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