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To separate shrinkage from creep, the compliance function (, ′), defined as the stress-produced strain (i.e., the total strain minus shrinkage) caused at time t by a unit sustained uniaxial stress = applied at age ′, is measured as the strain difference between the loaded and load-free specimens.
Concrete has a very low coefficient of thermal expansion, and as it matures concrete shrinks. All concrete structures will crack to some extent, due to shrinkage and tension. Concrete which is subjected to long-duration forces is prone to creep. The density of concrete varies, but is around 2,400 kilograms per cubic metre (150 lb/cu ft). [1]
Concrete is a brittle material and can only withstand small amount of tensile strain due to stress before cracking. When a reinforced concrete member is put in tension, after cracking, the member elongates by widening of cracks and by formation of new cracks. Figure 1 Formation of internal cracks
Normal concrete contains 19 mm (0.75 in) equivalent diameter aggregate which is 35-45% of concrete, fibers longer than 20 mm (0.79 in) are more effective. However, fibers that are too long and not properly treated at time of processing tend to "ball" in the mix and create work-ability problems.
The derivation of the maximum arching moment of resistance of laterally restrained concrete bridge deck slabs utilised Rankin's [21] idealised elastic-plastic stress-strain criterion for concrete, valid for concrete cylinder strengths up to at least 70N/mm 2, which he had derived on the basis of Hognestad, Hanson and McHenry's [23] ultimate ...
ASTM C1293: "Test Method for Concrete Aggregates by Determination of Length Change of Concrete Due to Alkali-Silica Reaction". It is a long-term confirmation test (1 or 2 years) at 38 °C in a water-saturated moist atmosphere (inside a thermostated oven) with concrete prisms containing the aggregates to be characterised mixed with a high-alkali ...
It models concrete considering concrete stresses in principal directions summed with reinforcing stresses assumed to be only axial. The concrete stress-strain behaviour was derived originally from Vecchio's tests and has since been confirmed with about 250 experiments performed on two large special purpose testing machines at the University of ...
The concrete can develop high compressive and tensile strengths, while shrinkage and creep remain acceptable, but will generally be less rigid than conventional mixes. The most obvious advantage is the low density, but these concretes also have low permeability to water and greater thermal insulation.