Batching, Mixing, Transporting, and Handling Concrete Design and Control of Concrete Mixtures Chapter 13 Overview Ordering concrete Performance specifications Batching Mixing Transporting and Handling 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 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 Batching Mixing Concrete Mobile Batcher Mixed Concrete 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 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 Transporting and Handling Choosing Placement Method Below, at, above ground level Rapid without segregation or waste Avoids cold joints 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 Above Ground Summary Ordering concrete Performance specifications Batching Mixing Transporting and Handling Questions