Polymer Cement Mortar Research Articles

Efficiency of different BFRP-based strengthening techniques in improving flexural behavior of RC slabs

This study aims to analyze the flexural behavior of one-way reinforced concrete (RC) slabs strengthened with basalt fiber-reinforced polymers (BFRP). A total of six slabs were constructed and subjected to four-point flexural experimental tests. One slab served as the control specimen, and two slabs were strengthened with externally bonded (EB) BFRP sheets and near-surface mounted (NSM) BFRP bars, respectively. The other three slabs were strengthened with a composite reinforced mortar (CRM) layer composed of BFRP grids and polymer cement mortar, of which the BFRP grids for one slab were nonprestressed, and those for the remaining two slabs were prestressed. The experimental results indicated that the types of strengthening techniques including EB, NSM and CRM affected the failure mode of the strengthened slab. In comparison with the EB and NSM techniques, the CRM technique was more efficient in improving the serviceability and ultimate behavior of RC slabs, and it was considerably more economical. Meanwhile, the application of prestress in the CRM technique could further improve the cracking load and flexural stiffness of the strengthened slabs. Additionally, an analytical model was presented to predict the cracking and yield loads of the strengthened slabs, and the predictions showed a good agreement with the experimental results.

Failure behavior and reinforcing design of degraded tunnel linings based on the three-dimensional numerical evaluation

Void diseases behind the lining can commonly occur in tunnel structures. In this research, the failure behavior and reinforcing design of degraded tunnel linings with double void diseases were investigated. The effect of void disease on the three-dimensional distribution of inner force was explored. Subsequently, the stress distribution and plastic failure behavior of degraded tunnel linings with void diseases were studied. Then, the reinforcing behavior of the fiber-reinforced plastic (FRP)-polymer cement mortar (PCM) method was concerned. Finally, the distribution of potential cracking zone was discussed. The main results in this research indicated that the three-dimensional distribution of bending moment is greatly affected by the voids behind the lining, and the lining exhibits obvious bending outwards phenomenon within the void-affected zone. Concerning the failure characteristics between the double voids, plastic shear failure is prone to occur at the outer surface, but tensile-shear failure is likely to generate at the inner surface. In addition, the failure rate can be significantly affected by the spatial distribution of voids. Furthermore, the FRP-PCM method can significantly reduce the failure rate of the tunnel linings. Moreover, the distribution of potential cracking zone including the tensile cracking zone (TCZ), shear cracking zone (SCZ), and tensile-shear cracking zone (TSCZ) was determined.

Seismic Performance of Dam Piers Retrofitted with Reinforced Polymer Cement Mortar

The deterioration of existing reinforced concrete (RC) structures is regarded as a problem worldwide. In Japan especially, the deterioration of RC dam structures has become severe. Many such dams meet design standards that were in place at the time of construction but do not meet the current seismic design standards, and appropriate seismic retrofitting is required. If the dam pier, which is an important part of the dam related to water storage, is damaged by an earthquake, the gate cannot be opened or closed, and the amount of water stored cannot be controlled. Therefore, the seismic retrofitting of dam piers is a top priority. However, various construction restrictions exist for dam piers, such as only the cross-section on the downstream side can be reinforced, and not on the upstream side where water is stored. Thus, it is difficult to apply the same reinforcement method that is applied to the piers of general road bridges. Therefore, in this study, we confirm the effectiveness of the SRS method (seismic retrofitting using cement mortar for shotcrete), which is suitable for partial reinforcement. Specifically, the dam piers of four types of existing dams were modeled using the three-dimensional finite element method, and a seismic response analysis was performed by inputting two types of seismic waveforms having different characteristics. As a result, the reinforcement effect of this method was verified according to structural characteristics. Furthermore, the effect of the reinforcement range on the reinforcement effect was clarified.

Experimental study on bond behavior of corroded rebars coated by anti-corrosive materials in polymer cement mortar

This study investigates the bond behavior of anti-corrosive coated corroded rebars in a polymer cement mortar (PCM) as a common patching material to repair corrosion-induced damaged reinforced concrete structures. Cementitious and epoxy types of anti-corrosive coating materials are utilized. The corroded rebars are prepared by accelerated corrosion test in laboratory with a 5–10% target corrosion degree. The single effect of the coating materials on the bond behavior is investigated using coated round and deformed rebars. The combined effects of the corrosion and the coating materials are investigated using coated corroded deformed rebars. To thoroughly understand the bond behavior and mechanism, the effects of the corrosion and the coating materials on the change in the geometrical properties and surface roughness of the rebars are quantitatively analyzed by laser scanning tests. Finally, a two-end pull-out test is conducted to measure and investigate the bond-slip relationship, ultimate bond strength, bond toughness, and bond ductility.Similar to the findings on cementitious coated deformed rebar confined in concrete in a previous study by the authors, the results of the current study revealed that in the PCM, the cementitious coated rebar presents promising good bond performance regardless of the corrosion degree compared to the epoxy coated rebar. This is because when the ribs of the deformed rebars would deteriorate owing to corrosion, the rough surface of a cementitious coated rebar can sustain well its bond performance compared with the smooth and glassy surface of an epoxy coated rebar. Moreover, the direct effect of the surface roughness characteristics of these coating materials is clarified using coated round rebars. Consequently, the cementitious coated rebar achieves a considerably higher bond strength with a brittle behavior than the epoxy coated rebar, which presents a ductile behavior.

Residual bond strengths of epoxy and cement-bonded CFRP reinforcements to concrete interfaces after elevated temperature exposure

This paper presents the results from a comparative study on the residual bond performance of epoxy and cement-bonded carbon fiber-reinforced polymer (CFRP) reinforcement to concrete interfaces that experienced different levels of elevated temperature exposure. In total twelve groups of concrete beams strengthened with CFRP sheet and grids of the same tensile stiffness, through epoxy and cement-based adhesive bonding, respectively, were carefully prepared and exposed to different test temperature levels from 20 °C to 600 °C. Both polymer cement mortar (PCM) and ductile engineered cementitious composite (ECC) were adopted as the cement binder. The strengthened beams were tested under three-point monotonic bending after different levels of elevated temperature exposure. It was found that with increasing the exposure temperature, the failure modes of the strengthened beams shifted from debonding in a thin layer of concrete substrate to debonding near the fiber-adhesive interface and tearing off of CFRP grids from the ECC matrix. The peak loads of concrete beams strengthened with cement-bonded CFRP grids are at least 50% higher than their counterparts strengthened with epoxy-bonded CFRP sheets given the same temperature exposure.

The Influence of Cement Substitution by Biomass Fly Ash on the Polymer-Cement Composites Properties.

The generation of energy for the needs of the population is currently a problem. In consideration of that, the biomass combustion process has started to be implemented as a new source of energy. The dynamic increase in the use of biomass for energy generation also resulted in the formation of waste in the form of fly ash. This paper presents an efficient way to manage this troublesome material in the polymer–cement composites (PCC), which have investigated to a lesser extent. The research outlined in this article consists of the characterization of biomass fly ash (BFA) as well as PCC containing this waste. The characteristics of PCC with BFA after 3, 7, 14, and 28 days of curing were analyzed. Our main findings are that biomass fly ash is suitable as a mineral additive in polymer–cement composites. The most interesting result is that the addition of biomass fly ash did not affect the rheological properties of the polymer–cement mortars, but it especially influenced its compressive strength. Most importantly, our findings can help prevent this byproduct from being placed in landfills, prevent the mining of new raw materials, and promote the manufacture of durable building materials.

Bond durability of epoxy and cement- bonded CFRP reinforcement to concrete interfaces subject to water immersion

Durability is a critical concern for concrete structures externally bonded with fiber-reinforced polymer reinforcement. This paper presents the results from an experimental study which compared the bond durability of epoxy-bonded CFRP sheets and cement-bonded CFRP grids to concrete interfaces subjected to water immersion. Totally twelve groups of CFRP sheet or grid-strengthened concrete beams with a notch at their midspan were carefully fabricated through epoxy- and cement-based bonding systems and tested under monotonic loading before and after water immersion exposure, respectively. The cement binder included polymer cement mortar (PCM) and ductile engineered cementitious composite (ECC). The CFRP grids and sheets were designed with the similar tensile stiffness. The duration of water immersion ranged from 0 to 6 months. The test results indicated that debonding in concrete adjacent to the concrete-adhesive interface in accompany with a diagonal concrete crack near the notch was the main failure mode of the beams strengthened with epoxy-bonded CFRP sheet and ECC-bonded CFRP grid, while the tearing off of CFRP grids from the PCM matrix was the main failure mode of the beams strengthened with PCM-bonded CFRP grids. After water immersion exposure, the ultimate loads of the beams with cement-based CFRP grids were at least 50% higher than their epoxy-bonded counterparts, confirming the superior moisture durability of cement based bond to epoxy-bonded ones. The interfacial fracture energy was found to exhibit an exponential decline trend with water immersion duration.

A study on spalling behaviour of geopolymer mortars using ring restraint test

This paper presents the spalling behaviour of two types of geopolymer mortars (fly ash geopolymer and fly ash-slag geopolymer) using ring restraint specimens and is compared with normal cement mortar and polymer cement mortar. All mortar specimens are exposed to fire according to RABT 30 fire curve. Spalling depth, area and volume of all mortar specimens are measured to grade the spalling performance according to Japan Concrete Institute (JCI) spalling evaluation guide. Restraint stress, vapour pressure and temperatures at various depths from heated surface of all mortar specimens are also measured to evaluate the spalling behaviour. Results show that the fly ash-slag geopolymer mortar, normal cement mortar and polymer cement mortar spall compared to no spalling of fly ash geopolymer mortar. However, micro cracking is observed on the heated surface of fly ash geopolymer mortar specimen. Among the three mortars which showed spalling, the fly ash-slag geopolymer mortar took longer time to spall. The moisture content of both geopolymer mortars is lower than that of normal cement mortar and polymer cement mortar and this might be the reason for better spalling behaviour of former than that of latter mortars. Based on JCI spalling evaluation criteria the fly ash geopolymer mortar exhibited much better performance than the other mortars. Sharp increase in vapour pressure and sudden drop of vapour pressure are observed in all three mortar specimens which showed spalling behaviour, except the fly ash geopolymer mortar where no such sudden drop in vapour pressure is observed.

Quantitative assessment on the reinforcing behavior of the CFRP-PCM method on tunnel linings

In this paper, the carbon fiber reinforced plastic (CFRP) grids embedded in polymer cement mortar (PCM) shotcrete (CFRP-PCM method) was conducted to repair the degraded tunnel linings with a cavity. Subsequently, the reinforcing effect of the CFRP-PCM method under different degrees of lining deterioration was quantitatively evaluated. Finally, the limit state design method of the M-N interaction curve was conducted to determine whether the structure reinforced by the CFRP-PCM method is in a safe state. The main results indicated that when the cavity is at the shoulder, the lining damage rate is more serious. In addition, the remarkably reinforcing effect on the degraded tunnel linings could be achieved by applying a higher grade of CFRP grids, whereas the optimization effect is no longer obvious when the grade of CFRP grids is too high (CR8); Furthermore, it is found that the M-N numerical values of the ten reinforcing designs of the CFRP-PCM method are distributed outside the corresponding M-N theoretical interaction curves, and these designs should be avoided in the corresponding reinforcing engineering.

Experimental study on bond behavior of interface between fiber-reinforced polymer grids and concrete substrate

The aim of this study is to investigate the bond behavior of the interface between fiber-reinforced polymers (FRP) grids and concrete substrate. The examined parameters were as follows: (a) FRP grid widths (50, 100, and 150 mm); (b) FRP grid types (basalt, glass, and carbon FRP grids); (c) bonding material types (polymer cement mortar and epoxy resin); (d) FRP product types (FRP grids and sheet). Sixty bonded joint specimens were fabricated and subjected to single-shear experimental tests. The results indicated that the bond behavior of the FRP grid–concrete interface was significantly influenced by the width ratio of the FRP grids to concrete specimen, FRP grid stiffness, and bonding material type. In comparison with the FRP sheet-concrete interface, the FRP grid–concrete interface possessed significantly higher interfacial fracture energy, even though the stress transfer mechanism of this interface was more complicated. Additionally, based on the regression analysis of experimental data, empirical models for the width factor, bond–slip relationship, effective bond length, and bond strength of the FRP grid–concrete interface were developed.

Recycled Nylon Fiber from Waste Fishing Nets as Reinforcement in Polymer Cement Mortar for the Repair of Corroded RC Beams.

Waste fishing nets were utilized as recycled nylon (RN) short fiber to improve the mechanical properties of cement mortar. RN and manufactured polyethylene (PE) fibers were added to polymer cement mortar (PCM) as a reinforcement, and fiber-reinforced PCM was sprayed on the section of reinforced concrete (RC) beams. Normal RC beams and the upgraded RC beams were placed in the tidal zone for 14 months to induce rebar corrosion. Consequently, a repair operation took place by the removal of the concrete cover then spraying fiber-reinforced PCM. The tested RC beams were subjected to four-point flexural tests to study their load-carrying capacity. It was found that the fibers helped transfer stresses through cracks and distribute stresses by transforming a single wide crack into many small cracks. Overall, the experimental results showed that recycled nylon fibers from waste fishing nets have great potential to be used as a strengthening fiber in cementitious material.

Influence of Lowered Temperature on Efficiency of Concrete Repair with Polymer-Cement Repair Mortars.

This paper presents research dealing with the evaluation of the efficiency of concrete repairs with polymer-cement mortars made at low temperatures with two types of cement and modified by copolymer acrylic-styrene. The low temperature used for the tests, of about 8 °C, is representative for Central Europe, and was established based on the analysis of mean temperatures in Poland during the last 45 years. A comparative analysis of the basic properties of the mortar tested, important from the point of view of repair efficiency, was performed, i.e., flexural and compressive strength, modulus of elasticity, adhesion to the substrate, and porosity for mortars applied and cured at 8 °C and 21°, respectively. The studies were conducted using standard methods and supported with an assessment of microscopic images (1000× magnification). It was shown that when the temperature of polymer-cement composite (PCC) mortar application is lowered to values slightly exceeding the minimum film-forming temperature (MFT) temperature of the polymer modifier, the type of cement determines the effectiveness of the repair. Only for PCC mortar with CEM I sulfate-resistant types of cement was it possible to achieve the same strength parameters as at 21 °C, during 28 days of mortar curing, and at a lowered temperature. Starting from day seven of setting at both above-mentioned temperatures, a relation between the values of the flexural and compressive strength expressed as a quotient of these values, amounting to ca. 0.14–0.19, was found.

Study on Physical Properties of Mortar for Section Restoration Using Calcium Nitrite and CO2 Nano-Bubble Water.

This study investigated the physical properties of section-restoration mortar with calcium nitrite (Ca(NO2)2) and carbon dioxide (CO2) nanobubble mixing water to develop materials and methods for the repair and reinforcement of cracks in reinforced concrete (RC) structures. As the calcium nitrite content increased, the generation rate and generated amount of nitrite-based hydration products also increased, owing to the rapid reaction between NO2− ions in calcium nitrite and C3A(Al2O3). Further, the reaction with C3S and C2S was accelerated, thereby increasing the generation rates of Ca(OH)2 and C-S-H. The large amount of Ca2+ ions in these hydration products reacted with CO32− ions in CO2 nanobubble water, thereby increasing the generation of calcite-based CaCO3 in the cement matrix. This appears to have affected strength development and durability improvement via the densification of the structure. These results suggest that the performance of polymer cement mortar for repairing concrete structures can be improved if calcium nitrite and CO2 nanobubble water are properly combined and applied.

Designing the Composition of a Cement-Based 3D Construction Printing Material

The physical and technological properties of the 3D construction printing material are formulated. It is shown that the composition should have unique rheological characteristics, controlled setting time, high adhesion, and fast strength. It is determined that a similar material with the required properties can be obtained by creating a composite material based on two active substances: a cementing material and a polymer binder, on one hand, and modification of the particles surface with a superplasticizer, on the other hand. The regularities of the influence of organic components (polymer binder and oligomeric superplasticizer) on the cement matrix are obtained. The mortar mobility, setting time, strength characteristics, and microstructure of the polymer–cement mortar are investigated. A patented composition of the composite material is developed for the innovative construction industry based on Portland cement and polyvinyl acetate dispersion. By modifying the phase boundary of the colloidal system, the proposed composite has the required plastic strength, high setting rate, high fast strength, crack resistance, and a number of other properties necessary for 3D printing of large-sized products and off-formwork structures.

The Influence of Crystalline Admixtures on the Properties and Microstructure of Mortar Containing By-Products

Crystalline admixtures and industrial by-products can be used in cement-based materials in order to improve their mechanical properties. The research examined long-term curing and the exposure to environmental actions of polymer–cement mortars with crystalline admixture (CA) and different by-products, including Bengħisa fly ash and Globigerina limestone waste filler. The by-products were introduced as a percentage replacement of the cement. A crystallization additive was also added to the mixtures in order to monitor the improvement in durability properties. The mechanical properties of the mortar were assessed, with 20% replacement of cement with fly ash resulting in the highest compressive strength after 540 days. The performance was analyzed with respect to various properties including permeable porosity, capillary suction, rapid chloride ion penetration and chloride migration coefficient. It was noted that the addition of fly ash and crystalline admixture significantly reduced the chloride ion penetration into the structure of the polymer cement mortar, resulting in improved durability. A microstructure investigation was conducted on the samples through Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS). Crystals forming through the crystalline admixture in the porous structure of the material were clearly observed, contributing to the improved properties of the cement-based polymer mortar.

Experimental investigation on shear behavior of RC beams strengthened by CFRP grids and PCM

This paper presents the experimental results of four-point bending tests for reinforced concrete (RC) beams strengthened by carbon fiber reinforced polymer (CFRP) grids and sprayed polymer-cement-mortar (PCM). The reinforced arrangements of CFRP grids, stirrups and longitudinal steel rebars were selected as changing parameters. The maximum loads, mid-span deflections and strains for the PCM, longitudinal steel rebars, stirrups and CFRP grids were obtained. The mechanical behavior of CFRP grids and the cooperation work performance between CFRP grids and steel rebars were investigated emphatically. The research results indicated that the shear strengthening effect of the CFRP grid-PCM reinforcing layers bonded along both sides of RC beams was sufficient. The shear contribution of the vertical CFRP grid was similar to that of the stirrup, but the stress distribution of vertical CFRP grid was not uniform due to the resistant action of grid points. Moreover, the vertical CFRP grids bore the lateral extruding action with opposite directions in tension and compression zones due to the compressive and tensile behavior of horizontal CFRP grids, resulting in the complex stress state of the vertical grid which differs from the stirrup. There exists the cooperation work between CFRP grids and steel rebars in shear strengthening RC beams. So as to clarify the shear mechanism of RC beams strengthened by CFRP grids and PCM, the complex stress state of vertical CFRP grid, influence of the horizontal CFRP grid and the preconditions for the normal work of CFRP grid should be taken into account. The proposed shear capacity calculation formula based on truss-arch model could satisfy the design requirements.

Study on Optimized PVA Fiber-Volume Fraction for Polymer Cement Mortar

Study on Optimized PVA Fiber-Volume Fraction for Polymer Cement Mortar

Enhancement of the concrete-PCM interfacial bonding strength using silica fume

Recently, the polymer cement mortar (PCM) overlaying method has gained popularity as a repair/retrofitting technique. The debonding issue at the interface hinders the worldwide application of this strengthening method. Accompanying the occurrence of debonding at the interface, the strengthening effect of the PCM is lost, causing a sudden decrease in the load-carrying capacity. To prevent premature debonding, this study aims to enhance the concrete-PCM interface by using silica fume. The bi-surface shear test was selected as the test method, and three levels of surface roughness (highest level with sandblasting, medium and lowest levels with steel wire brushing) and two different concrete compressive strengths (low strength type (LS) with 16.73 MPa and normal strength type (NS) with 29.59 MPa) were given as experimental parameters. When the surface is roughened by sandblasting, the specimens with 5% silica PCM increase the interfacial strength compared to that of the normal PCM cases by approximately 36.84% and 35.05% for the “LS” and “NS” types of concrete, respectively. The percentage increase is even higher when the surface is roughened by steel wire brushing (high and low), with an increase of approximately 135.35% and 181.12%, respectively. This fact indicates that silica fume inclusions can enhance the chemical bonding at the concrete-PCM interface. The mixing of silica fume in PCM and a higher surface roughness level shifts the pure interface failure (I) mode closer to the concrete cohesion (C) failure mode for “LS” type concrete and to the composite fracture mode (I-P) for “NS” type concrete. Conclusively, it is confirmed that mixing silica fume into PCM strengthened the interface bonding strength.

231 ポリマーセメントモルタルによる外装タイル張りの耐久性調査 : 実際の建物についての経時測定

231 ポリマーセメントモルタルによる外装タイル張りの耐久性調査 : 実際の建物についての経時測定

Flexural behavior of RC beams strengthened with prestressed and non-prestressed BFRP grids

This study was aimed to investigate the flexural behavior of reinforced concrete (RC) beams strengthened with a thin composite layer consisting of a basalt fiber-reinforced polymer (BFRP) grid and polymer cement mortar (PCM). Ten RC beams were tested in the four-point flexural experiments, and following variable parameters were examined: (1) the FRP grid type, (2) amount of FRP grid, (3) types of bonding materials, (4) prestress, and (5) number of prestress release. The experimental results demonstrated that the BFRP grid effectively improved the serviceability and ultimate behavior of RC beams. The prestressed BFRP grid further improved the cracking load, yield load, and flexural stiffness of the RC beams owing to its higher strength utilization efficiency. Moreover, the failure mode of the prestressed beams changed from “concrete cover separation” to “concrete crushing” or “BFRP grid rupture” when the number of prestress release increased. Based on the strain compatibility and classical flexural theory of RC members, the prediction of the ultimate load of the FRP grid-strengthened beams exhibited a good agreement with the experimental results.