Controlled Low-strength Material Research Articles

Pond ash as a fine aggregate for controlled low-strength materials (CLSM): a study of its geotechnical and geoenvironmental aspects

Pond ash as a fine aggregate for controlled low-strength materials (CLSM): a study of its geotechnical and geoenvironmental aspects

Utilization of high fine-grained shield tunnel spoil in CLSM and effect of foam agent content on properties

The volume of shield tunnel spoil (STS) is very large, its effective management is difficult, and it even causes environmental pollution. In this study, to achieve its recycling, a novel controlled low strength material (CLSM) was prepared by utilizing high fine-grained STS as partial aggregates instead of sand, and its engineering performance was thoroughly evaluated. In the process of mix proportion design, key parameters such as the STS-to-total aggregate ratio (TS/TA), foam agent content (F), water-to-binder ratio (W/B), binder-to-total aggregate ratio (B/TA), and fly ash-to-cement ratio (FA/C) were employed. Workability aspects (i.e., flowability, bleeding rate, and setting time) and physical and mechanical properties (i.e., unconfined compressive strength and density) were evaluated. Additionally, the pH of bleeding and leachate, as well as the impact of foam agent content on CLSM properties, were examined. The findings revealed that an increase in the TS/TA ratio was associated with a decrease in flowability, density, and compressive strength, as well as an extension in setting time. The CLSM, with a flowability range of 150–300 mm, exhibited a bleeding rate below 2%, setting times between 3.6 and 6.1 hours, 28-day strength ranging from 1.06 to 3.24 MPa, and fresh density ranging from 1810 to 2060 kg/m³. Generally, these results met the required specifications, although the fresh density was slightly lower. The pH results indicated that the CLSM is non-corrosive. Furthermore, our investigation highlighted the substantial influence of foam agent content on flowability and setting time. An increase of 0.1‰ in the proportion of foam agent within the total aggregates resulted in a flowability increase of 2.1–2.6 mm and a setting time increase of 4.25–4.99 minutes. Therefore, it is feasible to utilize high fine-grained STS in the production of CLSM.

Optimization of Controlled Low-Strength Material from Multi-Component Coal-Based Solid Waste

Recently, controlled low-strength material (CLSM) has been considered an easy-to-mix material, and the raw material is usually derived from solid waste, suggesting lower production costs. Moreover, the resource utilization of waste fosters the sustainable advancement of both society and the environment. In the present work, a CLSM with excellent performance was developed by adopting fly ash, bottom ash, desulfuration gypsum, and cement as the main cementitious materials, as well as gasification coarse slag and coal gangue as aggregates. An orthogonal experiment with three factors and three levels was designed according to the ratio of cement to binder, the contents of water, and the water-reducing agent. Further, the macroscopic properties of flowability, dry density, bleeding, compressive strength, fresh density, porosity, and absorption rate of the CLSM mixtures were tested. To optimize the CLSM proportion, the ranges of three indicators of CLSM were calculated. Experimental results manifested that the fresh and dry densities of the mixtures were within the range recommended by ACI 229. The optimal levels of cement–binder ratio (i.e., the ratio of cement to binder), water content, and water-reducing agent content are 0.24, 248 kg·m−3, and 0.80 kg·m−3, respectively. Under this condition, the flowability was 251 mm, the bleeding was 3.96%, and the compressive strength for 3 d, 7 d, and 28 d was 1.50 MPa, 3.06 MPa, and 7.79 MPa, respectively. Furthermore, the leaching values of eight heavy metals in CLSM and raw materials were less than the standard requirements, indicative of no leaching risk.

Experimental Study and Application of Controlled Low-Strength Materials in Trench Backfilling in Suqian City, China.

When backfilling narrow spaces, controlled low-strength materials (CLSM) can be used to achieve an effective backfilling effect. The pipeline engineering in Yahnghe Avenue of Suqian, China, provides a favorable on-site condition for the use of CLSM. However, no guidance exists for the determination of the material mixture ratio of CLSM for this geological condition. Laboratory tests were performed to investigate the basic physical parameters of excavated soil and the optimal mixture ratio of CLSM. Results indicate that the sand and silt account for 29.76% and 57.23% of the weight of excavated soil, respectively. As the water content increases (from 40% to 50%), the flowability of the CLSM approximately shows a linear increase (slumps values from 154.3 mm to 269.75 mm for 9% cement content), while its compressive strength shows a linear decreasing trend (from 875.3 KPa to 468.3 KPa after curing for 28 days); as the cement content increases (from 6% to 12%), the flowability approximately shows a linear decreasing trend (from 238.8 mm to 178.5 mm for 45% water content), while the compressive strength shows a linear increasing trend (from 391.6 KPa to 987.6 KPa after curing for 28 days). By establishing the relationship between compressive strength/flowability and the water-cement ratio, the optimal material ratio is determined to be 9% cement content and 40-43% water content. The engineering application results indicate that the use of CLSM can achieve efficient and high-quality backfilling effects for pipeline trenches. The findings of this research may provide a reference for the application of CLSM in fields with similar geological conditions.

Evaluation of the applicability of gasification coarse slag as a fine aggregate in controlled low-strength material: preparation, performance, and environmental effect.

Gasification slag (GS) is rich in SiO2, Al2O3, and Fe2O3, and has excellent particle size gradation, which has the potential to be employed as an aggregate in the field of controlled low-strength material (CLSM). Nevertheless, the large-scale application of GS as the fine aggregate for the preparation of CLSM has been scarcely investigated. In the present work, the applicability of replacing part of coal gangue (CG) with gasification coarse slag (GCS) as fine aggregate for the preparation of CLSM was investigated. The results revealed that using GCS as a fine aggregate improved the flowability of CLSM, and increasing the GCS content from 0 to 50 wt% improved the flowability from 250.0 to 280.0 mm. The 28-day compressive strength of all CLSM conformed to the requirements of ACI Committee 229. Compared to the Blank group, the 7- and 28-day compressive strength of the CLSM increased by 23.07% and 26.80%, respectively, at a GCS content of 50 wt%. The increase in compressive strength was mainly due to the pore-filling and hydration-promoting effect of the GCS, which made the structure denser. The dense structure reduced the expansion rate, absorption, and porosity rate of CLSM and increased the wet density. The optimal process parameter was the addition of 10 wt% of GCS. The results of heavy metal ion leaching showed that the optimal sample GS10 leached all heavy metal ions in much less than the limit values of GB 8978-1996 and GB 5085.3-2007. The results will provide new ideas and technical approaches for the large-scale application of GCS as the fine aggregate in CLSM.

Investigation on Mechanical Parameters and Microstructure of Soil-Based Controlled Low-Strength Materials with Polycarboxylate Superplasticizer

This study aims to optimize the sustainable utilization of excavated soil by incorporating it exclusively as a fine aggregate and cement in the formulation of soil-based controlled low-strength materials. The polycarboxylate superplasticizer was introduced to enhance flowability. Various factors, including the cement contents, initial water contents, and curing time, were systematically analyzed for their effects on the fresh properties, mechanical parameters, transverse relaxation time distribution, pore size distribution, porosity, and corrosivity of soil-based controlled low-strength materials. The results indicate that polycarboxylate superplasticizer effectively dispersed clay minerals and cement particles, enhancing the flowability. The unconfined compressive strength increased with the rising cement content and decreased with the increasing initial water content. Additionally, the transverse relaxation time distribution curves of the soil-based controlled low-strength materials exhibited two peaks. These curves shifted to smaller transverse relaxation time values with the increasing cement content, while gradually shifting to larger transverse relaxation time values with the increasing initial water content. An increase in the cement content resulted in higher volume percentages of small and mesopores, while extra-large pores and macropores decreased. The addition of the polycarboxylate superplasticizer had minimal impact on the pore volume percentage distribution. Furthermore, porosity experienced a decline with the rise in the cement content and curing time, in contrast to a notable increase with a higher initial water content. This investigation provides valuable insights into the engineering properties and microstructural characteristics of soil-based controlled low-strength materials, offering a foundation for sustainable waste management practices in geotechnical applications.

Sustainable Approach for Using M-Sand Slurry as a Controlled Low Strength Material

The national-level practice of handling and disposal of industrial wastes create many challenging environmental implications including extensive pollution, resource seclusion and economic losses. The assessment of potentiality for their reuse and/or recycling has conceived tremendous opportunity in various engineering applications with a clear insight of circular economic sustainability. Meanwhile, the handling and disposal of mining wastes were posing serious environmental challenges for their substandard engineering properties. To restore the conventional, backfill materials, a flowable fill known as controlled low strength materials (CLSM) consisting of various ingredients of fine aggregate-sized materials can be employed. In general, CLSM mixtures consist of routinely available materials such as Portland cement, fly ash, fine aggregate, and water. It was expected that the vital characteristics of the mixture, such as flowability, excavatability, and requirements of minimum mechanical strength compared with concrete enable the use of industrial wastes for the production of CLSM. The present study deals with the feasibility of regenerating the silt fraction of M-Sand, known as M Sand Slurry (MSS), to be used for the creation of flowable fills. Mix proportions are developed based on the plastic and mechanical properties with a small quantity of cement and water content. Preliminary plastic (flowability) and hardening properties (compressive strength) results indicate that' s the possibility of the effectiveness of MSS by minimizing the cement addition (up to a maximum of 6%) to attain the unconfined compressive strength above 0.7MPa as per the specifications recommended by ACI standards. It was proposed that an optimum combination of materials can be effectively incorporated in preparing CSLM materials while reducing the requirements of cement, thereby analysed the cost benefits for sustainable developments.

Characterization of controlled low-strength materials from waste expansive soils

Expansive soil from civil excavation projects is often considered waste material due to its propensity to swell. This study pioneers a novel approach to sustainable infrastructure by exploring the viability of repurposing expansive soils in the production of controlled low-strength materials (CLSM), incorporating sand and cement into the mix. Laboratory tests were conducted on CLSMs with varying mix proportions to assess their fresh (flowability, bleeding rate, and setting time) and hardened (swelling, unconfined compressive strength, and dry-wet durability) properties. The investigation focuses on three critical parameters: sand-to-soil ratio (S), cement-to-aggregate ratio (C), and water-to-solid ratio (W). Experimental results indicate the problematic swelling behavior of CLSM is mitigated when C surpasses 18%, at an S value of 10%. Adjusting either W or S enhances flowability but also elevates the bleeding rate. An increase in C has a marginal effect on flowability and bleeding rate, but markedly accelerates the setting time. Flowability follows a negative exponential relationship with time. Furthermore, increasing C or decreasing W markedly enhances both residual strength after dry-wet cycles and compressive strength. When S is below 10%, both compressive and residual strengths show a positive correlation with S. Conversely, when S exceeds 10%, a negative correlation is observed with compressive strength. A predictive model for the compressive strength and flowability of CLSM made from expansive soil has been developed, utilizing data normalization techniques. This model assists in determining the optimal mix proportions appropriate for applications in narrow backfills.

Study on Controlled Low-Strength Materials Using Ultra-Rapid-Hardening Cement and Stone Sludge for Backfill and Subbase Application in Road Excavation and Restoration Work

A significant amount of stone sludge is generated as a by-product during the production of crushed stone aggregate, and most of it is disposed of in landfill as waste. In order to recycle this stone sludge, this study evaluated a controlled low-strength material (CLSM) using ultra-rapid-hardening cement and stone sludge for application as backfill and subbase material for road excavation and restoration work. In addition, considering the limited construction time of excavation and restoration work in urban areas, backfill and subbase materials must simultaneously satisfy conditions of fluidity, workability, quick curing time, and certain levels of strength. Therefore, in this study, CLSM was manufactured according to various mixing ratios and flow, slump, and compressive strength tests with age were evaluated. Additionally, the change trend in the microstructure of the CLSM with age was analyzed. Through indoor experiments, the optimal mixing ratios for backfill and subbase CLSM were determined, and field applicability and performance of field samples were evaluated through small-scale field construction. It was concluded that CLSM, which contains a large amount of stone sludge, can be sufficiently applied as a backfill and subbase material for excavation and restoration work if appropriate admixtures are adjusted according to the weather conditions at sites.

The influence of geo-environmental properties on the plastic and in-service properties of flowable fills: a comprehensive state-of-the-art review.

There is a recognized need to address the mismanagement of industrial by-products, as their accumulation severely threatens the environment. Efficient reutilizing of industrial waste is indispensable in realizing environment-friendly sustainable development. Towards this end, supervised adoption of controlled low-strength materials (CLSM) can be a solution. CLSM are cement-based materials which are environmentally safe, with self-levelling and self-consolidating properties. CLSM's long-term sustainable applications exclusively depend on its geo-environmental properties during and after the construction phase. This comprehensive review explores the impact of geo-environmental properties on the plastic and in-service properties of industrial by-products used for CLSM creation. It critically examines various geo-environmental properties of CLSM comprising interlaced aspects of chemical composition, mineralogical composition, leaching behavior, pH value, and thermal conductivity. It is shown that the geo-environmental properties of CLSM are determined mainly by the characteristics and content of raw materials, wastes, and the quantity of water used in the final blend. Further, the review accentuates the geo-environmental properties' detrimental effects on the plastic and in-service properties of CLSM. The comprehensive review can aid in effectively utilizing CLSM to reduce environmental concerns while achieving sustainable development.

Investigation on the impact of curing conditions on the behavior of controlled low-strength material as basement of rural roads in the Mekong Delta

This study investigates the performance of controlled low-strength material (CLSM) in the challenging Mekong Delta climate, which experiences rapid weather fluctuations, acid rain erosion, uneven mixture gradation, and subpar aggregate quality. Additionally, difficulties in sieving and quality control have led to the disposal of dredged soil in construction sites. The research aims to enhance the practical use of CLSM as a foundation for rural roads in the Mekong Delta by incorporating dredged soil and mineral additives (6% silica fume, 25% bottom ash) under various curing conditions, including normal, acidic, and salted environments. The study assesses CLSM strength through flowability, setting time, and unconfined compressive strength tests. Findings highlight the significant influence of curing conditions on both early and 28-day CLSM strength, with harsh environments compromising cement hydration. Optimizing dredged soil content and mineral components can bolster CLSM strength and promote sustainable use of dredged soil in construction.

Sustainable utilization of industrial by-products spent foundry sand and cement kiln dust in controlled low strength materials (CLSM)

In the present study, industrial by-products, spent foundry sand (SFS) and cement kiln dust (CKD) were used for developing controlled low strength materials (CLSM) and their various fresh and hardened state properties were examined. Embedded energy (EE), Embedded carbon dioxide (ECO2) as well as leachate toxicity of CLSM were also evaluated. Conventional fine aggregates were completely replaced by SFS; while CKD replaced cement at 0%, 25%, 50%, 75% and 100% levels; with the binder to aggregate ratio as 1:10. All the CLSM mixes were obtained while maintaining the flowability at around 250 mm. Addition of CKD increased flow and bleeding, delayed setting time and reduced compressive strength. The findings also indicate that SFS with even 100% CKD can be successfully utilized to prepare excavatable, eco-friendly and sustainable CLSM with bearing resistance equivalent to well compacted sands, suitable for general purpose backfill and utility trench filling. Mix with 75% CKD and 100% SFS as the only fine aggregate proved most suited from most of the aspects of a practical CLSM. All the proposed CLSM mixes were found to be environment friendly w.r.t leachate toxicity, low EE and ECO2. The study offers CLSM as an important alternative for the sustainable utilization of by-products in large quantities.

Unlocking the potential of iron ore tailings in controlled low-strength material: Feasibility, performance, and evaluation

Iron ore tailings (IOT), the predominant solid by-products of iron ore mining and refining, present significant environmental challenges due to their sheer volume. This paper endeavors to scrutinize the prospective deployment of IOT as an alternative to soft soil in the fabrication of controlled low strength materials (CLSM) for backfill applications. The flowability of the CLSM is evaluated by adjusting the IOT, soft soil, and water contents and subsequent appraisal of mechanical properties of the cured CLSM samples is performed via unconfined compressive tests, dry-wet cycles, and direct shear tests at the flowability of 20 cm. Furthermore, scanning electron microscopy and mercury intrusion porosimetry tests are deployed to investigate the impact of IOT on the microstructure of the cured CLSM. Experimental results demonstrate that an increase in IOT content considerably reduces the requisite water content to achieve a flowability of 20 cm for CLSM. Both unconfined compressive strength (UCS) and direct shear tests signal that the infusion of IOT into CLSM substantially enhances the UCS (e.g., from 200 to 440 kPa) along with improving the cohesion (e.g., from 65.9 to 103 kPa) and friction angle (e.g., from 11.5° to 16.3°) of the cured CLSM samples. The mass loss of CLSM, post dry-wet cycles, is notably mitigated, and the corresponding UCS is also bolstered by increasing the IOT content. Microstructural observations in conjunction with pore size characterizations corroborate that the strength augmentation of the CLSM mixture can be attributed to the densification of the microstructure and the proliferation of cement hydration products with increased IOT content. Consequently, this investigation sheds light on the promising potential of employing IOT as a central ingredient in CLSM production.

Lightweight and Alternative Backfills for Highway Applications: State-of-the-Art Practice in the U.S.A.

The use of lightweight and alternative materials in geotechnical applications may be advantageous when compared with more conventional structural backfills. This paper focuses on using seven lightweight and alternative backfill materials in highway applications: controlled low-strength materials (CLSM); expanded shale, clay, and slate (ESCS); foamed glass aggregates (FGA); lightweight cellular concrete (LCC); polystyrene geofoams; recycled glass aggregates; and tire-derived aggregates (TDA). The current knowledge and the state-of-the-art practice for using these materials in highway geotechnical applications of interest, that is, retaining walls, bridge abutments, pipes/culverts, embankments, and slope stabilization, were evaluated. The paper first introduces the materials, including the unit weight ranges for each lightweight and alternative fill material, and their applications. Then, the key aspects and advantages of each material for highway geotechnical applications are listed and evaluated. Further, for each material, the physical, chemical, and mechanical material properties are discussed, as well as the design requirements and guidelines, construction and placement guidelines, and the environmental considerations. Finally, the technology-ready aspects of each material studied with regard to its application to highway geotechnical problems, and the identified barriers to the deployment of each one were summarized and discussed. Based on the current knowledge, some lightweight and alternative materials (e.g., ESCS, CLSM, TDA) have been more widely used in the U.S.A. for geotechnical applications, whereas others are still emerging technologies. Further, certain materials (e.g., LCC, TDA, geofoam) have well-developed design guidelines, whereas others (e.g., CLSM, FGA) require more research.

Development of High-Performance Fly-Ash-Based Controlled Low-Strength Materials for Backfilling in Metropolitan Cities

Controlled low-strength materials (CLSMs) have been developed using various byproducts for backfilling or void-filling around pipelines or culvert boxes. However, these CLSMs have encountered issues related to their inadequate placement around underground facilities, despite satisfying the performance requirements, especially flowability, recommended by the American Concrete Institute (ACI) 229 committee. In this study, a new CLSM is developed to ensure a significantly higher flowability, lower segregation, and faster installation compared with previously developed CLSMs. This is achieved through a series of laboratory tests. To enhance the flowability and prevent segregation, a calcium-sulfoaluminate-based binder and fly ash are used in combination with two types of additives. The measured flowability of the new CLSM is 700 mm, while its compressive strength and bleeding satisfy the general criteria specified by the ACI 229R-13. In addition, the performance of the developed CLSM is compared with that of predeveloped CLSMs. The new CLSM was not only shown to exhibit the highest flowability, but also to satisfy the specified requirements for compressive strength and bleeding. Overall, it is anticipated that the developed CLSM can significantly reduce the costs related to the disposal of old pavements, the installation of new pavements, and other construction expenses compared to the costs related to the conventional method, even though the expenses for the backfill materials could increase due to the higher production costs of CLSMs than soil. In addition, there is a need to investigate its field applicability in order to evaluate the precise costs, maintenance, and long-term stabilities after installation.

Prospects of sustainable geotechnical applications of manufactured sand slurry as controlled low strength material

Rapid changes in the construction industry for infrastructure development require extensive use of building materials from a variety of sources. As natural resources deplete at a faster rate in recent years, new materials are being explored, and recycled materials are being discovered for various applications. The slurry obtained during the washing of mined quarry sand (also called as M Sand Slurry or MSS) is found to be disposed as mining waste causing environmental pollution. In the present study, we propose an innovative methodology to recycle the MSS as a suitable replacement of fine aggregate by imparting sufficient strength and workability to produce a composite, commonly called as controlled low strength material (CLSM). We have optimized the mix proportioning of MSS by adding fly ash (up to 15%) and Portland cement (up to 10%). Various tests on the plastic properties (flowability, bleeding, hardening time) and hardened properties (ultimate compressive strength or UCS) were performed on the selected mixtures. The optimum mixture of CLSM with MSS provided excellent flowability (at 200 mm), bleeding rate (3–5%) and UCS up to 1.12 MPa. The improved binding effect on the poor-graded MSS has been attributed to the pozzolanic reaction in presence of fly ash and cement, as evident from the microstructural analysis. Based on the excavation criteria (ACI 229R), the selected mixtures have high removability modulus (1.2–2.5) except for two proportions (with only MSS, and with very low fly ash) while all combinations have sufficient strength (UCS < 2.1 MPa), making them suitable for various geotechnical applications. Further, to address the sustainability aspects of MSS-based CLSM utilization, a strategic framework is proposed based on the Life Cycle Assessment (LCA) approach for the mining industries. It is observed that MSS-based CLSM can reduce the cost of earthworks approximately by 62% (compared to the river sand) and 32% (compared to the available alternate sand). Hence, based on the environmental, economic and mechanistic aspects, we demonstrate that MSS-based CLSM can be effectively adopted for sustainable geotechnical applications.

The Influence of Fiber on the Mechanical Properties of Controllable Low-Strength Materials.

Numerous studies have been conducted on fiber-reinforced concrete; however, comparative investigations specifically focusing on the utilization of fibers in CLSM remain limited. In this study, we conducted a systematic investigation into the mechanical properties of controlled low-strength material (CLSM) by manipulating the length and doping amount of fibers as control variables. The 7-day compressive strength (7d-UCS), 28-day compressive strength (28d-UCS), and 28-day splitting strength of CLSM were employed as indicators to evaluate the material's performance. Based on our comprehensive analysis, the following conclusions were drawn: (1) A positive correlation was observed between fiber length and material strength within the range of 0-6 mm, while conversely, a negative correlation was evident. Similarly, when the fiber doping was within the range of 0-0.3%, a positive correlation was identified between material strength and fiber doping. However, the strength of CLSM decreased when fiber doping exceeded 0.3%. (2) SEM and PCAS analyses provided further confirmation that the incorporation of fibers effectively reduced the porosity of the material by filling internal pores and interacting with hydration products, thereby forming a mesh structure. Overall, this study offers valuable insights into the manipulation of fiber length and doping amount to optimize the mechanical properties of CLSM. The findings have important implications for the practical application of CLSM, particularly in terms of enhancing its strength through fiber incorporation.

Utilization of waste marine dredged clay in preparing controlled low strength materials with polycarboxylate superplasticizer and ground granulated blast furnace slag

To solve the disposal of massive waste marine dredged clay (MDC), this study proposes a new method of utilizing it in preparing controlled low strength materials (CLSM). In which the polycarboxylate superplasticizer (PCE) and ground granulated blast furnace slag (GGBS) were used to break the current dilemma that the flowability and strength can only be guaranteed by simultaneously increasing the water content and cement content. The flowability, strength and hydration conductivity were investigated through a series of flow tests, unconfined compression strength (UCS) tests and hydraulic conductivity tests, the microstructure and mineralogical tests were performed to reveal the mechanism of PCE and GGBS accordingly. The results show that GGBS provides more active silicon and active aluminum to promote the generation of hydrated calcium silicate (CSH) and hydrated calcium silicate aluminate (CASH), leading to a higher strength and impermeability of CLSM with GGBS than CLSM with pure ordinary Portland cement (OPC). PCE disperses both MDC and PCE in the CLSM and improves flowability through electrostatic force and steric hindrance, contributing to a rapid increase of flowability under 0.4% of PCE content. Under the collaborative effects of PCE and GGBS, MDC-based CLSM achieves higher strength and flowability at relatively lower cement content and water content, which not only solves the contradiction between flowability and strength of conventional CLSM, but also offers scientific references to the broad application of solid wastes (MDC and GGBS) in CLSM preparation, which promotes the sustainable development of green construction materials significantly.

Sustainable controlled low strength material from waste materials for infrastructure applications: State-of-the-art

In recent years, controlled low strength material (CLSM) has been utilized as an alternate backfill material for various infrastructure applications such as filling of voids, construction of pavement bases, trench backfilling, bed for pipelines, etc. Efforts have been made by researchers to utilize various waste materials/industrial by-products such as slag, fly ash, pond ash, cement kiln dust, red mud, sludge, construction and demolition waste and crumb rubber for development of sustainable CLSM. The present work discusses in details the evolution of CLSM, recent advances in the development of CLSM with different waste materials/industrial by-products, and the effect of these sustainable materials on flowability, strength, hardening time and other properties of CLSM. Further, the benefits/challenges and applications of different sustainable CLSM mixes have been compared. The inferences from pilot/field scale studies for CLSM and alkali activated CLSM have been discussed, and assessment of the sustainability coefficient of select CLSM combinations considered from the literature have been performed. The study quantifies the sustainability of different CLSM mixes, and presents the challenges that needs to be addressed in future to increase the utilization of sustainable CLSM for future infrastructure development.

Use of fly ash and quarry waste for the production of the controlled low strength material

This study investigates the potential of utilizing quarry waste and fly ash in the production of controlled low-strength materials (CLSM). Fly ash and quarry waste were mixed in various proportions and the properties of the mix were studied in both fresh and dry states. Cement in low proportions was used as a binder. Flowability, bleeding, density, settlement, air content, pH, and electrical resistivity of the mix was studied in their fresh state. The flowability of the mix was enhanced by the addition of quarry waste. However, incorporating higher amounts of quarry waste caused the mix to exhibit more bleeding, leading to greater settlement. Increasing the concentration of cement was found to mitigate bleeding in the mix. The corrosivity of the mixture was found to be in the permissible limits for use as an excavatable material in utility fills. Unconfined compressive strength, water absorption, density, SEM, and XRF analysis were performed on hardened samples. Unconfined compressive strength tests were performed on the various mix proportions of the samples at 1, 7, 14, and 28 days. The CLSM samples were found to have a low strength of 0.08 to 0.35 MPa at 28 days and hence suitable for use as an excavatable material. SEM analysis revealed that the C-S-H gel was the chief component that contributed to the strength gain of the mixture with time.