Admixtures Fly Ash Research Articles

Effect of steam curing on strength, durability and microstructure of concretes with and without mineral admixtures

This research explores the effect of steam curing on the strength, durability and microstructure of concretes with and without mineral admixtures of fly ash (FA) and ground granulated blast-furnace slag powder (SL). Two types of C55 strength grade concretes (one was pure cement concrete, the other was a concrete made by replacing part of the cement with 12% FA and 18% SL) were prepared and their compressive strength, chloride diffusion coefficient and carbonation depth under standard and steam-curing conditions were measured and compared. The phase composition and microstructure of the concretes under the two curing conditions were tested by X-ray diffraction, scanning electron microscopy and mercury intrusion porosimetry. The results showed that, on the one hand, compared with standard curing, steam curing is beneficial to the early strength, but not conducive to the later strength development and chloride permeability resistance of both types of concretes. Furthermore, for the steam-cured concrete, the 28 days carbonation depth of the forming surface is higher than that of the bottom surface. In addition, steam curing can reduce the carbonisation resistance of pure cement concrete and improve the carbonisation resistance of concrete mixed with FA and SL. On the other hand, composite mineral admixtures of FA and SL reduce the early strength and the carbonisation resistance of concrete cured by standard curing, but improve the later strength, the carbonisation resistance and chloride permeability resistance of concrete cured by steam curing. FA and SL are thermally activated under steam curing and can react with the calcium hydroxide formed by cement hydration in the early stage, which produces a larger amount of secondary hydration products to improve the pore structure and interfacial microstructure of the concrete with FA and SL. In this way, the adverse effects of steam curing on later strength and durability of concrete are significantly restrained by composite mineral admixtures of FA and SL.

Fly ash admixture originating from lignite combustion in construction mortars – Time evolution of technical parameters and heavy metals leachability

The production of cement, the predominant construction binder, is associated with high energy consumption, enormous raw material depletion, and a large volume of CO2 emissions, making cement one of the most polluting materials. This study aims to contribute to the sustainability of the construction industry by significantly reducing the proportion of Portland cement (PC) in the composition of mortars. The binder content reduction was achieved by the addition of large amounts of fly ash admixture (FA) from lignite combustion while studying the effectiveness of the immobilization of heavy metals (HMs), which are present in FA, in the PC/FA matrix. Along with the analysis of the FA admixture amount on the properties of the prepared mortars, emphasis was put on the study of the influence of prolonged curing on the development of the physical parameters of the mortars and the immobilization efficiency of the HMs. It was revealed that FA can be added to PC by up to 20 wt%, enabling the production of construction mortars with high strength and low porosity, while confining hazardous substances such as HMs in the matrix. Prolonged curing at elevated relative humidity led to the continuous evolution and solidification of the mortar structure, improving its engineering properties and HMs immobilization efficiency.

Study on the micro-rheological properties of fly ash-based cement mortar

Aiming at the shortcomings of poor rheological properties and low strength of tailings filling mortar, solid waste materials such as fly ash, steel slag, and desulfurization ash were introduced to improve the filling mortar. The Response Surface Methodology (RSM) was used to design the test ratios to determine the significance of the effect of fly ash, steel slag and desulphurization ash on the physical properties of the mortar. The rheological characterization law of filling mortar was studied based on macroscopic L-tube test. The mechanism of filling mortar improvement was analyzed by Scanning Electron Microscopy (SEM), and Energy-Dispersive X-ray Spectroscopy (EDS) and other microscopic tests. The results show that the response-factor model fit regression is significant, with the highest model satisfaction at 12 % fly ash dosing, 15 % steel slag dosing, and 10 % desulfurization ash dosing. The self-flowing extension diameter of the mortar is 15.34 cm, and the 3d and 28d strengths are 0.58 MPa and 3.24 MPa, respectively. Fly ash has effectively improved the phenomenon of mortar segregation and precipitation, and the yield stress of mortar is reduced by 35.1∼64.9 % when the dosage is 8∼12 %. The fractal dimension and mortar workability are positively correlated with fly ash admixture. Fly ash incorporation will gradually consume the calcium hydroxide (CH) to generate alumina ferrite (Aft) and calcium silicate hydrate (C-S-H), which reduces mortar porosity and promotes long-term strength growth. The research results not only realized the effective utilization of solid waste resources, but also significantly improved the performance of the filler and ensured the safe production of the mine.

Study on the Effect of Fly Ash on Mechanical Properties and Seawater Freeze–Thaw Resistance of Seawater Sea Sand Concrete

When using seawater and sea sand as mixes, the mechanical properties and durability of concrete are adversely affected because the raw materials themselves contain harmful ions. Fly ash is the tailings formed in the process of industrial production, the use of which does not require the burning of clinker, reducing CO2 emissions. Moreover, it belongs to a new type of cementitious materials with low emissions and high environmental protection. Fly ash enhances the properties of concrete and reduces the effect of harmful ions on concrete. Based on the above considerations, the corresponding specimens were prepared and subjected to cubic compressive strength, flexural strength, and seawater freezing and thawing resistance tests by using fly ash admixture as the main variable. A combination of macro-analysis and micro-analysis was used to investigate the effect of fly ash on the performance of seawater sea sand concrete. The results showed that fly ash significantly enhanced the mechanical properties and resistance to seawater freezing and thawing of seawater sea sand concrete. The best improvement in compressive strength and resistance to seawater freezing and thawing was achieved at a substitution rate of 20%. The maximum increase in compressive strength was 13.22%. The maximum reduction in mass loss rate was 57.26% and the strength loss rate was 43.14% after the specimens were subjected to seawater freezing and thawing 75 times. The maximum enhancement in flexural strength was 17.06% for a substitution rate of 10%. Through microanalysis, it can be seen that the incorporation of coal ash can enhance the compactness of concrete through the microaggregate effect as well as the volcanic ash reaction to promote the secondary hydration reaction, so as to strengthen the seawater freeze–thaw resistance of seawater sea sand concrete. Finally, the damage prediction model established using the mean GM (1, 1) model of gray system theory meets the requirements of the first level of prediction accuracy and can accurately predict the damage of seawater sea sand concrete under seawater freezing and thawing.

Machine Learning Method to Explore the Correlation between Fly Ash Content and Chloride Resistance.

Chloride ion corrosion has been considered to be one of the main reasons for durability deterioration of reinforced concrete structures in marine or chlorine-containing deicing salt environments. This paper studies the relationship between the amount of fly ash and the durability of concrete, especially the resistance to chloride ion erosion. The heat trend map of total chloride ion factor correlation displayed that the ranking of factor correlations was as follows: sampling depth > cement dosage > fly ash dosage. In order to verify the effect of fly ash dosage on chloride ion resistance, three different machine learning algorithms (RF, GBR, DT) are employed to predict the total chloride content of fly ash proportioned concrete with varying admixture ratios, which are evaluated based on R2, MSE, RMSE, and MAE. The results predicted by the RF model show that the threshold of fly ash admixture in chlorinated salt environments is 30-40%. Replacing part of cement with fly ash in the mixture of concrete below this threshold of fly ash, it could change the phase structure and pore structure, which could improve the permeability of fly ash concrete and reduce the content of free chloride ions in the system. Machine learning modeling using sample data can accurately predict concrete properties, which effectively reduce engineering tests. The development of machine learning models is essential for the decarbonization and intelligence of engineering.

Influence of Mineral Admixtures on the Performance of Pervious Concrete and Microscopic Research

Pervious concrete is an innovative eco-friendly construction material. Through the application of mineral admixtures and microscopic analysis to optimize its performance and analyze its mechanisms, its traits as a sustainable building option may be further improved. This study primarily examines the impact of the optimal blend quantities of fly ash, silica fume, and reinforcing agent on the attributes, micro-morphology, and phase composition of porous concrete. The optimal admixture was chosen after analyzing the effects of various factors on the mix ratio and properties of permeable concrete. To understand the degree of impact, performance tests were conducted on the 28-day compressive strength, water permeability coefficient, and porosity. Furthermore, the micro-mechanisms of the admixtures and reinforcing agents on the properties of permeable concrete were analyzed from a microscopic point of view using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. This research found that the advantageous properties of permeable concrete were enhanced by the simultaneous integration of appropriate quantities of fly ash, silica fume, and reinforcing agent. This resulted in a 28-day compressive strength of 18.33 MPa and a permeability coefficient of 8.27 mm/s. Compared with the unadulterated mineral admixture, the optimal admixture of fly ash, silica fume, and reinforcing agent at the same time increased the 28-day compressive strength by about double; the permeability coefficient was reduced by 36%, but it was still at a high level; and the measured porosity did not differ much from the designed porosity. Through thorough microanalysis, the hydration reaction was significantly improved, which could enhance the microstructure and pore structure of the concrete. This was supported by a substantial increase in the macroscopic compressive strength and a decrease in the water permeability coefficient, which were consistent with the aforementioned enhancement found in the microanalysis.

Improvement of subgrade California Bearing Ratio (CBR) using recycled concrete aggregate and fly ash

The study aims to understand the effect of different admixtures on improving the quality of flexible pavement subgrades. In this paper, recycled concrete aggregates (RCA) and Fly Ash were used as the admixtures in improving the maximum dry density (MDD), swelling potential, and California bearing ratio (CBR) of subgrade soil. The percentages of RCA and fly Ash used were 5%, 10%, and 15%. With the upscaling in fly ash dosage, the optimum moisture content and the California bearing ratio increased. However, the MDD of soil decreased for higher fly ash contents. On the contrary, the optimum moisture content (OMC) of the soil decreased and the MDD and California Bearing Ratio increased with an increase in RCA content. Both RCA and fly ash-treated soil demonstrated lower values of swelling. At 5% dosage, both RCA and fly ash admixtures were found to improve CBR. However, at higher percentages (10% and 15%) of fly ash, the CBR values decreased while in comparison, soil samples performed significantly better in the CBR test with the increasing dosage of RCA. The findings of this research can be used to examine the suitability and effects of recycled aggregate and fly ash on the performance of soil in terms of CBR, particularly when the soil is planned to be used as a subgrade in highways.

A study of the shear strength properties of expansive soil treated with fly ash admixture

The behavior of clay minerals in expansive soils causes them to exhibit shrink-swell characteristics, making them unsuitable for engineering purposes in their natural state. To address this problem, researchers conducted direct shear experiments using fly ash as an admixture and black cotton soil as an expanding soil to explore the strength parameter. The experiments were conducted with varying amounts of fly ash ranging from 2% to 20%. Two arrangements of test series were made, and in the principal series, tests were made utilizing five unique densities and comparing dampness contents. The outcomes showed that the point of inside grating and union expanded directly up to the ideal dampness content and most significant dry thickness before diminishing. The subsequent series showed that the end of inward rubbing grew straightly with the expansion of fly debris admixture, yet attachment reduced after 10% admixture. The decrease in shear strength was because of the diminished passion, as the fly debris' cohesionless attributes took over as the admixture rate increased above 10%. Based on these findings, adding fly ash in small quantities to black cotton soil is recommended to avoid weakening it.

A Study on the Hydrothermal Synthesis of Calcium Silicate Products by Calcination of Full-Component Waste Concrete

In order to achieve the reuse of waste concrete, the hydrothermal synthesis of low-temperature calcined calcium silica products with an ideal admixture of fly ash and waste concrete as raw materials was investigated and various properties were studied. The findings suggest that the optimal method involves adding 10% fly ash to waste concrete to lower the temperature at which calcium carbonate decomposes. The compressive strength of the specimens generally increases with increasing calcium–silicon ratio and pressure can reach up to 43.98 MPa. Nevertheless, the duration of holding requires adjustment in line with autoclave pressure: the higher the pressure, the shorter the holding time, and vice versa for lower pressure. Most of the specimens are water-resistant with softening coefficients above 0.6 and up to 0.91. The macroscopic strength is determined by the way in which the microstructure of the hydration products forms under different conditions. The optimum design for the experimental conditions should be that the pressure, holding time and calcium–silica ratio should be 1.0 MPa, 9 h and 1.0, respectively. Due to their potential for resource conservation and environmental improvement, autoclaved silicate materials manufactured from waste concrete may be a viable alternative as a green construction material.

Study of synergistic effect of fly ash and superabsorbent polymers on properties of cement pastes

The main goal of this study is to observe changes in microstructural properties and the mutual interaction of cement pastes containing superabsorbent polymers (SAPs) and fly ash. SAP is a type of hydrogel additive, able to absorb large amounts of liquid in its structure. In cement-based materials, it is often used in the early stages of matrix hydration to absorb excess mixing water and to release it in the later stages, which is even more desirable when the material is exposed to higher temperatures. Another research goal is a partial substitution of binder (Portland cement) by the energy by-product of high-temperature ash, produced by the combustion of brown coal. A further goal is the observation of the interactions of these binders with the SAPs on the microstructural scale. For this purpose, computed tomography (CT), X-ray diffraction (XRD), differential thermal analysis (DTA), and scanning electron microscopy (SEM) were performed. Basic physical and mechanical properties such as compressive strength, flexural strength, and bulk density were also determined. In the early stages of hydration, viscosity and chemical shrinkage were determined. From the results obtained, it is obvious that the presence of SAPs has a significant impact on the properties of cement pastes. From the two tested SAPs, SAP HM has a positive effect on volume stability and the flexural strength of the composite. The results of the mineralogical composition showed that the effect of SAP incorporation influences the crystallization of portlandite, alite, belite, and calcite. SEM analysis confirmed the results of XRD analysis and proved that hydration products can grow into SAP cavities. It is clear from the evaluation of the pore structure that SAPs increase the porosity of cement composites. The admixture of high-temperature fly ash has a positive effect on reducing the volumetric changes of mixtures. The mechanical parameters of the composite with fly ash were similar to that of the reference test specimens.

Investigation of Uniaxial Compression Stress–Strain Relationship of Early Age Manufactured Sand Concrete and Its Application

To improve the construction efficiency of the manufactured sand concrete engineering at an early age, the uniaxial compressive stress–strain relationship of C50 manufactured sand concrete is investigated starting at 2 days to 28 days. With the characteristics of the stress–strain relationship, the uniaxial compression constitutive model is determined for the C50 manufactured sand concrete at early age. The influence of age, water-to-binder ratio, and fly ash admixture on the peak stress and peak strain of manufactured sand concrete is analyzed for the parameters of the constitutive model. Results show that the stress–strain curve of manufactured sand concrete is essentially similar to that of ordinary concrete. Via six typical constitutive models, the Sargin model produced the best fitting: its R2 mean is 0.9775, MAE mean is 0.1335, and MSE mean is 0.0175. Considering the influence of different factors, the early age uniaxial compressive constitutive models of manufactured sand concrete were proposed based on the Sargin model. Combined with the on-site construction process of the high pier formwork climb, the finite element analysis was carried out using the proposed early age uniaxial compressive constitutive model. Compared with the measured results of strain near the climbing cone, the error was less than 10% from the simulated value. The findings confirm that the proposed early age uniaxial compressive constitutive model presents great reasonableness for the manufactured sand concrete construction at an early age.

Performance Analysis of High-Performance Concrete Materials in Civil Construction.

This paper develops the mechanical and durable samples of C50 high-performance concrete, studies the mechanical properties, crack resistance, sulfate attack resistance, frost resistance, and impermeability of concrete with different mineral admixtures of mineral powder and fly ash, and obtains the best mineral admixture of mineral powder and fly ash to improve the performance of high-performance concrete. The results show that the doping effect is the best when the ratio of prepared mineral powder to fly ash is 3:2. With the increase in the mineral powder-fly ash admixture, the slump and expansion of high-performance concrete decrease rapidly at first and then slowly. In total, 60% doping is the turning point; the compressive and flexural strengths of concrete decreased slowly at first and then rapidly. Taking 30% of the admixture as the turning point, 35% of the mineral powder fly ash is generally selected. By mixing and adding a certain proportion of fly ash and mineral powder admixtures, the crack resistance of concrete is enhanced, and the shrinkage and cracking are reduced. The corrosion resistance coefficient will exceed 88%, the relative dynamic elastic modulus will exceed 95%, and the impermeability grade will reach P17. The durability of concrete can be improved by adding mineral admixtures.

Study on the Effect of Fly Ash Admixture on the Performance of Recycled Pervious Concrete

In order to solve the problems of recycling of a large amount of coarse aggregate produced after the crushing of waste concrete and urban flooding, this project prepares the recycled coarse aggregate of 4.75-9.5 mm into 100 mm × 100 mm × 100 mm cubic permeable concrete specimens, and researches the influence law of different fly ash admixture on the pore space, water permeability and mechanical properties of the recycled aggregate permeable concrete, and determines the best design The optimal design ratio was determined. The experimental results show that the permeable concrete specimens prepared with recycled coarse aggregate of 4.75-9.5mm particle size and mixed with fly ash were cured in water, and the longer the curing age, the higher the compressive strength. With the increase of fly ash dosage, the compressive strength first rises and then decreases, and the porosity and permeability coefficient decreases continuously. When the fly ash dosage is 15%, the 28d compressive strength of recycled aggregate pervious concrete is the highest, which is 12.8 MPa. At this time, the porosity is 23.9%, and the permeability coefficient reaches 3 mm/s. Considering the overall situation, the optimum dosage of fly ash for recycled aggregate pervious concrete is recommended to be about 15%.

Experimental study and evaluation of bonding properties between fiber and cement matrix under sulfate attack

The toughening effect of fibers on cementitious composites mainly comes from the bridging effect of fibers, and the core of the bridging effect depends on the bonding performance of fibers to the cement matrix. To study the fiber-cement matrix bonding performance under the action of sulfate-dry and wet cycles of erosion, fiber pull-out tests with different Na2SO4 solution concentrations (0–15%) and fly ash admixtures (0–30%) were carried out in this paper. Based on the principle of energy dissipation, the mathematical relationship between the toughness index and energy absorption index of fiber-cement-based mortar was established, and a comprehensive evaluation method of fiber-cement matrix bonding performance based on the weight determined by the CRITIC method is proposed. The results show that 15% Na2SO4 solution has a great influence on the erosion rate and erosion degree of interface bonding performance, and the peak load corrosion resistance coefficient is reduced by 43.7%. When the content of fly ash is 20%, the interface transition zone has the best resistance to sulfate attack, and the maximum value of bonding performance index B is 0.59 when the dry-wet cycle is 60 times. The findings can provide a theoretical basis for the interfacial adhesion resistance to sulfate attack and its degradation law under sulfate attack.

Effects of Different Admixtures on the Mechanical and Thermal Insulation Properties of Desulfurization Gypsum-Based Composites

The single-factor experiments are designed to quantitatively investigate the effects of silica fume, mineral powder, and fly ash on the mechanical and thermal insulation properties of desulfurization gypsum-based composites (DGCs). The effect mechanism is discussed from the microscopic morphology of the internal structure, and the corresponding relationship between the strength and thermal conductivity of this material is evaluated by the regression model. The results show that the admixture of silica fume, mineral powder, and fly ash improves the strengths and thermal insulation properties of DGCs, with the order of influence silica fume > mineral powder > fly ash. The optimal 28 d compressive strength and thermal conductivity are 34.17 MPa and 0.2146 W/(m·K), respectively, at a silica fume dosage of 35%. The enhancement effects on the strength and thermal insulation performance of DGCs are attributed to the increase in the hydration products C-S-H gel and Aft. Moreover, the thermal conductivity linearly decreases with the increase in the compressive strength of DGC after adding silica fume, mineral powder, and fly ash. The linear regression models exhibit good precision for evaluating the corresponding relationships between the compressive strength and thermal conductivity of DGCs with different admixtures.

Basic properties, characteristic heavy metals leaching and migration of coal incineration fly ash-based mortar

Accumulation of fly ash causes waste of land resources and certain environmental pollution problems, mainly from coal incineration. As a result, to investigate the leaching, migration law, and environmental safety of these distinctive heavy metals, this study used representative fly ashes from two power plants as research objects to screen out the characteristic heavy metals and prepare and test mortar specimens. The results of the study show that after four heavy metal risk assessment methods, it was concluded that the characteristic heavy metals where are in A power plant’s fly ash were Hg, Cr, Pb and As, and in that of power plant B were Hg and As. The best fly ash admixture was 20% and the best water-binder ratio was 0.48, as learned from the compressive strength experiment. The heavy metal leaching test was done for block mortar and crushed mortar on the use of the best mix ratio. When compared to the raw materials, the specimens' heavy metal leaching content was significantly lower. And the heavy metals in crushed mortar were easier to leach. After the analysis of the migration transformation model, the heavy metals migrated downward in the mortar under the action of gravity. According to the one-dimensional diffusion model of Fick's second law, the migration of the various characteristic heavy metals was ranked from strong to weak as Pb, As, Cr, and Hg, and the ranking of the maximum safe age was ranged from large to small as Hg, Pb, Cr, and As. The findings of the study will provide fundamental theoretical support for the environmental safety risk posed by heavy metals and safety controls like the leaching of characteristic heavy metals in current fly ash-based mortar products. They will also provide further guidance on how to use fly ash as a resource.

Development of Pore Pressure in Cementitious Materials under Low Thermal Effects: Evidence from Optimization of Pore Structure by Incorporation of Fly Ash.

Studies on durability of cementitious materials have focused on harsh environments, but less attention has been paid to low thermal loading situations. In this paper, with the aim of exploring the evolution of internal pore pressure and microcrack extension of cementitious under low thermal environment, cement paste specimens with thermal environment slightly below 100 °C and three water-binder ratios (0.4, 0.45 and 0.5) and four fly ash admixtures (0, 10%, 20% and 30%) were designed. Firstly, the internal pore pressure of the cement paste was tested; secondly, the average effective pore pressure of the cement paste was calculated; and finally, the phase field method was used to explore the expansion of microcracks inside the cement paste when the temperature gradually increased. It was found that the internal pore pressure of the paste showed a decreasing trend as the water-binder ratio and fly ash admixture increased, and the numerical simulation found that the sprouting and development of cracks were delayed when 10% fly ash was added to the cement paste, which was consistent with the experimental results. This work provides a basis for the durability development of concrete under low thermal environment.

Effect of Mineral Admixtures on the Mechanical and Shrinkage Performance of MgO Concrete.

Shrinkage deformation of concrete has been one of the difficulties in the process of concrete performance research. Cracking of concrete caused by self-shrinkage and temperature-drop shrinkage has become a common problem in the concrete world, and cracking leads to a decrease in the durability of concrete and even a safety hazard. Mineral admixtures, such as fly ash and mineral powder, are widely used to improve the temperature drop shrinkage of mass concrete; fly ash can reduce the temperature rise of concrete while also reducing the self-shrinkage of concrete, there are different results on the effect of mineral powder on the self-shrinkage of concrete, but the admixture of fly ash will reduce the strength of concrete, and mineral admixtures have an inhibitory effect on the shrinkage compensation effect of MgO expander(MEA). The paper investigates the effect of mineral admixtures on the mechanical and deformation properties of C50 mass concrete with a MgO expander(MEA), aiming to determine the proportion of C50 mass concrete with good anti-cracking properties under working conditions. The experiments investigated the effect of fly ash admixture, mineral powder admixture and MgO expander admixture on the compressive strength and deformation of concrete under simulated working conditions of variable temperature and analyzed the effect of hydration of magnesite in MgO expander and pore structure of cement paste on deformation. The following main conclusions were obtained: 1. When the concrete compounded with mineral admixture was cured under variable temperature conditions, the compounded 30% fly ash and mineral powder decreased by 4.3%, 6.0% and 8.4% at 7d age, and the compounded 40% fly ash and mineral powder decreased by 3.4%, 2.8% and 2.3% at 7d age, respectively. The incorporation of MEA reduced the early compressive strength of concrete; when the total amount of compounding remained unchanged, the early compressive strength of concrete was gradually smaller as the proportion of compounding decreased. 2. The results of concrete deformation showed that when the temperature rose, the concrete expanded rapidly, and when the temperature dropped, the concrete also showed a certain shrinkage, and the deformation of concrete basically reached stability at 18d. 3. The compounding of 30% fly ash and mineral powder As the compounding ratio decreases, the deformation of concrete increases, and the 28d deformation of concrete with a compounding ratio of 2:1 is 280 × 10-6, while the final stable deformation of concrete with a compounding ratio of 2:1 in compounding 40% fly ash and mineral powder is the largest, with a maximum value of 230 × 10-6, respectively. Overall, the concrete with a total compounding of 30% and a compounding ratio of 2:1 has the best shrinkage resistance performance.

Inhibitory mechanism of fly ash on alkali-silica reactivity of siliceous rock fine aggregate: A case study of Yangxi concrete dam

The fine aggregate of siliceous rock has the advantages of high production efficiency, stable yield and low construction and transportation cost. The Yangxi concrete dam was firstly apply siliceous rock as fine aggregate to a large concrete project of three million m3. However, siliceous rock aggregate has high SiO2 content, which is easy to trigger alkali-silicate reactivity. To investigate the alkali-silica reactivity characteristics of siliceous rock fine aggregate and its inhibitory measures, in this work, we used fly ash, ordinary silicate cement, and siliceous rock fine aggregate to prepare cement mortar. The effects of fly ash admixture on the expansion rate, as well as the flexural and compressive strength of the mortar were investigated by the mortar rod rapid method and mechanical tests. The inhibition mechanism of fly ash on the siliceous rock fine aggregate was analyzed by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) techniques. The results showed that the addition of 30 % fly ash to the siliceous rock mortar could effectively limit the mortar expansion and its late strength growth was the most rapid. Compared to siliceous rock mortar without fly ash, the FA30 specimen mixed with 30 % fly ash had a denser structure, the hydration products at the ITZ were more closely arranged, and the C-A-S-H gel with a low calcium-silica ratio was generated internally, which could effectively inhibit the ASR of the siliceous rock fine aggregate.

Effect of Calcium Hydroxide on Compressive Strength and Microstructure of Geopolymer Containing Admixture of Kaolin, Fly Ash, and Red Mud

The current study aims to investigate the effect of calcium hydroxide on the geopolymer derived from an admixture of the natural mineral (kaolin) and industrial by-products (fly ash, red mud). The compressive strength and microstructure were studied using compressive strength tests, X-ray diffraction, infrared spectroscopy, BET method, and scanning electron microscopy. For the investigated NaOH activator concentrations ranging from 4 M to 10 M, the compressive strength of the geopolymer first increases, then decreases with the increase of calcium hydroxide content. The optimal content of calcium hydroxide, which can give the highest compressive strength of the geopolymer prepared, is about 13% wt. of solid raw materials. The geopolymer materials produced at the 8 M NaOH activator have higher compressive strength than those prepared at 4 M, 6 M, and 10 M NaOH. There is a coexistence of geopolymerization gel and C-S-H/C-A-S-H gel in the materials prepared. Both porosity and the formation of N-A-S-H/C-S-H/C-A-S-H during the polymerization process are important for the mechanical properties of materials.