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By adjusting the content of geopolymer in geopolymer stabilized phosphogypsum (GSP) as roadbed filler, along with the mixing ratio, this paper mainly explores tendencies in the mechanical properties and water stability of GSP. This research is based on macro-mechanical properties such as unconfined compressive strength, resilience modulus, California bearing ratio and shear strength. It is also based on water stability tests, such as the water soaking test, dry and wet cycle test and expansion test, to explore changes in water stability. As for the durability of GSP, this paper is mainly based on the realization of a long time observation of mechanical properties and water stability. In the existing research, most of the stabilized phosphogypsum (PG) base material or roadbed filler consists of cement, lime, etc. In this paper, a new exploration is carried out on the composition of stabilized PG material, realized without the participation of cement. The 28 d compressive strength of GSP reaches 2.5 MPa, and over time this strength grows, which prevents the phenomenon of strength inversion that may occur in conventional cement-stabilized PG. In addition, a long-term soaking experiment was designed in this study based on the material after the strength was stabilized for up to 90 d. After the strength was steady, the GSP with the best water stability still had a softening coefficient of 80% after experiencing water immersion for 7 d. After determining the feasibility of the mechanical properties and water stability of GSP as roadbed filler, we further explored the strength formation mechanism of GSP by microscopic tests (XRD and SEM). This shows that geopolymer can stabilize PG in two main ways: one is the hydration reaction with PG to generate C-S-H gel and ettringite, and the other is to connect PG not involved in the chemical reaction to form a dense whole through generated hydration products. Geopolymer, stabilizing a high amount of PG, not only provides a new method for the consumption of PG, but also has more stable performance than cement, and has certain advantages in economy. In addition, the advantage of this study is that good performance can be achieved by simply sieving PG and adjusting the geopolymer ratio in practical engineering projects. [ABSTRACT FROM AUTHOR]

Soil stabilization using additives is considered as one of the sustainable alternative techniques to deal with acute material shortages. Critically reviewing the contemporary works on soil stabilization would help practitioners and researchers to comprehend the merits and demerits of each stabilization method, influential parameters, and associated constraints. Furthermore, the critical analysis might aid the authorities to develop standard protocols about the use of various additives for soil stabilization, which would persuade the industry personnel to adopt sustainable practices. This paper presents a methodical review of the present soil stabilization methods under five key areas namely, underlying chemistry, the influential factors, performance indicators, economic and environmental aspects, and industrial perspectives. Findings of the review indicate that cement-based stabilizers perform well irrespective of soil type and curing conditions, on the contrary, lime-based stabilizers require appropriate temperature and pH for strength development. The degree of stabilization depends mainly on soil type, compaction level, and curing type and condition. Most of the soils treated with different additives exhibited a reduction in plasticity index, and maximum dry density against stabilizer dosage irrespective of soil type. The typical values of unconfined compressive strength and California bearing ratio of inorganic and organic soils except for peat, treated with a 5% dosage of all common types of stabilizers, fall in between 700 and 1,500 kPa and 30–60%, respectively. Cement and cementitious blends exhibited better cost-to-strength, energy-to-strength, and CO2 emission-to-strength ratios for soils with low plasticity whereas lime-blended stabilizers seemed effective for high-plastic soils. [ABSTRACT FROM AUTHOR]

Significant amounts of Natural Aggregate (NA) materials are being used to meet the requirements of pavement structure. Simultaneously, enormous amounts of demolition waste, such as demolished concrete and reclaimed pavement materials, are dumped into landfills along roadsides, creating pressure on the environment. Therefore, the recycling of demolished materials and their utilization for pavement construction would result in conservation of natural aggregates, this would alleviate the problems related to geo-environment and bring several benefits for the environment and ensure sustainability. Several studies have been carried out to describe the mechanical properties of recycled concrete aggregate (RCA) with and without stabilization. A thorough understanding of performance-related engineering properties of unbound RCA and stabilized RCA is essential for mechanistic-empirical pavement design. This paper reviewed the mechanical properties such as compaction, California bearing ratio, resilient modulus, and permanent deformation in the case of unbound RCA, and unconfined compressive strength, flexural strength, and stiffness for stabilized RCA from accessible works of literature on the application of RCA for pavement base. The findings from the literature indicated that RCA is source-dependent, moisture sensitive, and subjected to particle breakdown under wheel load that results in reduced shear strength. Further, if RCA is treated with mechanical stabilization by geosynthetics, the interface shear strength properties improve, and permanent deformation is reduced. Chemically stabilized RCA is a promising technique as its strength and durability complied with stabilized NA. Therefore, this review will be helpful for pavement engineering practitioners to explore RCA use in pavement base or subbase layers. [ABSTRACT FROM AUTHOR]

Unbound graded aggregates are used to construct the base and subbase of road pavement. The mechanical properties of unbound graded aggregates depend significantly on aggregate size and grading, especially on the maximum particle size (Dmax) and fines content (Fc; typically, the particle size of fines < 0.075 mm). Nowadays, not only natural aggregates (NA) but also recycled aggregates (RA) from construction and demolition waste are used in road construction. Many studies have been done to characterize the mechanical properties of RA, but a comprehensive understanding of the effects of aggregate size and grading on the mechanical properties has not been fully achieved due to the wide variety of material types and properties of RA. Therefore, this paper searched previous studies and reviewed the effects of particle size, type of aggregate, and mixing proportions of RA on mechanical properties such as compaction, bearing capacity, resilient modulus, and shear strength. In addition, some information on the environmental safety of RA, such as leachate pH and leaching of elements, are summarized. The results collected from the literature indicate that the mechanical properties of RA and their mixtures are mostly comparable to those of NA and can be used to construct road base and subbase. As well as the type of aggregate, Dmax of RA was also found to affect highly the relationships between the mechanical indices (e.g., the maximum dry density and California bearing ratio) and Fc and/or mixing proportion. [ABSTRACT FROM AUTHOR]

Nowadays, for soil stabilisation and cleaner production of geo-composites, the possibility of utilizing waste rubber is in vogue. The present paper deals with experimentally investigating the mechanical and micro-structural characteristics of weak Indian clayey soil partially substituted with lime (0–3.5%) and waste rubber tyre powder (0–15%). It was observed that, with increasing lime and rubber powder content, the plasticity index of the soil decreases. The shear strength and compaction testing results reveal that adding lime and rubber tyre powder (RTP) enhances the geotechnical performance of clayey soil up to an optimum dosage value. Also, the tri-axial shear testing was performed to obtain stress-strain curves for all considered soil mixes. For modified clayey soil containing 3% lime and 12.5% rubber powder, the cohesion values and bearing capacities improved phenomenally by 36.1% and 88.6% respectively, when compared to clayey soil. Further for this mix, SEM analysis reveals a compacted microstructure which improves dry-density and California's bearing ratio among all modified mixes. The novel co-relations upon regression analysis are found able to predict plasticity index, dry density, bearing capacity and shear strength with higher confidence levels. Overall, the cost-benefit analysis worked out to obtain the optimum cost of construction of footings and flexible pavement shows cost deductions up to 19% and 39% respectively while utilizing modified clay soil mixes containing 3% lime and 12.5% rubber powder in subgrade, ultimately making production stronger, cheaper and environment friendly. • Experimental investigations on finding synergistic performance of clayey soil, lime and waste rubber tyre powder. • Atterberg's limits, shear, compaction, CBR, & microstructural characteristics shows better performance of modified mixes. • Optimised clay-lime-RTP mix reports 44% and 88.63% improvements in shear strength and bearing capacities respectively. • Decrement in productional cost of up to 39% for modified geo-mixes in road pavement and foundation constructions. [ABSTRACT FROM AUTHOR]

This paper aims to study the feasibility of low cement content foamed concrete using waste lime mud (LM) and fly ash (FA) as mineral additives. The LM/FA ratio was first optimized based on the compressive strength. Isothermal calorimetry test, ESEM, and XRD were used to investigate the role of LM during hydration. Afterward, the optimized LM/FA ratio (1/5) was used to design foamed concrete with various wet densities (600, 700, 800 and 900 kg/m3) and LM–FA dosages (0%, 50%, 60%, 70% and 80%). Flowability measurements and mechanical measurements including compressive strength, flexural strength, splitting strength, elastic modulus, and California bearing ratio were conducted. The results show that the foamed concretes have excellent workability and stability with flowability within 170 and 190 mm. The high alkalinity of LM accelerated the hydration of FA, thereby increasing the early strength. The significant power functions were fitted for the relationships between flexural/splitting and compressive strength with all correlation coefficients (R2) larger with 0.95. The mechanical properties of the foamed concrete increased with the density increasing or LM–FA dosage decreasing. The compressive strength, tensile strength, CBR of all prepared foamed concretes were higher than the minimum requirements of 0.8 and 0.15 MPa and 8%, respectively in the standard. [ABSTRACT FROM AUTHOR]

Phosphogypsum, which contains toxic components (e.g., heavy metal elements and fluoride), is one of the byproducts of phosphoric acid production, and filling subgrade is one of the recycling methods for it. In this study, phosphogypsum was stabilized by lime to improve the mechanical properties [California bearing ratio (CBR), resilience modulus, unconfined compressive strength, and shear strength], water stability, and harmful substances dissolubility. Combined with scanning electron microscopy, the strength formation and water stability enhancement mechanism of lime-stabilized phosphogypsum (LSP) were explored. The results demonstrated that the mechanical properties of LSP were better with the lime content of 6%–10%. The CBR, resilience modulus, unconfined compressive strength, and shear strength were 3.35 times, 2.46 times, 8.61 times, and 1.39 times that of plain phosphogypsum, respectively. An intensity prediction model with a correlation of 97% was constructed. The CBR and resilience modulus softening coefficient of LSP reached best values when lime content was 6%–8%. The leaching concentration of arsenic, chromium, and lead of LSP with 2% lime met the quality standards of groundwater levels I, II, and IV, respectively. Fluoride and phosphate were not detected in LSP when lime content was greater than 6.0%. The results show that LSP is feasible as subgrade filler. Considering the mechanical properties, water stability, and dissolution of hazardous substances of LSP, it is recommended to add 6%–8% lime content to LSP as highway subgrade filler. [ABSTRACT FROM AUTHOR]

• The models are applicable to various engineer fields. • The relationships between the UCS and other mechanical indices. • Generalized function for capturing the effect of curing time. Given the wide application of lime stabilized loess in road base and subbase, subgrade, building foundations and slopes, a set of generalized and accurate mechanical estimation models of lime stabilized loess is essential for quality control. In this research, three modified models were proposed to capture the effects of lime content and compactness on the unconfined compressive strength (UCS), California bearing ratio (CBR), resilience modulus (M R), internal friction angle (φ), cohesion (c) and compression coefficient (a 1-2) of lime stabilized loess at both 7-day and 28-day curing periods. Compared with the logarithmic model, the hyperbolic model can more reasonably characterize the effect of the curing period on these mechanical indices. Taking those factors together, a set of three-factor estimation models based on both 7-day and 28-day references were developed and show high reliability. Moreover, the establishment of relationships between UCS and CBR , M R , φ and c provides a shortcut for the mechanical property estimation of lime stabilized loess. Finally, based on multiple sets of UCS data sourced from numerous papers, a hyperbolic model with a wider application range was established to link normalized UCS to curing time. The proposed estimation models can be adopted for design checking and quality evaluation of lime stabilized loess applied in various engineering fields. [ABSTRACT FROM AUTHOR]

Promoting the utilization of solid wastes such as mineral waste residue in highway engineering is a meaningful way to accelerate the development of green highway construction and to reduce environmental pollution caused by waste residue stacking. To comprehensively evaluate the engineering properties of waste argillaceous gangue–filled subgrade and recommend reasonable construction parameters, the effects of parameters such as moisture content, compaction work, and coarse grain content (CGC) on the engineering properties of waste argillaceous gangue were compared in this study. A multiobjective comprehensive evaluation model based on grey relational degree (GRD) and principal component analysis (PCA) was constructed, and the reliability of the model was verified. The results showed that the mechanical properties of argillaceous gangue are sensitive to various influencing factors. With increased coarse particle content, unconfined compressive strength (UCS) first increased and then decreased, while resilient modulus and California bearing ratio (CBR) gradually increased. The impact of compaction work on different mechanical properties was noticeable. When calculating the comprehensive GRD, the weights of UCS, CBR of unsoaked samples, CBR of soaked samples, and resilient modulus were 0.203, 0.318, 0.278, and 0.201, respectively. The comprehensive performance prediction model can be effectively applied to evaluate the correlation between technical parameters and engineering properties of argillaceous gangue, and the fitting degree reached 98.21%. The model provides a scientific basis for engineering design and construction parameter optimization of subgrade filled with waste argillaceous gangue. [ABSTRACT FROM AUTHOR]

• Strength and stiffness of calcareous sand is enhanced by using PFA for chemical stabilization. • The influence of PFA on calcareous sand characteristics are different for varying particle gradation. • The shear strength as well as CBR of calcareous sand is greatly improved when stabilized by PFA. • The test results are useful in determining the optimum content of PFA to be used in a particular calcareous sand with specific particle gradation. The calcareous sand existing at the South China sea is characterized by low shear strength with high compressibility. Associated with particle breakage, foundations built on such problematic soil initiates undrained failure with uneven foundation settlement, unless adequate ground improvement technique is adopted. In this paper, chemical soil stabilization is carried out by applying Polyurethane Foam Adhesive (PFA) to the virgin soil. Improvement of strength and stiffness of the treated soil have been investigated in detail by a series of triaxial consolidation and drainage tests followed by California bearing ratio tests. The effect of particle gradation on the stress–strain curve and CBR values of the stabilized calcareous sand as well as the influence on peak shear stress and shear strength index has been studied. The test results show that the PFA is effective in improving the mechanical properties of calcareous sand. The particle gradation has significant effects on the stress–strain response of the stabilized calcareous sand under different PFA contents. Optimal PFA content for each grading of calcareous sand was proposed. The test results of this work would be beneficial for engineering practice in dealing with the bearing capacity and settlement of foundations involving calcareous sand. [ABSTRACT FROM AUTHOR]

Dredged soils are weak soil deposits generated by dredging of water bodies. Construction of engineering structures on weak soils is considered unsafe and hence it becomes essential to utilize such deposits to reduce the load on engineers in finding alternative sites. In this study, a waste material produced post crushing of boulders in crushing units being left in huge quantities and posing enormous environmental, health as well as disposal problems was chosen as an additive for stabilization. Boulder dust being a natural waste has no harmful constituents or chemicals present in it, making it a sustainable product. The mechanical properties of the treated soil were studied by adding boulder crusher dust (BCD) in increments of 4%. Consistency limits, compaction characteristics, California bearing ratio and unconfined compressive strength were studied. Curing period of 7 and 21 days was given to the UCS samples in order to determine the effect of bonding due to possible cementitious material formations. The strength at 16% BCD and 21 days curing increased from 46 kN/m2 in the untreated state to 192 kN/m2. The experimental results were further supported by micro structural analysis indicating that the BCD is a promising additive for stabilization of the dredged soils and hence, can be used in various engineering applications like sub grade, backfill material, landfills, embankments etc. without affecting the ecology of the site and restoring the damages done by the waste material. [ABSTRACT FROM AUTHOR]

• Solid wastes were used as raw material to prepare green calcium sulphoaluminate cement. • The prepared standard green calcium sulphoaluminate mortar meets the current commercial standard for 52.5 N cement. • Blinds of ordinary Portland cement and green calcium sulphoaluminate cement are used produce foamed concrete for the use of road embankment. • Both fresh and hardened state properties measurements show that the proposed mixture design allows for the application of cast-in-situ foamed concrete for road embankment. This paper aims at using green calcium sulphoaluminate (GCSA) cement to prepare foamed concrete for the use of road embankment. Solid wastes were used as raw material to prepare the GCSA cement. X-ray diffractometer (XRD) analysis shows that ye'elimite, gehlenite and belite are the main mineral phases in the produced GCSA clinkers, which is in accordance with the sulphoalumiate cement (CSA). Afterwards, the GCSA cement was blended with ordinary Portland cement (OPC) as binder to make the foamed concrete. The dosage of GCSA cement in the blinds was first optimized by comparing the 3-d and 28-d compressive strengths of mixes having different amount of GCSA cement. The optimized blinds (with 25% GCSA cement) was used to design foamed concrete mixes with wet density of 700 kg/m3, 800 kg/m3 and 900 kg/m3 using different amount of foam. Stability and consistency measurements were conducted at the fresh state. Mechanical measurements including compressive strength, flexural strength, splitting strength, elastic modulus and California bearing ratio were conducted at the hardened state. The measurements show that the proposed mixes have good spread ability and stability and high strength, elastic modulus and bearing capacity, indicating that the proposed mixtures can be accepted in industry practice for the in-situ foam concrete road embankment. [ABSTRACT FROM AUTHOR]