civ2043 6.manufacture and handling of concrete Flashcards
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
what is Ready mixed concrete?
- concrete manufacture at a specialised stationary concrete manufacture or batching plant
what is precast concrete ?
-concrete members batched , mixed ,placed compacted ,finished ,and cured offsite at specialised precast concrete manufactures and then transported to site to be assembled by contractors
give 4 aspects to consider when choosing a method of manufacture
-Quality control
-Labour
-production rate
-access to site
Things to consider when transporting concrete
-Method of concrete manufacture
-Site Condition
-Is placement continuous
-equipment availability
methods of mixing
-hand mixing
-machine mixing
what is the aim of mixing concrete
-Each material is roughly dispered throughout concrete
-concrete consistence
methods of transporting concrete?
-Tower crane
- Wheelbarrows and dumperes
-chutes –useful when moving concrete down
- Belt conveyors– useful moving concrete horizontally
pump - moves concrete in any direction
-
methods of placing concrete
-Extruded concrete
-Slip forming
-sprayed
-Roller-compacted concrete
why does concrete need to be compacted ?
Remove entrapped air as this may reduce strength , durability,watertightness,and bond between reinforcement and concrete
methods of compacting ?
Hand compaction
- but is slow ,labour intensive and require high workability
mechanical compaction
-poker vibrator
-surface vibrator
-form vibrator
why are wearing surfaces finished ?
Ensures concrete is strong ,hard,flat and smooth
give too stages of finishing concrete
-floating –embed aggregates , remove ridges and fill in cavities
-Trawelling – produce smooth surface
why do we protect fresh concrete
-protect it from loss of moisture before and during placing
-rapid drying
-extreme temperature
external damage
what is Curing concrete ?
-maintain moisture and temperature conditions in freshly placed concrete
Why is concrete cured?
-allow continuation of cementing reactions such that full potential of concrete(degree of hydration,strength and permeability) is realised.
Methods of curing
-curing with water
*spraying
*placement of wet sand
-curing by sealing
*plastic sheeting
*leaving formwork
