Increasing Silica Fume Content Research Articles

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.

Effects of silica fume on physicochemical properties and piezoresistivity of intelligent carbon black-cementitious composites

Carbon black (CB) filled cementitious composites as cement-based sensors with intrinsic piezoresistivity have the potential applications for structural health monitoring (SHM). Effect of silica fume (SF) replacement ratio on the physicochemical, mechanical and piezoresistive properties, and microstructure of CB-cementitious composite were experimentally investigated in this study. The results show that 5% or 10% replacement ratio of SF can improve the water impermeability, setting time and electrical conductivity, but decrease the fresh flowability. Cementitious composite with 10% SF exhibiteds excellent compressive and flexural strengths. Moreover, cement hydration in the acceleration stage decreased with the increase of SF content in the early stage, but the phase analysis after 28 days curing demonstrates that with the addition of SF, there are more hydrated products and less ettringite. In addition, the microstructures of cementitious composites without SF present more porous structures and CB agglomerations. In contrast, the amount of micropores or voids was significantly reduced by the addition of SF due to the physical filling effect and less CB agglomerations. In terms of piezoresistivity, SF can obviously improve the fractional changes of resistivity (FCR) under cyclic compression. With 10% SF, CB-cementitious composites as cement-based sensors exhibited excellent FCR and electrical stability, which will promote their development and application in the SHM for smart infrastructures.

Microstructure, Compressive Strength and Sound Insulation Property of Fly Ash-Based Geopolymeric Foams with Silica Fume as Foaming Agent

Geopolymer as an alternative to cement has gained increasing attention. The aim of this article is to study the influence of the silica fume content and activator type on the porous fly ash-based geopolymer with silica fume as foaming agent. Geopolymeric foams were fabricated using low-calcium fly ash, silica fume, and sodium-based alkaline activator as initial materials. The designed silica fume contents were 0, 15, 30, and 45 wt % and two kinds of activators of water glass and sodium hydroxide were used for comparison. Phase composition, microstructure, mechanical properties and sound insulation properties of as-prepared bulks were systematically investigated. It was found that, with increasing silica fume content, the density and compressive strength decreased simultaneously, whereas the porosity and sound insulation performance were effectively enhanced. At the silica fume content of 45% with sodium hydroxide as activator, the porosity was increased 3.02 times, and, at the silica fume content of 45% with water glass as activator, the mean sound insulation value of 43.74 dB was obtained.

Mechanical and fracture properties of ultra-high performance geopolymer concrete: Effects of steel fiber and silica fume

This study investigates the effects of steel fiber and silica fume on the mechanical and fracture properties of ultra-high performance geopolymer concrete (UHPGC). Four volume fractions of steel fiber (0%, 1%, 2% and 3%) and four contents of silica fume by the mass of total binders (5%, 10%, 20% and 30%) were used. The mechanical and fracture properties evaluated include the compressive, splitting tensile and ultimate flexural strengths, modulus of elasticity, flexural behavior, fracture energy and stress intensity factor. In addition, the correlations among the compressive and splitting tensile strengths, and compressive strength and elastic modulus were studied. The results indicated the increase of steel fiber dosage resulted in the decrease of the workability, but the continuous improvement of mechanical and fracture performance of UHPGC. The empirical equations for predicting elastic modulus of conventional ultra-high performance concrete overestimated the elastic modulus of UHPGC, however some prediction formulas for the splitting tensile strength of PC-based concretes could be applied for UHPGC. Silica fume had a complicated influence on workability and hardened properties of UHPGC, which is strongly dependent on its amount. The inclusion of 10% silica fume induced the increase of the flowability, but the sharp degradation of the mechanical performance, while the specimens with 20% and 30% silica fume possessed the superior mechanical characteristic to that with 5% silica fume. The steel fiber dosage could be decreased without sacrificing the mechanical and fracture performance of UHPGC, via the increase of silica fume content.

Effect of Curing on Micro-Physical Performance of Polypropylene Fiber Reinforced and Silica Fume stabilized Expansive Soil Under Freezing Thawing Cycles

This study presents the micro-physical investigation of polypropylene (PP) fiber-reinforced, and silica fume (SF) stabilized expansive soil (BC) subgrade. The coupling effect of soil, PP fiber, and SF has been evaluated under the freezing-thawing (F-T) cycle to assess the durability of treated BC Soil. The curing method and duration staggeringly influence the strength of SF treated BC soil; therefore, three different curing method, i.e., moisture-controlled curing (MC), gunny bag curing (GC), and water submerged curing (SC) to a period of 7, 14, and 28 days were considered. The BC soil has been reinforced with 0.25%, 0.50%, and 1.00% PP fiber and stabilized with 2%, 4%, 6% and 8% SF. The physical, chemical, and microstructural properties were determined before and after 2,4,6,8,10 F-T cycles. With the increase in SF content, the unconfined compressive strength of the expansive soil has been increased due to the formation of Calcium Silicate Hydrate (C-S-H) gel. The chemically inert, hydrophobic, non-corrosive nature, and higher tensile strength of PP fiber, it has a higher potential to reinforce the BC soil for durability under tensile failure. This research confirms the possibility of incorporating SF and PP Fiber in road work applications, with significant environmental benefits.

Fractal dimension of concrete incorporating silica fume and its correlations to pore structure, strength and permeability

In this study, we focused on the correlations among the fractal dimension, compressive strength, and permeability of concrete incorporating silica fume. The fractal dimension was calculated from SEM images by using a box-counting method, and the pore structure, compressive strength, and permeability were tested by mercury intrusion, compression and water penetration tests, respectively. Results show that increasing silica fume content improves compressive strength but decreases permeability and fractal dimension. The filling of available space, the promotion of heterogeneous nucleation of cement hydrates and the pozzonlanic reaction of silica fume itself, which densifies and homogenizes concrete microstructures, account for the effects of silica fume on the strength, permeability, and fractal dimensions of concrete. Compressive strength shows no appealing correlations with total porosity, but decreases as median pore size increases. Increasing meso porosity tends to strengthen concrete, whereas coarse pores are always harmful to compressive strength. The relationship between permeability and threshold pore size roughly follows the Katz-Thompson relation. Increasing fractal dimension can linearly depress compressive strength but nonlinearly promote permeability.

Development of cemented paste backfill based on the addition of three mineral additions using the mixture design modeling approach

Large-scale mining operations have produced large amounts of iron ore tailings (IOT) and stopes. IOT will cause air and water pollution, and open stopes may lead to surface subsidence or even geological disasters. Using cemented paste backfill (CPB) which is composed of IOT and binders to fill stopes can well solve the above two problems. Based on the alkali-activated theory, slag and desulfurized gypsum are selected as basic materials, cement (C), lime (L) and silica fume (SF) are chosen as mineral activators. Mixture design, an experimental design method, is used to model the effect of C, L, and SF on the spread, compressive strength and shrinkage ratio of CPB. The models are helpful to know the interaction between three mineral additions. Results show that the optimal spread is reached when the content of C and SF are 8% and 5%, respectively in C-SF binary system. The compressive strength at 3,7,28 days increase and then decrease with the increase of each admixture in L-SF and C-SF binary system. The maximum compressive strength at 28 days is 0.83 MPa, which can provide support for the adjacent mine structure and keep a stable working platform for miners. The shrinkage ratio decreases with the increase of SF content and increases with the increase of C content in C-SF binary system. However, in C-L binary system, the shrinkage ratio increases with the increase of L or C content. The minimum shrinkage ratio is 1.16% (corresponding to the proportion of 7% of C, 3% of L and 5% of SF). Finally, the morphology of hydration products at different ages are compared by scanning electron microscopy (SEM). The results show that the derived models are very effective in explaining the influence of three mineral admixtures on the workability and mechanical property of CPB. This design method is a useful tool to select the optimal mix proportions to achieve engineering objectives and reduce cost.

High‐ and Low‐Temperature Properties and Thermal Stability of Silica Fume/SBS Composite‐Modified Asphalt Mortar

Recently, China has started paying more attention to environmental protection, and the efficient utilization of exhaust gases produced by smelting has emerged as a key problem concern. The silica fume collected from the exhaust gases produced by smelting ferrosilicon or industrial silicon was often used as a cement concrete admixture. Using silica fume as an asphalt modifier can make exhaust gases profitable. In this study, silica fume/SBS composite‐modified asphalt mortar was prepared to improve the performance of asphalt. The effects of the silica fume content, temperature, and ratio of filler asphalt on the composite‐modified asphalt mortar were studied through the cone penetration, softening point, viscosity, dynamic shear rheological (DSR) test, and bending beam rheometer (BBR) test. The thermal stability of composite‐modified asphalt was analyzed through the thermal analysis test. The results showed that with the increase of silica fume content and ratio of filler asphalt, the high‐temperature performance of asphalt mortar was improved; the content of silica fume had a great influence on the low‐temperature performance of asphalt mortar, the optimum silica fume content was 7%; increasing the ratio of filler asphalt reduced the low‐temperature cracking resistance of asphalt mortar; the incorporation of silica fume enhanced the initial decomposition temperature, thermal residual rate, temperature in which the weight loss rate reaches the maximum, and the endothermic peak of maximum temperature and improved the properties of asphalt.

The Effect of Silica Fume on Engineering Properties of Collapsible Soil Present in Edfu- Aswan, Egypt.

In recent times the population of Egypt went to get out of the narrow valley on the banks of the river Nile to the reconstruction in desert zones, in which problematic soils appeared, among these types was the collapsible soil. The problematic soil has been given a great attention by geotechnical engineers and researchers. In general, all soils, which cause types of damages or difficulty in constructing new structures or utilizing existing structures, could be classified as problematic soils. The soil chosen in this research was extracted from a site in Edfu- Aswan, Egypt. These soils have caused many problems in this region and due to the development in water and sewage lines, which led to settlements and cracks in buildings. The main objective of this study is to investigate the effect of adding silica fume (SF) on the engineering properties of collapsible soils. Silica fume is a mineral composed of ultra – fine solid, amorphous glassy spheres of silicon dioxide (SiO2) obtained from the metallurgical industries company (E.J.S.C.) in Edfu. A series of laboratory experiments have been implemented on samples prepared with different percentage of SF 1%, 3%, 5%, 7%, and 9%. Test results show that the blend could diminish the collapse potential. Liquid limits and Plasticity Index would also decrease with the increasing the silica fume content. The unconfined compression strength increases from 1.57 to 2.37 kg / cm2 when mixing with SF ratios of 0 to 9%, prepared at optimum moisture content at zero days. The increase in the unconfined compression strength continued consistently for curing times of 7, 14, and 28 days. The increase in the unconfined compression strength is attributed to the internal friction of silica fume particles and chemical reaction between silica fume and soil. An increase in silica fume content in soil has made the stabilized soil samples more brittle than the natural soil samples, which is the ductile one as compared to all the stabilized samples. Their maximum dry density would increase from 1.92 to 2.02 gm/ cm3 at an SF ratio 0 to 9% and the corresponding optimum moisture content increased as well from 21.33% to 27.25%. The silica fume works as a filler material fills the voids in the soil matrix. Thus, - results indicated that by blending Silica Fume and collapsible soil together, the engineering properties of collapsible soils can be enhanced.

Mechanical properties of CFF/MC/SF composite prepared using vacuum infusion impregnation method

Carbon fiber felt (CFF)/microfine cement (MC)/silica fume (SF) composite was fabricated by using vacuum infusion impregnation method to infiltrate mechanically stirred mixing slurry of MC, SF, and water into CFF. MC, SF, and water were mixed, with a water-cement ratio of 0.5, SF was used to in place of MC in percentages of 0%, 5%, 10%, 15%, 20%, 25%, 30% and 35%. Drainage method was used to determine the density of CFF/MC/SF composite. The bending strength and compressive strength of CFF/MC/SF composite were characterized by universal testing machine. The microstructure of the fracture surface of CFF/MC/SF composite was studied by scanning electron microscopy. Toughening mechanism of CFF/MC/SF composite was also analyzed. The results show that the density and mechanical strength of CFF/MC/SF composites first increases and then decreases as SF content increases. Crack propagation process includes several toughening and reinforcing mechanisms, such as, fiber/matrix debonding, fiber bridging, fiber friction, crack deflection, and fiber pull-out. At 20% SF content, the compactness and mechanical strength of the CFF/MC/SF composite are optimum, with density, flexural strength, and compressive strength at 1.53g/cm3, 51.08MPa, and 53.56MPa, respectively.

Fracture behavior of fly ash concrete containing silica fume

Effect of silica fume on fresh properties, compressive strength at 28 days and fracture behavior of fly ash concrete composite were studied in this paper. Test results indicated that the fluidity and flowability of fly ash concrete composites decreased and fly ash concrete composite are more cohesive and appear to be sticky with the addition of silica fume. Addition of silica fume was very effective in improving the compressive strength at 28 days of fly ash concrete composite, and the compressive strength of fly ash concrete composite has a trend of increase with the increase of silica fume content. Results also indicated that all the fracture parameters of effective crack length, fracture toughness, fracture energy, the critical crack opening displacement and the maximum crack opening displacement of fly ash concrete composite decreased with the addition of silica fume. When the content of silica fume increased from 3% to 12%, these fracture parameters decreased gradually with the increase of silica fume content. Furthermore, silica fume had great effect on the relational curves of the three-point bending beam specimen. As the silica fume content increased from 3% to 12%, the areas surrounded by the three relational curves and the axes were becoming smaller and smaller, which indicated that the capability of concrete composite containing fly ash to resist crack propagation was becoming weaker and weaker.

Preparation and Properties of High-Performance Concrete with Ceramic Coarse Aggregate

High-performance concrete was prepared by using ceramic waste as coarse aggregate. The influences of several factors, such as the contents of ceramic coarse aggregates, fly ashes and silica fumes, on the properties of concrete material were investigated. The results show that the compressive strength of semi-porcelain coarse aggregate concrete are slightly lower than that of natural concrete, and the splitting tensile strength and the ratio of compressive strength and splitting tensile strength is similar to the ones of natural concrete. After fly ash and silica fume mixed, the compressive strength, the splitting tensile strength and the resistance to water penetration of concrete with semi-porcelain coarse aggregate increase significantly with the increase of silica fume content which meet the requirements of high-performance concrete. Concrete with orcelain coarse aggregate is only suitable for low strength concrete.

Effect of elevated temperature on the properties of silica fume and recycled rubber-filled high strength concretes (RHSC)

This paper presents the influence of temperature on the compressive strength of HSC with silica fume and containing different ratios and sizes of recycled tire rubber. The aims of including elastomeric material in a cementitious matrix are reducing the stiffness of HSC in order to make it compatible with other materials of the building, recycling of solid wastes and improving fire resistance.The inclusion of low mass fraction recycled rubber reduces the high risk of explosive spalling of HSC under high temperature because water vapour can exit through channels where the polymeric material gets burned.Two groups of concrete were employed to carry out this study. The first group consists of four mixes produced with a cement content of 500kg, 0.3 water–binder ratio, gravel as coarse aggregate and 0%, 10%, 15%, and 20% silica fume (SF) replaced of cement weight. The concrete formulation of the second group (four mixes) was produced with the replacement of cement by 20% SF along with 0%, 3%, 5% recycled fine rubber (2mm) and 3% coarse rubber (5mm). Dolomite as a coarse aggregate was used in the second group in order to improve the performance of concrete mixtures containing rubber under high temperature.The results obtained show high resistance to fire with increasing SF content up to 20% replacement of cement. Additional improvement was obtained with using dolomite and 3% of recycled rubber (2mm, 5mm).

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.

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 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.

Thermogravimetry of ternary cement blends

This study reports the microstructure characteristic and compressive strength of multi-blended cement under different curing methods. Fly ash, ground bottom ash, and undensified silica fume were used to replace part of cement at 50 % by mass. Mortar and paste specimens were cured in air at ambient temperature, water at 25, 40, and 60 °C and sealed with plastic sheeting for 28 days. In addition, these specimens were cured in an autoclave for 6, 9, and 12 h. Results indicated that the compressive strength of multi-blended mixes containing silica fume 10 % by mass cured with plastic sealed and cured in water at 25 and 40 °C was similar to or higher than the corresponding Portland cement control at 28 day. Moreover, the mixes containing silica fume 10 % by mass cured in water at 60 °C had higher compressive strength than Portland cement control. X-ray diffraction and thermogravimetry results confirmed that there was increased pozzolanic reaction with increasing silica fume content which relates to the increasing in strength. For autoclaved curing, the compressive strength of multi-blended cement specimens with silica fume (total of 50 % replacement) was noticeably higher than control Portland cement mix and was highest when autoclaving time was 9 h. X-ray diffraction results showed the pattern of 0.9, 1.1, and 1.4 nm tobermorite crystalline phases as the main product of this curing. Thermogravimetry results showed dehydration of 1.4 nm tobermorite and 1.1 nm tobermorite at about 80–90 and 135–150 °C, respectively. Tobermorite (also shown by scanning electron microscope) thereby as a result lead to significant compressive strength improvement in the short time of autoclaved curing.

Compressive Strength of Blended Portland Cement Mortars Incorporating Fly Ash and Silica Fume at High Volume Replacement

Fly ash has been widely used as a replacement of Portland cement at high content levels, but the compressive strength of Portland cement blended with fly ash is lower at early ages. Thus, this study compares the compressive strength of ternary blended Portland cement mortars incorporating fly ash (40-70 wt%) and silica fume (5-10 wt%) with binary blended Portland cement mortars incorporating fly ash only. Blended Portland cement mortars were designed with a constant water/binder ratio of 0.485 and the flow table tested was carried out. A fine aggregate to binder ratio of 2.75 was used. The compressive strength of all blended Portland cement mortars that cured in water at 23 °C was tested at 28 days. The results show that the flow of blended Portland cement mortars increased with increasing fly ash content and tended to decrease with increasing silica fume content, at the same replacement level. Moreover, the compressive strength of blended Portland cement mortars decreased with increasing fly ash content. However, compressive strength gains were obtained from ternary blended Portland cement mortars incorporating silica fume, tending to increase with increasing silica fume content.

Fracture Properties of High Performance Concrete Containing Silica Fume

A parametric experimental study has been conducted to investigate the effect of silica fume on the fracture properties of high performance concrete (HPC), with five silica fume contents (1.5%, 3%, 6%, 9% and 12%) used. The results indicate that the addition of silica fume has greatly improved the fracture parameters of HPC, such as fracture toughness, fracture energy, effective crack length, the maximum mid-span deflection, the critical crack opening displacement and the maximum crack opening displacement of concrete. The fracture parameters of HPC containing silica fume are increasing gradually with the increase of silica fume content when the silica fume content increases from 0% to 3%, while, the fracture parameters begin to decrease after the silica fume content increases beyond 3%. However, the values of the fracture parameters of HPC with the silica fume content below 12% are still higher than that of the concrete without silica fume. It seems a small content of silica fume has an advantage of improvement of the fracture properties of HPC, while an overlarge silica fume content may adversely affect the fracture properties of HPC.

Fracture properties of high performance concrete containing silica fume

A parametric experimental study has been conducted to investigate the effect of silica fume on the fracture properties of high performance concrete (HPC), with five silica fume contents (1.5%, 3%, 6%, 9% and 12%) used. The results indicate that the addition of silica fume has greatly improved the fracture parameters of HPC, such as fracture toughness, fracture energy, effective crack length, the maximum mid-span deflection, the critical crack opening displacement and the maximum crack opening displacement of concrete. The fracture parameters of HPC containing silica fume are increasing gradually with the increase of silica fume content when the silica fume content increases from 0% to 3%, while, the fracture parameters begin to decrease after the silica fume content increases beyond 3%. However, the values of the fracture parameters of HPC with the silica fume content below 12% are still higher than that of the concrete without silica fume. It seems a small content of silica fume has an advantage of improvement of the fracture properties of HPC, while an overlarge silica fume content may adversely affect the fracture properties of HPC.