Silica Fume Content Research Articles

Experimental Study on Stiffness and Energy of Modified Recycled Columns with Silica Fume and Hybrid Fiber

For the sake of compensating the defect of recycled aggregate and making full utilization of the mineral admixture’s unique characteristics, six recycled concrete columns with silica fume and hybrid fiber were tested under cyclic loading, the main variable of which was the different content of silica fume and fiber. Through the comparison of experimental phenomena analysis, the general rules of coefficient stiffness and energy dissipation capacities were obtained, and the corresponding theories could be analyzed with the experimental data. The results showed that the silica fume decreased early regeneration concrete column stiffness, the fiber of which increased, both the attenuation speeded increasingly with the increase in volume. Before the peak load, the energy consumption increased along with the lateral displacement’s increase, but after, the addition of fibers could make energy consumption increasing amplitude, which was better than silica fume.

Mechanical properties and microstructure of reactive powder concrete using ternary pozzolanic materials at elevated temperature

To provide fundamental data on developing an economical and practical Reactive Powder Concrete (RPC), a modified RPC was made in this study. This modified RPC significantly reduced the content of cement and silica fume compared to the conventional RPC mixture by the combination of ternary pozzolanic materials (silica fume, blast furnace slag, and fly ash). A series of fire tests was conducted on modified RPC specimens, and their mechanical properties and microstructures were investigated under high temperatures. The results clearly showed that the mechanical performance of the modified RPC under high temperatures was superior to that of the conventional RPC mixture (SF25 type) with only silica fume (SF/C = 25%). The residual compressive, flexural, and tensile strength of the modified RPC after exposure to 1000oC resulted in more than 62 MPa, 8 MPa, and 4 MPa, respectively. The range of 400~800℃ may be regarded as the critical temperature range for the strength loss of the modified RPC, which led to significant changes in the microstructure of the RPC matrix, as shown in the results of the pore structure analysis and XRay Diffraction (XRD).

Effect of Sand Content on Properties of Self-Consolidating, High-Performance Cementitious Mortar

The workability and compressive strength of a high-performance cementitious mortar (HPCM) produced by using a natural siliceous sand were studied as a function of sand content [expressed as sand-to-cementitious materials ratio (s/cm)], silica fume (SF) content, and high-range water reducing admixture (HRWRA) dosage. The purpose of this study was to maximize the proportion of sand content without negatively affecting workability and mechanical and durability properties when these characteristics were achieved at a low cost. Test results indicated that the workability of HPCM became less sensitive to sand content when the SF content increased. Statistical analysis showed that the compressive strength of self-consolidating HPCM was not significantly affected by sand content up to a certain maximum level, which was dependent on the HRWRA and SF dosage. On the basis of combined consideration of both workability and compressive strength, the maximum s/cm ratio to produce a self-consolidating HPCM with SF content at 0%, 10%, and 20% was 1.6, 1.6, and 2.0, respectively. Also, increasing the sand content was helpful in improving the durability of HPCM, because chloride ion permeability and drying shrinkage decreased.

Mechanical Behavior and Durability of Fibre Reinforced Mortar in an Aggressive Environment

This study was carried out to examine the mechanical behavior and durability of mortar with or without addition of silica fume, with and without steel fibre reinforcement. Three tests were carried out: strength, depth of pH reduction and micro-structural analysis by SEM. The mixes studied had two water cement ratios (0.5; 0.65); with a 0.5% steel fibre content and 10% silica fume content (in substitution of cement). To characterize the durability performance of the mortars studied, samples were exposed to one-year in three environments: wet environment (control samples under laboratory conditions, 20°C and 95% RH) and exposure samples: in cyclic environment (wetting and drying) and a sewage pumping station sump (an aggressive environment). SEM observations were carried out on samples to study the micro structural changes in the mortar's matrix. One sees the organic matter deposits located inside a pore and one can see the formation of the secondary ettringite. It is concluded that the compressive strength of the samples are relatively unaffected by mix type and environment. The samples exposed to sewage exhibited evidence a depth of pH reduction.

Role of Polyfunctional Admixture Based on Silica Fume and Carbon Nanotubes in Forming the Structure of Gypsum Cement Composition

One of the topical areas of regulating the structure of gypsum cement compositions is modifying the morphology with ultrafine and nanodisperse systems. The study has analyzed the possibility of changing the structure and properties of new formations of gypsum cement pozzolanic matrix by adding multifunctional admixture based on silica fume and multi-walled carbon nanotubes (MWCNTs) dispersed in a surfactant medium. The optimum content of complex admixture has been determined as 0.006% of MWCNTs and 10% volume content of silica fume as part of modified gypsum cement pozzolanic binder (GCPB) providing the increase of compressive strength by 55% and water resistance by 32%. Studying the structure of modified GCPB by means of physico-chemical analysis (scanning electron microscopy, infrared-spectral analysis and differential scanning calorimetry) has proved the improvement of physical and mechanical properties due to changes in mineralogical composition of new formations in hardening composition and morphology of the forming crystal hydrates in the structure of modified gypsum cement pozzolanic matrix. At the same time, it is noted that gypsum crystalline hydrates are coated with calcium silicate hydrates compacting the structure of the composition and increasing the total contact surface of the new formations. At the same time calcium silicate hydrates prevent water from the surface of crystals of calcium sulfate dihydrate, thereby increasing the water resistance of the composition.

Properties of a foamed concrete with soil as filler

Ordinary Portland cement, soil and foaming agent are the raw materials used to make soil-based foamed concrete. The effects of foam content and silica fume on the physical properties of soil-based foamed concrete, such as the dry density, 28-day compressive strength, thermal conductivity, water resistance and pore structure, were studied. The experimental results indicate that the foam and silica fume contents have a large impact on the physical properties of soil-based foamed concrete. The thermal conductivity, density, water resistance and compressive strength decrease with increasing volume fractions of foam. The compressive strength, the thermal insulation and water resistance are all improved by increasing the content of silica fume. Soil-based foamed concrete consisting of 20% silica fume with a density of 800kg/m3, compressive strength of 7.5MPa and thermal conductivity of 0.16W/mK can be used as water-resistant lightweight concrete. The hygroscopic tests were performed and the results indicate that the addition of silica fume has some effect on the hygroscopic property of soil-based foamed concrete. Several fitting curves have been obtained, the fitted functions developed by the Kumaran model and Cubic function have better fitting parameters.

CA6 impact on the corrosion behavior of cement-bonded spinel-containing refractory castables: An analysis based on thermodynamic simulations

This work focuses on the evaluation of the corrosion behavior of Al2O3–MgO cement-bonded castables based on thermodynamic calculations, in order to understand the reaction steps and some scientific and technological issues that still need to be better explained when such materials come into contact with basic industrial slags at high temperatures. Special attention was given to analyzing the role played by the calcium hexaluminate phase (CA6) during the first heating stage of the samples and their further chemical attack. Experimental measurements (cup tests at 1500°C) and thermodynamic simulations were carried out considering a basic slag (CaO/SiO2=4.2) and four refractory castables with different spinel (MgAl2O4) sources (pre-formed or in situ) and with or without silica fume (0 or 1wt%). Considering the attained results, a novel corrosion mechanism is proposed pointing out that a suitable design of the castable compositions can induce the formation of CA6 at the border of the coarse aggregates, preventing their further dissolution and increasing the overall wear resistance of these refractories. In Addition, incorporating optimized contents of silica fume and cement to the spinel-containing castables helps to master the generation of the CA6 and CA2 protective layers, resulting in a lower chemical attack at high temperatures.

Relationship between slump flow and rheological properties of self compacting concrete with silica fume and its permeability

The fresh state behavior including yield stress and plastic viscosity of silica fume modified concrete was measured by using a wide-gap viscometer. Bingham model was used to describe the rheology of fresh concrete. Besides, the slump flow was also measured at different time after water addition (TW). The permeation test was then performed after 28days’ curing. According to the experimental results, the rheological parameters were found strongly influenced by the silica fume content as well as TW value. The yield stress increase with silica fume content, while the plastic viscosity decreased at the beginning and then increased. The slump flow decrease with both TW and silica fume content. Furthermore, the relationship between slump flow and rheological properties were proposed. The research also shows that the permeation coefficients of different mix proportions have a larger fluctuation during the early period, especially the control group. After that the coefficients gradually change to be steady and then achieve stable values with the permeated time. At the early permeation durations, the permeability coefficient declines with silica fume content, while in the final, the situation concluded that the permeability coefficient is falling back to a lower value comparing to control group after a rise. It should be noted that the peak value also appears at 4% SF content.

MECHANICAL PROPERTIES OF FLY ASH-BASED ALKALI-ACTIVATED CEMENT USING A STATISTICAL ANALYSIS TECHNIQUE

This paper presents the mechanical properties of fly ash-based alkali-activated cement (AAC). A statistical analysis method was used to determine the effect of mix proportion parameters on the dry density and compressive strength of fly ash-based AAC pastes and mortars. For that purpose, sample mixtures were designed according to Taguchi’s experimental design method, i.e., in a L9 orthogonal array. Four factors were selected: “silica fume content” (SF), “sand to solid ratio” (s/c), “liquid to solid ratio” (l/s), and “superplasticiser content” (SP). The experimental results were analysed by using signal to noise for quality control of each mixture, and analysis of variance (ANOVA) was used to determine the significant effect on the compressive strength of fly ash-based AAC. Furthermore, a regression-analysis method was used to predict the compressive strength according to the variation of the four factors. Results indicated that silica fume is the most influencing parameter on compressive strength, which could be decreased by superplasticiser and l/s ratio. There is no significant effect of sand-to-cementitious ratio on compressive strength of fly ash-based AAC. The dry density decreases as the sand-to-cementitious ratio is decreased. The increasing l/s ratio and superplasticiser dosage could further decrease the dry density of fly ash-based AAC.

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.

Experimental Study of Frost-Resistance Properties of Silica Fume Concrete

The frost resistance of low strength concrete is researched. In order to evaluate the effect of different content of silica fume on frost resistance，the quality of the cement 6%, 9%, 12% silica fume are respectively added into concrete. Freezing-thawing test results show that: the silica fume concrete has good frost resistance. Content of silica fume on concrete is not almost effect to quality loss rate. In 0-250 times of freezing-thawing cycle range, it is smaller that relative dynamic elastic modulus change rate. Relative dynamic elastic modulus of ordinary concrete decreases rapidly after 250 times of freezing-thawing cycle while dynamic elastic modulus decrease rate of the silica fume concrete tends to slow. The freezing -thawing cycles up to 350 times, silica fume concrete relative dynamic elastic modulus is 1.5 times that of ordinary concrete that show the silica fume concrete frost resistance is better than that of ordinary concrete.

Interface pullout properties of macrosynthetic fibres in latex modified cement based nanosilica and silica fume composites

In this study, the bond properties between macrosynthetic fibres and latex polymer modified cement composites (LMCCs) were evaluated at different nanosilica and silica fume (microsilica) contents. The bond tests were evaluated according to Japan Concrete Institute SF-8, in which the nanosilica and silica fume contents in the cement were set to 0, 2, 4, 6 8, or 10%, based on cement weights. The addition of nanosilica and silica fume significantly influenced the bond properties between macrosynthetic fibres and LMCCs. Both bond strength and interface toughness improved with increasing silica fume content up to 10%. Both bond strength and interface toughness increased with nanosilica content up to 6% and then decreased with nanosilica content of 8% or more. This result was confirmed by observing an increase in scratching due to friction forces. This study was validated using microstructural analysis of torn macrosynthetic fibres after the bond tests.

Influence of silica fume on stress–strain behavior of FRP-confined HSC

Confinement of high-strength concrete (HSC) columns with fiber reinforced polymer (FRP) composites has been receiving increasing research attention due to the advantageous engineering properties offered by the composite system. The use of silica fume as a concrete additive is a widely accepted practice in producing HSC. However, the influence of the presence and amount of silica fume on the efficiency of FRP confinement is not clearly understood. This paper presents the results of an experimental study on the influence of silica fume on the compressive behavior of FRP-confined HSC. 30 FRP-confined and 30 unconfined concrete cylinders containing different amounts of silica fume were tested under axial compression in two phases. In the first phase of the study, specimens with a constant water–cementitious binder ratio were tested. The results of this phase indicate that for a given water–cementitious binder ratio, the compressive strength of unconfined concrete increases with an increase in the amount of silica fume. It is found that this increase in strength leads to an increased concrete brittleness, which adversely affects the effectiveness of FRP confinement. In the second phase, water–cementitious binder ratios of the specimens were adjusted to attain a constant unconfined concrete strength for specimens containing different amounts of silica fume. The results of these tests indicate that for a given unconfined concrete strength, strength enhancement ratios of FRP-confined HSC specimens are not influenced by the silica fume content of the concrete mix. On the other hand, it is found that the silica fume content influences the axial strain enhancement ratios of these specimens. In addition, the transition zones of the stress–strain curves of FRP-confined HSC are observed to be sensitive to the amount of silica fume used in the mix.

An investigation on mechanical and physical properties of recycled aggregate concrete (RAC) with and without silica fume

Experimental studies for determining the mechanical and the physical properties of the recycled aggregate concrete (RAC) with and without silica fume (SF) is inspired by the Urban Renewal Law which regulates circumstance of existing structures in Turkey. According to this law, the structures which have been built lacking quality engineering, built without considering urban planning, and are risk prone (i.e. susceptible to earthquakes), will be demolished and rebuilt using recent Turkish Standards. Implementing this law is expected to increase the quantity of waste concrete. Minimizing waste disposal through structural and non-structural areas without a harmful effect on nature has a vital importance in Turkey. In this study, demolished-building-rubble is used as recycled aggregate (RA) with and without SF in concrete mixtures. Twelve concrete mixtures in three groups are produced, and the mechanical properties of the concrete specimens such as compressive strength, tensile splitting strength and elasticity modulus, and physical properties of the concrete specimens such as density and water absorption ratio are determined. The proportion 30% of RA in concrete mixtures is proposed as the optimum ratio. Low regression coefficient of RAC with SF is observed in the short-term. It is found that 5% SF content in the RAC is more convenient to improve the low properties of RAC (i.e. compressive strength).

Low-Temperature Sintering of SiC Reticulated Porous Ceramics Using Al2O3-SiO2 as Sintering Aids

Currently, one of the most popular methods for the production of reticulated porous ceramics (RPCs) is the polymer sponge method, which was invented by Schwartzwalder and Somers. SiC RPCs can be fabricated by using the A12O3-SiO2 as sintering aids at low temperature as 1200-1300 °C in cases with SiC (20-50 % (mass percent)). However, when the content of SiC powders (relative to total weight of solids) was higher than 50 % (mass percent), the most suitable sintering temperature was higher than 1400 °C. In this work, SiC reticulated porous ceramics (SiC RPCs) was fabricated via the polymer sponge method using Al2O3-SiO2 as sintering aids at 1100-1500 °C. In order to obtain SiC RPCs with optimized mechanical performance, the properties of the slurry and influence of sintering temperature have been investigated. It was found that, rheological properties, solid content of the slurry and sintering temperature all have influence on the physical and mechanical properties of SiC RPCs. In order to achieve optimal properties of SiC RPCs, the optimal pH value ,solid content, sintering temperature and content of silica fume were 11, 73.4 % (mass percent), 1300 °C and 17 % (mass percent), respectively.

등가재령 방법에 의한 혼화재 치환 고강도 시멘트 모르타르의 자기수축 해석에 관한 연구

본 연구에서는 양생온도변화에 따른 자기수축의 예측을 위하여 FA 및 SF를 치환한 시멘트모르타르를 대상으로 자기수축변화를 측정하고 이를 등가재령방법으로 해석하고자 하였다. 이를 위해 수화반응의 온도민감도를 고려하는 Ea의 변화에 따라 지수함수모델을 이용하여 자기수축 해석을 실시하였는데, 경화단계의 <TEX>$E_a$</TEX>를 이용할 경우 응결단계의 <TEX>$E_a$</TEX>를 사용한 경우보다 정확한 해석이 가능한 것으로 나타났는데, 이는 경화의 전단계에 걸친 수화의 온도민감도 영향을 반영한 <TEX>$E_a$</TEX>값에 기인된 결과로 사료된다. The objective of this study is to investigate an effect of curing temperature on autogenous shrinkage of high strength cement mortar with 0.15 of W/B incorporating fly ash and silica fume in terms of equivalent age. The contents of fly ash and silica fume are varied from 10% to 30%. Non linear regression model applying equivalent age was used to estimate the autogenous shrinkage evolution. To obtain apparent activation energy(<TEX>$E_a$</TEX>), setting time method by Pinto and existing method were calculated and compared respectively. Test results showed that use of silica fume increased autogenous shrinkage while use of fly ash decreased it. It was also found that poor agreements were obtained when <TEX>$E_a$</TEX> by setting time was applied. But, application of existing <TEX>$E_a$</TEX> resulted in a good agreement between calculated autogenous shrinkage and measured one.

Influence of Silica Fume on the Reflectivity and Transmission Efficiency of Cement-Based Materials

As a kind of mineral admixture, silica fume has low permittivity, which will affect the electromagnetic properties of cement-based materials. To study the effect of silica fume on the properties of cement-based materials, the reflectivity, transmission efficiency and pore structure were analyzed by using the vector network analyzer and mercury injection apparatus. Results show that silica fume can make the mortar more compact and the porosity of sample with 9% silica fume is only 17.8%, which is far lower than the control sample; With the increase of the silica fume content, the peak of reflectivity curve increases from -23.2 dB to -16.0 dB, and then decreases from -16.04 dB to -28.7 dB in the frequency range of 6 – 18 GHz. Reflectivity of sample with 3% content of silica fume is lower than other samples within 26.5 - 40 GHz; Transmission efficiency of samples shows the trend of increase with silica fume content increases from 0% to 6% within 8.2 - 12.4 GHz, 12 - 18 GHz and 26.5 - 40 GHz, but when the content increases from 6% to 9%, the transmission efficiency of samples reduces.

Effect of the key mixture parameters on shrinkage of reactive powder concrete.

Reactive powder concrete (RPC) mixtures are reported to have excellent mechanical and durability characteristics. However, such concrete mixtures having high amount of cementitious materials may have high early shrinkage causing cracking of concrete. In the present work, an attempt has been made to study the simultaneous effects of three key mixture parameters on shrinkage of the RPC mixtures. Considering three different levels of the three key mixture factors, a total of 27 mixtures of RPC were prepared according to 33 factorial experiment design. The specimens belonging to all 27 mixtures were monitored for shrinkage at different ages over a total period of 90 days. The test results were plotted to observe the variation of shrinkage with time and to see the effects of the key mixture factors. The experimental data pertaining to 90-day shrinkage were used to conduct analysis of variance to identify significance of each factor and to obtain an empirical equation correlating the shrinkage of RPC with the three key mixture factors. The rate of development of shrinkage at early ages was higher. The water to binder ratio was found to be the most prominent factor followed by cement content with the least effect of silica fume content.

Study on the Dense-Packing Effect and Properties of Multi-Component Cementitious Material

The paper studied the effects of single addition of ultrafine fly ash (UFA) and mixed addition of silica fumeultrafine fly ash (SF-UFA) on powder pressure entity dense packing density, mechanical performance and microstructure structure of composite cement paste. The results show that, the ternary system of mixed addition of SF-UFA can effectively further reduced the compacting voidage and more increased packing density of composite powder, compared with the binary system of single addition of UFA. And when the content of SF is 8%, the compacting voidage is the lowest. Next, in the ternary system of mixed with silica fume, ultrafine fly ash and cement (SF-UFA-C), with the increase of silica fume (SF), the total porosity and pore diameter of hardened cementing paste decreased further compared with binary system, and with 8% content of SF and 17% content of UFA, the total porosity of hardened cement paste is the lowest, decreased by 60% than that of reference sample. At last, mixed addition of SF-UFA can improve the long-term strength of composite cement paste either, the compressive strength of 60 days hydration increased by nearly 9% compared with UFA-C and increased 41% compared with the reference sample.

Study of radon transport through concrete modified with silica fume

The concentration of radon in soil usually varies between a few kBq/m3 and tens or hundreds of kBq/m3 depending upon the geographical region. This causes the transport of radon from the soil to indoor environments by diffusion and advection through the pore space of concrete. To reduce indoor radon levels, the use of concrete with low porosity and a low radon diffusion coefficient is recommended. A method of reducing the radon diffusion coefficient through concrete and hence the indoor radon concentration by using silica fume to replace an optimum level of cement was studied. The diffusion coefficient of the concrete was reduced from (1.63 ± 0.3) × 10−7 to (0.65 ± 0.01) × 10−8 m2/s using 30% substitution of cement with silica fume. The compressive strength of the concrete increased as the silica-fume content increased, while radon exhalation rate and porosity of the concrete decreased. This study suggests a cost-effective method of reducing indoor radon levels.