- 792 - SECTION 1007 -- CHEMICAL ADMIXTURES
1007.01 Description
1.Admixtures are materials added to Portland cement concrete to change characteristics such as workability, set time, strength, permeability, freezing point, and curing.
2.The Department's concrete admixture types are:
a.Type A - Water-Reducing Admixture - An admixture that reduces the quantity of mixing water re quired to produce concrete of a given slump.
b.Type B - Retarding Admixture - An admixture that slows down the setting of concrete.
c.Type C - Accelerating Admixture - An admixture that speeds up the setting and early strength development of concrete.
d.Type D - Water-Reducing and Retarding Admixture - An admixture that reduces the quantity of mixing water required to produce concrete of a given slump and slows down the setting of concrete.
e.Type E - Water-Reducing and Accelerating Admixture - An admixture that reduces the quantity of mixing water required to produce concrete of a given slump and speeds up the setting and early strength development of concrete.
f.Type F - Water-Reducing, High Range Admixture - An admixture that reduces the quantity of mixing water required to produce concrete of a given slump by 12% or greater.
g.Type G - Water-Reducing, High Range and Retarding Admixture - An admixture that reduces the quantity of mixing water required to produce concrete of a given slump by 12% or greater and slows down the setting of concrete.
h.Air-Entraining - An admixture that encapsulates air in the concrete.
i.Lithium Nitrate – An admixture used to control the Alkali-Silica- Reaction (ASR) in concrete.
1007.02 Material Characteristics
1.Type A through G admixtures shall meet the requirements in ASTM C 494.
2.Air-entraining admixtures shall meet the requirements in ASTM C 260.
3.Use of admixtures other than t hose cited may be requested by the Contractor.
4.Admixtures shall not contain mo re than 1% of chlorides calculated as calcium chloride.
5.Admixtures shall be used at the manufacturer's recommended dosage rates.
6.The air-entraining admixture char acteristics shall produce concrete with satisfactory workability and a total air content as described in Table 1002.02. Chemical Admixtures 1007.03 - 793 - 7. a. When using the Lithium Nitra te admixture, the Contractor shall submit to the Engineer:
1.A five pound sample of Portland cement that will be used on the project.
2.The Manufacturer’s method for determining the recommendation for the required dose rate based on the equivalent alkali content.
3.Water content of the Lithium Nitrate admixture solution. b. The Engineer will report th e equivalent alkali content to the Contractor. The Contractor shall use th e reported equivalent alkali content to determine the required dose rate based on the manufacturer’s recommendation.
1007.03 Procedures
1.Field Addition of Admixtures:
a.The process for adding admixtures to a ready mix truck on the project site involves positioning the load of concrete up to the truck chute, stopping short of discharge.
b.The admixture is then poured over the surface of the concrete and mixed for at least 5 minutes.
c.No more than 1.3 gallons (5L) of water shall be used to rinse the admixture from the fins and top ch ute. This water must be shown on the proportioning report and shall not cause the water cement ratio of the mix to be exceeded.
d.When Lithium Nitrate is used, t he portion of the ad mixture that is water will be shown on the proportioning report and shall not cause the water cement ratio of the mix to be exceeded.
e.The Contractor is responsible for the addition of the admixture.
2.Field adjustment of Air Content:
a.If the air content is less than the minimum specified, addition of air-entraining admixtures is allowed.
b.The Contractor shall take measures based on manufacturer’s recommendations that are within complia nce of Department Specifications, to bring the load of concrete into t he Department described limits according to Table 1002.02.
c.If the air content is then ou tside the limits in Table 1002.02, the load of concrete shall be rejected. - 794 - SECTION 1008 -- FLY ASH
1008.01 Description
1.Fly ash shall be Class C or F meeting the requirements of ASTM C 618.
1008.02 Material Characteristics
1.All fly ash will be acceptance tested by the Department. This includes production plant samples and field samples.
2.Fly ash shall conform to the requirements of Class C or Class F pozzolan as defined in ASTM C 618 except that the maximum loss on ignition for Class F pozzolan shall be 3.0%. Either class of fly ash shall not contain more than 1.5% of available alkalis as Na 2O.
3.Fly ash produced in furnace operations utilizing liming materials or soda ash (sodium carbonate) as an additive will not be acceptable.
1008.03 Procedures
1.Fly ash shall be protected, stored, handled, and sampled in the same manner as specified for Portland cement in Sections 1002 and 1004 and the Department’s Materials Sampling Guide .
2.Each shipment of fly ash sent to the project or ready mix plant shall be accompanied with a certificate of compliance from the supplier. The certificate must include the following information:
a.Name of the supplier.
b.Source of the fly ash.
c.Consignee and desti nation of the shipment.
d.Project number to be used on, if available, and date shipped. e. Railroad car number or truck identification number.
f.Weight of the shipment. g. Certified test number repres enting the material being shipped.
h.An unrepeated order number or other identification number so that each shipment is separately identified.
i.The Department’s specificat ions that the product is in compliance with.
3.The following signed certificati on statement, or similar wording, must also be included on the form: ”This is to certify that this shipment of fly ash meets the specification requirements of the Nebraska Department of transportation for Class _____ fly ash.” Signed ___________________________________ For ______________________________________ (Supplier)
4.Two copies of the certificate of compliance shall be sent with the shipment for the Engineer. The Engineer will retain one copy for his/her file and send the other copy to the Department’s Materials and Research Division to serve as notification of rece ipt and identification of the fly ash.
Source: Nebraska Standard Specifications for Highway Construction, 2017 Edition. Pages 826–827 of 1,048.