Silica Fume Content Research Articles

COMPRESSIVE STRENGTH AND THERMAL CONDUCTIVITY OF WATER AND AIR CURED PORTLAND CEMENT-FLY ASH-SILICA FUME MORTARS

This paper investigated the compressive strength and thermal conductivity of water and air cured Portland cement-fly ash-silica fume mortars. The results showed that density, compressive strength and thermal conductivity of blended cement mortars with fly ash were lower than Portland cement control. However, blended cement mortars that contained silica fume as replacement cement both in binary and ternary phase were higher than fly ash mixes and tends to increase with increase silica fume used as cement replacement due to increased C-S-H phase formation from pozzolanic reaction and its filler effect. In ternary phase, compressive strength and thermal conductivity of 10FA5SF and 5FA10SF mixes had values higher than Portland cement control while 20FA10SF mixes had values similar to Portland cement control. The density, compressive strength and thermal conductivity of blended cement mortars those cured in saturated lime water were higher than air cured specimens. Moreover, relationships between compressive strength and thermal conductivity as well as density and thermal conductivity were compared. X-ray diffraction traces show that intensity of C-S-H phase increased while intensity of Ca(OH)2 decreased with increased silica fume content due to the increased pozzolanic reaction when compared to the reference FA mix.

Effects of silica fume on mechanical strength and microstructure of basalt fiber reinforced cementitious composites (BFRCC)

In this study, the effect of different silica fume contents (0%, 5%, 10%, 15% by binder mass) as a replacement for cement on the mechanical strength and microstructure of cementitious composites containing chopped basalt fibers (0%, 1% and 1.5% by volume) has been evaluated. Flowability, compressive strength, flexural strength, toughness, water absorption and specific electrical resistivity of cementitious composites specimens have been investigated. The quality of fiber bonding in microstructure of cementitious matrix at 28-day age have been also analyzed and evaluated by the scanning electron microscope images (SEM). The results showed that clumping occurred at high amounts of fibers (1.5%) and silica fume (15%) which caused mixing and casting problems. Adding basalt fibers increased the flexural strength and toughness 2 and 6 times, respectively; however, it caused 47% decrease in compressive strength. Including silica fume had positive effects on fiber-matrix transition zone structure while increasing mechanical strength and specific electrical resistivity up to 20 times due to production of pozzolanic reactions and decreased portlandite so that it raised uniformity and density as well as bond quality.

Effect of silica fume on compressive strength of oil-polluted concrete in different marine environments

In the present research, effect of silica fume as an additive and oil polluted sands as aggregates on compressive strength of concrete were investigated experimentally. The amount of oil in the designed mixtures was assumed to be constant and equal to 2% of the sand weight. Silica fume accounting for 10%, 15% and 20% of the weight is added to the designed mixture. After preparation and curing, concrete specimens were placed into the three different conditions: fresh, brackish and saltwater environments (submerged in fresh water, alternation of exposed in air & submerged in sea water and submerged in sea water). The result of compressive strength tests shows that the compressive strength of the specimens consisting of silica fume increases significantly in comparison with the control specimens in all three environments. The compressive strength of the concrete with 15% silica fume content was about 30% to 50% higher than that of control specimens in all tested environments under the condition of using polluted aggregates in the designed mixture.

Mechanical properties of recycled aggregate concrete containing ternary blended cementitious materials

Abstract This paper presents the effect of silica fume (SF) on early-age and long-term mechanical properties of recycled aggregate concrete containing slag. In this study six series of mixes are considered. The first series is control concrete containing 100% ordinary Portland cement (OPC) and 100% natural aggregates. The second series is similar to the first series in every aspect except the natural coarse aggregate (NCA) which was partially replaced by 50% (by wt.) recycled coarse aggregate (RCA). The third series is also similar to the second series except the OPC which is partially replaced by 50% slag. The effects of 5, 10 and 15% (by wt.) SF on mechanical properties of concrete is evaluated in fourth, fifth and sixth series, respectively. Compressive strength, indirect tensile strength and modulus of elasticity of above concretes are measured at 3, 7, 28, 56 and 91 days. Results show that the addition of 50% slag significantly reduced the above mechanical properties of concrete containing 50% RCA at early age. Among three SF contents, the 10% SF improved the above mechanical properties of recycled aggregate concrete containing slag at early ages (3 and 7 days) as well as at 28 days. The addition of 10% SF also improved the 56 and 91 days compressive and tensile strengths of recycled aggregate concrete containing slag. It is also found that the long-term (56 and 91 days) compressive and tensile strengths of recycled aggregate concrete containing slag and 10% SF are even higher than the OPC concrete containing 50% RCA and control concrete, respectively. It is also observed that the slow pozzolanic reaction of slag contributed to the long-term compressive and tensile strengths of recycled aggregate concrete containing slag and 10% SF. Strong correlations of measured compressive strength with indirect tensile strength and elastic modulus of above environmentally friendly concretes are also established.

INFLUENCE OF SILICA COLLOID ON RHEOLOGY OF CEMENT PASTE WITH SUPERPLASTICIZER

Information of rheological behavior of binder paste is important for proportioning high slump concrete mixture at low water to cement ratios. This paper presents experimental data on the rheological property of silica colloid incorporated binder paste using naphthalene based and polycarboxylate based superplasticizer, compared to that of silica fume incorporated binder paste. Experimental data showed that silica colloid incorporated binder is compatible to tested superplasticizers in the all investigated range of silica colloid content, whereas the pastes incorporated with high silica fume content (over 10%) indicated incompatibility, especially to naphthalene based superplasticizer. There was also found out saturated content of superplasticizer corresponding to every kind of binder and water-binder ratio, with and without set retarding admixture.

Mix Design Aspects of High Performance Concrete Comprised of Silica Fume and Fly Ash

With massive developments taking place in the construction industry, the demand for high performance concrete (HPC) is steadily increasing. It is possible to use industrial by-products such as silica fume (SF) and fly ash (FA) as supplementary cementitious materials (SCMs), to enhance the attributes of HPC. Although numerous investigations have been carried out to identify the optimum replacement levels of these SCMs, some inconsistences are noticed in the results. In this context, a study was conducted to look into the combined effect of SF and FA on the strength and workability of HPC. Four SF replacement levels: 5%, 10%, 12.5%, and 15%; and five FA replacement levels: 0%, 5%, 10%, 15% and 20% were proposed. A total of nineteen mix proportions were used including a control mix. Water-binder ratio was kept constant at 0.35. The mixes were tested for 7 and 28-day compressive strengths and for their workability. Results obtained revealed that the maximum 7-day compressive strength was in the mix with 10% of SF with no FA and the maximum 28-day compressive strength was in the mix with 12.5% of SF and 5% of FA. The workability increased with the addition of fly ash while the SF content kept below 10%. In terms of economy, the best strength to cost ratio was found in the control mix. The extension of the k-value concept for the water/binder ratio found in EN 206 for SF-FA combinations revealed that the existing parameters kSF = 2.0 and kFA = 0.4 show a good correlation with the experimental results.

Curing optimization for strength and durability of silica fume and fuel ash concretes under hot weather conditions

This paper reports the influence of hot weather conditions and subsequent curing requirements on the strength and durability of multi-cementitious concrete. Five curing schemes were considered using persistent moist curing for various ages followed by exposure to natural hot weather conditions. It was observed that curing in hot weather tended to increasethe initial strength of ternary blended concrete for up to 28days; however, the development of long-term strength had insignificant effect. Binary blended concrete with silica fume (SF) exposed to hot weather have higher early age strength development compared to those under standard curing. The compressive strength and permeability of concrete was more sensitive to hot weather curing at an early age as its fly ash (FA) content increased. However, the effects of curing age diminished with high FA content and the susceptibility of long-term strength to hot weathering decreased as SF content increased. The porosity of concrete cured with continuous moistening was lower compared to those under hot weathering. The chloride permeability of binary blended concrete containing SF was less affected by hot weather curing. Using numerical models, it was found that the optimized persistent moist curing age for concrete without SF was dependent on target strength and durability requirements.

Experimental investigation of the effect of silica fume on the thermal spalling of reactive powder concrete

The distinct spalling performances of reactive powder concrete (RPC) specimens with various silica fume (SF) contents exposed to high temperatures were observed via high-resolution photography. The RPC microstructures and pore structures after high-temperature exposure were characterized using scanning electron microscopy and mercury intrusion porosimetry. The results provide experimental evidence of the high-temperature spalling mechanism of RPC. Increasing the SF content in RPC increases its compressive strength and compactness, offering greater mitigation of devastating spalling behaviour, but also producing more pulverized spalling remnants. This is attributed to the post-heating cracked microstructure and refined pores, which promote localized rather than entirely explosive spalling.

Eco-efficient ultra-high performance concrete development by means of response surface methodology

The research described in this paper represents a statistically based model with the help of response surface methodology (RSM) aiming to study the applicability of this method to ultra-high performance concrete (UHPC) mixture design and its optimization. Besides, the effects of silica fume, ultra-fine fly ash (UFFA) and sand as three main variable constituents of UHPC on workability and compressive strength as the main performance criteria and responses of this high-tech material were investigated. The models proposed here demonstrate a perfect correlation among variables and responses. Furthermore, through performing a multi-objective optimization, cement and silica fume, as two main constituents of UHPC affecting its eco-efficiency and cost, were substituted by UFFA and sand as much as possible. Finally, an eco-efficient UHPC with cement and silica fume content of 640 kg/m3 and 56.3 kg/m3 respectively and compressive strength and flow diameter of 160.3 MPa and 19 cm was developed.

Experimental study on the bond and durability properties of mortar incorporating polyacrylic ester and silica fume

The bond and durability properties, including the drying shrinkage, abrasion resistance, water permeability, freeze–thaw and carbonation resistance of mortar containing polyacrylic ester (PAE) and silica fume (SF) were analysed and compared in this study. Results showed that mortars containing PAE and SF had higher bond strength, lower drying shrinkage, superior abrasion resistance, water impermeability, freeze–thaw and carbonation resistance compared with the control mortar (M0), which contains no PAE or SF. With the addition of 30% PAE and 10% SF by weight of cement, an abrasion resistance strength of specimens up to 36·98 h/(kg/m2) was achieved, which was 53·19% more than M0. The water penetration depth of specimens with the same contents of PAE and SF decreased to 9·56 mm, whereas the value for M0 was 26·85 mm. Therefore, mortars incorporating PAE and SF can be utilised as repair materials, especially in repairing hydraulic concrete structures, as they have excellent bond strength and durability properties.

Effects of supplementary cementitious materials on mechanical and durability properties of high-performance non-shrinking grout (HPNSG)

High-performance non-shrinking grout (HPNSG) is a high strength material designed for precision grouting and general construction applications. The main purpose of this research study is to develop HPNSG using fly ash, slag, and silica fume. These supplementary cementitious materials were tested in different replacement percentages by examining mechanical and durability properties. Both fresh and hardened properties of grouts were assessed. The compressive strength, shrinkage, dynamic modulus of elasticity, electrical resistance, shrinkage, and abrasion of the grouts were tested. The compressive strength increased with increasing slag and silica fume content, which is attributed to the higher pozzolanic reactivity of these materials than that of fly ash and pumice. However, the effect of incorporating materials into grout mixtures was very slight at early ages. By passing the time, C–S–H gel grew outward from the cement particles and resulted in less porosity.

Dispersion of carbon fibers and conductivity of carbon fiber-reinforced cement-based composites

Abstract Dispersion of carbon fibers in the cement matrix remains a hot topic in the preparation of carbon fiber-reinforced cement-based composites (CFRC) because it affects greatly both the mechanical and electrical properties of the composites. In this work, a new dispersant hydroxyethyl cellulose was used with the aids of pre-dispersion by ultrasonic wave to realize the uniform distribution of chopped carbon fibers in the cement matrix. The fracture surface of the prepared CFRC was observed by scanning electron microscopy, the elemental distribution was investigated by energy dispersive spectroscopy, and the components was analyzed by X-ray diffraction. Influences of carbon fiber lengths and contents, water/cement weight ratio, molding process, curing time, and silica fume content over the conductivity of the CFRC composites were studied. The mechanism of conductivity was discussed. Results shown that the electrical resistivity intended to decrease with the increasing of carbon fiber contents. The mass fraction 0.6% of carbon fibers was a turning point. The concentration of hydroxyethyl cellulose between 1.66% and 1.86% was mostly beneficial for the dispersion of carbon fibers. The resistivity was increased first and decreased then with the increase of water/cement ratio. When the CFRC sample was prepared by the vibrating pressing method, the resistivity of the sample was reduced far greatly than that of the sample by the vibrating method. The incorporation of silica fume into the CFRC composites exerted not only a good effect on the dispersion of carbon fibers, but also increased the density of the composites to further influence the conductivity of the CFRC.

Influence of steel slag-silica fume composite mineral admixture on the properties of concrete

A composite mineral admixture was prepared by grinding a mixture of steel slag and silica fume (steel slag/silica fume ratio is 92:8 or 84:16, by mass). A layer of silica fume was uniformly adsorbed on the steel slag particles. The influence of this steel slag-silica fume composite mineral admixture on the hydration of a cement-based composite binder and the properties of its concrete were investigated. The results show that the silica fume in the composite mineral admixture contributes significantly to the consumption of Ca(OH)2 and enhances the connection between the steel slag particles with the surrounding C-S-H gel. The activity of the composite mineral admixture improves with an increase in the silica fume content. The retarding effect of the composite mineral admixture on the early hydration of cement is significant. However, a proper cement replacement by the composite mineral admixture can improve the late-age pore structure of hardened paste as well as the strength, chloride ion resistance, carbonation resistance, and sulfate attack resistance of concrete. The proper addition of the composite mineral admixture can reduce the drying shrinkage of concrete.

Effect of Partial Replacement of Cement by Mixture of Glass Powder and Silica Fume Upon Concrete Strength

All over the world the most common consuming construction material is concrete. It is well know that concrete is the combination of cement, aggregates and water. The production of cement results in the formation of carbon dioxide gas causes the environmental pollution. About 7 percent of carbon dioxide gas is evolved from cement industries to atmosphere. Keeping in view about the environmental pollution which may leads to some serious issues of health, so it is essential to use locally available pozolanic materials as a partial replacement of cement because these materials are economical as compared to Portland cement and also friendly to the environment without compromising on concrete strength. In concrete cement can be partially replaced by different supplementary cementitious materials. In the recent years pozzolonic materials, glass powder and silica fume are used in concrete as a partial cement replacement to improve the strength of concrete. In this research work the mixture of glass powder and silica fume were used in concrete as a partial cement replacement, to study its effect upon concrete strength. The mix proportion of 1:2:4 was selected for all the concrete samples with water to binder ratio of 0.55. For comparison, a control sample of concrete was prepared without mixture of glass powder and silica fume to compare it with the various samples containing different percentages of mixture of glass powder and silica fume as a partial replacement of cement in concrete. Results discovered that the usage of mixture of glass powder and silica fume in concrete as a partial replacement of cement increases the concrete strength. Such as compressive strength increases up to 8.64%, tensile strength increases up to 15% and flexural strength increases up to 7.08% at the age of 28 days. It is concluded that maximum strength is achieved at 28 days by 30 percent replacement of cement through mixture of glass powder and silica fume in concrete and the strength was decreased by increasing the mixture of glass powder and silica fume content beyond 30 percent. Therefore 30 percent replacement of cement is the optimum amount to achieve the higher strength. From the SEM analysis of concrete samples it’s proved that both the pozzolonic materials contribute in hydration process and further validated the strength test results.

Flexural response and crack development properties of ferrocement panels reinforced with steel fibers

Effect of partial replacement of cement with silica fume on flexural strength and cracking of ferrocement simply supported panels reinforced with steel fiber and wire mesh was explored. For the purpose of this study, various dosages of silica fume and steel fiber were mechanically mixed with reference mortar. The ferrocement panel specimens were prepared with 1, 2, and 3 layers of galvanized wire mesh. The water-cement ratio was fixed at 0.35 for all the test specimens. The main objective of this study is to evaluate the 28-day flexural strength of simply supported panels by laboratory center point flexural tests. The results of 15 simply supported ferrocement panels indicated that the fabricated ferrocement panels with silica fume content up to 15% by binder weight exhibited superior flexural performance as compared to the control ferrocement panels with no silica fume content. Flexural performance parameter used for comparison was flexure stress–deflection response. The number of cracks developed at failure was also taken into account with measurements of average crack width and crack spacing. It was further revealed that for a 15% cement replacement with silica fume and 4% steel fiber addition in mortar mix, approximately 3.6-fold increase in 28-day flexural strength was observed when compared to the conventional mortar. In summary, inclusion of 4% steel fibers in a mortar of fabricated ferrocement panel improved the crack resistance and flexural capacity.

Effect of silica fume on mechanical properties of concrete containing recycled asphalt pavement

This paper presents the results of a study that investigated the improvement of the mechanical properties of coarse and fine recycled asphalt pavement (RAP) produced by adding silica fume (SF) with contents of 5%, 10%, and 15% by total weight of the cement. The coarse and fine natural aggregate (NA) were replaced by RAP with replacement ratio of 20%, 40% and 60% by the total weight of NA. In addition, SF was added to NA concrete mixes as a control for comparison. Twenty eight mixes were produced and tested for compressive, splitting tensile and flexural strength at the age of 28 days. The results show that the mechanical properties decrease with as the content of RAP increases. And the decrease in the compressive strength was more in the fine RAP mixes compared to the coarse RAP mixes, while the decrease in the splitting tensile and flexural strength was almost the same in both mixes. Furthermore, using SF enhances the mechanical properties of RAP mixes where the optimum content of SF was found to be 10%, and the mechanical properties enhancement of coarse RAP were better than fine RAP mixes. Accordingly, the RAP has the potential to be used in the concrete pavements or in other low strength construction applications in order to reduce the negative impact of RAP on the environment and human health.

Interaction of magnetic water, silica fume and superplasticizer on fresh and hardened properties of concrete

After passing through a magnetic field, the physical quality of water improves, and magnetic water (MW) is produced. There are many investigations on the effects of magnetic field on water that shows MW properties like saturation and memory effect. This study investigates the fresh and hardened properties of concrete mixed with MW, which contains silica fume (SF) and superplasticizer (SP). The test variables included the magnetic field intensity for producing MW (three kinds of water), SF content replaced cement (0 and 10 percent), water-to-cementitious materials ratio (W/CM=0.25, 0.35 and 0.45) and curing time (7, 28 and 90 days). The results of this study show that MW had a positive impact on the workability and compressive strength of concrete. By rising the intensity of the magnetic field which was used for producing MW, its positive influence on both workability and compressive strength improved. MW had greater positive impacts on samples containing SP that did not have SF. Moreover, the best compressive strength improvements of concrete achieved as W/CM ratio decreased.

Influence of silica fume content on the quality of bond conditions in high-performance concrete specimens

The paper presents the analysis of the impact of silica fume content in high-performance concrete (HPC) on bond conditions along the height of tested elements. The tests were performed on the specimens made of six different HPC mixes with varying content of silica fume (0, 5 and 10% by mass of cement) and superplasticizer. The used specimens allowed for determining the changes of bond at individual levels of elements with a total height of 480 and 960mm. The rebars in the elements were placed perpendicularly to the direction of concreting. The reference element, characterised by the parallel orientation to the direction of concreting, was also prepared. The tests indicated that the quality of bond conditions in HPC deteriorates as the distance from the formwork bottom increases. The experiment results indicate that concrete modification with silica fume can both increase and decrease the quality of bond conditions. The influence of silica fume depends on the thickness of the concrete cover, which determines the mechanism of bond failure.

Compressive strength and microstructure of fly ash based geopolymer blended with silica fume under thermal cycle

This work aims to reveal the effects of silica fume on properties of fly ash based geopolymer under thermal cycles. Geopolymer specimens were prepared by alkali activation of fly ash, which was partially replaced by silica fume at levels ranging from 0% to 30% with an interval of 10%, by mass. Microstructure, residual strength and mass loss of fly ash based geopolymer blended with silica fume before and after exposed to 7, 28 and 56 heat-cooling thermal cycles at different target temperatures of 200 °C, 400 °C and 800 °C were assessed and compared. The experimental results reveal that silica fume addition enhances strength development in geopolymer. Under thermal cycles, the compressive strength of geopolymer decreases, and the compressive strength loss, as well as the mass loss, increases with increasing target temperature. The strength loss is the same regardless of silica fume content after thermal cycles. Microstructure analysis uncovers that pore structure of geopolymer degrades after thermal cycles. The pores of geopolymer are refined by the addition of silica fume. The incorporation of silica fume optimizes the microstructure and improves the thermal resistance of geopolymer. Silica fume increases the strength of the geopolymer and even though the strength loss is the same, the strength after heat cycle exposure is still good.

Shrinkage Properties of Cement-Silica Fume Blended Pastes in Early Age

The cement-silica fume blended pastes were prepared with different silica fume (SF) dosages of 0%, 5%, 10%, and 15% at different water-binder ratios (W/B) of 0.4 and 0.5. The autogenous shrinkage (AS) and the drying shrinkage (DS) of the paste samples in the hydration period of 7d (168 hours) were measured by a new measurement technique to explore the influence of W/B and silica fume incorporation on the shrinkage in early age. The study results can provide reference for high performance concrete mix design.It is found that ether the AS or the DS of the paste samples shows a similar pattern, and the AS development with hydration time appeared a temporary expansion period after a rapid growth, especially in the samples at a higher W/B or with a lower SF content. However, the DS development did not occur obvious expansion period.Three development trends were obtained for the factors of W/B and SF content. 1) the AS and DS of the pastes mainly occurred in early ages. The lower W/B, the shorter the rapid growth periods, and the higher the shrinkage ratio of 1d to 7d. For the pastes with W/B of 0.4, the AS grew rapidly in 1d and the DS grew rapidly in the first 10h, and the AS value in 1d reached to 63.6% of 7d, and the DS value reached to 62.1% of 7d in the paste with SF of 10%. For the pastes with W/B of 0.5, the rapid growth periods of the AS and DS respectively extended to 30~33h and 12h, and the AS value in 1d reached to 60.0% of 7d, and the DS value reached to 57.2% of 7d in the paste with SF of 10%. 2) The lower W/B, the higher the shrinkage ratio of the AS to the DS. When the SF dosage is 10%, the ratio of the AS value to the DS value of 7d is 21.66%~21.15% for W/B of 0.4, and only 6.06%~5.78% for the W/B of 0.5. 3) the higher SF content results in the higher AS in cement-SF blended pastes. For the pastes with W/B of 0.4, the ratio of the AS to the DS increased from 6.98% to 30.16% with the increase of content of SF from 5% to 15% in 1d, from 15.1% to 28.19% in 3d, from 16.78% to 26.16% in 7d.