Volume Changes of Concrete Design and Control of

Overview n Early age volume changes n Moisture changes n Temperature changes n Curling

Volume Changes of Concrete n Many reasons for volume changes n Understanding volume changes

Subsidence n Vertical shrinkage before initial set n Caused by bleeding, escaping air, and

Moisture Changes – Effect of Materials n Aggregates restrain shrinkage n Second greatest influence

Temperature Changes of Hardened Concrete n Concrete expands as temperature rises n Average value

Temperature Changes – Low Temps n Subfreezing volume changes depend on moisture content and

Chemical Changes and Effects n Carbonation shrinkage n Sulfate expansion n Alkali-aggregate expansion

Summary n Early age volume changes n Moisture changes n Temperature changes n Curling

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Volume Changes of Concrete Design and Control of Concrete Mixtures – Chapter 10

Overview n Early age volume changes n Moisture changes n Temperature changes n Curling and warping n Elastic and inelastic deformation n Creep n Chemical changes and effects

Volume Changes of Concrete n Many reasons for volume changes n Understanding volume changes is useful n Restraint of volume changes leads to cracking

Early Age Volume Changes

Chemical Shrinkage

Autogenous Shrinkage

Subsidence n Vertical shrinkage before initial set n Caused by bleeding, escaping air, and chemical shrinkage n May be a symptom of lack of consolidation n May lead to cracking over embedments

Plastic Shrinkage Cracking

Swelling

Moisture Changes of Hardened Concrete

Moisture Changes

Moisture Changes – Effect of Materials

Moisture Changes – Effect of Materials n Aggregates restrain shrinkage n Second greatest influence behind total water content n Quartz, granite, feldspar, limestone, and dolomite produce lower shrinkage

Moisture Changes – Effect of Materials

Moisture Changes – Effect of Curing

Temperature Changes of Hardened Concrete n Concrete expands as temperature rises n Average value about 10 millionths per degree Celsius (5. 5 millions per degree Fahrenheit) n Range: 6 -13 millionths/degree Celsius (3. 2 -7. 0 millionths/degree Fahrenheit)

Temperature Changes

Temperature Changes – Low Temps n Subfreezing volume changes depend on moisture content and behavior, aggregate type n Low temperatures also increase strength of moist concrete---little effect on dry concrete

Temperature Changes – High Temps

Curling and Warping

Elastic and Inelastic Deformation

Elastic/Inelastic Deformation

Poisson’s Ratio

Shear and Torsional Strain

Creep

Chemical Changes and Effects n Carbonation shrinkage n Sulfate expansion n Alkali-aggregate expansion

Summary n Early age volume changes n Moisture changes n Temperature changes n Curling and warping n Elastic and inelastic deformation n Creep n Chemical changes and effects

Question s ?