1. Selection and Design of Concrete Mixes Concrete Technology George R. White

2. Objectives of properly mixed concrete • Required Qualities of Hardened Concrete • Workability of Fresh Concrete

3. Assumptions • Size of concrete member being cast and location and spacing of rebar within member • Environmental Exposure • Required strength of concrete

4. Water to Cement Ratio • Initial selection based on environmental exposure and type of structural member being cast

5. Water to Cement Ratio • Secondary selection based on required strength at specified break ( e.g. 3000 psi @ 28 days) • Add 15% for revised compressive strength

6. Water to Cement Ratio • Chose the LOWER (more conservative) W/C Ratio that satisfies BOTH criteria

7. Maximum Aggregate Size • No more than one-fifth minimum dimension of member • No more than three-fourths clear space between rebar or cover • For un-reinforced slabs, no more than one-third slab thickness • Choose maximum aggregate size that meets ALL above criteria

8. Air Content • Assume maximum aggregate Size • Determine whether concrete is air-entrained • Find recommended air content

9. Slump • Slump often specified • Slump an indicator of workability; with water-reducing admixtures, no longer a reliable indication of strength • See table for recommended slumps for various structural members

10. Freeze-Thaw Minimum Concrete Member: 8” Cover: 1.5” Required 28 day strength: 3000 psi W/C Ratio 0.5 Maximum Aggregate Size: 1” Air Entrainment: yes Amount of Air Entrainment: 6% ( by volume) Expected Slump Given/ Determined

11. Mix Design Table (1CY) • Water: 280# • Cement: 560# • Fines: 1020# • Coarse: 1940#

12. Admixtures for Concrete

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