Search Results (26)

This study explores the influence of the water–cement ratio and fiber content in engineered cementitious composite (ECC) on the mechanical characteristics of foamed lightweight soil (FLS) through experimental analysis. Two types of cementitious materials—ECC and ordinary Portland cement (OPC)—were utilized to create FLS specimens under identical parameters to examine their mechanical performance. Results indicate that ECC-FLS exhibits superior toughness, plasticity, and ductility compared to OPC-FLS, validating the potential of ECC as a high-performance material for FLS. To assess the influence of the ECC water–cement ratio, specimens were constructed with varying ratios at 0.2, 0.25, and 0.3, while maintaining other parameters as constant. The experimental results indicate that as the water–cement ratio of ECC increases, the flexural strength, compressive strength, flexural toughness, and compressive elastic modulus of the lightweight ECC-FLS gradually increase, exhibiting a better mechanical performance. Moreover, this study investigates the effect of basalt fiber content in ECC on the mechanical properties of FLS. While keeping other parameters constant, the volume content of basalt fibers varied at 0.1%, 0.3%, and 0.5%, respectively. The experimental results demonstrate that within the range of 0 to 0.5%, the mechanical properties of FLS improved with increasing fiber content. The fibers in ECC effectively enhanced the strength of FLS. In conclusion, the adoption of ECC and appropriate fiber content can significantly optimize the mechanical performance of FLS, endowing it with broader application prospects in engineering practices. ECC-FLS, characterized by excellent ductility and crack resistance, demonstrates versatile engineering applications. It is particularly suitable for soft soil foundations or regions prone to frequent geological activities, where it enhances the seismic resilience of subgrade structures. This material also serves as an ideal construction solution for underground utility tunnels, as well as for the repair and reconstruction of pavement and bridge decks. Notably, ECC-FLS enables the resource utilization of industrial solid wastes such as fly ash and slag, thereby contributing to carbon emission reduction and the realization of a circular economy. These attributes collectively position HDFLS as a sustainable and high-performance construction material with significant potential for promoting environmentally friendly infrastructure development. Full article

Sustainable foam lightweight soil (FLS) with the introduction of solid waste-based binders and dredged mud has shown high engineering and environmental value in expressway reconstruction and extension projects. Accelerated testing through high-temperature curing is considered a crucial method for early-stage assessment of sustainable FLS construction quality. This study aims to explore the curing temperature effect on the strength development of the FLS with different mix proportions and the applicability of accelerated curing method. Strength tests were first conducted on kaolin clay-based FLS with three wet densities and three water contents under different curing temperatures (T), and the strength of the dredged mud-based FLS was also tested to broaden the applicability. Results indicate that higher T and increased wet density significantly enhance the strength of clay-based FLS at any curing age, while higher water content reduces it. The wet density and water content of the proposed FLS recommended in this study considering the strength and lightweight requirements are 800 kg/m³ and 100%, respectively. Moreover, the effectiveness of the accelerated aging method for clay-based FLS is demonstrated by the fact that no dramatic strength loss occurs due to foam expansion and collapse at elevated T of up to 50 °C. On this basis, a strength prediction model based on the concept of activation energy is proposed for both kaolin clay-based and dredged mud-based FLS considering the temperature effect. Changes in wet density have a minimal impact on model parameters, but variations in soil type and water content require updating these parameters to ensure prediction accuracy. Finally, an early quality control method is introduced for applying the sustainable FLS in field projects. Full article

The flexural behavior of geogrid-reinforced foamed lightweight soil (GRFL soil) is investigated in this study using unconfined compressive and four-point bending tests. The effects of wet density and reinforcement layers on flexural performance are analyzed using load–displacement curves, damage patterns, load characteristics, unconfined compressive strength, and flexural strength. A variance study demonstrates that increasing the wet density significantly increases unconfined compressive strength. Bond stress mechanisms enable geogrid integration, efficiently reroute stresses internally, and greatly increase flexural strength. With a maximum unconfined compressive strength of 3.16 MPa and a peak flexural strength increase of 166%, this reinforcement increases both strength and ductility by changing the damage pattern from brittle to ductile. The principal load is initially supported by the foamed lightweight soil, and in later phases, geogrids take over load-bearing responsibilities. Additionally, the work correlates the ratio of unconfined compressive to flexural strength with wet density and informs the development of predictive models for unconfined compressive strength as a function of reinforcing layers and wet density. Full article

In this study, in order to solve the problems of resource utilization of electrolytic manganese residue and the destruction of natural resources by the over-exploitation of raw materials of traditional ceramics, electrolytic manganese residue (EMR), red mud (RM), and waste soil (WS) were used to prepare self-foaming expanded ceramsite (SEC), and different firing temperatures and four groups with different mixing ratios of these three raw materials were considered. Water absorption, porosity, heavy metal ion leaching, and compressive strength in the cylinder of SEC were evaluated. The chemical composition and microscopic morphology of SEC were investigated by XRD and SEM. The mechanism behind the reaction among EMR, RM, and WS and self-foaming was discussed. The results showed that both the temperature and mixing ratio significantly influenced the basic performance of SEC. With the temperature lower than 1200 °C, sphere appearance could be maintained in all of these four groups; however, the density, porosity, and compressive strength in the cylinder seemed unacceptable. When the temperature rose up to 1220 °C, sphere appearance could be only found in the group whose mixing ratio of EMR, RM, and WS was 2:2.5:0.5. Under this condition, the excellent performance of SEC was observed, with a porosity of 46.7%, bulk density of 0.61 g/cm³, and 3 d compressive strength in a cylinder of 26.82 MPa. The mechanism behind the reaction among EMR, RM, and WS could be described: when the temperature is up to 1180 °C, an obvious chemical reaction took place, followed by the liquid phase being produced and the gas released by the decomposition of Fe₂O₃ in RM and gypsum in EMR. When the temperature is up to 1200 °C, the viscosity of the liquid phase and the rate of gas generation achieved the balance, and the liquid phase encapsulated the gas and anorthite (CaAl₂Si₂O₈) began to grow slowly. As time passed, self-foaming expanded ceramsite was prepared. The results of this study are of great significance in the field of artificial lightweight aggregate and industrial solid waste resource utilization. Full article

From both economic and environmental points of view, the reuse of dredged sediments in the direct onsite casting of concrete represents a promising method for replacing sand. The aim of this study was to develop a cementitious material that (i) reuses the thin particles of sediments; (ii) has a low density due to the incorporation of air foam in the material; and (iii) achieves a minimum mechanical strength of 0.5 MPa for embankment applications. This study focused on the characterization of a non-standard “concrete”, which is a mixture of a synthetic soil (80% montmorillonite and 20% calibrated sand) and cement. To reduce its density, air foam was incorporated into the material during the manufacturing process (air-foamed lightweight clay concrete—AFLCC). The study results highlight that a density around 1.2 (unit: g/cm³/1 g/cm³) can be obtained. This density reduction can be obtained with a certain degree of workability when the material is in a fresh state. To obtain this workability, a certain amount of water must be added; however, the addition of water has a significant impact on the compressive strength of the AFLCC. As such, a mathematical equation correlating the compressive strength, the density, and the percentage of cement is proposed in this study. The mechanical strength results of the AFLCC at different times, in conjunction with the Vicat results, show that the porosity created by the air foam has the effect of slowing down the hydration mechanism of the cement. The porosities obtained are consistent with the density results. The characteristic radii indicate large pore sizes for formulations with low fluidity in the fresh state when air bubbles are incorporated. Full article

This paper introduces a novel retaining wall structure that integrates a traditional mechanically stabilized earth (MSE) retaining wall with foamed lightweight soil (FLS) as the fill material. To evaluate the performance of the structure, a numerical approach based on the finite difference method was employed. Firstly, numerical models were developed based on a centrifuge test model designed by previous researchers, and the results were compared with the measured data. The close agreement between the experimental values and simulations demonstrates the reliability and validity of the proposed numerical models. Subsequently, a series of parametric studies were conducted to reveal the effect of key parameters on the performance of the newly proposed retaining wall. Furthermore, this paper proposes a modified harmonic search algorithm (MHSA), which is based on the original harmonic search algorithm (OHSA), to optimize the design of the proposed retaining wall structure. The results indicate that the proposed retaining wall structure can effectively reduce the differential settlement between the existing road and the newly constructed road at a relatively lower cost. The MHSA can serve as a practical design guidebook for engineers and potential users, enabling rapid and efficient design. Full article

Foam concrete has been used in various real-life applications for decades. Simple manufacturing methods, lightweight, high flowability, easy transportability, and low cost make it a useful construction material. This study aims to develop foam concrete mixtures for various civil and geotechnical engineering applications, such as in-fill, wall backfill and soil replacement work. A blended binder mix containing cement, fly ash and silica fume was produced for this study. Its compressive strength performance was compared against conventional general purpose (GP) cement-based foam concrete. Polypropylene (PP) fibre was used for both mixtures and the effect of various percentages of foam content on the compressive strength was thoroughly investigated. Additionally, two types of foaming agents were used to examine their impact on density, strength and setting time. One foaming agent was conventional, whereas the second foaming agent type can be used to manufacture permeable foam concrete. Results indicate that an increase in foam content significantly decreases the strength; however, this reduction is higher in GP mixes than in blended mixes. Nevertheless, the GP mixes attained two times higher compressive strength than the blended mix’s compressive strengths at any foam content. It was also found that the foaming agent associated with creating permeable foam concrete lost its strength (reduced by more than half), even though the density is comparable. The compressive stress–deformation behaviour showed that densification occurs in foam concrete due to its low density, and fibres contributed significantly to crack bridging. These two effects resulted in a long plateau in the compressive stress–strain behaviour of the fibre-reinforced foam concrete. Full article

A substantial amount of bauxite tailings (BTs) at abandoned mine sites have been stored in waste reservoirs for long periods, leading to significant land occupation and environmental degradation. Although many studies of the resource utilization of BTs were conducted to address this challenge, there is still a lack of efforts to systematically review the state of the art in BTs. In the present paper, a systematic literature review was carried out to summarize and analyze the properties, treatment, and resource utilization of BTs. Physical characteristics and the mineral and chemical composition of BTs are introduced. The efficacy of physical, chemical, and microbial treatment methods for BTs in terms of dehydration are outlined, and their respective benefits and limitations are discussed. Moreover, the extraction process of valuable elements (e.g., Si, Al, Fe, Li, Na, Nd, etc.) from BTs is examined, and the diverse applications of BTs in adsorption materials, ceramic materials, cementitious materials, lightweight aggregates, foamed mixture lightweight soil, among others, are studied. Finally, an efficient and smart treatment strategy for BTs was proposed. The findings of the present review provide a scientific basis and reference for future research focusing on the treatment and resource utilization of BTs. Full article

Steel slag micronized powder, granulated blast furnace slag, and cement were used as cementitious materials to prepare a foamed lightweight soil for roadbed filling to reduce the settlement and additional stress of the foundation and to solve the environmental problems caused by the storage of large amounts of steel slag. However, the instability of steel slag and the multi-angular nature of its surface limit the resource utilization of steel slag. Currently, concrete technology is unable to achieve a large amount of steel slag. Therefore, it is necessary to deeply explore the influence of steel slag content and the specific surface area of steel slag on the working performance, compressive strength, durability, and micro-mechanism of foam light soil. Through the modification of steel slag and the improvement of the production process, the preparation of foam light soil with a large amount of steel slag can be realized. In this study, the foamed lightweight soil with 1.0 Mpa was prepared by cementitious materials composed of 40% cement and 60% multi-mixture of steel slag micronized powder and granulated blast furnace slag. The study of SEM images and BET demonstrated that the larger specific surface area of steel slag powder was more conducive to improving the durability of the foamed lightweight soil. Meanwhile, XRD analyses confirmed that the reactions of f-CaO and f-MgO in steel slag were slowly released in the porous foamed lightweight soil system, which compensated for the shrinkage properties of porous materials. When the SSMP content was 0%, the shrinkage rate was 2.34 × 10⁻³, while when the SSMP content was 60%, the shrinkage rate was only 0.54 × 10⁻³. Furthermore, our study of the hydration process of samples indicated that the strong alkalinity of steel slag micronized powder hydration was helpful to stimulate the potential activity of the slag powder, which was beneficial to the improvement of the compressive strength of foamed lightweight soil. Thus, this study provides a valuable idea for reducing the settlement and additional stress of the original foundation and for solving the environmental problems caused by a large amount of steel slag storage. Full article

Embankment and pavement widening of an existing road is a viable option to cope with increased traffic volume. One of the common challenges in road expansion is the occurrence of differential settlement between the old and the new portions. This article pertains to the field case study of the National Highway-120, where pavement distresses developed in the weak sections of the highway following the operation of traffic within a few months. Field monitoring and geotechnical tests, including the requisite in situ as well as laboratory tests, were conducted on soil specimens from the study area, followed by the performance of a numerical analysis using the two-dimensional finite element software Abaqus CAE 2021 to investigate the weak section of the road. Different techniques such as geogrid reinforcement, installation of cement–fly-ash–gravel (CFG) piles, and lightweight foamed concrete (LWFC) embankment fill were used to analyze the reduction in differential settlement between the old and the widened portions. Among the applied reinforcement techniques, the use of LWFC as embankment fill in the widened portion was determined to be most effective in minimizing the differential settlement in the weak section of the highway. Full article

With the rapid growth of road transportation, the increase in road subgrade and pavement diseases has become a pressing issue, requiring the development of cost-effective filling materials that meet both strength and economic requirements. Foam lightweight soil, as a novel construction material, offers excellent characteristics such as adjustability in density and strength, high fluidity, and self-supporting capabilities. It has been widely utilized in various engineering applications, including road subgrade backfilling and retaining wall fillings. However, the conventional application of foam lightweight soil, predominantly cement-based, has raised concerns about pollution and high energy consumption due to large cement dosages. To address this issue, this study proposes the integration of phosphogypsum, a byproduct of wet-process phosphoric acid production, into foam lightweight soil. Phosphogypsum has a significant annual discharge and accumulation, but its comprehensive utilization rate remains relatively low. The research investigates the combination of phosphogypsum and foam lightweight soil by introducing mineral admixtures such as microsilica and slag powder to improve early strength development and reduce the influence of fluoride impurities on early strength. The optimal mix proportions for two types of foam lightweight soil, namely phosphogypsum cement microsilica foam (PGCF) and phosphogypsum cement slag powder foam (PGCS), were determined based on single-factor tests. The key parameters considered for optimization were water–binder ratio, foam content, and phosphogypsum dosage. The findings indicate that both PGCF and PGCS foam lightweight soil possess superior mechanical properties and thermal conductivity. By incorporating phosphogypsum into the mix, the early strength development of foam lightweight soil is effectively improved. Moreover, with suitable mix proportions, the maximum phosphogypsum dosage can be achieved, demonstrating potential economic and environmental benefits. In conclusion, this research provides valuable insights into the effective utilization of phosphogypsum in foam lightweight soil, offering a promising solution for the challenges associated with phosphogypsum disposal and the demand for sustainable construction materials in highway engineering. Full article

Coastal reclamation projects generate an accumulation of wastewater and waste soil, resulting in highly saturated soft soil. Presently, there is a scarcity of research regarding the lightweight solidification and three-dimensional mechanical properties of these soils. Additionally, there is a dearth of specialized models for stabilizing soils containing wastewater using lightweight solidification technology, and pertinent engineering solutions are lacking. By introducing solidifying agents and foaming agents to treat wastewater in soft fill soil, a novel type of solidified lightweight material is produced, imparting strength. This study investigates its three-dimensional mechanical properties. During triaxial tests with equal stress (σ3) and equal b values, the softening of the curve noticeably diminished at b = 0.25. In the plane strain test, cohesion increased by 10.7% compared to the traditional triaxial tests, and the internal friction angle increased by 11%. Subsequently, a three-dimensional Cambridge model was established. At elevated confining pressures, the corrected curve closely approximated the test curve, demonstrating a minimum model accuracy of approximately 96% at a confining pressure of 20 KPa. These findings offer valuable numerical references and a theoretical foundation for the efficient utilization of wastewater and waste soil. Full article

Foamed lightweight soils (FLS) have been extensively used as backfill material in the construction of transportation infrastructures. However, in the regions consisting of salt-rich soft soil, the earth structure made by FLS experiences both fluctuation of groundwater and chemical environment erosion, which would accelerate the deterioration of its long-term performance. This study conducted laboratory tests to explore the deterioration of FLS in strength after being eroded by sulfate attack and/or wet-dry cycling, where the influencing factors of FLS density, concentration of sulfate solution, and cation type (i.e., Na⁺ and Mg²⁺) were considered. An unconfined compressive test (UCT) was conducted, and the corrosion-resistant coefficient (CRC) was adopted to evaluate the erosion degree after the specimens experienced sulfate attack and/or dry-wet cycling for a certain period. The research results show that the erosion of the FLS specimen under the coupling effect of sulfate attack and dry-wet cycling was more remarkable than that only under chemical soaking, and Na₂SO₄ solution had a severe erosion effect as compared with MgSO₄ solution when other conditions were kept constant. An empirical model is proposed based on the test results, and its reliability has been verified with other test results from the literature. The proposed model provides an alternative for engineers to estimate the strength deterioration of FLS on real structures in a preliminary design. Full article

The properties of prepared foamed lightweight soils (FLSs) using prefabricated foam requires high foam stability. This paper investigates the geometrical characteristics of different foam densities, different types of foaming agents in the air, and the presence of slurry. Then, it studies their effects on the pore structure and mechanical properties of FLS. Results show that with the increase in foam density the bleeding rate of foam in the air for 1 h increases and the foam with a foam density of 50 kg/m³ is the most stable in the air. The stability of foam in slurry is not directly related to the property of foam in the air. The FLS prepared with the same foaming agent had the best performance with the FLS designed with a foam density of 50 kg/m³, which had the smallest average pore size and the most minor pore size distribution, and had the highest compressive strength. Among the three different foaming agents, Type-S was the best, and the slurry had the lowest rate of increase in wet density after the defoaming test, indicating that the foam had the best stability in the cement slurry. The FLS prepared with the density of 50 kg/m³ using the Type-S foaming agent and mixed with the slurry of cement, fly ash:slag:water = 105:105:140:227.5, was hardened to a mean pore size of 299 μm, and the 7 days, 28 days, and 56 days compressive strengths were 0.92 MPa, 2.04 MPa, and 2.48 MPa, respectively, which had the smallest average pore size and the highest compressive strength among the FLSs prepared using the three foaming agents. Full article

Foamed lightweight concrete has been applied in different fields of civil engineering because of its superior properties, but the related research considering internal pore damage is limited. Based on statistical damage theory and considering the uneven distribution of fracture damage and strength between the pores of light concrete, a damage constitutive model of foamed lightweight concrete was established based on the Weibull function. The parameters of the damage model were determined through a triaxial compression test, and the rationality was verified by combining the existing test data. Comparative tests show that the theoretical calculation results of the proposed statistical damage model of foamed light soil are consistent with the general trend of the experimental results, reflecting the value of the peak stress and strain and describing the overall development law of the stress and strain. The best fit was obtained when the confining pressure was 0.3 MPa and the density was 700 kg·m⁻³. The suggested damage constitutive method is highly applicable, which is of great significance to the microscopic mechanical analysis of foamed light concrete and the structural design in civil engineering. Full article