Fly Ash Cement Research Articles

The effect of an osmotic crystalline surface protectant agent on the performance of cement fly ash stabilized Aeolian sand bases

This paper studies the use of cement fly ash to stabilize the graded gravel and the use of aeolian sand instead of fine aggregates in the design of mixture composition. Firstly, the effect of different cement-fly ash ratios on the aeolian sand bases was investigated, and then the synergistic effects of osmotic crystalline surface protectant (OCSP) and different cement-fly ash ratios on the mechanical properties and water-blocking properties of aeolian sand were analyzed. The results indicated that the optimal water content and maximum dry density of the mixture are increased and the unconfined compressive strength of the 7 d and 28 d both is downward by fly ash. The unconfined compressive strength of the aeolian sand base treated by OCSP was significantly improved, and the enhancement effect was more significant with the increase of cement content. The water absorption rate of each group of specimens increased rapidly during the first 10 hours of immersion., However, the water absorption rate of the specimen treated with OCSP was almost zero in the whole water absorption process after 10 hours.

Feasibility Study of Low-Environmental-Load Methods for Treating High-Water-Content Waste Dredged Clay (WDC)—A Case Study of WDC Treatment at Kumamoto Prefecture Ohkirihata Reservoir in Japan

The effective and sustainable treatment of high-water-content waste dredged clay (WDC) remains a significant challenge in water conservancy engineering. In this study, we focused on the treatment of WDC produced by Kumamoto Ohkirihata Reservoir. The study examined the effect of two types of cement-based solidifiers, namely, ordinary Portland cement (OPC) and cement–fly ash agent (DF), on three clay samples collected from different locations. The cone index test was used to assess the samples’ properties. The dosage of cement required for effective improvement with DF was significantly reduced (by about 47–55%), compared to OPC. Moreover, the dewatering efficiency of WDC improved by the simple dewatering method of vertically placing environmental protection materials. Within seven days, the average water content of the WDC decreased to below the liquid limit compared with natural air drying. Finally, the dosage of DF required to stabilize the WDC under effective improvement conditions was reduced by 37–58%, which is higher than the dosage of OPC reduction (22–50%). The reduction in water content reduced the pore space of the soil particles, benefiting the internal bonding of DF-stabilized clay. Dewatering methods facilitate the use of DF solidifiers, facilitating sustainable and environmentally friendly improvement in WDC.

Model test study on the deformation and failure mechanism of high-speed railway subgrade obliquely crossing ground fissure zones

Ground fissure is a special geological disaster widely distributed around the world and occurs frequently in China. Questions about the influence of ground fissure activity on high-speed railway subgrade and whether the subgrade can cross a ground fissure zone are important issues in high-speed railway construction. To answer them, we conducted physical model test combined with numerical simulation of a high-speed railway subgrade obliquely crossing a ground fissure that allowed us to analyze the stress characteristics of the Cement Fly-ash Gravel (CFG) composite foundation subgrade, the structural deformation and damage, and the influence area of the subgrade under the influence of ground fissure. The results show that the head pressure of CFG piles in the hanging wall decreases with the increase of ground fissure dislocation but that the opposite in the footwall. The subgrade shows obvious uneven settlement deformation near the ground fissure, and as long as the ground fissure dislocation takes place, the reinforced concrete slab under the subgrade is compressed in the hanging wall and tensioned in the footwall. The deformation and failure of subgrade obliquely crossing ground fissure is tensile-bending failure mode. When the actual ground fissure dislocation reaches 0.8 m, the track bed gets destroyed; the reinforced concrete slab bends due to tensile failure; the CFG piles in the hanging wall cracks and tilts; and compression bending failure occurs in the footwall. This suggests that subgrade with a range of 32 m in the hanging wall and 16 m in the footwall need to be strengthened, and the high-speed railway should cross the ground fissure at as large an angle as possible.

Fresh Properties of Self-Consolidating Expired Cement-Fly Ash Cold Bonded Lightweight Aggregate Concrete With Different Mineral Admixtures

The experimental program evaluated the fresh properties of self-consolidating lightweight concretes (SCLC) produced from expired cement EC cold-bonded lightweight coarse aggregates (ALA) with silica fume (SF) and fly ash (FA). Twelve mixtures of SCLC were prepared, the binder in the control mix was just Portland cement (PC), whereas other mixes included binary and ternary of (PC), 20% of (FA), and/or (10%) of (SF) with (0%, 50%, and 100%) as partial replacement of (ALA) with coarse natural aggregates. Fresh features of (SCLC) were evaluated by measuring their slump flow diameter, T500 slump flow time, V-funnel flow time L-box height ratio, and column segregation, (SCLC) with and without mineral admixtures have their fresh characteristics compared. It was found that increasing the quantity of ALA replacement resulted in a reduction in the amount of superplasticizer required to obtain a constant slump flow diameter of SCLC. Combining (SF) and/or (FA) lowered both the V-funnel flow time and the slump flow time, whereas the L-box height ratio increased from (0.82) to (0.86) with the addition of fly ash for reference mix. With the combined action of mineral admixtures, the percentage of column segregation decreases by (16.7%) compared with the reference mix. The maximum slump flow was (792) mm with a mix of (M6).

Understanding reactive amorphous phases of fly ash through the acidolysis

It is well understood that the reactive components of fly ash (FA) in alkali cement are mainly donated by amorphous phases. The acidolysis method is typically employed to dissolve these amorphous phases for separate analysis; however, such method is not truly convincing, especially the testing and analysis processes. This paper investigates the hydrofluoric acid (HF, 1%) dissolution process (from 0.5 h to 20 h) of two Class-F FAs with different physical and chemical characteristics. The time-dependent quantitative analysis results indicate that in addition to amorphous phases, some crystalline phases are also dissolved in 1% HF solution. Further, the chemical statistics on the dissolved amorphous phases was extracted from the scanning electron microscopy images. Amorphous aluminosilicates in FA can be quantitatively classified into six groups, of which the three reactive amorphous aluminosilicates are defined.

Novel agricultural waste based hardening accelerator for early strength development of fly ash-based concrete

Rapid urbanization is leading to a rise in demand for precast elements to reduce the time and cost of construction. However, precast elements consume the time to remove formwork during production depends on the early strength development of fresh concrete. On the other hand, thermal power plants produce a significant amount of fly ash, which also cause environmental issues. One solution to this problem is to use fly ash in cement and concrete to enhance their pozzolanic properties and address environmental concerns. However, using fly ash can delay the early strength development of concrete resulting deacceleration in the production cycle of precast elements. To speed up the process, some may opt for chemical-based hardening accelerator and high temperature curing. However, this may negatively impact the hydration kinetics of the concrete, pose environmental risks, and compromise the reinforced concrete’s durability.To overcome such limitations, impurity free C-S-H seed based hardening accelerator was synthesized from agricultural waste product namely, bagasse ash using novel chemical synthesis process which could effectively accelerates the early strength development of concrete without altering the conventional hydration process. The proposed synthesis process provides a platform for the reaction between the target calcium and silicate ions simultaneously eliminating the harmful elements (like chloride etc.) responsible for degradation of health of reinforced concrete structure.In order to study the effectiveness of a synthesized C-S-H seed, a blended ordinary Portland cement (OPC) was prepared by replacing 10%, 15%, and 20% of the cement weight with fly ash. Various amounts of the C-S-H seed were then added to the blend. Presence of developed C-S-H seed effectively reduced the setting time and eliminated the induction period during hydration of fly ash blended cement. Presence of additional seeds effectively reduces the critical free energy of nucleation which in turn accelerates the precipitation of hydration product responsible for the early strength development of fly ash-based concrete. Based on the setting time and heat of hydration analysis, it has been observed that the presence of C-S-H seed has the potential to accelerate the early strength gain process of fly ash-based concrete.

The effectuation of seawater on the microstructural features and the compressive strength of fly ash blended cement at early and later ages

AbstractThe current work scrutinizes the effectuation of seawater on morphological properties, pore structure, and compressive strength during the hydration process of fly ash blended cement at 3, 7, 28, 56, and 90 days to better understand the influence of salinity conditions of seawater on the microstructural modification and strength development of the hydration products as well as the total porosity. The chemical reaction's mechanism of mightily soluble salts, for example, Mg2SO4 and NaCl, with hydrated fly ash and blended cement (calcium‐bearing phases) was also confirmed. Fourier‐transform infrared spectroscopy has been appointed to observe and characterize the energetics of variation in the formulation of portlandite (CH), calcium silicate hydrate, gypsum (Gy), ettringite (AFt), and calcium chloroaluminate (Friedel's salt [FS]) throughout the hydration process of fly ash blended cement with seawater in comparison with deionized water. X‐ray diffraction analysis exposed that the peak intensities of FS, portlandite, and some particular phases of the hydrated fly ash blended cement in seawater are higher and sharper than the comparable peaks in deionized water. Mercury intrusion porosimetry‐measurements have been appointed that the total porosity of artificial seawater (ASW) was decreased from 28.9% at 3 days to 19.4% at 56 days. In addition, the average, median, and critical pore diameter were decreased in ASW while compared to deionized water (DIW). The reaction products of this work were also characterized using scanning electron microscopy, EDS, compressive strength, and isothermal calorimeter.

Prediction equations for corrosion rate of reinforcing steel in cement-fly ash concrete

ABSTRACT This study is to incorporate the time-dependent development of microstructures of cement-fly ash concrete into the evaluation of corrosion severity for newly constructed structures and existing structures. The electrical resistivity, corrosion potential, and corrosion rate were determined for twelve series of concrete mixtures prepared with various water-to-binder ratios, fly ash contents, and chloride contents. The time-dependent developments of cement-fly ash paste, including hydration degree, pozzolanic reaction degree, and capillary porosity, are adopted based on previous models. The correlation between the corrosion rate and the time-dependent developments was considered for the proposed equations. The experimental results indicate that low water-to-binder ratio concrete and fly ash concrete show a low corrosion rate of reinforcement. Because the microstructure of concrete became denser, represented by a high degree of hydration and low porosity. This phenomenon increases the corrosion resistance of concrete. Besides, the chloride ions can accelerate the corrosion rate of reinforcement. Its effects of corrosion acceleration are found to be different in fly ash concrete because the fly ash can capture free chloride ions.

Performance of Cement–Fly Ash Masonry Mortar with Sand from Mine Overburden as an Environment-Friendly Alternative to Conventional Fine Aggregate

Abstract There is an increasing demand for fine aggregate for use in concrete and mortar. In this study, sand extracted from mine overburden from two locations through the wet-sieving process was used as alternative fine aggregate in mortar. The behavior has been benchmarked with mortar using conventional river sand and coarse and fine sand obtained from crushed stone. Combination mortar with ordinary portland cement and Class C fly ash was used as a binder. The sand-to-binder ratio was fixed as 3, as per ASTM C270-19ae1, Standard Specification for Mortar for Unit Masonry, whereas the fly ash–to–cement ratio was varied from 0.75 to 3. The water required to achieve a constant flow value of 110 ± 5 % was determined. The water retention of fresh mortar and dry density, compressive strength, and drying shrinkage of hardened mortar were determined. Mortar mixtures with sand from mine overburden with a fineness modulus of 2.36 conformed to the water retention requirement of ASTM C91/C91M-18, Standard Specification for Masonry Cement, whereas very fine sand did not satisfy. Masonry mortar with different mixture proportions and fineness modulus of fine aggregate resulted in a range of compressive strengths, satisfying a wide range of mortar designations as per ASTM C270-19ae1, BS EN 998-2, Specification for Mortar for Masonry - Part 2, and IS 2250, Code of Practice for Preparation and Use of Masonry Mortars. For mortar with a fine aggregate of different origins (river sand, crushed stone coarse sand, sand from overburden with fineness modulus 2.67, 3.01, and 2.36, respectively), a marginal variation in drying shrinkage across strength was observed. The maximum drying shrinkage of the higher fly ash–to–cement ratio of the mixture with finer sand was 1,600 microstrain.

Strength and durability of concrete by partial replacement of cement by fly ash and fine aggregates by granite dust

The building sector is one of the most dynamic and potentially important contributors to national income. It's possible that concrete, as a composite building material, plays a pivotal role in the market. Common concrete calls for the use of natural sand, often known as stream sand. Since river sand is becoming more scarce and prohibitively costly, we have had to go elsewhere for this material. With the ever-increasing need of the construction industries for materials that fulfil their functional, strength, and durability needs, a wide range of novel materials has been produced in the area of concrete technology in recent years.In this investigation, fly ash was substituted for the fine combination of Quarry Dust and cement. Partially substituting Fly Ash for Cement at 0%, 5%, 10%, 15%, 20%, and 25%. The increased moisture electrical resistance and resulting toughness that results from the micro-filling effect gives concretes a leg up on the competition. Compressive and flexural strengths of M40-grade concrete are the primary focus of the experiments. Examine the mechanical and sturdiness characteristics at various ages, including 7 days, 28 days, 56 days, and 90 days. Durability and tensile strength tests, including exposure to acid and chloride for 28 days. The results publicized that by taking 0% to 25% of Fly ash to the weight of cement that specimen when compared with conventional concrete the compressive strength is increased 32.63% by replacement of cement with 10% of Fly Ash for 28 days. Comparing to normal concrete the compressive strength is increased 29.25% with 10% of Fly ash for 56 days. Comparing to conventional concrete the compressive strength is increased 16.93% with 10% of Fly ash for 90 days. SPT values enhanced by 16.67% with 10% of Fly ash at 28 days of curing.

Study the Variation of Properties of Concrete Mix Using Binding Material Portland Cement and Fly Ash Cement

bstract: In the current study, a number of experiments were carried out to compare the mechanical properties of concrete mixes made with Portland cement, fly ash cement, and their mixtures (in 1:0.5 and 1:1 proportion). A replacement silica fume of 5%, 10%, 15%, and 20% was added to concrete mixtures. The materials are combined in the ratios of 1: 1.5: 3. After three days, 14 days, and 28 days, the compressive strengths, workability, and porosity characteristics were examined. By making different types of binder mixes denser, silica fume increases their strength.

Efficiency comparison of mixture formulations in the stabilisation/solidification of the loess silt contaminated with zinc in terms of mechanical properties

The effectiveness of various types of binders in stabilizing/solidifying (S/S) contaminated soils is strongly dependent on the type of soil and contaminants present. The literature abounds with studies of stabilisation/solidification of clayey soils, which provides a background for initial assumptions in design of the method application for contamination of this type of soil. However, studies on the stabilisation/solidification of loess silt contaminated with heavy metals are not available. Filling this deficiency is important in order to ensure the rapid adoption of the most effective remedies in case of contamination and their immediate implementation in the subsoil. This paper has enabled the determination of the most effective mixture among the examined for the remediation of loess silt contaminated with zinc in terms of compressive strength. Strengths were determined with the implementation of 30% Portland cement (2.63 MPa), 30% of fly ash-cement mixture (2.21 MPa), an incinerated sewage sludge ash-cement mixture (0.93 MPa) and mixtures in which cement was replaced by an MgO activator (0.18 MPa for fly ash and 0.63 MPa for incinerated sewage sludge ash). In addition, the determination of strength was carried out for samples containing a mixture of fly ash, activator and cement (0.26 MPa) and incinerated sewage sludge ash, activator and cement (0.26 MPa), with weight ratios of 5:4:1 respectively. In summary, fly ash and cement in a 2:1 ratio can be considered the most effective binding mix in terms of unconfined compressive strength increase.

Effects of Curing Methods on the Permeability and Mechanism of Cover Concrete

Curing methods are one of the most important factors in determining the quality and compactness of cover concrete. The effect of curing methods on the water absorption and sorptivity coefficient of cover concrete with the substitution ratio of fly ash (FA) and ground granulated blast slag (GGBS) for cement between 30 and 40 wt % was studied by capillary water absorption test. The vacuum saturation test and mercury intrusion test were employed to characterize these differences in the pore structure of cover concrete under different curing methods. With further analysis of the compactness of microstructure by SEM, the mechanism of the impact of curing methods on the permeability of cover concrete was revealed. The results obtained indicate that the effect of curing methods on the water absorption, sorptivity coefficient and porosity of cover concrete shows the trend of natural curing > cover curing > water curing > standard curing. It is also shown that reasonable curing is advantageous to reduce the porosity and permeability of cover concrete. In natural curing conditions, the appearance of porosity increasing and pore structure coarsening is more critical for cover concrete with mineral admixtures than for pure cement concrete. Therefore, the permeability of cover concrete with mineral admixtures is more sensitive to the early-age curing methods.

Relationship between fractal feature and compressive strength of fly ash-cement composite cementitious materials

Microscopic pore structure and compressive strength of fly ash-cement composite cementitious materials at 20 °C and 60 °C measured by mercury intrusion porosimetry and compressive strength test. Microscopic pore structure was analyzed from porosity, pore volume, total pore surface area, average pore diameter, median pore diameter, most probable diameter, threshold diameter and fractal feature. The fractal dimensions of each specimen were calculated by Menger Sponge. The regression analysis between fractal dimension and pore structure parameters were fitted by linear function, quadratic polynomial function, power function and exponential function, respectively. Eventually, the relationship between pores structure and compressive strength was characterize by the mathematical model between the optimal comprehensive parameter of pores structure and compressive strength. And the T-test and F-test were used to reveal the significance of the regression parameter and function. Research results showed that the fractal curves of all specimens consist of four segments. The pores have obvious fractal features in Region I and Region IV, while presented no-fractal feature in Region II and Region III. In Region I and Region IV, fractal dimension followed the exponential function with average pore diameter, median pore diameter, most probable diameter and threshold diameter, consistent with quadratic polynomial function with porosity, pore area and pore volume, and accords with the positive power exponential function with compressive strength. Thus, the morphology of hierarchical aggregates expressed by fractal dimension can reflect the relationship compressive strength and pore structure in fly ash-cement composite cementitious materials more directly.

Understanding the effect of high-volume fly ash on micro-structure and mechanical properties of cemented coal gangue paste backfill

The utilization of coal gangue and fly ash to produce cemented paste backfill is an effective strategy to mitigate the environmental impact of such bulk solid wastes. In this study, we aimed to investigate the hardening properties of cemented coal gangue paste backfill (CCGPB) containing high-volume fly ash using macroscopic and microscopic characterization techniques. Specifically, uniaxial compressive strength (UCS) and slump were measured to evaluate the hardening properties of CCGPB, while Scanning Electron Microscopy (SEM) and Mercury Intrusion Porosimetry (MIP) were used to characterize the internal microstructure and internal pores. A total of 216 mixture proportions were designed through variations in the contents of cement, fly ash, water, and curing time. The resulting experimental data were used to develop a random forest model. This model was subsequently employed to evaluate the impact of different variables on the development of UCS in CCGPB. The results revealed that the slump increased with increasing fly ash contents and mass concentration. The maximum UCS was achieved at the mass concentration of 0.81 and the fly ash-cement replacement ratio of 0.42, which was also verified by the SEM showing a more compact interfacial transition zone with hydration products of calcium silicate hydrates, calcium aluminosilicate hydrates, and ettringites. The MIP results showed that the addition of fly ash had slight effect on the pores less than 1 μm, while pores larger than 1 μm increased with increasing fly ash content. The porosity ratio decreased by only 4% when fly ash was increased from 30% to 50%. The simulation results by the developed RF model indicated that the curing age had the highest relative importance (47.7%), while the UCS gain was less sensitive to the fly ash content compared with the cement. Overall, this study provides valuable insights into the application of fly ash and coal gangue to cemented paste backfill.

Heavy metal removal from coal fly ash for low carbon footprint cement

Development of cementitious materials with low carbon footprint is critical for greenhouse gas mitigation. Coal fly ash (CFA) is an attractive diluent additive in cement due to its widespread availability and ultralow cost, but the heavy metals in CFA could leach out over time. Traditional acid washing processes for heavy metal removal suffer from high chemical consumption and high-volume wastewater streams. Here, we report a rapid and water-free process based on flash Joule heating (FJH) for heavy metals removal from CFA. The FJH process ramps the temperature to ~3000 °C within one second by an electric pulse, enabling the evaporative removal of heavy metals with efficiencies of 70–90% for arsenic, cadmium, cobalt, nickel, and lead. The purified CFA is partially substituted in Portland cement, showing enhanced strength and less heavy metal leakage under acid leaching. Techno-economic analysis shows that the process is energy-efficient with the cost of ~$21 ton−1 in electrical energy. Life cycle analysis reveals the reuse of CFA in cement reduces greenhouse gas emissions by ~30% and heavy metal emissions by ~41%, while the energy consumption is balanced, when compared to landfilling. The FJH strategy also works for decontamination of other industrial wastes such as bauxite residue.

High-volume coal gasification fly ash–cement systems: Experimental and thermodynamic investigation

Coal gasification fly ash (CGFA) as a silica-rich material can be potentially used as a supplementary cementitious material (SCM) in concrete. In this study, the cements prepared by CGFA and ordinary Portland cement (OPC) mixtures were systematically investigated to explore the possibility of large-volume utilization of CGFA in cement industry. The hardened cements were subjected to experimental and thermodynamic investigation. The selective dissolution tests suggested that the CGFA had a generally low reaction degree in the CGFA-OPC reaction systems, although the XRD pattern indicated it was a highly amorphous material. The mechanical property tests suggested that the incorporation of 10% CGFA into OPC did not significantly influence the material properties, and the CW-1 mixture (10% CGFA) achieved the compressive strength of 33.8 MPa and the flexural strength of 8.2 MPa. In addition, the drying shrinkage increased with increasing CGFA content in the mixtures. The phase assemblages generated by thermodynamic simulation show that the CGFA always causes reduction in the amount of C-S-H in the hydration products, although the pozzolanic reaction of CGFA can contribute to the formation of secondary C-S-H. The volume of simulated free water is higher in CGFA-rich mixtures, which explains the larger drying shrinkage strains in those mixtures. This study can provide a preliminary guideline for the beneficial utilization of CGFA in OPC and contribute to the recycling and reuse of the waste solid from coal gasification.

Pressure-aided fabrication of CNT-incorporated composites made with fly ash or slag-blended Portland cement

In the present study, the pressure-aided fabrication of CNT-incorporated composites made with fly ash or slag-blended Portland cement was introduced. Specimens having a water-to-binder ratio and CNT content of 0.1 and 0.5 – 4.0 wt% by mass of binder, respectively, were produced by applying an instant pressure of 33 MPa to the fresh mixture. The electrical properties of the specimens were found to be stable at a CNT content of 1.0 wt%. In particular, the electrical resistivity of the specimens was not altered with the curing time due to the inhibition of hydration. In addition, specimens containing 25 and 50 wt% of fly ash or slag in the binder also showed fine and stable electrical resistivity of less than 100 Ω·cm. Specimens with fly ash showed temperature increase higher than 30 °C while those with slag showed temperature increase less than 20 °C as an input voltage of 20 V was applied. The observed electrical resistivity of the present study was compared to the outcomes reported in the previous studies to indicate the superior electrical conductivity (less than50 Ω·cm) with only 1 wt% of CNT inclusion.

Use of detoxified MSWI fly ash for cement stabilized macadam mixture: mechanism, mechanical and environmental considerations

Use of detoxified MSWI fly ash for cement stabilized macadam mixture: mechanism, mechanical and environmental considerations

Using ensemble model to predict isothermal hydration heat of fly ash cement paste considering fly ash content, water to binder ratio and curing temperature

It is widely accepted that fly ash (FA) addition in cement impairs the reaction of silicate phase and promotes the reaction of aluminate phase. Meanwhile, FA also retards early-age hydration heat release of cement. No generalized hydration prediction model is available for accurate description of the isothermal heat release of FA cement paste. In this study, we try to adopt an ensemble model, one of the machine learning approaches, to predict the early-age isothermal hydration heat flow of FA cement paste. Effect of curing temperature, water to binder ratio (w/b), FA content and curing time on heat release is thoroughly considered in the ensemble model, and the hyperparameters of the model are tuned by Bayesian optimization with 5-fold cross validation. The results indicate that whether for the training data or the testing data, the root-mean-square error (RMSE) and mean-absolute-error (MAE) have been well controlled at approximately 0.1 and 0.06 mW/g paste, respectively. The optimized model is also applied to predicting the time-dependent isothermal hydration heat flows of three different FA cement systems cured under different temperatures. The coefficient of determination (R2) values for both the predicted heat flow rates and the calculated cumulative heat have attained 0.98, proving the applicability of the trained model on isothermal heat prediction for FA cement paste. Sensitivity analysis is also conducted for the optimized model. Curing temperature and time are revealed to be the two most important input variables for isothermal heat prediction using machine learning, followed by FA content, and the least important one is w/b. Neglecting any of them reduces the prediction accuracy of the model.