Silica Fume

MATERIAL SAFETY DATA SHEET
Advanced Cement Technologies Silica Fume (Dry Powder-S)

SECTION I – PRODUCT INFORMATION

EMERGENCY TELEPHONE:CHEMTREC 1-800-424-9300

Synonyms:Amorphous Silica, Silicon Dioxide, Microsilica, Corrochem, Micropoz.

SECTION II – INGREDIENT INFORMATION & EXPOSURE LIMITS

Measured as respirable fraction of the aerosol.

• Silica Fume produced from silicon metal alloys.
• Silica Fume produced from ferro silicon metal alloys.
  **Respirable Dust
  N.E. Not Established

Other Constituent Materials3:

3.Manufacturer can provide a detailed elemental analysis including other trace elements. The (wt %) values will        change if silica fume is from ferro silicon production.

SECTION III – PHYSICAL DATA

*The melting point temperature is dependent on the type of amorphous silica as well as the source.

SECTION IV – STABILITY AND REACTIVITY DATA

SECTION V – FIRE AND EXPLOSION HAZARD DATA

SECTION VI – HEALTH HAZARD IDENTIFICATION DATA

Silica Fume is generally considered a nuisance dust of low toxicity. Use and handling of Silica Fume does not represent a health risk when normal safety rules are observed. Silica Fume when handled and stored in accordance with this document is unlikely to cause harmful effects. It is possible for Silica Fume to contain trace amounts (<0.05%) of crystalline silica, which has been shown to cause silicosis, and has been identified by IARC and NTP as a possible human carcinogen.

SECTION VII – FIRST AID MEASURES

SECTION VIII – SAFE HANDLING AND STORAGE

SECTION IX – EXPOSURE CONTROL & PERSONAL PROTECTION

SECTION X – TOXICOLOGICAL INFORMATION

A. Acute Effects: No data available

B. Chronic Effects:

Silica Fume is generally considered a nuisance dust of low toxicity consequently it is considered to pose minimal risk of pulmonary fibrosis (silicosis). Avoid prolonged exposure to silica fume dust concentrations above the recommended exposure limits, unless the protective equipment is used.

It is possible for Silica Fume to contain trace amounts (<0.05%) of crystalline silica, which has been shown to cause silicosis, and has been identified by IARC and NTP as a possible human carcinogen.

SECTION X –TOXICOLOGICAL INFORMATION (Con’t.)

B. Chronic Effects (Con’t.):

Heating Silica Fume at temperatures above 500ºC (930ºF) for prolonged time periods will convert amorphous silica to the crystalline phases Cristobalite and Tridymite that may cause silicosis. Increased temperatures will increase the formation rate of these phases.

SECTION XI – ECOLOGICAL INFORMATION

No adverse effects are expected. Silica Fume is not considered dangerous to the environment.

SECTION XII – ACCIDENTAL RELEASE & DISPOSAL CONSIDERATIONS

SECTION XIII – TRANSPORTATION INFORMATION

SECTION XIV – REGULATORY INFORMATION

SECTION XIV –REGULATORY INFORMATION (Con’t.)

SECTION XV – ADDITIONAL INFORMATION

All information, recommendations, and suggestions in this MSDS, concerning our products are based on tests and data believed to be reliable, it cannot be guaranteed. Since the actual use by others is beyond our control it is the user’s responsibility to determine the safety, toxicity and suitability for their own use of the product described herein.

Silica Fume Reduces Permeability

In many situations, the durability of concrete is directly related to its permeability. The contribution of silica fume is to reduce the permeability of the concrete. By reducing the permeability, the time is extended to prevent any aggressive chemical to get into the concrete where it can do its damage. Here are a few examples of how reducing permeability is used in actual structures.

Chloride damage to reinforcing steel:

Corrosion of reinforcing steel is the most significant and costly cause of concrete deterioration. It doesn’t matter whether the chloride comes from the ocean or from deicing salts, the results are the same. Silica-fume concrete is used widely in applications where the concrete is exposed to salt from any source. The reduced permeability of this concrete can result in many years of extended life for a structure.

Corrosion damage in concrete is a multi-step process as follows:

1. The chloride ions slowly work into the concrete to reach the level of the reinforcing steel. Once a certain amount of chlorides, called the threshold amount, reach the steel, corrosion begins.
2. As the iron ions are removed from the reinforcing steel, they go through several stages of oxidation or rusting. The volume of the iron increases with each stage.
3. As the amount of rust increases, rust stains will be seen on the surface of the concrete. Next, cracking will be seen. Finally, the cracking will result in delaminations and spalling of concrete over the reinforcing steel.

Sulfate attack:

While the chemistry of the portland cement used plays a role in sulfate attack, it has been shown that the water-cementitio us materials ratio (w/cm) is also a critical factor. Reducing the w/cm effectively reduces the permeability of the concrete. Adding silica fume will further reduce the permeability resulting in further delays of any adverse reactions.

Acid or other chemical attack:

The overall resistance of silica-fume concrete to attack by an aggressive chemical is not significantly different from that of conventional portland cement concrete. However, the reduced permeability of silica-fume concrete may extend the life of a concrete structure or extend the time between repairs simply by slowing down the rate of the attack. If protection against a particular chemical is required on a project, we strongly urge testing to include exposure of specimens of varying silica fume contents to the particular chemical.

The reduction in permeability is not the only contribution of silica fume to durability. There is ample evidence that silica fume, when used alone or in conjunction with a suitable fly ash, can reduce or eliminate the potential for alkali-aggregate reaction when reactive aggregates are used. Again, testing will be required to determine the appropriate amount and types of cementitious materials to be used for each particular application.

Finally, the higher strength of silica-fume concrete will add additional abrasion resistance. For concrete made with a particular aggregate, the higher the compressive strength, the higher the abrasion resistance. High-strength silica-fume concrete has been used in applications such as trash transfer stations and stilling basins in major dams.

Advantages in Various Applications

Another way to look at the use of silica fume is from the viewpoint of constructability. Here, we are actually stepping across the boundary between effects on fresh and hardened concrete to take advantage of all aspects of the performance of silica-fume concrete to make construction easier or, in some cases, even possible. Here are a few examples:

• One-pass finishing: In this case, we are taking advantage of the lack of bleeding in silica-fume concrete to complete finishing of flatwork in a single, continuous operation. The owner will get a better surface and the contractor will be able to complete the finishing in a shorter time using fewer finishers.
• Reduced heat of hydration: Although silica fume contributes about the same amount of heat of hydration as does portland cement on a pound-for-pound basis, its strength contribution is much greater on the same basis. Therefore, by balancing portland cement and silica-fume in a mixture, heat of hydration can be reduced while strength is maintained.

More and more state DOTs are using combinations of silica fume and fly ash to reduce the heat of   hydration  for concrete used in bridge decks. Reducing the total amount of cementitious material will reduce heat and help prevent early-age cracking.

• Use of three cementitious materials:There is an ever-increasing emphasis on using more waste materials such as fly ash and slag in concrete. However, the early age strength of concrete may suffer as a result. Adding small amounts of silica fume can offset this reduction in early strength. Usually, using combinations of three cementitious materials will reduce the cost of concrete. Mixtures containing three cementitious materials are referred to as “ternary mixtures”.
• Shotcrete:Silica-fume shotcrete is being widely used, in both the wet and dry processes and with and without steel fibers. The cohesive nature of this shotcrete allows for many applications that would have been difficult, uneconomical, or impossible to accomplish without the silica fume.

REFERENCES

Information provided by US DEPARTMENT OF TRANSPORTATION –Federal Highway Administration –Silca Fume Association -April 2005

 

Silica Fume In Fresh Concrete
Increased Cohesion

Fresh concrete made with silica fume is more cohesive and therefore less prone to segregation than concrete without silica fume. To offset this increased cohesion when placing, silica-fume concrete is typically placed at 40 to 50 mm greater slump than concrete without silica fume in the same placement.

The main benefit from increased cohesion can be seen in shotcrete, whether it is for new construction, repair of existing structures, or ground support in tunneling operations. Using silica fume in shotcrete allows for greater thickness of shotcrete layers, particularly when shooting overhead, and a significant reduction in rebound. Silica-fume shotcrete frequently includes steel fibers to provide increased flexural strength. Silica fume is compatible with all of the accelerators that are commonly used in shotcrete. Once the shotcrete is in place, all of the expected benefits of silica fume in hardened concrete come into play. An additional benefit is the increased bond strength of the silica-fume shotcrete to the underlying material and between lifts of layers in multi-pass applications.

Reduced Bleeding

Because of the very high surface area of the silica fume and the usually very low water content of silica-fume concrete, there will be very little, if any bleeding. Once a silica fume content of about five percent is reached, there will be no bleeding in most concretes.

Concrete bleeds as the heavier components (cement and aggregates) settle under the influence of gravity before the concrete stiffens. As the heavier components settle, the lighter water is forced upward. Some of the water is trapped under aggregate particles or reinforcing steel and some of it reaches the surface of the concrete. This movement of water takes place in what are called capillary channels. Once the water evaporates, these channels serve as shortcuts for aggressive agents such as chloride ions from deicing salts or sea water to get back into the concrete. Therefore, the reduction or elimination of these channels improves the durability of the concrete.

n addition to the improvements in durability, the lack of bleeding allows a more efficient finishing process to be used with silica-fume concrete flat work. For conventional concrete, it is critical not to conduct finishing operations until all bleeding has stopped and all bleed water has evaporated from the surface. Thus, there is usually a several hour waiting period after the initial placing and finishing operations. Once bleed water has disappeared and the concrete has gained sufficient strength, final finishing is started.

With silica-fume concrete showing no bleeding, the finishing operation can be continuous from placement to texturing and curing. This approach is called “one-pass” or “fast-track” finishing and is particularly advantageous in structures where silica fume is likely to be specified for durability such as bridge decks or parking structures. Unless a special finish is required, it is not unusual for finishing of silica-fume concrete to be completed within a half hour of concrete arriving on the deck.

REFERENCES

Information provided by US DEPARTMENT OF TRANSPORTATION –Federal Highway Administration –Silca Fume Association -April 2005

SILICAFUME-TECHNICALDATASHEET

SILICA FUME is a very fine pozzolanic material,composed of amorphous silica produced by electric arc furnaces as a byproducto f the production of elemental silicon or ferrosilicon alloys.

SILICA FUME can be used in a variety of cementitious products such as concrete, grouts ,mortors,fibercement products, plus refractory and ceramics, elastomer and polymer applications.

SILICA FUME is produced in conformance with the ASTM C 1240 specifications.The quality is controlled and monitored throughout the entire production process to ensure that it meets or exceeds specification requirements.

MECHANISM OF SILICA FUME’S
POZZOLANIC REACTION IN A CEMENTITOUS SYSTEM

SILICA FUME in contact with water goes into solution within an hour.The silica in solution forms an amorphous silica-rich,Ca-poor,gel on the surface of the silica fume particles and agglomerates. After time the silica-rich,Ca-poor,coating dissolves and the agglomerates of  silica fume react with free lime (CaOH2) to form calcium silicate hydrates (CSH). This reaction is called the pozzolanic reaction.

STORAGE

SILICA FUME should be kept dry, out of weather and the elements.

SAFETY AND HANDLING PRECAUTIONS

SILICA FUME is generally considered a nuisance dust.Use and handling of silica fume does not represent  a health risk when normal safety rules are observed. Direct contact may cause irritation of eyes. Prolonged contact may cause skin irritation. Inhalation may cause respiratory irritation resulting in coughing and shortness of breath.Th is product may be harmful if swallowed. Do not get in eyes and avoid prolonged skin contact .Do not take internally. Wash thoroughly with water after handling. For more detail, see the MSDS.

WARRANTY STATEMENT

The information given here is based on best knowledge,and is believed it to be true and accurate.Advanced Cement Technologies assumes no responsibility for the use of these statements,recommendations or suggestions,nor are they intended as are commendation for any use,which would infringe any patent or copyright.

 

Silica Fume Introduction
Silica Fume
SupplementaryCementitious Materia

The American Concrete Institute (ACI) defines silica fume as “very fine non-crystalline silica produced in electric arc furnaces as a by-product ofthe productions of elemental silicon or alloys containingsilicon” (ACI 116R). It is usually a gray colored powder, somewhat similar to portland cement or some fly ashes.

Silica fume is usually categorized as a supplementary cementitious material. This term refers to materials that are used in concrete in addition to portland cement.

Silica fume is frequently referred to by other names:

• Condensed silica fume
• Microsilica
• Volatilized silica

Silica fume is a by-product of producing silicon metal or ferrosilicon alloys in smelters using electric arc furnaces. These metals are used in many industrial applications to include aluminum and steel production, computer chip fabrication, and productions of silicones, which are widely used in lubricants and sealants. While these are very valuable materials, the by-product silica fume is of more importance to the concrete industry.

Densified and Undensified Silica Fume

Silica fume has historically been available in three basic product forms: undensified, slurried, and densified. There is no data available, after many years of testing, to show that any one of the product forms will perform better in a concrete mixture than any of the others.

Slurried silica fume is no longer available in the U.S. market. Undensified silica fume is available,but it is not frequently used in ready-mixed or precast concrete. Undensified silica fume is primarily used in pre-bagged products such as grouts or repair mortars.

Densified silica fume is produced by treating undensified silica fume to increase the bulk density up to a maximum of about 400 to 720kg/m3. This increase in bulk density is usually accomplished by tumbling the silica-fume particles in a silo, which causes surface charges to build up. These charges draw the particles together to form weak agglomerates. Because of the increased bulk density, this material is more economical for truck transportation.

Densified silica fume works very well in concrete. However, one caution when working with this product form is to ensure that the mixing is adequate to break up the particle agglomerations. Mixing in some types of mixers such as those that are used in dry mix shotcrete, roof tiles, or other applications where coarse aggregate is not present may not be adequate to break up the agglomerations. In those situations, an undensified silica fume may be more appropriate. Contact the Silica Fume Association for assistance in these types of applications.

REFERENCES

Information provided by US DEPARTMENT OF TRANSPORTATION –Federal Highway Administration –Silca Fume Association -April 2005