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Microbial induced calcite precipitation (MICP) is an environmentally friendly technology to bond sand particle together to form sandstone like materials. In this paper, MICP-treated bio-specimen was developed through MICP. The property of bio-specimen was compared with beams or bricks made through lime modification and cement modification. Ottawa sand was used in MICP-treated bio-specimen preparation. The proportion of lime or cement was in the range of 10–40% by weight of dry sand. The four-point bending tests, brick compression tests and unconfined compression tests were conducted. The test results indicated that flexure strength of MICP-treated bio-specimen was 950 kPa which was similar to flexure strength of 20–25% cement-treated sand beams, but was much higher than flexure strength of 30% lime-treated sand beams. The brick compression strength of MICP-treated bio-specimen achieved 500 kPa, which was similar to brick compression strength of 30% lime-treated sand bricks. The unconfined compression test results showed that the unconfined compression strength (UCS) of MICP-treated bio-specimen (1300 kPa) was higher than UCS of 10% cement-treated specimen (900 kPa), and much higher than UCS of lime-treated sample (around 140 kPa). The relative uniformity of precipitated CaCO3 distribution was achieved through the sample immersing preparation method. SEM images showed that failure pattern of MICP-treated, cement-treated and lime-treated specimens were bond-particle failure.

In western China, artificial freezing is the main effective technology to excavate the deep water-rich strata in mining. The mechanical strength of the frozen wall is the focus of attention in artificial freezing design. Uniaxial compression test was performed on the frozen sandstone samples to investigate the effect of temperature and water content on uniaxial compression strength (UCS); the results indicated that UCS of the wet sandstone increased linearly with the decrease of temperature from − 5 °C to − 20 °C, and the growth rate of the mechanical strength firstly increased and then decreased with increasing water content. Additionally, samples were scanned by X-ray computed tomography (X-ray CT) to explain the variation of macro-mechanical strength of frozen sandstone. The electrical resistivity of frozen sandstone was then measured with decreasing temperature under different water content conditions. The relationship between electrical resistivity and UCS of the frozen sandstone was determined from experimental data, which showed that the UCS of the frozen sandstone increased logarithmically with the increase of electrical resistivity under various water contents.

Genetic programming (GP) is presented as a new tool for the unconfined compression strength of expansive soils (‘UCS-ES’) by utilizing an experimental database with 195 datapoints. The five input parameters employed in formulation of gene expression programming (GEP) and multi gene expression programming (MEP) models are clay fraction (CF), liquid limit (LL), plasticity index (PI), specific gravity (Gs), maximum dry density (ρdmax), optimum moisture content (OMC), and swell percent (Sp). Simplified mathematical expressions were derived for both the GEP and MEP models to compute the UCS-ES. Various statistics, i.e., mean absolute error (MAE), root mean square error (RMSE), Nash–Sutcliffe efficiency (NSE), and correlation coefficient (R), scatter plots, and the sensitivity and parametric study, were used to evaluate the performance of these models. The results revealed that the UCS-ES are accurately determined by both the approaches, with the GEP model producing relatively superior performance (R2TrD = 0.806, R2TsD = 0.668). Furthermore, when the formulated models were compared with other AI models, it was found that they performed more efficiently. Hence, both the GEP and MEP models can reliably be deployed for determining the UCS-ES which reduces the time-consuming and laborious testing, thereby attaining sustainability in countering the problematic water-sensitive soils.

Phosphogypsum (PG) stockpiles occupied a large amount of land resources, and serious environmental pollution problems have attracted the attention of countries around the world. Cemented backfill can reduce the environmental problems caused by tailings stockpiles and is an important development trend in green mine construction. To investigate the effect of binder type on the performance of PG cemented backfill, this paper used ground granulated blast furnace slag (GGBFS) to substitute part of Portland cement (PC) as binder and studied the effect of different ratios of binder on the uniaxial compressive strength (UCS), surface crack extension, acoustic emission (AE) characteristics, and microstructure of PG cemented backfill. The results show that substituting part of PC with GGBFS is beneficial to improve the mechanical properties of PG cemented backfill. When PC was substituted by 50% of GGBFS, the 28d UCS of the backfill was increased from 1.535 to 4.539 MPa. Furthermore, the UCS of the backfill gradually increased as the GGBFS substitution level increased, and more AE signals could be monitored during uniaxial compression. Compared with PC, the sulfate in PG participates in the hydration reaction of GGBFS, more hydrated calcium-aluminum-silicate-hydrate (C-A-S-H) gels and ettringite (AFt) are formed, and the microstructure of the backfill is denser, and the required strength can be obtained with less binder. Thus, substituting part PC with GGBFS as a binder can provide an economical and environmentally friendly alternative for the consumption and reuse of large quantities of PG.

In this study, the effect of lithium slag (LS) on the frost resistance of cement-soil was evaluated. The results of freeze–thaw damage on the surface of the cement-soil, freeze–thaw mass loss, unconfined compression strength, triaxial shear strength, cohesion, and internal friction angle were tested at various freeze–thaw cycles after 90 days of curing when LS was incorporated into the cement-soil at different proportions (0%, 6%, 12%, and 18%). Combining nuclear magnetic resonance (NMR) T2 distribution and scanning electron microscopy (SEM) microscopic images, the mechanism of the effect of LS on the cement-soil was also analyzed. The experiment confirmed that the surface freeze–thaw damage degree and mass loss value of the cement-soil decreased after incorporating different LS contents, and that the unconfined compression strength, triaxial shear strength, cohesion, and internal friction angle also improved significantly compared with the specimens without LS. In this experiment, the optimization level of the cement-soil performance with different LS content was ranked as 12% > 18% > 6% > 0%. According to the NMR and SEM analysis results, the LS content of 12% can optimize the internal pore structure of the cement-soil and strengthen the bond between aggregate particles, hence inhibiting the extension of freeze-swelling cracks induced by freeze–thaw cycles. In conclusion, LS can effectively enhance the frost resistance of cement-soil, and the optimum content in this experiment is 12%.

For safe disposal of wastes in landfills, compacted bentonite is recommended as bottom liners due to their significant cation exchange (CEC) and swelling capacity, low permeability and large specific surface area (SSA). The present investigation carried out various experimental studies determining the compressibility behaviour and unconfined compressive strength (UCS) of two different compacted bentonites in the presence of municipal solid waste (MSW) and synthetic MSW leachates. Various examinations were conducted determining alterations in consolidation parameters like the coefficient of consolidation ( c v ), time taken for 90% consolidation ( t 90 ) and compression index ( C c ) with both leachates. The outcomes reveal that C c and t 90 values of both bentonites declined; however, c v value rose. Results also indicated that under any given consolidation pressure, a lesser void ratio was achieved for leachates. UCS of both bentonites reduced with leachates’ interaction yet, lying within the recommended a value higher than 200 kPa. A comparative assessment of the two bentonites displayed that bentonite having higher CEC and swelling capacity, and SSA unveiled more excellent C c and t 90 values and a reduction in the UCS. A higher variation in behaviour of bentonites was perceived in the existence of MSW leachate in comparison to synthetic MSW leachate.

The proper disposal of discarded waste tires is becoming a serious matter of concern worldwide as huge proportion of this waste is being generated which makes the proper disposal virtually infeasible. About 1000 million of waste tires are discarded every year, and by the year 2030, it will turn up to 1200 million per year. If this enormous quantum of waste remains unattended, it would led to serious health and environmental problems. The investigation aims at appraising the compaction and strength characteristics of clayey soil incorporated with waste crumb rubber and cement for its sustainable use in geotechnical application. A series of unconfined compression strength and split tensile strength tests were carried out on clayey soil incorporated with two percentages of cement (3 and 6%) by weight and four percentages of crumb rubber (2.5, 5.0, 7.5, and 10.0%) by weight. Moreover, scanning electron microscope analysis was also carried out to get better intuition about the behaviour of the composite. Test results suggested that crumb rubber (up to 5%) could be mixed with uncemented/cemented clay soil with the congruent impression. The inclusion of discarded waste tires in cemented clay would be one of the congenial methods for the disposal of this waste as it substantially reduces the deleterious influence of waste tire disposal on human health and ecology.

The application of stabilised soil in agricultural construction works such as shallow foundation fills and subgrade material for farm roads is in demand due to the improved geotechnical properties. This study focused on improving the compressive capabilities and the permeability characteristics of rice husk ash (RHA)-treated clayey soils using basalt fibre. Basalt fibres are made from naturally occurring basalt rock, yet their use in soil stabilisation has not been realised due to limited research for its validation in ground stabilisation. Essential variables in the stabilised soil matrix included basalt fibre length (3 mm, 6 mm, and 12 mm), RHA percentages (5%, 10%, and 15%), and cement percentage (3%). In addition, the optimum moisture content of each admixture was determined by standard proctor compaction tests and reduced by 3% to prepare the specimens for unconfined compression strength test, constant head permeability test, and scanning electron microscope (SEM) test. It was observed that the unconfined compression strength of the RHA-basalt fibre stabilised clayey significantly increased when the specimens wet cure for 28 days. Similarly, adding fibres into the soil improved the permeability coefficient. The SEM test showed a porous morphology that increased permeability. Furthermore, through SEM, the randomly oriented basalt fibres’ portrayed the reinforcing phenomenon related to improved compressive strength and sufficient bearing capacity to support structures built upon this class of soils.

Purpose: This paper studies a 3-dimensional pallet loading problem considering interlock stacking pattern, box dimensions, humidity, and storage time, where overlapping and overhanging are not allowed. Despite the importance of this problem in the literature, our work provides the first method that considers the environmental conditions such as 1) storage time and 2) humidity, and their tremendous impacts on the strength of the boxes, as has been observed widely in the DHL supply chain.Design/methodology/approach: This paper proposes a two-phase heuristic algorithm to solve a 3-dimensional pallet loading problem under real conditions (relative humidity, and storage time) considering interlock stacking patterns, where overlapping and overhanging are not allowed. In phase 1, the horizontal layer configuration is determined by block techniques. Three types of horizontal layers are created based on box dimensions perpendicular to the base. In phase 2, a novel mathematical model is propounded to improve the pallet volume utilization, and stability considering the pallet's maximum allowable height and weight, and the dynamic compression strength of boxes. The dynamic compression strength of boxes is calculated by the modified McKee formula. Two performance measures, pallet volume utilization and stability (load height), are utilized to evaluate the performance of the proposed heuristic algorithm in real-world instances (DHL Supply Chain). Findings: The results illustrated that the dynamic compression strength of boxes decreases as the relative humidity and storage time increase. The load height changes dynamically along with box dimensions, box alignment, direction, relative humidity, and storage time. Increasing relative humidity and storage time and applying an interlock stacking pattern reduce the pallet utilization, however, enhance the pallet stability. Finally, the proposed heuristic algorithm's efficacy increases as the identical boxes dimensions' heterogeneity increases.Originality/value: It is believed in the supply chain where these characteristics are observed, the implementation of the heuristic algorithm will help them improve the pallet volume utilization and stability.

Introduction. Recent years have seen a pressing need to dispose of municipal solid waste due to rapid urbanization. The municipal solid waste incineration fly ash (MSWIFA) produced from solid waste incineration power plant exhibits pozzolanic properties and poses concern of toxicity leaching when used directly as building materials. This paper presents an alkali-activation method to produce sustainable alkali-activated MSWIFA materials (AAFMs) with various MSWIFA dosages and investigate the corresponding fabrication and performance. Materials and Methods. Composited alkali activators activate the MSWIFA with constant alkalinity of 5% and the molar ratio of Si/Na = 0.86. The resulting geopolymers' bulk densities, mineral composites, morphology, and compression strength are thoroughly examined. Results and discussions. Results show that the use of MSWIFA may lead to more loose structures because the bubbles are generated from metallic aluminum and alkali activators. Additionally, the production of multiple crystals also accounts for increasing porosity. The generated multi-crystals such as Sylvite, Halite, Hydrocalumite, Calcium Hydroxide, and Ettringite are further detected from the morphology and mineral analysis. Furthermore, compression tests and toxicity characteristic leaching procedures (TCLP) are conducted to investigate the mechanical performance and heavy metals solidification performance of AAFMs, with an optimal compression strength of 19.99MPa at 28 days for AAFM-10 while toxicity leaching is subject to regularity limits. Conclusions. This study shows that great potential of using the alkali-activation method to recycle hazardous municipal solid fly ash into construction materials with both ecological safety and high performance.