In order to study the cement-industrial waste-based synergistic curing of silt soil, orthogonal design tests were used to prepare a new curing agent using cement, fly ash, blast furnace slag, and phosphogypsum as curing materials. In order to evaluate the cement-industrial waste-cured soils, unconfined compressive strength tests, fluidity tests, wet and dry cycle tests, and electron microscope scanning tests were carried out. The mechanical properties and microstructure of the cement-industrial slag were revealed and used to analyze the curing mechanism. The results showed that, among the cement-industrial wastes, cement and blast furnace slag had a significant effect on the unconfined compressive strength of the specimens, and the optimal ratio for early strength was cement-fly ash-slag-phosphogypsum = 1:0.11:0.44:0.06; the optimal ratio for late strength was cement-fly ash-slag-phosphogypsum = 1:0.44:0.44:0.06. In the case of a 140% water content, the 28d compressive strengths of curing agent Ratios I and II were 550.3 kPa and 586.5 kPa, respectively. When a polycarboxylic acid water-reducing agent was mixed at 6.4%, the mobilities of curing agent Ratios I and II increased by 32.1% and 35.8%, and the 28d compressive strengths were 504.1 kPa and 548.8 kPa, respectively. When calcium chloride was incorporated at 1.5%, the early strength of the cured soil increased by 33% and 29.1% compared to that of the unadulterated case year on year, and the mobility was almost unchanged. From microanalysis, it was found that the cement-industrial waste produced the expansion hydration products calcium alumina (AFt) and calcium silicate (C-S-H) during the hydration process. The results of this study provide a certain basis and reference value for the use of marine soft soil as a fluid filling material.

Structural damage and foundation leakage are major concerns for earthen dams. To minimize seepage, cutoff walls are typically installed beneath the dam core to act as impermeable barriers. While concrete cutoff walls are widely used, their limited ductility and strength incompatibility with foundation soil present design challenges. Plastic concrete, a modified form of conventional concrete incorporating bentonite and pond ash, offers improved ductility and reduced brittleness, making it a suitable alternative. This study investigates the use of pond ash-based flowable fill as a replacement for normal concrete in plastic concrete cutoff walls. The unconfined compressive strength (UCS) of plastic concrete mixes was analyzed using four advanced regression machine learning algorithms: multivariate adaptive regression splines, extreme neural network (ENN), extreme gradient boosting (XGBoost), and gradient boosting machine (GBM). Several performance indices were used to evaluate model accuracy. The MARS model achieved the highest accuracy, with R2 = 0.990 for training and R2 = 0.963 for testing, followed by XGBoost, GBM, and ENN. SHAP analysis revealed that curing period has the most significant positive effect on UCS, followed by water and cement contents, while bentonite showed the least impact. Key properties were evaluated to determine an optimal mix design. This research enhances the understanding of CLSM-based plastic concrete and supports its application in cutoff walls by developing accurate UCS prediction models, contributing to the improved suitability and sustainability of dam foundation systems.

Limestone calcined clay cement (LC3) is now about to become a new type of cement. Replacing a considerable part of cement with calcined clay makes the new cement more sustainable than ordinary Portland cement. In this investigation, locally available non-kaolinite clayey soil is studied in two stages. Firstly, the calcined temperature, the replacement level of calcined clay, and the ratio of the calcined clay to limestone were optimized. The results were 750 degrees C, 40%, and 3:1, respectively. The optimized mixtures were reinforced with recycled polyethylene terephthalate (PET) and polypropylene (PP) fibers at ratios of 0%, 0.5%, 1%, and 1.5% of the binder's weight. Flowability was measured for the fresh mortar. Mechanical properties such as compressive strength, flexural strength, and splitting tensile strength were studied. Durability properties like fire resistance, water absorption, water sorptivity, and porosity were examined. The results show that 1.5% of PET fiber and 1% of PP fiber showed the best results in terms of mechanical and durability properties. Flexural strength increased from 6.35 to 8.45 MPa and to 7.52 MPa when PP and PET fiber were increased from 0 to 1 and 1.5% respectively. Similarly, tensile strength increased from 3.78 to 4.25 MPa and to 5.25 MPa when PP and PET fiber were increased from 0 to 1.5% and 1%, respectively. However, increasing fibers consistently decreased flowability. This investigation demonstrates the potential of using the locally available non-kaolinite clayey soil to be used as pozzolanic material and to produce LC3. Consequently, LC3 shows the potential to use as a structural material.

Geopolymer-based cementitious materials known for their robust durability and lower environmental impact make them an ideal choice for sustainable construction. The main focus of this study is to understand the influence of chemical admixtures which plays a pivotal role in improving the properties of geopolymer mortar (GM). This research integrates various chemical admixtures, including calcium chloride, sodium sulphate, sodium hexametaphosphate, and MasterGlenium SKY 8233 (SKY) which falls under the category of either accelerators, retarders, or superplasticisers. Assessments were conducted on the fresh and hardened states of flyashbased GM mixes with varying proportion of river sand (RS), laterite soil (LS) and copper slag (CS), encompassing flowability, setting times, compressive strength, durability study in aggressive environmental conditions and microstructural analyses after 56 days of ambient curing. Findings reveal that calcium chloride and sodium sulphate efficiently decrease the initial and final setting times of the geopolymer paste, highlighting their roles as accelerators, with calcium chloride showing greater efficacy than sodium sulphate. On the other hand, sodium hexametaphosphate serves as a retarder, substantially extending the initial setting time of the geopolymer paste. Introducing the modified polycarboxylic ether (PCE) based superplasticiser SKY into the mortar matrix caused the initial setting time to be extended and resulted in a slight drop in compressive strength compared to the other mixes. Durability tests confirmed the superior resistance of GM mixes to harsh environments like acid, sulphate, and marine water exposure. These findings highlight the potential for tailoring geopolymer blends to achieve desired properties under ambient curing conditions using chemical admixtures.

Dredged soil has the disadvantages of high moisture content and low strength, making it unsuitable for practical engineering application. However, a gelling agent system composed of ground granulated blast-furnace slag (GGBS) and carbide slag (CS) can enhance the strength of dredged soil. Additionally, phosphogypsum (PG) can react with the products of this system (calcium silicate hydrate) to form ettringite and improve strength. In this study, CS, GGBS, and PG were selected to solidify dredged soil with high moisture content. The flowability test, unconfined compression test, and direct shear test were employed to evaluate the engineering properties of the dredged soil, while the scanning electron microscope test (SEM), X-ray diffraction test (XRD), nuclear magnetic resonance test (NMR), and toxicity characteristic leaching procedure test (TCLP) to investigate the microstructure evolution of the cured dredged soil. The results indicated that the decreased flowability of cured dredged soil showed a decreasing trend with increased curing agent content. The strength of cured dredged soil increased first and then decreased, and increased finally with the increase of PG content. The optimum PG content was identified as 10 % when the GGBS content was set as 15 %. The internal friction angle of cured dredged soil increased with increased PG content. The change of pore structure and hydration reaction were identified as the main root cause for the change of sample strength. The new cementing material composed of CS, GGBS and PG can effectively resolve the insufficient strength and high water content problems of dredged soil, while having negligible impact on the environment. Moreover, since it is made up of industrial by-products, it has a lower carbon footprint than the traditional cementing materials of lime or cement.

A series of laboratory tests were conducted to investigate the properties of fiber-reinforced underwater flowable solidified soil (UFSS) as a novel material for scour protection in marine structures. The tests included flowability, underwater anti-dispersion, unconfined compressive strength (UCS), and anti-scour resistance. Results showed that adding fibers reduced UFSS's flowability and significantly enhanced its underwater anti-dispersion, exhibiting a similar trend with increasing fiber content. Increasing fiber length initially decreased and then increased flowability, with the opposite trend for anti-dispersion. The least favorable fiber lengths for flowability were 6 mm for PVA fiber and 9 mm for both basalt and glass fibers, whereas these lengths were optimal for antidispersion. Fibers improved both UCS and anti-scour resistance of UFSS, with both properties first increasing and then decreasing as fiber content and length increased. Excessive fiber content or length reduced both properties. In this study, the optimal fiber content for improving UCS was 0.3% for PVA and 0.2% for basalt and glass fibers, with an optimal length of 6 mm for all three. An empirical exponential relationship between UCS, critical scour resistance velocity, and critical scour shear stress at typical times (t = 3 h, 5 h) was established for rapid prediction of UFSS's anti-scour resistance.

To decrease the environmental impact and increase the high-quality resource utilization of construction spoil (CS), the alkali-activated slag (AAS) was selected to solidify CS and prepare solidified construction spoil (SCS). SCS with certain working and mechanical properties can be used as building materials, such as unsintered bricks. However, the preparation of SCS is inefficient, mainly because the properties of SCS are affected by various factors, and the formula is difficult to determine. This study intensively investigated the effects of the liquid-solid ratio (W/ (B + S)), clay content of CS, and binder-soil ratio (B/S) on the flowability and compressive strength of SCS. It was found that W/(B + S) was the main factor controlling compressive strength, and both W/(B + S) and clay content significantly affected the flowability of SCS. Based on an assumption for the flowability prediction method and the relationship between flowability and liquid-solid ratio of CS, AAS, and SCS, a method to predict the flowability of SCS was proposed and validated. Additionally, the extended Abrams' law was applied to fit the compressive strength variation of SCS. Combining the flowability prediction method and the extended Abrams' law, a novel formula design method for SCS was proposed and proven effective in validation experiments.

Civil excavation projects frequently yield substantial excess spoil, posing challenges to sustainable construction. This study explores repurposing such spoil for creating controlled low strength material (CLSM), emphasizing the novel use of polycarboxylate superplasticizer (PCE) to reduce the water requirement. The work also distinctively utilizes water film thickness (WFT) theory to elucidate the effects of PCE dosage and WFT on material properties, thereby advancing CLSM mix design. First, using an experimental approach, a series of fresh CLSM samples are prepared, with varying the water-to-solid ratio (W/S) and PCE dosage, to evaluate their packing density, WFT, flowability, and bleeding rate. It is demonstrated that both packing density and WFT experienced a non-linear increase with rising PCE dosage. Regression analysis of the experimental data reveals that the flowability and bleeding rate linearly increase with the rising WFT, and the enhancements are more pronounced at higher PCE dosage. Notably, at a given WFT, the impact of PCE dosage on flowability and bleeding rate reduce as WFT decreases. Additionally, the research identifies specific WFT thresholds correlating with maximum flowability and a 5% bleeding rate. These thresholds mark the critical point at which WFT ceases to influence flowability and delineate the maximum WFT that satisfies the bleeding rate requirements, respectively. These insights are important for optimizing the design of CLSM with PCE in terms of flowability and bleeding rate.

In urban areas, backfilling voids with complex and narrow shapes necessitates alternative backfill methods and materials, such as controlled low-strength materials (CLSMs), to minimize ground subsidence caused by improper compaction of backfill soils. This study aims to propose a predictive methodology for the mechanical properties of CLSMs using regression analysis and a deep neural network (DNN). CLSM mixtures are prepared with various mixing ratios of calcium sulfoaluminate (CSA) expansive admixture, water, Portland cement, fly ash, sand, silt, and alkali-free accelerator. The flow consistency and compressive strength at 12 hrs and 7 days post-mixing are estimated. The relationships between CLSM mixing ratios and the estimated mechanical properties are established through multiple regression analysis and DNN. The DNN's performance is evaluated, with coefficients of determination being 0.0874, 0.8432, and 0.6826 for flowability, and compressive strength at 12 hrs and 7 days, respectively. To address the low performance, oversampling algorithms like the synthetic minority oversampling technique (SMOTE) and the conditional tabular generative adversarial network (CTGAN) are utilized. Analysis of the oversampled data using SMOTE indicates improved performance, with the coefficients of determination rising to 0.6818, 0.9856, and 0.983 for flowability, and compressive strength at 12 hrs and 7 days, respectively. This study illustrates that the identified correlations may be effectively used to predict flowability and compressive strength based on the mixing ratio.

Dynamically loaded soils can exhibit large-deformation flow liquefaction or limited-deformation cyclic mobility mechanisms, depending on the initial state of the soil. Undrained cyclic triaxial tests were performed on saturated calcareous and silica sand specimens prepared with different relative densities and subjected to various effective confining pressures and cyclic stress ratios to study the flowability of viscous liquefied sand. The cyclic shear stress-strain rate relationship for calcareous and silica sands transitioned from an elliptical shape to an asymmetric Lame curve shape as excess pore pressures accumulated under cyclic loading. The asymmetric Lame curve-shaped relationship demonstrates that the saturated sand exhibited low shearing resistance and high fluidity under elevated excess pore pressures for the conditions evaluated. The average flow coefficient, kappa over bar , defined as the maximum shear strain rate triggered by the unit average cyclic shear stress, and the flow curve defining the variation in kappa over bar with the number of loading cycles, describes the flowability of the saturated sand and is used to quantify the cyclic failure potential of the saturated sand under a proposed viscous fluid flow failure criterion. The effect of relative density, effective confining pressure, and cyclic stress ratio on the flow curves and the number of cycles to failure under the proposed viscous fluid flow failure criterion is discussed and compared with the cyclic resistance determined from widely used excess pore pressure- and strain-based cyclic failure criteria. The viscous fluid flow cyclic failure criterion is more stringent than these alternative criteria, and the corresponding axial strains are consistent with those associated with liquefaction triggering under cyclic strain approach.