Amount Of Silica Fume Research Articles

Time-dependent rheological characteristics of self-consolidating concrete containing various mineral admixtures

The study herein was intended to evaluate the influence of elapsing time on rheological properties and thixotropy of self-consolidating concrete (SCC) mixtures containing various mineral admixtures. For this purpose, variation of T50 flow time, torque plastic viscosity, apparent yield stress and thixotropy were investigated as a function of time in a standstill condition. Various amounts of silica fume (SF), metakaolin (MK), Class F fly ash (FAF), Class C fly ash (FAC) and granulated blast-furnace slag (BFS) were utilized in binary, ternary and quaternary cementitious blends in 17 different SCC mixtures having a constant slump flow value. The results showed that SCC mixtures containing various mineral admixtures were highly stable or moderately stable (VSI between 0 and 1) at 0min according to ASTM C 1611. However, mixtures containing FAC, FAF and BFS exhibited some bleeding and segregation at 50min. In a standstill condition, apparent yield stress and thixotropy increased significantly with time while torque plastic viscosity values changed only in a limited range. In addition, with elapsing time, MK and FAC were found to have more influence on torque plastic viscosity and yield stress values in comparison with the other admixtures. However, increase in the yield values were more pronounced in comparison with the torque plastic viscosity values. Increase in thixotropy with time for the SF and MK blended mixtures were higher when compared to the control mixtures and mixtures containing the other mineral admixtures.

Study on the Deterioration Mechanism of Concrete Pavement for the Deicer-scaling

The mechanical properties of concrete pavement were studied under the various frost-salt conditions using Capillary Suction of De-icing Chemicals and Freeze-thaw Test Method (CDF method). The test results show that: with the increasing of freeze-thaw cycles, concrete surface damage has a tendency to accelerate. The concrete which is in a 5% concentration chloride snow-thawing agent solution has the greatest impact damage after 150 frost-salt cycles compared with soaking in other different densities (3%, 20%). Mixing appropriate amount of silica fume and high-performance air-entraining agent in concrete can effectively improve the resistance of frost-salt scaling. With the frost-salt cycles increase, the concrete strength and the relative dynamic elastic modulus continues to decrease.

Study on the Deterioration Mechanism of Concrete Pavement for the Deicer-scaling

The mechanical properties of concrete pavement were studied under the various frost-salt conditions using Capillary Suction of De-icing Chemicals and Freeze-thaw Test Method (CDF method). The test results show that: with the increasing of freeze-thaw cycles, concrete surface damage has a tendency to accelerate. The concrete which is in a 5% concentration chloride snow-thawing agent solution has the greatest impact damage after 150 frost-salt cycles compared with soaking in other different densities (3%, 20%). Mixing appropriate amount of silica fume and high-performance air-entraining agent in concrete can effectively improve the resistance of frost-salt scaling. With the frost-salt cycles increase, the concrete strength and the relative dynamic elastic modulus continues to decrease.

Thixotropy and structural breakdown properties of self consolidating concrete containing various supplementary cementitious materials

In this study, thixotropy and structural breakdown of 57 self-consolidating concrete (SCC) mixtures containing various supplementary cementitious materials (SCM) were investigated by different approaches. The effects of SCM type and content on high range water reducer demand and plastic viscosity were also studied. For these purposes, various amounts of silica fume (SF), metakaolin (MK), Class F fly ash (FAF), Class C fly ash (FAC) and granulated blast-furnace slag (BFS) were utilized in binary, ternary, and quaternary cementitious blends in three water/binder (w/b) ratios. Results showed that except BFS, use of SCM in SCC mixtures increased thixotropy values in comparison with the mixtures containing only portland cement (PC). Good correlations were established between structural breakdown area and drop in apparent viscosity values for all w/b ratios. The different methods used to evaluate the thixotropy and structural breakdown got more consistent with each other as w/b decreased.

Permeability properties of self-consolidating concrete containing various supplementary cementitious materials

In this study, permeability properties of 17 self-consolidating concrete (SCC) mixtures containing various supplementary cementitious materials (SCM) were investigated by different experimental approaches. The effects of SCM type and content on the compressive strength, rapid chloride ion permeability (RCPT), water penetration depth, water absorption and sorptivity were studied. For these purposes, various amounts of silica fume (SF), metakaolin (MK), Class F fly ash (FAF), Class C fly ash (FAC) and granulated blast-furnace slag (BFS) were utilized in binary, ternary, and quaternary cementitious blends. Results showed that partial replacement of PC by SCM increased the compressive strength of control mixtures at 28 and 90days (except for FAF at 28days). Mixtures containing MK presented a better performance compared to other SCM at 7days. The utilization of SCM reduced the RCPT results of almost all mixtures compared to the control mixtures and the reduction was more significant with an increase in the SCM content. All of the mixtures containing SCM had lower penetration depths when compared to reference mixtures at 28 and 90days. Good correlations were established between the percentage of permeable voids and water absorption. Moreover, there was an inverse but almost linear relationship between permeable voids content and compressive strength of the mixtures.

Investigating Effects of Application of Silica Fume to Reduce Asphalt Oxidative Aging

This paper investigates the feasibility of using silica fume to enhance the rheological properties of asphalt binder. It has been widely reported that asphalt binder oxidation is one of the phenomena that reduces the service life of asphalt pavement by negatively impacting its rheological properties. This in turn can lead to a more brittle pavement which is more prone to cracks due to thermal stress and traffic loading. Prior research has shown that introduction of nano-silica to asphalt can reduce asphalt oxidation aging; however, the main challenge with use of nano-silica found to be agglomeration of nano-particles to form micro size clusters which can reduce nano-silica effectiveness while making asphalt binder more susceptible to shear. Therefore, this paper studies effectiveness of using silica fume to reduce asphalt oxidative aging while alleviating agglomeration issue. To do so, various percentages of silica fume was introduced to a base asphalt binders and the rheological properties and high temperature performance of each specimen was evaluated by measuring the rotational viscosity and complex shear modulus before and after oxidative aging. Analysis of the experimental results showed that silica fume reduced asphalt aging index significantly; in addition the temperature susceptibility of asphalt binder was reduced as the percentage of silica fume increased. The flow of modified mixtures increased and the loss of stability of samples decreased as the amount of silica fume increased. The positive effect of silica fume on base asphalt’s rheological properties could be attributed to the high surface area and the low degree of agglomeration of the silica fume due to their high polarity. This in turn could improve silica fume’s blending properties resulting in a uniformly distributed silica fume modified matrix with enhanced oxidative aging resistance.

Effect of various supplementary cementitious materials on rheological properties of self-consolidating concrete

In design of self-consolidating concrete (SCC) for a given application, the mixture’s rheological parameters should be adjusted to achieve a given profile of yield stress and plastic viscosity. Supplementary cementitious materials (SCM) can be useful for this adjustment in addition to their other advantages. In this study, the rheological properties of 57 SCC mixtures with various SCM were investigated for a constant slump flow value. For this aim, various amounts of silica fume (SF), metakaolin (MK), Class F fly ash (FAF), Class C fly ash (FAC) and granulated blast-furnace slag (BFS) were utilized in binary, ternary, and quaternary cementitious blends in three water/binder ratios. Results showed that SF and BFS decreased plastic viscosity and V-funnel time values in comparison with mixtures containing only Portland cement (PC). However the opposite tendency was observed when MK, FAC and FAF were incorporated with PC. Substitution of PC with SF, MK and FAC increased high range water reducer (HRWR) demand in the SCC mixtures having constant slump flow. Use of SCM in SCC mixtures increased yield stress values. Good correlations were established between plastic viscosity and V-funnel flow time values for all w/b ratios.

Study physico-chemical properties of blended cements containing fixed amount of silica fume, blast furnace slag, basalt and limestone, a comparative study

The present study investigates the effect of substitution of Portland cement by 20% of basalt, as natural pozzolana, on the physico-chemical properties of blended cement in comparison to silica fume, granulated blast furnace slag and limestone. For this purpose, a reference sample and four cements containing up to 20% w/w of silica fume, granulated blast furnace slag, basalt and limestone were tested. Bulk density, compressive strength, total porosity and chemically combined water were determined up to 360days. The hydration products were investigated with FT-IR and DSC. The results showed that basalt has lower pozzolanic activity at early ages than that of silica fume and slag but at later age increases. Whereas the basalt acts as filled materials at early ages and then its reactivity increase due to pozzolanic reaction. It is concluded that basalt has low pozzolanic activity and has a better filling effect on cement hydration with better physico-mechanical properties than other pozzolanic materials.

Corrosion resistant self-compacting concrete using micro and nano silica admixtures

In this paper, enhancement of corrosion and chloride resistance of high performance self compacting concrete (SCC) through incorporating nanosilica into the binder has been investigated. For this purpose, different mixtures were designed with different amounts of silica fume and nano silica admixtures. Different binder contents were also investigated to observe the binder content effect on the concrete properties. Corrosion behavior was evaluated by chloride penetration and resitivity tests. Water absorption and capillary absorption were also measured as other durability-related properties. The results showed that water absorption, capillary absorption and Cl ion percentage decreased rather significantly in the mixtures containing admixtures especially blend of silica fume and nano silica. By addition of the admixtures, resistivity of the SCC mixtures increased which can lead to reduction of corrosion probability.

Penetration Resistance to Chloride Ions of Silica Fume Concrete

The penetration resistance to chloride ions of concrete is one of the important factors affecting the durability of concrete structures. The penetration resistance to chloride ions of concrete is measured with the increasing substitution amount of silica fume in this paper. For the low water-binder ratio of 0.28, 0.30 and 0.32, compared with the reference concrete, with the increase of age, the penetration resistance to chloride ions of concrete can be enhanced with the increasing substitution amount of silica fume, but the increased range is smaller. The penetration resistance of chloride ions of concrete is not necessarily improved by gradually decreasing the water-binder ratio. Considering the substitution amount of silica fume, water-binder ratio and concrete age, the best mix proportions are that the substitution amount of silica fume is 9% or 12% when the water-binder ratio is 0.28 and the substitution amount of silica fume is 12% when the water-binder ratio is 0.30.

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.

Properties of Reactive Powder Concrete Using Densified Silica Fume

This paper presents some experimental results on the physical and mechanical properties of reactive powder concrete (RPC) using two different characteristics of densified silica fume (f1 and f2). The silica fume/cement ratio (f/c) varied from 15% to 35% by weight. The flow, the micromorphology by scanning electron microscopy (SEM) and the compressive strength at the ages of 3, 7 and 28 days were studied. The effects of the silica fume agglomerations on the properties of the RPC were considered and discussed. The test results indicated that the properties of RPC depended on the type of silica fume, amount of silica fume and amount of superplasticizer used.

Enhanced effect of carbon nanotube on mechanical and electrical properties of cement composites by incorporation of silica fume

Utilization of silica fume in CNT/cement composites was recently proposed as a mean of improving the dispersion of CNTs and enhancing the interfacial interaction between CNTs and the hydration products. The present study focuses on the enhanced effect of CNTs on mechanical and electrical properties of cement composites by incorporation of silica fume. A qualitative analysis using SEM images was carried out to observe the surface morphology and microstructure of cement composites with different amounts of silica fume and CNT addition. The effects of silica fume addition on the porosity, compressive strength, and electrical resistance of the CNT/cement composites were then systematically investigated. It was found that the improved dispersion of CNTs by incorporation of silica fume might yield the enhancement of the mechanical and electrical properties of CNT/cement composites, whereas the CNT additions in cement composite without silica fume had an insignificant effect on the mechanical and electrical properties of the cement composites.

Influence of different curing temperatures on mechanical properties of alkali activated silica fume and fly ash based geopolymer

Alkali activated silica fume and fly ash based geopolymer (ASFG) were prepared through vibromoulding process, the optimum mix amount of silica fume and influence of different curing temperatures of room temperature (RT), 60, 80 and 210°C on the mechanical properties of ASFG were evaluated respectively. Results of mechanical properties shown silica fume could reinforce and toughen alkali activated fly ash based geopolymer, and the optimum additive amount of silica fume was 10 wt-% as the starting materials in various curing systems. The results of mercury intrusion porosimetry and scanning electron microscope showed that the smaller pore volume of ASFG decreased with increasing curing temperatures and formed amorphous porous network structure due to accelerated geopolymerisation; the weight loss decreased gradually and temperatures of weight loss improved with increasing curing temperatures derived from the increased content of bound water through the results of thermogravimetric analysis.

Performance of self-compacting concrete containing different mineral admixtures

Self-Compacting Concrete is an innovative concrete that does not require vibration for placing and compaction. It is able to flow under its own weight, completely filling formwork and achieving full compaction, even in the presence of congested reinforcement. One of the disadvantages of self-compacting concrete is its cost, associated with the use of high volumes of Portland cement and use of chemical admixtures. One alternative to reduce the cost of self-compacting concrete is the use of mineral admixtures such as silica fume, ground granulated blast furnace slag and fly ash, which is finely, divided materials added to concrete during mixture procedure. When these mineral admixtures replace a part of the Portland cement, the cost of self-compacting concrete will be reduced especially if the mineral admixtures are waste or industrial by-product. Moreover, the use of mineral admixtures in the production of self-compacting concrete not only provides economical benefits but also reduces heat of hydration. The incorporation of mineral admixtures also eliminates the need for viscosity-enhancing chemical admixtures. The lower water content of the concrete leads to higher durability, in addition to better mechanical integrity of the structure. This paper presents an experimental investigation on strength aspects like compressive, flexural and split tensile strength of self compacting concrete containing different mineral admixtures and workability tests for different mineral admixtures (slump, L-box, U-box and T50) are carried out. The methodology adopted is that mineral admixtures are replaced by 30%, 40% and 50% for Portland cement and performance is measured and compared. The influence of mineral admixtures on the workability, compressive strength, splitting tensile strength and flexural strength of self-compacting concrete was investigated. The mix proportion is obtained as per the guidelines given by European Federation of producers and contractors of special products for structure. The following inferences were made; optimum dosage of super plasticizer enhanced the flow property of the concrete. As a result, overall improvements in the flow and filling ability of the self-compacting concrete were observed. It is observed that when mineral admixtures used in self-compacting concrete, can reduce the amount of super-plasticizer necessary to achieve a given fluidity. It should be noted that the effect of mineral admixtures on admixture requirements is significantly dependent on their particle size distribution as well as particle shape and surface characteristics. From this view point, a cost effective self-compacting concrete design can be obtained by incorporating reasonable amounts of silica fume, fly ash, and ground granulated blast furnace slag.

Transport properties of high-performance cementitious composites incorporating micro and nano SiO2 into the binder

AbstractIn this paper, transport properties of high-performance self-compacting concrete (SCC), as one of the important cementitious composites incorporating micro and nano silica (NS) (SiO2) into the binder, have been investigated. For this purpose, different mixtures were designed with different amounts of silica fume (SF) and NS admixtures. Different binder contents were also investigated to observe the binder content effect on the concrete properties. Corrosion behavior was evaluated by chloride penetration and resistivity tests. Water absorption and capillary absorption were also measured as other durability related properties. The results showed that water absorption, capillary absorption, and Cl ion percentage decreased rather significantly in the mixtures containing admixtures especially the blend of SF and NS. By addition of the admixtures, resistivity of the SCC mixtures increased, which can lead to reduction of corrosion probability.

The assessment of carbonation effect on chloride diffusion in concrete based on artificial neural network model

In this paper the effect of carbonation on chloride diffusivity in concrete is investigated. An artificial neural network model was used to determine the relation between chloride diffusion coefficients and concrete mix design in carbonated and non-carbonated concretes. The models were trained by results of chloride profile experiments. Input parameters were water-to-binder ratios, the amount of silica fume, rapid chloride ion permeability test and capillary absorption coefficient. The output parameter was chloride diffusion coefficient. The neural network models are multi-layer perceptron models and they differ in the number of hidden layers and neurons.

Effect of Silica Fume on Durability of Wood Fiber Reinforced External Wall Board

In order to improve the durability of the wood fiber reinforced external wall board, silica fume, a kind of inorganic silica material was added in the board. The properties of the boards containing different amount of silica fume were studied. The durability was effectively characterized by determining the fracture work and bending strength after wetting-drying cycles test of the board. The results showed that the fracture work and bending strength of the board obviously increased when the proportion of silica fume and cement was 1:9~1:3.

Performance of high strength concretes at elevated temperatures

In this study, the effect of temperature on compressive strength, spalling and mass loss of High Strength Concretes (HSCs) by fc′>65 MPa is discussed. Average compressive strength of the HSCs was from 65 to 93 MPa, which was optimized by Taguchi’s method as a powerful tool for optimizing the performance characteristic of a product/process. This paper presents results of an experimental program on the effects of elevated temperature exposure on the mechanical properties and potential for explosive spalling of HSCs. Effects of four parameters; water to cement ratio (w/c), sand ratio, silica fume ratio and amount of silica fume (sf) addition are considered in tests. Mechanical properties of HSCs were measured by heating 150×300 mm cylinders at 20∘ C/min to temperatures of up to 800∘ C. The tests include sixteen mixtures; twelve contain sf and four are without sf that are selected by Taguchi’s method. The paper presents results of measurement that indicate the effect of sf, cement, fine aggregate, coarse aggregate and water on residual strength, spalling and mass loss of the HSCs. The presence of silica fume had no statistically significant effect on the relative compressive strength while it had an overall statistically significant effect on increasing spalling. The type of aggregate had a significant influence on the thermal properties of HSCs at elevated temperatures. In most cases, by increasing sand ratio, residual compressive strength increased while this trend is inversed for coarse aggregate.

Study of interfacial microstructure, fracture energy, compressive energy and debonding load of steel fiber-reinforced mortar

The properties of the interfacial transition zone (ITZ) of steel fiber and the bulk matrix were quantified using the backscattered electron imaging analysis (BSE-IA) and the scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX), and their relationship with the mechanical properties of steel fiber-reinforced mortars was studied. The water and binder ratio (w/b) of mortar, the amount of silica fume and steel fiber were varied. From the quantitative analysis, a higher build-up of calcium hydroxide was found from the steel fiber’s interface up to 2 or 4 μm distance away and its build-up was reduced with the 10% cement replacement by silica fume. Porosity in the ITZ and bulk matrix decreased the fracture energy, compressive energy and debonding load of steel fiber-reinforced mortar. However, its effect became marginal if a substantial amount of C–S–H or steel fibers appeared in the ITZ and bulk matrix, which increased the studied mechanical properties.