Silica Fume Applications & Benefits
Concrete:
High Performance Concrete (HPC) containing silica fume has been identified as one of the most important advanced materials necessary in the effort to rebuild the nation's infrastructure. In addition to increased strength and enhanced durability, HPC produced with silica fume delivers increased toughness, increased resistance to abrasion, corrosion and chemicals, sustainability and life-cycle cost efficiencies.
Highway bridges, parking decks, marine structures and bridge deck overlays are subject to constant deterioration caused by rebar corrosion current, abrasion and chemical attack. Silica fume will protect concrete against deicing salts, seawater, traffic and heavy impact. Rebar corrosion activity and concrete deterioration are virtually eliminated, which minimizes maintenance expense. Key benefits include:
High-strength concrete enhanced with silica fume provides architects and engineers with greater design flexibility. Traditionally used in high-rise buildings for the benefit of smaller columns (increasing usable space) high-strength concrete containing silica fume is often used in precast and prestressed girders allowing longer spans in structural bridge designs.
Key advantages include:
High Performance Concrete (HPC) containing silica fume has been identified as one of the most important advanced materials necessary in the effort to rebuild the nation's infrastructure. In addition to increased strength and enhanced durability, HPC produced with silica fume delivers increased toughness, increased resistance to abrasion, corrosion and chemicals, sustainability and life-cycle cost efficiencies.
Highway bridges, parking decks, marine structures and bridge deck overlays are subject to constant deterioration caused by rebar corrosion current, abrasion and chemical attack. Silica fume will protect concrete against deicing salts, seawater, traffic and heavy impact. Rebar corrosion activity and concrete deterioration are virtually eliminated, which minimizes maintenance expense. Key benefits include:
- Very low permeability to chloride and water intrusion
- Extremely high electrical resistivity (20 to 100 times greater than ordinary concrete)
- Increased abrasion and impact resistance on decks, floors, overlays and vertical structures
- Superior resistance to chemical attack from chlorides, acids, nitrates and sulfates
High-strength concrete enhanced with silica fume provides architects and engineers with greater design flexibility. Traditionally used in high-rise buildings for the benefit of smaller columns (increasing usable space) high-strength concrete containing silica fume is often used in precast and prestressed girders allowing longer spans in structural bridge designs.
Key advantages include:
- Compressive strengths up to 20,000 psi (140 Mpa)
- High modulus of elasticity exceeding 7 million psi (40,000 Mpa)
- High flexural strengths up to 2,000 psi (14 MPa)
- High early strengths for fast-track construction projects and precast applications
Shotcrete
Silica-fume Shotcrete delivers greater economy, greater time savings and more efficient use of sprayed concrete. Silica fume produces superior shotcrete for use in rock stabilization, mine tunnel linings, and rehabilitation of deteriorating bridge and marine columns and piles. Greater bonding strength assures outstanding performance of both wet and dry process shotcreting with less rebound loss and thicker applications with each pass of the shotcrete nozzle. Some performance characteristics are:
Silica-fume Shotcrete delivers greater economy, greater time savings and more efficient use of sprayed concrete. Silica fume produces superior shotcrete for use in rock stabilization, mine tunnel linings, and rehabilitation of deteriorating bridge and marine columns and piles. Greater bonding strength assures outstanding performance of both wet and dry process shotcreting with less rebound loss and thicker applications with each pass of the shotcrete nozzle. Some performance characteristics are:
- Reduction of rebound loss up to 50%
- Improved production time, with one-pass application thicknesses up to 12 inches
- Higher bonding strength
- High electrical resistivity and low permeability
- High compressive and flexural strengths
Oil Well Grouting
Whether used for primary (placement of grout as a hydraulic seal in the wellbore) or secondary applications (remedial operations including leak repairs, splits, closing of depleted zones), the addition of silica fume enables a well to achieve full production potential. Besides producing a blocking effect in the oil well grout that prevents gas migration, it provides these advantages:
Whether used for primary (placement of grout as a hydraulic seal in the wellbore) or secondary applications (remedial operations including leak repairs, splits, closing of depleted zones), the addition of silica fume enables a well to achieve full production potential. Besides producing a blocking effect in the oil well grout that prevents gas migration, it provides these advantages:
- Improved flow, for easier, more effective application
- Dramatically decrease permeability, for better control of gas leakage
- Increased durability and compressive strength
- Lightweight
Repair Products (Mortars & Grouts)
Silica fume is used in a variety of cementitious repair products. Mortars or grouts modified with silica fume can be tailored to perform in many different applications—overhead and vertical mortars benefit from silica fume’s ability to increase surface adhesion. Silica fume dramatically improves cohesiveness making it ideal for use in underwater grouts, decreases permeability in grouts used for post-tensioning applications and increases the resistance to aggressive chemicals.
Silica fume is used in a variety of cementitious repair products. Mortars or grouts modified with silica fume can be tailored to perform in many different applications—overhead and vertical mortars benefit from silica fume’s ability to increase surface adhesion. Silica fume dramatically improves cohesiveness making it ideal for use in underwater grouts, decreases permeability in grouts used for post-tensioning applications and increases the resistance to aggressive chemicals.
- Non-bleeding and non-segregating
- Low permeability
- Lightweight
- Increased resistance to attack from chlorides, acids, nitrates and sulfate
Refactory & Ceramics
The use of silica fume in refractory castables provides better particle packing. It allows for less water to be used while maintaining the same flow characteristics. It also promotes low temperature sintering and the formation of mullite in the matrix of the castable. This produces a castable that has a low permeability to avoid gas, slag and metal penetration. Castables incorporating silica fume are stronger than non-silica fume containing castables especially at high temperatures with higher density they attain lower porosity and are more volume stable.
The use of silica fume in refractory castables provides better particle packing. It allows for less water to be used while maintaining the same flow characteristics. It also promotes low temperature sintering and the formation of mullite in the matrix of the castable. This produces a castable that has a low permeability to avoid gas, slag and metal penetration. Castables incorporating silica fume are stronger than non-silica fume containing castables especially at high temperatures with higher density they attain lower porosity and are more volume stable.
Sustainability
Without a doubt, the use of silica fume, pound for pound, provides the most positive Sustainability impact of all the Supplementary Cementitious Materials (SCM), only three of which (Silica Fume, Fly Ash and Slag Cement) are also known as Recovered Mineral Components (RMC) as identified by the Environmental Protection Agency (EPA).
Silica fume is by comparison a small volume SCM but with the largest relative impact, requiring minimal production and transportation efficiencies, making the incorporation of silica fume environmentally conscientious. With the ability to significantly reduce the concrete footprint, silica fume also has a profound impact on extending the life cycle of concrete, the premiere global building material. Long service life, durability and the potential to withstand catastrophic events, silica fume concrete will provide excellent resilience, furthering the cause of Sustainability.
Click here for a table of data derived from EPA report to Congress EPA 530-R-08-007, Life 365 version 2.0, and Bath University’s Inventory of Carbon & Energy (ICE).
Without a doubt, the use of silica fume, pound for pound, provides the most positive Sustainability impact of all the Supplementary Cementitious Materials (SCM), only three of which (Silica Fume, Fly Ash and Slag Cement) are also known as Recovered Mineral Components (RMC) as identified by the Environmental Protection Agency (EPA).
Silica fume is by comparison a small volume SCM but with the largest relative impact, requiring minimal production and transportation efficiencies, making the incorporation of silica fume environmentally conscientious. With the ability to significantly reduce the concrete footprint, silica fume also has a profound impact on extending the life cycle of concrete, the premiere global building material. Long service life, durability and the potential to withstand catastrophic events, silica fume concrete will provide excellent resilience, furthering the cause of Sustainability.
Click here for a table of data derived from EPA report to Congress EPA 530-R-08-007, Life 365 version 2.0, and Bath University’s Inventory of Carbon & Energy (ICE).
- Minimize your Concrete Carbon Footprint
- 4 : 1 Cement Replacement
- Maximize Structure Life-Cycle
- Save Energy and Lower CO2 Emissions
- Increase Resilience of Concrete, (already the most durable global building material)
Viscosity Modification
Field practitioners in the late 1980’s and early 1990’s discovered that at very high slump ranges, high performance concrete containing silica fume facilitates placement and consolidation and is generally much more manageable. They also found that silica fume inclusion in a mix design makes concrete more forgiving in that it can practically provide non-segregating, very high workability ranges.
The nature of silica fume as a mix ingredient in concrete (very fine particle size and high surface area) acts as a stabilizing agent by reducing the mobility of water, an effect often witnessed in fresh concrete as “little or no bleeding”. The “ball-bearing” effect of the spherical silica fume particles between the already hydrating and larger cement and SCM particles can significantly affect plastic viscosity. Different viscosity effects can be achieved with different dosages of silica fume addressing a broad spectrum of applications, from shotcrete to pervious concrete and from conventional to Self-Consolidating Concrete (SCC) & Ultra-High Performance Concrete (UHPC).
The rheology of silica fume has played a significant role in providing SCC characteristics in the construction (Two Union Square, Seattle 1989 and Society Tower, Cleveland 1991) of high strength columns where mechanical consolidation was not practical. This was at a time when terminology for SCC had not yet been coined, predating actual cast-in-place SCC field applications by approximately a decade. It has been stated that “silica fume is likely more important in high performance concrete due to its effect on fresh rather than hardened concrete.” With material-engineered plastic concrete behavior, unusual complementary characteristics can be achieved, such as pumping a very flowable mixture which upon placement can maintain a slope, and resist gravity, a.k.a. cohesive concrete.
Furthermore, with silica fume as part of the mix design it is possible to produce SCC with more conventional Sand-To-Total-Aggregate ratios (S/A <= 0.40) as well as utilize traditional high range water reducers (HRWR) which are melamine or naphthalene based. This is in contrast to typical SCC production utilizing higher than conventional concrete design S/A from 0.40 to 0.55, synthetic co-polymer HRWR and often in conjunction with viscosity modifying admixtures (VMA), such as cellulose based liquids or fillers such as limestone dust. Silica fume can facilitate an optimized engineered performance SCC with lower shrinkage and creep values due to optimized lower total cementitious (binder) contents, alongside higher attainable compressive and flexural strength achievement. Leaving more of the concrete volume dedicated to (a quality) coarse aggregate can provide elevated modulus of elasticity values utilizing conventional mix ingredients and proportioning.
Field practitioners in the late 1980’s and early 1990’s discovered that at very high slump ranges, high performance concrete containing silica fume facilitates placement and consolidation and is generally much more manageable. They also found that silica fume inclusion in a mix design makes concrete more forgiving in that it can practically provide non-segregating, very high workability ranges.
The nature of silica fume as a mix ingredient in concrete (very fine particle size and high surface area) acts as a stabilizing agent by reducing the mobility of water, an effect often witnessed in fresh concrete as “little or no bleeding”. The “ball-bearing” effect of the spherical silica fume particles between the already hydrating and larger cement and SCM particles can significantly affect plastic viscosity. Different viscosity effects can be achieved with different dosages of silica fume addressing a broad spectrum of applications, from shotcrete to pervious concrete and from conventional to Self-Consolidating Concrete (SCC) & Ultra-High Performance Concrete (UHPC).
The rheology of silica fume has played a significant role in providing SCC characteristics in the construction (Two Union Square, Seattle 1989 and Society Tower, Cleveland 1991) of high strength columns where mechanical consolidation was not practical. This was at a time when terminology for SCC had not yet been coined, predating actual cast-in-place SCC field applications by approximately a decade. It has been stated that “silica fume is likely more important in high performance concrete due to its effect on fresh rather than hardened concrete.” With material-engineered plastic concrete behavior, unusual complementary characteristics can be achieved, such as pumping a very flowable mixture which upon placement can maintain a slope, and resist gravity, a.k.a. cohesive concrete.
Furthermore, with silica fume as part of the mix design it is possible to produce SCC with more conventional Sand-To-Total-Aggregate ratios (S/A <= 0.40) as well as utilize traditional high range water reducers (HRWR) which are melamine or naphthalene based. This is in contrast to typical SCC production utilizing higher than conventional concrete design S/A from 0.40 to 0.55, synthetic co-polymer HRWR and often in conjunction with viscosity modifying admixtures (VMA), such as cellulose based liquids or fillers such as limestone dust. Silica fume can facilitate an optimized engineered performance SCC with lower shrinkage and creep values due to optimized lower total cementitious (binder) contents, alongside higher attainable compressive and flexural strength achievement. Leaving more of the concrete volume dedicated to (a quality) coarse aggregate can provide elevated modulus of elasticity values utilizing conventional mix ingredients and proportioning.
