PROPORTIONING OF HIGH STRENGTH CONCRETE

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When developing mixture proportioning for high-strength concrete, three fundamental factors must be considered in order to produce a mix design satisfying its intended property requirements:

• Mechanical properties of the aggregates,
• Mechanical properties of the paste,
• Bond strength at the paste-aggregate interfacial transition zone.

Upon satisfactorily addressing relevant mechanical and durability properties, the fresh concrete should be capable of satisfying the following constructability-related requirements:

• Be easily produced and delivered.
• Exhibit reasonably within-batch and between-batch uniformity.
• Maintain the desired consistency throughout the intended placement period.
• Resist segregation when placed and consolidated.
• When necessary, exhibit satisfactory finishing characteristics.

Broadly stated, the procedures for proportioning normal weight concrete by absolute volume consists of a series of steps, which when completed provide general estimations for a mixture meeting strength and workability requirements based on the combined properties of the individually selected and proportioned components.

The general steps of proportioning high strength concrete are:

1. Indentify relevant mechanical, durability and constructability requirements.
2. Select desired consistency (slump or slump spread).
3. Select the nominal maximum aggregate size (based on dimensional and constructability constraints.
4. Estimate the water content based on the cementitious materials used, aggregate characteristics, admixture characteristics, and air content requirements.
5. Estimate the target water-cement ratio considering both mechanical and durability requirements.
6. Estimate amount and proportions of cementitious material based on estimated water content and desired water-cement ratio.
7. Estimate the required dosage range of each chemical admixture.
8. Estimate the volume of coarse aggregate considering physical properties of coarse and fine aggregates and workability requirements.
9. Calculate required fine aggregate content.
10. Conduct laboratory trials for the purpose of evaluating the ability of the mixture to satisfy required mechanical, durability, and constructability properties, while chemical checking for possible constituent material incompatibility and adjusting the materials or mixture proportions as needed.
11. Conduct field trials tests replicating anticipated job conditions, adjusting the materials or proportions as needed.