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For more information, please visit 90% Undensified Silica Fume.
The Reef Ball Foundation, working closely with concrete experts, has developed a typical mix design suitable to create artificial reef modules in complex molds with a minimal pH and to enhance the settlement and growth of typical marine species such as hard corals. Specific biological goals, such as oyster settlement, may require specialized designs. If you can not find local materials to match these specifications because of admixture or cement type availability, there are several acceptable substitutions, contact us for information. In general, this starting mix design has the highest amount of Portland Cement to help insure that you don't break your Reef Balls when handling them. However, Reef Ball usually don't need this much Portland cement when handled carefully, and there are additional biological benefits of using less cement because this can further reduce concrete pH. If you are reaching your goal of 95% or better of your modules not being broken you might consider reducing your cement proportions. Remember that best concrete practices are required for good pH neutralization; primarily the use of fresh cement, complete mixing, and good curing conditions (high humidity for at least 30 days)....without good practices all the microsilica in the world won't prevent a high pH.
Contact us if you have any questions about your mix design, to obtain approval for deviations or if you need a custom design for a specific project.
PART I - GENERAL
1.01 Section Includes
A. Concrete proportioning and products to be used to secure concrete, which when hardened will produce a required strength, permeability, and resistance to weathering in a reef environment.
1.04 References
A. ACI-211.191-Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete.
B. ASTM C 260- Standard Specifications for Air-Entraining Admixtures for Concrete.
C. ASTM-C 1116 Type III- Standard Specifications for Fiber Reinforced Concrete or Shotcrete.
D. ACI - 305R -91- Hot Weather Concreting.
E. ACI - 306R -88- Cold Weather Concreting.
F. ACI - 308- Standard Practice for Curing Concrete.
G. ASTM C 618-Fly Ash For Use As A Mineral Admixture in Portland Cement Concrete.
H. ASTM C 494-92- Standard Specifications for Chemical Admixtures for Concrete.
I. ASTM C 1202-91- Electrical Indication of Concrete's Ability to Resist Chloride Ion Penetration.
J. ASTM C 33- Concrete Aggregates.
K. ASTM C 94- Ready Mix Concrete.
L. ASTM C 150-Portland Cement.
M. ACI 304- Recommended Practice For Measuring, Mixing, Transporting and Placing concrete.
N. ASTM C 39 (Standard Specifications For Compressive Testing)
O. ASTM C-1240-93 (Standard Specifications for Silica Fume Concrete)
PART II PRODUCTS
2.01 Portland Cement: Shall be Type II and conform to ASTM C-150
2.02 Fly Ash: Shall meet requirements of ASTM C-618, Type F. And must be proven to be non-toxic as defined by the Army Corps of Engineers General Artificial Reef Permits. Fly Ash is not permitted in the State of Georgia and in most Atlantic States. (In October, 1991, The Atlantic States Marine Fisheries Commission adopted a resolution that opposes the use of fly ash in artificial reefs other than for experimental applications until the Army Corps of Engineers develop and adopt guidelines and standards for use.)
2.03 Water: Shall be potable and free from deleterious substances and shall not contain more that 1000 parts per million of chlorides or sulfates and shall not contain more than 5 parts per million of lead, copper or zinc salts and shall not contain more than 10 parts per million of phosphates.
2.04 Fine Aggregate: Shall be in compliance with ASTM C-33.
2.05 Coarse Aggregate: Shall be in compliance with ASTM C-33 #8 (pea gravel). (Up to 1 inch aggregate can be substituted with permission from the mold user.) Limestone aggregate is preferred if the finished modules are to be used in tropical waters.
2.06 Concrete Admixtures: Shall be in compliance with ASTM C-494.
2.07 Required Additives: The following additives shall be used in all concrete mix designs when producing the Reef Ball Development Group's product line:
A. High Range Water Reducer: Shall be ADVA Flow 120 or 140.
B. Silica Fume: Shall be Force 10,000 Densified in Concrete Ready Bags as manf. by W.R. Grace. (ASTM C-1240-93) or any of the permitted equivalent silica fume Brands as defined in the training manual Appendix K
C. Air-Entrainer: ONLY IF ADVA is not used: Shall be Darex II as manf. by W.R. Grace (ASTM C-260)
2.08 Optional Additives: The following additives may be used in concrete mix designs when producing Reef Ball Development's product line.
A. Fibers. Shall be either Microfibers as manf. by W.R. Grace, or Fibermesh Fibers (1 1/2 inches or longer) as manf. by Fibermesh. Either November 1, 2007 ators: Any Non- Calcium Chloride or Daracell as manf. by W.R. Grace may be used. (ASTM C-494 Type C or E)
C. Retarders: Shall be in compliance with ASTM-C-494-Type D as in Daratard 17 manf. by W.R. Grace
2.09 Prohibited Admixtures: All other admixtures are prohibited. Other admixtures can be submitted for approval by the Reef Ball Foundation Inc. Services Division by sending enough sample to produce five yards of concrete, the current MSDS, and chemical composition (which will be kept confidential by RBDG Ltd.) A testing fee of $2,500 must accompany the sample. Temporary approval will be granted or denied within 10 days based on chemical composition, but final approval may take up to 3 months since samples must be introduced in a controlled aquarium environment to assess impacts on marine and freshwater species.
PART III Concrete Proportioning:
A. General: The intent of the following proportions is to secure concrete of homogeneous structure which will have required strength and resistance to weathering.
B. Proportions:
One Cubic Yard
One Cubic Meter
Cement:
600 lbs. (Min.)
356 kg
Aggregate:
1800 lbs.
1068 kg
Sand:
1160 lbs
688 kg
Water:
240 1bs. (Max.)
142 kg
Force 10K:
50 lbs
30 kg
Grace Microfibers
.25 bag
.3 bag
*Adva Flow 120 or
Adva Flow 140
3.5-5 ounces per 100 lbs cement
or
6-10 ounces per 100 lbs cement
1
*NOTE: Adjust Adva dosage as needed to obtain workable, placeable mix (170-250mm / 7-10 inch slump), and to achieve .40 w/c ratio.
Fibers: 0-3# (Max.) as needed to reduce micro cracking 1# (Min.) required if Silica Fume exceeds 50#
Accelerator: As needed to achieve de-molding no sooner than: 3-4 hours for heavy duty molds (All Polyform side balls) 6-7 hours for standard molds (Molds with any tether balls)
NOTE: Silica Fume or Force 10K shall be dosed at a 10# minimum in Bay Balls and Pallet Balls while Ultra & Reef Balls shall require a minimum of 25#. All molds must use at least 50# for floating deployments. All mold sizes must use at least 50# for use in tropical waters unless special curing procedures are followed.* This product is being specified not only for strength, but also to reduce pH to spur coral growth, to reduce calcium hydroxide, and to increase sulfate resistance. It is a non-toxic pozzalan.
* Special curing procedures for tropical waters without 50# of Silica Fume per yard should include storage in a fresh water or high humidity environment for a minimum of 60 days or less with higher temperatures, or until the surface pH of the modules is below 9.5 pH when placed in seawater.
NOTE: End of day concrete may be used, but follow these additional requirements.
-Do not use concrete that has a temperature of over 100 degrees Fahrenheit -The original mix must have been at least 3,500 PSI -50# of added microsilica or more is required unless microsilica at that dose was already in the starting mix -Add additional Portland if needed to achieve a .4 w/c ratio. Take into account water added on site -Advise mold user to allow extra time for curing to achieve minimum de-molding strength. -Mold or module user must be notified that EOD waste was used.
NOTE: Fly Ash, when permitted, may be used as a substitution for cement up to a maximum replacement of 15% and as an additional substitute for microsilica at 30% to 40% of cementitious material. (Call RBDG for details.)
Part IV Concrete Testing Requirements:
A. Compressive strengths shall be tested in accordance with ASTM C 39. Compressive strengths shall reach a minimum of the following table at the time of use of at least:
Super/Ultra/Reef Ball
Pallet Ball
Bay Ball and all smaller sizes
Floating Deployment
8,500+
7,000+
6,000+
Barge Deployment
7,000+
5,500+
4,000+
To remove from mold
750+
750+
750+
To lift from base
1,500+
1,200+
1,000+
B. Permeability of concrete shall be tested in accordance with ASTM C 1202-91. Coulomb requirement shall be 2500 coulombs or less at 90 days. End of day waste shall be 3000 coulombs or less at 90 days.
THIS SPECIFICATION SHEET IS ONLY A SAMPLE. CONTACT RBDG FOR CUSTOM SPECIFICATIONS.
1) All deployments made by authorized contractors must have at least 90% of modules upright and intact or they must supply free deployed replacement to purchaser. This is REGARDLESS of what the customer says is acceptable.
2) All new construction after Jan. 1, 1998 must use ADVA Flow superplastisizer rather than WRD-19, Reduce the amount of air entrainment by 35-50% so that entrainment remains at 6% +/- 2%. (This will not impact your costs).
2a) All new construction after July 2002 must have Attachment Adapter Plug system installed and at least 50% of the recommended number of attachment adapters for the particular sized Reef Ball must be usable.
3) All Reef Balls must be constructed with a "wavy" bottom formed by adding sand in the mold before inserting center bladder.
4) The rinsing of the outside layer of concrete is not optional to expose the surface texture due to the pH rise on the surface of the poorly set concrete. (If rinsing is impractical, use a non-oil based biodegradable mold-releasing compound instead of sugar water. Increase air entrainment to 8% and do not tap the concrete into the mold heavily to create as much "honeycombing" as you can.)
5) The following are MINIMUM guidelines for microsilica use, primarily for pH reduction. Again, these are REGARDLESS of what the customer says is acceptable.
Hard Corralled Waters (Florida border & south on East Coast, Hernando County and south on Gulf.) (Anywhere near the Flower Gardens of Texas, anywhere near Grey's Reef in SC)
Deployed less than 45 days from casting = 50 lbs/yard
Deployed > 45 days < 90 days from casting = 45 lbs/yard
Deployed > 91 days < 120 days from casting = 40 lbs/yard
Deployed > 121 days < 150 days from casting = 35 lbs/yard
Deployed > 151 days < 180 days from casting = 30 lbs/yard
Deployed > 181 days < 210 days from casting = 25 lbs/yard
Deployed > 211 days < 240 days from casting = 20 lbs/yard
Deployed > 240 from casting = 15 lbs/yard
Temperate / Cool Waters (North of above & all of West Coast)
The company is the world’s best 85% Densified Silica Fume supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.
Deployed less than 29 days from casting = 50 lbs/yard
Deployed > 30 days < 90 days from casting = 30 lbs/yard
Deployed > 91 days < 120 days from casting = 25 lbs/yard
Deployed > 121 days < 150 days from casting = 20 lbs/yard
Deployed > 151 days < 180 days from casting = 15 lbs/yard
Deployed > 181 days < 210 days from casting = 10 lbs/yard
Deployed > 211 days < 240 days from casting = 5 lbs/yard
Deployed > 240 from casting = not required
6) End of day waste still requires full 50 lbs/yard of Mircosilica regardless of location/time
7) All other proprietary standards, including an approved mix design must be upheld.
SI Concrete Systems
4019 Industry Drive
Chattanooga, Tennessee 37416
Toll Free (800) 621-1273
Phone (423) 892-8080
Fax (423) 892-0157
Website www.siconcretesystems.com
E-mail fibermesh@sind.com
Specifier Notes: This product guide specification is written according to the Construction Specifications Institute (CSI) 3-Part Format as described in The Project Resource Manual—CSI Manual of Practice. The section must be carefully reviewed and edited by the Architect or Engineer to meet the requirements of the project and local building code. Coordinate this section with other specification sections and the Drawings. Delete all “Specifier Notes” when editing this section.
Section numbers are from MasterFormat 1995 Edition, with numbers from MasterFormat 2004 Edition in parentheses. Delete version not required.
SECTION 03240 (03 24 00)
SYNTHETIC FIBER REINFORCEMENT
Specifier Notes: This section covers SI Concrete Systems Fibermesh® 150 polypropylene fibers for use as concrete secondary reinforcement. Consult SI Concrete Systems for assistance in editing this section for the specific application.
PART 1 GENERAL
1.1 SECTION INCLUDES
A. Polypropylene fibers used as concrete secondary reinforcement.
1.2 RELATED SECTIONS
Specifier Notes: Edit the following list of related sections as required for the project. List other sections with work directly related to this section.
A. Section 02750 (32 13 00) - Rigid Paving.
B. Section 03210 (03 21 00) - Reinforcing Steel.
C. Section 03300 (03 30 00) - Cast-in-Place Concrete.
D. Section 03370 (03 37 13) - Shotcrete.
E. Section 03500 (03 50 00) - Cementitious Decks and Toppings.
1.3 REFERENCES
Specifier Notes: List standards referenced in this section, complete with designations and titles. This article does not require compliance with standards, but is merely a listing of those used.
A. ASTM C 94 - Standard Specification for Ready-Mixed Concrete.
B. ASTM C 1116 - Standard Specification for Fiber-Reinforced Concrete and Shotcrete.
C. Southwest Certification Services (SWCS), Omega Point Laboratories No. 8662-1.
D. UL Report File No. R8534-11.
1.4 SUBMITTALS
A. Comply with Section 01330 (01 33 00) - Submittal Procedures.
B. Product Data: Submit manufacturer’s product data, including application rate and mixing instructions.
Specifier Notes: Delete samples if not required.
C. Samples: Submit manufacturer’s sample of synthetic fiber reinforcement.
D. Manufacturer’s Certification:
1. Submit manufacturer’s certification that synthetic fiber reinforcement complies with specified requirements.
2. Submit evidence of manufacturer’s ISO 9001:2000 certification.
3. Submit evidence of satisfactory performance history of synthetic fiber reinforcement.
1.5 QUALITY ASSURANCE
A. Manufacturer’s Qualifications:
1. Synthetic fiber reinforcement manufactured in ISO 9001:2000 certified facility.
2. Minimum 10-year satisfactory performance history of specified synthetic fiber reinforcement.
1.6 DELIVERY, STORAGE, AND HANDLING
A. Delivery: Deliver synthetic fiber reinforcement in manufacturer’s original, unopened, undamaged containers and packaging, with labels clearly identifying product name, unique identification number, code approvals, directions for use, manufacturer, and weight of fibers.
B. Storage:
1. Store synthetic fiber reinforcement in clean, dry area indoors in accordance with manufacturer’s instructions.
2. Keep packaging sealed until ready for use.
C. Handling: Protect synthetic fiber reinforcement during handling to prevent contamination.
PART 2 PRODUCTS
2.1 MANUFACTURER
A. SI Concrete Systems, 4019 Industry Drive, Chattanooga, Tennessee 37416. Toll Free (800) 621-1273. Phone (423) 892-8080. Fax (423) 892-0157. Website www.siconcretesystems.com. E-mail fibermesh@sind.com.
2.2 SYNTHETIC FIBER REINFORCEMENT
A. Synthetic Fiber Reinforcement: Fibermesh 150.
1. Material: 100 percent virgin homopolymer polypropylene multifilament fibers, containing no reprocessed olefin materials.
2. Conformance: ASTM C 1116, Type III.
3. Fire Classifications:
a. UL Report File No. R8534-11.
b. Southwest Certification Services (SWCS), Omega Point Laboratories No. 8662-1.
Specifier Notes: Specify graded or single-cut lengths.
4. Fiber Length: [Graded] [Single-cut lengths].
5. Alkali Resistance: Alkali proof.
6. Absorption: Nil.
7. Specific Gravity: 0.91.
8. Melt Point: 324 degrees F (162 degrees C).
PART 3 EXECUTION
3.1 MIXING
A. Add synthetic fiber reinforcement to concrete mixture in accordance with manufacturer’s instructions.
B. Add synthetic fiber reinforcement into concrete mixer before, during, or after batching other concrete materials.
Specifier Notes: Lower application rates may be acceptable depending upon local building codes. Consult SI Concrete Systems for more information.
C. Application Rate: Add synthetic fiber reinforcement at standard application rate of 1.5 pounds per cubic yard (0.90 kg/m3) of concrete.
D. Mix synthetic fiber reinforcement in concrete mixer in accordance with mixing time and speed of ASTM C 94 to ensure uniform distribution and random orientation of fibers throughout concrete.
Concrete Products
Technical Guide Specification
Microsilica Concrete
SECTION 03320
PART 1 - GENERAL
1.01 SUMMARY
A. This section specifies microsilica (silica fume) admixture for the reduction of concrete permeability to protect against intrusion by chlorides and other aggressive chemicals, and for the production of high-strength concrete.
B. Related Sections: Other specification sections which directly relate to the work of this Section include, but are not limited to, the following:
1. Section 03300 - Cast-In-Place Concrete.
2. Section 03365 - Post-Tensioned Concrete.
3. Section 03400 - Precast Concrete.
1.02 SUBMITTALS
A. Product Data: Submit manufacturer’s product data, installation instructions, use limitations and recommendations for each material.
B. Test and Performance Data: Submit independent test data substantiating the product’s ability to reduce concrete permeability by chlorides and other aggressive chemicals.
1.03 QUALITY ASSURANCE
A. Manufacturer: Concrete admixture shall be manufactured by a firm with a minimum of 5 years experience in the production of similar products. Manufacturers proposed for use but not named in these specifications shall submit evidence of ability to meet all requirements specified, and include a list of projects of similar design and complexity completed within the past five years.
B. Materials: For each type of material required for the work of this Section, provide primary materials which are the products of one manufacturer.
C. Pre-Construction Conference: A pre-construction conference shall be held two weeks prior to commencement of field operations to install the specified product in order to establish procedures to maintain optimum working conditions and to coordinate this work with related and adjacent work. Agenda for meeting shall include concrete and admixture handling, placing, finishing, and curing.
D. Manufacturer’s Representative: A representative of the manufacturer shall be present for project start-up during initial concrete placement. Engineer may waive requirement for manufacturer’s representative if Contractor provides sufficient evidence that producer and finisher have adequate experience with admixtures required.
E. Trial Mix: Provide a minimum 4 cubic yard (3 m3) trial mix containing proposed concrete design mix placed at the job site in location acceptable to the Engineer. Engineer may waive requirement for trial mix if Contractor provides sufficient evidence that producer and finisher have adequate experience with low water cement ratio mixes.
1.04 PROJECT CONDITIONS
A. Perform work only when existing and forecasted weather conditions are within the limits established by the manufacturer of the materials and products used.
PART 2 - PRODUCTS
2.01 MANUFACTURER
A. Provide Force 10,000® microsilica concrete admixtures by Grace Construction Products meeting specified requirements. For customer service in North America:
Call toll free: 877-4AD-MIX1 (877-423-6491)
Fax toll free: 877-4AD-MIX2 (877-423-6492)
2.02 MATERIALS
A. Microsilica Admixture: Provide Force 10,000 concrete admixture by Grace Construction Products complying with ASTM C 1240.
2.03 CONCRETE MIXES
A. Application Rate:
NTS This section may be used for concrete permeability requirements or high-strength concrete. Application rate (dosage rate) of microsilica may vary depending on individual project requirements. Application rates may be stated in dry pounds per cubic yard, percent of weight of cement, or as required to meet a performance criteria. Typical application rates for low permeability concrete varies from 30 to 60 lbs/cy. Specifier should use only one of the three sections which follow for A. Application Rate.
NTS Force 10,000 Sample Specification For Permeability Requirements
This sample specification may be used by the design engineer when specifying Force 10,000 microsilica for the reduction of concrete permeability to protect against intrusion by chlorides or other aggressive chemicals. Force 10,000 is a microsilica-based admixture manufactured by Grace Construction Products of W. R. Grace & Co.-Conn.
The high silicon dioxide content of microsilica combines with the excess calcium hydroxide in the concrete to form more calcium silicate hydrate “glue.” This chemical reaction plus its fine particle size allows Force 10,000 to fill in the voids between the cement grains and aggregate to deliver less permeable concrete. When chlorides migrate through the concrete and attack the steel reinforcing, corrosion occurs. By reducing the permeability of the concrete, chlorides take much longer to reach the steel which extends the service life of the structure considerably. Chlorides are typically present from deicing salts or from a marine environment. Structure applications of Force 10,000 include parking garages, bridge decks and overlays, reinforced pavements, and all structures in a marine environment. Structural concrete design criteria shall follow ACI 318, 357 and 201 guidelines. Parameters used in this sample specification, such as water/cementitious ratio and concrete cover over reinforcing steel, are taken from these guidelines and are conservative values.
There are two ways to specify microsilica concrete for permeability requirements: by prescription or by performance. The prescription method mandates the number of pounds of microsilica per cubic yard to be used while the performance method uses ASTM C 1202 test method to measure “coulombs.” Please use one method (prescription or performance) but not both. If the “performance method” is the preferred choice, use ASTM C1202 for mix design purposes only, not as a mix acceptance or rejection criteria during the construction phase. Since the chloride’s loading rate and final concrete quality are unknown factors, W. R. Grace cannot guarantee the longevity of the protection offered by Force 10,000. Quality concrete as recommended by ACI and the addition of Force 10,000 will slow the ingress of chlorides into the concrete. Neither quality concrete nor Force 10,000 will stop corrosion forever, but both will retard the onset of corrosion.
Prescription Method
1. Provide microsilica admixture Force 10,000 as manufactured by Grace Construction Products.
2. Microsilica shall be added at a rate of (50) pounds dry weight of microsilica per cubic yard [(30) kg/m3] of concrete.
3. Compressive strength shall be a minimum of (5,000) psi [35 MPa] at 28 days as measured using (4” x 8”) (100 mm x 200 mm) cylinder specimens.
4. A maximum water-to-cementitious ratio of 0.40 is required.
5. Microsilica may be counted as cementitious material in calculations.
6. Add microsilica as a liquid slurry or in dry densified form in 25 lb (11.4 kg) Concrete Ready BagsTM packaging.
7. Blended cements with interground microsilica will not be allowed.
Performance Method
1. Provide microsilica admixture Force 10,000 as manufactured by Grace Construction Products.
2. Microsilica shall have a minimum of (5,000) psi [35 MPa] at 28 days as measured using (4” x 8”) (100 mm x 200 mm) cylinders.
3. Permeability of microsilica concrete shall be tested by ASTM C 1202. Results of tests shall be expressed in electrical units of coulombs. Coulomb tests shall be made on two (4” x 8”) (100 mm x 200 mm) representative samples, moist cured for 56 days. Test cylinders shall be made according to ASTM C 31. Coulomb requirement shall be (_____) coulombs or less at 56 days. ASTM C 1202 testing shall be used as an indicator of concrete permeability at mix design submittal only.
4. A maximum water-to-cementitious ratio of 0.40 is required.
5. Microsilica may be counted as cementitious material in calculations.
6. Add microsilica as a liquid slurry or in dry densified form in 25 lb (11.4 kg) Concrete Ready Bags packaging.
7. Blended cements with interground microsilica will not be allowed.
NTS: Force 10,000 Sample Specification For High-Strength Concrete Requirements
This sample specification may be used by the design engineer when specifying Force 10,000 microsilica for the production of high-strength concrete. The design engineer should fill in the compressive strength required. Force 10,000 is a microsilica-based admixture manufactured by Grace Construction Products of W. R. Grace & Co.-Conn. The high silicon dioxide content of microsilica combines with the excess calcium hydroxide in the concrete to form more calcium silicate hydrate “glue.” This produces a stronger, tighter bonding paste structure. Additionally, the extreme fineness of the microsilica enables it a less permeable paste. These two factors contribute to providing higher strength, more durable concrete.
Structural applications for high strength Force 10,000 concrete are broad, but include usage in structural columns, beams and girders. Structural concrete design criteria shall follow ACI 318, 357 and 201 guidelines. Parameters used in this sample specification, such as water-to-cementitious ratio are taken from these guidelines and are conservative values. This sample specification is based on the performance method, whereby the compressive strength of the concrete is mandated by the design engineer.
High-Strength Concrete Requirements
1. Provide microsilica admixture Force 10,000 as manufactured by Grace Construction Products.
2. Microsilica high-strength concrete shall have a minimum of (____) psi [(___) MPa] at 28 days.
3. Test cylinders shall be 4” x 8” (100 mm x 200 mm).
4. A maximum water-to-cementitious ratio of 0.40 is required.
5. Microsilica may be counted as cementitious material in calculations.
6. Add microsilica as a liquid slurry or in dry densified form in 25 lb. (11.4 kg) Concrete Ready Bags packaging.
7. Blended cements with interground microsilica will not be allowed.
B. Concrete Cover Over Reinforcement: Minimum concrete cover over reinforcement shall be (____) inches [(____) mm].
NTS: Follow ACI 318 recommendations for concrete cover over reinforcement. For deicing salt and marine environments, ACI 318-89, section R7.7.5, requires 2 inches (50 mm) for walls and slabs and 2-1/2 inches (64 mm) for other members. For marine environments, ACI 357 recommends 2-1/2 inches (64 mm).
C. Air Entrainment: For freeze-thaw durability comply with ACI 318 freezing and thawing exposure requirements, as determined by ASTM C 173 or ASTM C 281.
D. Water-to-Cementitious Ratio: Provide 0.40 maximum. Microsilica, fly ash, blast furnace slag and cement are considered cementitious materials. The water content of Force 10,000 slurry shall be included as mix design water.
E. Recommended Cementitious Content for Workability:
Maximum Aggregate Minimum Cementitious
3/8” (10 mm) 700 pounds/cu.yd. (415 kg/m3)
1/2” (13 mm) 680 pounds/cu.yd. (400 kg/m3)
3/4” (20 mm) 650 pounds/cu.yd. (385 kg/m3)
1” (25 mm) 630 pounds/cu.yd. (375 kg/m3)
F. Compressive Strength: Minimum 28 day compressive strength for microsilica concrete shall be (5,000) psi [(35) MPa] unless stated otherwise in Section 2.03 A. Application Rate.
G. Concrete Slump for Flatwork: 5 to 8 inches (125 to 200 mm). Concrete slump may be 2 inches (50 mm) over normal concrete slumps as microsilica concrete can be sticky and has a surface that is harder to close than normal concrete.
H. Concrete Admixtures: High-range water reducers are mandatory to control slump, mixing, cementitious ratio and proper distribution of the microsilica, and shall be plant added. Additional water reducers may be added at the job site when required.
I. Additional Concrete Admixtures: Additional concrete admixtures conforming to ASTM C 494 or equivalent CSA 266 standards may be used as required including the following:
1. Type A: Water-reducing admixture, WRDA® series or Daracem®-55 by Grace Construction Products.
2. Type D: Water-reducing and retarding admixture, Daratard®-17 by Grace Construction Products.
3. Type F or G: Water-reducing, high-range admixture, WRDA-19, Daracem-100 by Grace Construction Products. This type of admixture must be included in all Force 10,000 concrete.
4. Type C: Accelerating admixture, PolarSet® by Grace Construction Products.
5. Grace MicroFibers® for flatwork, at 1 pound per cubic yard (600 grams/m3) addition rate.
6. DCI® or DCI-S Corrosion Inhibitor by Grace Construction Products may also be used if required at rate recommended by manufacturer.
J. Special Mixing Requirements for Densified Microsilica: Densified microsilica requires enhanced mixing to ensure full dispersion. The following mix requirements shall be adhered to:
1. For all types of mixing equipment, mix times shall be increased by 40% over the minimum mix time required to achieve mix uniformity as defined by ASTM C 94.
2. For truck-mixed and central mixed concrete, maximum allowable batch size shall be 80% of the maximum as called out by ASTM C 94.
PART 3 - EXECUTION
3.01 EXAMINATION
A. Examine conditions of substrates and other conditions under which work is to be performed and notify Owner, in writing, of circumstances detrimental to the proper completion of the work. Do not proceed until unsatisfactory conditions are corrected.
3.02 CONCRETE PLACEMENT, FINISHING AND CURING
A. Concrete Finishing and Curing: Microsilica concrete typically exhibits little or no bleeding. To reduce plastic or drying shrinkage cracks, comply with ACI 302 “Guide for Concrete Floor and Slab Construction”, ACI 308 “Standard Practice for Curing Concrete”, ACI 306 “Standard Practice for Cold Weather Concreting”, and ACI 305 “Hot Weather Concreting.”
1. Underfinish microsilica concrete by limiting finishing operation to screeding, bull-float, and broom finish. Curing shall be initiated within one hour of concrete placement.
2. The use of wind breaks, sun shades, and fog misting are recommended to minimize the rate of evaporation at the concrete surface.
3. Light fog misting above the concrete to keep the environment above the concrete surface at high humidity is recommended during the placing and finish operations.
4. Fog misting is required when the rate of evaporation at the concrete surface exceeds 0.1 pound per square foot per hour as determined by ACI 308 Section 1.2.1. Fogging shall continue after the finishing operation until prewetted burlap or other approved curing material is placed over the concrete. When fog misting is not available or possible, an evaporation retarder shall be applied before and after bull-floating and during final finish to protect the concrete.
5. Wet curing is the preferred method for curing. Use prewetted burlap to cover all flatwork and keep wet for a minimum of seven days or until the time necessary to attain 70 percent of the specified compressive strength, as recommended by ACI 308 Section 3.1.3.
3.03 PROTECTION
A. Protect completed work from damage and construction operations throughout finishing and curing operations.
Concrete is highly heterogeneous. It is a material highly in demand for the construction industry all over the globe. Significant material involved in making concrete is cement but overuse of cement is a major environmental concern. Thus, to overcome this problem and precisely to keep intact the strength of concrete, it is essential to seek out new supplementary cementing materials. Therefore, in recent years, researchers are into finding better alternatives for concrete and have tried developing materials that consists properties acquired by concrete by adding alternative byproducts in construction.Some additives which can reduce Co2 emission with additional strength and durability are as follows:
Mentioned above are all pozzolanic materials. Pozzolanic material consists of siliceous and aluminous mineral substance. Hence, they have some inbuilt cementitious properties and conjointly a byproduct. Here we are discussing about only one supplementary cementing material i.e. silica fume or micro silica.
Silica fume is a byproduct of ferrosilicon and silicon. According to ‘ACI Concrete Terminology- CT-13’ (An ACI Standard), silica fume is very fine non-crystalline silica produced in electric arc furnaces as a byproduct obtained while manufacturing elemental silicon or alloys containing silicon. It rises in the form of oxidized vapour. Later when it cools and condenses, it is collected in cloth bags.
A further process is conducted to remove impurities in it and to control the size of its particle. Silica fume has a spherical shape. It is an extremely fine particle with size less than 1 (micron) and an average diameter of around 0.1 (micron). It is about 100 times smaller than an average cement particle. Silica fume has a specific surface area of about 20000 m2/kg as that of 225 to 300 m2/kg of cement, which is responsible for the compressive strength and durability of concrete.Silica fume is also known as condensed silica fume, micro silica and volatized silica. It is basically silicon dioxide (more than 90%) in a non-crystalline form. Silica fume has both the pozzolanic as well as cementitious properties. It is also recognized as a pozzolanic admixture or supplementary cementing material. Silica fume effectively enhances the mechanical properties to a great extent. It is durable and offers a good resistance against corrosion of embedded steel.
Silica fume when added to the concrete, initially it remains inert. Once cement and water in the mix start reacting with each other, primary chemical reactions produce two chemical compounds. In other words, once the hydration process starts between the cement and water, two chemical compounds are produced namely:
According to the ‘European Silica Fume Committee’, when silica fume is added to the concrete, it gives highly pozzolanic effect, due to its extreme fineness and very high amorphous silicon dioxide content. It reacts with the free lime (CH) and produces additional gel (CHS) in many of the voids around hydrated cement particles. This additional gel makes a dense matrix of the concrete. This improves compressive, flexural and bond- strength as well as reduce the permeability of the concrete.
Silica Fume
According to ‘Silica Fume Association- U.S.’ (Published in Technical Report), there are various other materials which holds physical and chemical properties very similar to silica fume. These materials may or may not be a byproduct. Some of these materials may perform well in concrete but considering their cost factor i.e. they are quite costly, their use is restricted. This is because; cost factor is amongst one of the major aspects taken into consideration while raising a structure. Mentioned below are such kind of materials:
(a) It gives a high early compressive strength of concrete.
(b) It gives high tensile strength and flexural strength and modulus of elasticity.
(c) It provides higher bond strength to concrete.
‘A.M. Neville’ (Author of Properties of Concrete) specifies that,
How Can Silica Fume be Added in the Concrete?
Condensed silica fume or micro silica can be added directly into the concrete as an admixture or blended as an individual ingredient with ordinary Portland cement. Silica fume can replace 9-15% by mass of Portland cement.
Followings are Different Manufacturers whose Products are Easily Available in the Market:
Micro Silica Products
01. High Water Demand:
02. Workability of Concrete:
03. Bleeding and Segregation:
04. Permeability:
05. Strength:
06. Chemical Diffusion:
07. Unit Weight:
Summing up, the use of silica fume gives rise to a variety of concretes with different properties which can be used in fresh as well as in the hardened state with less cement. Silica fume provides high durability to the concrete. Where at one end there are advantages associated with it, there are few difficulties in the form of disadvantages too associated to work with silica fume. Therefore, usage of water-reducing admixtures or high range water reducing admixtures or both is recommended to maintain the desired w/c ratio as well as workability as the addition of silica fume increases water demand.If this is handled properly, it is certainly a new-age material that can achieve high strength concrete above M40 grade and simultaneously give impermeable, dense and durable concrete, thereby extending the basic life of the structure and lessening the pollution.
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