Concrete Repair Systems Research Articles

Detection of “zero-volume” defects in concrete repair systems using impact-echo method

Adhesion in this system is one of the most important factors that affect the reliability and durability of repair. According to the many standards and guidelines, a pull-off test is recommended for assessment of a bond quality in repair systems. However, a growing interest in development of non-destructive techniques (NDT) for evaluation of concrete structures is recently noted. A majority of NDT methods mentioned in EN 1504-10 for repair efficiency assessment are based on propagation of stress waves. The impact echo method is considered as a one of the promising. The literature data confirmed that the “non-zero volume” defects containing air are relatively easy to detect with impact-echo method if they are large enough. It is more complex to detect “zero-volume” defects, e.g dust or any other antiadhesion material. In this work usability of impact-echo for detection of “zero-volume” defects in repair systems is discussed.

Unveiling the Effects of Quicklime on the Properties of Sulfoaluminate Cement-Ordinary Portland Cement-Mineral Admixture Repairing Composites and Their Sulphate Resistance.

Aiming at the problem of repeated repair of concrete caused by the damage of concrete structure repair system in a sulphate environment, the quicklime modified sulphoaluminate cement (CSA)-ordinary Portland cement (OPC) -mineral admixture composite repair material was utilised to obtain the law and mechanism of quicklime, improving the mechanical properties and sulphate resistance of composite repair materials. In this paper, the effects of quicklime on the mechanical properties, as well as sulphate resistance of CSA-OPC-ground granulated blast furnace slag (SPB) and CSA-OPC-silica fume (SPF) composites, were studied. The findings reveal that the addition of quicklime improves the stability of ettringite in SPB and SPF composite systems, promotes the pozzolanic reaction of mineral admixtures in composite systems, and significantly increases the compressive strength of both SPB and SPF systems. The 8 h compressive strength of SPB and SPF composite systems increased by 154% and 107%, and the 28 d compressive strength enhanced by 32% and 40%. After the quicklime was added, the formation of C-S-H gel and calcium carbonate in SPB and SPF composite systems was promoted, the porosity was reduced, and the pore structure was refined. The porosity was reduced by 2.68% and 0.48%, respectively. The mass change rate of various composite systems under sulphate attack was reduced, and the mass change rate of the SPCB30 and SPCF9 composite systems decreased to 0.11% and -0.76% after 150 dry-wet cycles. Additionally, the mechanical strength of different composite systems under sulphate attack was improved, so that the sulphate resistance of different ground granulated blast furnace slag and silica fume composite systems was improved.

Repair of corroded steel bridge girder end regions using steel, concrete, UHPC and GFRP repair systems

Practical means of affecting in situ repair of corrosion-induced section loss of steel bridge girders at their supports are compared. Potential repair strategies are reviewed leading to large-scale experimental evaluation of four methods of repair: conventional bolted steel repair, encasement in conventional reinforced concrete (RC), encasement in ultra-high performance concrete (UHPC), and reinforcement with externally bonded fiber-reinforced polymer (FRP) plates and sections. Modified W24x55 girders representing half-scale 1400 mm deep plate girders were used. Section loss mimicking typically-observed severe corrosion was machined into the girder ends. Monotonic load tests to failure were conducted on the repaired girders and companion tests were conducted of identical specimens subject first to one million cycles of fatigue loading before being loaded to failure. Results indicate the efficacy of conventional bolted steel repair methods. UHPC and RC encasement was also shown to perform well and may be suited to certain scenarios. Despite extensive surface preparation and chemical enhancement, the bond of the FRP system to the damaged substrate steel was poor; this system is not an appropriate repair method for this damage scenario.

Mesoscale analysis of dry shrinkage fractures in concrete repair systems using FEM and VEM

ABSTRACT A novel numerical method that used a FEM coupled with a virtual element method was proposed to evaluate the drying shrinkage of concrete repair systems. The stress distribution, crack development of the concrete repair systems due to drying shrinkage were investigated using this method. (1) The mortar along the tangent direction of the aggregate boundary was subjected to the aggregate constraint, allowing shrinkage cracks to form easily. The overlay first developed a significant number of microcracks on surface, followed by debonding at both ends of the interface. (2) Owing to the confinement of the aggregate below the surface, the surface tensile stress of the overlay had a ‘hump’ distribution. After cracking, the surface was divided into several contraction zones, with tensile and compressive stresses applied to the boundary and interior of the contraction zone, respectively. (3) As the interface de-bonded, the tensile and shear stresses of the interface began to increase from both sides and moved inward. The rise in local compressive and shear stresses were induced by the constraint of the aggregate in the bonding interfacial region. (4) Tensile stress caused the first damage, and the shear stress caused interface debonding to evolve.

Robotic spray coating of self-sensing metakaolin geopolymer for concrete monitoring

Sensors and new materials can support optimised concrete maintenance, and produce the data needed to justify new, low carbon structural designs. While these technologies are affordable, the process of manual installation in a construction context comes with acute and unfamiliar risks to productivity, personnel safety, and confidence in the quality of workmanship. The installation of smart materials using robotics could address some of these issues, but there are few proofs-of-concept at the time of writing. Here, we present a robotically controlled process for spray coating geopolymers — a class of self-sensing concrete repair materials. By tuning mix design, robotic toolpaths and spray dispenser parameters, we show reliable and automated spray coating of 250 mm2 patches in a laboratory setting. The cured geopolymer has a compressive strength of 20 MPa, and a bond strength to the concrete substrate of 0.5 MPa. Electrical interrogation of patches, via a set of four electrodes, produces strain and temperature measurements of the underlying concrete substrate with resolutions of 1 με and 0.2 °C, respectively. This demonstration multifunctional material deposition using robotics is a step towards remote, traceable, and low-risk technology deployment across civil engineering sectors. This could support more widespread adoption of novel concrete health monitoring and repair systems in future.

Drying shrinkage crack simulation and meso-scale model of concrete repair systems

Repairing materials and interfacial bonding quality are the two crucial factors that affect the shrinkage performance of concrete repair systems. The objective of this paper is to provide a fine meso-scale modelling method of concrete repair systems and to get a better understanding of shrinkage cracks propagation mechanism due to the influence of overlay materials, interface roughness and bonding strength. Through the laser scanning test and different algorithms, e.g. random cutting and random midpoint interpolation algorithm, geometry models of the 2D actual aggregate and rough interfaces with different fractal dimensions were generated. Besides, zero-thickness cohesive elements were inserted in mesh as the reserved path for cracks by modifying the inp file of ABAQUS. The validity of the model was verified by comparing with LI's experiment. Results of the simulation suggested that the final length of surface cracks and interface debonding depended on the overall shrinkage of the repair system and surface cracks mainly occurred in high bonding strength cases; aggregate nearby the interface caused the initial damage at low bonding strength interface, leading to the “stepped” debonding with time; The rough interface was more difficult to debond because it required more fracture energy and local shear stress was converted into compressive stress to prevent the development of debonding.

Effects of Sustained Loading and Temperature on a Concrete–Epoxy Bonded Interface

AbstractThe mechanical behavior of the concrete–epoxy bonded interface is of high importance in concrete strengthening and repair systems. This paper presents the effects of cure time, sustained lo...

Failure Modes in Concrete Repair Systems due to Ongoing Corrosion

Corrosion of steel reinforcement is the main cause of deterioration in reinforced concrete structures. It can result in cracking and spalling of the concrete cover. After the damaged cover is repaired, reinforcement corrosion might continue and even accelerate. While the development of the corrosion cell is difficult to control, the damage can be possibly delayed and controlled by use of a suitable repair material. The lattice fracture model is used in this paper to investigate the performance of strain hardening cementitious composite (SHCC) in concrete repair systems exposed to ongoing corrosion. Numerical results were verified by experimental tests when SHCC, nonreinforced material (repair mortar), and commercial repair mortar are used as repair materials. In experiments, reinforcement bars (surrounded by a repair material) were exposed to accelerated corrosion tests. The influence of the substrate surface preparation, the type of repair material, the interface, and the substrate strength on the resulting damage and failure mode of repair systems are discussed. In general, SHCC repair enables distributed cracking with small crack widths, up to several times smaller compared to repair mortar. Furthermore, more warning signs prior to the final failure are present in the SHCC repair system.

On the evaluation of interface quality in concrete repair system by means of impact-echo signal analysis

According to Concrete Repair Manual as well as ACI 562-16 and European EN 1504-10 standards, a bond strength as a measure of adhesion is one the main feature of repair system necessary to be assessed. The most common laboratory and engineering method for bond strength evaluation is pull-off test. This is however a semi-destructive method that needs a repair in a place of measurement. Recently, the great interest in nondestructive techniques (NDT) development is noted. Impact-echo (IE) is considered as one of the most promising methods for this purpose.In this paper, the study on the usability the IE test based on frequency spectrum analysis for bond strength evaluation is analyzed. Both Finite Element Method (FEM) simulation and experimental tests were performed in order to obtain potential relations between IE frequency spectrum and parameters characterizing concrete substrate quality that may affect the final bond strength and the real value of pull-off bond strength measured on samples as well. It was concluded that the IE method can be a useful tool for interface quality and bond strength evaluations in concrete repair system. However, more complex signal analysis, e.g. wavelet analysis, should be considered in the future.

Compatibility of repair materials with substrate low-modulus cement and asphalt mortar (CA mortar)

The compatibility of the mechanical properties of low-modulus cement and asphalt mortar (CAM) and repair materials was studied using the four-point bending test method. According to the bearing characteristics of CAMs, a four-point bending fatigue test was further developed to evaluate the compatibility of this material with the repair material. With the help of a finite element model, the effect of the difference in the modulus of the substrate mortar and the repair mortar on the stress and strain distribution of a composite sample was studied. The results indicated that the CAM compatibility criteria with repair materials were different from those of the concrete repair system. The difference in the moduli of the substrate mortar and repair mortar determined the loading transfer efficiency and failure mode, which mainly influenced the compatibility of the mechanical properties. The repair materials were compatible with substrate CA mortar when its modulus was approximately 0.75–1.28 times the substrate mortar modulus according to the experimental results. The four-point fatigue test met the requirements of the bearing characteristics of the CA mortar and the present quantitative experimental results, which provide supplementary information for compatibility evaluation.

A 3D Lattice Modelling Study of Drying Shrinkage Damage in Concrete Repair Systems.

Differential shrinkage between repair material and concrete substrate is considered to be the main cause of premature failure of repair systems. The magnitude of induced stresses depends on many factors, for example the degree of restraint, moisture gradients caused by curing and drying conditions, type of repair material, etc. Numerical simulations combined with experimental observations can be of great use when determining the influence of these parameters on the performance of repair systems. In this work, a lattice type model was used to simulate first the moisture transport inside a repair system and then the resulting damage as a function of time. 3D simulations were performed, and damage patterns were qualitatively verified with experimental results and cracking tendencies in different brittle and ductile materials. The influence of substrate surface preparation, bond strength between the two materials, and thickness of the repair material were investigated. Benefits of using a specially tailored fibre reinforced material, namely strain hardening cementitious composite (SHCC), for controlling the damage development due to drying shrinkage in concrete repairs was also examined.

Numerical study of shrinkage cracking in concrete and concrete repair systems

The shrinkage cracking processes in a cement-based composite, which include crack initiation, propagation and coalescence, as well as diffusion-damage coupling, are numerically studied using a mesomechanical numerical model to better understand the shrinkage cracking growth mechanisms and the effects of cracks on moisture diffusion. This study analyzes the shrinkage crack initiation and growth processes in a repair layer of mortar, which is cast on the top of an old concrete substrate and initially saturated with water. The potential shrinkage crack development is driven by the associated drying process. The results illustrate the fracture infilling, saturation and delamination processes in the concrete repair system by decreasing the bond strength between the repair mortar and the substrate from 4 to 1 MPa. Large concrete repair system bond strengths cause cracks to initiate on the surface of the repaired mortar and propagate to the interface. However, debonding is observed at lower bond strengths. The numerical model is shown to be a viable tool for damage analyses under both mechanical loads and hygral gradients.

Effect of Moisture Exchange on Interface Formation in the Repair System Studied by X-ray Absorption

In concrete repair systems, material properties of the repair material and the interface are greatly influenced by the moisture exchange between the repair material and the substrate. If the substrate is dry, it can absorb water from the repair material and reduce its effective water-to-cement ratio (w/c). This further affects the hydration rate of cement based material. In addition to the change in hydration rate, void content at the interface between the two materials is also affected. In this research, the influence of moisture exchange on the void content in the repair system as a function of initial saturation level of the substrate is investigated. Repair systems with varying level of substrate saturation are made. Moisture exchange in these repair systems as a function of time is monitored by the X-ray absorption technique. After a specified curing age (3 d), the internal microstructure of the repair systems was captured by micro-computed X-ray tomography (CT-scanning). From reconstructed images, different phases in the repair system (repair material, substrate, voids) can be distinguished. In order to quantify the void content, voids were thresholded and their percentage was calculated. It was found that significantly more voids form when the substrate is dry prior to application of the repair material. Air, initially filling voids and pores of the dry substrate, is being released due to the moisture exchange. As a result, air voids remain entrapped in the repair material close to the interface. These voids are found to form as a continuation of pre-existing surface voids in the substrate. Knowledge about moisture exchange and its effects provides engineers with the basis for recommendations about substrate preconditioning in practice.

Effect of Misalignment on Pulloff Test Results: Numerical and Experimental Assessments

The successful application of a concrete repair system is often evaluated through pulloff testing. For such in-place quality control (QC) testing, the inherent risk of misalignment might affect the recorded value and eventually make a difference in the acceptance of the work. The issue of eccentricity in pulloff testing has been ignored in field practice because it is seen as an academic issue. This paper presents the results of a project intended to quantify the effect of misalignment on pulloff tensile strength evaluation and provide a basis for improving QC specifications if necessary. The test program consisted first of an analytical evaluation of the problem through two-dimensional finite element modeling simulations and, in a second phase, in laboratory experiments in which the test variables were the misalignment angle (0, 2, and 4 degrees) and the coring depth (15 and 30 mm [0.6 and 1.2 in.]). It was found that calculations provide a conservative, but realistic, lower bound limit for evaluating the influence of misalignment upon pulloff test results: a 2-degree misalignment can be expect to yield a pulloff strength reduction of 7 to 9%, respectively, for 15 and 30 mm (0.6 and 1.2 in.) coring depths, and the corresponding decrease resulting from a 4-degree misalignment reaches between 13 and 16%. From a practical standpoint, the results generated in this study indicate that when specifying a pulloff strength limit in the field, the value should be increased (probable order of magnitude: 15%) to take into account the potential reduction due to testing misalignment.

Shrinkage-induced Damage Evolution for Concrete Overlay

Abstract In this paper, we investigate the development of stress and the debonding behavior of thin bonded concrete overlays under restrained conditions. The results show us that the fractured mode of a concrete repair system will change clearly along the new concrete with higher shrinkage deformation to crack along the interfacial layer, and with increasing intensity strength, the interfacial layer becomes stronger so that it is hard for the concrete repair system to fail. It is difficult to predict the exact crack pathway of a concrete repair system unless the condition of the meso-structure is known.

Sika puts seal on woodhead tunnel with concrete repair system

Sika puts seal on woodhead tunnel with concrete repair system

Preliminary Study on the Bond Properties of the PDCC Concrete Repair System

Pseudoductile cementitious composite (PDCC) is an effective and durable repair material for concrete structures. Silane is commonly used to enhance the resistance of concrete to water and chemical penetration. By combining PDCC with silane, a novel repair and/or protection system for concrete structures can be produced. Because silane application may affect the PDCC-concrete interfacial interaction and bond capacity, the effects of silane application on the bond properties of the PDCC concrete repair system were investigated in this study with the direct shear test and pull-off test. Specimens with and without silane treatment were prepared for both kinds of tests. Results show that the direct shear test and the pull-off test can be employed to study the bond properties of the PDCC concrete repair system. The interfacial interaction between PDCC and sufficiently cured concrete is strong even though the concrete has been moistly cured for 4 months when the PDCC is cast. When silane is applied between concrete and PDCC, the PDCC-concrete bond capacity measured in the direct shear test shows almost no change, and the PDCC-concrete bond capacity measured in the pull-off test is reduced.

1A1-C01 自昇降式コンクリート柱補修装置の開発(建設・解体ロボット・メカトロニクス)

Authors are developing the concrete column inspection and repair system. The system is for the extermination of work at the height place, and the safety work, and the shortening time of construction, and the corresponding to the serious disaster. This system is climbing the concrete column for inspection and repairing by self-climbs and remote control. This report explains the performance of the concrete column inspection and repair system is a climbing evaluated by the climbing experiment.

Water Sorptivity and Permability of New-Old Concrete Composite System

Several experiments were carried out to investigate the effects of water to binder ratio(w/b) and mineral admixtures on water sorptivity and permeability of new-old concrete composite system in this paper in order to further understand the transport properties and thus degradation mechanism of new-old concrete repair system. Results indicate that a reasonable choice of w/b of new concrete is of great importance for obtaining new-old concrete composite with a low water sorptivity. Addition of ultrafine powder such as silica fume as one of component of repairing materials will benefit for effectively reducing water sorptivity and permeability of new-old concrete repair system in practice. The linear correlative coefficient between capillary sorption coefficient, coulomb electricity and porosity of new-old concrete composite sample is bad and lower compared with those of corresponding new concrete samples. The total porosity of new-old concrete composite sample is not an exclusive factor determined its water sorptivity and permeability. The pore structure of new-old concrete composite sample, especially interfacial transition zone between new and old concrete plays more important role on transport properties of sample.

Effects of Cyclic Loading, Freeze-Thaw and Temperature Changes on Shear Bond Strengths of Different Concrete Repair Systems

An experimental study was performed to evaluate the residual shear bond strengths between different cementitious and resinous repair materials and substrate concrete after being subjected to cyclic loading, freeze-thaw, and temperature changes. In this paper, techniques and results of test methods that induce shear along the repair/concrete interface are discussed. In addition to the effect of surface preparation on the strength of the old concrete surface, which proved the saw cut surface as the most suitable substrate concrete for shear bond strength assessment, by means of cylindrical shear and friction-transfer methods, the effects of cyclic loading, freeze-thaw, and temperature changes on the shear bond strengths of six different repair systems are illustrated. Analysis of the results indicated that: in order to avoid fatigue failure, the maximum safe stress level to be applied should be between 20 to 40% of the original shear bond strength of the repair system, and the critical stress level differs for different repair materials; 300 freeze-thaw cycles can reduce the shear bond strength of a resin mortar by up to about 80%; and 200 cycles, of temperature changes can reduce the original shear bond strength of a cementitious mortar by up to about 90%.