Fresh Slurry Research Articles

Influence of FA and HPMC on the fresh properties and anisotropy of 3D printing engineered cementitious composites (3DP-ECC)

To investigate the effect of material compositions on the fresh properties and anisotropy of 3DP-ECC, the shape retention and the anisotropy of the compressive strength of 3DP-ECC with different contents of fly ash (FA) and Hydroxypropyl methyl cellulose (HPMC) were studied. The research results indicated that FA could weaken the shape retention, but HPMC significantly enhanced the shape retention of the fresh slurry of 3DP-ECC. The compressive strength in different directions was ranked as Z > Y > X. With the increase of dosage (FA/HPMC), the isotropy in the compressive strength of 3DP-ECC with HPMC decreased, but the difference of 3DP-ECC with FA became more obvious gradually.

Potential of copper tailings as supplementary siliceous materials in the preparation of autoclaved aerated concrete

The storage of copper tailings (CT) not only consumes considerable land resources but also tends to cause a series of ecological and environmental issues. To achieve the circular economy and green industry development, CT is utilized as a supplementary siliceous material of autoclaved aerated concrete (AAC) in this study. The effects of substitution rate of CT for quartz sand are evaluated though the flow and gas-foaming properties of fresh slurry, and the physical and mechanical properties of AAC products. Meanwhile, the relationship between the macroscopic properties and hydration products is analyzed by multiple microscopic tests, including the Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The experimental results shows that the bulk density, compressive strength and thermal conductivity of AAC incorporating CT show a trend of first decreasing and then increasing as the substitution rate of CT for quartz sand increases from 0 to 50 wt%, while the specific strength continues to decrease. When the substitution rate of CT for quartz sand is less than 40 wt%, the performances of AAC can meet the specifications of B05 A2.5 level according to Chinese national standards. These findings are closely related to the characteristics of air pore structure and the ordering, quantity and morphology of hydration products. With increasing the substitution rate of CT for quartz sand, the ordering of tobermorite gradually decreases, and its morphology transforms from plate-like to grass-like and then to needle-like, which can reduce the mechanical properties of AAC.

Ground granulated blast furnace slag-modified magnesium phosphate cement used as grouting material: Workability, mechanical property and corrosion resistance optimization

Calcium oxide and alumina, which are significant components of ground granulated blast furnace slag (GGBS), can participate in the hydration reaction with phosphate. This study examines the effect of incorporating GGBS as a mineral admixture on the fresh, mechanical, and durability properties of two-component magnesium phosphate cement (MPC)-based grouting materials. The findings reveal that GGBS replacement not only reduces the setting time and the heat released during hydration but also optimizes the fluidity of the fresh slurry at the appropriate replacement level. The optimal content of 20 % GGBS replacement significantly improves the mechanical properties of MPC grouts, achieving up to 28.4 MPa at 28 days, and enhances their resistance against the corrosion of water, chloride, and sulfate ions. XRD results show that the incorporation of GGBS leads to the formation of amorphous phases and secondary hydration products. These findings are corroborated by SEM analysis, which reveals gel-like new hydration products in matrices containing GGBS. Additionally, the incorporation of GGBS reduces the appearance of microcracks and gaps, resulting in a denser microstructure of the MPC matrix.

Effect of phosphate impurities on the properties of β-hemihydrate gypsum pastes plasticized by polycarboxylate superplasticizer

This study aims to investigate the effect of HPO42-/PO43- on the working performance and mechanical strength of β-hemihydrate gypsum pastes containing polycarboxylate superplasticizer (PCE) and reveal its underlying mechanism. The results showed that HPO42-/PO43- has a detrimental effect on the fluidity, compressive strength, and softening coefficient of β-hemihydrate gypsum pastes. However, in the presence of PCE, all properties were improved compared to the blank group when the HPO42-/PO43- content was less than 0.3 %. The fluidity and compressive strength of the pastes can be increased by up to 95 % and 32 %, respectively. It was found that HPO42-/PO43- reacted with Ca2+ to form insoluble calcium phosphate salt (ICPS), and the adsorption of PCE on the surface of ICPS increased the total adsorption amount, thereby enhancing the dispersion ability of PCE and increasing the fluidity of fresh slurry. In addition, the adsorption behavior of PCE on the surface of ICPS weakened its inhibitory effect on the hydration of hemihydrate gypsum, which was confirmed by TG-DSC. The increased hydration products and reduced water requirements significantly improved mechanical properties. These findings enhance the understanding of the interaction between phosphorus impurities and PCE, which can guide the improvement of the performance of β-HPG and promote the resource utilization of phosphogypsum.

Optimal development of the new type of ultra-fine fly ash semi flexible pavement grouting material: Rheological, mechanical, pore distribution, and hydration characteristics

In order to solve the problems that the fluidity of semi-flexible pavement grouting materials (SFPGM) is not up to standard, the early strength is not enough, or the fluidity meets the requirements but the early strength is not up to standard, the power plant by-Product -ultra-fine fly ash (UFA) was used to optimized the performance of grouting materials (GM) in this study. The microstructure of hardened slurry was analyzed by XRD, FTIR, MIP and SEM. The findings indicate that when the UFA content increases, the fluidity of the GM initially increases and then declines, whereas the compressive strength initially reduces and then increases. The sample exhibits optimal fluidity performance when the content of UFA is 9 %. The flow cone fluidity of the initial and 20 min is 12.33 % and 17.63 % lower than that of the reference sample. When the amount of UFA is 12 %, the compressive strength of sample is the highest at each age. Additionally, that the fluidity of sample S12 is sub-optimal in all samples, only worse than that of sample S9. In the early stage of GM hydration, UFA with slow hydration rate produces a significant ‘ball-bearings effect’ between irregular cement particles. This is beneficial to the relative sliding between the slurry particles, reduces the yield stress and plastic viscosity of the fresh slurry, and improves the flow performance of the GM. The pozzolanic effects of UFA in GM primarily manifests during the later stages of hydration. The primary hydration products of UFA modified GM include ettringite, C-S-H gel, C-A-S-H gel, calcium carbonate, and aluminium glue (AH3). During the progression of the hydration reaction, the quantity of ettringite (AFt) in the slurry steadily augments, causing the initial fine needle-like structure to evolve into a more fully formed needle-like structure. A complex three-dimensional network of interlocking spatial structures is formed by many hydration products that continually interlace and develop, improving strength. The higher the perfusion rate of the GM, the higher the compactness of the SFPGM, and the better the high temperature stability and low temperature crack resistance.

Analysis on Chemical and Physical Properties of Dried Sago Bagasse

The uncontrollable of sago bagasse waste from sago industry production become an environmental issue as it just dumping directly into nearby rivers which can affect a river pollution if not treated well. As it still has about 70% starch content, it has a potential to be converted to the others value-added product such as animal feed. However, before it can be converted to others product, it should go through a drying process to reduce its higher moisture content (90 wt.%), as well to prevent any micro bacteria growth and for long lasting packaging. Thus, this study focused on the evaluation of drying process at T=70 and 80 °C on reducing of its final moisture content by using three drying approaches: fluidized bed dryer (FBD), micro-oven and direct sunlight drying. Then, these samples of dried sago were analysed to determine its properties of starch, fibre, and ash, as well to study its functional organic chemical group by using Fourier infrared transform (FTIR) method. The results show the reduction of sago water content by FBD shown a significant result as compared to others drying methods as the FBD method produces a good solid mixed between particles. Besides, the drying rate using the FBD was achieved in a shorter time within 30 min as compared to oven which within 2 hours and sunlight drying within 6 days to achieve similar final desired moisture content at 11 wt.%. The analysis on the starch properties using the FBD was also almost 75% more higher than oven, which is about 70% starch content. Moreover, the presence of starch was successful proven by the presence of acrylic acid at a wavelength of 1539.72 cm-1 for FBD sample by using FTIR. In addition, using the FBD, the sago waste can maintain its quality as an animal feed by reached a brightness level, W1 as compared to the slurry sago waste where the dried sago using FBD is 58.78%, meanwhile the fresh slurry sago waste is 93.31%. In conclusion, the sago drying in the FBD at T=80 °C was selected as the optimum drying condition as it had achieved a short drying rate for desired final 11 wt.% moisture content and resulted in better on the chemical and physical analysis.

Carbonation curing of magnesium-coal slag solid waste backfill material: Study on properties of flow, mechanics and carbon sequestration

To expedite the achievement of the ''30–60 double carbon'' goal, it is imperative to create a novel, low-carbon, cost-effective, and sustainable backfill material for mining purposes. Against this background, this paper investigates the workability, carbonation performance and carbon sequestration capacity of coal gangue (CG), magnesium slag (MS) and fly ash (FA) as magnesium coal slag solid waste backfill material. The results of the study show that: (1) The rheological properties of the CFM fresh slurry conform to the Herschel-Balkley (H-B) model, and its flowability meets the requirements of mine backfill transport. With increasing MS content, the yield stress, apparent viscosity, thixotropy and shear thickening of CFM fresh slurry increase, and the micro-slump and diffusion diameter decrease. (2) Carbonation curing can effectively improve the early UCS of CFM. The highest UCS of CFM was 8.854 MPa after 7 days of carbonation curing, which was 27.84 times higher than that of standard curing. In addition, the UCS of CFM increased with the increase of curing age and MS content. (3) CFM produces a large number of carbonation products such as calcium carbonate after carbonation curing, which makes its microstructure denser. (4) CFM can absorb up to 14.55 % of CO2 after carbonation. (5) The volume stability of CFM is significantly improved after carbonation curing. In summary, CFM is not only a new type of low-cost, low-carbon and sustainable solid waste backfill material, but its practical application in the field of mine backfilling also has great potential for the realization of magnesium coal slag solid waste resource utilization and CO2 sequestration.

Effect of particle size on cement foams

This work attempts to elucidate the foaming kinetics, hierarchical structures, engineering properties and mechanisms of cement foams with high-volume quartz powder (QP) of different fineness from 200 to 2000 meshes. Comprehensive experiments were conducted to measure the fresh slurry properties, foaming process, penetration strength, and structure of the foams and skeletons. Foaming kinetics was analyzed using fractional-kinetic (FK), pseudo first-order (PFO) and pseudo second-order (PSO) models. Results show that the increase of QP fineness can, respectively, keep, increase and decrease the pH, viscosity, and flowability. The FK model shows the best fitting goodness of foaming kinetics, and the slurry with the QP fineness of 600 meshes possesses the fastest foaming speed. Fine QP shortens the induction time and exothermic peak time, and improve the collapse strength. Coarse QP induces more small bubbles and severe breakage of skeleton, and coarsen the nanopores. The interrelationships among the experiment outcomes and the mechanisms of colloidal adhesion, nucleation and growth of bubbles and cement hydrates, and microstructure development in skeletons are profoundly discussed. The findings deepen the mechanistic understanding of cement foams with different size particles.

The influence of selected mineral ingredients on the technological properties of sealing slurries

Sealing slurries used to modify the subsoil should meet a number of requirements, including: rheological properties, setting time, appropriate mechanical strength and durability. The study determined the technological properties of sealing slurries prepared with ordinary Portland cement and blended binders containing appropriately selected mineral additives. The tests used granulated blast furnace slag, silica fly ash and ash obtained in the fluidized bed combustion of coal. The assessment of the technological properties of fresh slurries included the selection of an appropriate rheological model and the assessment of the rheological properties of the sealing slurry, such as: plastic viscosity, apparent viscosity and yield point. The research determined the factors causing improvement of the technological properties of fresh slurry. The use of supplementary cementitious materials, also in systems with fluidizing admixtures, allowed for a significant modification of the rheology of the tested sealing slurries. The obtained results indicate their beneficial effect on the functional properties of slurries, enabling their use as binder components replacing Portland cement, while limiting or even eliminating the addition of superplasticizers.

Numerical modelling of diaphragm wall construction

AbstractDiaphragm walls are rectangular shaped cast in place deep foundations. There are two critical phenomena occurring, according to which the final quality can be affected: bentonite suspension exfiltration and concrete placement. Some imperfections seem to appear recurrently on the surface of the final wall. The defects are known as shadowing pathologies. The main reasons can be attributed to the dual effect of exfiltration mechanisms and kinematics of concrete flow. The objective of this study is developing a numerical tool to prevent the appearance of shadowing pathologies by visualizing the concrete flow in the presence of a bentonite suspension. This paper presents the results obtained from 2D and 3D models of diaphragm wall construction using COMSOL Multiphysics. The CFD model helped in solving a multifluid and particularly a two‐phase flow. The 2D modeling has considered a fresh slurry and an exfiltrated (or polluted) suspension neighboring soil and followed concrete flow with two rheological behaviors in two reinforcement configurations. Then, 3D simulations were compared to actual experimentation results, which were undertaken to construct diaphragm walls in the laboratory. By comparing the results of the simulations to the experimental outcomes, it has been possible to validate the model. The resulting simulations could clearly explain the occurrence of the pathology where the flow pattern and volume fraction of the fluid flow were determined. From the results obtained, it can be conducted that a compliant concrete mix but at the lower limit for the consistency recommendations, leads to pathologies, just like a polluted slurry.

Influence of liquid-to-solid ratios on properties and microstructure of coal gasification slag-based one-part geopolymer

Limited studies have been conducted on the synthesis of one-part geopolymer involving coal gasification slag by alkali fusion and component additive method (AFCAM). The ratio of liquid-to-solid (L/S) is the key aspect that has a major impact on the one-part geopolymer's compressive strength (UCS). Our research aims to determine how different L/S ratios affect the microstructure and characteristics of one-part geopolymers. MIP analysis and hydration heat test were conducted to analyze the influence caused by different L/S ratios. The results showed that as the L/S ratio increased, the UCS of geopolymers decreased, and the setting time of fresh slurry increased steadily. Additionally, geopolymer with 0.25 as an L/S ratio (G-L/S-0.25) achieved a higher UCS at 48.31 MPa, whereas the total setting time was more than 23 h. The low L/S ratio produced more gel pores and less total porosity in the geopolymer matrix, which improved the UCS. Moreover, lower porosity suggested that the geopolymer sample had higher compactness and a better internal structure. It is found that the dissolution of the fusion product released heat in the first hour, and no coal gasification slag dissolution heat was detected after one hour. This suggested coal gasification slag showed low reactivity as the additive and was embedded in the geopolymer matrix after 28-day curing. The tested results showed that G-L/S-0.25 had a greater reaction degree. This study illustrated the effects of the L/S ratio on one-part geopolymer and provided a new thought to enhance the UCS of coal gasification slag-based geopolymer.

Influence of temperature effect on properties of modified magnesium slag-based low-carbon paste backfill materials

Coal mining subsidence and bulk solid waste storage are the bottleneck problems for achieving green and low-carbon development in northern Shaanxi. Aiming at the demand of filling mining in coal mines in northern Shaanxi, a modified magnesium slag-based low-carbon paste backfill materials (MMS-PBM) was proposed, which realized the safe disposal and resource utilization of solid waste. In-depth understanding of the influence of temperature effect (initial temperature: 5 ∼ 50 °C and curing temperature: 20 ∼ 50 °C) on the performance of MMS-PBM is helpful to optimize the mix ratio and filling period of filling materials. Based on this, relevant tests and tests (including setting time test, Mini-slump test, rheological test, uniaxial compressive strength test, microscopic test and leaching toxicity test) were carried out to explore the influence mechanism of temperature effect on the performance of MMS-PBM. results showed: (1) The rheological curve of fresh MMS-PBM slurry is highly consistent with the Herschel-Bulkley (H-B) model, and the fluidity meets the pumping requirements of coal mine filling. With the increase of initial temperature, the yield stress and apparent viscosity of fresh slurry increased, while slump, expansion and thixotropy decreased. (2) The increase of initial temperature inhibits the development of early mechanical properties of MMS-PBM, which is mainly affected by the metastable film hypothesis. (3) The curing temperature is conducive to the development of mechanical properties of MMS-PBM, and meet the requirements of mechanical properties of coal mine. With the increase of curing temperature, the main growth range of mechanical properties gradually changes from 7–28 d to 3–7 d, which is consistent with the change of microstructure. (4) The leaching concentration of heavy metals in MMS-PBM meets the requirements of national standards, but the increase of curing temperature has an inhibitory effect on the solidification of heavy metals. The above results show that MMS-PBM is a safe, green and low-carbon all-solid waste filling material, which is beneficial to the coordinated development of coal resource mining and environmental protection.

Feasibility study on superabsorbent polymer (SAP) as internal curing agent for cement-based grouting material

The closed working condition of grouting materials leads to insufficient curing water supply during their strength development. In this work, the superabsorbent polymer (SAP) was used as the internal curing agent for grouting material. The effects of SAP content on the rheological and mechanical properties of grouting material were studied under various water-cement ratios (w/c) and curing environments. The time-dependent variation of fresh slurry's viscosity was measured by Brinell viscometer. The pore structure and micromorphology characteristics were analyzed by Mercury Intrusion Porosimetry (MIP) and Scanning Electron Microscope (SEM). The results indicate that the addition of SAP increases the viscosity of fresh slurry and decreases its fluidity, thereby improving the slurry's internal uniformity at a higher w/c. And in its actual working condition, grouting material's strength can be boosted with less than 0.3% SAP dosage. Although SAP will introduce some irregular mesoscopic pores (0.2 − 0.3 mm), the MIP data analysis proves SAP refines the microscopic pore structure of grouting materials. SEM data analysis proves SAP optimizes the microstructure of grouting material, which cured in dry environment. In general, SAP improves the internal uniformity of grouting material by absorbing excess mixing water and gradually releasing it to promote cement hydration, which improves the strength of grouting material. Hence, SAP is a practicable internal curing agent for grouting material and 0.2% is the recommended dosage.

Experimental study on application performance of foamed concrete prepared based on a colloidal NanoSiO2-stabilized foam

In this study, colloidal nanoSiO2 (CNS) was added into the foaming agent at 0, 0.5, 1, 1.6, and 2 wt% of the binder mass to enhance the stability of foaming agent and prefabricated foam, further the stability of foamed slurry and hardened foamed concrete. First, the stability of CNS on foaming agent and prefabricated foam was investigated by examining surface tension, surface viscoelastic modulus E, foam parameters, surface shear viscosity, and morphology. Prefabricated foam containing CNS was then used to prepare foamed concrete with a dry density of 700 kg/m3. The rheological characteristics, volume change, setting time, hydration properties, and gas content for fresh foamed slurry and the pore characteristics, compressive strength, and thermal conductivity of hardened foamed concrete were characterized. The microstructural crystalline structures of the foamed slurry and hardened foamed concrete were also investigated. Results of this study indicated that nanoSiO2 nanoparticles in colloidal state improved the stability of foam, especially when the CNS dosage was ≥ 1 wt%, because CNS caused increases in the surface viscoelasticity modulus E of the foaming agent and the surface shear viscosity of the prefabricated foam. Moreover, foamed slurry with a shorter hydration induction period, more stable volume, a shorter initial setting time, and higher viscosity was obtained when the CNS dosage was ≥ 1 wt%. Hardened foamed concrete with higher early compressive strength and superior thermal insulation properties was correspondingly obtained when fresh slurry with higher stability was used. However, the effect of CNS will decrease on the compressive strength of the hardened foamed concrete after 14 days of hydration. Finally, mechanisms were proposed regarding the stabilization effects of CNS on the prefabricated foams, foamed slurry, and hardened foamed concrete.

Comparative study of the effects of magnesium aluminum silicate and bentonite clay on the properties of magnesium phosphate cement-based grouting material

In this paper, mineral admixtures of magnesium aluminum silicate (MAS) and bentonite clay (BC) were added to magnesium phosphate cement-based grouting material (MPCG) to improve its poor water resistance and large shrinkage deformation of the matrix, and the effects of MAS and BC on the properties of fresh slurry, compressive strength, volume stability and microstructure of MPCG were comparatively studied. The research results showed that MAS and BC reduced the shrinkage deformation of MPCG, increased MPCG’s density, and decreased porosity. After curing for 28 d, the compressive strength and water resistance of MPCG were improved by adding 2.0 wt% of MAS or BC, and the compressive strength and softening coefficient were 13.9 ± 0.4 MPa and 0.87 (MAS), 12.2 ± 0.7 MPa and 0.84 (BC), respectively, which were all higher than the control group. The hydration heat and phase composition showed that the addition of MAS or BC reduced the cumulative heat of MPCG, but no new crystal phase was formed. The addition of MAS increased the formation of K-struvite (MgKPO4·6H2O), while BC reduced the formation of K-struvite. Therefore, MAS and BC could be used as admixtures of MPCG to improve its workability.

Strength behavior and deformability characteristics of paste backfill with the addition of recycled rubber

ABSTRACT This study aims to research the implications of rubber powder utilisation, from tires recycling, in the deformability and strength properties of CPB. In the end, it will be concluded that mine paste backfill with recycled rubber materials contributes to the decrease of waste tire pollution and improve some mechanical properties of the filling body. For that purpose, tests were carried out to determine the uniaxial compressive strength, the elastic energy of deformation, Young’s modulus, and Poisson’s ratio in specimens made up of mine tailings, Portland cement, wastewater, rubber powder, and plasticisers. The analysis of experimental data determines that recycled rubber makes fresh slurry have better performance in flow characteristics. In the hardened state, recycled rubber reduces the uniaxial compressive strength of the specimens and Poisson’s ratio, but other features like deformability increase (Young’s modulus decrease) that enhance the ability to absorb elastic strain energy of the filling body. As a result, the study indicates that recycled rubber is applicable to rockburst prevention. The findings of this study provide both invaluable information and industrial applications for the efficient management of solid waste, based on sustainable development and circular economy.

Research on Influences of Ultrasonic Vibration Agitation Stirring on Carbonation Resistance of Cement-Based Materials after Absorption of CO2

To disclose influences of ultrasonic vibration agitation on the carbonation resistance of cement-based materials after absorption of CO2, the variation laws in internal carbonization zone were explored by the testing carbonization depth and carbonization range (pH variation range) of cement mortar after CO2 absorption at different ages. Results demonstrated that when CO2 absorption volumes of the cement mortar before carbonization were 0.44%, 0.88%, 1.32%, 1.76%, and 2.20% (28 d), the carbonization depth under ultrasonic vibration decreased by 5.5%, 12.3%, 21.7%, 20.7%, and 26.7% compared to those under mechanical stirring, respectively. When the ultimate CO2 absorption volume increased to 2.2% of cement mass, the extended degree of cement mortar was 103.23 mm, which decreased by 5.4% compared to that before CO2 absorption. pH variation values of the carbonization range under ultrasonic vibration presented a rising trend with the increase of CO2 absorption volume of cement mortar before carbonation. This indicated that, with the increase of CO2 absorption volume of cement mortar before carbonation increases under ultrasonic vibration, the carbonization process of the hardened body of cement mortar might be decelerated to some extent. Additionally, changes in internal composition and physical images of cement-based materials after absorption of CO2 were analyzed through microtest means like SEM and XRD. A carbonation resistance model was constructed, thus enabling disclosure of the variation mechanism of carbonation resistance of cement-based materials after absorption of CO2 under mechanical stirring and ultrasonic vibration. Results demonstrated that the higher CO2 absorption volume of fresh slurry generated more “nano-level” CaCO3 crystal nucleus. Accordingly, it could improve the porous structure of the cement mortar, decrease the quantity of capillary tubes significantly, improve the compaction degree of cement-based materials effectively, and lower the diffusion rate of CO2 in the cement paste base, thus improving the carbonation resistance. Research conclusions have important significance to decrease CO2 emissions and improve carbonation resistance of concrete.

Rheological behavior with time dependence and fresh slurry liquidity of cemented aeolian sand backfill based on response surface method

Slurry transportation in pipelines is the key link in the filling process. Liquidity and rheological behavior are important bases for evaluating the feasibility and stability of slurry pipeline transportation and the rheological behavior is time-dependent. Research on the performance and application of cemented aeolian sand (AS) backfill (CASB) is in the preliminary stage, and the time effect and continuous response of various factors to the rheological behavior of CASB slurry have not been studied. Here, the CASB slurry contained AS as an aggregate, fly ash (FA) as an auxiliary material, ordinary Portland cement (PO) as a cementitious material, and water. The response surface method (RSM) was adopted to analyze the influence of PO content (x1), FA–AS ratio (x2), concentration (x3), and their interaction terms (x1x2, x1x3, and x2x3) on the rheological parameters (yield stress (τ0) and viscosity coefficient (η)) of slurry at 0, 40, 80 and 120 min. Additionally, liquidity (slump flow (Sf) and bleeding rate (Br)) of fresh slurry was evaluated. The rheological parameters increased with PO content, FA–AS ratio, and concentration, except that the bleeding rate first decreased and then increased with PO content, the slump flow and bleeding rate decreased with each response factor. The interaction term, x2x3 had a significant influence on τ0 and η at each curing time and Sf and Br, x1x3 had a significant influence on the τ0 and η at 40, 80, and 120 min, and x1x2 influenced τ0 and η at 80 and 120 min significantly. An improvement in one factor promoted the strengthening of another factor. τ0 increased as a quadratic function, and η increased as a primary or quadratic function with curing time. The fitting degree between τ0, η, and curing time was > 0.9, indicating that the rheological parameters of the slurry had a strong time dependence. In conclusion, this study determined the influence and mechanisms of PO content, FA-AS rate, concentration, and their interaction terms on the rheological behavior with time dependence and fresh slurry liquidity of CASB, thereby providing theoretical and engineering guidance for CASB filling.

The intrinsic relationship between flocculation effect and apparent viscosity of fresh slurry

Apparent viscosity considerably influence the migration and diffusion of the slurries. However, the effect of particle structure on the slurry viscosity is still indeterminate. In this study, the distribution of flocculent particles was measured using a particle track analyzer with focused beam reflectance measurement (FBRM) system. A rheometer was used to measure apparent viscosity of fresh slurry. Three factors of water-cement ratio (W/C), particle shape, and particle fineness directly change the particle structure, and indirectly affect apparent viscosity of slurry. Increased W/C reduces the flocculation degree, the particle fineness increases the particle interparticle in the slurry, and the microbead action of fly ash makes it challenging to form flocculent structures. These factors affect the ratio of bound water, flocculent water, and free water, as well as the interparticle force, thereby changing the slurry viscosity. Further, an effective volume fraction was proposed, and revealed a change in viscosity as the result of the particle structure. The results demonstrate the rationality of the analysis and the predictions. The established relationship provides design basis for the application of other materials and additives. The paper's originality is that the effective volume fraction (ϕm) is proposed and the relationship between flocculent structure and slurry viscosity is established under multiple factors.

Enhancing fly ash utilization in backfill materials treated with CO2 carbonation under ambient conditions

The environmental concerns resulting from coal-fired power generation that produces large amounts of CO2 and fly ash are of great interest. To mitigate, this study aims to develop a novel carbonated CO2-fly ash-based backfill (CFBF) material under ambient conditions. The performance of CFBF was investigated for different fly ash–cement ratios and compared with non-CO2 reacted samples. The fresh CFBF slurry conformed to the Herschel-Bulkley model with shear thinning characteristics. After carbonation, the yield stress of the fresh slurry increased significantly by lowering fly ash ratio due to gel formation. The setting times were accelerated, resulting in approximately 40.6% of increased early strength. The final strength decreased when incorporating a lower fly ash ratio (50% and 60%), which was related to the existing heterogeneous pores caused by rapid fluid loss. The strength increased with fly ash content above 70% because additional C–S(A)–H and silica gels were characterized to precipitate on the grain surface, so the binding between particles increased. The C–S(A)–H gel was developed through the pozzolanic reaction, where CaCO3 was the prerequisite calcium source obtained in the CO2-fly ash reaction. Furthermore, the maximum CO2 uptake efficiency was 1.39 mg-CO2/g-CFBF. The CFBF material is feasible to co-dispose CO2 and fly ash in the mine goaf as negative carbon backfill materials, and simultaneously mitigates the strata movement and water lost in post-subsurface mining.