Solidification Agent Research Articles

Optimization of silty soil solidification agent ratio and mechanism of strength change based on design-expert

ABSTRACT In order to achieve the resource utilization of silty soil, based on the solidification mechanism of existing inorganic solidification agents, coal gangue and fly ash were selected as substrates, and quicklime and sodium silicate were used as activators to study a new type of muddy soil solidification agent. This project adopts mixture experimental design and unconfined compressive strength testing methods, and uses design expert software to analyze each component to obtain independent variable relationship strength prediction formulas. By using scanning electron microscope, Particles (Pores) and Cracks Analysis System, the changes in micro pore structure characteristics of Reinforced soil were obtained. The research results indicate that the relationship between the influence of various variable factors on strength gain is as follows: sodium silicate>calcium oxide>fly ash>coal gangue. As the age increases, the porosity shows a trend of first increasing and then decreasing. It has been revealed that the strength growth of Reinforced soil with curing agents is mainly due to the compaction and filling effects of hydrated calcium silicate, hydrated calcium aluminate, and a small amount of ettringite. This study is expected to provide reference for the solidification of high moisture content muddy soil.

Study on performance and application of O-QGS soil curing agent for waste clay with low liquid limit

To reuse industrial solid wastes and waste clay with low liquid limit, a kind of soil solidification material by using cement, quicklime and industrial solid wastes such as ground granulated blast-furnace slag (GGBS), silica fume (SF) was developed in this study. Response surface methodology (RSM) based on central composite design (CCD) was used to design the experiment and optimize the mix ratio of GGBS, quicklime and SF under certain cement content conditions (i.e., the content ratio of cement, GGBS, quicklime, and SF was 5: 9.14: 1.7: 2.13). A soil solidification agent named O-QGS was developed to solidify waste clay with low liquid limit. To clarify the solidification mechanism of solidified soil, a series of laboratory experiments such as UCS test, water stability test, and scanning electron microscopy (SEM) test were carried out to capture the mechanical properties, water stability, and microstructure of O-QGS solidified soil and cement solidified soil. For practical purpose of O-QGS, a method for forming prefabricated pile by using O-QGS solidified soil was developed, and a method for strengthening soft foundations with prefabricated O-QGS solidified soil pile was proposed. Based on the results of load tests, the bearing capacity of prefabricated O-QGS solidified soil pile and cement high-pressure rotary jet grouting pile, as well as the composite foundations bearing capacity of prefabricated O-QGS solidified soil pile and cement high-pressure rotary jet grouting pile used for strengthening soft foundations, were analyzed. The feasibility of prefabricated O-QGS solidified soil pile used for strengthening soft foundations was verified in practice. The present study shows that the UCS of O-QGS solidified soil is 7.25 MPa at 28 days, and the water stability coefficient of O-QGS solidified soil is larger than 0.8. Compared with the method of cement high-pressure rotary jet grouting pile to reinforce soft foundation, the bearing capacity of prefabricated O-QGS solidified soil pile to reinforce soft foundation is higher, and the cost can be saved by 22.4 %.

Solidification of Radioactive Wastes Using Recycled Cement Originating from Decommissioned Nuclear-Energy Facilities

Hundreds of thousands of tons of waste are generated from decommissioned nuclear- power facilities, and it has become a critical global issue to secure technology for reducing and recycling this waste. Concrete waste (CW) is estimated to comprise 60–80% of the total waste, and concrete-waste powder (CWP) includes enough inorganic substances used as effective materials for waste treatment. Accordingly, it can be used to produce recycled cement (RC). This study aimed to evaluate the performance of a solidification agent manufactured using recycled cement (SRC) for the safe packing of radioactive wastes, such as coarse aggregates of CW, waste soil, and metal wastes originating from decommissioned nuclear facilities. The experimental results indicated that the most relevant incineration temperature of CWP for RC was 700 °C. The optimum water-to-binder ratio was determined to be 0.4, and the most relevant substitution ratio of ground granulated blast furnace slag for CWP was determined to be 15%. In addition, calcium silicate hydrate is the most effective hydration product for improving the compressive strength of SRC. The maximum packing capacities of the SRC for coarse aggregates, waste soil, and metal waste, which were simulated as radioactive wastes, were determined to be 30, 5, and 7 wt%, respectively. The results of leaching tests using SRC containing radioactive wastes contaminated with Co, Cs, and Sr indicated that their leachability indices met the acceptance level for disposal. Consequently, the RC composed of CWP can be used as a solidifying agent to safely dispose of radioactive wastes, such as coarse aggregates, waste soil, and metal waste.

The mechanisms of thermal solidification agent promoting steam diversion in heavy oil reservoirs

At high cycles of steam huff & puff, oil distribution in reservoirs becomes stronger heterogeneity due to steam channeling. Thermal solidification agent can be used to solve this problem. Its solution is a low-viscosity liquid at normal temperature, but it can be solidified above 80 °C. The plugging degree is up to 99% at 250 °C. The sweep efficiency reaches 59.2%, which is 7.3% higher than pure steam injection. In addition, simultaneous injection of viscosity reducer and/or nitrogen foams can further enhance oil recovery. The mechanism of this technology depends on its strong plugging ability, which changes the flowing pattern of steam to effectively mobilize remaining oil. Viscosity reducer and nitrogen foams further expand the sweep range and extends the effective period. Therefore, thermal solidification agent can plug steam channeling paths and adjust steam flowing direction to significantly enhance oil recovery at high cycles of steam huff & puff.

Experimental Study on Mechanical Properties of Marine Mud Slurry Treated by Flocculation-Solidification-High Pressure Filtration Combined Method

For the massive quantities and negative impacts of dredged mud slurry, its disposal and utilization have become one of the most noticeable issues in the world. In this paper, the flocculation-solidification-high pressure filtration combined method is proposed to effectively dispose of marine mud slurries. The advantages of this method are demonstrated herein in the following three aspects: dewatering performance, material savings, and the shear strength of the treated marine mud slurry. Then, the effects of the anionic polyacrylamide (APAM) dose, composite solidification agent dose, initial water content of marine mud slurries, and initial thickness of geo-bags on the mechanical properties of the marine mud slurry treated by the flocculation-solidification-high pressure filtration combined method are studied. Experimental results show that with increasing doses of APAM, the structures of mud slurries become more stable, and the optimal dose of APAM is determined as 0.16%. Moreover, the increase in the composite solidification agent dose and initial water content of the marine mud slurry, and the decrease in the initial thickness of geo-bags both contribute to the increase in the shear strength of the marine mud slurry treated by the flocculation-solidification-high pressure filtration combined method.

Preparation and reaction mechanism of low environmental load mud solidification agent from multivariate solid waste

Utilizing various industrial solid waste to replace cement to prepare mud solidification materials could achieve energy conservation, carbon reduction and sustainable development. This research conducted solidification mud (SM) experiments using solidification agent (SA) compounded by mixing five types of solid waste. The focus was on studying the performance of SA and SM in the presence of different activators, as well as the influence of different activators on the SA curing mechanism. The results indicate that the SA and SM specimens with 3.0% Na2SiO3 addition had the highest compressive strength values at 1 d and 28 d, respectively. In addition, the microscopic test analysis showed that when 3.0% Na2SiO3 was added, the hydration activity of SA was relatively high, and the continuous distribution of cluster gel in the hydration product made its overall structure more compact.

Evaluation of the Solidification of Radioactive Wastes Using Blast Furnace Slag as a Solidifying Agent.

The decommissioning process of nuclear power facilities renders hundreds of thousands of tons of various types of waste. Of these different waste types, the amount of concrete waste (CW) varies greatly depending on the type of facility, operating history, and regulation standards. From the previous decommissioning projects, CW was estimated to comprise 60-80 wt.% of the total weight of radioactive wastes. This represents a significant technical challenge to any decommissioning project. Furthermore, the disposal costs for the generated concrete wastes are a substantial part of the total budget for any decommissioning project. Thus, the development of technologies effective for the reduction and recycling of CW has become an urgent agenda globally. Blast furnace slag (BFS) is an industrial byproduct containing a sufficient amount (higher than 30%) of CaO and it can be used as a substitute for ordinary Portland cement (OPC). However, there have been few studies on the application of BFS for the treatment of radioactive waste from decommissioning processes. This study was conducted to evaluate the performance of the solidification agent using ground granulated BFS (SABFS) to pack radioactive wastes, such as the coarse aggregates of CW (CACW), waste soil (WS), and metal waste (MW). The analytical results indicated that the CaO content of the ground granulated BFS was 36.8% and it was confirmed that calcium silicate hydrate (CSH) could be activated as the precursor of the hydration reactions. In addition, the optimum water-to-binder ratio was determined to be 0.25 and Ca(OH)2 and CaSO4 were found to be the most effective alkaline and sulfate activators for improving the compressive strength of the SABFS. The maximum packing capacities of the SABFS were determined to be 9 and 13 wt.% for WC and WM, respectively, when the content of CW was fixed at 50 wt.%. The results of the leaching tests using SABFS containing radioactive wastes contaminated with Co, Cs, and Sr indicated that their leachability indices met the acceptance level for disposal. Consequently, the SABFS can be used as a solidifying agent for the safe disposal of radioactive waste.

Experimental study on bio-treatment effect of the dredged Yellow River silt based on soybean urease induced calcium carbonate precipitation

As the river with highest silt content in the world, the Yellow River is dredged annually to relieve the pressure of flood control. Prior studies indicated that the dredged Yellow River silt cannot be directly utilized as construction filling material because of the deficiency in strength and stability. In this study, soybean urease induced calcium carbonate precipitation (SICP) method was proposed to solidify the Yellow River silt for the purpose of promoting its mechanical properties. The influences of soybean powder concentration and pH value on the soybean urease activity were investigated. By estimating the urease activity of per unit mass, the soybean powder concentration with highest extraction efficiency were determined. The optimum bio-treatment recipe including cement solution concentration and grouting time of the biological solidification agent suitable for the Yellow River silt was characterized through unconfined compressive strength (UCS) test and CaCO3 content test. Meanwhile, scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis of the bio-treated Yellow River silt sample verified the effectiveness of solidification from microscopic viewpoint. The findings of this study suggest that soybean urease induced calcium carbonate precipitation (SICP) method can effectively improve the geotechnical engineering properties of Yellow River silt and provide a technical approach for the resource utilization of the Yellow River silt.

Studying the Properties of Chromium-Contaminated Soil Solidified by Polyurethane.

The solidification of chromium-contaminated soil using polyurethane (PU) was systematically investigated. The unconfined compression test was conducted to investigate the effects of the curing time, PU dosage and the content of chromium ions on the unconfined compressive strength (UCS) of chromium-contaminated soil. The effect of the PU dosage on the pore structure was investigated using nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM), and the mechanism of strength change was revealed by combining the strength law with the pore structure development law. In addition, the ability of the PU to solidify the chromium-contaminated soil was studied by the toxicity characteristic leaching procedure (TCLP). According to the above test results, the UCS and the ability of the PU to solidify the chromium ions increased with the increase in curing time. The NMR tests showed that with the increase in PU dosage, the porosity decreased and the soil became more compact, hence increasing the strength. When the chromium ion content was 2000 mg/kg and the PU dosage was 8%, the strength of the sample was 0.37 MPa after curing for 24 h, which met the requirement of 0.35 MPa set by the U.S. Environmental Protection Agency. Consequently, PU is a solidification agent with high-early strength.

Characteristics of waste mud treated by construction waste-slag based flocculation-solidification combined method

Nowadays, the flocculation-solidification combined method (FSCM) is considered suitable for mud treatment and recycling. However, the traditional FSCM uses ordinary Portland cement (OPC) as the main solidifying material, which pollutes the ecological environment. Currently, the evaluation mechanism of solidification efficiency is not accurate, the treatment of mud with different water content is not detailed enough, and the assessment of carbon emission is unclear. Accordingly, this paper introduces solid waste such as construction waste powder (concrete and brick mix recycled fine aggregate) and slag powder for solidification based on the traditional FSCM. Within the study context, the alkali activation effects of quicklime, NaOH, and NaSiO3 are compared to develop a new solidification agent. Besides, the flocculation time and peak settling rate are measured experimentally, and anionic polyacrylamide(APAM) is added separately to compare low-water-content mud (LW-MS) (ω < 70 %) and high-water-content mud (HW-MS) (70 %≤ω ≤ 300 %). The intrinsic flocculation-solidification mechanism is analyzed and demonstrated through microscopic testing.Finally, the feasibility of construction waste-slag based flocculation-solidification combined method (CWS-FSCM) is verified through field test. In terms of solidification effectiveness, carbon emissions and economy, CWS-FSCM performs better than the traditional FSCM.

Study on the solidification property and mechanism of soft soil based on the industrial waste residue

Abstract The solidification property and mechanism of soft soil based on the industrial waste residue was studied systematically. First, the properties of soft soil solidified by single blast furnace slag, phosphogypsum and cement were carried out, and the solidification effect of Portland cement was better compared with blast furnace slag and phosphogypsum. Second, the composite solidification agent formula with excellent solidification performance was developed, and the mass ratio of Portland cement, blast furnace slag and phosphogypsum was 1:2.3:0.8. At this time, compressive strength was up to 8845.1 kPa. Finally, the composition and microstructure of the solidification soft soil was studied by X-ray diffractometer and scanning electron microscope. Calcium hydroxide formed by the hydration of Portland cement and calcium sulfate in phosphogypsum were used as activators for hydration reaction of blast furnace slag, and more hydration products under the synergistic action of Portland cement hydration and blast furnace slag hydration were formed. Hydrated calcium silicate colloid and Ettringite crystal played an important role in skeleton and filling, and the structure of soft soil solidified by composite solidification agent was the most compact.

Leaching characteristics and solidification strategy of heavy metals in solid waste from natural graphite purification.

The tailings and fluorine-containing sludge were produced during the physical and chemical purification of natural crystalline graphite, containing heavy metals in different occurrence forms. To evaluate the threat of different heavy metals to the environment, this work uses the modified sequential extraction method (BCR) to study the presence of heavy metals in two solid wastes and their dissolution characteristics in different environments. The results show that the pollution risk of heavy metals in graphite tailings to the environment is ranked as Mn > Cr > Ni > Zn, and the pollution risk of Mn in fluorine-containing sludge is higher than that of Cr. This is because the Mn in the two solid wastes mainly exists in the form of weak acid extraction. The leaching number of heavy metals in the two solid wastes is directly proportional to the soaking time and soaking temperature, and inversely proportional to the pH value and the solid-to-liquid ratio. The number of heavy metals dissolved in solid waste landfills is significantly higher than that of acid rain and surface water environments. Based on the above results and the distribution of graphite solid waste, solidification agent was suggested to prevent heavy metal dissolution and reduce environmental risks.

Influence of Recycled Fine Aggregate Content on Properties of Soft Soil Solidified by Industrial Waste Residue.

The influence of recycled fine aggregate content on the properties of soft soil solidified by industrial waste residue was systematically studied. First, the addition of recycled fine aggregate may provide skeleton support, which was conducive to improving the solidification properties. Comparing the addition of recycled fine aggregate content and a composite solidification agent separately, the compressive strength increased 48.01 times and 1.32 times, respectively. Second, the composition and quantity of the hydration products were analyzed by X-ray diffraction (XRD) and thermal gravity analysis (TG/DTG). In addition to silicon dioxide and aluminum oxide, a number of new minerals, including hydrated calcium silicate, calcium hydroxide and ettringite, were produced under different recycled fine aggregate contents. The diffraction peak of hydrated calcium hydroxide was weak, which indicated that the crystallinity and relative content was low. The main reason for this was that it was consumed as the activator of the secondary hydration reaction of blast furnace slag. With the increase in recycled fine aggregate content, the total weight loss (hydration products, crystal water, impurities) increased significantly, at rates of 6.9%, 7.0%, 7.2%, 8.8% and 9.7%. The addition of recycled fine aggregate does not change the composition and quantity of the hydration products, and the increased weight loss in this part might be caused by the cement paste attached to the surface of the recycled fine aggregate. Finally, their microstructure was analyzed by scanning electron microscopy (SEM). Larger and more pores appeared in the solidification system with the increase in recycled fine aggregate, and a large amount of ettringite was prepared. An excess in recycled fine aggregate caused more pores, and the negative impact of too many pores exceeded the lifting effect of the aggregate, resulting in the decline of its mechanical properties. Therefore, there was a suitable range for the use of recycled fine aggregate, which was not more than 40%. In conclusion, recycled fine aggregate not only acts as a skeleton to improve solidification strength, but could also realize the comprehensive utilization of waste, which provided a new scheme for solid waste utilization and soft soil solidification.

Designing a composite solidification agent to improve mechanical properties and sulfate resistance of construction clay-residue

The utilization of construction clay-residue (CCR) through solidification treatment reduces the waste of land resources and environmental pollution. In this paper, a new composite solidification agent (CSA) containing calcined silt (CS), fly ash (FA), and ground granulated blast-furnace slag (GGBS) is designed to improve the performances of solidified CCR. The optimum proportion of CSA was determined based on the orthogonal test design and response surface methodology (RSM). The effects of CSA incorporation on the properties of CCR were investigated and compared with CCR solidified by ordinary Portland cement (OPC). The results indicate that the use of CSA in solidified CCR slightly decreases the unconfined compressive strength in comparison with OPC, however, significantly improves the resistance to sulfate attack. The strength reduction and mass loss of the CSA-solidified CCR after 28 cycles were less than that of the OPC-solidified CCR. Thus, the designed CSA is recommended to solidify CCR in engineering practice for economic and environmental benefits and better durability.

Microstructure and performances of sludge soil stabilized by fluorogypsum-based cementitious binder

As the byproduct in fluoride production, fluorogypsum is of slow hydration and poor concreting, playing a role of threat to environmental safety. Microstructure and performances of sludge soil stabilized by fluorogypsum-based cementitious binder were investigated in comparison with the solidified sludge blended with quicklime (LM) and PC32.5 cement (PC32.5) in this paper. The water content (wt%), pH value, unconfined compressive strength (UCS) and strength loss after soaking in water for 24 h of the solidified sludge with different solidifications were discussed. The solidified sludge blended with fluorogypsum-based cementitious binder (FB) possessed the lowest wt% of 9.24% (14 days, solidification agent dosage as 19%) indicating the good compressibility and potential to be a roadbed material. The pH value of 9.67 for FB (14 days, solidification agent dosage as 19%) was closer to neutral than LM and PC32.5. The UCS of FB stabilized for 14 days arrived at 4.7 MPa with the solidification agent dosage as 19%, which was 1.6 and 6.4 times as much as that of PC and LM, respectively, which further proved the good compression performance of FB. SEM and FT-IR demonstrated the formation of ettringite, portlandite and other hydration products, and explained the phenomenon that FB had sufficient early strength. The FB has not only a big specific surface area of 6.02 m2 g−1, but also a great pore volume of 2.25 × 10-2 cm3 g−1, which would improve the FB activity and accelerate hydration reaction. Based on the above characterization and analysis, the FB solidified sludge soil was clarified as a roadbed material and potential adsorbent.

Experimental study on mechanical properties and microstructure of metakaolin based geopolymer stabilized silty clay

Geopolymer is an environmentally friendly green building material with fast hardening, high strength, low shrinkage, low cost, and low carbon dioxide emission. Based on the above characteristics of geopolymer, this study aims to explore the feasibility of taking geopolymer as a new choice for silty clay foundation treatment. In this study, unconfined compressive strength tests, scanning electron microscopy (SEM), and X-ray energy dispersive spectroscopy (EDS) experiments were carried out on silty clay stabilized by metakaolin based geopolymer (MKG). The influences of metakaolin content, modulus, and concentration of alkali activator on the mechanical properties of geopolymer stabilized soil were discussed. The mechanism of MKG improving the soil strength was also discussed from the microscopic point of view. The result showed that when the modulus of alkali activator is 1.3, the concentration is 40%, and the mixed mass of metakaolin is 1.2 times that of alkali activator, MKG stabilized soil showed higher unconfined compressive strength (UCS). Through comparative tests with untreated plain soil, lime stabilized soil and ordinary Portland cement stabilized soil, the strength performance and stabilizing effect of MKG stabilized soil were further studied. MKG has an obvious effect on improving the UCS of soil, and its mechanical indexes including UCS, Young's modulus, failure strain were also enhanced compared with samples stabilized with lime and ordinary Portland cement. SEM observation confirmed the formation of cementitious materials in the stabilized soil sample, the soil showed a more uniform and denser microstructure after treatment with MKG. Through EDS energy dispersion spectroscopy analysis, it is not easy to cause salt swelling damage with no large amount of calcium ions in the sample. This experimental study indicated that MKG can be an effective soil solidification agent for silty soil.

Application Ranges of EPB Shield TBM in Weathered Granite Soil: A Laboratory Scale Study

Soil conditioning is a key factor in increasing tunnel face stability and extraction efficiency of excavated soil when excavating tunnels using an earth pressure balance (EPB) shield tunnel boring machine (TBM). Weathered granite soil, which is abundant in the Korean Peninsula (also in Japan, Hong Kong, and Singapore), has different characteristics than sand and clay; it also has particle-crushing characteristics. Conditioning agents were mixed with weathered granite soils of different individual particle-size gradations, and three characteristics (workability, permeability, and compressibility) were evaluated to find an optimal conditioning method. The lower and upper bounds of the water content that are needed for a well-functioning EPB shield TBM were also proposed. Through a trial-and-error experimental analysis, it was confirmed that soil conditioning using foam only was possible when the water content was controlled within the allowable range, that is, between the upper and lower bounds; when water content exceeded the upper bound, soil conditioning with solidification agents was needed along with foam. By taking advantage of the particle-crushing characteristics of the weathered granite soil, it was feasible to adopt the EPB shield TBM even when the soil was extremely coarse and cohesionless by conditioning with polymer slurries along with foam. Finally, the application ranges of EPB shield TBM in weathered granite soil were proposed; the newly proposed ranges are wider and expanded to coarser zones compared with those proposed so far.

A study on the pelletizing condition for roll compaction of powdered radioactive wastes

Dried powder of radioactive wastes cannot be disposed of as such unless it is solidified by an appropriate solidification agent. However, the volume of the solidified waste form increases to a large extent due to certain limitations (incorporation ratio) while mixing the wastes with a solidification agent. As a result, the cost of waste disposal increases and filling up the disposal facility's capacity occurs fast. To address this problem, roll compaction technology can be used to reduce the physical volume of the powdered wastes. Powdered wastes (contaminated soil and bio-shield concrete) were converted to rigid pellets of certain shape and size (H 6.5 x W 9.4 mm) by a special roll compactor. The operating parameters (hydraulic pressure, roll speed, feeding rate, roll gap) of the roll compactor were evaluated, and the volume reduction factor of each waste powder and the strength of the pellet were estimated.

Study on Preparation of Perforated Plate and Biofilm Colonization for Municipal Solid Waste Incineration Fly Ash

At present, municipal solid waste incineration (MSWI) fly ash is mainly based on the solidification agent and then landfilled. How to make the fly ash harmless and reuse it will become an important step in the circular economy. In this study, the fly ash was treated by water extraction and milling to remove the soluble chloride ions and stabilize the heavy metals, and then the perforated plate was prepared by adjusting the composition and sintering technology. Research on biofilm colonization on the perforated plates is expected to achieve the purpose of stabilizing and recycling the fly ash. The fly ash is subjected to a solid-liquid ratio of 1:5 with two-stage water extraction, 2h ball milling, and then mixed at a mass ratio of waste glass powder, Palygorskite powder and the milled fly ash of 7:2:1, and calcined at 850°C for 20 minutes to prepare perforated plate. The results show that the prepared perforated plate has a rough surface, developed internal porosity, and its water absorption rate is 19.5%. The perforated plate is used as the biofilm carrier to be applied to the biological contact oxidation tank, and the natural biofilm colonization method is adopted for the 36-day biofilm culture. The average growth rate of the biofilm on the perforated plate reached 672.22 mg/(L·d), and the maximum microbial biomass was 12.1g/L.

页岩气侧钻水平井油基泥饼固化剂性能评价与现场试验

页岩气侧钻水平井油基泥饼固化剂性能评价与现场试验