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Published byBenedict Pope Modified over 9 years ago
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Batching, Mixing, Transporting, and Handling Concrete Design and Control of Concrete Mixtures – Chapter 13
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Overview Ordering concrete Performance specifications Batching Mixing Transporting and Handling
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Ordering Concrete ASTM C94, Standard Specification for Ready- Mixed Concrete Ordering concrete Purchaser specifies slump, nom. max. size aggregate, and one of: Option A – designates strength Option B – selects proportions Option C – designates strength and cement content
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Performance versus Prescriptive Tradition – owner/agency establishes prescriptive proportions Puts risk of meeting performance targets on owner/agency New methods – owner/agency establishes performance targets Producer establishes proportions Flexibility, increased innovation, significant cost reductions Risk is on producer
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Batching
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Mixing Concrete
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Mobile Batcher Mixed Concrete
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Retempering Concrete Water additions are allowed if: Maximum w/cm not exceeded Maximum slump not exceeded Maximum mixing/agitating time not exceeded Concrete remixed a minimum 30 revolutions Not allowed for partial loads
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Transporting and Handling Delays Prior planning to optimize productivity Early stiffening and drying out High temperatures/hot weather/accelerators Cold temperatures/cold weather/retarders Segregation Excessive shrinkage, honeycombing
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Transporting and Handling
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Choosing Placement Method Below, at, above ground level Rapid without segregation or waste Avoids cold joints
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At and Below Ground Level Largest volume concrete placements Most methods are adequate Pumps, cranes, conveyors, chutes… Gravity is helpful Watch for air loss in pumps
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Above Ground
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Summary Ordering concrete Performance specifications Batching Mixing Transporting and Handling
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Questions
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