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Polyurethane grouting is a commonly employed technique for seepage prevention and reinforcement during tunnel construction. Gaining insights into the propagation behavior of polyurethane grout within rock fractures holds importance in guiding grouting operations. To investigate the effects of fracture aperture on the propagation of self-expanding polyurethane grout, experimental studies were first conducted to examine the polyurethane propagation characteristics in homogenous fractures. Subsequently, propagation mechanisms of polyurethane grout and cement grout were compared and analyzed by numerical simulation. Finally, the scanning electron microscope (SEM) tests were performed to analyze the effect of fracture aperture on the microscopic characteristics of filled polyurethane grout. The experimental results demonstrate that, larger fracture apertures result in smaller maximum propagation distances and shorter propagation time. Besides, in fractures with a large aperture, a noticeable pressure drop occurs after grout gelation. The simulation results demonstrate that an increase in the aperture is inversely proportional to the polyurethane filling rate, whereas it is directly proportional to the cement filling rate. This disparity is attributed to different injection modes and driving force sources for these two grouting materials. In addition, the SEM test results show that larger fracture apertures correspond to greater microscopic pore diameters and fewer pore numbers in filled polyurethane grouts, which provides a microscopic explanation for the observed pressure drop during experimentation. The outcomes of this study offer valuable experimental and theoretical foundations for enhancing the understanding of self-expanding polyurethane grouting in rock fractures. • The tests on polyurethane grouting in fractures with variable aperture are conducted. • The propagation and pressure of polyurethane grout in fractures are measured. • The propagation mechanism of cement and polyurethane grouts in fracture is compared. • The microscopic properties of filled polyurethane grout in fractures are investigated. [ABSTRACT FROM AUTHOR]

Cement grout is a fundamental material used in diverse engineering applications, such as mining, civil engineering, geothermal energy, and oil and gas industries, due to its role in stabilizing rock masses and sealing wellbores. Despite its widespread usage, grout's susceptibility to cracking, particularly under tensile stress, remains a major concern, compromising structural integrity and long-term performance. This study investigates the micro-cracking behavior of cement grout under tensile loading to gain a deeper understanding of the mechanisms governing fracture initiation and propagation. By employing acoustic emission monitoring and analyzing fracture surface characteristics, this research reveals the complex interplay between microcracking mechanisms and macro-fracture morphology. The results reveal significant differences in fracture behavior between the two loading regimes. Brazilian tests exhibited higher tensile strength due to the dominance of non-tensile microcracking mechanisms, such as compaction and shear, which enhance strength and dissipate more energy. These specimens showed smoother, less tortuous fracture surfaces, corresponding to lower with tensile strengths. In contrast, direct tensile tests, governed by tensile microcracks, produced lower strength and rougher, more tortuous fractures, highlighting the distinct influence of microcracking mechanisms on fracture morphology. Correlation analyses indicated consistent roughness characteristics across different fracture orientations and underscored the link between smoother surfaces and non-tensile microcracks. This study offers new insights into the interplay between microcracking mechanisms, fracture surface roughness, and tensile strength, emphasizing the impact of loading conditions on the fracture behavior of grout. The findings provide a deeper understanding of grout fracture processes, contributing to enhanced design and performance of grout-based structures in engineering applications. Future research could further explore the role of material microstructure on fracture development, aiming to improve the durability and reliability of cement grout in critical infrastructure. • Microcracking mechanisms significantly influence the tensile strength and fracture behavior of cement grout. • Different loading methods (direct tension vs. Brazilian tests) create distinct microcracking patterns and fracture morphologies. • Microcracks play a crucial role in initiating and propagating larger-scale fractures. • Fracture surface roughness analysis reveals energy dissipation mechanisms and the impact of microcracking on roughness. [ABSTRACT FROM AUTHOR]

Grouting is an effective way to prevent water inrush in underground engineering, with cement grout commonly used at ambient temperature. However, its properties change remarkably under high temperature. Existing research on this is inconsistent and limited. Thus, focusing on ordinary Portland cement, this paper investigated the basic properties and water plugging capacity of grout at various temperatures (20℃-95℃) and different water-cement mass ratios. Moreover, using a self-designed testing system, the grout retention ratio under dynamic water was explored. The influence mechanism of temperature on cement stone was studied through scanning electron microscopy, X-ray diffraction and thermogravimetric analysis as well. Here we show that as the temperature rose from 20℃ to 95℃, the grout fluidity, bleeding ratio, setting time and grout retention ratio under dynamic water all exhibited a downward trend. For the grout with a water to cement mass ratio of 1.0, when the temperature rose from 20°C to 95°C, the fluidity dropped by 30.2 %, the bleeding ratio by 73 %, the final setting time by 75 %, and the grout retention ratio by 84 %. The cement stone strength first increased and then decreased with rising temperature, peaking at 80°C for 1-day curing, 50°C for 3-day curing, and 35°C for 7-day curing. Beyond 65°C, ettringite decomposed, calcium hydroxide depleted, and monosulfoaluminate crystals fractured and distorted, reducing the compactness and compressive strength of the cement grout stone at high temperatures. • Laws of water plugging properties of grout under high temperature were studied. • A retention ratio test in dynamic water at high temperature was conducted. • A microscopic explanation for grout properties at high temperature was proposed. [ABSTRACT FROM AUTHOR]

The use of cementitious grout to enlarge the member size represents a method for strengthening RC columns, addressing limitations inherent in traditional section enlargement techniques. This study conducted experiments on the eccentric compression behavior of RC columns reinforced by enlarging the member size through the application of cementitious grout. The effects of eccentricity, strengthening thickness, new steel bars, and strengthening position on the bearing capacity of columns strengthened with cementitious grout were investigated. The results show that increasing the size of the members with cementitious grout can significantly improve the bearing capacity of columns under eccentric loads, with improvement ranging from 16% to 237%. Strengthening in the compression zone had a notably greater impact compared to strengthening in the tension zone for eccentric compression members. The ultimate compressive load of the strengthened columns experienced varying degrees of improvement with the increase in strengthening thickness and area of new steel bars. In addition, the study established a calculation formula for the bearing capacity of a strengthened column under eccentric load based on the plane section assumption and verified the availability of the calculation method by comparing the calculation results with the experimental results. [ABSTRACT FROM AUTHOR]

Understanding the mechanism of cement grout flow in fractured rocks is essential for controlling seepage in the construction of hydraulic projects. However, simulating grouting in fractured rocks is complex due to random fracture distribution and non-Newtonian grout flow. This study proposes a numerical model for simulating cement grout flow, considering the hydro-mechanical coupled process in a three-dimensional fracture network system based on the unified pipe-network method. A pipe-network equivalence method is used to derive equivalent pipes for the process of grouting displacement, and the flow field can be solved in unified pipe networks. The hydro-mechanical coupled process is achieved by incorporating an analytical solution for the stress distribution of the center borehole model on an infinitely large plane and a constitutive model for the estimation of the fracture aperture. The time-varying property of the cement grout flow is also considered in the simulation of grouting. The reliability of the numerical model is verified by comparing with analytical solutions for grout flow in a water-saturated fracture. Grouting experiments in fracture networks are also performed to demonstrate the applicability of the proposed method. The influence of various factors on the propagation of cement grout is further investigated in three-dimensional fracture network models. [ABSTRACT FROM AUTHOR]

Revealing the load transfer and failure mechanisms of the bolt-grout interface is crucial for the stability control design of rock mass engineering. Based on laboratory experiments, this study employs a FLAC-PFC coupling numerical simulation method to conduct shear numerical simulations under different normal stress, rib angle, and rib spacing conditions. The study investigates the impact of rib parameters on the load transfer and microscopic damage evolution of the bolt-grout interface. The results show that: When the rib angle is below 45°, the grout tends to climb along the ribs. As the rib angle increases, the normal stress F n between the grout and ribs gradually increases, leading the grout to adopt a sheared-crush failure mode. When the rib spacing is less than 12 mm, the grout tends to undergo an overall sheared-off failure mode. When the rib spacing is greater than 20 mm, the grout consistently undergoes a sheared-crush failure mode. As the rib spacing increases, the number of ribs gradually decreases, resulting in more intense interactions between each rib and the grout, and a larger damage area around the ribs. With the increase in normal stress, the interactions between the ribs and the grout become more intense, generating more cracks. [ABSTRACT FROM AUTHOR]

Researches on synchronous double-liquid plastic grout are limited, particularly for high water-cement (W/C) and volume ratios (V A /V B). To address these gaps, high W/C of 1.0–3.0 and high V A /V B of 7:1–20:1 were applied. Liquid A consisted of cement, bentonite and stabilizer, and liquid B was sodium silicate. Fresh-state performance, rheological properties and thixotropy of cement-bentonite single slurry were studied. Gel time, setting time, time-varying viscosity, strength, water dissolution resistance, drying shrinkage of double-liquid plastic grout were studied systematically. Hydration minerals and microstructural properties were characterized using XRD, SEM-EDS, FTIR, TG-DSC and MIP techniques. The results indicated that the H-B model was more applicable to all cement-bentonite single slurries. Yield stress, plastic viscosity, thixotropy and bleeding were negatively correlated with cement-bentonite ratio. Three periods i.e., low viscosity, rapid increase, and slow increase periods were categorized for the time-varying viscosity. The peak UCS was achieved with the optimal V A /V B of 10 and W/C of 2.75. Shrinkage rate was negatively correlated with V A /V B , the rapid shrinkage process mainly occurred within the first 3 d. Microscopic analyses revealed that sodium silicate significantly promoted the consumption of Ca(OH) 2 and the formation of C-S-H gel. This accelerated the early hydration process and improved microstructure compactness. At the W/C of 1.5, when V A /V B decreased from 18 to 16, small gel pores (< 10 nm) and large gel pores (10–50 nm) were reduced by 28.5 % and 53.5 % respectively. The W/C of 1.5–2.75 and V A /V B of 10–16 are suitable for engineering applications. • Plastic double-liquid grout with high volume ratio and W/C was optimized. • Optimal rheological model for single-liquid grout was evaluated. • Time-varying viscosity characteristics of double-liquid grout were revealed. • Optimum volume ratio and W/C are determined and discussed. • Reaction and microscopic mechanism of double-liquid plastic grout was studied. [ABSTRACT FROM AUTHOR]

• Increased grout and time consumption in holes with hydraulic jacking (HJ). • Significant correlation between grout consumption and HJ was found. • Grout consumption is higher when using OPC, than when using MFC. • More holes with no grout take in rounds grouted with MFC, than in rounds with OPC. • HJ appears more frequently when grouting with OPC, than when grouting with MFC. Pre-grouting is a common measure for reducing water ingress into tunnels. This study has investigated parameters which are expected to have an impact on grout consumption during high pressure pre-grouting of rock mass in Norwegian tunnelling, with special attention to the occurrence of hydraulic jacking of fractures. A significant positive correlation between grout consumption and hydraulic jacking was found, especially when grouting with microfine cement, but it was not established to what extent hydraulic jacking contributes to the total grout consumption. Also, there was found to be a general increase in time consumption for grout holes where hydraulic jacking was indicated. It was concluded that hydraulic jacking does not tend to be a good choice for the economy of the projects, because it involves longer grouting time and higher grout consumption, particularly when using microfine cement. [ABSTRACT FROM AUTHOR]

• Penetron Admix has no effect on viscosity and setting time of cement grout. • PA can significantly increase the concretion rate and compressive strength. • PA can significantly decreased the permeability of cement grout. • PA make the medium more compact and hence improve the strength and impermeability. • PA can be used as cement grout additive to treat tunnel leakage. This study investigates the feasibility of using a cement-based capillary crystalline material, Penetron Admix (PA), to enhance the performance of a cement grout for sealing tunnel leakage. A series of experiments were carried out to investigate the effects of PA on the viscosity, setting time, concretion rate, permeability and compressive strength of the cement grout. The experimental results show that inclusion of PA into cement grout has no effect on its viscosity and setting time, but can markedly increase the concretion rate, and the compressive strength of the grout concrete and reduce its permeability. Micro structure characterizations by CT scanning indicate that cement-gravel grout concrete samples with additional PA show a compact and smooth structure compared to those without PA; SEM images show that the dendritic crystals are observable under high magnification in the cement grout concrete samples with PA, and the number of crystals increases as the amount of PA increases. Based on the experimental results and the micro structure characterizations, it can be concluded that PA can be used as an additive to improve the rate of concretion, compressive strength, and impermeability of cement grout. To achieve an optimum leakage-sealing effect, the weight ratio of PA to cement of 1.4–1.6% is recommended. [ABSTRACT FROM AUTHOR]

The effects of xanthan gum (XG) and welan gum (WG) on the properties of cement grout at various hydration temperatures were studied. The laboratory tests including bleeding, rheology, and strength were carried out, and the microscopic analysis was carried out to reveal the mechanism. The results showed that the gums could thicken the cement grout. The apparent viscosity of cement grout containing XG increased with the rise in temperature, while the WG first increased and then decreased. XG could significantly decrease the bleeding rate, but this effect weakened in the high temperatures. WG first decreased then decreased the bleeding rate, and this variation was closely affected by the temperature. The addition of gums could decrease the strength and density of hardened grout. XG could diminish the differences between the upper and lower part of hardened grout, indicating the XG could resist the deterioration of high temperatures, while the XG enhanced the degraded effect. The addition of gums could cover the cement particles to inhibit the cement hydration but had a slight impact on the mineral phase composition. The Ettingite was not found because it decomposed in the high temperature. Meanwhile, the C-A-S-H gels were observed in the XRD patterns and SEM images, indicating that it was enhanced under high-temperature conditions. • The cement grout is modified by xanthan gum and welan gum. • The gums thicken the grout and enhance its stability at high temperatures. • Xanthan gum enhances stability and has a minor impact on strength. • Welan gum significantly decreases the strength and mitigates the cement hydration. [ABSTRACT FROM AUTHOR]

Polyvinyl alcohol (PVA) fibres are ultra-high-performance fibres that can be used to reinforce cementitious composites. This study experimentally investigated the compression and shear behaviours of grouted and hollow masonry constructed with fibre-reinforced mortar (FRM) used for the joints and/or PVA fibre-reinforced grout (FRG). In this regard, the effect of increasing the fibre content of 6 mm PVA fibres in the FRM on the behaviour of masonry was investigated. Moreover, the effect of changing the fibre length (8 mm and 13 mm PVA fibres) and the fibre content of 13 mm PVA fibres in the FRG on the behaviour of masonry was investigated. This was accomplished by constructing and testing 31 masonry prisms and 29 masonry assemblages. The behaviour of PVA-reinforced masonry was evaluated based on compressive strength, shear strength, modulus of elasticity, modulus of rigidity, compressive strain at peak compressive stress, shear strain at peak shear stress, compression ductility index and compression toughness. In addition, the compression and shear stress-strain curves, failure modes and crack propagation of PVA-reinforced masonry were compared with unreinforced masonry. It was concluded that using PVA fibres in the grout minimized the masonry face shell spalling, and most of the post-peak deterioration appeared in the form of masonry cracks and less face shell spalling compared with unreinforced masonry. In addition, using PVA-FRM only or PVA-FRM with PVA-FRG could increase the compressive strength of grouted masonry. In contrast, using PVA-FRM did not change the compressive strength of hollow masonry. Furthermore, all grouted assemblages with PVA-FRM and PVA-FRG (except for assemblages with 13 mm PVA-FRG with a fibre content of 0.10% by weight of grout) have similar average shear strength compared with unreinforced assemblages. Finally, As the fibre content of 6 mm PVA fibres in the FRM of hollow assemblages increased, the shear strength and the modulus of rigidity decreased. This study highlights the improvements and drawbacks of using PVA Fibres in mortar and grout on the compressive and shear performances of hollow and grouted masonry. • The compression and shear behaviours of PVA-reinforced masonry were evaluated. • 31 masonry prisms and 29 masonry assemblages were constructed and tested. • PVA-FRM or PVA-FRM with PVA-FRG could increase the compressive strength of grouted masonry. • PVA-reinforced masonry has a higher modulus of elasticity compared with unreinforced masonry. • As the FC of 6 mm PVA fibres in the FRM of hollow masonry increased, the shear strength decreased. [ABSTRACT FROM AUTHOR]

Grouting plays a crucial role in mitigating water inrush disasters and reinforcing weak surrounding rock formations, and the effectiveness of grouting operations is heavily dependent on the choice of grouting materials. This study undertakes an assessment of the feasibility of deploying polyacrylate latex modified cement grouting material (PLMC) for the purposes of water obstruction and surrounding rock reinforcement, achieved through a comparative analysis against six alternative grouting materials, each of which has been applied in practical engineering. The experimental results demonstrate that the initial setting time and fluidity of PLMC fall within the range of other grouting materials, meeting the project requirements. PLMC achieves the highest filling rate at 77.42%, while the filling rates of other grouting materials range from 39.69% to 74.13%. PLMC exhibits good performance in bleeding ratio (2.77%) and resilience against dynamic scouring (retention rate is 72.95%), ranking as the third highest among the seven compared materials for both indexes. Additionally, the uniaxial compressive strengths of PLMC grout stone body and grouting-reinforced body reached 11.94 MPa and 22.74 MPa, respectively, representing the best performances. In comparison, the highest levels of these two indexes for other grouting materials are 8.78 MPa and 21.46 MPa, respectively. Compared with other grouting materials, the porosity of PLMC grout stone body is the lowest, and the interface between rock and grout in PLMC-reinforced body exhibits no significant gaps. The findings suggest that polyacrylate latex modified cement grouting material exhibits exceptional workability characteristics, positioning it as a promising candidate for practical applications. • Polyacrylate modified cement grouting material for water blocking and reinforcement. • Polyacrylate modified cement grouting material exhibits excellent workability. • Polyacrylate modified cement grout fills the micropores of rock effectively. [ABSTRACT FROM AUTHOR]

Bond between two cementitious materials is crucial in applications such as repairs, overlays, and connections of prefabricated bridge elements (PBEs), to name just a few. It is the latter that has special interest to the authors of this paper. After performing a dimensional stability study on grout-like materials commonly used as connections between PBEs, it was observed that the so-called ‘non-shrink’ cementitious grouts showed a considerable amount of early-age shrinkage. This might have negative effects on the integrity of the structure, due not only to the grout material’s early degradation, but also to a possible loss of bond between the grout and the prefabricated concrete element. Many factors affect the bond strength between two cementitious materials (e.g., grout-concrete), the presence of moisture at the existing concrete substrate surface being one of them. In this regard, pre-moistening the concrete substrate surface prior to the application of the grout material is sometimes recommended for bond enhancement. This topic has been the focus of numerous research studies in the past; however, there is still controversy among practitioners on the real benefits that this practice might provide. This paper evaluates the tensile bond performance of two non-shrink cementitious grouts applied to the exposed aggregate surface of a concrete substrate, and how the supply of moisture at the grout-concrete interface affects the bond strength. “Pull-off” bond results show increased tensile bond strength when the concrete surface is pre-moistened. Reasons to explain the observed increased bond strength are given after a careful microstructural analysis of the grout-concrete interface. Interfaces where the substrate surface is pre-wetted, such that moisture movement from the grout is minimized, show reduced porosity and increased hydration on the grout side of the interface, which is thought to directly contribute to the increased tensile bond strength. [ABSTRACT FROM AUTHOR]

Numerous research has been conducted on the axial performance of cement-based grouts. However, much less work has been focused on the shear behavior of cement-based grouts. In this study, the shear behavior of a Portland cement grout was investigated with the triaxial test. Cylindrical samples with two different water-to-cement (w/c) ratios: 0.42 and 0.35 were cast and prepared. In the test process, a series of confining pressures was applied on the samples and the confining pressure was ranged from 1 MPa to 35 MPa. The results show that there is a bi-linear relationship between the maximum vertical stress and the confining pressure independent of the w/c ratio. Low w/c ratio can effectively increase the maximum vertical stress of grouts. Mohr-Coulomb models were used to fit the shear strength envelopes of grouts. The results show that the shear strength of grout with a w/c ratio of 0.35 is much higher than that with a w/c ratio of 0.42. When a w/c ratio of 0.42 was used, the grout has a cohesive strength of 31.4 MPa and an internal friction angle of 15.1° while when the w/c ratio was decreased to 0.35, the cohesive strength of grout increases to 34.2 MPa and the internal friction angle rises to 24.3°. [ABSTRACT FROM AUTHOR]

• The cement grout is modified by various polysaccharide-based admixtures (the gums). • The gums thicken the grout and enhance its stability at high temperatures. • The gums reduce the segregation of cement particles in the hardened grout. • The chelation between active groups and cement particles enhances the viscosity. • The gums cover the surface of particles, mitigating the cement hydration. The viscosity of the cement grout, affecting the water bleeding and particle sedimentation, is the key parameter in the control of water inrush disasters, and it is significantly affected by the temperatures. In this paper, various polysaccharide-based admixtures were used to thicken the grout at elevated temperatures. The water bleeding and viscosity of the cement grout doped with xanthan gum (XG), guar gum (GG), locust bean gum (LG), and konjac gum (KG) were conducted at 20 °C, 40 °C, 60 °C, and 80 °C. The differences in density and compressive strength between the upper and lower parts of the hardened grout were calculated to evaluate particle sedimentation, and microscopic analyses were conducted. The results indicated that the gums reduce water bleeding and enhance viscosity. However, the improvement in water bleeding reduction weakened as temperatures rose, while viscosity continued to increase. The addition of gums led to a decrease in the density and compressive strength of the hardened grout, but it also reduced the differences between the upper and lower parts were. Among the various gums tested, GG demonstrated a more pronounced effect in reducing water bleeding, enhancing viscosity, and decreasing particle sedimentation when compared to others. Additionally, the incorporation of various gums did not alter the mineralogical phase compositions. SEM results revealed the presence of films covering the surface of particles, which resulted from crosslinking and complexation between active functional groups within the polymer chains and Ca2+ and Al3+ ions. Moreover, elevated temperatures were found to increase the Al/Ca ratio within the C-S-H gels, leading to the formation of C-A-S-H gels characterized by higher Al/Ca and Si/Ca ratios. [ABSTRACT FROM AUTHOR]

The steel-fiber reinforced polymer composite bar (SFCB) can be used in concrete structures in harsh environments. However, their connection and end anchoring problems still need to be solved. Therefore, this article conducted tensile tests on grout sleeve splicing of SFCBs and pullout tests on SFCBs with anchor heads in concrete. Results indicate that bond performance between SFCBs and grout is independent of sleeve material (steel or GFRP) and bar diameter. The thickness of GFRP at the rib position of the steel bar should be at least 2 mm to avoid making the peak stress declining. To eliminate the influence of grout thickness on bond behavior, curing specimens in the water is necessary. Splitting slip, peak slip and residual slip increase with rib spacing. Residual stress decreases with the ratio of rib spacing to rib height. Peak stress and residual slip increase with compressive strength of grout. The ratio of splitting slip to peak slip varies little. The theoretical bond-slip curve is obtained, and the correlation coefficients between characteristic parameters and experimental values are 0.75–0.99. The peak splitting force is 43 % of the peak load. The differential equation has been established and solved, and results agree well with the test values. The minimal anchorage length of SFCBs (7 times the diameter) and its simplified calculation formula are obtained. Concrete strength, anchor-head length and tube material (steel or GFRP) do not affect pullout load-slip curves of SFCBs in concrete. • Tensile behavior for grout sleeve splicing of SFCBs was investigated. • The bond mechanism between the SFCB and grout was revealed. • The proposed model can accurately predict the bond-slip curves and peak load. • The anchor head, made of the grout-filled GFRP tube, of the SFCB was proposed. • Pullout behavior of the SFCB with the anchor head in concrete was studied. [ABSTRACT FROM AUTHOR]