Polyurethane Grout Research Articles

Impact resistance of ultra-high-performance concrete retrofitted with polyurethane grout material: Experimental investigation and statistical analysis

The brittle nature of ultra-high-performance concrete (UHPC) increased with strength and is regarded as a shortcoming in structural applications, particularly in regions prone to seismic incidents. To overcome the inherent brittleness of UHPC. This study evaluates the impact resistance of UHPC retrofitted with polyurethane (PU) grouting overlaid using a drop weight of 1.25 kg. Three different overlaid thicknesses, including 5 mm, 10 mm, and 15 mm, were cast on the top surface of U-shaped UHPC specimens. In addition, statistical analysis was performed on the impact resistance data. The results showed that PU grouting overlaid cast on the top of a U-shaped UHPC specimen has significantly improved the impact strength and energy absorption capacity of the UHPC. The improved impact resistance increases with PU grouting overlaid thickness. Due to the brittle nature of UHPC, the first crack strength in the reference UHPC occurred with only 1 to 2 blows. The average number of cracking blows at the failure stage of the UHPC-10 and UHPC-15PU is 381.42% and 1466.5% higher than that of UHPC-5PU, respectively. The crack propagation was controlled using a U-shaped specimen. The coefficient of variation of 18.46% to 41.63% was obtained in this study, which is lower than values obtained in the previous studies adopting the ACI 544-2R testing procedure. The U-shaped UHPC-PU specimen impact resistance data followed the probability function for the two-parameter Weibull distribution, and the reliability analysis result was consistent with the experimental result.

Effect of organosilicon modified epoxy resin on slurry viscosity and mechanical properties of polyurethane grouting materials

Polyurethane (PU) grouting reinforcement materials are widely used in the construction and maintenance of civil engineering works such as coal mine, high-speed railways, subways and tunnels. The initial viscosity, allowable operation time and the mechanical strength of the grouting material are important factors affecting its application and how to strike a balance between these three factors is a key challenge in this field. In this study, a new strategy was proposed to overcome these problems. The use of alkoxy silane groups attached to the main chain of epoxy resin can reduce the entanglement between molecular chains and thus increase the flexibility of polyurethane molecular chain. A series of organosilicon modified epoxy (ME) resins were synthesized by modifying bisphenol A epoxy resin E51 with silane coupling agent KH550. The viscosity, mechanical properties and thermal stability organosilicon epoxy modified polyurethane (MEPU) were studied by adjusting the amount of ME. The apparent viscosity and shear strain viscosity of organosilicon epoxy modified polyurethane (MEPU) were investigated by means of a rotational viscometer and a rotational rheometer. The effect of ME on the mechanical properties of MEPU was systematically studied through the mechanical properties test (compression test, tensile test and impact test). The surface properties and microstructure of MEPU were investigated by water contact angle testing and scanning electron microscopy. The resulting MEPU exhibits low slurry viscosity and high compressive strength. Slurry viscosity tends to decrease as the proportion of ME increases. Compared to the unmodified polyurethane grouting slurry, MEPU-15 shows a significant reduction in slurry viscosity and maximum curing temperature for 48.7% and 8 ℃ respectively, and the consolidation fracture toughness increases 28.7%. At the same time, the addition of ME changes the polyurethane grouting material from hydrophilic to hydrophobic. In this work, polyurethane grouting materials with low slurry viscosity, high mechanical strength and low exothermic reaction have been successfully synthesized. It is possible for polyurethane grouting material to be applied more widely.

Compressive fatigue resistance and related microscopic mechanisms in foamed polyurethane grouting materials for roadbed rehabilitation

Foamed polyurethane (PU) grouting materials are widely used for the non-destructive rehabilitation of roadbeds due to their expansion characteristics, lightweight, and high strength. However, their compressive fatigue resistance is still unclear. In this work, the relationships between density and strength/modulus were established by uniaxial compression tests. The fatigue damage evolution was divided into three stages by cyclic compression tests: adjustment stage, stable change stage, and cyclic failure or cyclic hardening stage. At high stress levels, the stiffness damage, deformation damage, maximum strain, and loss factor increased to about 16.07%, 60.14%, 5.25%, and 0.044 respectively after adjustment and stable change. Broken cells and cracks were observed in SEM images after cyclic failure. At low stress levels, the deformation damage is within the elastic range. The stiffness damage and loss factor always varied at a lower level and even tended to decrease. Obvious cracks were not observed in SEM images after cyclic hardening. The conclusion was drawn that density was the main factor affecting the compression fatigue performance of PU grouting materials, and high stress levels were the main reason for cyclic failure under the same density condition. Moreover, there was a functional relationship between the stress level and fatigue life of PU grouting materials. Some descriptions have been added in the revised manuscript.

Comment On Energy-Efficient Alternative for Different Types of Traditional Soil Binders

Abstract Due to urban sprawl, the demand for land has increased for the purpose of construction. It is unlikely that soil available at different construction sites will be suitable for designed structures. For improving the load-bearing capacity of the soil, different soil binders are used, which are present in distinct states. In this review, the authors have collected details about various binders, which are generally used in the soil stabilization, and their effect as a binding agent on the soil. In this article, the authors tried to review different traditional binders. After studying various research articles, the authors found that lime, ground-granulated blast slag (GGBS) polypropylene, polyurethane grouting, and asphalt mix are frequently used binders. However, the authors also gathered information about the negative environmental impact of these traditional soil binders, which led to the need for alternatives to these commonly used soil binders. To diminish this issue, different alternate hydraulic and non-hydraulic binders are discussed. The authors found alternatives to cement and lime with the alkali-activated material consisting of Na2O and silica modulus and belite-calcium sulfoaluminate ferrite, which is also known as “Aether™.” According to the research, both alternatives emit 20–30% less CO2 into the environment and also improve the compressive strength of the soil. The various studies promotes bitumen modification. Incorporating 20-mesh crumb rubber and bio-oil into the bitumen reduces its viscosity and improves its fatigue value. When waste oil is mixed with asphalt, it revitalizes the bitumen, improves fatigue resistance, and increases compressive strength. The soil particles treated by Eko soil are held together by enzymes, which give them the same strength as cement. Apart from that, low-carbon binders such as basic oxygen furnace slag, bamboo fiber, enzyme-based soil treatment, zebu manure for stabilization, and lignin-contained biofuels and coproducts are discussed. Replacing these traditional binders helps with energy savings. All waste products are recycled, and energy is saved by not manufacturing traditional binders. Additionally, energy is saved, which is required to avoid the detrimental effects of these conventional binders, making them energy-efficient alternate binders. The authors also summarize the methods used, impacts, and changes that occur in soil properties after using substitutes in place of traditional binders. From the review, the authors determined that different binders have various properties in terms of chemical and physical compositions, and they show different variations in terms of strength when added to soil with low bearing capacity or poor stability.

Study on the failure mechanism between polyurethane grouting material and concrete considering the effect of moisture by digital image correlation

The bond resistance between polyurethane (PU) grouting material and concrete consists of adhesion, friction, and mechanical interlocking and is crucial to the repaired concrete structures. During the repair of the leakage and subsidence of underground concrete pipelines by PU grouting material, the chemical adhesion between PU and concrete interfaces may be influenced by moisture caused by the pipeline leakage and groundwater. In this paper, shear tests and the digital imaging correlation (DIC) method were used to study the effect of moisture on the shear bond performance and failure process of the PU-concrete interface before and after grouting PU with different densities. The results reveal that the differences in bond strength, shear strain and horizontal displacement between the interfaces are significantly reduced with the polymer density, especially for moistened interfaces before grouting and testing. Finally, a finite element model was employed to simulate the bond strength between PU and concrete and validated based on the test results.

Variable angle shear test and finite element simulation of polyurethane – bentonite composite structure

Polyurethane grouting is more and more widely used in projects. In this paper, the variable angle shear test (VAST) was carried out on polyurethane – bentonite (PU-B) composite specimens using a set of angle adjustable shear test devices. The failure process of specimens was studied by digital image correlation (DIC) technology. The finite element model was established to simulate the shear failure process of PU-B specimens. The results show that, within the range of angles set in the test, the greater the shear angle, the greater the shear strength of the specimen. The normal component can improve the shear strength of the PU-B specimen to a certain extent. The relationship between the normal stress and the tangential stress in cases of specimen failure conforms to the linear law, from which the cohesion and internal friction angle of the PU-B composite specimen can be obtained. The finite element simulation results are basically consistent with the VAST results. The conclusions may play a role in the study of the shear properties of the interface between polyurethane and bentonite to some extent.

Analytical solution for expandable polyurethane grouting in a rock fracture

Expandable polyurethane grout has been extensively utilized for the reinforcement and sealing of rock fractures. The diffusion mechanism of this grout is particularly unique, owing to the time-dependent characteristics of both its density and viscosity. However, the non-synchronous relationship between the change in diffusion radius and pressure poses challenges in deriving analytical solutions. In light of this, our study presents an innovative analytical model to effectively simulate the diffusion behavior of expandable polyurethane within rock fractures. Notably, this model considers both the self-expanding source and the convective driving force. The outcomes of our research demonstrate that spread and pressure exhibit distinct characteristic times, allowing us to employ the same equations with diverse parameters, yielding a semi-deterministic approach. In this approach, the first run of the model is deterministic while the second entails empirical considerations. Further, a comparison of analytical results with experimental injections was made involving varying grouting quantities, revealing excellent agreement between the measured and calculated pressures. The present model can be employed for fitting and real-time monitoring after calibration, enabling the exploration of conventional stop criteria, as well as refusal and mass criteria. Additionally, this model facilitates the formulation of conditions to effectively achieve the target, considering vital factors such as the time-spread relation, expansion ratio, and gel time.

Construction of Dielectric Model of Nonaqueous Reactive Polyurethane Grouting Materials

In order to reveal the dielectric properties of the nonaqueous reactive polyurethane grouting material, combined with the electron microscope test analysis, it can be seen that the nonaqueous reactive polyurethane material is a porous two-phase body composed of a polyurethane matrix and closed cells. At the microscopic scale, the porous two-phase physical model is established, and the dielectric model of the material is constructed on this basis. In order to verify the dielectric model, 40 groups of nonaqueous reactive polyurethane specimens with different densities were designed and prepared in this paper. The dielectric permittivity was measured by a vector network analyzer (VNA) with an open coaxial probe within the frequency range of 1050 MHz~5010 MHz for the first time, and the dielectric properties and influencing factors were revealed according to the test data. The result shows that the dielectric permittivity of nonaqueous reactive polyurethane materials increases with the increase of density, and decreases slightly with the increase of frequency. Compared with the three models of the Rule of Mixture, Clausius-Mossotti Model and Lichtenecker Model, the calculation accuracy of the Maxwell-Garnett Model is higher, and the calculation results are more consistent with the experimental results of nonaqueous reactive polyurethane grouting materials. The experimental results can be applied to the nondestructive testing of polyurethane grouting materials and provide reference and basis for the quality evaluation of polymer structures.

Corrosion resistance of polyurethane grouting material in landfill site

Landfill has been a common way to deal with municipal solid waste. It is critical to prevent the leakage of landfill leachate with corrosivity and biotoxicity in landfill sites. Non-aqueous reacting polyurethane grouting material has been demonstrated to have excellent water-barrier performance. This study aimed to verify the feasibility of non-aqueous reacting polyurethane grouting material application to landfills. The corrosion resistance of the grouting material was investigated using laboratory immersion tests with 14 chemical solvents. The corrosion resistance was evaluated based on the weight gain rate of polyurethane samples and their microscopic damage. The test results show that the polyurethane grouting material showed good resistance to acids (sulfuric acid, nitric acid and propionic acid), salt solutions (calcium chloride, ferric chloride, zinc sulfate and lead acetate) and landfill leachate. However, methyl phenol could lead to chemical degradation. Hydrochloric acid, gasoline and ammonia may cause minor damage to polyurethane. The results are expected to provide reference for evaluating the chemical corrosion resistance of polyurethane grouting materials in landfill sites.

Mechanical behavior of concrete pipes with erosion voids and the effectiveness evaluation of the polyurethane grouting

Research on pipes ringed by erosion voids is mainly concerned with circumferential mechanical behavior but ignores longitudinal bending responses induced by the relative motion of the pipe joints at voids. There has been limited innovative experimental investigation into pipe behavior that assesses the effectiveness of polyurethane (PU) grouting in rehabilitating erosion voids. Mechanical behavior tests of concrete pipes of intact, with an erosion void at the invert, and PU grouted were performed using a self-developed large-scale disaster testing system, and the measured results were numerically verified. Results show that the peaks of the positive and negative longitudinal bending moments of the intact pipes and pipes with a void at the invert appear at SgL2 and SgR2, SgL3 and SgR3, respectively, and the positive longitudinal bending moment is about 1.6–3.0 times higher than the negative ones. Voids at the invert have a significant effect on the longitudinal bending moments of the pipe segments located on the adjacent sides of the void. The longitudinal bending moments of the pipes with different void widths decrease with the increase of void width at SgL1 and SgR1 and increase with the increase of void width at SgL2 and SgR2, SgL3 and SgR3. The longitudinal bending moments of the pipes with different void lengths increase with the increase of void length in the whole longitudinal length. The circumferential bending moments at the bell-and-spigot decrease as the void width and void length increase. The maximum increases in the vertical displacements and maximum shear displacements of the pipes with different void widths and void lengths are 63–150% and 150–221%, 225–325%, and 325–550%, respectively, compared with the intact pipes. The rehabilitation efficiencies of the longitudinal and circumferential bending moments and the vertical displacement ranged from 85–93% and 85–94%.

Preparation and Performance Enhancements of Low-Heat-Releasing Polyurethane Grouting Materials with Epoxy Resin and Water Glass

Polyurethane (PU) grouting materials possess excellent fluidity and strong injectability. However, the high heat release during the reaction process restricts its application. In this study, with the addition of water glass (WG), a prepolymer was prepared by epoxy resin reacted with isocyanate to form modified polyurethane. The effects of epoxy resin and water glass on the compressive properties, expansion rate, structure of the cell, and maximum reaction temperature of the grouting materials were also investigated. The results showed that the cell size of modified PU was smaller and more regular, the maximum reaction temperature of the modified PU was reduced to 89 °C, and the compressive strength and expansion rate went up to 0.27 MPa and 57, respectively. This investigation will expand the application of PU grouting materials in underground engineering.

Surface Free Energy Theory for Evaluating Moisture Damage in Expandable Polyurethane Grouting Materials

The resistance properties of the interface between polyurethane(PU) grouting materials and rocks subjected to water erosion are the theoretical basis for evaluating the long‐term performance, which, however, is not clear yet. Herein, surface free energy (SFE) theory is used to analyze the mechanism of water damage at the interface between the polyurethane and rock. The surface energy parameters of various PU grouting materials with different densities, limestone, and granite rock materials are tested. The adhesion and peeling work indices are calculated by the SFE theory. The results show that water brings little influence on PU grouting materials. The lower the density of PU is, the better the hydrophobicity is. The increase in the density of PU promotes adhesion between the PU and rock with and without water. Moreover, density increases the difference between SFEs of PU–rock and water–rock, decreasing the detachment tendency of PU over the rocks. Lithology also affects the adhesion of PU and rocks. PU–granite composite exhibits the largest adhesion work and smallest peeling work, which indicates that it has stronger water damage resistance. Finally, the validity of the surface energy theory is proved by mechanical, bond tests and the application.

Study on dynamic viscoelastic constitutive model of nonwater reacted polyurethane grouting materials based on DMA

Abstract Nonwater reacted polyurethane grouting materials are new materials developed to make up for the shortcomings of water-reactive materials in emergency rescue. However, its viscoelastic properties and constitutive model under dynamic loads have not been systematically studied. Based on dynamic thermal mechanical analysis (DMA), the dynamic viscoelastic indexes such as storage modulus, loss modulus, and loss factor of nonwater reacted polymer grouting material were obtained, and the frequency spectrum of polymer with different densities were analyzed. In addition, comparing and analyzing the classical viscoelastic constitutive models such as Maxewell model, Kelvin model, and Fractional model, the fourth-order generalized Maxwell model (GMM) was selected to construct the viscoelastic constitutive model of polyurethane grounding materials. Then, the parameters of the viscoelastic constitutive model of polyurethane grounding materials were obtained by using multi-objective shared parameter fitting method, and dynamic viscoelastic constitutive model of nonwater reacted polyurethane grouting materials was established. Furthermore, the viscoelastic constitutive model with different densities was verified by the DMA test. The results show that the dynamic viscoelastic constitutive model of nonwater reacted polyurethane grouting materials in the article can accurately and efficiently describe the dynamic viscoelastic properties of polyurethane grounding materials, which lays a foundation for the dynamic response analysis of polymer structures.

The Influence of Fly Ash on the Foaming Behavior and Flame Retardancy of Polyurethane Grouting Materials.

Polyurethane (PU) grouting material has been widely utilized to control water inrush in mining fields. However, the application has been limited by its high cost and poor flame retardancy. Here, we use the fly ash (FA), a waste from coal of the iron-making industry and power plants, as a partial replacement of conventional filler in PU grouting materials to reduce the production cost and the environmental pollution of FA. The surface-modified FA-filled PU (PU/FA) composites were prepared by room-temperature curing. The effects of FA contents (φ) on the structure, foaming behavior, thermal stability, mechanical properties, hydrophobic properties, and flammability of PU grouting materials were examined. Results showed that the higher the φ, the more porous the PU/FA composites are, resulting in a lower density and lower mechanical properties. The relationship between the compression modulus E and the density ρ of the PU/FA composites was E ∝ ρ1.3. In addition, the surface-modified FA improved the compatibility between the hard and soft segment of PU in the PU/FA composite, giving the composites enhanced thermal stability, high hydrophobicity, and flammability resistance.

Study of the mechanical properties and constitutive model of the roadbed rehabilitation polyurethane grouting materials under uniaxial compression

AbstractPolyurethane grouting materials are increasingly used in the non‐excavation rehabilitation of roadbeds. The compressive strength of roadbed rehabilitation polyurethane (RHPU) grouting materials is the key to achieving the desirable repair effect, whereas the constitutive model of RHPU grouting materials is not yet understood. Here, the mechanical properties of RHPU grouting materials under compression were experimentally investigated, followed by establishing the hyperfoam constitutive model. The variation laws of the critical parameters in the model with density were function fitted, and then the constitutive model was simplified as an equation of density as the single independent variable. The comparisons between the theoretical and experimental mechanical behavior of RHPU grouting materials were discussed to illustrate the applicability of the hyperfoam constitutive model. Results show that with the increasing density, both the yield strength (σ1), elastic modulus (E1), and secant modulus (Es) increases exponentially, and the Poisson's ratio (v) increases logarithmically. The maximum increase in σ1, E1, Es, and v are about 750%, 720%, 940%, and 50%, respectively. Compared to the effects of density on the mechanical properties, the effect of loading rate is much smaller, and the side length has no effect. For RHPU samples with a density not exceeding 0.35 g/cm3, the hyperfoam model can well describe the uniaxial compression mechanical behavior, but for those whose density exceeds 0.35 g/cm3, the model can only describe the mechanical behavior before yielding. The theoretical yield strength of the RHPU samples obtained from the model is close to the experimental value (with differences of about 0.1%–14.4%). This study provides a base to evaluate the compressive strength of the practically used RHPU grouting materials based on the density.

Polyurethane grouting materials with different compositions for the treatment of mud pumping in ballastless track subgrade beds: properties and application effect

Mud pumping in subgrade beds under ballastless tracks will deteriorate the dynamic performance of infrastructure under railway lines, reduce the smoothness of the railway lines, and seriously affect the comfort and safety of the trains. Due to their good mechanical properties, two-component polyurethane materials can be used for grouting to treat the fouling problems caused by ballastless track mud pumping. To develop a polyurethane formula suitable for the treatment of ballastless track mud pumping, we first performed indoor experiments to investigate the mechanical properties and gelation time of polyurethane elastomers synthesized with different raw material composition ratios, to determine an optimal composition ratio of the raw materials. Then, we conducted a dynamic field test to verify the remediation effect of the polyurethane material fabricated according to the design ratio. The results showed that polyurethane grouting material with the selected design ratios improved the contact characteristics between the surface layer of the subgrade bed and the base plate in the area, coordinating the dynamic response between the track structure and the subgrade bed. Thus, the obtained polyurethane grouting material could be used to renovate mud pumping areas of ballastless tracks with a good treatment effect.

Mechanical Properties of Green and Petroleum based Polyurethane as Grouting Materials

In this study, polyurethane grouting materials (PUG) were prepared using two different types of polyol which were castor-based polyol (CPUG) and petrochemical-based polyol (PPUG). Four different ratios of polyol (OH) to isocyanate (NCO) were used in this study. The effect of different compositions of Isocyanate on mechanical properties were investigated and compared. The flexural strength, and compression strength shows the increment with the increase of the NCO composition. Optimum flexural strength, flexural modulus, and compression strength obtained at composition of PPUG4 and CPUG4 with the ratio of NCO: OH, 2.6: 1. PPUG gives a higher value of mechanical strength as compared to CPUG, however, results obtained for both types of polyurethane are in the range of industrial PU grouting properties grade. The decrease in cell wall of CPUG and PPUG with the increase of NCO:OH indicating the increment in cell wall interaction resulting higher mechanical properties of PUG.

Fatigue Performance of Concrete–Polyurethane Composite Materials under Compression

Polyurethane grouting technology has been applied in the maintenance and reinforcement of transportation infrastructure such as airports, expressways, and high-speed railways. For rigid pavements with voids underneath concrete slabs, it can make a quick and efficient fix. However, polyurethane grouting materials applied underneath slabs for base enhancement are subjected to cyclic compressive loading from traffic, so their fatigue performance is critical in the concrete–polyurethane composite structure. There have not been many studies of this aspect. This paper investigated the influence of several key design factors, including grout thickness, grout density, and void shape, on the stress–strain and fatigue performance of the concrete–polyurethane composite structure. Laboratory compressive tests were conducted at various stress levels following a four-factor, three-level orthogonal experiment design. The results showed that the strain response of composite specimens under stress-controlled cyclic loading may be divided into three stages: an initial stage in which the cumulative strain changes little with the number of load repetitions, a second stage in which the cumulative strain increases steadily with the number of load repetitions, and a third stage in which the cumulative strain increases rapidly with the number of load repetitions. The third stage represents the occurrence of fatigue failure. The rank of the influences of the four factors on fatigue performance is, from high to low, grout thickness, stress ratio, void shape, and grout density.

Influence of different corrosion environments on mechanical properties of a roadbed rehabilitation polyurethane grouting material under uniaxial compression

The mechanical properties of the roadbed rehabilitation polyurethane (PU) grouting materials subjected to different chemical corrosion are the theoretical basis for evaluating the long-term performance, which, however, is not clear yet. Here, the PU grouting materials with different densities were immersed in water, H2SO4, HCl, and NaOH solutions for different times, followed by the P-wave velocity tests and uniaxial compression tests. The influences of different corrosion environments on the damage and uniaxial compressive strength of PU samples were analyzed, and the statistical damage constitutive model under the coupling effects of chemical corrosion and the external load was established. Results show that the water brings little influence whereas both the acid and alkaline environments degrade the strength of PU grouting materials, and the longer the chemical corrosion time is, the greater the decrease in strength. The maximum declines in the yield strength of PU samples corroded by H2SO4, HCl, and NaOH solutions are about 32.8%, 31.3%, and 21.4%, respectively. The theoretical stress–strain curves based on the statistical damage constitutive model are in agreement with the experimental ones before yielding (with the average difference of 0.077–1.017 MPa), indicating the rationality of the theoretical model.

Fracture Characteristics of Polyurethane Grouting Materials Based on Acoustic Emission Monitoring

In this study, 16 groups of tests were designed by the orthogonal test method, and a PU grouting material was prepared, which can be used for the construction of sealing wall in mined-out area of coal mine. The basic properties of the material were measured. Firstly, the viscosity of four groups of samples with different polyether polyol contents was measured by a dynamic rheometer. Secondly, the uniaxial compressive strength of pure slurry samples and sand-containing samples was measured by a universal testing machine. Finally, the failure process of sand-containing samples was monitored by acoustic emission equipment. Through the above research and analysis, a PU grouting material with excellent performance has been obtained. That is, when the ratio of polyether triol:polyether tetraol:catalyst:surfactant:chain extender:plasticizer is 11 : 9 : 0.5 : 1.0 : 1.2 : 6.0, PU grouting material has higher injectability and ideal compressive strength, which has been proved in grouting experiments.