Manufacture and handling of concrete Flashcards
What are the three main methods of concrete manufacture?
Site-batched concrete
Ready-mixed concrete
Precast concrete
What is site-batched concrete?
Concrete manufactured on-site using mobile batching and mixing facilities. Raw materials, formwork, and reinforcement are stored on-site.
What is ready-mixed concrete?
Concrete manufactured at a stationary batching plant and transported to the site via transit mixers. Raw materials are stored at the plant.
What is precast concrete?
Concrete members manufactured off-site, then transported and assembled on-site by the contractor.
What are the two methods of batching materials?
Volume
Mass (preferred)
What is the aim of mixing concrete?
Ensure uniform dispersion of materials.
Achieve consistent color, texture, and workability.
What are the two main types of machine mixing?
Free-fall (tilting drum, reversing drum, split drum)
Forced action (pan, single/twin-shaft)
What should be considered when transporting concrete?
Prevent segregation and contamination.
Maintain workability.
Method depends on site conditions, volume, and placement rate.
Name 5 methods of transporting concrete.
Tower crane and bucket
Wheelbarrows/dumpers
Chutes
Belt conveyors
Pumps
Why is concrete compacted?
To remove entrapped air, which can weaken strength, durability, and bond with reinforcement.
What are the methods of compacting concrete?
Hand compaction
Mechanical (poker vibrator, surface vibrator, form vibrator)
What are the stages of finishing concrete?
Floating (embed aggregates, smooth surface)
Trowelling (produce smooth finish)
Why is curing important?
To maintain moisture and temperature for cement hydration, ensuring full strength, durability, and low permeability.
What are the methods of curing concrete?
With water: Ponding, spraying, wet sand/hessian.
By sealing: Formwork, plastic sheeting, membrane compounds.
What are the four concrete construction methods?
Extruded concrete
Slip forming
Sprayed concrete
Roller-compacted concrete
What is slip forming?
Concrete is poured into a continuously moving formwork, used for vertical/horizontal structures like walls or paving.
What is roller-compacted concrete used for?
Roads and dams due to its low water content and compaction with vibratory rollers.
