CHEMICAL ADMIXTURES FOR CONCRETE
Air entraining admixtures shall meet the requirements of AASHTO M154. Water reducing and retarding, water-reducing, high range water reducing, and non-chloride accelerating admixtures shall meet the requirements of AASHTO M194. All chemical admixtures used for Portland Cement Concrete shall meet the requirements outlined in Section 4103 and other applicable Iowa Department of Transportation Standard Specifications. Approved brands of chemical admixtures for concrete are listed in the Materials Approved Products Listing Enterprise (MAPLE) as Appendixes A, B, C, D, E, F, G and H for different types of applications.
For all types of admixtures, the source, brand name, and lot/batch number must be identifiable by description on the invoice, bill of lading or delivery ticket. The manufacturer and supplier shall maintain a record of each shipment, which identifies source, the brand, lot/batch number and certified test data for each shipment. This data shall be made available to the contracting authority when requested.
The end user (concrete supplier) shall keep records of deliveries available for inspection for a minimum of 3 years after delivery.
To obtain approval for any admixture type, the manufacturer shall submit the following items to the Construction and Materials Bureau in Ames:
1. Product identification including brand name and product number
2. Complete manufacturer's recommendation for usage
3. A copy of Level 1 product test report for the submitted admixture from the National Transportation Product Evaluation Program (NTPEP). The test result reported will be evaluated for compliance with appropriate AASHTO specification. The NTPEP report is not required for admixtures for prestressed and precast concrete listed in the Appendix F.
4. A current Materials Safety Data Sheet (MSDS)
5. A one-quart (one-liter) representative sample may be required upon request
Specific requirements for each type of admixture are as follows:
A. Air Entraining Admixtures
Air entraining admixtures shall meet the requirements of Iowa Department of Transportation Standard Specifications Section 4103 and AASHTO M154.
Approved brands of air entraining admixtures are listed in the Appendix A of this IM.
B. Retarding, and Water-Reducing & Retarding Admixtures for Bridge Deck and Drilled Shaft Concrete Requiring Extended Working Time
Retarding, and water-reducing & retarding admixtures shall meet the requirements of AASHTO M194, Type B or Type D. These admixtures can be used for water reduction, retardation, or water reduction and retardation for bridge deck and drilled shaft concrete when extended working time is required.
Approved brands of retarding, and water-reducing & retarding admixtures for bridge deck and drilled shaft concrete requiring extended working time are listed in the Appendix B of this IM. The Appendix B also contains a guideline for dosage rates and working time limits based on an estimated maximum temperature of the concrete during placement at the point of discharge. Working time limits have been determined by AASHTO T197 using 200 psi (1.38 MPa) penetration resistance and shall be provided by manufacturer. In addition to the AASHTO M194 requirements, a minimum working time of 4.5 hours is required for the Type I/II cement mix using the maximum normal recommended dosage of an admixture and tested at the normal temperature (between 70oF and 75oF).
Retarding admixtures from Appendix B also act as water reducers. At higher dosages of retarding admixtures may necessitate a dosage reduction or elimination of water reducers from Appendix C. Water reducers from Appendix C can also aid with air entrainment. Check with the admixture supplier for recommendations.
C. Water-Reducing Admixtures
Water-reducing admixtures shall meet the requirements of AASHTO M194, Type A.
Approved brands of water-reducing admixtures with their proper dosage rates are listed in the Appendix C of this IM.
Mid-range water reducers used for bridge overlay concrete (Class HPC-O Mixture), without retarding admixtures, are noted in the Appendix C. In addition to the AASHTO M194 requirements, the use of these admixtures shall provide a maximum water content of 90% of the control at a normal dosage, and shall not result in a less initial set time as compared to the control. The intent of these mid-range water reducers is to achieve a workable, dense, low water to cementitious material ratio concrete for bridge overlay as described in Article 2413.02 of Standard Specifications. All other mid-range water reducers shall be used in conjunction with a retarder for the HPC-O mixtures.
A combination of a water-reducing admixture and a retarding admixture may be used to aid in air entrainment and slump retention.
D. High Range Water-Reducing Admixtures
High range water-reducing admixtures shall meet the requirements of AASHTO M194, Type F.
Approved brands of high range water-reducing admixtures with their recommended dosage rates are listed in the Appendix D of this IM. As indicated, some of these high range water reducers listed can be used to cast self-consolidated concrete. If needed, a viscosity-modified admixture produced by the same manufacturer is allowed to cast self-consolidated concrete.
E. Non-Chloride Accelerating Admixtures
Non-chloride accelerating admixtures shall meet the requirements of AASHTO M194, Type C or E. Total chloride content, which may come from some indirect sources, shall not exceed 0.1% in the admixtures.
Approved brands of non-Chloride accelerating admixtures with their recommended dosage rates are listed in the Appendix E of this IM.
F. Admixtures for Prestressed & Precast Concrete
In addition to the admixtures listed in other Appendixes of this IM, the admixtures listed in the Appendix F can also be used in prestressed and precast concrete. Benefits of those admixtures in the Appendix F include increasing production rate, improvement of visual appeal, greater strength, more durable, better compactability, and extension of life of molds and machines parts for dry-cast concrete. In order to get an admixture approval, its producer shall prove that the use of the admixture will not reduce strength of concrete, and provide evidence of the above-mentioned benefits.
G. Retarding, Water-Reducing & Retarding Admixtures for Concrete with Normal Working Times
Retarding, water-reducing and retarding admixtures shall meet the requirements of AASHTO M194, Type B or Type D. These admixtures can be used for water reduction, retardation, or water reduction and retardation for concrete.
When use as a retarder is specified or authorized by the engineer, the contractor shall be responsible for its use and application of the proper dosage rate. It may also be necessary to adjust the quantity of air entraining agent. When fly ash is used in the concrete, the dosage rate shall be applied to both the cement and fly ash combined.
Mixed-to-placed time period may be extended as per Iowa DOT Standard Specifications Section 2301.02.C.4. For patching with extended haul time, rate may be reduced to half dosage.
Approved brands of water-reducing and retarding admixtures with their recommended dosage rates are listed in the Appendix G of this IM.
H. Special Performance Admixtures
Special performance admixtures shall meet the requirements of AASHTO M194, Type S. These admixtures will provide a desired performance characteristic(s) other than reducing water content, or changing the time of setting of concrete, or both, without any adverse effects on fresh, hardened and durability properties of concrete as specified, excluding admixtures that are used primarily in the manufacture of dry-cast concrete products. Special performance admixtures with their recommended dosage rates are listed in the Appendix H of this IM.
CarbonCure is considered a special performance admixture. CarbonCure shall be added to the mix using the CarbonCure delivery system. The delivery system shall be provided and calibrated by CarbonCure and integrated into the PCC plant batching system. Use of CarbonCure without Portland cement reduction requires no approval. Use of CarbonCure with up to a 3 percent Portland cement reduction is allowed, provided the producer has completed the approval process in Appendix I of this IM. Portland cement reductions and mix proportions shall be completed as shown in IM 529.
A hydration stabilizer/controller will be evaluated for approval as a retarder (Type B) or a water reducing & retarding admixture (Type D), and listed and identified in the Appendix B or the Appendix G after approved.
If alternative requirements specified in AASHTO M194 are met, an admixture may be provisionally approved based on six-month test results. Producer shall submit one-year test results for final approval as soon as they become available. The failure or delay in submitting one-year results may lead to revoking of provisional approval.
At the beginning of each calendar year, the manufacturer shall submit an annual certification statement to the Construction and Materials Bureau. If the admixture to be supplied during that year is identical with the formulation previously tested and approved, then the manufacturer shall complete the quality control limits in the certification statement.
At the beginning of each calendar year, The distributor shall certify that admixtures to be supplied are not altered and will be distributed as received from the manufacturer.
Approval of admixtures may be withdrawn because of deficient test results; product changes made after original approval, or unsatisfactory field performance.
AGITATION OF ADMIXTURES
Air entraining admixtures shall be stirred, agitated, or circulated at least weekly, or as recommended by manufacturer, to ensure a uniform and homogeneous mixture of solids and solution. It is the admixture supplier's responsibility to the contractor to provide a quality product. Therefore the admixture suppliers shall be responsible for the system used to maintain the quality product described above.
Retarding, water-reducing, and high range water-reducing admixtures shall be stirred, circulated, or agitated thoroughly once a day prior to operation of the proportioning plant to maintain the solids in suspension. The agitating shall be done in such a way that the solution in the holding or storage tank is circulated for a minimum of five minutes each day per 100 gallons (380 liters) of solution or any fraction thereof. Use of a timer on the pump is recommended to prevent excessive heat from the pump. 5 minutes is adequate for smaller tanks to a maximum of 15 minutes for larger tanks. A circulating pump with a 250-watt (1/3 hp) pump motor and a 1-inch (25 mm) inside diameter hose will be considered as a minimum requirement. The engineer shall approve the method of agitation. NOTE: Introducing air into a tank will not be acceptable.
District Materials Inspector shall check approved brand and lot number of admixture prior to use.
Monitor samples will be obtained and sent to Central Materials for testing. Minimum sampling frequency shall be according to IM 204. The sample size shall be one 1 pint (0.5 liter).
Admixtures that exceed the manufacturer’s recommended shelf life will be sampled and tested prior to use. If retesting complies, the admixture will be allowed to use for another six months. Manufacturers shall be responsible to their customers to know if their product’s effectiveness diminishes during storage.
Samples will be tested for variation from the manufacturer target for solids, specific gravity and chloride content if needed.
If the test result of a monitor sample is outside the quality control limits specified by AASHTO M154 or M194 and provided by the manufacturer, all material in the storage tank shall be rejected. The admixture company is not allowed to mix new replacement material with the non-compliance material. The admixture manufacturer is responsible for the condition of storage tanks and should determine if the tanks should be cleaned to prevent cross contamination and further product failures.