of concrete is influenced by concrete compressive strength and strengthening scheme. The DIC results suggest that the strain limit for concrete surfaces between FRP strips should be in the range of 0.0055–0.008, as opposed to the limit of 0.004 set by ACI 440.2R-17. The use of the grooving method in certain systems also requires an increase factor of 1.65 and 1.45 for the effective strain of transverse and longitudinal FRP sheets.

Predicted Corrosion Performance of Organofunctional Silane Coated Steel Reinforcement for Concrete Structures: An Overview

This article provides a comprehensive overview of the potential use of organofunctional silane coatings in the corrosion protection of concrete reinforcement in close relation to other commercially used coating technologies—i.e., epoxy coatings and bath hot-dip galvanizing coatings. The application technology of the steel surface is described in detail, and the corrosion performance and bond strength in concrete are compared. The paper also points out the possibility of improving the durability of epoxy coatings by the addition of silanes and, in the case of application to the surface of hot-dip galvanized steel, they can prevent corrosion of the coating by hydrogen evolution. The application potential of organofunctional silanes is also presented in the form of hydrophobic coatings on concrete surfaces or as corrosion inhibitors in simulated concrete pore solutions. The use of a suitable type of modified silane coating on the surface of carbon steel reinforcement can increase the corrosion performance and can also increase the bond strength in concrete. However, these facts need to be experimentally verified.

Enhancing concrete bond strength with silicate-based curing agents: A focus on surface damage repair

In this study, the effects of varying concentrations of silicate-based curing agents on damage repair and bond strength between concrete surfaces were investigated. The results show that these agents interacted with the concrete to produce calcium silicate hydrate (C-S-H), which filled the surface pores and thus facilitated damage repair. Furthermore, the interfacial bonding strength (IBS) of concrete was assessed through direct tensile tests. Scanning electron microscopy (SEM) was used for microstructural analysis, and pigment identification technology (PIT) was used to quantify the shedding area. Results indicate that a dosage of 24 mol/L significantly reduced the IBS by 40 %, primarily due to the formation of surface film. However, when the concentration of curing agents was reduced to 1.5 mol/L, the IBS increased by 17.6 % compared to untreated surfaces, indicating an improvement in bond strength with decreasing concentrations of curing agents.

Experimental study on debonding and buckling of externally bonded carbon fiber reinforced polymer sheets in compression

Although the compressive strength of Fiber Reinforced Polymer (FRP) sheets is neglected in the design of FRP-retrofitted Reinforced Concrete (RC) elements, they may be subjected to compressive stress in some load combinations. In the present study, an experimental study is conducted to investigate the behavior of externally bonded Carbon Fiber Reinforced Polymer (CFRP) sheets in compression. The experimental program is carried out in two phases. First, the behavior of CFRP strips bonded on concrete cylinders and subjected to pure compressive load is assessed. At this stage, the influence of concrete compressive strength, the dimensions of CFRP strips (thickness, width, and free length), and the type of adhesive used for bonding CFRP strips on the concrete surface, on the behavior of CFRP strips in compression are investigated. According to the test results, the FRP strips bonded with weak resin exhibit debonding failure and simultaneously buckle at a relatively low compressive strain, while CFRP strips bonded with stronger adhesive do not exhibit debonding failure in compression until concrete crushing. The behavior of CFRP strips bonded on reinforced concrete (RC) beams subjected to compressive stress due to bending moment is investigated in the second phase of this study. For this purpose, nine RC beams with the same dimensions and reinforcement detailing are fabricated and retrofitted using CFRP strips with different configurations. Four-point bending test is conducted at this stage of the experimental program. The results of the bending tests show that debonding failure and buckling of CFRP strips are observed in specimens with relatively thick CFRP sheets (3 and 4-layer) and larger free lengths.