Search Results (58)

Pea-gravel grouting, which fills the gap between the lining of tunnels and the surrounding rock, is crucial for the structural stability and waterproofing of water delivery TBM tunnels. However, it is prone to defects due to complex construction conditions and geological factors. To provide practical insights for engineers to evaluate grouting quality and take appropriate remedial action during TBM tunnel construction, this paper assesses four types of pea-gravel grouting defects, including local cavities, less density, rich rock powder and rich cement slurry. Detailed numerical simulation models comprising segment lining, pea-gravel grouting and surrounding rock were built using the 3D finite element method to analyze the displacement and stress of the segments at the transition zone between different classes of surrounding rocks, labeled V–IV, V–III and IV–III. The results indicate that a local cavity defect has the greatest impact on the loading response of segment lining, followed by less density, rich rock powder and rich cement slurry defects. Their impact will weaken with better self-support of the surrounding rocks in the order of V–IV, V–III and IV–III. The tensile stress of segment lining is within the limit of concrete cracking for combinations of all four defects when the surrounding rock is of the class IV–III, and it is within this limit for two-defect combinations when the surrounding rock is of classes V–III and V–IV. When three defects or all four defects are present in the pea-gravel grouting, the possibility of segment concrete cracking increases from the transition zone of class V–III surrounding rock to the transition zone of class V–IV surrounding rock. Full article

This research focuses on improving the characteristics of recycled concrete and utilizing solid waste resources through the combination of industrial waste pre-impregnation and the carbonation process. A novel pre-impregnation–carbonation aggregate method is proposed to increase the content of carbonatable components in the surface-bonded mortar of recycled coarse aggregate by pre-impregnating it with carbide slag slurry (CSS). This approach enhances the subsequent carbonation effect and thus the properties of recycled aggregates. The experimental results showed that the method significantly improved the water absorption, crushing value, and apparent density of the recycled aggregate. Additionally, it enhanced the compressive strength, split tensile strength, and flexural strength of the recycled concrete produced using the aggregate improved by this method. Microanalysis revealed that CO₂ reacts with calcium hydroxide and hydrated calcium silicate (C-S-H) to produce calcite-type calcium carbonate and amorphous silica gel. These reaction products fill microcracks and pores on the aggregate and densify the aggregate–paste interfacial transition zone (ITZ), thereby improving the properties of recycled concrete. This study presents a practical approach for the high-value utilization of construction waste and the production of low-carbon building materials by enhancing the quality of recycled concrete. Additionally, carbon sequestration demonstrates broad promise for engineering applications. Full article

Geopolymer foam concrete (GFC) is a green, lightweight material produced by introducing bubbles into the geopolymer slurry. The raw materials for GFC are primarily silicon–aluminum-rich minerals or solid waste. Lead–zinc tailings (LZTs), as an industrial solid waste with high silicon–aluminum content, hold significant potential as raw materials for building materials. This study innovatively utilized LZTs to prepare GFC, incorporating MK, GGBS, and alkali activators as silicon–aluminum-rich supplementary materials and using H₂O₂ as a foaming agent, successfully producing GFC with excellent properties. The effects of different LZT content on the pore structure and various macroscopic properties of GFC were comprehensively evaluated. The results indicate that an appropriate addition of LZT effectively optimizes the pore structure, resulting in uniform pore distribution and pore shapes that are more spherical. Spherical pores exhibit better geometric compactness. The optimal LZT content was determined to be 40%, at which the GFC exhibits the best compressive strength, thermal conductivity, and water resistance. At this content, the dry density of GFC is 641.95 kg/m³, the compressive strength reaches 6.50 MPa after 28 days, and the thermal conductivity is 0.176 (W/(m·K)). XRD and SEM analyses indicate that under the combined effects of geopolymerization and hydration reactions, N–A–S–H gel and C–S–H gel were formed. The preparation of GFC using LZTs shows significant potential and research value. This study also provides a feasible scheme for the recycling and utilization of LZTs. Full article

Homogenized micro-crack crushing is an optimal rehabilitation technology for concrete pavement; however, when there are weak road base issues, some measures need to be taken to treat the diseases. Grouting is a common technique for addressing weak road base issues. This study developed a new visual indoor grouting test system to analyze the diffusion and consolidation of slag-based geopolymer slurry. The reactants of the geopolymer and the consolidation state of the slurry and aggregate were observed. Moreover, the reinforcement effect of the slurry on a weak road base was studied through the on-site grouting and excavation of the test pit. The results show that, during indoor grouting tests, as the size of the aggregate decreases, the slurry diffusion depth gradually decreases: only 9.5–4.75 mm aggregate formed a complete cylindrical specimen. In the tests of unformed cylindrical specimens, the 9.5–4.75 mm aggregate will develop 20–50 mm splitting surfaces, while the 4.75–2.36 mm aggregate will develop slurry bulbs and veins of different sizes, but the development is not obvious in the 2.36–1.18 mm aggregate. Fine aggregate grouting will exhibit the pressure filtration effect—especially for the 2.36–1.18 mm aggregate, the pressure filtration effect is the most obvious. An SEM microstructural analysis demonstrated that the geopolymer with a water–slag ratio of 0.4 has a faster hydration and dissolution, which results in a decrease in the density of local reactants. However, the polymerization of geopolymers is more complete. The pores of the coarse aggregate are larger and the slurry filling is denser, while the pores of the fine aggregate are smaller and the consolidation is loose locally. The consolidation of aggregates has cracks at local locations, but the width of the cracks is relatively small. On-site grouting applications revealed that the geopolymer slurry filled the bottom voids of pavement slabs and deep gaps in the road base layers, and the average deflection of the driveway decreased from 104.8 (0.001 mm) to 48 (0.001 mm) after grouting. Weak road base conditions were successfully treated, leading to a significant improvement in bearing capacity. Full article

Geopolymer-based grouting materials often have a higher early strength, better durability, and lower environmental impact than those of traditional cement-based grouts. However, existing geopolymer grouts face common challenges such as rapid setting and low compatibility with treated substrates. This study develops a new grouting material using industrial byproducts to overcome these limitations while optimizing performance for reinforcing silty mudstone slopes. The base materials used were ground granulated blast furnace slag (GGBFS) and zeolite powder, with calcium lignosulphonate (CL) serving as the retarding agent and NaOH as the alkali activator. The investigation focused on the effects of the mix ratio and water–binder ratio on the setting time, flowability, bleeding rate, concretion rate, and compressive strength of the new grouting material. Scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses were employed to examine the action mechanism of the material components in the slurry. The one-factor standard deviation method and Grey Relational Analysis (GRA) were used to assess the influence of each material component on the slurry performance indices and the correlation between each performance index and its optimal mix ratio. Subsequently, the optimal mix ratio of the new grouting material was ascertained. The results indicate that the setting time is positively correlated with the zeolite powder and CL dosages and the water–binder ratio, while it is inversely related to the NaOH dosage. The flowability is significantly enhanced with increasing zeolite powder and NaOH dosages, but decreases at a higher CL dosage and water–binder ratio. This insight is crucial for optimizing the workability of the grouting material under various conditions. The optimal ratio of the grout is zeolite powder:GGBFS:CL:NaOH = 30:70:5:7, with a water–binder ratio of 0.6. Compared to existing commercial grouting materials, the compressive strength of this new grout is comparable to that of silty mudstone. This significantly reduces the problem of stress concentration at the grout–rock interface due to strength differences, thus effectively reducing the risk of secondary cracking at the interface. These findings provide a new material solution for grouting and repairing fractured silty mudstone slopes. Full article

Cemented Sand, Gravel, and Rock (CSGR) dams have traditionally used either Conventional Vibrated Concrete (CVC) or Grout-Enriched Roller Compacted Concrete (GERCC) for protective and seepage control layers in low- to medium-height dams. However, these methods are complex, prone to interference, and uneconomical due to significant differences in the expansion coefficient, elastic modulus, and hydration heat parameters among CSGR, CVC, and GERCC. This complexity complicates quality control during construction, leading to the development of Grout-Enriched Vibrated Cemented Sand, Gravel, and Rock (GECSGR) as an alternative. Despite its potential, GECSGR has limited use due to concerns about freeze–thaw resistance. This project addresses these concerns by developing an air-entrained GECSGR grout formulation and construction technique. The study follows a five-phase approach: mix proportioning of C₁₈₀6 CSGR; optimization of the grout formulation; determination of grout addition rate; evaluation of small-scale lab samples of GECSGR; and field application. The results indicate that combining 8–12% of 223 kg/m³ cement grout with 2–2.23 kg/m³ of admixtures, mud content of 15%, a marsh time of 26–31 s. and a water/cement ratio of 0.5–0.6 with the C₁₈₀6 parent CSGR mixture achieved a post-vibration in situ air content of 4–6%, excellent freeze–thaw resistance (F300: mass loss <5% or initial dynamic modulus ≥60%), and permeability resistance (W12: permeability coefficient of 0.13 × 10⁻¹⁰ m/s). The development of a 2-in-1 slurry addition and vibration equipment eliminated performance risks and enhanced efficiency in field applications, such as the conversion of the C₁₈₀4 CSGR mixture into air-entrained GECSGR grade C9015W6F50 for the 2.76 km Qianwei protection dam. Economic analysis revealed that the unit cost of GECSGR production is 18.3% and 6.33% less than CVC and GERCC, respectively, marking a significant advancement in sustainable cement-based composite materials in the dam industry. Full article

Dam foundations are prone to leakage damage after being exposed to long-term water action, which seriously affects the operation safety of the dam. At present, concrete cut-off walls serve an important means of anti-seepage for dam foundations. However, due to construction challenges, the cut-off wall needs to be poured segment-by-segment during the construction process, and the joints between adjacent segments become weak parts for seepage prevention. Therefore, it is crucial to clarify the stress state of segmented discontinuous concrete cut-off walls. Based on the Lee-Fenves framework and the tension–compression constitutive relationship of fracture energy, a plastic damage calculation method was established in this paper to characterize the mechanical behavior of discontinuous cut-off walls. The method was then used to analyze the mechanical performance of discontinuous walls with segment joints containing slurry cake. The research results showed that compared to the continuous cut-off wall, the vertical settlement in the middle part of the discontinuous cut-off wall increased by 5.8%, and the displacement along the river flow direction decreased by 35.3%. As the wall segment width decreased, the joint opening and the degree of tensile damage were reduced accordingly, while the compressive damage in the middle and lower parts of the wall was intensified. As the wall depth decreased, the constraints and load on the bottom of the wall showed obvious changes, leading to a reduced stress and damage level of the wall. The findings provide reference for the design and safety control of cut-off walls. Full article

As coal resource development progresses deeper underground, the increasing depth of mine shafts poses significant challenges to the safety and stability of traditional shaft construction methods, further compounding operational difficulties. In this context, cast-in-situ concrete shaft walls in a slurry environment have emerged as an effective solution. The strength of these shaft walls is a crucial parameter for assessing their safety. To explore this, experiments were conducted on slurry preparation and mortar casting (used here as a substitute for concrete) under three different conditions: slurry environment, pure water environment, and dry environment. The cast specimens underwent compressive, tensile, shear, and microscopic observation tests to analyze the strength development patterns of the mortar specimens in these varied casting environments. The study yielded several key findings: As the casting environment becomes more complex, the strength of the mortar specimens gradually decreases. Specifically, specimens cast in a slurry environment exhibit strengths approximately 15% to 20% lower than those cast in a dry environment, although both environments show similar trends in strength development over time. Across all casting environments, the initial strength loss of the specimens is significant, while the rate of strength loss decreases in the later stages; the strength loss is minimal in specimens cast in a pure water environment and reaches its maximum in those cast in a slurry environment. Additionally, in specimens cast in a slurry environment, air void diameter tends to polarize, and the distribution of air void is denser compared to the other two environments. In conclusion, cast-in-situ mortar in a slurry environment exhibits the lowest strength and the greatest strength loss compared to specimens cast in dry and pure water environments. Nonetheless, the strength development trends over time remain similar across all conditions, providing theoretical and technical support for the construction of shaft walls in slurry environments. Full article

Superfine cement is widely used in building reinforcement and repair, special concrete manufacturing, and environmental protection engineering due to its high toughness, high durability, good bonding strength, and environmental friendliness. However, there are some problems in superfine cement slurry, such as high bleeding rate, prolonged setting time, and consolidated body volume retraction. In this article, on the premise of using the excellent injectability of superfine cement slurry, the fluidity, setting time, reinforcement strength, and volume expansion rate of novel expansive superfine cement slurries with varying proportions were analyzed by adding expansion agent UEA, naphthalene-based water reducer FDN-C, and triisopropanolamine accelerating agent TIPA. The results show that under most mix ratios, the bleeding rate and fluidity of the novel superfine cement slurry initially increase and decrease with rising water-reducing agent dosage. The initial setting time generally decreases with accelerating agent dosage, reaching a minimum value of 506 min, representing a 33.68% reduction compared to the benchmark group (traditional superfine cement). Under normal conditions, the compressive strength of the net slurry consolidation body is positively correlated with expansion agent dosage, achieving maximum strengths of 8.11 MPa at three days and 6.93 MPa at 28 days; these values are respectively higher by 6.7 MPa and 2.6 MPa compared to those in the benchmark group. On the seventh day, the volume expansion rate of the traditional superfine cement solidified sand body ranges from −0.19% to −0.1%, while that for the corresponding body formed from the novel superfine cement is between 0.41% and 1.33%, representing a difference of 0.6–1.43%. After the on-site treatment of water and sand-gushing strata, the core monitor rate of the inspection hole exceeds 70%. The permeability coefficient of the stratum decreases to a range between 1.47 × 10⁻⁶ and 8.14 × 10⁻⁶ cm/s, resulting in nearly a thousandfold increase in stratum impermeability compared to its original state. Hence, the findings of this research hold practical importance for the future application of such materials in the development of stratum reinforcement or building repair. Full article

A large amount of waste slurry water will be generated in the production process of concrete mixing plant, due to the complex composition of waste slurry water, if it is not handled in time when stored, serious coagulation will occur, which will accelerate the loss of equipment and reduce the utilization rate. In this paper, a super retarder suitable for waste slurry recycled water from concrete mixing plant was prepared using composite technology. The waste slurry recycled water mixed with super retarding agent was characterized by using microscopic testing means XRD, TG and DTG. The waste slurry recycled water mixed with super retarding agent was used to replace tap water in the production of concrete, and its effect on the workability and mechanical properties of concrete was investigated. It was found that the compounding of Butane 2-phospho-1,2,4-tricarboxylic acid (PBTCA) with Reclaimed water treatment agent (ACS) resulted in a setting time of 64 h for 10% concentration of recycled water, with optimal retarding effect. When PBTCA:ACS was 1:20, mixed at 1.5% of the mass of recycled water, the 1 h slump of concrete had no loss, the loss of extension was 15 mm, the 7 days compressive strength was increased by 3.5 MPa, and the 28 days compressive strength was increased by 3.0 MPa. The microscopic results showed that the use of ACS and PBTCA does not affect the type of cement hydration products, but only affects the the rate of hydration product generation. Full article

In this paper, we study the influence of density and the water–cement (W/C) ratio on the slurry fluidity, compressive strength, and water absorption of foamed concrete (FC) and its mechanism of action, with the aim of proposing an optimal mix ratio for FC to reduce cement usage and carbon emissions in the construction industry and ensure the good overall performance of FC. In this experiment, two groups of experiments were designed using the control variable method. Fluidity and uniaxial compression tests showed that when the density was 600 kg/m³ and the W/C ratio was 0.6, the FC slurry had maximum fluidity, but its mechanical properties were poor and it collapsed easily. Conversely, by analyzing the uniaxial compressive strength/cement (UCS/C) ratio, it was observed that the mix ratio had a maximum cement utilization rate (W/C ratio) of 0.5 and a density of 1000 kg/m³. Nondestructive testing methods were used to measure the ultrasonic pulse velocity (UPV) and rebound value of the FC test block, and the strength and durability of FC were analyzed. The water absorption rate of the FC test block was tested, and the final analysis showed that the optimal mix ratio of FC in this test was W/C = 0.5, with a density of 1000 kg/m³. Full article

The mining of the part of the inclined ore body below a goaf is crucial for improving resource extraction and safe production. In this study, the cementation properties of crushed stone during the mining of the inclined ore body were investigated by means of laboratory experiments, theoretical analysis, and numerical simulation. Additionally, orthogonal experiments were performed to assess how factors like water–cement ratio, crushed-stone particle size, and cement–sand ratio affect the strength of the grouting concretion body (GCB). Furthermore, the fluidity of the slurry under different ratios was also measured. Considering both the fluidity of the slurry and the strength of the GCB, the optimal ratios of the slurry were determined to be a water–cement ratio of 2.5:1 and a cement–sand ratio of 1:4. This ratio was then used for crushed-stone cementing under the poorest crushed-stone particle size conditions, based on which mechanical parameters were obtained from experiments. Theoretical analysis equated the problem of the grouting range to the width of the plastic zone of surrounding rock, and a conclusion was reached that the width of the GCB should be at least 29 m. The numerical simulation results reveal that among 30 mining rooms formed below the GCB, 24 mining rooms are in a stable state and 6 mining rooms are partially damaged on a small scale. As a whole, the GCB formed by grout filling into the goaf manages to effectively support the stope below, and it is verified that the theoretical calculation method of the width of the GCB is feasible. Full article

This study developed three composite slurries for coating recycled aggregate by incorporating polyacrylate emulsion, fly ash, and gypsum into a cement-based mixture. The filling and pozzolanic effects of fly ash help to improve microcracks in the recycled aggregates. The polyacrylate emulsion forms a strong bonding layer between the cement matrix and the aggregates, enhancing the interfacial bond strength. Based on relevant studies, the following mix designs were developed: Slurry 1 consists of pure cement paste; Slurry 2 contains 15% fly ash and 3% gypsum added to the cement paste; Slurry 3 adds 22% polyacrylate emulsion to the slurry. The study first compared the effects of the three composite slurries on the crushing value and water absorption of recycled aggregates, and then analyzed their impact on the mechanical properties, permeability, and drying shrinkage of concrete. Finally, the mechanisms behind the enhancement were investigated using the Vickers Hardness Test (HV), Mercury Intrusion Porosimetry (MIP), and scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS). The results showed that the polyacrylate emulsion composite slurry had the most significant improvement effect. For recycled aggregate AL, the crushing value decreased from 28.8% to 22.5% and the saturated surface–dry water absorption decreased from 15.1% to 13.8% after cement slurry modification. After coating with the composite slurry, the crushing value further dropped to 18.2% and the water absorption to 9.5%. Two aspects of the performance of recycled aggregates are enhanced with the polymer composite slurry: first, fly ash provides nucleation sites for CH, reducing the tendency for directional CH alignment. Second, the long chains of PAE (polyacrylic ester) encapsulate cementitious particles, effectively filling surface defects on the recycled aggregates, improving the bonding strength at the new-to-old interface, and significantly enhancing the performance of both recycled aggregates and recycled concrete. Full article

Bolivia has abundant pebbles, while the supply of crushed stone is limited and unstable. Thus, the resource utilization of local pebble as a coarse aggregate and the guarantee of concrete durability are the key scientific issues in the Sucre Highway Project. In this paper, a comparative analysis was conducted of the performance of crushed stone concrete and pebble concrete. Additionally, the impact of fly ash on the water permeability resistance of concrete was investigated. The results indicate that the apparent density, bulk density, and void ratio of pebbles are lower than those of crushed stone, and the aggregate gradation of pebbles is dispersed. The type of aggregate is the primary factor influencing the splitting tensile strength of concrete, with the main failure modes of pebble concrete being slurry cracking, aggregate crushing, and interface debonding. While aggregate and fly ash have a minor effect on compressive strength, they significantly impact flexural tensile strength; however, all concretes meet the requirements for extra-heavy, very heavy, and heavy traffic load levels. In terms of impermeability, fly ash effectively mitigates the negative impact of aggregate type on the impermeability of concrete. These findings support the application of pebble concrete in the highway project. Full article

The dissolution of calcium ions in concrete in a low-alkalinity environment is an important factor causing a significant increase in the porosity of internal concrete, leading to a deterioration in its mechanical properties and affecting the durability of the concrete structure. In order to improve the reliability of concrete durability design and significantly increase the service life of concrete structures located in soft water environments, it is crucial to establish an analytical method to predict the elastic modulus (E_dc) of cement slurry systems suffering from calcium dissolution. Firstly, the hydrated cement particles are regarded as a three-phase composite sphere composed of unhydrated cement particles (UC), a high-density hydrated layer (H-HL), and a low-density hydrated layer (L-HL). By introducing the equivalent inclusion phase (EQ) composed of UC and H-HL, the three-phase composite sphere model can be simplified into an equivalent hydrated cement particle model composed of EQ and L-HL. Finally, the E_dc of the two-phase composite sphere composed of the equivalent hydrated cement particles and the porosity of the dissolved cement slurry system are solved by using elasticity theory. The effectiveness of the developed analytical method is verified by comparing it with third-party numerical results. Based on this method, the effects of hydration degree, volume ratio of calcium hydroxide (CH) to hydrated calcium silicate (C-S-H), and volume ratio of inner C-S-H to outer C-S-H on the E_dc of the dissolved cement slurry system are analyzed. The parameter analysis indicates that among the three influencing parameters, the hydration degree has the greatest effect on the E_dc of the dissolved cement slurry system. This study provides an analytical method for predicting E_dc, which can provide some references for the durability design of concrete after calcium dissolution. Full article