CIV
Chapter 9-Volume Changes hooton2017.pdf

Reducing evaporation rates and reducing plastic

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Reducing Evaporation Rates and reducing plastic shrinkage Volume Changes of Concrete Swelling in Water Volume Changes of Concrete Drying and re-wetting in capillary pores (valid down to ~40% rh) Volume Changes of Concrete Shrinkage at nano-level in C-S-H (from 0-40% rh) Volume Changes of Concrete As aggregate to cement ratio increases, shrinkage reduces. As Elastic modulus of aggregate increases, shrinkage is also reduced Volume Changes of Concrete Volume Changes: Swelling and Drying cycles
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5 Volume Changes of Concrete Influence of Curing on Swelling and Shrinkage More curing reduces on-set and rate of drying shrinkage Feb 7 Volume Changes of Concrete Volume Changes of Concrete Shrinkage and Cracking Saw Cuts 1/3 Depth of 400mm thick airport pavement Contraction joint in Pavement
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6 Volume Changes of Concrete Control Shrinkage Cracking Volume Changes of Concrete Saw cut joints in the wrong places Volume Changes of Concrete Halifax area corroded bridge expansion joint filled with debris Forgot to continue the joint Volume Changes of Concrete Costco, Etobicoke Volume Changes of Concrete Feb 10 Volume Changes of Concrete
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7 Volume Changes of Concrete Shrinkage, RH, and Drying Time Volume Changes of Concrete Drying Shrinkage at 50% rh Big elements shrink more slowly Volume Changes of Concrete Long-Term Drying Shrinkage About 1/3 of drying shrinkage occurs after 1 month 80-90% in 1 year Volume Changes of Concrete Shrinkage and Water Content Therefore use of water reducers will reduce shrinkage --smaller paste fraction and more aggregate Volume Changes of Concrete Drying Shrinkage of Fly Ash Concretes Effects of cementing materials on shrinkage is small 25% fly ash Volume Changes of Concrete Shrinkage (Comité Euro-International du Béton (CEB) 1970 Method) Concrete undergoes drying shrinkage as it dries out in service. The amount of shrinkage is a function of relative humidity in the air, time of drying, the properties of the concrete (w/cm and cement content) the size of the structural element. The least dimension and area of surface exposed to drying, perpendicular to the direction of interest are expressed as an “effective thickness”, em.
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8 Volume Changes of Concrete Calc. effective thickness, e m The first step is to draw a sketch of the element, including the dimensions, direction of interest for the shrinkage calculation, and the direction(s) of drying.
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  • Fall '13
  • MarikoUda
  • CEB, autogenous

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