Properties Of Repair Materials Research Articles

Reliability analysis of composite laminate patch repaired structures based on response surface proxy model

In this paper, the reliability analysis of composite laminate patch repaired structures under unidirectional static load was studied by means of a probability model. First, a proxy model for the maximum static load carrying capacity of the repaired structure was established using quadratic polynomial response surface method (RSM) considering the repair material properties, repair patch design and adhesive layer thickness. Second, the probability distribution input of various basic random parameters including geometric characteristics and material properties were considered based on actual repair data. Finally, both the reliability and sensitivity analysis of the repaired structure were investigated by means of Monte Carlo simulation method. The results show that the reliability analysis model is of great significance for the subsequent design and properties evaluation of composite repaired structures.

Interfacial bonding properties of styrene-butadiene rubber and ethylene vinyl acetate emulsion-modified OPC–CAC–G repair mortar

Inorganic repair materials such as ordinary Portland cement–calcium aluminate cement–gypsum (OPC–CAC–G), which consist of ordinary Portland cement, aluminate cement, and gypsum, have advantages of fast hardening, high early strengths, and minimal expansion; however, they also have the disadvantages of low bond strengths and weak interface areas, which often lead to repair failure. The interfacial bonding properties of repair materials can be improved by adding highly flexible polymers. In this study, the effects of styrene-butadiene rubber (SBR) and ethylene vinyl acetate (EVA) on the interfacial bonding properties of OPC–CAC–G bonding and the mechanism of the effect of the microstructure are examined using X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy. The results show that and EVA are both effective in improving the interfacial bond strength of OPC-CAC-G repair mortars. SBR is suitable for the modification of repair mortars with an optimum dose of 20%; EVA is suitable for the use as an interface agent on the surface of damaged concrete substrates with an optimum concentration of 40%.

Application of plastic conjugated materials in the repair of sports injury.

For professional athletes or fitness crowd who often participate in sports, sports injury are more common. However, the traditional repair materials for sports injury have many problems, such as long recovery period and poor repair effect. In recent years, many studies have found that conjugated materials have good stability, small side effects and other excellent characteristics, and conjugated materials are used in sports injury repair materials. In order to study the repair effect of conjugated materials on sports injury tissues, this paper prepared nitrogen porphyrin conjugated organic skeleton materials with pyrrole and p-benzaldehyde as substrates, used chemical synthesis and selective laser sintering technology to form plastic conjugated scaffold materials with polyvinyl alcohol, polylactide and conjugated materials, and established mechanical properties and constitutive formula to evaluate the performance characteristics of repair materials. In order to test the effect of plastic conjugated materials on sports injury, experiments were carried out from the aspects of degradability, mechanical properties of repair materials, repair effect of radius defect and new bone formation area. Experimental data: The proportion of newly formed bone area at weeks 3, 6, and 9 using this method was 32%, 52%, and 68%, while the proportion of newly formed bone area at weeks 3, 6, and 9 using traditional methods was 12%, 18%, and 23%, indicating that this method had better bone repair effects than traditional methods. The research in this paper provided a new idea for the application of plastic conjugated materials in the field of sports medicine.

The bond properties between ultra-high-performance concrete and normal strength concrete substrate: Bond macro-performance and overlay transition zone microstructure

This study investigates the bond performance between ultra-high-performance concrete (UHPC) and normal strength concrete (NSC) substrate. A hoop constraint method is designed to assess the shrinkage effect of repair materials on bond macro-performance. The bond strength and permeability of the same specimen are determined using the hoop constraint method. Additionally, the properties of repair materials, such as drying shrinkage, thermal gravity analysis, and mercury intrusion porosimetry, were investigated. The overlay transition zone (OTZ) microstructure is analysed to reveal the bonding mechanism. The results indicate that the hoop constraint method effectively reflects the ability of UHPC to overcome the significant autogenous shrinkage effect and achieve good bond macro-performance. Moreover, the UHPC-combined substrate exhibits better bond strength than that of the NSC because the repair interface of the UHPC is more compact than that of the NSC. Furthermore, the OTZ width of the UHPC-combined substrate is narrower than that of the NSC, and in the OTZ, the modulus of the UHPC is higher than that of the NSC.

Investigating the effects of anti-corrosive coatings on the bond between corrosion-damaged rebar and concrete repair materials

Reinforcement corrosion causes destruction to the steel by a loss in cross section and rib height, which can affect the bond between steel and concrete. During repair of corrosion-damaged reinforced concrete members, a protective coating is usually applied to the cleaned corroded steel. There is, however, little information available on the bond performance of repair coatings. Furthermore, the effect of their coating thickness and other parameters like rebar diameter, corrosion degree and repair material properties are not well understood when considered in parallel with repair coatings. This paper seeks to contribute towards understanding the use of anti-corrosive coatings and the influence of their thickness on the bond between cleaned steel reinforcement and repair materials, when used in combination with different bar geometries at varying degrees of corrosion damage. In this investigation, two high tensile steel bars, Y12 and Y16, were considered. Rebar corrosion damage levels of 0%, 10% and 20% (of steel mass loss) were simulated by mechanical grinding of sound rebar samples to represent the condition of cleaned corroded rebar. A commercially available epoxy-modified, cementitious coating material was applied to the steel in one or two coats, with each coat being 0.6 mm thick. Three repair materials with CEM I 52.5N were considered in this study, which included one concrete with a w/b ratio of 0.45 and two mortars with w/b ratios of 0.47 and 0.65. Pull-out testing was conducted on 108 specimens, and the results analysed by means of the one-way ANOVA test to assess the effect of mainly coatings and other parameters on the bond. The results indicate applying coatings to 10% and 20% corroded steel does not significantly reduce the bond for the M65 and C45 mixes. Furthermore, the difference between one and two coats had little influence on the bond of corroded steel for all rebar geometries and repair mixes.

Investigating the structural contribution of patch repairs to reinforced concrete elements

The patch repair method is one of the most common approaches used by engineers for repairing reinforced concrete structures that have been damaged. Despite its popularity, the knowledge on material properties pertinent to a durable structural repair is still lacking. Most standards and guidelines on concrete repair currently specify arbitrary limits when it comes to the properties of repair materials. In the case of structural patch repairs, these arbitrary limits have led to the development of high-strength cementitious repair mortars, often marketed as “high-performance”, that are tailored to meet the specifications and not the needs on-site. The paper discussed here forms part of a greater study that aims to increase the understanding of patch repairs and inform existing guidelines on designing structural patch repairs. Three commercially available high strength cement-based repair materials were tested for their strength, elastic modulus, shrinkage, and creep properties. These properties were then used as inputs to an analytical model that was developed to determine the distribution of stress in a repaired element over-time. The results from the analytical model suggest that high strength materials do not structurally contribute in the long term, for patch repaired concrete elements under axial compression.

Field performance with state-of-the-art patching repair material

Significant efforts have been made to identify the correlations between pavement design, materials and construction variables and pavement performance for new pavement construction; in response to these efforts, specifications and design standards have been developed to optimize pavement performance. On the other hand, less positive correlations have been found between pavement repair materials/methods and the performance of repairs. This issue is primarily due to the incompatibility between existing pavement and repair materials including bonding at the repair interface, as well as the complex nature of pavement behavior near distressed areas. As a result, the variability in the performance of pavement repairs has been rather large. As more pavement sections have reached or even exceeded their design lives, with more frequent distresses, it is important to identify optimum repair methods and/or materials. This paper presents the field performance of several repair strategies with Fiber Reinforced Polymer Patching Binder (FRPPB) patching material for the repairs of spalling, partial-depth punchout and longitudinal joint separations in rigid pavement, for retarding reflection cracking in asphalt overlay on jointed concrete pavement, and for repairs at the transition area between rigid and flexible pavements by the Texas Department of Transportation (TxDOT). The repairs for these distress types have been a challenge to TxDOT districts; repair specifications with acceptable properties of repair materials and methods have not been as well-developed as the specifications for new construction have, resulting in a large variability in the performance of repairs of these distresses.The performance of repairs for the distresses mentioned above with FRPPB has been excellent, with no need for repeated repairs up to this point. The results from this study indicate that if the right materials are used for repairs, along with the correct repair method, the performance of pavement repairs and rehabilitations could be substantially enhanced, minimizing traffic delays and financial resources associated with further repairs and rehabilitations.

Influence of freeze–thaw cycles on properties of asphalt-modified epoxy repair materials

Abstract A high performance repair materials for concrete is prepared using epoxy resin as a base resin and asphalt as a modifier, respectively. The influence of the asphalt content, freeze–thaw circles, and chemicals on the structure and properties of the repair materials is investigated in detail in this work. Results show that the epoxy repair materials modified with 10 phr of asphalt has the excellent mechanical property, and the compressive strength and tensile shear strength can reach 56.6 MPa and 5.9 MPa, respectively. The compressive strength further increases while the weight change for all samples is below 1 wt% when the repair materials suffer 30 freeze–thaw circles and chemicals soakage at 80 °C for 2 weeks, indicating that the asphalt-modified epoxy repair materials have the outstanding water, acid, and alkaline resistance and salt tolerance. Therefore, a kind of asphalt-modified epoxy repair materials with excellent freeze–thaw resistance is developed in this research.

Static and Fatigue Performance of Repaired Reinforced Concrete Beams

Deteriorated concrete structures due to corrosion cracks and with fallen concrete cover are often repaired by removing the cracked concrete around the corroded reinforcement and replacing it with new concrete or with special repair mortar. This process is often referred to as “Mechanical Repair” and is widely used for repairing deteriorated reinforced concrete members. Mechanical repair leads to the formation of an ‘interface’ between the ‘parent concrete’ and repaired material. The structural behaviour of the repaired members is critically depended on the performance of the interface. This paper reports the results of static and fatigue tests performed on a total of 21 beams, cast in two stages to resemble the mechanical repair. Location and dimensions of the repair and the repair material are taken as variables in the study. Results of the static tests on repaired beams reveal that static performance can be restored by the mechanical repair. Compressive face repair can even improve the performance depending on the properties of repair material and the performance of the bond. However, the fatigue performance of the repaired members is found very different to their static performance. All most all repaired beams either the repair of the compression face or of the tension face failed at substantially lower number of cycles compared to the control beam. Among the repaired beam, tension face repaired beams showed the most significant reduction in the fatigue performance.

High-Early-Strength Engineered Cementitious Composites for Fast, Durable Concrete Repair—Material Properties

The lack of durability in concrete structures worldwide demands fast and durable repairs. To address this need, high-early-strength engineered cementitious composites (HES-ECC) were recently developed for concrete repair applications in which minimum operations disruption is desired. A detailed characterization of HES-ECC’s compressive, tensile, flexural, and shrinkage properties at different ages is reported in this paper. HES-ECC achieves a compressive strength of 23.59 ± 1.40 MPa (3422.16 ± 203.33 psi) in 4 hours and 55.59 ± 2.17 MPa (8062.90 ± 315.03 psi) in 28 days. Under uniaxial tension, HES-ECC exhibits tensile strain-hardening behavior with a strain capacity greater than 2.5%. Its flexural strength exceeds twice that of concrete with similar compressive strength. Under restrained shrinkage conditions, HES-ECC forms microcracks with a self-controlled crack width below 50 μm (0.002 in.). The combination of these properties suggests HES-ECC material is highly suitable for fast and durable concrete repairs with shortened downtime and improved longterm durability.

Effect of cracking, corrosion and repair on the frequency response of RC beams

This paper presents a laboratory investigation to study the effect of cracking, corrosion and repair on the frequency response of simply-supported reinforced concrete beams. The beams were subjected to four-point bending at 70% of their theoretical ultimate loads. Corrosion was then induced using an electro-chemical acceleration technique. The beams were then repaired to restore their load-carrying and deflection capacities. Based on response time histories, the fundamental frequency characteristics of the beams were deduced using Fourier transform (FT) and Hilbert-Huang transform (HHT). Experimental results revealed significant changes in the normalized frequency, R f , with decrease in R f associated with load-induced cracking, an increase in R f associated with moderate reinforcement corrosion and a subsequent decrease in R f associated with repair. The results of this study support the use of frequency response, obtained with an appropriate signal processing technique such as HHT, to infer the health of monitored structures, taking into account environmental conditions, likelihood of corrosion occurrence, properties of repair material and interfacial bonding.

Experimental Evaluation of Drying Shrinkage and Mechanical Properties of Repair Materials for Concrete Structures

The potentially aggressive environments in some parts of Saudi Arabia have resulted in premature deterioration of many concrete structures during their service life. To achieve more effective and long lasting repair materials, it is essential that the properties of the repair materials and the substrate are compatible. This study aims at evaluating the mechanical properties of selected classes of repair materials that are commonly used in repair application within the Kingdom. A total of 114 specimens were cast to investigate some of the important properties of nine widely used local repair materials available in the market. The properties evaluated in this study are: drying shrinkage, compressive strength and modulus of elasticity. Out of each of the selected repair materials, six specimens for shrinkage and six specimens for compressive strength and modulus of elasticity measurements were considered in the study. Additional specimens made from cement paste were used as control samples for the study. Results of the present study show that all repair materials must be checked experimentally to confirm the properties given by the supplier before their use in any field application. The study also recommends that the selection of suitable repair material should be based on the type of application, as application changes properties requirement changes. For example, for one application compressive strength requirement may be more critical, while in another application shrinkage may be of great concern.

Corrosion of concrete reinforcement and electrochemical factors in concrete patch repair

Corrosion of concrete reinforcement at a patch repair is a complex problem, and current knowledge of its mechanism is quite limited. This review examined the correlation between two corrosion mechanisms, macrocell and microcell corrosion, from fundamental electrochemical principles. It was found that both mechanisms could play significant roles in inducing corrosion damage, contrary to the prevailing opinion that macrocell corrosion is the main deterioration mechanism in patch repair. This has practical implications that need to be considered for an effective and durable repair. A review of the studies done to date also enabled the identification of the key factors in patch repair controlling the corrosion characteristics. Corrosion could occur at different locations in the vicinity of the patch — substrate, interface, or patch area — depending on the respective electrochemical environments induced by the repair material properties and treatments, as well as the in-service exposure and mechanical loading. The review indicates that much of the needed research should focus on identification of corrosion mechanisms to effect successful patch repair in reinforced concrete structures.Key words: patch repair, substrate, corrosion, macrocell corrosion, microcell corrosion.

Study on Basic Properties of Repair Material under Dryness Environment

Study on Basic Properties of Repair Material under Dryness Environment

Effect of hot-dry curing environment on the intrinsic properties of repair materials

The paper examines the properties of five different types of repair materials, including conventional cementitious, polymer and polymer-modified repair mortars. Assessment was carried out on the basis of the engineering properties (compressive strength, tensile strength and modulus of elasticity), pore structure (porosity and pore size distribution), transport properties (permeability and diffusion) and shrinkage. These properties were measured up to the age of 28 days after curing in a hot-dry environment. The epoxy resin repair mortar showed superior strength and transport characteristics with a very fine pore structure; however, its modulus of elasticity was remarkably low when compared with that of normal- and high-strength concretes. A hot-dry curing environment adversely affects the shrinkage and performance-related properties of conventional repair mortars; however, small improvements could be achieved by the use of mineral admixtures (fly ash and silica fume). The paper discusses also the different testing techniques which could be used to assess the potential performance of concrete repair mortars.

Application of tension softening diagrams to evaluation of bond properties at concrete interfaces

The bond properties at joint interfaces in concrete structures were evaluated through tension softening diagrams. For the joint surfaces between old and new concrete, the conditions to obtain good bond properties were clarified. The size effect on the flexural bond strength was well predicted through numerical analysis with tension softening diagrams. For the interfaces between repair materials and substrate concrete, the properties of repair materials and the conditions of interfaces were characterized by the shape of the tension softening diagrams and fracture energy. The shrinking and cracking behavior of repair materials was also investigated through experiments and numerical analysis.

Repair material properties for effective structural application

Strength and engineering properties of three generic repair materials which are likely to influence long-term performance of repaired concrete structures were studied. Measured properties include strength, stiffness, shrinkage and creep deformations, together with the complete compressive stress-strain characteristics including post-cracking behaviour. The repair materials considered in this investigation are commercially available and widely used. These included a high performance non-shrinkable concrete, a mineral based cementitious material with no additives or coarse aggregate size particles, and a cementitious mortar containing styrene acrylic copolymer with fibre additives. Performance comparisons are also made between these materials and plain concrete mixes of similar strength and stiffness, suitable for repair applications. The results show that shrinkage of the repair materials was significantly greater than the shrinkage of normal concrete. Moreover, the shrinkage of those modified with a polymer admixture was found to be very sensitive to the relative humidity of the exposure compared to normal concrete. The post-peak strain capacity of the material modified with a polymer admixture was markedly improved leading to a more pronounced falling branch of stress-strain curve. The ultimate stress level (at a maximum load) of specially formulated repair materials varies significantly, the lowest ultimate stress being recorded for the porous mineralbased material. The inclusion of aggregates improves the mechanical properties and dimensional stability of repair materials.

Repair material properties which influence long-term performance of concrete structures

The paper presents the results of an experimental investigation to determine some typical properties of three commercially available generic repair materials, which are of significance to the subsequent structural behaviour of repaired concrete members. It also compares the performance of these materials with plain concrete mixes of similar strength and stiffness, which are also suitable for repair applications. Data on strength, stiffness, shrinkage and creep under different temperature and humidity exposure are presented. In addition, water permeability coefficients of the materials have been determined. The results show that shrinkage of the repair materials is significantly greater than shrinkage of normal concrete. The shrinkage of the specially formulated repair mortars, especially those modified with a polymer admixture, is very sensitive to relative humidity of exposure compared with normal concrete. The permeability of normal concrete is similar to that of both the high performance non-shrinkable repair material and the polymer modified repair material. The other repair material based on a mineral cement binder is more permeable than normal concrete. The inclusion of aggregates improves the mechanical properties and dimensional stability of repair materials.

A unified failure envelope from the evaluation of concrete repair bond tests

This paper compares the core pull-off and slant-shear tests with the patch test (see Magazine of Concrete Research, September 1993 v45 n164) as methods of evaluating the bond of shallow concrete patch repairs. The effects of repair material properties, surface roughness and soundness, moisture condition and artificial partial debonding on bond performance are described, with reference to both physical tests and material modelling. The pull-off and patch tests were found to be sensitive to surface roughness and soundness and to incomplete bonding. In contrast, the slant-shear test was found to be insensitive to changes in surface roughness and soundness, and with rough surfaces was also relatively insensitive to partial debonding. The bond strength values obtained from the two tests are not directly comparable because of the different stress rates along the repair interface. A bond failure envelope is proposed which enables a meaningful comparison of information from different test methods to be made. Bond failure envelopes are presented for the two plain sand- cement mortars, which emphasize the superior bond performance of the one with the higher water-cement ratio. Bond failure envelopes for the two polymer-modified materials could not be established because bond failure did not occur. (A)

Restrained shrinkage in repaired reinforced concrete elements

This paper describes an analytical model of restrained shrinkage in repaired reinforced concrete elements. The results of analysis and test show that the effect of restrained shrinkage on the serviceability of the repaired element is quite significant. The computer based analysis proposed can be applied to predict progressive crack development in a repair material subjected to restrained shrinkage during construction. The properties of repair materials, such as ultimate strain in tension, creep coefficient and free shrinkage, are major factors influencing the performance of structural repairs. Restrained shrinkage is related to the stiffness of a repaired section of known structure. The effect of moment redistribution on restrained shrinkage is significant in elements of indeterminate structure. The stress and strain caused by restrained shrinkage in elements of indeterminate structure are higher than in elements of known structure, and an example given in this paper shows an increase in strain of about 30%.