Ready-mixed concrete shall conform to the requirements of ASTM C 94. Concrete mixes shall be proportioned in accordance with ACI 211.1, and ACI 301.
The contractor shall employ an independent testing laboratory to establish the proportions of the design mixes and provide preliminary cylinder testing. The cost of the design mix and preliminary cylinder tests shall be paid by the contractor.
Types of Concrete Mixes and their Strengths
Mix Design
Strength
All concrete shall have a minimum compressive strength of 4000 psi at 28 days, unless otherwise specified on the contract drawings.
Water-Cement Ratio
The maximum permissible water-cement ratio for concrete shall conform to the following table, unless strength data or trial mixtures are available. The amount of water and the proportion of mortar to coarse aggregate for each mix shall (at all times) be the least which will produce uniformly dense concrete, free from aggregate pockets or honeycombs.
| Concrete Strength (psi) | Water-Cement Ratio(max) | Water-Cement Ratio (max) |
| (non air-entrained) | (air-entrained) | |
| 2000 | 0.76 | 0.62 |
| 3000 | 0.58 | 0.46 |
| 4000 | 0.44 | 0.35 |
These values are not applicable when concrete contains admixtures other than those used exclusively for entraining air.
Air Entrainment
Air entrainment shall be in accordance with ASTM C 260.
All concrete shall contain 6% air entrainment with an allowable tolerance of 1%, unless otherwise specified on the contract drawings.
Workability
The proportions of aggregate to cement for any concrete mix shall produce a mixture that will work readily into the corners and angles of the forms and around reinforcement with the method of placing employed, but without permitting the materials to segregate or excess free water to collect on the surface. The proportion by volume of coarse aggregate to cement shall be as specified in ACI 211.1.
Slump
Concrete slumps shall be as indicated in this section. A tolerance of up to 1 inch above the maximum indicated will be allowed for one batch in any five consecutive batches tested.
Concrete shall be proportioned to comply with the slump requirements as follows:
Slump Requirements (All Dimensions in Inches)
| Concrete Use | Maximum Aggregate Size |
Working Slump |
Maximum
Slump (Rejection) |
| Foundations and Grade Beams | 1 1/2 | 4 | 5 |
| Water Retaining Structures | 3/4 | 3 | 4 |
| Slabs/Walls less than 8 in | 3/4 | 4 | 5 |
| Tremie | 3/4 | 4 | 6 |
| Backfill | 2 | 5 | 6 |
| All Other Normal Weight Concrete | 1 1/2 | 4 | 5 |
The maximum slump of the concrete may exceed the values listed in this table if the mix has included a high range water reducing admixture which is necessary for the type of placement. This type of deviation must be approved in writing by the design engineer.
Concrete may be supplied with a slump less than the working slump listed above if it can be properly placed and consolidated.
Concrete Mix Submittals
The contractor shall submit the proposed concrete mix to the Air Products representative for approval. All mix designs must be submitted at least 15 days in advance of the concrete operation to which the mix applies. A proposed mix design must be submitted for each concrete compressive strength required by contract drawings and specifications.
All of the following information shall accompany each mix design:
- Type of structure(s) to which mix applies, that is. , floors, foundations, and walls.
- Sources of aggregate and test data certifying the requirements of ASTM C 33.
- Complete gradation and fineness modulus of both fine and coarse aggregates.
- Specific gravity of both fine and coarse aggregates and cement.
- Dry, rodded unit weight of both fine and coarse aggregate.
- Quantities of all components of the mix, including air entrainment agents, superplasticizer, and other admixtures, if used.
- Where admixtures are used, the manufacturer’s information shall accompany the mix design.
- Results of a 7-day and 28-day cylinder test using the proposed mix. (All tests shall be conducted in accordance with paragraph 10 and any subsections thereof.)
- Plant standard deviation, if available.
- Type of cement, such as, Type I, II, or III.
No substitution of materials of an approved mix design shall be made without the prior written approval of the Air Products representative. All of the above must be submitted to obtain approval.
Client or Company approval of the concrete design mix does not relieve the contractor of the responsibility to furnish materials and construction in full conformance with the drawings and specifications.
If, during the progress of the work, it is desired to use materials or proportions other than those originally approved or if the materials from the sources originally approved change in characteristics, the contractor shall submit for approval evidence that the new combinations of materials will produce concrete meeting the requirements of this specification and will not bring about objectionable changes in color, appearance, or structural strength.