For use in the Denver Water Service Area

Materials Specification – 18
for
Normal Weight And Precast Concrete

1. Concrete Mix Submittal:

A minimum of 10 days prior to starting concrete work, concrete mix designs shall be submitted in accordance with ACI 301 for Denver Water approval. No changes shall be made in the amounts or sources of the approved mix ingredients without written approval of Denver Water. Production inspection and field testing of the approved mix may be made by Denver Water.

2. Concrete Products:

A. Cementitious Materials:

1) Cement

All Cement used shall be Type II portland cement which shall conform to the requirements of ASTM C 150.

2) Fly Ash:

Fly ash may be used in the concrete mixes. The amount of fly ash shall be 15% by weight of the total cementitious materials. Fly ash additions to the mix will be on a cement substitution basis. The fly ash shall conform to ASTM C 618.

B. Aggregates:

1) Fine Aggregates

Fine aggregate shall consist of natural sand or a blend of natural sand and crushed sand provided the quantity of crushed sand is not more than 50% of the total sand by dry weight. All fine aggregate shall conform to the grading and quality requirements of ASTM C 33.

2) Coarse Aggregates

Coarse aggregate shall consist of gravel or crushed stone and shall conform to the grading and quality requirements of ASTM C 33 for Size No. 467, No. 57, or No. 67. Nominal maximum size of coarse aggregate shall comply with ACI 318.

If the aggregates used are known to be reactive with high alkali cement, as determined by ASTM C 295, or if the reactivity of the aggregate is not known, the use of low alkali cement is required to assure adequate protection from alkali-aggregate reaction.

C. Water:

The batch mixing water and mixer washout water shall conform to the requirements ASTM C 94.

D. Admixtures:

Calcium chloride shall not be used.

An air-entraining agent shall be used in all concrete. The agent sued shall conform to ASTM C 260. It shall be added to the batch in accordance with ASTM C 94.

Chemical admixtures which do not contain calcium chloride and which conform to ASTM C 494 for concrete may be used. All chemical admixtures shall be compatible with the cement and all other admixtures in the batch.

All damages or difficulties occurring as a result of the use of any admixtures shall be the responsibility of the user. Denver Water will not provide any compensation for concrete because of such difficulties. Use of admixtures shall in no way relieve the responsibility for protection and curing of the concrete.

3. Concrete Proportions:

Concrete shall be made in two classes: Class A concrete and Class B.

Class A concrete shall have a minimum 28 day compressive strength of 4000 psi when molded and cured as in compliance with ASTM C 31 and shall be used for all structural and precast concrete.

Class B concrete shall have a minimum 28 day compressive strength of 2500 psi when molded and cured as in compliance with ASTM C 31 and may be used for concrete kickblocks exclusively.

All concrete shall be air entrained to a total air content of 5% plus 2% or minus 1% of the volume of the batch. The minimum slump shall be 2 inches and the maximum slump shall be 4 inches as when tested in accordance with ASTM C 143.

Fine aggregates shall be between 36% and 44% by volume of the total aggregates in the concrete.

4. Enforcement of Strength Requirements:

Should the strengths by the laboratory cured test specimens made and tested in accordance with the provisions of the Standards and evaluated by the methods recommended in ACI 318 fall below the specified values, Denver Water shall have the right to require changes in the proportions of the concrete mix to be used on the remainder of the work.

Denver Water may require a minimum of three concrete cores drilled in the manner described in ASTM C 42 and tested for compressive strength in the manner described in ASTM C 39 for each portion of the work where the laboratory cured concrete test cylinders indicate failure to meet the specified strength requirement within the specified time period.

If the results of this test do not satisfy the strength requirements of this Standard, Denver Water shall have the right to require strengthening or replacement of those portions of the structure which have failed to develop the required strength.