Ultrafine Cement Research Articles

An Experimental Study on the Performance of Materials for Repairing Cracks in Tunnel Linings under Erosive Environments

Addressing the current lining cracking problem in coastal tunnels, this paper independently introduces a novel type of repair material for tunnel lining cracks—the composite repair material consisting of waterborne epoxy resin and ultrafine cement (referred to as EC composite repair material). Through indoor testing, we have analyzed the change rule of the mass change rate, compressive strength, flexural strength, and chloride ion concentration of the repair material samples in erosive environments, with the dosage of each component in the EC composite repair material being varied. We have also investigated the working performance, mechanical properties, and microstructure of the repair material. The results of this study show that when the proportion of each component of ultrafine cement, waterborne epoxy resin, waterborne epoxy curing agent, waterborne polyurethane, defoamer, and water is 100:50:50:2.5:0.5:30, the performance of the EC composite repair material in a chloride ion-rich environment is optimal in all aspects. When the mixing ratio of each component of the EC composite repair material is as stated above, the repair material exhibits the best performance in a chloride ion erosion environment. With this ratio of components in the EC composite repair material, the fluidity, setting time, compressive strength, flexural strength, and bond strength of the repair material in a chloride ion erosion environment can meet the requirements of relevant specifications, and it is highly effective in repairing tunnel lining cracks. The polymeric film formed by the reaction between the waterborne epoxy resin emulsion and the curing agent fills the pores between the hydration products, resulting in a densely packed internal structure of EC composite repair material with enhanced erosion resistance, making it very suitable for repairing cracks in tunnel linings in erosive environments.

Coherence analysis of the crack strain field in coal rock with borehole-crack composite defects

Cracks in the coal mass surrounding boreholes for gas extraction will significantly impact the efficiency of gas extraction. The primary objective of this research is to explore the effects of original cracks and borehole grouting on cracks propagation in the coal mass around the boreholes. Accordingly, this research employs coal mass with borehole, borehole-cracks composite coal mass, and borehole-cracks-grouting coal mass as experimental subjects. The digital image correlation (DIC) platform of the coal deformation and damage was used to carry out the damage experiment of the coal mass around the boreholes. The Matlab GUI crack detection system was used to extract the crack skeleton, and time domain characteristics of strain and strain rate coherence coefficients in the area near the cracks before and after grouting were obtained according to the Pearson product-moment coherence analysis method. The research findings obtained in this article are as follows: (1) The tips of the prefabricated fractures act as stress concentration zones, where the further extension of wing cracks severely degrades the continuity and uniformity of the coal mass. The injection of ultrafine cement significantly enhances the overall deformation resistance of the coal mass. However, the local stiffness under specific stress conditions shows limited improvement due to the presence of micro-damage around the prefabricated cracks. (2) The expansion of the cracks around the borehole and the wing cracks at the tips of the prefabricated cracks is primarily due to tensile forces. As the cracks extend to the top of the specimen, they transition to a mixed mode of tensile-shear, with the extension of Type II wing cracks being faster and more unstable compared to Type I. (3) The correlation coefficient between multiple crack fields and their highly significant characteristics indicate that crack propagation influences each other. This influence diminishes as the specimen progressively damage. (4) The mechanical properties of the specimen show a strong correlation with the average interference coefficient R̅ of the cracks. Better mechanical properties of the coal rock are associated with higher geometric similarity in the strain and strain rate curves across multiple strain fields, the cracks tend to propagate synchronously.

Investigating the sealing efficiency of grouting in joints: insights from effects of the rheological properties of grout and joint characteristics

ABSTRACT In tunnel construction, grouting is frequently used to decrease the permeability and increase the rock mass strength. One of the most challenging steps in grouting is choosing the best grout type to achieve the highest penetration and sealing efficiency in the joints. The main purpose of this study is to investigate the sealing efficiency of different grout types in the joints of a high-risk section of the Kerman water conveyance tunnel (KWCT). For this purpose, the penetrations of three types of grouts including Ordinary Portland Cement (OPC), Ultra-Fine Cement (UFC), and silica sol were determined using analytical equations. Thereafter, the sealing efficiency of each type of grout in joints with different apertures was calculated. Also, the penetration radius of each type of grout was simulated and calculated using UDEC code. Based on the results of the analytical equations, by performing the grouting for 20 min using silica sol-based grout, the joints of the high-risk section of the KWCT with apertures of 0.5–2.5 mm and 2.5–10 mm can be sealed at ‘Fair’ and ‘Excellent’ levels, respectively. Furthermore, based on the results of numerical simulations, the UFC and silica sol-based grouts can seal the joints in ‘Good’ and ‘Excellent’ levels, respectively.

Experimental Study on Water-Plugging Performance of Grouted Concrete Crack.

In this paper, ordinary Portland cement, ultrafine cement, polyurethane, and epoxy resin were selected as typical grouting materials. Grouting simulation tests were first conducted to prepare the grouted concrete crack sample. The effect of concrete crack parameters (i.e., crack aperture and roughness), grout water-cement ratio, and grouting pressure on the water-plugging performance of different grouting materials was explored through the impermeability test. The microstructure of grouted concrete cracks was analyzed by means of scanning electron microscopy (SEM) and computed tomography (CT), and the difference in water-plugging performance of different grouting materials was explained at the micro level. The results show that the impermeability of the four grouting materials was ranked as follows: Epoxy resin > polyurethane > ultra-fine cement > ordinary Portland cement. The concrete cracks grouted by epoxy resin have the highest plugging failure water pressure and the lowest permeability, which is the optimal grouting material. The effectiveness of crack grouting in water-plugging was directly proportional to the grouting pressure, provided the pressure did not exceed a certain value. When the pressure surpassed the threshold, the increase in pressure did not have a significant impact on the water plugging performance. For the two cement-based materials, the threshold pressure was 1 MPa, while for the other two chemical grouts, it was 2 MPa. The two cement-based grouts with a water-cement ratio of 0.8 showed optimal water-plugging performance. The water-plugging performance of ordinary Portland cement paste, ultra-fine cement pastes, and polyurethane grout was negatively correlated with crack aperture and positively correlated with crack roughness. However, the water-plugging performance of epoxy resin grout was not affected by crack aperture or roughness.

Study on the mechanical properties and hydration synergy of MEA and UEA modified ultrafine cement grouting materials

Ultrafine cement is widely used in micro-fracture grouting due to its very small particle size, and the expansion agent can improve the dry shrinkage and cracking phenomenon of ultrafine cement grouting materials, and at the same time produce self-stress to enhance the sealing effect, but at present, there are fewer researches on the hydration synergistic effect of ultrafine cement and expansion agent. For this reason, this paper explored the effects of two commonly used expansion agents, U-type and MgO-type, on the mechanical properties, hydration heat, hydration products and microscopic morphology of ultrafine cement materials. The results demonstrated that the expansion performance of MgO-type expansion agent (MEA) was better than that of U-type expansion agent (UEA); At the same time, the MgO-type expansion agent delays the exothermic cement hydration and inhibits the transformation of hydration products, and the stress concentration generated by its delayed expansion effect leads to brittle damage of the material. UEA participates in cement hydration and produces swelling crystals, and at this time, the specimen was mainly cemented in the form of particles, and the pre-generated internal expansion stress densifies the pore structure of ultrafine cement, which enhanced the mechanical strength of the specimen.

Machine learning for optimal ultra-fine cement plugging system in simulated high permeability sandstone reservoirs

The properties of a cement system dictate its potential applications, yet creating a reliable cement plugging system with controllable setting times, robust injection capacity, and high compressive strength often requires a lot of time and resources in advanced oilfield development. To address this issue, a machine learning-based XGBoost model was created to optimize plugging system performance, reduce costs, and enhance efficiency by analysing the initial setting time, final setting time, viscosity, and compressive strength of ultra-fine cement. The results demonstrate an impressive accuracy of 96.08%, 96.10%, 94.35%, and 90.42% for these respective parameters, with a prediction time of 0.0068 seconds. In response to sandstone reservoirs with permeability greater than 500 mD, an intelligent optimization integrated model was established, resulting in three plugging system formulations that meet the requirements. The injection speed was 1 mL/min and the slug combination used was 0.2PV polymer and 0.7PV plugging system. The maximum injection pressure change recorded remained below 0.8 MPa. The plugging rate achieved was over 90%, reaching a maximum of 96.28%. This study provides theoretical guidance for the construction and injection process in the mining field test area and also offers valuable insights for the intelligent development of oilfields.

Effect of grouting on damage and fracture characteristics of fractured rocks under mode I loading

Grouting is widely used to improve the mechanical properties of fractured rocks, but its impact on the fracture behavior of fractured rocks remains incompletely understood. This research aims to investigate the effects of grouting on the damage and fracture characteristics of fractured rocks under mode I loading. We used epoxy resin and ultrafine cement to grout granite and sandstone centre-cracked Brazilian disc specimens. We conducted Brazilian splitting tests on intact specimens, as well as specimens with and without grouting under mode I loading. Acoustic emission (AE) and digital image correlation (DIC) techniques were utilized to study the effect of grouting on rock fracture behavior. Furthermore, we employed an improved fracture toughness calculation method to evaluate the anti-fracture capacity of grouted specimens. The results show that grouting positively reinforces fractured rocks by increasing the shear crack ratio, mitigating the stress concentration effect at the crack tip, and fostering a more complete and stable development of the fracture process zone (FPZ). Materials with superior strength and bonding properties can effectively improve the mechanical performance of fractured rocks. Notably, epoxy resin significantly boosts the strength, deformation adaptability, and anti-fracture capacity of the specimens, outperforming ultrafine cement in terms of grouting effect. The entropy change of AE energy during the loading process indicates that the rock system undergoes three stages of order-to-disorder-to-order. The second stage and the abrupt changes in entropy value can serve as precursors to rock damage and fracture. This research enriches our understanding of how grouting influences the damage and fracture behavior of fractured rocks, providing valuable insights for risk assessment and disaster prediction in geotechnical grouting engineering.

Optimization on overall performance of Modified Ultrafine Cementitious Grout Materials (MUCG) and hydration mechanism analysis.

Given the challenges encountered in injecting grout into micro-cracked rock masses, a modified ultrafine cementitious grout material (MUCG) was developed using ultrafine cement, polyvinyl alcohol (PVA) fibers, and a high-efficiency superplasticizer. To identify the optimal ratio of constituents for grouting these rock masses, extreme difference and multiple linear regression analyses were conducted based on test results of flowability and mechanical properties. A mix comprising 9% silica fume, 0.2% bentonite, 0.3% PVA fibers, 0.15% superplasticizer, and 2% setting accelerator was identified as the optimal mix. The microstructure characteristics of the optimal MUCG (MUCGop) grout cemented body were analyzed using XRD, FTIR, BET, and SEM. XRD and FTIR analyses indicated that a substantial amount of C-(A)S-H gel, CH, and AFt were formed within the first 3 days, highlighting the early strength characteristics of MUCGop. Over time, the content of C-A-H stabilized at 22%, the amount of CH decreased from 19% to 14%, whereas the amount of AFt increased to 15.9% by Day 28. Unexpectedly, CaCO3 content increased due to carbonation, reaching 37.3% by Day 28. BET and SEM analyses demonstrated that the specific surface area and porosity (most probable pore size) gradually decreased over time. At various ages, mesopores (cumulative pore diameter, median pore diameter) initially increased and then decreased. Micro-cracks appeared in the cemented body by Day 7, resulting in a slight decrease in strength (3.92%) from Day 3 to Day 7. The formation of well-developed needle-like AFt, C-(A)S-H gel, and small-volume plate-like CH contributed to uniform cementation and a denser structure. From Day 7 to Day 28, there was a slight increase in strength, by an amount of 10.66%. These findings have significant scientific implications for understanding the mechanisms of grouting reinforcement in micro-cracked rock masses.

Analysis of the Effect of Ultra-Fine Cement on the Microscopic Pore Structure of Cement Soil in a Peat Soil Environment

Treating peat soil foundations around Dianchi Lake and Erhai Lake in Yunnan is a complex problem in practical engineering projects. Peat soil solely reinforced with ordinary cement (OPC) does not satisfy demand. This study aims to solidify soil to achieve better mechanical properties. The preparation of peat soil incorporates a humic acid (HA) reagent into cohesive soil, and cement and ultra-fine cement (UFC) are mixed by stirring to prepare cement soil samples. They are then immersed in fulvic acid (FA) solution to simulate cement soil in the actual environment. X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and pores and cracks analysis system (PCAS) tests are used to study the impact of the UFC on the microscopic pore structure of cement soil in a peat soil environment. The unconfined compressive strength (UCS) test is used for verification. The microscopic test results indicate that incorporating UFC enhances the specimen’s micropore structure. The XRD test results show the presence of C–S–H, C–A–S–H, and C–A–H. SEM and PCAS tests show that the UFC proportion increases by between 0% and 10%, and the percentage reduction in the macropore volume is the largest, at 38.84%. When the UFC admixture is 30%, the cumulative reduction in the percentage of macropore volume reaches 71.55%. The MIP test results show that the cumulative volume greater than 10 µm in pore size decreases from 7.68% to 0.17% with an increase in the UFC proportion. The UCS test results show that the maximum strength growth of cement soil is 12.99% when the UFC admixture is 0–10%. Incorporating UFC to form a compound curing agent solves the problem of the traditional reinforcement treatment of peat soil foundation being undesirable and decreases the amount of cement. This study provides practical guidance for reducing carbon emissions in actual projects.

Development and application of novel high‐efficiency composite ultrafine cement grouts for roadway in fractured surrounding rocks

AbstractThe fractured surrounding rocks of roadways pose major challenges to safe mining. Grouting has often been used to reinforce the surrounding rocks to mitigate the safety risks associated with fractured rocks. The aim of this study is to develop highly efficient composite ultrafine cement (CUC) grouts to reinforce the roadway in fractured surrounding rocks. The materials used are ultrafine cement (UC), ultrafine fly ash (UF), ultrafine slag (US), and additives (superplasticizer [SUP], aluminate ultrafine expansion agent [AUA], gypsum, and retarder). The fluidity, bleeding, shrinkage, setting time, chemical composition, microstructure, degree of hydration, and mechanical property of grouting materials were evaluated in this study. Also, a suitable and effective CUC grout mixture was used to reinforce the roadway in the fractured surrounding rock. The results have shown that the addition of UF and US reduces the plastic viscosity of CUC, and the best fluidity can be obtained by adding 40% UF and 10% US. Since UC and UF particles are small, the pozzolanic effect of UF promotes the hydration reaction, which is conductive to the stability of CUC grouts. In addition, fine particles of UC, UF, and US can effectively fill the pores, while the volumetric expansion of AUA and gypsum decreases the pores and thus affects the microstructure of the solidified grout. The compressive test results have shown that the addition of specific amounts of UF and US can ameliorate the mechanical properties of CUC grouts. Finally, the CUC22‐8 grout was used to reinforce the No. 20322 belt roadway. The results of numerical simulation and field monitoring have indicated that grouting can efficaciously reinforce the surrounding rock of the roadway. In this research, high‐performance CUC grouts were developed for surrounding rock reinforcement of underground engineering by utilizing UC and some additives.

Mechanical and Acoustic Emission Characteristics of Grouted Reinforcement in Fissure-Containing Rock-like Specimens

In order to study the reinforcing effect of the different grouting materials applied in fissure rock engineering, ultra-fine cement slurry, cement–silicate slurry, and MARITHAN® were used to carry out grouting tests on specimens of fissure-containing rocks. With the help of a uniaxial compression acoustic emission test system, the mechanical characteristics of the grouted specimens were obtained, and the damage process of the specimens was revealed by using the acoustic emission signals. The tested results showed the following: the residual strength of the grouted specimens using the three grouting materials increased by 16.931%, 13.075%, and 39.998%, respectively; the ultra-fine cement grouting and cement–silicate grouting specimens showed damage patterns of shear-slip damage along the original rupture surface; the specimens of MARITHAN® grouting cracked from a position near the end of the specimen with no damage to the grouted body portion; the cumulative acoustic emission energy curves of the grouted specimens showed obvious stage characteristics; and the acoustic emission energy distribution characteristics of the grouted specimens differed depending on the grouting materials.

Research on the preparation and diffusion characteristics of coal seam bottom fracture grouting material based on solid waste synergy

Fracture in the top and bottom plates of the coal seams in the Lubei Mining Area of China have developed to communicate with the Austrian gray pressurized water, and the threat of water damage is extremely serious. The rapid development of China's domestic economy has led to an increasing amount of industrial solid waste, which seriously jeopardizes the safety of the ecological environment. Based on the current problem, the slag powder (S) and waste rubber particles (R) were used as the main material, supplemented by cement (C) reinforcement with alkali slag (AS) excitation, and the mine fissure grouting and sealing reinforcement material was developed. The effects of water-cement ratio and (S: R) mass fraction on the physical and chemical properties of the grouted rock mass were analyzed using indoor tests, and the optimal components were determined; secondly, three-dimensional slurry-water-rock flow-solid coupling two-phase seepage simulation was realized using COMSOL, which revealed the diffusion morphology of the solid-waste slurry, preliminarily verified the feasibility of the grouting diffusion inside the rock mass, and determined the diffusion rule of the solid-waste slurry concerning the grouting pressure. The results indicate that at a water-cement ratio of 0.7 and a mass fraction of (S: R) at (70%:30%), the slurry has a flow degree of 275 mm, a water precipitation rate of 7.4%, a 28d compressive strength of 6.9 MPa, and follows the Bingham rheological model, with good injectability. Moreover, the slurry diffuses in simulated fracture grouting in a similar pattern to ultrafine cement slurry, satisfying the reinforcement requirements of field grouting. The research content realizes the combination of mine water damage control and solid waste scale, which is critical to ensuring production safety and the mine's green sustainable development.

Effect of Ultrafine Cement (UFC) on the Corrosion Resistance of Cement Soil in Peat Soil Environment.

Many peat soils are distributed around plateau lakes, and the reinforcement of peat soils with high organic matter content by ordinary cement cannot meet the actual engineering requirements. In order to obtain better mechanical properties and durability of the reinforcement, this experiment prepared peat soil by mixing humic acid reagent into the alluvial clay soil with low organic matter content. The cement soil samples were prepared by adding cement and ultrafine cement (UFC) by stirring method; the samples were then soaked in fulvic acid solution to simulate the cement soil in the peat soil environment. Using the unconfined compressive strength (UCS) test, scanning electron microscope (SEM) test, and pores and cracks analysis system (PCAS) test, the effect of UFC content change on cement soil's humic acid erosion resistance was explored, and the optimal UFC content range was sought. The results of the UCS test show that with an increase in immersion time, the strength curves of cement soil samples gradually increase to the peak strength and then decrease. Significant differences in the time correspond to the peak strength, and the overall presentation is two processes: the strength enhancement stage and the corrosion stage of the sample. The incorporation of UFC makes the cement soil in the peat soil environment exhibit excellent corrosion resistance, and the optimal UFC content is 10%. The results of the SEM and PCAS tests show that the microstructure of cement soil after immersion time exceeds 90 days, increases with an increase in immersion time, and its structural connectivity gradually weakens. The excellent characteristics of UFC particles, such as small particle size, narrow particle size distribution, fast hydration reaction rate, high hydration degree, and many hydration products, weakened the adverse effects of humic acid on the cement soil structure to a certain extent. Therefore, although the number of macropores increases, they are not connected. It still presents a relatively compact honeycomb overall structure, which correlates well with the UCS results.

Effect of Ultra-Fine Cement on the Strength and Microstructure of Humic Acid Containing Cemented Soil

The peat soil in the Dianchi Lake area of Yunnan, China, is widely distributed, bringing many problems to engineering. The peat soil foundation is usually treated by the cement mixing method, and the reinforcement effect of cemented soil is mainly affected by humic acid (HA). Ultra-fine cement (UFC) can improve cement performance and reduce cement consumption, decreasing CO2 emissions and the impact of human activities on the environment. Simulated peat soils in different environments are prepared with HA reagent and cohesive soil, reinforced by composite cement curing agent mixed with ultrafine cement (UFC). The relationship among the UFC proportion, HA reagent content, soaking time, and sample strength was studied. The unconfined compressive strength test (UCS), scanning electron microscope (SEM), and PCAS microscopic quantitative test techniques were used to explore the mechanism of the effect of UFC on the strength of HA-containing cemented soil. The increasing UFC proportion in the composite cement curing agent gradually increased HA-containing cemented soil’s strength. UFC significantly reduced the percentage of macropores in HA-containing cemented soil and made the microstructure denser. The HA-containing cemented soil’s qu increased the most when the UFC proportion increased from 0% to 10%. The solidification effect of the composite cement curing agent mixed with UFC was always stronger than that of OPC. The composite cement curing agent with a UFC proportion of 10% is practical. Cement is still an important building material in the current construction industry, and UFC provides a new method for reducing environmental impact in engineering construction.

Effect of UFC on the Microscopic Pore Structure of Cemented Soil in Humic Acid Environment

Peat soil is widely distributed in the Dianchi Lake area of Yunnan, and the effect of the cement deep-mixing method on peat soil foundation is mainly affected by humic acid (HA). In this paper, a composite cement curing agent is formed by adding different proportions of ultra-fine cement (UFC) to ordinary Portland cement (OPC) and used to cure the HA-containing cohesive soil. Mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and X-ray powder diffraction (XRD) are used to study the influence mechanism of UFC on the micropore structure of HA-containing cemented soil. The unconfined compressive strength test (UCS) is used to verify it. MIP, SEM, and XRD results show that UFC can significantly improve the microscopic pore structure of the samples. The hydration reaction rate of cement increases with the increase in the proportion of UFC, and the generated hydration products can fill the pores of the samples. The filling effect of hydration products on macropores is enhanced, and the pores change from fibrous filling to cemented filling. The enhanced cementation of the hydration products improved the loose and overhead structure inside the sample. Enhancing the cementation of hydration products improves the loose and overhead structure inside the sample and the integrity of cemented soil. UCS verified that the increase in the UFC proportion increases the HA-containing cemented soil strength. It achieves the purpose of reducing the amount of cement when curing peat soil foundations and supports reducing carbon emissions in practical projects.

Pre-Reinforcement Mechanism and Effect Analysis of Surface Infiltration Grouting in Shallow Buried Section of Long-Span Tunnel

In order to solve the problem that the hole-forming rate of boreholes is low and it is difficult to reach the designed length when supporting a long pipe shed in loose stratum in a shallow buried section of a long-span tunnel, it is necessary to pre-reinforce the loose stratum in order to improve the strength and integrity of the surrounding rock. Relying on the grouting project of the shallow buried section at the exit of Botanggou tunnel, it is assumed that the grouting material is Newtonian fluid and the steel floral tube shows cylindrical infiltration and diffusion. Through the analysis of the structural characteristics of the injected stratum, the conceptual model of infiltration grouting is established. Twelve groups of test slurry were prepared with ordinary Portland cement and ultra-fine cement, and through the analysis of the slurry parameters of each group, ordinary Portland cement slurry was selected with a water–cement ratio of 1:1 plus 3% water glass to strengthen the gravel layer, and ultra-fine cement slurry with a water–cement ratio of 1:1 plus 3% water glass and 0.3% polycarboxylate superplasticizer to strengthen the fully and strongly weathered porphyritic granite layer. Through the on-site single-hole grouting test and combining with the empirical formula, the maximum diffusion radius of single-hole infiltration grouting is calculated, and the sliding width of the sidewall is deduced using Terzaghi theory. To ensure the grouting effect, the 5 m expansion of the excavation profile is taken as the grouting range. Grouting construction adopts the overall order of periphery and then interior, and three-sequence opening and grouting are adopted in the same row of grouting holes, which can effectively prevent grouting running and grouting. For the strata treated by surface grouting, the construction of the long pipe shed is smooth and reaches the designed length, and there is no large deformation of the surrounding rock when excavated using the CD method. The treatment effect is analyzed by the P-Q-t control method, excavation observation method, and deformation monitoring method. The results show that the injected stratum is fully infiltrated and gelled, forms an obvious grouting stone body, the integrity and strength of surrounding rock are obviously improved, and the convergence values of the tunnel surface, vault subsidence, and clearance do not exceed the alarm value of 60 mm. The research results provide some awareness and understanding of the grouting pre-reinforcement of loose stratum in a shallow buried section of a long-span tunnel in the future.

Study on Physical and Mechanical Properties of Micro-Cement Grouting Materials with Different Water-Cement Ratio

The water-cement ratio is one of the key parameters of grouting materials, which greatly affects the working performance and mechanical properties of grouting materials. This paper studies the physical properties, such as density, fluidity, consistency, bleeding rate, and stone rate, and the mechanical properties of flexural and compressive strength of micro-cement grouting materials with a water-cement ratio of 0.8:1, 1:1, 1.5:1 and 2.0:1 are investigated through a variety of indoor experiments. The results show that with the gradual increase of water-cement ratio, the density, consistency value, stone rate, flexural strength, and compressive strength of micro-cement grouting material gradually decrease, while the fluidity and bleeding rate of micro-cement slurry gradually increases. Although the slurry with a water-cement ratio of 1.5:1 and 2:1 has good fluidity, the high bleeding rate and the low stone body strength result in more water injected into the reinforced formation and low reinforcement strength. On the contrary, the slurry with a water-cement ratio of 0.8:1 has a low bleeding rate and high stone body strength, but low fluidity. The grouting performance and mechanical properties of the slurry with a water-cement ratio of 1:1 are relatively balanced. This study provides a basis for the subsequent on-site ultra-fine cement grouting project. A reasonable water-cement ratio can be selected according to the specific needs to ensure the reinforcement quality and safety of the grouting operation.

Performance evaluation of ultrafine cement as a grout for reservoir impermeability improvement

Performance evaluation of ultrafine cement as a grout for reservoir impermeability improvement

Research on Carbon Fiber Polymer Ultrafine Cement Grouting Material

With the gradual development of deep coal mining, the demand for roadway support strength is also increasing. For ordinary grouting materials, it cannot be injected into ultra-fine pores, and the tensile strength of its consolidated body is not high. Therefore, in this paper, ultra-fine cement and carbon fiber are used as the raw materials of the grouting fluid to increase the injectability of its fine pores and the tensile strength of the consolidated body. By designing experiments with different carbon fiber content, the grouting material with the best mix ratio was formulated. The test results show that: after the grouting material is mixed with graded sand to prepare a test block, the mechanical properties of the grouting material are optimal when the carbon fiber content is 1%, and the compressive strength is 17MPa and the tensile strength is 1.34MPa.

Experimental and Mechanistic Characterizations of Oil-Based Cement Slurry Flow Behavior Through Fractures in a Carbonate Reservoir

Abstract In this paper, techniques have been developed to experimentally and mechanistically describe the oil-based cement slurry (OBCS) flow through fractures in carbonate reservoirs when it is co-injected with a pad fluid. Experimentally, a three-dimensional (3D) physical model is used to simulate flow behavior within fractures in carbonate rocks by using the ultra-fine cement and class G cement with or without pad fluids. The injection pressures of an OBCS flow are measured and recorded as a function of time during the experiments at a constant flowrate, while effects of fracture width (i.e., 0.5 mm and 1.0 mm) and cement type (i.e., the class G cement and the ultra-fine cement) on injection pressure are examined and analyzed. Theoretically, the Navier–Stokes (NS) equations are modified and integrated to obtain the explicit velocity equations of visco-plastic materials in a planar fracture, and to further quantify the injection pressure of the slurry flow as a function of viscosity, flowing distance of the injected slurry, fracture width, and flowrate. It is found from the experimental measurements that the fracture width imposes a much larger impact on injection pressure along the fracture than other parameters. Once slurry is made in contact with water, its injection pressure not only increases rapidly with one or two orders of magnitude or even larger but also is changed from its linear to exponential relationship with time after a certain time. During the linear stage, the injection pressure of ultra-fine cement is smaller than that of the class G cement, while an opposite pattern is yielded during the exponential stage, i.e., the exponent of the injection pressure formula pertaining to the ultra-fine cement is found to be about 1.5 times larger than that of the class G cement. By incorporating the experimentally measured patterns of the slurry distribution within the fracture model, the newly developed mechanistic model has been validated by reproducing the experimental pressure measurements, allowing us to perform reliable characterization of the OBCS flow behavior in a fracture and then to efficiently and accurately predict and optimize its water-plugging performance.