Controlled Low-strength Material Mixtures Research Articles

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.

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.

STUDY ON USE THE BOTTOM ASH FROM WASTE INCINERATION PLANT AS FINE AGGREGATE IN MANUFACTURE OF CONTROLLED LOW-STRENGTH MATERIALS

This research investigates the manufacture and properties of controlled low-strength materials (CLSM) that were produced using bottom ash (BA) as fine aggregate (F). Mixtures of CLSM were prepared with various volume ratios of F-to-BA (100/0, 90/10, 70/30, and 50/50) and a constant amount of 5% cement, 10% slag, 82% fly ash and 3% CaCL2. CLSM mixtures were prepared at an initial ratio of water to powder (w/p) of 0.35 and added water to obtain the flow of 30±2cm. The properties of CLSM were evaluated by relevant standards. The experimental results show that the flow of all CLSM mixtures met high flowability requirements under ACI 229R. Using BA as fine aggregate reduced the fresh unit weight of CLSM but delayed the setting time. Moreover, CLSM mixtures could serve as a re-excavation and pavement subbase.

Performance of dredged sediments based controlled low-strength material

The process of depleting the natural sources of virgin sand and aggregate makes it challenging to satisfy the demand for construction work. Therefore, in a context of sustainable construction, this study examined the feasibility of utilizing dredged sediments (DS) as a substitute for sand in non-structural controlled low-strength materials (CLSM). A total of two types of dredged sediments, coarser and finer, were collected from two different sources. Then, nine CLSM mixtures were prepared by using different proportions of natural sand (virgin sand) and dredged sediments. Each mixture was tested for flowability, unconfined compressive strength, density and excavatability. Flow consistency decreased with the amount of dredged sediments and presence of finer material in CLSM. Strength results were found within required specification for all nine CLSM tested in this study. Overall, flow consistency, strength and excavatability were found dependent on the characteristics of dredged sediments. This study showed that up to 50% of substitution of sand with DS in CLSM improved strength and density. Furthermore, flow consistency was found to decrease with increase in the amount of DS in CLSM mixtures.

Performance of dredged sediments based controlled low-strength material

The process of depleting the natural sources of virgin sand and aggregate makes it challenging to satisfy the demand for construction work. Therefore, in a context of sustainable construction, this study examined the feasibility of utilizing dredged sediments (DS) as a substitute for sand in non-structural controlled low-strength materials (CLSM). A total of two types of dredged sediments, coarser and finer, were collected from two different sources. Then, nine CLSM mixtures were prepared by using different proportions of natural sand (virgin sand) and dredged sediments. Each mixture was tested for flowability, unconfined compressive strength, density and excavatability. Flow consistency decreased with the amount of dredged sediments and presence of finer material in CLSM. Strength results were found within required specification for all nine CLSM tested in this study. Overall, flow consistency, strength and excavatability were found dependent on the characteristics of dredged sediments. This study showed that dredged sediments can be successfully used as a sand substitute for CLSM production.

The Effect of Bottom Ash Ball-Milling Time on Properties of Controlled Low-Strength Material Using Multi-Component Coal-Based Solid Wastes

As the conventional disposal method for industrial by-products and wastes, landfills can cause environmental pollution and huge economic costs. However, some secondary materials can be effectively used to develop novel underground filling materials. Controlled low-strength material (CLSM) is a highly flowable, controllable, and low-strength filling material. The rational use of coal industry by-products to prepare CLSM is significant in reducing environmental pollution and value-added disposal of solid waste. In this work, five different by-products of the coal industry (bottom ash (BA), fly ash, desulfurized gypsum, gasification slag, and coal gangue) and cement were used as mixtures to prepare multi-component coal industry solid waste-based CLSM. The microstructure and phase composition of the obtained samples were analyzed by scanning electron microscopy and X-ray diffraction. In addition, the particle size/fineness of samples was also measured. The changes in fresh and hardened properties of CLSM were studied using BA after ball milling for 20 min (BAI group) and 45 min (BAII group) that replaced fly ash with four mass ratios (10 wt%, 30 wt%, 50 wt%, and 70 wt%). The results showed that the CLSM mixtures satisfied the limits and requirements of the American Concrete Institute Committee 229 for CLSM. Improving the mass ratio of BA to fly ash and the ball-milling time of the BA significantly reduced the flowability and the bleeding of the CLSM; the flowability was still in the high flowability category, the lowest bleeding BAI70 (i.e., the content of BA in the BAI group was 70 wt%) and BAII70 (i.e., the content of BA in the BAII group was 70 wt%) decreased by 48% and 64%, respectively. Furthermore, the 3 d compressive strengths of BAI70 and BAII70 were increased by 48% and 93%, respectively, compared with the group without BA, which was significantly favorable, whereas the 28 d compressive strength did not change significantly. Moreover, the removability modulus of CLSM was calculated, which was greater than 1, indicating that CLSM was suitable for structural backfilling that requires a certain strength. This study provides a basis for the large-scale utilization of coal industry solid waste in the construction industry and underground coal mine filling.

Development and characterization of a controlled low-strength material produced using a ternary mixture of Portland cement, fly ash, and waste water treatment sludge

Controlled low-strength material (CLSM), a widely used replacement for conventional compacted filling material, is self-leveling and self-compacting, currently used in many structural applications. The properties of a CLSM mixture made from cement, fly ash, and waste water treatment sludge (WTS) were examined in this study. The CLSM mixtures were prepared using several water-to-binder (w/b) ratios (0.5, 0.65, and 0.8) and WTS weight ratios (0, 20, 40, and 80%). A solution of 5M NaOH was employed as a mixture accelerator. The influences of WTS addition on the characteristics of both fresh and hardened CLSM were examined. Toxicity characteristic leaching procedure (TCLP) and the change in minerals and microstructures of the CLSM samples were also investigated. The experimental results demonstrated that incorporating WTS into CLSM results in significant changes in fresh unit weight and mixture workability. The CLSM properties were found to be strongly affected by both the w/b ratio and accelerator dosage. Moreover, the TCLP test confirmed that WTS can be used as a safe by-product because the leached levels of heavy metals from raw WTS and resulting CLSM were significantly less than the permitted thresholds. Finally, the CLSM designed using a w/b ratio of 0.65, accelerator of 5%, and 40% WTS achieved the highest performance that meets current relevant Taipei City design regulations for excavatable backfilling.

Upcycling of wastes for sustainable controlled low-strength material: A review on strength and excavatability.

In recent decades, the use of controlled low-strength material (CLSM) in densely populated cities has increased. CLSM is designed for future excavation with great fluidity, appropriate early strength, and low final strength. CLSM mixtures exhibit variable strength properties and performance due to the distinctive features of wastes (i.e., combustion residues, industry slags, and construction and other solid wastes) produced from various sources. CLSM should increase early strength quickly enough to allow traffic to resume within a few hours while maintaining a low strength for future re-excavation. It is suggested that the initial mixture design for each waste reported in the literature be changed until the combination meets the application standards defined in ACI 229R-13. The effects of adjusting other ingredients (i.e., cement, water, and admixtures) in the wastes incorporated into CLSM mixtures on the strength and re-excavatability properties are also detailed and discussed in this review. From practical and economic perspectives, the supply of materials in the waste streams, transport distance, and material properties and cost are important aspects to consider before their introduction to the construction industry.

Experimental study on the application of red mud to controlled low strength material made of excavated soil

To improve the resource utilization of solid waste, excavation abandoned soil and red mud, a by-product of alumina industry, were introduced into the preparation of controlled low strength material (CLSM). By carrying out the flowability test, bleeding test and compressive strength test, the relationship between properties of CLSM mixture and the amount of red mud was analysed. The experiment results indicate that the flowability and bleeding rate of the mixture decrease with the increase of red mud content. When the red mud content is less than 20%, the mixture shows good flowability. The addition of red mud can accelerate the completion time of bleeding and play a positive role in the bleeding stability of the mixture. When the red mud content is 10%, the strength of the mixture reaches the maximum, while the strength of the mixture with other contents decreases with the increase of red mud content. For the CLSM made of excavated soil, red mud has a good application prospect in terms of bleeding stability and strength.

The Need of Statistical Approach for Optimising Mixture Design of Controlled Low-Strength Materials

The statistical phase method was introduced to achieve optimal mixing controlled low-strength material (CLSM) proportions, utilising statistical studies. There is no well-known explicit formulation for predicting hardened properties (in terms of unconfined compressive strength (UCS)) of CLSM. The proposed approach to optimising CLSM mix design is demonstrated in the most common case where experimental mixing was considered in compliance with the full factorial experimental design involving three variables with two levels (2³) and the Box-Wilson central composite design (CCD) method. Twenty CLSMs with six replicates (one hundred and twenty specimens) were considered in changing the levels of the main factors that affect CLSM compression strength, the water/cementitious ratio (2.53-2.73) and the wastepaper ash (WSA) percentage (50-100%) and cementitious materials content (160-200 kg/m³). The experimental results were used to analyse variance and design a UCS polynomial regression equation for design factors considered in this research. In order to emphasise how to optimise CLSM mixtures with different options, a statistical model was developed.

Effect of Fly Ash on Strength and Stiffness Characteristics of Controlled Low-Strength Material in Shear Wave Monitoring.

Fly ash, the main component for controlled low-strength material (CLSM), has physical and chemical characteristics according to the resources used in the thermal power plant, and thus fly ash type can influence the physical and strength properties of CLSM. This study investigates the effect of fly ash type on the engineering properties of CLSM and establishes relationships between mechanical properties of CLSM and shear wave velocity (SWV) for long curing times. Six fly ashes with different physical properties and chemical components are used for preparing the CLSM mixtures. The air content, unit weight, flowability, and setting time of CLSM are measured. Unconfined compressive strength (UCS) and elastic modulus (E) are obtained from unconfined compressive tests, and SWV (Vs) is determined using a bender element-based wave measurement system. Experimental results show that the stiffness and strength characteristics of CLSM are relevant to the contents of two oxides (SiO2 and Al2O3) and the fineness of fly ash. Because the evolution of SWV is influenced by the fly ash type, the relationships UCS-Vs and E-Vs are well established. Thus, considering the fly ash type, shear wave monitoring may be effectively used for estimating strength and stiffness characteristics of CLSM.

Statistical models to develop optimised controlled low-strength materials with wastepaper sludge ash

This study aims to create robust controlled low-strength material (CLSM) mixes of wastepaper sludge ash (WSA) binders and recycled fine aggregates (RFAs). A factorial design was carried out to mathematically model the effect of three main mix design parameters on the plastic and hardened properties of wastepaper sludge ash CLSM (WSA-CLSM) mixtures. The criteria were the ratio of water to cementitious materials (w/cm), the proportion of WSA replacement content, and the total cementitious material (cm) content. Flowability, bleeding, segregation, initial stiffening time, densities, water absorption, and unconfined compressive strength were the derived statistical models' responses. With the intention of extracting the statistical models, twenty mixes were prepared, and ten mixes were used to validate the precision of the produced models. The models are valid for mixtures of 2.53 to 2.73 w/cm, 50 to 100% of WSA (by total cm content) and 160 to 200 kg/m3 of total cm content. The regression methods were synthesised and analysed by classifying the key factors and their correlations to measure their properties in terms of the impacts of w/cm, WSA% and total cm content. Three optimum WSA-CLSM mixtures with significant positive desirability were formulated and tested using the established models. Robust WSA-CLSMs that meet the Department of Transportations (DOTs) specifications for CLSM backfill material classifications may be developed.

Bio-based alkali-activated controlled low strength material: Engineering properties

This study investigated the potential of unifying construction and agricultural sectors’ goals to meet the global demand for green construction implementation. Saving natural resources and solving waste disposal of issues, through utilizing agriculture waste as a replacement for natural aggregate was adopted. Environmental-friendly controlled low strength materials (CLSMs) using alkali-activated binders as a replacement for regular cement was selected as a green application. Fresh, hardened and durability performance for mixtures with various agriculture waste contents (i.e. 0% up to 40% as replacement of fine natural aggregate) and binder activation levels were evaluated. Results reveal that increasing the agriculture waste content (i.e. >10%) increased the potential to achieve a lightweight green CLSM. All CLSM mixtures had exhibited strength below 8.3 MPa, satisfying the strength requirements for structural filling according to ACI committee 229. Only mixtures with agriculture waste contents >20% meet the desired strength for future re-excavation CLSMs (i.e. 2.1 MPa). Hence, low strength requirements for CLSMs had accommodated the strength reduction induced by agriculture waste addition. The findings pave the way for a wider implementation of agriculture wastes in green construction, providing economic and environmental benefits for both construction and agriculture sectors.

Properties of bio-based controlled low strength materials

This study investigates the feasibility of enhancing construction materials sustainability using bio-based by-products as a partial replacement for natural sand. Controlled low strength material (CLSM) was selected as a practical application, thanks to its low strength requirements. The fine black spruce residual was added to different strength levels CLSM mixtures at rates 0%, 5%, 10%, and 20% as a partial replacement of natural sand. Fresh and hardened properties, including flowability, bleeding, density, compressive and tensile strengths, were evaluated. CLSM mixtures incorporating fine black spruce residuals were exposed to sulfate environment to examine their durability. The experimental results demonstrate that adding spruce-residuals had reduced the compressive strength; however, this reduction was within the acceptable limit. Moreover, results indicated that mixtures with high cement content could incorporate >20% spruce-residuals while maintaining adequate performance. The fine spruce-residuals have some filling effect and can reduce the pores leading to lower absorption rates. Dry/wet cycles will adversely affect the volume stability of CLSM, forming wide cracks that, in turn, accelerate degradation. Producing CLSM for farm applications is a feasible method for reusing such waste.

Development of thermally enhanced controlled low-strength material incorporating different types of steel-making slag for ground-source heat pump system

This study aims to develop a thermally enhanced controlled low-strength material (CLSM) that functions as a heat transfer medium in the ground source heat pump (GSHP) system based on by-products. Steel-making slags (raw and ground slags) and fly ash were used as main materials of CLSM mixture. The general properties of the CLSM mixture, such as flowability, bleeding properties, initial setting time, unconfined compressive strength (UCS), permeability, thermal conductivity, and environmental impact, were investigated with different steel-making slag contents. Finally, the total construction costs of GSHP with different backfill materials were calculated to assess the benefits of the proposed CLSM mixtures. As the results, the steel-making slag based CLSM exhibited good flowability and bleeding and a significantly enhanced UCS and hydraulic resistance with respect to those of CLSM. However, the thermal conductivity, UCS, and hydraulic resistance tended to decrease when the raw steel-making slag exceeded a certain amount. Furthermore, all proposed CLSM mixtures satisfied the environmental regulations for their safe use in the underground. The cost analysis revealed that proposed CLSM mixtures slag can reduce the total construction costs of GSHP system by up to 41.36%, 0.73%, and 20.44% when compared to those of conventional materials.

Utilization of controlled low strength material (CLSM) as a novel grout for geothermal systems: Laboratory and field experiments

Over the past decade, controlled low-strength material (CLSM) has been used extensively as fill material in flowable fills, structural fills, and void fills. However, owing to its good flowability and low shrinkage, CLSM can be considered a heat transfer medium as long as it has sufficiently high thermal conductivity. The main purpose of this study is to evaluate the use of controlled low strength material (CLSM) as a novel grout for geothermal systems by both laboratory and field experiments. Laboratory tests were performed first on various CLSM mixtures to evaluate their performance on general characteristics coupled with thermal conductivity, and the construction cost analysis. As a laboratory test result, all CLSM mixtures satisfied aspects of the abovementioned properties. In addition, in order to prove the proficiency of CLSM based-grout for geothermal systems, a large-scale test was also conducted to verify the workability and heat exchange rate of CLSM based-grout in the field with five boreholes and two control buildings. The workability of CLSM-based grout from the field tests was in the acceptable requirements reported in ACI 229R, (1999). In addition, the heat exchange rate of the proposed CLSM from the field test was found to be better than that of silicate sand and bentonite (i.e., conventional grouts). In conclusion, good workability and sufficient heat exchange rate obtained from the field test strongly reinforced the feasible use of the proposed CLSM as a thermal grout for geothermal systems.

Utilization of marine dredged soil in controlled low-strength material used as a thermal grout in geothermal systems

Abstract To date, controlled low-strength material (CLSM) has been used widely as fill material in flowable fills, structural fills, and void fills. However, owing to its good flowability and low shrinkage, CLSM can be considered a heat transfer medium as long as it has sufficiently high thermal conductivity. In this study, a newly developed CLSM, a blend of natural sand, marine dredged soil (MDS), and binders, was investigated and evaluated for the feasibility of it being used in geothermal systems. In addition to its general properties (flowability, fresh density, and unconfined compressive strength), thermal conductivity (i.e., heat transfer capacity), bleeding rate (i.e., involving volume compensation for boreholes), and environmental impacts (i.e., involving the potential risk of water pollution) were broadly investigated in this study. A bleeding-rate-based volume compensation concept is described for an actual large-scale geothermal system to evaluate total cost. All of the prepared CLSM mixtures performed well in terms of general and environmental characteristics. Moreover, the thermal conductivity of the developed CLSM-based grout was much higher than that of conventional grouts (i.e., bentonite and silicate sand). More importantly, an outstandingly positive effect of MDS was discovered: a sufficient addition of MDS to CLSM-based grout can lead to a considerable decrease in bleeding rate; hence, to only a small volume compensation of required boreholes. Ultimately, the total cost for geothermal construction can be reduced.

Development of a new cementless binder for controlled low strength material (CLSM) using entirely by-products

The aim of this study is to develop of a new binder using entirely by-products for a production of CLSM. The new cementless binder, tentatively named Fa-RmLG, was made from fly ash (Fa), lime (L), gypsum (G) and red mud (Rm). Various CSLM mixtures were produced with pond ash and different proportions of the new cementless binder Fa-RmLG. To assess the technical feasibility of this cementless binder in CLSM, three phases corresponding with three mix proportions were performed in this study. A preliminary proportion (phase I) was conducted to evaluate the engineering properties of five proposed CLSM mixtures in which the ratio of gypsum to red mud (G/Rm) varied in the range of 0.4–6.0. Subsequently, the best CLSM mixture was selected to be the control mix for a further study, which investigated the effect of fly ash content (phase II) and lime content (phase III) on the engineering properties of all CLSM mixtures in these phases. The obtained results showed that the engineering properties (flowability, bleeding, setting time, unconfined compressive strength, and microstructural analysis) and environmental impacts (corrosivity, heavy metals) of CLSM made with the proposed cementless binder met the ACI 229R requirements through a control of the cementless binder proportions. In conclusion, it was found a feasibility of using the developed Fa-RmLG binder for the production of CLSM.

New approach for proportioning of controlled low strength materials

Controlled Low Strength Material (CLSM) can be a valuable application for the safe and efficient use of recycled and by-product materials. These nonstandard materials affect the mixture properties in less predictable ways, and hence, increase the number of trial batches required to attain the desired CLSM characteristics. In the present study, a laboratory experiment was carried out to explore an efficient methodology for proportioning CLSM mixtures without an extensive trial and error process.In the new methodology, CLSM mixture are proportioned using relative ratios between constituent materials, including the paste volume ratio to the total volume of mixture (PVR), mass ratios of water to cementitious materials (w/cm) and portland cement to cementitiuos materials (pc/cm). These parameters can be adjusted independently, and therefore, the proposed methodology allows for better understanding of the effects of the above parameters on mixture properties.The experimental results showed that the relative ratio parameters can provide adequate control over the relevant CLSM properties in terms of the ability to flow and compressive strength. The PVR parameter had a more significant effect on flowability compared to the w/cm ratio; though, it had little effect on strength development of CLSM mixtures. A mixture design procedure based on the new methodology is provided.

Thermal conductivity of controlled low strength material (CLSM) under various degrees of saturation using a modified pressure plate extractor apparatus – A case study for geothermal systems

Conventionally, controlled low strength material (CLSM) is defined as a self-compacting and self-leveling material. High thermal conductivity CLSM can be, however, used as the heat transfer medium (thermal grout) in geothermal systems due to its good flowability and low shrinkage. Similar to general soils or earlier developed thermal grouts, the degree of saturation of CLSM is strongly related to its thermal conductivity, which is an input parameter in the design of geothermal systems. Hence, this relationship should be explored for the optimum design in these systems. This paper addresses the thermal conductivity of CLSM made with coal ash and excavated soil as a function of the degree. In order to do this, the pressure plate extractor apparatus (SWC-150) was modified by coupling with a single thermal needle probe. In the experimental program, all general properties (e.g. flowability, bleeding, fresh density, initial setting time, and unconfined compressive strength) were performed first. Afterward, thermal conductivity, the degree of saturation, and matric suction were measured simultaneously by the modified apparatus. As a result, all general properties of the prepared CLSM satisfied the specifications of CLSM. In addition, linear relationships between thermal conductivity and degree of saturation of the proposed CLSM mixtures were observed. It is interesting to note that thermal conductivity of CLSM incorporating excavated soil, which works as filler the CLSM mixture, was relatively improved when compared to that of CLSM without excavated soil. Finally, new predictive models for thermal conductivity estimation of CLSM were proposed based on both normalization and regression methods.