Silica Fume Fly Ash Research Articles

Research on the Configuration of Multi-Component Solid Waste Cementitious Materials and the Strength Characteristics of Consolidated Aeolian Sand

Developing green, low-carbon building materials has become a viable option for managing bulk industrial solid waste. This paper presents a kind of all solid waste cementitious material (SWCM), which is made entirely from six common industrial wastes, including carbide slag and silica fume, that demonstrate strong mechanical properties and effectively stabilize aeolian sand (AS). Initially, we investigated the mechanical strength of waste-based cementitious materials in various mix ratios, focusing on their ability to stabilize river sand (RS) and aeolian sand. The results show that it is necessary to use alkaline solid waste carbide slag to provide a suitable reaction environment to achieve the desired strength. In contrast, the low reactivity of coal gangue powder did not contribute effectively to the strength of the cementitious material. Further orthogonal experiments determined the impact of different waste dosages on the strength of stabilized AS. It was found that increasing the amounts of carbide slag, silica fume, and blast furnace slag powder improved strength, while increasing fly ash first increased and then decreased strength. In contrast, higher additions of desulfurization gypsum and coal gangue powder led to a continuous decrease in strength. The optimized mix is carbide slag—desulfurization gypsum—fly ash—silica fume—blast furnace slag powder in a ratio of 4:2:2:3:3. The experimental results using SWCM to stabilize AS indicated a proportional relationship between strength and SWCM content. When the content is ≥20%, it meets the strength requirements for road subbases. The primary hydration products of stabilized AS are C-(A)-S-H, AFt, and CaCO3. Increasing the SWCM content enhances the reaction degree of the materials, thereby improving mechanical strength. This study highlights the mechanical properties of cementitious materials made entirely from waste for stabilizing AS. It provides a reference for the large-scale utilization of industrial solid waste and practical applications in desert road construction.

Development of Rheology in the Area of High-Performance Concrete – A Review

Abstract The rheological or flow quality high-performance concrete (HPC) are significant as they affect several parameters, including ease of placing, compatibility, durability and strength. For the selection of component materials and prediction of the fresh and hardened characteristics of HPC, an adequate understanding of rheology is required. This literature review gives a gist of the works done in the field of rheological study of HPC. The flow models and equations to explain the flow behaviour of HPC mixes as proposed by the researchers are presented. Yield stress and plastic viscosity are the basic rheological parameters that are used in these equations. Various rheometers developed to measure and estimate these rheological parameters of HPC are also presented in this paper. This review provides a thorough analysis of the effects of various constituent materials on the rheological properties of HPC. This includes aggregates, cement, various supplementary cementitious materials like fly ash silica fume, slag etc. Also, the effect of mineral admixtures like superplasticizers and viscosity modifying agents along with the synergic effects is discussed. Finally, the prospects of the study on the unexplored areas and future challenges in the field of study are discussed.

Study on the effect of double mineral admixtures on the properties of high water materials

In this paper, different contents of fly ash, silica fume, slag, and Nano-SiO2 were added to the high water material. Then, fly ash-silica fume, slag-silica fume, and Nano SiO2-silica fume are mixed into the high water material. Through the strength test of two groups of specimens, the influence of different types of mineral admixtures and blending ratios on the physical and mechanical properties of high-water materials was studied. The mechanical parameters of high water doped materials were measured by ultrasonic method, and the internal pore structure of high water doped materials was analyzed. In the case of double mixing, the optimal mixing amount is 4% fly ash and 6% silica fume, and the 7 d compressive strength of this group of specimens is increased by 15.85% compared with the original high water material. Through ultrasonic detection, the first wave is smooth and stable, the longitudinal wave amplitude curve is flat, the peak difference is slight, and the periodic amplitude is uniform, indicating that the structure of this group of specimens is dense. The shear modulus is increased by 20.31%, Young’s modulus is 1.3 times, and the volume modulus is 8.9 times that of the original high water material. The research findings suggest that high water materials can be modified by double mixing.

Enhancing the elastic modulus of concrete prepared with recycled coarse aggregates of different quality by chemical modifications

Due to the presence of attached old mortar in recycled concrete aggregate (RCA), the elastic modulus of the prepared recycled aggregate concrete (RAC) is generally lower than that of normal concrete, which limits the application of RAC as structural concrete. To improve the elastic modulus of RAC, three different chemical modification methods, including fly ash-silica fume (FS) slurry, nano-SiO2 (NS) solution and carbonation modifications, were carried out in this study. RCAs of different quality were used to verify the applicability of the three methods. The SEM and XRD tests were used to reveal the modification mechanism. The results show that the elastic modulus of RAC can be improved by any of the proposed chemical modification methods, among which the effect of the FS slurry is the most significant with the growth rate of 7.56%–10.56% in terms of different RAC. The modification effect of different methods on the elastic modulus of RAC, which is similar with the corresponding peak stress, is consistent with that on the quality of recycled aggregate. The SEM and XRD results show that the modified RAC has less micro-pores, denser interfacial transition zone and hydration products, which are also the main reasons for the improvement of the elastic modulus.

Global warming potential-based life cycle assessment and optimization of the compressive strength of fly ash-silica fume concrete; environmental impact consideration

In this research study, extensive literature searches on the compressive strength of concrete produced from the addition of fly ash (FA) and silica fume (SF) as extra constituents to the conventional concrete mixes, which gave rise to 330 mix points of concrete database. Due to the worrisome environmental impact of concrete production and usage in concrete activities, it has been pertinent to conduct the life cycle impact assessment of this procedure. Secondly, due to the over dependence of concrete production experts on laboratory exercise, there is also an urgent need to propose equations that reduce this dependence, that can be used in design, construction and performance evaluation of concrete infrastructure, hence the multi-objective nature of this research work. The results of the global warming potential (GWP) based on cement dosage show that Portland cement contributes about 90% of the total score. This is followed by the use of coarse aggregate contributing 6%, superplasticizer, 3% and fine aggregates, 2%. These show the functions of CO2 emissions and other greenhouses gas emissions in the entire system. Also, the result of the terrestrial acidification potential (TAP) for the concrete mixes in this study show that the lowest cement mix “C340-FAg658-FA0-SF15ˮ has a human toxicity, both carcinogenic and non-carcinogenic that showed an added impact of about 14 kg of 1, 4 equivalents of dichlorobenzene (DCB eq.). This result is 428% less impact than other studies found in the literature that used FA. Finally, it was found that the addition of FA and SF in concrete has a lowering effect on the environmental impact indicators due to reduced cement dosage. Furthermore, the results of the model predictions show that ANN with a performance index of 0.986 (4.8%) showed decisive superiority to predict the compressive strength of the FA-SF concrete over EPR, 0.951 (8.7%), GP, 0.94 (9.5%) and GEP, 0.93 (10%).

Test and Mesoscopic Analysis of Chloride Ion Diffusion of High-Performance-Concrete with Fly Ash and Silica Fume

High performance concrete (HPC) is a kind of concrete with mineral admixtures, which has better resistance ability to chloride ions diffusion than ordinary concrete. In the present study, the authors carried out a chloride ion diffusion experiment for the HPC with fly ash and silica fume. The influence of the water–binder ratio (W/B), binary (Portland cement–Fly ash (PC-FS) and Portland cement–Silica fume (PC-SF) and ternary (Portland cement–Fly ash–Silica fume (PC-FA-SF)) combinations on the concrete compressive strength and chloride ion diffusion was investigated. It was found that the compressive strength of normal concrete and HPC increase with the decrease in the W/B, the ratio of W/B deceasing value to strength increasing value for normal concrete is 0.74, and for the HPC is 0.20, so the influence of the W/B on the concrete strength for normal concrete was obviously more than the HPC. The influence of the contents of the SF or FA on developing the concrete strength was limited. The concrete compressive strength of ternary combination specimens decreases with the increase in FA or SF when the content of the other mineral admixture SF or FA remained unchanged. The ternary combination was more efficient in prohibiting chlorides ingress insider the specimens than the binary combination. The mesoscopic simulation and the tested value of the chloride ion under the same depth was close, the average ratio of simulation value to tested value was 0.91. The aggregate shape and distribution also had a negligible influence on chloride diffusivity in the HPC, but the chloride ion concentration increased with the increase in aggregate size.

Partial Substitution of Binding Material by Bentonite Clay (BC) in Concrete: A Review

Concrete consumes millions of tons of cement, which causes global warming as cement factories emit huge amounts of carbon dioxide into the atmosphere. Thus, it is essential to explore alternative materials as a substitute of OPC, which are eco-friendly and at the same time cost-effective. Although there are different options available to use industrial waste instead of cement, such as waste glass, waste marble, silica fume fly ash, or agriculture waste such as rice husk ash, wheat straw ash, etc., but bentonite clay is also one of the best options to be used as a binding material. There are a lot of diverse opinions regarding the use of bentonite clay as a cement substitute, but this knowledge is scattered, and no one can easily judge the suitability of bentonite clay as a binding material. Accordingly, a compressive review is essential to explore the suitability of bentonite clay as a cementitious material. This review focuses on the appropriateness of bentonite clay as a binding material in concrete production. The attention of this review is to discuss the physical and chemical composition of BC and the impact of BC on the fresh and mechanical performance of concrete. Furthermore, durability performance such as water absorption, acid resistance and dry shrinkage are also discussed. The results indicate that bentonite clay increased the mechanical and durability performance of concrete up to some extent but decrease its flowability. The optimum proportion of bentonite clay varies from 15 to 20% depending on the source of bentonite clay. The overall study demonstrates that bentonite clay has the creditability to be utilized partially instead of cement in concrete.

Experimental investigation on paver blocks of fly ash-based geopolymer concrete containing silica fume

Utilisation of geopolymer may reduce the global warming potential of concrete.. This study examines geopolymer concrete as interlocking paver blocks. Three concretes are compared: conventional cement, fly ash-geopolymer and fly ash–silica fume geopolymer. Sodium hydroxide solution is used in both geopolymer concretes, and sodium silicate solution is used in fly ash-based geopolymer concrete only. Rectangle and uni shape blocks are tested for compressive strength, flexural strength, abrasion resistance and freeze–thaw resistance. Dynamic drop loading test is conducted on block pavement with herringbone laying pattern . Results revealed that resistance to abrasion and water absorption of geopolymeris improved by adding silica fume . Freeze–thaw resistance is the lowest for cement concrete paver blocks. Lowest deflection occurred in block pavement of uni shape. Geopolymer concrete provides uniform load distribution than cement concrete. Cement concrete is slightly costlier than geopolymer concrete. This study concluded the geopolymer as suitable option for paver block applications. .

Use of Mixture Design Approach for the Optimization and Performance of Cost-Effective Cementitious Quaternary System: Portland Cement–Fly Ash–Silica Fume–Phosphogypsum

Use of Mixture Design Approach for the Optimization and Performance of Cost-Effective Cementitious Quaternary System: Portland Cement–Fly Ash–Silica Fume–Phosphogypsum

Development of magnesium oxychloride cement with enhanced water resistance by adding silica fume and hybrid fly ash-silica fume

In this paper, a water-resistant magnesium oxychloride cement (MOC), an environment friendly cementitious material, was developed by incorporating silica fume and the hybrid of silica fume and fly ash. The effects of these admixtures on the water repellence of MOC were investigated via comprehensive macroscopic physical and mechanical tests and micro-scale studies. A formula design of MOC blended with 15% silica fume and 15% fly ash retained the compressive strength as high as 100% and 95% after 28 days' and 56 days’ immersion in water, respectively. Micro-scale studies, including XRD, FTIR, SEM, MIP, TG/DSC and XRM, were conducted to discover the mechanism of the enhanced water resistance of the new MOC. Besides, a clear and precise distribution of the hydration products in well-cured MOC specimens was demonstrated with the X-ray mapping (XRM) technique. It was found that adding silica fume or the hybrid of silica fume and fly ash optimised the porous structure of MOC and thereby increased the density and compressive strength leading to the enhanced water resistance. The filling effect of fine silica fume and fly ash particles, as well as the formation of Mg–Cl–Si–H gel, was found to be the main reason for the densified microstructure of MOC. The fractional contribution of phase 5, i.e. the main phase of MOC, decreased with the combined silica fume and fly ash, and this helped to relieve the internal stress and improve the stability of MOC, leading to enhanced water repellence.

Performance of square steel tubular stub columns in-filled with fly ash and silica fume self-compacting concrete under concentric loading

Concrete filled steel tube (CFST) column is a composite member comprising of structural hollow steel tube and concrete core. This paper evaluates the effect of fly ash (FA) and silica fume (SF) on square CFST stub columns’ behavior under concentric loading. The self-compacting concrete (SCC) grade used is M60 with the addition of 50% FA and 10% SF as a partial replacement of Portland cement. The performances of the fly ash-silica fume selfcompacting (FSS) CFST columns are examined through the axial compression capacity, the load-shortening response, and the failure mode of stub columns. The axial load of the FSS CFST columns is compared with the international design codes to validate the available design codes’ accuracy. The results yield that the FSS CFST columns’ ultimate axial load capacities range between 1408.80 kN and 808.70 kN, while the reference CFST columns’ capacities range between 1332.80 kN and 789.20 kN. FSS concrete improves the concrete contribution ratio and strength index of the square CFST stub columns. However, reference CFST columns demonstrate better ductility than FSS CFST columns. This is attributed to the brittleness of the FSS concrete. All the square CFST stub columns fail via local buckling. Eurocode 4 slightly over predicts the square CFST columns’ ultimate capacity by an average of 4.58%. The American Concrete Institute (ACI) code, on the other hand, over predicts the axial capacity of the CFST stub columns by an average of 17.46%.

3D Printing Concrete: A Review

3D Printing concrete is new developed technology with no reinforcement or by providing reinforcement as like cable in the year 1987. The printing concrete is printed with the printer in different shapes and sizes. Size of aggregate used is very minimum which passes through the nozzle of printer. The strength of 3DPC is tested by compression, flexural, tensile, shear tests for identifying durability, extrudability, workability of printing concrete. The slump flow is carried for finding the flowability of concrete that passes through the nozzle of the printer. Fibers such as polypropylene, PVA, GGBS, Steel were used in addition of mix to increase the strength of 3DPC. Superplasticizers, Fly ash Silica fume, Geopolymer are used in concrete with percentage addition into the mix for raising the strength of the printing concrete. Result shows the strength of PC in different mix proportions along with varring size of specimens. Pumpabality and Buildability of printing concrete is analysed by slump flow test. Reinforcement for this concrete is provided as in form of cables that passes freely through nozzle for printing the concrete.

Properties of fly ash geopolymer modified with red mud and silica fume: a comparative study

Alkali-activated geopolymer has emerged as a sustainable alternative to highly polluting conventional cement. The present paper investigates the activation of fly ash-based geopolymer paste modified by red mud and silica fume. Three geopolymer mixes are considered: (1) fly ash; (2) fly ash—red mud; and (3) fly ash—silica fume. Mass proportions of modifiers in the respected mixes varied by 0, 5%, 10%, 15%, 20%, and 25% of total binder. Heat curing (60 °C) provided for 24 h just after casting. Alkaline activator consists of sodium hydroxide and sodium silicate solutions. Workability results reveal that both red mud and silica fume triggered the reduction in workability with the later one had a greater impact. A flash set was obtained with the silica fume content of more than 15%. Both the modifiers cause a decrease in the setting time at ambient temperature, and silica fume proved to be more productive with the reduction of more than 65% of setting time. Mixes containing red mud exhibit slightly higher density. Water absorption of fly ash geopolymer increases with red mud. Compressive strength increases with the addition of modifiers, and geopolymer containing silica fume possesses the highest compressive strength among the three mixes considered. Compressive strength exhibited a linear correlation with molar ratios (Si/Al and Na/Si) of source materials. XRD and SEM methods showed that the geopolymerization reaction is affected by the red mud and silica fume. It is recommended that the flash set and setting time at higher contents of modifiers must be examined for the design of a modified geopolymer mix.

Environmental impact assessment of fly ash and silica fume based geopolymer concrete

Alkali activated geopolymer is an attractive solution to limit the adverse consequences of cement manufacturing. In this paper, an evaluation of environmental impacts of geopolymer containing fly ash and silica fume is conducted. Life cycle assessment is performed by benchmarking the environmental impacts of three geopolymer concrete mixes against the conventional cement concrete, namely: fly ash geopolymer (with hydroxide and silicate of sodium); fly ash–silica fume blend geopolymer (with hydroxide and silicate of sodium); and fly ash–silica fume blend geopolymer (with sodium hydroxide). Impact analysis is performed by using ReCiPe midpoint and endpoint methods in life cycle assessment software UMBERTO NXT using database of Ecoinvent 3.0. Sensitivity analysis is performed to determine the effect of transportation. One mix design for each concrete of equal water to binder ratio and 28-days compressive strength of more than 35 MPa is analysed. Results of life cycle assessment indicate that alkaline activators and cement are the major sources of negative environmental impacts for geopolymer and cement concrete, respectively. Global warming potential of geopolymer concretes is lower than conventional cement concrete. Fly ash–silica fume geopolymer concrete activated without sodium silicate has lowest environmental impacts. Transportation of raw materials is found to increase the overall negative of all four concrete mixes. Cost reduction of 10.87%–17.77% per unit volume is achieved with the use of fly ash – silica fume based geopolymer concrete. Sustainability in terms of cost and environmental benefits of geopolymer concrete can be further increased by using silica fume. It can be concluded that the use of fly ash – silica fume blended geopolymer in the construction industry has huge possibility to improve its sustainability. Furthermore, waste management can be effectively done by utilization of industrial by-products in concrete.

Immobilization of cesium in fly ash-silica fume based geopolymers with different Si/Al molar ratios

Geopolymers are considered as promising matrixes for waste solidification. However, the effects of the Si/Al molar ratio of geopolymer on the immobilization efficiencies for metal ions have not been fully studied and understood. In the present study, geopolymers with different Si/Al ratios were synthesized from coal fly ash and silica fume. Adsorption tests were conducted to evaluate their immobilization efficiencies for Cs+. The results indicated that geopolymer with low Si/Al ratio could have a better immobilization performance for Cs+ than that with high Si/Al ratio. High Si/Al ratio could contribute to a more compact structure of geopolymer. Each sorption process fitted better with the pseudo-second-order model, and all of them were governed by film diffusion. However, the diffusion mode was gradually closed to particle diffusion with the increase in the Si/Al ratio. Both Langmuir and Freundlich models could well fit the sorption data, and the free energy of each sorption process decreased with the increase in the Si/Al ratio according to D-R equation. The distribution of AlO4 tetrahedron in the geopolymer structure plays a significant role in the immobilization of Cs+. Low Si/Al ratio could result in that more AlO4 tetrahedrons distribute in the small rings (<eight-member), which has stronger locking effects on Cs+. However, high Si/Al ratio leads to the distribution of AlO4 tetrahedrons mainly in larger rings (≥eight-member), and this could contribute to the high leaching amount of Cs+. In addition, high-temperature treatment could contribute to the formation of nepheline or pollucite in geopolymer matrix. These minerals locked Cs+ in their structures, and the leaching amount of Cs+ was reduced correspondingly from high levels (26.36%, 27.26%, and 66.92%) to very low levels (0.67%, 0.53%, and 0.95%).

Hydration, mechanical properties and durability of high-strength concrete under different curing conditions

The properties of high-strength concrete under standard curing condition (20 °C, 95% RH), high-temperature curing condition (50 °C) and temperature match curing condition were comparatively investigated. The cumulative hydration heat of composite binder containing fly ash and silica fume is lower than that of composite binder containing the same amount of slag. Addition of fly ash and silica fume clearly reduces the adiabatic temperature rise of concrete, but adding slag leads to higher adiabatic temperature rise than Portland cement concrete. High-temperature curing condition and temperature match curing condition lead to the sustainable increase in compressive strength of concrete containing mineral admixture, but they hinder the later-age strength development of Portland cement concrete. For cement–slag paste and cement–fly ash–silica fume paste, the non-evaporable water contents increase significantly and the pore structures are much finer under high-temperature curing condition and temperature match curing condition, which negatively affect the pore structure of Portland cement paste. The differences in properties of concrete among three curing conditions become smaller with time. The properties obtained under standard curing condition can approximately reflect the long-term properties of high-strength concrete in the real structure. The concrete prepared with cement–fly ash–silica fume composite binder has the highest compressive strength, finest pore structure and best resistance to chloride permeability under any curing condition. This composite binder is very suitable to prepare the high-strength concrete with large volume.

Thermogravimetry analysis, compressive strength and thermal conductivity tests of non-autoclaved aerated Portland cement–fly ash–silica fume concrete

This paper reports the investigated thermogravimetry analysis, compressive strength and thermal conductivity tests of non-autoclaved aerated Portland cement–fly ash–silica fume concrete. The mixes were cured in water and air for 3, 7 and 28 days. Thermogravimetry results showed that calcium silicate hydrate (C–S–H), ettringite, gehlenite (C2ASH8), calcium hydroxide [Ca(OH)2] and calcium carbonate (CaCO3) phases were detected in all mixes. The compressive strength and thermal conductivity of aerated Portland cement–fly ash–silica fume concrete increased when compared with aerated Portland cement–fly ash concrete after 28 days. The compressive strength and thermal conductivity of aerated concrete cured in water had higher values than air-cured specimens. X-ray diffraction and thermogravimetry showed that Ca(OH)2 decreased with increased silica fume content. This is due to the increased pozzolanic reaction when compared with the Portland cement–fly ash mixes, which corresponds to an increase in compressive strength and thermal conductivity.

Physico-mechanical properties of composite cement pastes containing silica fume and fly ash

This works aims to study the effect of partial substitution of ordinary Portland cement (OPC) by silica fume (SF) and fly ash (FA) on the physico-mechanical properties of the hardened OPC–FA–SF composite cement pastes. The OPC was partially replaced by 20% and 30% fly ash along with 5% and 10% silica fume. The phase composition of the hydration products was investigated using XRD and DTA techniques. It was found that, the increase of FA content in OPC–FA–SF composite cement decreases the water consistency values and increases the setting times. On the other hand, the increase of SF content leads to increase the water of consistency and decrease the setting times. The partial substitution of OPC by FA and SF leads to higher porosity values with a consequent decrease in the compressive strength values especially during the early ages of hydration. At the later ages of hydration, however, the OPC–FA–SF cement pastes possess total porosity and compressive strength values close to those of the neat OPC paste. The lower of free lime contents were obtained for OPC–FA–SF composite cement pastes with the formation of further additional amounts of CSH as a result of the pozzolanic reaction. The results showed also that, the physico-mechanical properties of composite cement paste [OPC (65%)–FA (30%)–SF (5%)] were improved at later ages.

Strength and resistance to sulfate and sulfuric acid of ground fluidized bed combustion fly ash–silica fume alkali-activated composite

Fluidized bed combustion (FBC) is an environmentally friendly process for burning of coal and is used in many small factories located in urban area. The FBC fly ash is an environmental problem and needs good disposal or utilization. This research studied the strength and resistance to sulfate and acid of alkali-activated FBC fly ash–silica fume composite. The FBC fly ash was interground with silica fume (at the dosage levels of 1.5%, 3.75% and 5.0%) to make the source material homogenous with increased reactivity. Addition of silica fume enabled the adjustment of SiO2/Al2O3 ratios (6.55-7.54) of composite and improved the strength and resistance to sulfate and acid of composite. The composite with 3.75% silica fume showed the optimum strength with 28-day compressive strength of 17.0MPa. The compressive strengths of composite with 3.75% silica fume immersed in 5% magnesium sulfate solution and 3% sulfuric acid solutions were substantially higher than the control. The strength loss was from the high calcium content of FBC fly ash and incorporation of silica fume thus increased the durability of the composite.

Carbonation of filler typed self-compacting concrete and its impact on the microstructure by utilization of 100% CO2 accelerating techniques

Via the use of accelerated carbonation techniques with 100% CO2 concentration, an experimental programme was performed to investigate the carbonation and associated microstructural changes of three different self-compacting concrete (SCC) in which some of the cement had been replaced by limestone powder, fly ash and/or silica fume. Accelerated carbonation tests were conducted on these “filler-typed” SCCs after 28days water curing. Approximately 33% of the total binder (450kg/m3) was replaced by limestone powder, fly ash or a fly ash–silica fume blend.The results revealed that the replacement of limestone powder (LP) increased the depth of carbonation during the accelerated test relative to the effect of the fly ash (FA) or the combination of the fly ash and the silica fume (FA+SF) replacements. However, the modelling of the normal pressure accelerated carbonation tests with 100% CO2 showed all the SCCs studied have no risk of carbonation induced corrosion in the natural environment. Overall, the research suggests that carbonation of filler typed SCC may not be chemically controlled, rather, the internal pore structure may play an important role. Furthermore, the effect of carbonation on the internal pore structure and the chemistry of the concrete matrices were more noticeable in SCC containing FA+SF than in those with LP and FA replacements.