Application of Eco-Friendly Materials in Repair of Reinforced Concrete Members: A State-of-the-Art Review

Asphalt pavement is the most widely used type of pavement in the world and is mainly utilised in the construction of infrastructures such as highways, urban roads, parking lots and airstrips. Pavement maintenance technology and materials are gradually developing towards systematisation and diversification with the extensive use of asphalt pavement. Choosing more economical technologies and fast and sustainable materials is the future of asphalt pavement maintenance work. This paper provides an overview of asphalt pavement repair technology and asphalt pavement repair materials. It categorises and summarises pavement repair technologies, which include cost-effective technologies such as crack sealing, overlay, seal coats and hot in-place recycling. Further, it summarises the repair materials applied in repair technologies and compares the performance, cost-effectiveness and sustainability of these materials. The study shows that asphalt and cement are the most commonly used repair materials. The higher-potential, more economical and more sustainable materials for asphalt pavement repair include epoxy resin, polyurethane and hydrogel. The future of asphalt pavement repair requires advancing towards rapid, sustainable, environmentally friendly and economical repairs. A survey indicates that in addition to improving the performance of existing repair materials (e.g. modified asphalt, binder processes, material composition or ratios), attention can be given to new materials such as polyurethanes and hydrogels that have the potential for rapid repair and are low cost. More research can be done to perfect the application of new materials in road engineering.

The repair and strengthening of reinforced concrete members are very important due to several factors, including unexpected increases in load levels and/or the damaging impact of aggressive environmental conditions on structural concrete members. Many researchers have turned to using materials for the repair and strengthening of damaged structures or the construction of new concrete structural members. Ultrahigh‐performance fibre‐reinforced concrete (UHPFRC), characterized by superior structural and durability performance in aggressive environmental conditions, is one of the materials that have been considered for the repair and strengthening of concrete structural members. The repair or strengthening of concrete structures using UHPFRC needs a thorough knowledge of the behaviour of both the strengthening material and the strengthened concrete structure at service load conditions, in addition to an understanding of the design guidelines governing the use of such materials for effective repair and strengthening. In this study, the recent issues and findings regarding the use of UHPFRC as a repair or strengthening material for concrete structural members are reviewed, analysed, and discussed. In addition, recommendations were made concerning areas where future attention and research on the use of UHPFRC as a strengthening material needs to be focused if the material is to be applied in practice.

In this study, a continuous rape-rice rotation plot experiment was conducted over three years. Repair materials were continuously applied in the first two years, and no repair materials were applied in the second year. The repair effects of hydroxyapatite, lime, biochar, bio-organic fertilizer, and nano-materials on copper contaminated soil and the enrichment of copper in different parts of rape and rice were investigated. The results show that hydroxyapatite, lime, and nanomaterials can significantly increase soil pH, and different restoration materials can effectively inhibit the movement of soil copper. The effective copper treatment with lime restoration soil had the largest decrease. The four seasons of continuous application of restoration materials were 38.9%, 34.9%, 27.88%, and 29.04%, respectively, and the subsequent effect of lime passivation of effective copper was better than other restoration materials. The application of the repair material significantly reduced the copper content in edible parts of rape and rice. In the four seasons of application of the repair material, the maximum copper content in edible parts of different crops decreased by 46.03%, 22.2%, 29.44%, and 31.71%, respectively. Due to the application effect of the repair material, the copper content in the edible part of the two season crops, without the repair material, did not exceed the national food safety limit. With the use of different repair materials, the yields of rapeseed and rice were improved. This test can provide some theoretical basis and technical support for soil improvement in copper-contaminated areas.

Structural elements such as beams, slabs, and columns may require strengthening or repair during their service life. Different repair materials (RMs) are available and it is usually difficult to choose the best ones, especially when considering the cost of such materials. This paper presents the results of an experimental investigation of patch RMs on plain concrete prisms as well as on reinforced concrete beams. Three cement-based RMs available in the market with different mechanical properties and an ordinary Portland cement (OPC) mix produced in the lab were used in the study. Damage was induced in prisms/beams and then repaired using different materials. The experimental work included assessment of the flexural strength of damaged/repaired plain concrete prisms; slant shear (bond) strength between the concrete and the RM; axial strength of damaged/repaired plain concrete prisms and bond of the repair materials in damaged/repaired reinforced concrete beams loaded to failure. The test results showed that all RMs performed well in restoring the strength of damaged plain concrete. Compatibility of the RMs with substrate concrete was found to be more important in the behavior than superior mechanical properties of the RMs. No difference was noted in the behavior between the RMs in repairing reinforced concrete beams at the tension side.

Different techniques including the application of steel elements, composite materials and polymeric resins have been used in the past to repair damaged timber beams. However, there is a growing need to replace these materials with those with minimal environmental impact. In addition, stringent requirements of conservation authorities on the compatibility between repair and parent materials have also necessitated search for innovative repair materials for timber beams. Therefore, an increasing shift of focus towards the use of materials derived from natural sources in repairing and reinforcing timber structures is currently experienced. This paper presents the results of an exploratory study on the use of natural resins (rosin and bone glue) in repairing oak timber beams. 15 oak timber beams with cross section dimensions of 67 x 67 mm and 1100 mm in length were tested in four-point bending to failure. Undamaged, damaged (unrepaired) and damaged but repaired timber beams (with rosin and bone glue) were tested. The effectiveness of the repair material and technique was analysed based on the bending capacity and mid span deflection at failure. The initial results show negligible effectiveness of rosin in repairing timber beams. In fact, about 16% reduction (average) in load carrying capacity with a corresponding 5% decrease (average) in maximum displacement was recorded. Relatively higher level of effectiveness was recorded with the use of bone glue (about 10 % average increase in load carrying capacity). However, over 30% corresponding average increase in the maximum displacement was also recorded. Further work investigating different repair techniques and other natural resins is presently underway.

The paper reviews the recent applications of piezoelectric materials in structural health monitoring and repair conducted by the authors. First, commonly used piezoelectric materials in structural health monitoring and structure repair are introduced. The analysis of plain piezoelectric sensors and actuators and interdigital transducer and their applications in beam, plate and pipe structures for damage detection are reviewed in detail. Second, an overview is presented on the recent advances in the applications of piezoelectric materials in structural repair. In addition, the basic principle and the current development of the technique are examined.

Performance assessment of repair material for deteriorated concrete slabs using chemically bonded cement

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.

The research presented in this thesis develops a new methodology for the structural health monitoring of structures. The methodology is based on the use and the application of smart materials and specifically the piezoelectric materials (lead zirconate titanate PZT). These materials are installed and applied in the concrete members of a structure. Therefore, the specific characteristics of the PZTs in combination with their interaction with the structure are used in order to develop the new health monitoring technique. Physical changes in the structure cause changes in the structural mechanical impedance. Due to electromechanical coupling between the piezoelectric material and the structure, the change in structural mechanical impedance induces a change in the electrical impedance of the piezoelectric material. The proposed methodology is based on the interaction of PZT with the structure according to the Electro-Mechanical Impedance EMI or its inverse Electro-Mechanical Admittance EMA. The methodology uses the electromechanical data in frequency response with statistical techniques to damage detection. This includes two stages, in first stage the detection of damage, and if provided that this exists, in second stage the location and level of the damage. Since the widespreadest building material in the existing structures is concrete, the examined numerical application of the proposed methodology is a concrete structural element. The well-known strengthening technique of deficient concrete members using epoxy bonded Fibre Reinforced Polymer (FRP) materials is used herein in order to examine the application of smart materials and the proposed methodology in a FRP concrete component. These composite materials have experienced a continuous increase of use in structural strengthening and repair applications around the world in the last decade. High stiffness-to-weight and strength-to-weight ratios of these materials combined with their superior environmental durability have made them a competing alternative to the conventional strengthening and repair materials. From a structural mechanics point of view, an important concern regarding the effectiveness and safety of this method is the potential of brittle and premature failures due to the debonding of the FRP materials. Such failures, unless adequately considered in the design process, may significantly decrease the effectiveness of the strengthening. In this thesis, a new method that prevents FRP debonding using smart piezoelectric materials is investigated. The technique consists of the installation of system of piezoelectric (sensor - actuator) at the edge of the epoxy bonded FRP to the concrete member. The application of this system in combination with a specific optimisation method that is based on the EMA response of PZT, can produce controlled local forces and moments with opposite effect to that of a harmonic load at the middle of the beam. These forces are capable to reverse and to compensate the imminent debonding of the edge of the FRP which are based on a new repair criterion. Using the proposed method, the control of the FRP debonding in a concrete member under dynamic loading is achieved. Further, a special criterion for the “active” repair of the continuous contact between FRP and concrete is proposed. Thus, the application method of a “smart and readjusted FRP” for the repair of FRP concrete components under dynamic load is developed. Achieve The effectiveness of the proposed method is analytically investigated using the finite element program COMSOL (former FEMLAB) for the simulation of the smart structural system. The statistical process of the EMA response data and the development of the proposed optimisation methods are achieved using MATLAB environment developed for the purposes of this study.

Durability enhancement of cement-based repair mortars through waterborne polyurethane modification: Experimental characterization and molecular dynamics simulations

The purpose of hernioplasty is to repair defects and restore abdominal wall function, and ultimately to improve the quality of patients′ life. With the innovation of basic theories, anatomical concepts, surgical techniques and repair materials, hernioplasty has made tremendous progress, but its basic principles of treatment have not changed. In recent 20 years, hernia surgery in China has entered a period of comprehensive and rapid development, showing a leap in the level of diagnosis and treatment, surgical technology, the number of operations and other aspects. Meanwhile, a series of clinical quality control systems, such as training, registration and adverse event monitoring, have been established, making China the top level of the world as a whole. At present, the surgical methods of abdominal wall hernia are flourishing and developing rapidly. The application of different levels, different approaches and different materials in the treatment of individualized patients has shown good clinical results. Of course, there is no repair material that meets the requirements of ideal patch . Although the implantation of synthetic materials has greatly improved the clinical effect of hernia, the permanent presence of foreign materials also brings about the possibility of long-term complications. A series of absorbable materials represented by tissue-induced biomaterials are closer to human tissues, which may represent the direction of the development of hernia repair materials, but long-term follow-up results are still needed to confirm their clinical efficacy. Key words: Hernia; Abdominal hernia; Surgery; Materialogy

The progressive deterioration of concrete surface structures is a major concern in construction engineering that requires precise repairing. While a number of repair materials have been developed, geopolymer mortars have been identified as potentially superior and environmentally friendly high-performance construction materials, as they are synthesized by selectively combining waste materials containing alumina and silica compounds which are further activated by a strong alkaline solution. Geopolymers as Sustainable Surface Concrete Repair Materials offers readers insights into the synthesis, properties, benefits and applications of geopolymer-based materials for concrete repair. • Discusses manufacturing and design methods of geopolymer-based materials • Assesses mechanical strength and durability of geopolymer-based materials under different aggressive environmental conditions • Characterizes the microstructure of these materials using XRD, SEM, EDX, TGA, DTG and FTIR measurements • Describes application of geopolymer-based materials as surface repair materials • Compares environmental and cost benefits against those of traditional OPC and commercial repair materials This book is written for researchers and professional engineers working with concrete materials, including civil and materials engineers.

Proper surface preparation is essential for the durability of the repaired structure as well as specific saturation level of the concrete. Moreover, the repair material is often blamed for “not sticking”, but the general source of the trouble lies with the substrate surface conditioning. The extensive research project has been undertaken to develop specifications and performance criteria for surface preparation of concrete substrates, one of the tasks of which was to develop a field test to evaluate the optimum moisture conditioning of the substrate concrete prior to application of repair material. The Autocalm system has been calibrated and compared with destructive and non destructive tests (Schmidt hammer, microscope observations and water absorption) on three types of concrete and two types of surface preparation. In order to evaluate different saturation levels, concrete samples have been stored in more than 12 modes of conservation. Saturated Surface Dry (SSD) conditioning of the substrate prior to application of cementitious repair materials is usually recommended and used, which underlies the “layman’s” instinctive procedures to avoid problems, rather than achieving the most effective bond. Various investigators came to the conclusion that different substrates and repair materials correspond to different optimum interface moisture conditions at the time of casting. The problem is that there is presently no test method to determine the

PURPOSES : This study aims to develop a repair material that can enhance pavement performance, inducing rapid traffic opening through early strength development and fast setting time by utilizing MgO-based patching materials for repairing road pavements. METHODS : To consider the applicability of MgO-based patching materials for repairing domestic road pavements, first, strength development and setting time of the materials were evaluated, based on MgO to ratio, water to binder ratio, and addition ratio of retarder (Borax), by which the optimal mixture ratio of the developed material was obtained. To validate the performance of the developed material as a repair material, the strength(compressive strength and bonding strength) and durability (freezing, thawing, and chloride ion penetration resistance) was checked through testing, and its applicability was evaluated. RESULTS : The results showed that when an MgO-based patching material was used, the condensation time was reduced by 80%, and the compressive strength was enhanced by approximately 300%, as compared to existing cement-based repair materials. In addition, it was observed that the strength (compressive strength and bonding strength) and durability (freezing and thawing, and chloride ion penetration resistance) showed an excellent performance that satisfied the regulations. CONCLUSIONS : The results imply that an emergent repair/restoration could be covered by a rapid-hardening cement to meet the traffic limitation (i.e. the traffic restriction is only several hours for repair treatment). Furthermore, MgO-based patching materials can improve bonding strength and durability compared to existing repair materials.

Evaluation of the bond strength of a novel concrete for rapid patch repair of pavements