Patch Repair Material Research Articles

Hybrid alkali-activated fly ash-Portland cement binders with modified polymer as patch repair

The alternative patch repair derived from hybrid alkali-activated binders (HAAB) were investigated in this paper. The HAAB mortar was produced with fly ash (FA), Portland cement (PC), and polymer-modified material (PMM). The additives (PC and PMMs) were used to replace FA at the dosage of 30 % by weight of binder. The proportions of PC-to-PMM at 30:0, 20:10, 10:20, and 0:30 were investigated. Sodium silicate (NS) and sodium hydroxide (NH) solutions were used as the alkaline activators. Constant NS-to-NH ratio of 2.0 and liquid/solid binder ratio of 0.60 were used for all mixtures. Experimental results showed that the setting time, compressive and shear bond strengths of the HAAB mortars met the requirement for repair material as specified by ASTM standard. The 7-day bond strength increased with increasing PMM replacement up to an optimum level; thereafter, it started to decline. A combination of PC and PMM in FA-based HAAB enhanced the adhesion at contact zone. Moreover, the HAAB mortars showed greater durability compared to conventional PMMs after immersion in sulfate and acid solutions, as evidenced by its relatively low strength loss. The increased formation of ettringite might be the main factor for the substantial reduction in the strength of PMM mixes. Therefore, the HAAB mortar is an attractive choice for patch repair material in terms of excellent durability, high bond strength, cost-effectiveness, and low carbon footprint compared to conventional PMM.

Creep Behavior of Fiber Reinforced Mortars and Its Effect to Reduce the Differential Shrinkage Stress

This research aims to develop durable repair materials that can resist shrinkage cracking by exploring the role of creep in reducing shrinkage stress. In this regard, the creep effect can only be quantified if an accurate creep prediction model and theoretical analysis of the shrinkage stress in the patch repair system exist. For this purpose, the research was carried out in the following sequences: first, the research investigated the short-term creep of the patch repair materials containing accelerator and micro-synthetic fibers in the 0.00–0.12% volume fraction range. This short-term creep was measured on five-cylinder specimens (having a diameter of 75 mm and a height of 275 mm). Three specimens were used to determine the deformation of the repair material under unloading conditions, while those remaining were used to determine the total deformation under loading conditions. The amount of creep deformation was determined by taking away the unloaded (shrinkage) and instantaneous (elastic) deformations from the total deformation of the loaded specimens. Secondly, a modified prediction model of ACI 209R-08 is introduced to accurately capture the rate and magnitude of the observed creep of the repair materials. Finally, a formulated theoretical analysis of shrinkage stress in the patch repair system was proposed to examine how creep potentially reduces the repair material's cracking tendency. The results show that the asymptotic value of the creep curve is attained at an earlier age and that its magnitude is greater than that of most concrete. The modified ACI 209R-08 prediction model can closely estimate the repair materials' creep behavior. The best-fit line, residual values, and coefficient of error analyses confirm the modified model's prediction accuracy. The analysis of tensile stress development in the repair layer suggests that creep can reduce stress by up to 50%. With such a reduction, the repair material is expected to be durable in resisting shrinkage and cracking tendency. Doi: 10.28991/CEJ-2023-09-08-014 Full Text: PDF

Analysis of Geopolymer Mortar Compressive Strength Based on Fly Ash and GGBFS as Patch Repair Material

Damages that often emerge in concrete include cracks, delamination, spalling, wear, fracture, porous, voids (perforated). These damages need to be repaired, one of which is by patch repair. With consideration of strength and frugality, a self-made repair material was developed using mortar as a base material, i.e., geopolymer mortar. Geopolymer mortar is a mortar with natural materials and materials that have a high content of silica oxide and alumina (such as Fly Ash and GGBFS) as a binder that must be activated with an alkaline activator in the form of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). The use of Fly Ash and GGBFS as a binder to replace cement in geopolymer mortar has a positive impact from an environmental point of view because it can reduce the use of cement and can reduce environmental pollution due to Fly Ash and GGBFS waste. In this research, the effect of variations in Fly Ash and GGBFS and variations in the molarity of NaOH on the compressive strength of geopolymer mortar were investigated, in order to obtain the optimum composition of the geopolymer mortar mixture that meets the requirements of compressive strength as a repair material. From the results of the research, the maximum compressive strength occurred in GF91 16 M mortar at 56 days of 73.77 MPa was obtained. Geopolymer mortar has a higher compressive strength and a cheaper price when compared to Sika Grout mortar so that the use of geopolymer mortar as a patch repair material is better than Sika Grout mortar in terms of strength and frugality.

Monitoring of repaired water leaks using surface wave tomography

Cracks with water leakage have been found in an underground concrete structure, and they have been repaired by injecting waterstop agents and applying patch repair materials after V-shaped removal of existing materials. Since recurrence of the problem has been frequently reported after the repair, test construction has been made by using more proper repair materials. However, an underground structure surrounded by earth is accessible only from the inside for inspection. The authors adopted the surface wave tomography which enabled single-side access soundness evaluation of internal concrete, without requiring the source and receiving sensors to be placed on the opposing sides of an object. The results confirmed the effectiveness of the repair, with the velocity structure found to have improved from that before the repair. It was also found that the velocity has already decreased at some repaired sites, and that they were in agreement with the locations of the recurrence of water leakage detected by the visual inspection. Detection of recurrence of water leakage is important because the water ingress from the surrounding ground is one of the factors leading to reduced durability of the underground structure. The findings of this study suggested that the technique would be also useful for subsequent monitoring.

INTERFACIAL BOND STRENGTH BETWEEN MICRO-SYNTHETIC FIBER-REINFORCED PATCH REPAIR MORTAR AND CONCRETE SUBSTRATE BASED ON PUSH-OFF TEST

A micro synthetic fiber-reinforced mortar has been developed as a patch repair material. The bond strength of this material is a crucial parameter for successful repair applications. The state of stress occurring at the interfacial plane between the repair material and the concrete substrate influences the bond strength requirements of patch repair material. Therefore, bond strength envelope criteria should be established using, among others, the interfacial adhesion and friction coefficient parameters. This research aims to determine the composite’s interfacial bond strength parameters (adhesion and friction coefficient) between micro-synthetic fiber-reinforced patch repair mortar (MSFRPRM) and concrete substrate by push-off tests. At this stage, the smooth joint texture limits the investigation. The fiber volume fraction and age of repair are considered. The tests were conducted at the age of 1, 3, 7, and 28 days. In addition to the laboratory experiment, this research used ATENA Science GiD to numerically simulate the push-off test and study the influence of the fiber volume on the adhesion and friction coefficient. The results show that at a fiber volume of 0.06%, the adhesion and friction coefficients increase from 1.15 to 2.33 MPa and 0.74 to 0.85, respectively, corresponding to age. Numerical simulation indicates that the maximum adhesion and friction coefficient occurs at the fiber volume fraction of 0.06%. Thus, the overall simulation results can be used in the future as a parameter to establish MSFRPRM and concrete substrate bond strength envelopes that will be useful for evaluating the suitability of MSFRPRM as repair materials under various states of stress. Keywords: Bond Strength, Concrete Patch Repair, Concrete Substrate, Micro-Synthetic Fiber-Reinforced Repair Mortar, Push-Off Test DOI： https://doi.org/10.35741/issn.0258-2724.58.1.20

STUDY OF A REPAIR EFFECT OF SAP-MIXED PATCH REPAIR MATERIL FOR RC MEMBER DETERIORATED BY CHLORIDE INDUCED CORROSION

The effect of Superabsorbent polymer (SAP) admixture in patch repair materials on the adhesion to the base concrete and the protection performance of reinforcing bars was investigated. In the experiment, one side of RC joint specimens were exposed to water. Water leakage from the interface between the base concrete and the repair material was reduced in the SAP specimen compared to the conventional Polymer modified mortar specimen. In addition, the half-cell potential and polarization resistance of the SAP specimens showed noble and high values, respectively, indicating the inhibition of corrosion of reinforcing bars.

Effective Use of Sacrificial Zinc Anode as a Suitable Repair Method for Severely Damaged RC Members Due to Chloride Attack

In many cases, the repair strategy by using sacrificial anodes for cathodic protection in real RC structures requires additional zinc anodes after several years due to the decreasing protective area. This experimental study evaluates the effectiveness of time lag application of sacrificial anode cathodic protection applied to RC beam specimens that deteriorated severely due to chloride attack. In the experiment, sacrificial anodes and cathodic protection (SACP) were applied to 41-year-old RC beam specimens exposed to natural marine environments in which the embedded steel bars were significantly corroded. The repair work was performed in three stages. Instant-off and rest potential tests of steel bars were conducted periodically to demonstrate the time-dependent depolarization value. In the first stage, a polymer-modified mortar as a patch repair material was cast to replace the concrete in the middle tensile part with small sacrificial anodes embedded in the mortar. After the protective current reaches an equilibrium state, the sacrificial anodes are disconnected from the steel bars for a year, defined as the second stage. During the one year in the second stage, the steel bar in the patch repair area remained passive, without any sign of corrosion. As for the third stage, additional sacrificial anodes were installed in the existing concrete part to protect the steel in it. From one year of observation after applying sacrificial anodes to old concrete parts, the time lag SACP application of both in patch and non-patch repair parts was clarified to be effective in stopping the corrosion of steel bar in both parts until 20–30 years based on the service life prediction. Doi: 10.28991/CEJ-2022-08-07-015 Full Text: PDF

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.

Microstructural evolution/durability of magnesium phosphate cement paste over time in neutral and basic environments

This study investigates the evolutions of the mineralogy, pore solution and porosity of magnesium potassium phosphate cement pastes (MKPC) over time in neutral and basic environments, media that MKPC pastes might encounter when used as patch repair materials or as stabilization materials for hazardous wastes. Mineralogy evolutions were characterized by X-ray diffraction/Rietveld (XRD) and thermogravimetric analyses (TGA) and completed with scanning electron microscopy (SEM/EDX) microanalyses. Pore solution compositions (ICP-OES, IC) and the porosity of the materials were also analyzed. The results showed an amorphization of MKPC pastes over time that might be related to structural changes for the K-struvite phase. Achieving chemical equilibrium between the cementitious waters and the MKPC pore solution can result in porosity evolutions within the materials. Transport and mechanical changes might be expected, especially for MKPC pastes kept in basic media, since K-struvite [MgKPO4·6H2O], could be partially dissolved, leading to a higher total pore volume.

Experimental investigation on the behaviour of patched reinforced concrete column under eccentric loading: a case of compression failure

The performance of reinforced concrete (RC) element may be deficient for a variety of causes. Correct actions should be taken to resume the performance of the deficient element to maintain the strength and serviceability of the structure. A deficient RC column element may be identified in the form of spalling of concrete cover. A patching method could be selected to recover the damaged area and, hopefully, regain the strength of the damaged RC column to its original value. This research aims to investigate the suitability of patch repair material to recover the performance of damaged RC column. The investigation is carried out by comparing the behaviour of patched RC columns with the corresponding normal RC column. The eccentric loading has been set up in this investigation to induce compression failure of the RC columns. The simulated area of damage is patched using unsaturated polyester resin mortar (UPR mortar). The results indicate that the mode of failure is not induced at the patched sections. The presence of patching causes a redistribution of stress at the patched section in such a way, so a higher stress transfer occurs in the undamaged zone and in the longitudinal reinforcements compared to those of the normal column. The capacity of the patched RC columns is only 71–92% of the normal RC column.

Experimental Investigation on Mechanical Properties of SBR-Modified Mortar with Fly Ash for Patch Repair Material

Experimental Investigation on Mechanical Properties of SBR-Modified Mortar with Fly Ash for Patch Repair Material

Evaluation of Repair Effect of Patch Repair Materials Containing Fly Ash and Lithium Nitrite

Evaluation of Repair Effect of Patch Repair Materials Containing Fly Ash and Lithium Nitrite

Alternative patch repair materials for rebar corrosion damage

One of the most common methods adopted in the rehabilitation of corrosion-damaged concrete is the patch repair procedure. However, in practice this method has shown to often be unreliable as a consequence of the widespread occurrence of shrinkage induced cracking and poor substrate-patch adhesion leading to debonding of the patch repair. From a practical point of view, such failed repair systems essentially restore the repaired concrete back to a deteriorated state. There is a common belief that repairing concrete with specialised proprietary repair materials would guarantee durability. However, the widespread premature failure of patch repairs conducted using such materials has proven the contrary. This paper presents an understanding of the materials and issues concerning the durability and serviceability of concrete patch repairs, with the aim of identifying alternative non-structural patch repair materials for the effective repair of corrosion-damaged concrete structures. The potential patch repair materials researched were polymer-cement concrete (copolymer of vinyl acetate and ethylene with 5% cement replacement) and 60%, 80% and 100% fly ash (FA) mortar. Patch repairs were conducted on substrate moulds to test application and observe cracking/debonding occurrence. Furthermore, compressive strength, durability index, accelerated drying shrinkage, restrained shrinkage, workability and scanning electron microscopy (SEM) tests were conducted to determine the properties of the materials developed with reference to performance requirements of durable concrete repairs. It was concluded that the 60% FA and polymer-cement concrete repair materials had the best overall performance. This research established that innovative alternative repair materials such as a 60% FA or polymer-cement concrete material, can be developed for non-structural patch repairs with improved long-term performance relative to conventional materials.

Mechanical Properties of Unsaturated Polyester Resin (UPR)-Mortar and its Potential Application to Restore the Strength and Serviceability of Patched Reinforced Concrete Slab

Degradation of reinforced concrete could occur in various forms including spalling of concrete cover as a result of reinforcement corrosion. The degradation would shorthen the service life of the reinforced concrete structure. Patch repair method may be employed to recover this type of degradation using a suitable patch repair material. The authors have developed a patch repair material made from unsaturated polyester resin (UPR)-mortar. In this paper, the mechanical properties of this material which includes compressive strength, elastic modulus, flexural strength and bond strength are highlighted. Comparisons are also made with the normal mortar to emphasize the superior properties of UPR-mortar. Based on these properties, the potential application of UPR-mortar for repairing damaged reinforced concrete slab is examined through finite element simulation. It is pointed out that the tensile stress intensity in the UPR-layer is reduced with a consequence of reducing a risk of cracking in the repair zone. In addition, the patching of damaged zone with UPR-mortar could minimize the deflection.

Shear Failure of Patched Reinforced Concrete Beam without Web Reinforcements

Degradation of reinforced concrete (RC) element could lead to a reduction of its strength and serviceability. The degradation may be identified in the form of spalling of concrete cover. For the case of RC beam, spalling of concrete cover could occur at the web of the shear span due to corrosion of the web reinfocements. The shear strength of the damaged-RC beam possibly will become less conservative compared to the corresponding flexural strength with a risk of brittle failure. Patch repair could be a choice to recover the size and strength of the damaged-RC beam. This research investigates the shear failure of patched RC beam without web reinforcements with a particular interest to compare the shear failure behaviour of patched RC beam and normal RC beam. The patch repair material used in this research was unsaturated polyester resin (UPR) mortar. The results indicate that the initial diagonal cracks leading to shear failure of patched RC beam occur at a lower level of loading. However, the patched RC beam could carry a greater load before the diagonal crack propagates in length and width causing the beam to fail in shear.

Comparison of shrinkage related properties of various patch repair materials

A patch repair material has been developed in the form of unsaturated polyester resin (UPR)-mortar. The performance and durability of this material are governed by its compatibility with the concrete being repaired. One of the compatibility issue that should be tackled is the dimensional compatibility as a result of differential shrinkage between the repair material and the concrete substrate. This research aims to evaluate such shrinkage related properties of UPR-mortar and to compare with those of other patch repair materials. The investigation includes the following aspects: free shrinkage, resistance to delamination and cracking. The results indicate that UPR-mortar poses a lower free shrinkage, lower risk of both delamination and cracking tendency in comparison to other repair materials.

Cracking behaviour and its effect on the deflection of patched-reinforced concrete beam under flexural loading

Under the influence of aggressive environment, structural concrete could exhibit degradation in various forms. One of the symptoms of the degradation could be shown in the form of local delamination of concrete cover. Patching method could be a preference choice to repair this type of degradation to regain its structural performance and durability. This paper presents the structural behaviour of patched-reinforced concrete beam under flexural loading with particular interest on the use of unsaturated polyester resin (UPR) mortar as patch repair material. The repair area is replicated in the tensile zone of the beam. The behaviour investigated in this study is the cracking evolution of the patched – reinforced concrete beam and its effect on the deflection. It is shown that the higher strength of the UPR-mortar leads to a reduction in the intensity of cracks compared to that of un-repaired (normal) reinforced concrete beam. The lesser cracks intensity is beneficial to restore the flexural stiffness of the beam.

Performance of Cement-Based Patch Repair Materials in Plain and Reinforced Concrete Members

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.

Flexural Behaviour of Patch-Repair Material Made from Unsaturated Polyester Resin (UPR)-Mortar

Repair materials have been produced using an unsaturated polyester resin (UPR) as a matrix of a binder. Other ingredients are sand, cement and fly ash. No water is added to the mixture, so both the cement and fly ash only act as fillers. The UPR content is in the range of 50-60% by weight of total filler (cement plus fly ash). Their flexural performance has been characterized in term of the load-deflection behaviour, modulus of rupture, flexural modulus and stiffness. The results show that the flexural capacity of these materials at early age is at least 20 MPa, but they tend to have a lower elastic modulus. At early age, the higher amount of UPR content tends to gain a higher flexural characteristic. However, at later age there is a little influence of UPR content.

Bond Strength Characteristic of Concrete Patch Repair Material Made from Unsaturated Polyester Resin (UPR)-Mortar

Patch repair materials made from unsaturated polyester resin (UPR)-mortar have been investigated to determine their bond strength characteristic by slant shear test method. The relative mechanical properties of UPR-mortar and substrate concrete for composing the specimens are: lower modular and high strength ratio. The experimental results show that the combination of materials causes the observed bond strength are dictated by failure of substrate concrete. The actual bond strength could be higher as most of the specimens fail without separation of the UPR-mortar and substrate concrete at the bond plane.