Repair Materials For Concrete Structures Research Articles

Experimental and Numerical Study on Flexural Behavior of Concrete Beams Using Notches and Repair Materials

In a concrete beam, cracking is generated on the tension side under the effect of flexure, shear, and torsional loadings. Accordingly, these weak concrete members require repair and/or strengthening to increase or restore their internal load capacity. In the current experimental and numerical investigations on concrete beams, the impact of using notches with different width to depth ratios on the ultimate flexural load under a three-point test was considered. Further, the flexural behavior performance of a notched concrete beam repaired using the three repair materials—cement mortar, bacterial mortar, and adhesive—was also examined. Consequently, a comparative study was implemented between the experimental and numerical results. A concrete damage plasticity (CDP) model was used for the finite element numerical analysis of the beams. The differences in numerical and experimental measured results ranged from 0.65 to 22.20% for the ultimate load carrying capacity. As the notch size increased, the ultimate load carrying capacity of the beam reduced. Additionally, a linear regression model was used to predict the ultimate load values at a notch width interval of 5 mm up to a maximum notch width of 100 mm. It was observed that the ultimate load capacity for a repaired beam increased as compared to the notched beam for all three repair materials under consideration. And the maximum ultimate load increased in the case of notched beams repaired using adhesive. Furthermore, in comparison to the cement mortar, the performance of the bacterial mortar in terms of the ultimate load was more. The bacterial mortar was found to be more sustainable and more durable as a repair material for concrete structures.

Response of hybrid concrete incorporating eco-friendly waste PET fiber: Experimental and analytical investigations

• Eco-friendly high strength concrete containing waste PET fiber was used as a repair material for deteriorated normal concrete. • Structural and material performance of hybrid RC beams, made with normal concrete and PET fiber HSC, were examined. • Interfacial surface roughened by sand blast technique provided proper bonding between normal concrete and PET fiber HSC. • Analytical solution for the behavior of RC hybrid beams, with PET fiber, was developed considering aspect ratio and content of fiber used. High Strength Concrete (HSC) has the ability to strengthen deteriorated concrete members. The performance of HSC incorporating waste polyethylene terephthalate (PET) fibers as a repair material for concrete structures has not been examined extensively in current literature. Thus, more investigations are considered essential in this direction. This endeavor is devoted to examining the flexural behavior of hybrid reinforced concrete beams (HRCB) made with normal concrete (NC) repaired by or bonded to HSC containing waste PET fibers (FRC). The workability and mechanical properties of fresh and hardened FRC were investigated. Moreover, the efficiency of HSC overlay as a repair material for NC substrate was evaluated through a slant shear test (SST) which considered four modes of roughening of the NC interfacial surface. A third-point load test was used to evaluate the structural behavior of the HRCB. The results of the slant shear and flexural tests indicated that the highest bond strength among all of the members was achieved by employing sandblasted and grooved interfacial surfaces between NC and HSC. The flexural capacity for the beams was also predicted via modification of the ACI 318–19 and Jarquio’s models, using regression analysis of present experimental records. Good matching was observed between the predicted and experimental ultimate load of the hybrid beams. Finally, the testing observations are noteworthy in the direction of using FRC as a repair material.

Hydraulic Resistance Analysis Based on Cohesive Strength and Toughness of Synthetic Polymerized Rubber Gel Used as Water-Leakage Repair Material for Concrete Structures

As construction in urban centers increases internationally, many concrete infrastructures are being built at 100 m or more underground, and the influence of groundwater on these facilities is also increasing. Accordingly, the importance of waterproofing and leak-proofing technology for securing long-term durability and safety of underground concrete facilities has been greatly emphasized. The most important required performance of such leak repair technology is to withstand structural behavior and groundwater pressure well. Currently, as a leak repair material for underground concrete facilities, a synthetic rubber-based polymer rubber gel with adhesive flexibility is used internationally. However, quantitative data on how deep the material can perform underground are lacking. In general, the water pressure resistance evaluation of leak repair materials only checks whether it withstands the water pressure of 30 m (0.3 MPa) underground. Therefore, in this study, the toughness of the synthetic rubber polymerized gel (SPRG) leak repair material was calculated using three factors: viscosity, cohesive strength (adhesion strength), and elongation, and an analysis method that can be replaced with water pressure resistance was proposed. In addition, in the correlation between toughness and underground water pressure, it was possible to find out the thickness of the leak repair material used by the underground depth. As a result, it was possible to know the required thickness of the leak repair material according to the depth of the structure to be built underground.

Bond strength evaluation of polymer modified cement mortar incorporated with polypropylene fibers

Bond strength is the adhesion between an overlay and a substrate mortar; it is the key parameter ensuring durability and having a monolithic system. A proper bond is essential to resist any stresses associated with volume changes, freeze-thaw cycles, and vibrations at the interface. Polymer-modified cement mortar (PCM) is one of the most well-known adhesive materials, used widely as a binding agent in engineering construction. Two forms of PCM were investigated in this study. These products are known commercially as Sika MonoTop®− 620, a form of repair material for concrete structures, and DCP Cemfix 2CS, which is occasionally used as an adhesive to connect the tiles to the concrete base. The effect of polypropylene fiber with volume fractions of 0, 0.5, 0.75, and 1 % was investigated using three different water-to-binder ratios. A total of 24 distinct mixes were made. The material's compressive strength, flexural strength, and bond strength were all determined. The bond strength of each mix was assessed using the Slant-Shear and Pull-off test methods. The bond strength values derived by Slant-Shear and Pull-off tests had a high correlation, about 85 %. Furthermore, bond strength was connected with the material's compressive and flexural strength with 95 % and 86 % with Slant-Shear, and 80 % and 76 % with Pull-off, respectively.

Cement-Based Repair Materials and the Interface with Concrete Substrates: Characterization, Evaluation and Improvement.

Surface damages usually occur in concrete structures. In order to restore the functions and prolong the service life of concrete structures, their surface damages should be repaired in time. This paper reviews the main requirements for repair materials for concrete structures and the most used inorganic repair materials, such as cement-based materials, alkali-activated materials and polymer modified inorganic repair materials. Moreover, techniques to characterize and even improve the interfaces between these repair materials and concrete substrate are summarized. Cement-based material has the advantages of good mechanical properties and consistency with concrete substrate while having the problems of high shrinkage and low flexibility. Polymer modified materials were found as having lower shrinkage and higher flexural strength. Increasing the roughness or humidity of the surface, adding fibers and applying interfacial agents can improve the bond strength between cement-based repair materials and concrete substrates. All of these repair materials and techniques can help to build a good interfacial bonding, and mechanisms of how they improve the interface are discussed in this article. These are of great importance in guaranteeing the effectiveness of the repair of the concrete surface and to guide the research and development of new repair materials.

Preparation of Magnesium Ammonium Phosphate Mortar by Manufactured Limestone Sand Using Compound Defoaming Agents for Improved Strength and Impermeability

Magnesium ammonium phosphate cement (MAPC) mortar has recently risen up as high performance rapid repair material for concrete structures. But high costs of the raw materials limit its restoration and maintenance projects on a wide application range. This study proposes the use of manufactured limestone sand with lower cost and wider range of sources in replacement of quartz sand as fine aggregates to produce MAPC mortar. However, the limestone fines of manufactured sand were initially found to have negative effects on the performance of MAPC mortar, causing significant blistering and volume expansion and decreased compressive strength and interfacial bonding strength. To minimize these negative effects, polyether modified silicone (PMS) defoamer and its compound use with mineral admixtures Portland cement and silica fume were investigated on the effectiveness in reducing expansion and improving other properties of MAPC mortar. Results showed that the compound use of PMS defoamer and Portland cement as a new defoaming formula effectively reduced the volume expansion from 7.92% to 0.91%. The compressive strength and interfacial bonding strength were significantly improved by over 34% and 60% respectively. Moreover, this defoaming formula showed improvements in water-tight performance and resistance to chloride penetration. According to the mercury intrusion porosimetry (MIP) analysis, the total porosity of MAPC mortar after defoaming treatment was decreased by about 40% and the pore structure was also modified to be finer by significantly reducing the harmful macropores. Overall, the use of manufactured limestone sands as fine aggregates turned out to be a feasible and economic approach for promoting the filed application of MAPC mortar.

An Experimental Investigation on the Effects of Limestone Fines in Manufactured Sands on the Performance of Magnesia Ammonium Phosphate Mortar

Magnesium ammonium phosphate cement (MAPC) prepared with ammonium dihydrogen phosphate (NH4H2PO4, ADP) and dead-burned Magnesium oxide (MgO) is a new type of rapid patch repair material for concrete structures. In order to reduce the material costs of MAPC mortar, manufactured limestone sands, being a more widely-available resource with lower cost, was investigated in this study as an alternative to quartz sands for the preparation of MAPC mortar. The limestone fines in manufactured sands were found to be the key factor that influences properties of MAPC mortar by causing bubbling and volume expansion before hardening. As a result, the mechanical strength of MAPC mortar decreased with the increasing content of limestone fines due to increased porosity. According to microstructure analysis, the mechanism of these negative effects can be inferred as the reaction between limestone fines and ADP with the gas generation of CO2 and NH3. This reaction mainly occurred during a short period before setting while most limestone fines remained unreactive in the hardened MAPC mortar. Based on the above detailed experimental findings on the effects of limestone fines in manufactured sand on the properties of MAPC mortar, this paper pointed out that effective defoaming methods for inhibiting bubbling was the key to the utilization of manufactured sands in preparation of high performance MAPC mortar.

Eco-UHPC as Repair Material-Bond Strength, Interfacial Transition Zone and Effects of Formwork Type.

A reduced carbon footprint and longer service life of structures are major aspects of circular economy with respect to civil engineering. The aim of the research was to evaluate the interfacial bond properties between a deteriorated normal strength concrete structure and a thin overlay made of Eco-UHPC containing 50 wt% of limestone filler. Two types of formwork were used: untreated rough plywood and surface treated shuttering plywood. The normal strength concrete elements were surface scaled using water jets to obtain some degradation prior to casting of the UHPC overlay. Ultrasonic pulse velocity (UPV), bond test (pull-off test), and Scanning Electron Microscopy (SEM) combined with Energy Dispersive Spectrometry (EDS) were used for analysis. Elements repaired with the Eco-UHPC showed significantly improved mechanical properties compared to the non-deteriorated NSC sample which was used as a reference. The bond strength varied between 2 and 2.7 MPa regardless of the used formwork. The interfacial transition zone was very narrow with only slightly increased porosity. The untreated plywood, having a rough and water-absorbing surface, created a surface friction-based restraint which limited microcracking due to autogenous shrinkage. Shuttering plywood with a smooth surface enabled the development of higher tensile stress on the UHPC surface, which led to a more intensive autogenous shrinkage cracking. None of the formed microcracks penetrated through the entire thickness of the overlay and some were partly self-healed when a simple water treatment was applied. The project results showed that application of UHPC as repair material for concrete structures could elongate the lifespan and thus enhance the sustainability.

Strength Development Characteristic of Cementless Mortar for Repair of Concrete

Repair materials for concrete structures are often required to exhibit high bond strength at a concrete substrate, and it typically consists of ordinary Portland cement (OPC) incorporating expensive admixtures at a low water-to-binder ratio. Meanwhile, cementless mortar employs alkali-activation of cementless and pozzolanic precursors such as ground granulated blast-furnace slag (GGBFS) and fly ash (FA). The final product develops strength relatively faster than OPC, and its strength can be flexibly talyored by controlling the type and dosage of the activator. The present study investigates the strength development characteristic of cementles mortar for use in repair of concrete structures. Independent variables include mix proportions and curing conditions, which were chosen to optimize the performance of the cementless mortar.

Material selection for repair of structural concrete using VIKOR method

The premature failure of repaired concrete structures has become a big concern for civil engineers in recent years. While premature failure can be greatly reduced through the selection of an appropriate repair material, civil engineers must take into account a large number of conflicting criteria for candidate repair materials to make the final decision. In this paper, a procedure coupled with the VIKOR method is proposed to obtain the best repair material for concrete structures. This procedure can aid civil engineers in modeling and selecting suitable repair materials according to a set of predefined criteria. A case study is included to validate the accuracy of the outcomes of the proposed procedure. Since weights play a significant role in the ranking of results for the repair materials, sensitivity analysis is conducted using three different methods for assigning weights to find more reliable results.

Evaluation of the Compatibility of Repair Materials for Concrete Structures

This study evaluates the compatibility of repair materials for concrete bridge decks. A new compatibility test set-up was designed and tested based on the concrete bridge deck cracking and delamination mechanism theory. The repair materials used in this study include lab formulated inorganic nano-aluminum silicates and commercially available organic two-part epoxy systems. Two different lab test-setups are proposed in this study: a prototype and a full-scale test. The developed test procedures were effective in communicating results in terms of compatibility of material properties, performance and quality. The prototype beams test can successfully serve as a small scale screening test providing insights on materials selection for the full-scale beam tests. The full-scale beams demonstrated the compatibility of the repaired system by providing data on authentic field conditions. Based on the observations it can be concluded that the proposed test setup is effective in examining the concrete bridge deck repair materials performance and selection, and compatibility in terms of mechanical properties and further guarantee the repaired structure safety.

TRC or CFRP strengthening for reinforced concrete beams: An experimental study of the cracking behaviour

Cement-based composites are emerging as strengthening and repair materials for concrete structures, because of their advantages related to fire safety and their relatively low cost. To be able to compete with the existing Carbon Fibre Reinforced Polymer (CFRP) solutions, the cement matrix must be reinforced with textiles in high fibre volume fractions. Extensive experimental verification of the contribution of these Textile Reinforced Cements (TRC) as external reinforcement with regard to the load bearing and cracking behaviour of reinforced concrete beams is still necessary. This paper compares the existing CFRP and TRC solutions with a strong focus on the cracking behaviour by performing seventeen bending experiments monitored with Digital Image Correlation (DIC). It shows that the TRC-reinforced beams exhibit a similar cracking behaviour to the CFRP-reinforced beams. Moreover, precracking of the concrete beams before the application of the external reinforcement reduces only the initial high stiffness, but does not influence the cracking behaviour, failure mode or ultimate load. These test results indicate the relevance of non-precracked tests that have been performed in the past.

The effect of using high strength flowable system as repair material

The maintenance and the repair of concrete structures have become more needed in the field of Civil Engineering. The selection of repair materials for concrete structures requires an understanding of the material behavior. Therefore, this research is conducted to provide a clear indication and understanding of the behavior and structural performance in engineering construction. The combined system of substrate concrete with different mix proportions of flowable high strength system reinforced by hybrid fibers was used to study its mechanical properties. The experimental tests are: compressive strength, splitting tensile strength, flexural strength and pull-out test. It was found that the high strength flowing concrete (HSFC) provides the best performance when the compressive strength of the repaired system is needed, whereas the high strength flowable mortar (HSFM) has the best performance when the tensile strength of repaired system is required. The best value of pull out test was obtained from using the flowable high strength mortar reinforced with 1.5% steel fiber +0.25% palm fiber +0.25% Barchip fiber as the repair material, whereas, the least value of pull-out test was obtained from samples using epoxy.

Feasibility of Basalt Fiber Reinforced Inorganic Adhesive for Concrete Strengtening

Phosphate based binders are high early strength materials with a short setting time. Usually, they are used as rapid repair material for concrete structures. The feasibility of a basalt fiber reinforced inorganic binder for strengthening concrete was studied. We successfully compounded suitable phosphate binder (PB) for concrete strengthening. In the current paper, phosphate binder was to adjusted to has excellent workability, suitable setting time and fluidity. Compressive strength of phosphate binder mortar, bonding strength between PB and Portland cement mortar, and strengthening effect of PB sticked basalt fiber on concrete beam were measured. Results showed that PB has excellent adhesion with Portland cement mortar. The strengthening effect of basalt fiber reinforced PB composite on concrete beam is evident. It is feasible that concrete strengthening by basalt fiber reinforced inorganic adhesive.

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.

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.