Cementitious Repair Materials Research Articles

Pore properties and moisture loss of repair mortars under low-impact microwave curing

PurposeMicrowave curing (MC) can facilitate rapid concrete repair in cold climates without using conventional accelerated curing technologies which are environmentally unsustainable. Accelerated curing of concrete under MC can contribute to the decarbonisation of the environment and provide economies in construction in several ways such as reducing construction time, energy efficiency, lower cement content, lower carbonation risk and reducing emissions from equipment.Design/methodology/approachThe paper investigates moisture loss and pore properties of six cement-based proprietary concrete repair materials subjected to MC. The impact of MC on these properties is critically important for its successful implementation in practice and current literature lacks this information. Specimens were microwave cured for 40–45 min to surface temperatures between 39.9 and 44.1 °C. The fast-setting repair material was microwave cured for 15 min to 40.7 °C. MC causes a higher water loss which shows the importance of preventing drying during MC and the following 24 h.FindingsPortland cement-based normal density repair mortars, including materials incorporating pfa and polymer latex, benefit from the thermal effect of MC on hydration, resulting in up to 24% reduction in porosity relative to normal curing. Low density and flowing repair materials suffer an increase in porosity up to 16% due to MC. The moisture loss at the end of MC and after 24h is related to the mix water content and porosity, respectively.Originality/valueThe research on the application of MC for rapid repair of concrete is original. The research was funded by the European commission following a very rigorous and competitive review process which ensured its originality. Original data on the parameters of porosity and moisture loss under MC are provided for different generic cementitious repair materials which have not been studied before. Application of MC to concrete construction especially in cold climates will provide environmental, economic and energy benefits.

Application of polymer cement repair mortar in underground engineering: A review

Polymer-modified cementitious repair materials have gained attention as innovative and environmentally friendly construction materials due to their superior water retention, adhesion, freeze-thaw resistance, corrosion resistance, air permeability, and shrinkage resistance compared to ordinary repair materials. Adding a small amount of polymer can alter the concrete microstructure and form a composite material through the interaction between polymer film formation and cement hydration. This review shows that adding a certain percentage of polymers to concrete can improve the physical, fresh properties, durability, mechanical properties and microstructural development of concrete and improve the effectiveness of concrete repair treatment of underground structures. The discovery of different types and amounts of polymer cement from both physical and chemical perspectives can significantly enhance the performance of cement mortar. Various modifications, such as fibers and nanomaterials are explored to improve the properties of polymer cement for optimal treatment results. Finally, this paper summarizes key findings and provides recommendations for future research.

Relationship between electrical Conductivity, Half cell Potential, Linear polarization resistance and Macrocell current of cementitious repair materials

Corrosion degradation of RC could lead to instability and eventually the collapse of structures if not detected early. Electrochemical methods like Half Cell Potential (HCP), Linear Polarization Resistance (LPR), Macrocell Current and Electrical Conductivity were used in this research to evaluate the relationship between these four non-destructive methods. These four Non-Destructive Test (NDT) methods were used to assess the resistance against chloride attack on three different types of cement-based materials and Ordinary Portland Cement mix (control). Experimental research conducted in this study reveals that there is a linear relationship between electrical conductivity and corrosion current. There is also a fairly good relationship between corrosion current and half cell potential when measuring the degree of corrosion potential and corrosion current for all three repair materials and the control, showing a R2 = 0.72. However, there is an insignificant relationship between corrosion current and macrocell current showing a value of R2 = 0.66.

Effects of Nitrite/Nitrate-Based Accelerators on Strength and Deformation of Cementitious Repair Materials under Low-Temperature Conditions

This study aimed to develop a cementitious repair material that can be constructed in cold weather conditions. The addition of nitrite/nitrate-based antifreezing agents has been shown to increase the initial strength of cementitious repair materials in cold weather. However, increasing the amount of these agents may lead to an increase in deformation behavior and shrinkage cracking. In this study, the effects of different types and amounts of nitrite/nitrate-based antifreezing agents on the strength development and deformation behavior of cementitious repair materials under low-temperature conditions were evaluated. As a result, it was found that the addition of a large amount of calcium nitrite can promote hydration and improve the initial strength of the repair material, irrespective of the type of antifreezing agent. However, this also leads to an increase in shrinkage and the concern of shrinkage cracking. Therefore, a repair material that is repairable in winter was developed by balancing the initial strength and deformation behavior through the appropriate selection of antifreezing agents. The developed repair material can be used to repair structures in cold weather conditions, which is of great significance for the construction industry in Hokkaido, Japan.

Repairing performances of novel cement mortar modified with graphene oxide and polyacrylate polymer

Abstract Most cementitious repair materials have non-ignorable drawbacks such as low strength, insufficient bonding, and low anti-permeability. Although the bonding and anti-permeability of repair mortars modified by polymer will be substantially improved, the compressive strength and component integrity will be decreased. Hereby six groups of cement mortars modified by varied dosages of Graphene Oxide (GO) and PA copolymer (GOPARMs) were prepared. The flexural strength (f t), compressive strength (f c), f t/f c, bond strength (f b), and chloride ion migration coefficient (λ c) of GOPARMs were systematically studied by axial compressive, three-bending, pull-out, RCM method, along with microstructure analysis. When GO and PA dosages are fixed at 0.03 and 5 wt%, respectively, the f t, f c, f t/f c, f b, and λ c of GOPARMs reach the best comprehensive performances, which are 6.4, 46.5, 0.14, 6.73 MPa, and 1.179 × 10−12 m2/s. Compared with the control mortar, the f t, f c, f t /f c, and f b of GOPARMs are improved by 5.7, 12.3, 7, and 103%, respectively, and the corresponding λ c is dramatically reduced by 40.4%. Scanning electron microscope (SEM) shows that trace of GO can play a template nucleation effect on the hydration products’ morphology and microstructure of GOPARMs. Meanwhile, cured PA polymer can form hydrophobic film and fill the interfacial pores among hydration products, finally superior repairing performances of GOPARMs with optimal mix can be achieved.

Properties of Cementitious Repair Materials for Concrete Pavement

This review aims to provide an insight into concrete pavement repair materials by gathering the relevant research outcomes and specifications. It provides a systematic literature review that focuses on pavement repair and types of cementitious repair material. In general, conventional cementitious repair materials can be divided into 4 categories: ultra-rapid, rapid, accelerated, and normal strength gain. The mechanical and durability properties of conventional cementitious repair materials, i.e., calcium sulphoaluminate-based, calcium aluminate-based, polymer-modified concrete, and ordinary Portland cement-based repair materials are highlighted. The paper also discusses the newly developed ultra-high performance concrete and alkali-activated materials as potential repair materials for concrete pavement due to the good mechanical and durability performance. As a final point, this review may help readers to understand and determine the appropriate type of repair material when distress occurs in concrete pavement.

Numerical Simulation on Cement Hydration and Microstructure Development in Repair-Substrate Interface

One of the key parameters for the performance of concrete repairs is the quality of the interface between the repair material and concrete substrate, which is determined by cement hydration and microstructure development. The moisture exchange between the repair material and concrete substrate plays an important role in the cement hydration and porosity of cementitious repair materials. To better understand the influence of moisture exchange on the hydration of cementitious repair materials, this paper presents a numerical simulation of cement hydration and microstructure development of repair materials, considering moisture exchange. The simulation results reveal that the moisture exchange between the repair material and concrete substrate results in a water content change in two parts. Before the repair material setting, the water absorption of an unsaturated concrete substrate causes a reduction in the w/c ratio in the repair material, decreasing the hydration rate of the repair material. After the repair material setting, the water migrates from the concrete substrate to the repair material to provide additional water to accelerate the hydration of unhydrated cement in the repair material.

Concrete substrate moisture requirements for durable concrete repairs – a field study

In concrete repair specifications, the required moisture condition of the substrate, which can play an important role for bond development, and, ultimately, on the long-term repair / overlay durability, is generally ill-defined and addressed without due consideration to the given substrate characteristics. The standard specification, if any, is to require saturated surface dry (SSD) condition of the substrate prior to application of cementitious repair materials, which is theoretically achieved after saturating the substrate and then letting the surface just start to dry out. This does provide an intuitive solution founded on rational considerations, but it has never really been precisely defined, measured, nor validated. The influence of substrate surface moisture on the bond between the existing concrete and the new repair material is an issue of significant importance. This paper revisits the question, in light of results from a project designed to develop guidelines for moisture conditioning of a concrete substrate prior to a cementitious repair, which was part of a larger effort to develop guidelines for surface preparation of concrete prior to repair. Over the course of the project, multiple series of test slabs were repaired after being subjected to different surface moisture conditioning and then tested for bond strength tests at different ages. The findings are discussed, together with those from previous studies, and recommendations are issued.

Service Life Evaluation for RC Sewer Structure Repaired with Bacteria Mixed Coating: Through Probabilistic and Deterministic Method.

Since a concrete structure exposed to a sulfate environment is subject to surface ion ingress that yields cracking due to concrete swelling, its service life evaluation with an engineering modeling is very important. In this paper, cementitious repair materials containing bacteria, Rhodobacter capsulatus, and porous spores for immobilization were developed, and the service life of RC (Reinforced Concrete) structures with a developed bacteria-coating was evaluated through deterministic and probabilistic methods. Design parameters such protective coating thickness, diffusion coefficient, surface roughness, and exterior sulfate ion concentration were considered, and the service life was evaluated with the changing mean and coefficient of variation (COV) of each factor. From service life evaluation, more conservative results were evaluated with the probabilistic method than the deterministic method, and as a result of the analysis, coating thickness and surface roughness were derived as key design parameters for ensuring service life. In an environment exposed to an exterior sulfate concentration of 200 ppm, using the deterministic method, the service life was 17.3 years without repair, 19.7 years with normal repair mortar, and 29.6 years with the application of bacteria-coating. Additionally, when the probabilistic method is applied in the same environment, the service life was changed to 9.2–16.0 years, 10.5–18.2 years, and 15.4–27.4 years, respectively, depending on the variation of design parameters. The developed bacteria-coating technique showed a 1.47–1.50 times higher service life than the application of normal repair mortar, and the effect was much improved when it had a low COV of around 0.1.

Hydration and Microwave Curing Temperature Interactions of Repair Mortars

Microwave curing of repair patches provides an energy efficient technique for rapid concrete repair. It has serious economic potential due to time and energy saving especially for repairs in cold weather which can cause work stoppages. However, the high temperatures resulting from the combination of microwave exposure and accelerated hydration of cementitious repair materials need to be investigated to prevent potential durability problems in concrete patch repairs. This paper investigates the time and magnitude of the peak hydration temperature during microwave curing (MC) of six cement based concrete repair materials and a CEM II mortar. Repair material specimens were microwave cured to a surface temperature of 40-45 °C while their internal and surface temperatures were monitored. Their internal temperature was further monitored up to 24 hours in order to determine the effect of microwave curing on the heat of hydration. The results show that a short period of early age microwave curing increases the hydration temperature and brings forward the peak heat of hydration time relative to the control specimens which are continuously exposed to ambient conditions (20 °C, 60% RH). The peak heat of hydration of normal density, rapid hardening Portland cement based repair materials with either pfa or polymer addition almost merges with the end of microwave curing period. Similarly, lightweight polymer modified repair materials also develop heat of hydration rapidly which almost merges with the end of microwave curing period. The peak heat of hydration of normal density ordinary Portland cement based repair materials, with and without polymer addition, occurs during the post microwave curing period. The sum of the microwave curing and heat of hydration temperatures can easily exceed the limit of about 70 °C in some materials at very early age, which can cause durability problems.

Specimen preparation for nano-scale investigation of cementitious repair material

Cementitious Repair Materials (CRMs) in the construction industry have been used for many decades now and has become a very important part of activities in cement world. The performance of some of these CRMs when applied to retrofitting concrete structural elements is also well documented. However, the characterization of some of the CRMs at the micro- and nano level is not fully documented. The first step to studying materials at the microscopic level is to be able to fabricate proper specimens for microscopy. In this study, a special and newly developed class of CRM was selected and fabricated by Focused Ion Beam (FIB) using well-known “Lift-out” technique. The prepared specimen was later examined using various analytical techniques such as energy dispersive x-ray analysis using one of the highest and most stable Scanning Transmission Electron Holography Microscopy (STEHM) around the world. This process enabled understanding of the composition, morphology, and spatial distribution of various phases of the CRM. It was observed that the microstructure consisted of a very fine, compact, and homogenous amorphous structure. X-ray analysis indicated that there was considerable deviation between the Si/Ca ratios for the hydrated product.

Cement hydration and microstructure in concrete repairs with cementitious repair materials

One of the key parameters for the performance of concrete repairs is the quality of the interface between repair material and concrete substrate. To understand the properties of the interface in concrete repairs with cementitious repair materials, cement hydration and microstructure were experimentally studied using non-evaporable water test, mercury intrusion porosimetry, and scanning electron microscopy techniques. The experimental results reveal that the moisture exchange between repair material and concrete substrate results in a change of the moisture content in the repair material and thus affects the cement hydration process and pore structure development. Backscattered electron images demonstrate the existence of an interfacial transition zone of high porosity, since the cement particles of the repair material have a poor packing on the surface of concrete substrate.

Improving the Failure Mode of Over-Reinforced Concrete Beams Using Strain-Hardening Cementitious Composites

AbstractOver-reinforced sections fail suddenly by compression concrete crushing when their ultimate compressive strain has been exceeded but the longitudinal reinforcement strain has not yielded. This study investigates the use of cementitious repair materials for the compression side of over-reinforced concrete beams to change their failure mode to ductile failure. In this study, 11 over-reinforced concrete beams were cast (1 as a control specimen and 10 as strengthened beams). The study’s strengthening material was an ultra-high-performance strain-hardening cementitious composite (UHP-SHCC). The effect of shear connectors with the strengthening material was investigated. Meanwhile, replacement of the concrete cover, use of a welded wire mesh inside the additional layer, and concrete strength were tested. Crack pattern and failure modes were noted, and deflection behavior, failure loads, steel strains, and crack width were measured. The tests results showed that using strengthening UHP-SHCC material is a...

Nano-Modified Fly Ash Concrete: A Repair Option for Concrete Pavements

Efficient repair of concrete pavements typically requires a rapid-setting material to accelerate opening the road to traffic. While numerous high-early-strength cementitious repair materials are commercially available, many of them are vulnerable to premature deterioration. On the other hand, despite its improved long-term performance, concrete incorporating fly ash is rarely used as a repair material due to the delay in setting time, strength gain, and microstructural development at early ages. Nevertheless, these performance limitations can be mitigated by incorporation of nanoparticles (for example, nanosilica) in fly ash concrete. In this study, an effort was made to develop nano-modified fly ash concrete as a repair material for concrete pavements. The performance of the newly developed mixtures was compared to that of two commercial cementitious products. The results indicate that the nano-modified fly ash concrete has balanced performance in terms of hardening time, strength development, bonding with substrate concrete, and resistance to infiltration of fluids and salt-frost scaling.

Performance Evaluation of Different Repair Concretes Proposed for an Existing Deteriorated Jetty Structure

Performance of different cementitious repair materials is studied as part of an ongoing repair project on an existing reinforced concrete jetty in harsh environment of Persian Gulf. Concrete repair materials with different cementitious binders including ordinary portland cement, silica fume, and ground granulated blast furnace slag were tested. Different performance criteria such as mechanical properties, durability characteristics, and dimensional compatibility with substrate concrete were studied according to a proposed rational approach. It is concluded that a repair technique containing ternary pozzolanic materials has the best performance and could be proposed for marine environment.

Deterioration of Bond Integrity between Repair Material and Concrete due to Thermal and Mechanical Incompatibilities

The slant shear test highlighted by British Standard 6319 No. 4 was used to evaluate the bond strength between selected repair materials and parent concrete. Seven resinous and six cementitious repair materials were used to repair fractured specimens. Repaired test specimens were aged by subjecting them to heat-cool cycles that simulated repeated extreme summer day in the southern part of the United States (e.g., Mississippi). The results of thermal cycling showed a strong correlation between the difference in the coefficient of thermal expansions, as well as the difference in elastic moduli, between repair materials and concrete, and the reduction in bond strength. Although resinous materials possessed a higher bond strength to concrete, they showed higher reduction of bond strength than cementitious materials.

Analysis of Compatibility between Repair Material and Substrate Concrete Using Simple Beam with Third Point Loading

Due to the availability of a wide variety of repair materials in the industry with a wide range of physical and mechanical properties, it is important to determine the compatibility of a repair material with the substrate concrete. In this paper, the writers investigate the compatibility between selected cementitious repair materials and a substrate concrete using a modified ASTM C 78 test procedure. The flexural strength and load-deflection curves of composite beams prepared with substrate concrete and repair materials were compared to the results from the substrate beam to assess the compatibility. In addition, the influence of three different types of curing conditions was evaluated on the compatibility between the repair materials and substrate concrete. Compressive strength, flexural strength, split tensile strength, and drying shrinkage of the repair materials and substrate concrete were individually measured to aid in the analysis of compatibility between repair and substrate materials. It was observed that not only did significant differences in strength between the repair material and substrate concrete cause incompatible failures, but high drying shrinkage of the repair materials was also found to cause incompatible failure. These findings validate previous research findings.

Flexural Performance of RC Beams Repaired with Commercial Repair Materials

Different types of cementitious repair materials are commercially available in the local market. Almost all repair material suppliers claim that their products are most suitable for concrete repair under different environmental and loading conditions. This necessitates the need to check all aspects of the repair materials which include their behavior when used in structural elements. The objective of this research was to investigate the performance of the most commonly used cementitious repair materials when used to repair structural elements. This was achieved through the evaluation of the flexural performance of 24 RC beams repaired using nine selected types of the most commonly used repair materials (supplied by three leading suppliers in the country). The results were compared with two identical beams repaired with concrete and also with two identical beams cast with concrete monolithically (no repair). The results showed that the repair materials subjected to tensile stresses had no significant contribution (to beam response) compared to normal concrete. However, the influence of the repair materials was much better when used to repair structural parts subjected to compressive stresses.

Flexural behavior of reinforced concrete beams with cementitious repair materials

Flexural behavior of reinforced concrete beams with cementitious repair materials

Flexural behavior of reinforced concrete beams with cementitious repair materials

There is an urgent need to develop efficient methods for the repairs and rehabilitation of currently existing structures, they are being deteriorated over time, and also the magnitude of loadings keeps rapidly increasing for such structures. Possibly one of the most challenging taks in the rehabilitation processes is to upgrade the overall capacity of deteriorated concrete structures. Recently, considerable efforts are being directed toward developing new construction materials. This paper presents the experimental study for the flexural behavior of reinforced concrete beams repaired by Polymer Cement Mortar (PCM) and Ordinary Portland Cement Mortar (OPCM) in the tension region. Tests were performed for eight reinforced concrete beams with varying reinforcement ratios, repair materials and repair lengths. Emphasis is given to overall bending capacity, deflection, ductility index, failure mode and crack development of repaired beams. The results are compared with those from the control beam.