concrete 3 Flashcards
what is hydration/curing?
the process of the concrete becoming hard
what is curing?
the rapid strength gain of the concrete when the cement is able to hydrate
what should be controlled during the curing process and why?
the moisture and the temperature, because of the fact that loss of moisture leads to plastic shrinkage (produces surface cracks)
what could cause moisture loss?
winds, heat and cement content
what is plastic shrinkage?
what there is significant moisture loss in the concrete (caused by the evaporation of bleeding water)
what are ways of controlling plastic shrinkage?
wind breaks, sun shields, covering concrete with polythene sheets
what happens to concrete in LOW temperatures?
the hydration and curing process happen slowly, the water within the concrete freezes then melts which creates voids
what happens to concrete in HIGH temperatures?
loss of moisture causing plastic shrinkage
what are the 2 main properties of hardened concrete?
strength and stiffness
what is stiffness of concrete affected by?
durability
what are the 2 types of strength of concrete?
the characteristic strength (tested in lab), the factorised strength for design (characteristic strength with safety factor for design purposes)
what factors could affect the concrete strength?
water cement ratio, the type and quality of the aggregates and the cement, the batching, mixing, curing process and temperature
what are the 2 methods of testing compressive test?
the cube test (BS) and the cylinder test (BES)
what is the equation for finding the strength once you’ve done the compressive tests
cube/cylinder strength= crushing load / X-sectional area
what would the euro code be for a normal concrete with the cube strength of 50?
1) find the cylinder strength: Fcyl= 0.85 x Fcu - 1.6
2) write the form of: type of concrete, cylinder strength / cube strength
how would the lab determine the strength of the concrete after testing a batch
by using the equation: Fcu = Fcmean - 1.64 x standard deviation
the Fcu must be < Fcmin + 4
what are the method of testing tensile strength
Brazilian test and prism test
how do we test the shear strength?
no don’t, concrete in bad under shear stress we add reinforcement bars
