concrete 2 Flashcards
(19 cards)
what are the three methods of mixing concrete?
ratio method
British standard method
british euro standard method
what is the BS for getting the concrete to the site?
25% should be mixed on site (should arrive within 2hours of the ready mix (75%)), drum should rotate at 10-15 rpm for at least 3 minutes
what are the different methods of transportation?
short- for low consistency concrete and rapid placement
long- for high consistency concrete (so it doesn’t set in the truck) and slow placement
what are the different methods of placement?
direct and indirect (when the concrete is pumped- high consistency)
what is compaction?
the process of removing air voids (electric rep used)
what the different types of finishing?
smooth, exposed aggregate, tooled and textured
what is fresh concrete?
what concrete is transported and placed
what is early age concrete?
a few days after its placement
what is means by consistency / workability?
how easily the concrete flows, mould, compacts and finishes
what is strength?
maximum stress a material can take
what is consistency affected by?
aggregate size, share and surface texture
is it okay to add water to increase concrete’s consistency?
no, water is not a safe way of increasing consistency as there is risk of segregation and it weaken the concrete
what cohesiveness?
when concrete that resist segregation during its transportation, placement and compaction
how can cohesiveness be improved?
by adding sands and cement
what are the tests made to measure cohesiveness?
slump test, slump flow test, flow table table and compacting factor test
what is segregation?
the separation of coarse aggregates from the finer materials within the concrete
what meant by the term “bleeding”?
what the concrete is being compacted too much and water starts to rise and the heavier materials sink to the bottom
what is a flash set and what are its different types?
it is the early loss of conistency
hot: insufficient gypsum
cold: incorrect gypsum
what is plastic settlement?
the restrain of the settlement of concrete when it falls around reinforcements bars
