Increasing Silica Fume Content Research Articles

Hydration kinetics and apparent activation energy of cement pastes containing high silica fume content at lower curing temperature

To promote the application of silica fume (SF) in civil engineering in cold regions, relative influences from SF content and low temperature environment on the early hydration kinetics of composite cement pastes were evaluated based on the isothermal calorimetric method. The effect of high SF content on the apparent activation energy (Ea) of Portland cement and the filler effect (via the index of area multiplier) of SF on the hydration parameters was also analyzed. The results showed that the intensity of the shoulder peak (Al peak) of the hydration kinetic curve (heat flow curve) gradually grew as the SF content increased, and the double-peak phenomenon was gradually clear. The heat flow peak is delayed and lowered with the decreasing curing temperature, while the final time of the induction stage and the duration of the acceleration stage are delayed. Moreover, the duration of the acceleration stage was slightly extended with the increase of SF content. The full-width at half-maximum (FWHM) value of the heat flow curves dropped as the SF content and curing temperature increased. The low temperature environment and the inclusion of SF inhibited the growth in early hydration degree. The higher SF content mitigated the impact of low temperature on the hydration time parameter τ. The apparent Ea results also indicated that the SF reduced the temperature sensitivity of the hydration process of the composite cement pastes, which might contribute to the development of the hydration reaction at low temperatures. The AM (Area Multiplier) factor increased approximately linearly with increasing SF replacement levels. Apparent Ea decreased linearly with increasing AM, which may be attributed to a further reduction in the diffusion-controlled hydration rate of composite cement pastes with larger AM.

Effect of silica fume on the performance of high-early-strength UHPC prepared with magnesium ammonium phosphate cement

Although ultra-high performance concrete (UHPC) prepared from Portland cement has high long-term strength and durability, its early strength development is still can be enhanced for shortening the prefabrication period or using it as a rapid repair material. Therefore, magnesium ammonium phosphate cement ultra-high performance concrete (MAPC-UHPC) was prepared using magnesium ammonium phosphate cement (MAPC), sand, steel fiber, and silica fume (SF) in this study. The effects of replacing MAPC with SF (5%–15%) on the fluidity, strength, and microstructure of MAPC-UHPC were studied. The results showed that the spread diameter of the MAPC-UHPC mixture was greater than 200 mm, and the setting time was between 5.5 and 8.5 min. Meanwhile, the 6-h compressive strength of MAPC-UHPC was higher than 100 MPa and could reach about 140 MPa in 28 d. When the 5%–15% binder was replaced by SF, the MAPC-UHPC fluidity and setting time increased with the increase in SF content. When 5% SF was used, the 6-h and 28-d compressive strengths of MAPC-UHPC increased by 3.91% and 3.86%, respectively, compared with the plain sample. The addition of SF promoted the formation of struvite and refined the pore structure, which also increased the compactness of the microstructure.

IMPROVING THE ENGINEERING PROPERTIES OF CLAYEY SOIL USING SILICA FUME AND SISAL FIBER

Building on soft soils continues to be a challenge for civil engineers in the modern world, despite the rapid development of infrastructure projects and advancements in construction technology. They exhibit a large volumetric change upon contact with water, which is the cause of their limited bearing capacity. Various stabilization strategies can be used to handle the soft clay's shear strength issue. In this experiment, sisal fibers and silica fumes were added in different amounts to the clay soil in order to determine the ideal moisture content and strength parameters for reaching the maximum dry density of the soil. By adjusting the amount of sisal fiber for each amount of silica fume, the Unconfined Compressive Strength (UCS) test has been used to examine the strength of both natural clay and clay modified with silica fume (6%, 12%, 18%) and sisal fibers (0.5%, 1.0%, 1.5%) separately, as well as the combination of all the materials. Using a small compaction device, standard proctor test was used to determine the ideal moisture content and maximum dry density. According to the test results, the maximum dry density falls with increasing silica fume content likewise, the maximum dry density increases with increasing sisal fiber content. The addition of 12% silica fume and 2.0% sisal fiber to the clay sample results in a maximum strength when taking the strength parameter into account. Key Words: Compaction test, CBR, UCS, Silica fume, Sisal Fiber

Piezoresistive response of geopolymer pastes activated by silica fume-derived alkaline solution

This study examined the self-sensing performance of metakaolin-based geopolymer paste samples activated by an alkali activator, which is a solution mixture of potassium hydroxide and silica fume (SF). Their piezoresistive response under repeated compressive loads was found to improve with increasing SF content. It was found from their XRD, SEM, and FTIR results that the change in the SF content did not alter the phase composition of the geopolymer matrices. The factorial change in the electrical resistivity of geopolymer samples with a maximum SF content was calculated to be about 0.024. Their pore solutions were detected to be mainly filled with potassium and silicon ions due to the use of higher concentrations of SF particles. The UV spectrophotometry measurements of this study confirm that all the geopolymer samples displayed semiconductor behaviour. The SF-derived alkaline activator can enable the self-sensing character of geopolymer-based concrete, which isenvironmentally friendly and has recently shown great potential to monitor structural integrity under applied external loads.

High strength rubberized porous concrete for sustainable pavements: Engineering properties and life cycle assessment

This study investigates the performance of Pervious Concrete (PC) with varying quantities of Natural Coarse Aggregate (NCA) replaced by Waste Tire Rubber (WTR) (5%, 10% and 15% by weight) whereas Silica Fume (SF) (5%, 10% and 15%) and Fly Ash (FA) (10% constant) were employed as substitute for cement. This research aims at optimizing the mix of High Strength Rubberized Pervious Concrete (HSRPC) using Supplementary Cementitious Materials (SCMs), comparing experimental stress-strain graphs with the developed constitutive models and conducting a Life Cycle Assessment (LCA). Physical and mechanical performance of PC were examined using permeability and strength indices. X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) observed microstructural variations and Interfacial Transition Zone (ITZ) development. The use of WTR increased the permeability and decreased the strength indices. The permeability of mixes with 5, 10 and 15% WTR was found to be 4.00, 4.21 and 4.49 mm/s, which were more than control mix permeability. The compressive strength of PC with 5%, 10%, and 15% WTR was determined to be 32.48, 29.29, and 26.94 MPa, respectively, which were lower than control PC compressive strength which was 35.41 MPa. However, the addition of SF and FA enhanced the mechanical properties while causing a decrease in the permeability. Increasing SF content from 0% to 15% enhanced the compressive strength of PC containing 5% WTR, from 32.48 to 40.71 MPa. Developed constitutive models compared the stress-strain response of PC. Life cycle assessment showed that WTR, SF, and FA-based PC reduced the global warming.

Experimental study and simulation of workability and compressive performance of SCC with high-volume mineral admixtures

Using industrial waste such as fly ash and silica fume to substitute most of the cement to prepare self-compacting concrete can not only greatly reduce the cement consumption, but also improve the resource utilization of solid waste powder, which is conducive to cost reduction and environmental protection. In this paper, the fly ash (FA) and silica fume (SF) replacement ratio of 40%, 50% and 60% was adopted to produce self-compacting concrete with high-volume mineral admixtures (HVMA-SCC). The slump flow test, L-box test and compression test were conducted, and the effect of different high replacement ratio on the workability, compressive performance and stress–strain relationship of HVMA-SCC were analyzed. The experimental results showed that when the total content of mineral admixtures was the same, an increase in SF content was beneficial for the development of early compressive strength. Under the same SF dosage, the larger the FA dosage, the faster the strength development rate, which was conducive to the sustained growth of HVMA-SCC strength in the later stage. Moreover, a stress–strain calculation model of HVMA-SCC was proposed based on damage theory. Besides, the workability and compression tests were simulated with the discrete element method (DEM). The results showed that the simulated stress–strain curves were in good agreement with experimental curves, and the mesoscopic failure characteristics of HVMA-SCC were analyzed from the development of cracks, stress conditions, and failure modes.

Effects of incorporating polynary SCMs on sulfate resistance and chloride impermeability of concrete considering capillary action in dry-wet cycling environment

The incorporation of supplementary cementitious materials (SCMs) in concrete can improve the properties of concrete partially immersed in salt solution. However, the current partial immersion environment only considers the capillary action above the still water level, does not consider the capillary action above the fluctuating water level in dry-wet cycling environment. In this paper, a series ofindoor exposure experiments were carried out to investigate the effects of incorporating polynary SCMs including fly ash (FA), ground granulated blast furnace slag (GGBFS) and silica fume (SF) on the sulfate resistance and chloride impermeability of concrete considering the capillary action above the fluctuating water level in dry-wet cycling environment. A total of 15 groups of concrete with different mix proportions (total 150 concrete specimens) were designed to study the effects of different replacement levels of polynary SCMs on concrete properties. The effects of incorporating polynary SCMs on the chloride impermeability of concrete above and in the fluctuating water level zone were investigated. The scanning electron microscope (SEM), x-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) tests were used to analyze the microstructure of concrete. The results indicate that when concrete is incorporated with polynary SCMs and subjected to capillary action above the fluctuating water level, the compressive strength and chloride impermeability first increase and then decrease with the increase of FA content; the compressive strength and chloride impermeability decrease with the increase of GGBFS content; the compressive strength first increase and then decrease with the increase of SF content, and the chloride impermeability increase with that. The transport process of chloride in concrete above the fluctuating water level zone includes the longitudinal transport under capillary action and the transverse transport under concentration gradient action. The combined effects of both cause the higher chloride concentration in concrete above the fluctuating water level zone. Comprehensively considering the influence of different mix proportions on the sulfate resistance and chloride impermeability of concrete, it is determined that 20% FA + 5% SF is the optimal replacement level with the excellent performance considering the capillary action above the fluctuating water level in dry-wet cycling environment.

Enhancing Concrete Properties Using Silica Fume: Optimized Mix Design

In the current work, concrete mixes containing (7.0-33.11) weight % silica fume as a partial replacement of cement with a water /cement ratio (0.42-0.48) were prepared according to an adopted two factorial central composite design. The samples were tested, optimized, and modeled for compressive strength and density. The estimated results confirmed that compressive strength and density increase with increasing silica fume content up to 11.9 wt.%. Response surface analysis results confirmed that silica fume concrete with developed compressive strength (53.42 MPa) could be prepared by incorporation of 11.9 wt. % silica fume as partial replacement of cement using 0.42 water/cement ratio. An increase in compressive strength and density (up to 39.3% and 2.6% ) respectively was recorded for silica fume concrete mixes compared to Portland cement concrete. Overall, the research findings revealed that silica fume concretes prepared with appropriate silica fume content and water/cement ratio exhibited superior strength and density characteristics candidate them to be used effectively in civil engineering applications.

Role of silica fume in alkali-activated slag/glass powder paste

The influences of silica fume (SF) on the properties of sodium silicate-based alkali-activated slag/glass powder (AASG) pastes were systematically investigated. Evaluation of fresh properties (including setting time, flow spread, and rheological behavior) and compressive strength of AASG pastes were carried out. Dispersion properties of the precursors in the alkali solution were observed to explain the rheological behavior. The heat evolutions and microstructural properties of AASG pastes were evaluated to understand the mechanism of setting time developments and compressive strength, respectively. The test results showed that the use of SF prolonged the setting time of AASG pastes and different sources of SF, of which the pH values were different, had different influences. Incorporating SF can significantly increase the yield stress of the fresh AASG paste and its plastic viscosity at a low shear rate (<10 s−1), while decreasing its plastic viscosity at a high shear rate (>20 s−1). The compressive strength of AASG paste increased first and then decreased with the increase of SF content, and the optimal SF content was about 10%. The increase in compressive strength was due to the filling and nucleation effect of SF and the formation of additional C-(N)-A–S–H gel with a lower Ca/Si ratio, which resulted in a reduced amount of large capillary pores (100 nm to 1000 nm) and increased amount of small capillary pores (10 nm to 100 nm). When too much SF (>15%) was incorporated in AASG paste, it increased the amount of large capillary pores, leading to reduced strength.

Influences of Silica Fume on Compressive Strength and Chemical Resistances of High Calcium Fly Ash-Based Alkali-Activated Mortar

Although elevated temperature curing can increase the compressive strength of alkali-activated mortar, its field applications are still limited. In this study, alkali-activated mortars were prepared using high calcium fly ash (FA) as a precursor. Small amounts of silica fume were used to partially replace high calcium fly ash at 3–9% by weight to increase the strength of alkali-activated mortar. All mixtures had a liquid to binder ratio of 0.60 and sand to binder ratio of 2.75 by weight. A ratio of NaOH to Na2SiO3 solution was kept at 2:1 by weight. Mortar flow was also held between 105–115 using a superplasticizer. Compressive strength and durability were investigated in terms of acid and sulfate resistance. The effects of silica fume addition and curing temperature on compressive strength were found to be significant. The optimum content of silica fume was 6%, providing compressive strength as high as that of alkali-activated mortars cured at 45 °C. The weight loss of alkali-activated mortar due to sulfuric acid attack decreased with increasing silica fume content and curing temperature. All alkali-activated mortars were found to have a better performance than (ordinary) Portland cement (OPC) mortars and mortars containing 40% FA. Alkali-activated mortars immersed in magnesium sulfate solutions had compressive strength that decreased with an increase in curing temperature. The expansion of alkali-activated mortar due to sodium sulfate attack increased with increasing silica fume content, and the expansion decreased with increased curing temperature. All alkali-activated mortars performed better than OPC mortars after 98 days of sulfate attack.

Effect of Silica Fume on the Rheological Properties of Cement Paste with Ultra-Low Water Binder Ratio

The effect of silica fume on the rheological properties of a cement–silica fume–high range water reducer–water mixture with ultra-low water binder ratio (CSHWM) was studied. The results indicate that the W/B ratio and silica fume content have different effects on the rheological parameters, including the yield stress, plastic viscosity, and hysteresis loop area. The shear-thickening influence of CSHWM decreased with the increased silica fume content. When the silica fume content increased from 0% to 35%, the mixture with W/B ratio of 0.19 and 0.23 changed from a dilatant fluid to a Newtonian fluid, and then to a pseudoplastic fluid. When the silica fume content was less than 15%, the yield stress was close to 0. With the increase of silica fume content, the yield stress increased rapidly. The plastic viscosity and hysteresis loop area decreased slightly with the addition of a small amount of silica fume, but increased significantly with the continuous increase of silica fume. Compared with the Bingham and modified Bingham models, the Herschel–Buckley model is more applicable for this CSHWM.

Effect of silica fume and basalt fibers on the fracture parameters of magnesium phosphate cement incorporating fly ash

Magnesium phosphate cements are implemented for several purposes demonstrating significant mechanical properties in limited durations. However, brittle behavior of this material needs utmost concern and tensile performance may be enhanced with the proper application of fibers increasing both ductility and energy absorption capacity. This research studies the effect of basalt fibers (BF) and silica fume (SF) on the fracture parameters of magnesium phosphate cement (MPC). MPC mortar mixtures were prepared with different SF (0, 5, 10%) and BF amounts (0, 0.5, 0.75, 1 % by wt.). Also fly ash was adopted with a constant ratio for all mixes. Compressive strength and splitting tensile strength results indicated that addition of SF into mixtures extensively developed the matrix structure and improvements were noted with the increasing SF content. The inclusion of BF enhanced the flexural behavior although there were significant improvements in the fracture energy as well as the double-K parameters. Improvements in the tensile capacity of specimens with high BF were prone to the amount of SF percentage such that inclusion of 1 % BF performed best with 10 % SF added mixtures. Load-CMOD (crack mouth opening displacement) curves obtained from notched three-point tests were given for all specimen series and parameters were calculated according to the double-K criterion. Addition of BF resulted in higher toughness values however presence of SF was very significant in establishing appreciable development in toughness values. Brittleness index was implemented to establish clear conclusions on the findings and best performance was seen for specimens with 10% SF and 1% BF.

The potential application of cement kiln dust-red clay brick waste-silica fume composites as unfired building bricks with outstanding properties and high ability to CO2-capture

In this paper, a simple eco-sustainable approach was applied to synthesize unfired building bricks, in which cement kiln dust (CKD), red clay brick waste (RCBW), and silica fume (SF) were the main ingredients. The CKD-RCBW-SF composite was adjusted at different weight ratios of 50-50-0, 50-40-10, 50-30-20, and 50-20-30 wt%. The fabrication process included three main stages, i.e. dry blending, water mixing, and casting. Different curing conditions were applied (water, air, and CO2-gas) to assess the effect of curing type on the performance of the prepared bricks. The results demonstrated that increasing SF content caused an increase in compressive strength escorted by a significant decrease in bulk density of the hardened bricks, regardless of curing type. All over of the curing media, the hardened samples cured in water showed the highest performance. The highest 28-days compressive strength value (47 MPa) was achieved by hardened CKD-RCBW-SF composite (at a weight ratio of 50-20-30 wt%, respectively) cured in water. Unlike its effect on the physical and mechanical performances, increasing SF content negatively influenced the capability of the hardened bricks to CO2-sequestration. Specifically, the hardened bricks with no SF cured in CO2 gas for 28-days can sequestrate higher CO2 content (~75 kg/ton) compared to the hardened samples containing 30 wt% SF (~59 kg/tonne). The proposed method is not only considered as an innovative approach for mitigating CO2 emission resulted from the traditional bricks industry, but also strongly contributed to waste disposal, the conservation of the reserve of natural materials, the decrease of energy demand and processing cost, and the enhancement of the ability of the hardened bricks to CO2-capture.

A Rheological Model for Evaluating the Behavior of Shear Thickening of Highly Flowable Mortar.

Neither the modified Bingham model nor the Herschel–Bulkley model can be used to characterize and calculate the performance of shear thickening of highly flowable mortar because of their incalculability of the rheological parameters. A new exponential rheological model was established to solve the characterization and calculation of shear thickening of the lubrication layer (highly flowable mortar) during the pumping of concrete in this paper. This new exponential rheological model has three rheological parameters, namely, yield stress, consistency coefficient, and consistency exponent. They can quantitatively describe the yield stress, differential viscosity, and shear thickening degree of highly flowable mortar. The calculating results of the rheological parameters of the newly established model for the mortars with different compositions showed that the consistency exponent of mortar decreased with the increase of its sand-binder ratio or the dosage of fly ash in the binder. This indicates that the shear thickening degree of mortar decreases. The consistency exponent of mortar initially decreases and subsequently increases with the increase in silica fume content or the dosage of the superplasticizer. It illustrates that the degree of the shear thickening of mortar initially decreased and subsequently increased. These varying patterns were confirmed by the rheological experiment of mortars.

Micromechanical Properties of Steel-Fiber-Reinforced Cementitious Composites Characterized with Nanoindentation

The micromechanical properties of the steel-fiber-reinforced cementitious composites with different water-binder ratios and silica fume contents were studied by nanoindentation. The elastic modulus, indentation hardness, total input energy, and ratio of the elastic deformation energy to the total input energy were analyzed in the interfacial transition zone (ITZ) and the cement matrix. The results show that with the reduction of water-binder ratio in the range of 0.18–0.24, the elastic modulus, indentation hardness, elastic deformation capacity, and energy dissipation capacity increased in the ITZ and cement matrix, and the increase of the ITZ was greater than that of the matrix, yet the ITZ did not disappear. With the increase of silica fume content in the range of 0–30%, the weak ITZ was gradually strengthened or even disappeared. In terms of obtaining the stronger ITZ, adding silica fume is more effective than reducing the water-binder ratio. When the water-binder ratio was high at 0.24, large silica fume contents (30%) had significant effects on enhancing the micromechanical properties of the ITZ and matrix. At a low water-binder ratio of 0.18, large silica fume contents (30%) enhanced the micromechanical properties of the ITZ while degrading those of the cement matrix.

Investigation of moisture transport in cement-based materials using low-field nuclear magnetic resonance imaging

Moisture transport has a great impact on concrete durability. In this study, a hard-pulse one-dimensional frequency coding sequence of low-field nuclear magnetic resonance (LF-NMR) imaging was applied to investigate moisture transport in cement-based materials (CBMs) considering the influences of the water/binder (w/b) ratio, sand/cement (s/c) ratio and contents of silica fume (SF) and super-absorbent polymer (SAP). A weighing method was also applied and the results were compared with the LF-NMR imaging measurements. The results showed that the moisture distribution curves can be divided into three stages by height. In addition, it was found that the moisture absorption height (h) increased with time and the growth rate of water absorption proceeded from fast to slow. Additionally, as the w/b ratio of the sample was increased, h increased. The value of h decreased with increasing s/c ratio and increased with an increase in SF content. When SAP was mixed into the CBMs, the values of h increased with 0·15% SAP addition but decreased with the addition of 0·30% SAP. The LF-NMR imaging measurements were in agreement with the results of the weighing method.

Influence of Silica Fume on the Performance of Moderately Weathered Phonolite Concrete

The effect of silica fume on the performance, mechanical properties, durability and air tightness of airtight concrete was studied. The results showed that with the increase of silica fume content, the concrete performance will decrease, the compressive strength of airtight concrete will increase first, and reach the highest when the silica fume content was 8%, and then it will decrease gradually. With the increase of silica fume content, the corrosion resistance coefficient of concrete increased gradually, then decreased. The permeability coefficient of concrete decreases with the increase of silica fume content, and the air tightness of concrete was improved obviously; In the project, it was advisable to use silica fume to prepare airtight concrete, and the amount of silica fume should be controlled at 4% - 8%.

Influence of Silica Fume Content on Performance of High - Performance Concrete

The influence of different silica fume content on the slump, expansion, compressive strength and flexural strength of high-performance concrete was studied. The results show that with the increase of silica fume content, the slump, expansion, compressive strength, and flexural strength of high-performance concrete show a trend of increasing first and then decreasing. The optimal silica fume content of HPC(Highperformance concrete) is 3% to 6%.

Properties and microstructure of basic magnesium sulfate cement: Influence of silica fume

Silica fume (SF) as an important supplementary cementitious material has been widely used in Portland cement, but few published articles have reported on the effect of SF on the performance and hydration mechanism of basic magnesium sulfate cement (BMSC). In the present work, the properties, microstructure and hydration mechanism of BMSC influenced by SF was studied systematically. The results show that the setting time and compressive strength of BMSC may increase with the increase of SF content, while the hydration heat will decrease with the increase of SF content. Mercury intrusion porosimetry (MIP), X-ray computed tomography (X-CT), scanning electron microscope- Energy dispersive spectrometer (SEM-EDS) results show that SF exhibits filling effect in the BMSC matrix, which makes the microstructure of BMSC matrix with SF more compact. In addition, solid-state magnetic resonance (NMR) and SEM-EDS analysis indicate that the activity of SF was excited in the BMSC matrix, resulting in the formation of M−S−H gel.

Fresh, strength and microstructure properties of geopolymer concrete incorporating lime and silica fume as replacement of fly ash

The need to cure fly ash-based geopolymer at elevated temperatures has limited the practicability and sustainability of the composite. Hence, there is an imminent need to find ways at which fly ash-based geopolymers can be cured at ambient conditions. This paper presents the results from the experimental investigation of the effect of lime and silica fume on the properties of geopolymer concrete cured at ambient conditions. Lime and silica fume were used as the partial replacement of fly ash as an aluminosilicate precursor and the corresponding effects on the fresh, strength and microstructure of the geopolymer concrete were investigated. The findings from this study showed that the slump and setting times of the geopolymer concrete increases with increasing silica fume content and reduces with increasing lime content. Also, the use of lime and silica fume as 7.5% and 2% respectively, replacement of fly ash yielded the highest compressive strength. Microstructural investigation showed that the combined use of lime as silica fume in GPC resulted in a densified microstructure.