Presence Of Silica Fume Research Articles

Atomistic Insight on Effect of Silica Fume on Intermolecular Interactions between Poly(carboxylate) Superplasticizer and Calcium Ions in Concrete.

Understanding how poly(carboxylate)s of chemical admixtures interact with calcium ions in cement pore solutions in the presence of silica fume is fundamental to developing better chemical admixtures for concrete production. In this work, the intermolecular interactions of calcium ions with a poly(carboxylate) superplasticizer type of chemical admixture was investigated via classical all-atom molecular dynamics (MD) simulations and Density Functional Theory (DFT) calculation methods in the presence of silica fume. The classical all-atom MD simulation and DFT calculation results indicate that calcium ions are interacting with oxygen atoms of the carboxylate group of PCE. The better interaction energy could mean an improved adsorption of the PCE segment with calcium ions. In this regard, it can be noted that the ester-based PCE segment could have a better adsorption onto calcium ions in comparison with the ether-based PCE segment. Moreover, the presence of silicon dioxide could improve the adsorption of the PCE segment onto calcium ions.

Incorporation of High Loss-on-ignition Fly Ash in Producing High-strength Flowable Mortar

A large amount of fly ash with a high loss on ignition (over the maximum allowance value stipulated by ASTM C618) is being released and increasing daily in Vietnam. The recycling of this fly ash is still limited, while a big remaining part is disposed of in storage yards, causing environmental pollution. On the other hand, the demand for high-strength mortar as a repair material is increasing for high-rise buildings and important projects, gradually depleting natural resources. However, the application of this fly ash in the production of mortar is restricted in the literature. In this study, local fly ash with a high loss on ignition is used to replace 0%, 15%, 30%, 45%, and 60% cement content in producing high-flowability and high-strength mortar. Changes in the fresh and hardened mortar properties were systematically investigated using samples produced with various fly ash contents. Test results indicate that the effect of impurities in fly ash on the mortar’s workability can be neglected due to the spherical shape of fly ash. The unit weight, thermal conductivity, and drying shrinkage of mortars decreased with increasing fly ash content. Although some other properties of mortar are reduced due to the use of high loss-on-ignition fly ash, all mortars produced in this study still showed good quality with the presence of silica fume. In addition, the relationships between compressive strength and flexural strength with ultrasonic pulse velocity were established to predict the strength of mortar in a non-destructive method.

Study of patched ternary blended concrete using fiber glass wire mesh

Concrete is one of the most widely used construction materials. The cement industry is one of the main sources of carbon dioxide, a potent greenhouse gas. The cement industry produces nearly 8% of all man-made greenhouse gas emissions worldwide. Industries are becoming increasingly interested in reducing concrete-related carbon emissions. Many studies have been performed on the development of green concrete by substituting other renewable and sustainable materials for cement. In the current study, the traditional concrete has been replaced by a special concrete called Ternary Blended Concrete. Ternary Blended Concrete is mixture of three different cementitious materials combined with aggregates. In this concrete, cement was fragmentally replaced by silica fume and GGBS. Silica fume and GGBs are added at different proportions. Cylinders and cubes are casted for the final mix and tested for Split Tensile Strength, Compressive Strength and Flexural Strength.The presence of silica fume at 8%, 10% and 12% shows increase in compressive strength by 8.70%, 15.11% and 1.41% and GGBS at 25%, 30% and 35% shows increase in compressive strength by 0.60%, 9.85% and 0.26% when compared to compressive strength of control concrete. The split tensile strength of silica fume at 8%, 10% and 12% shows increase by 0.02%, 3.22% and 2.05% and GGBS at 25%, 30% and 35% shows increase by 0.29%, 2.34% and 0.87% when compared to control concrete.

Experimental investigation on the effect of Nano-silica on the silica fume-based cement composites

The purpose of this work is to explore the effects of incorporation of nano-silica, in presence of silica fume and plasticizer, in cement mortar and concrete, in order to determine their appropriateness and advantages for concrete building. The research's goals were to optimize the amount of nanosilica used and to conduct tests on different fresh and hardened characteristics. To accomplish this goal, fresh characteristics of pastes (IST, FST, Consistency) and mortars (flow) as well as hardened characteristics of concrete (compressive strength) were investigated. SEM analysis was used to characterize the specimens morphologically. Based on the experimental investigation increase in consistency and decrease in IST, FST and flow was detected with increasing dosage of nanosilica. Intensification in compressive strength was higher at early age as compared to the strength at advanced age. Maximum compressive strength in concrete mixes was observed for specimen containing 3% nano-silica in presence of 10% silica fume and thereafter decrease in strength was observed but was still higher than that of the control specimen. The findings from SEM revealed that nano particles not only serve as filler but also as a promoter of the hydration process that improved the microstructure of concrete resulting in higher strength. The appropriate usage of nano-silica may thus enhance the performance of cemented materials.

Mechanical and Durability Characteristics Assessment of Geopolymer Composite (GPC) at Varying Silica Fume Content

The present study aimed at assessing mechanical and durability characteristics of ground granulated blast furnace slag (GGBS)-based geopolymer composites at 5%, 10%, 15%, 20%, 25%, and 30% replacement proportion of silica fume at 12 molarity of NaOH. Mechanical properties were assessed using compression and tension tests, whereas durability characteristics were evaluated using ultrasonic pulse velocity test (UPV), acid test, and rapid chloride permeability test (RCPT), and water absorption (WA) test. Additionally, reduction in mass and strength were also determined due to the acid action on the developed composites. A correlation of compressive strength was also established with the splitting tensile strength, UPV, RCPT, and WA. The presence of silica fume and high NaOH concentration in GPC tends to improve the mechanical strength up toa certain level. UPV values obtained were falling in the range of medium to good category. Chloride ion penetration and water absorption values were reduced by around 23% and 26%, respectively, at 10% silica fume replacement. Mass loss and strength loss were reduced as the % of silica fume increased. A good correlation of compressive strength was obtained with tensile strength, UPV, and RCPT with a coefficient of determination of 0.9681, 0.9665, and 0.9208, respectively. Poor correlation was obtained between compressive strength and water absorption.

Ultra-high performance concrete made from the insertion of glass residues as supplementary cement material

Portland cement concrete manufacturing techniques in the world have an immense variability, since each location concentrates natural resources with unique characteristics, sometimes similar, but with always different process conditions, such as: labor, equipment, environmental conditions, processing, storage, among others. The aim of this work is to develop cementitious composites partially replacing mineral admixtures by powdered glass residues, evaluating the physical-mechanical behavior through axial compression strength, as well as the production of hydrated phases through x-ray diffraction, both at 28 days. Cement, silica fume, metakaolin, powder glass residue, polycarboxylic ether-based superplasticizer, and low temperature water were used to prepare different compositions of ultra-high performance concrete. The preparation took place with the aid of a mechanical bench mixer, and the densification was carried out with the aid of an immersion vibrator in cylindrical molds 50 x 100 mm. After unshaped, the specimens received heat treatment, with isotherm at 60°C for 36 hours, followed by wet curing in a tank saturated with calcium hydroxide, until the tests of compression strength and x-ray diffraction were carried out. The results show that the composition added with the residue, replacing metakaolin, behaved in an adequate manner, with compressive strength equivalent to the reference composition (silica fume + metakaolin), as well as the production of the same hydrated compounds. However, the application of only the glass residue or metakaolin reduced the intensity of the pozzolanic reactions, justified by the presence of a high content of calcium hydroxide in the compositions, which allows us to conclude that the powder glass residue presents viability as a filler, when replacing metakaolin in the presence of silica fume, as it does not compromise the performance of the mixtures made.

Some Geotechnical Properties of Clay Soil Enhanced with Silica Fume

Engineering structures found in, or on, some clay soil types may be subject to different damages due to the problematic nature and unfavorited properties of these soils. The unfavorited properties of these soils include shrink and swell changes, high settlement, and low bearing capacity. These soils have high sensitivity to moisture change. The way to reduce or overcome the unfavorited properties of problematic soils is the treatment or enhancement of these soils using different mechanical or chemical methods. In the present paper, silica fume selected as a soil stabilizer material, the effect of different contents of this material on the geotechnical properties of expansive clay soil has been experimentally investigated. Tests included soil specific gravity, soil plasticity, soil compaction, and soil compressibility. It was noted that silica fume, with different contents, decreased the specific gravity, and compaction density, while the compaction water content and Atterberg limits increased. The consolidation parameters of the expansive clay soil were affected by adding the silica fume. The silica fume reduced the consolidation parameters values of the clay soil. At low content silica fume, less than 10%, a very slight reduction can be seen especially for the rebound index value. The final findings of this paper appeared that the high settlement of clay soil can be reduced with the presence of silica fume.

Properties of slag geopolymer concrete modified with fly ash and silica fume

This research focused on the role of fly ash and silica fume on slag geopolymer concrete through investigating workability (slump, and slump loss), initial setting time, final setting time, and mechanical properties of slag geopolymer concrete (S-GPC) (compressive strength, splitting tensile strength, modulus of elasticity) in addition to scanning electron microscope (SEM) and X-ray analysis. The considered variables included fly ash content as a replacement of ground granulated blast furnace slag (GS) (0%, 10%, 20%, 30%, and 40%), presence of silica fume as a replacement for slag, concentration of sodium hydroxide, NaOH, (molarity: 10, 16, and 18 mol/L), additional water content (7.5%, 11%, 14%, and 20%), and curing type (thermal, air, and water curing). S-GPC yielded rapid stiffening and high slump loss with high mechanical properties. The use of silica fume or fly ash or a mix of both enhanced workability, decreased rate of slump loss, and delayed setting time. The ACI 318 equation overestimates splitting tensile strength of FS-GPC.

Strength and microstructural analysis of nano-silica based cement composites in presence of silica fume

Replacement of cement with pozzolanic materials has addressed numerous inquiries identified with impact of these materials on the microstructural and other properties of cement composites. On the other hand, because of the absence of technique and pertinent supporting information, an appraisal of general execution of such admixtures is hard to be completed. The utilization of pozzolanic materials as cement substitution in mortar has enhanced the execution of their physico-chemical and mechanical properties. In this study, the composition of silica fume (SF) was differed as 3%, 6%, 9% and 12% at a fixed composition of nano-silica (NS) as 0.5% by weight for substitution of cement. The fresh and hardened properties of cement mortars were analyzed and microstructural analysis was performed. The specimens were found to exhibit better developed microstructure and enhanced compressive strength with inclusion of optimized dosage of SF in presence of NS. The study has confirmed that the simultaneous replacement of cement with the optimized dosage of pozzolanic materials brings improvement in the properties of the cement mortar and can be used to partially substitute cement for the beneficiary effects.

Investigation on Mechanical Strength of Cellular Concrete in Presence of Silica Fume

Over the past decade, Cellular Lightweight concrete has gained popularity in the construction industry. Despite its advantageous low weight, thermal insulating, and fire-resistant nature, its comparatively low strength is a matter of concern. To develop the strength of this type of concrete, a thorough characterization of its main characteristics must be studied thereafter in addition to supportive cementitious materials. The effect of polyurethane on density and strength of cellular concrete subjected to varying curing conditions have been investigated in this report. Besides, Silica Fume has been used as a partial substituent of cement and as supportive cementitious material. The cellular concrete has been obtained by varying silica fume (0-20% by weight of cement) and polyurethane (0-20% by volume) at 7, 28, 56, and 90 days of curing. Density, compressive strength, split tensile strength and flexural strength have been investigated for all the specimens. The findings revealed a decrease in density and strength of cellular concrete in the absence of SF and the presence of polyurethane. The introduction of silica fume resulted in higher density and strength revealing the beneficial use of this pozzolanic material.

Performance evaluation of polypropylene fiber waste reinforced concrete in presence of silica fume

Abstract The worldwide application of high-performance concrete is particularly suitable for high-level towers, long bridges and special structures. Concrete binder products (used in high-level concrete), due to their low expense, reliability and ample compression strength in the structural framework, are desirable for use as construction materials. Failure is attributed to its features of poor tensile strength and effect and its sensitivity to increases in moisture. The fiber reinforcement can be a simple, functional and cost-effective way to resolve such limitations. The application of fibers as concrete reinforcement will improve many of its properties, in particular strength, fatigue, permeability, and barrier properties. Various consequences of the addition of silica fume (SF) and polypropylene fiber waste (PFW) to the mechanical characteristics of the concrete have been analyzed in this study. The current study aimed at analyzing the effects of cement substitution with SF, PFW and their combinations. SF content was ranged between 4%, 8%, 12%, and 16% and PFW as 0.4%, 0.8%, 1.2% and 1.6% by weight substitution of cement in order to analyze the effect on workability, compressive strength & tensile strength investigated at 7 days, 28 days, & 90 days of curing ages. The efficiency of the concrete w.r.t mechanical properties was improved severalfold in ternary composites. The XRD and SEM assessment correlated the microstructure with the improved mechanical properties of the composites.

Effect of aggressive environment on durability of concrete containing fibrous rubber shreds and silica fume

AbstractThe present study deals with the investigation of durability properties of reinforced concrete fabricated by incorporating fiber type rubber shreds as fine aggregate in concrete and silica fume as a supplementary cementitious material. Concrete designs were produced to replace natural fine aggregate and cement by rubber shreds, and silica fume, respectively. The concrete mixes were studied for compressive strength up to 365 days, abrasion resistance, and water absorption up to 28 days. The carbonation and acid resistance (H2SO4 and HCl) properties were studied up to 90 and 180 days, respectively. Corrosion samples were tested up to 18 months for both macrocell current and half‐cell potential. The incorporation of rubber shreds lowered the compressive strength of concrete and resistance to water absorption, carbonation, and corrosion. However, the resistance to abrasion and acid attack was enhanced on the utilization of rubber shreds in concrete. The presence of silica fume considerably enhanced the mechanical and durability properties of rubber shreds concrete and lowered the probability of corrosion.

Characterization and properties of cementitious composites with cellulose fiber, silica fume and latex

In this investigation, the behavior of the composites was analyzed through mechanical and physical tests, scanning electron microscopy and X-ray diffraction at 28 days cure time. Central composite design with four center points and using alpha for orthogonality of 1.41421, resulting in 18 experiments, was used. The diffractograms show a possible decrease of portlandite in mixtures with the presence of silica fume and natural rubber latex. Micrographs show a good synergy between cellulose fiber and natural rubber latex. In addition, the cellulose fibers are predominantly stripped from the matrix during fracture of the composites. The regression models were validated and it was possible to obtain an ideal composite with 13.55% silica fume, 14.55% cellulose fiber and 1.40% natural rubber latex, and good mechanical properties as a modulus of rupture of 13.34 MPa.

Microstructural parameters of fiber reinforced cement-based foam and their influence on compressive and thermal properties

This study presents the results of microstructural parameters of fiber reinforced cement-based foam and examines their influence on thermal conductivity and compressive strength, for a range of density and pozzolanic admixtures. X-ray tomography, which is a non-destructive technique, was employed for measuring the pore size distribution, pore spacing, and shape factor. The thermal conductivity was evaluated by using the Transient Plane Source. Three series of cement-based foam mixtures were prepared by adding polypropylene (PP) micro-fibers at a volume fraction of 0.2% and cast to 800, 600 and 400 kg/m3. In two separate series of mixtures, 20% of cement was replaced by fly ash and silica fume, respectively. The results showed that a mean pore diameter of 30 μm was the optimal pore size across all mixtures, including pozzolans blended binders. The optimum pore spacing recorded was 1110 μm for 800 kg/m3, and 270 μm for 600 kg/m3 and 400 kg/m3 , respectively. It was found that the inclusion of fibers increases the number of pores, as does the presence of silica fume. Most of the pores were found to be spherical. Furthermore, the median pore diameter (D50) and spacing (SP50) values were found relating linearly to compressive strength and thermal conductivity.

Fluorescence Microscopic Investigations of the Retarding Effect of Superplasticizers in Cementitious Systems of UHPC.

The adsorption of superplasticizer molecules to particle surfaces in cementitious systems is a very important aspect for the desired liquefaction of pastes and concretes. This way, the comb shaped polymers shield attractive forces between the particles and induce a well-dispersed, homogeneous suspension. These admixtures allow the usage of fine fillers even in combination with low amounts of mixing water, and thus, are the basis for modern high performance concretes. However, the adsorption does not cause beneficial effects only: The polymer covered particle surfaces, especially clinker, are hindered to interact with water, thus hydration is retarded. This is the reason for lower early strength and is very disadvantageous for certain applications. Today it is known that the molecular structure of the polymers, for instance the chain length and charge density, affects the retardation strongly. The complexity and diversity of cementitious systems is the main reason why research in this field is quite empiric and time as well as cost intensive. To investigate the adsorption of superplasticizers in various systems in-situ, a fluorescence microscopic approach was applied: By staining the polymers with fluorescent dye they become localizable and the adsorption quantifiable. This work shows the influence of molecular structure to adsorption characteristic of different polymers and the correlation to the retarding effect of superplasticizers, especially concerning the presence of silica fume, which is indispensable for ultra-high performance concrete (UHPC).

Thermodynamical and Experimental Study of the Effects of Ball Clay-Silica Fume Combination on the Hydration and Strength

The production of ordinary Portland cement (OPC) as the most expensive constituent of concrete is associated with destructive environmental effects and significant energy consumption. Thus, the use of supplementary cementitious materials such as Natural or synthetic pozzolans is a fundamental solution that affects the kinetics of hydration of cementitious materials. In this article, to evaluate the effect of ball clay in the presence or absence of silica fume on the performance of cementitious materials, compressive strength and ultrasonic tests were performed at replacement weight percentages of 0, 10 and 20% for ball clay and 0 and 7% for silica fume. Also, thermodynamic modeling during hydration was carried out based on the Gibbs free energy minimization. The results showed that mere presence of ball clay does not have a positive effect, but it can improve the structure and strength of cement in the presence of silica fume, since it resulted in complete consumption of portlandite and consequently increasing C-S-H gel. In addition to examine the type and volume of phases formed during hydration, the optimum substitution of ball clay and silica fume was studied. Accordingly, the best overall performance of ball clay was observed in the 10% substitution in the presence of 7% silica fume.

Influence of thiourea synthesis with silica fume on the corrosion rate of reinforcement concrete

ABSTRACT The examination of corrosion rate for steel reinforcement existent in concrete was carried out in the presence of silica fume and thiourea. The ordinary Portland cement (OPC) replacement was conducted with silica fume material at 5 and 10% by cement weight for concrete production, in addition to that using various percentage of thiourea (1, 2, 3 4 and 5%) added to concrete. Monitoring and estimating the corrosion rate for reinforcing steel existent in concrete with and without silica fume and thiourea was held with the usage of corrosion test cell. Besides, compressive and splitting tensile strength submerged in fresh and salty water of hardened concrete with and without silica fume and thiourea that were considered in the study. The immersion for all the samples of steel reinforcement with salty water (tap water with 1.5% of calcium sulphate and 3% of sodium chloride) for about 90 days of exposure were studied. The best results for the lowest corrosion rate were obtained when a mixture of silica fume with thiourea is used with concentrations of 10 and 3%, respectively compared with the ordinary concrete.

Comparative Study on the Performance of Blended and Nonblended Fly Ash Geopolymer Composites as Durable Construction Materials

This article represents that the mechanical and microstructural properties and durability of fly ash-based geopolymers blended with silica fume and borax are better than those of conventional fly ash-based geopolymers. Fly ash itself contains the sources of silica and alumina which are required for geopolymerisation. But a sufficient amount of high-reactive silica is able to rapidly initiate geopolymerisation with activation. Pure potassium hydroxide pellets and sodium silicate solution were used for preparation of alkaline activator solution. Fly ash geopolymer paste exhibited better mechanical properties in the presence of silica fume with slight portion of borax. The effect of silica fume-blended geopolymer paste on temperature fluctuation (heating and cooling cycle at certain temperatures) showed better performance than nonblended fly ash-based specimens. Durability property was evaluated by immersion of geopolymer specimens in 10% magnesium sulfate solution for a period of one year. The change in weight, strength, and microstructure was studied and compared. In the magnesium sulfate solution, a significant drop of strength to around 37.26% occurred after one year for nonblended fly ash-based specimens. It is evident that specimens prepared incorporating silica fume had the best performance in terms of their properties.

Bonding durability of polymer-modified concrete repair overlays under freeze–thaw conditions

One of the main issues associated with the reliability and durability of concrete in cold regions is the effect of freezing and thawing cycles on concrete structures. Polymer-modified concrete (PMC), which consists of Portland cement concrete with a polymer modifier, has advantages of good bonding strength to the substrate concrete, high tensile and flexural strengths, and low shrinkage and permeability. Due to their performance and durability, PMC overlays can be considered as a method of preserving damaged concrete structures. In this research, the durability of PMC overlays bonded to conventional concrete substrates under freeze–thaw cycles was investigated. In total, 25 PMC mix designs for repair overlays were examined. To investigate the effects of the type and amount of polymer and the presence of silica fume, two different types of modifier polymer (based on styrene butadiene rubber (SBR) or acrylic) at different replacement percentages and various amounts of silica fume were considered. For both polymer modifiers, maximum bonding occurred with the addition of 20% polymer by cement weight. The best durability was observed with the addition of 5% silica fume. The SBR-based PMCs showed stronger bonding and better durability than the acrylic-based PMCs.

Effect of fly ash and silica fume on transition zone, pore structure and permeability of concrete

The effect of fly ash (10, 20 and 30%) and silica fume (5 and 10%) as a substitute for cement in binary and ternary mixtures on the properties of fresh and hardened concrete are investigated. To determine mechanical properties, the compressive strength, splitting tensile strength and modulus of elasticity tests are used. Also, water penetration depth, water sorptivity, specific electrical resistivity, rapid chloride permeability and rapid chloride migration tests are applied to evaluate concrete durability. To examine the pore structure and transition zone morphology of concrete specimens, mercury intrusion porosimetry and scanning electron microscopy are used, respectively. The fresh concrete results show that the presence of silica fume in binary and ternary mixtures reduces workability and air content, but fly ash increases them. Adding silica fume to mixtures containing fly ash increases the mechanical strength at the ages of 7, 28 and 90 d. In addition to increasing the quality of the aggregate–cement matrix bond and improving the pore structure, the presence of supplementary cementitious materials has a considerably positive effect on the transport properties of concrete at all ages.