Cement Permeability
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Transcript of Cement Permeability
8/9/2019 Cement Permeability
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PermeabilityOf concrete
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Permeability
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
Durability of concrete: ability to resistweathering action, chemical attack,abrasion, or any process ofdeterioration
Permeability
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Permeability
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
chemical processes of degradation
physical processes of degradation
Water Causes
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Permeability
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
Water Structure
The H-O-H molecule is covalent bonded. Due todifferences in the charge centers of hydrogen and oxygen,the positively charged proton of the hydrogen ionbelonging to a water molecule attracts the negativelycharged electrons of the neighboring water molecules.
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Permeability
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
Water Structure
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Permeability
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
Water in Concrete
In concrete, water is a necessary ingredient for thecement hydration reactions and an agent that facilitatesthe mixing of the components of concrete, water ispresent from the beginning.
Gradually, most of the evaporable water in concrete islost, leaving the pores empty or unsaturated.
Concrete will not be vulnerable to water-relateddestructive phenomena if there is a little or no evaporablewater left after drying and provided that the subsequentexposure of the concrete to the environment did not causeto resaturation of the pores. The latter, to a large extent,depends on the hydraulic conductivity, which is alsoknown as the coefficient of permeability (K).
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Permeability
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
Definition
Permeability is defined as the property thatgoverns the rate of flow of a fluid into a poroussolid.
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Permeability
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
Darcy’s law
For steady-state flow, the coefficient ofpermeability K is determined from Darcy'sexpression:
where Dq/dt is the rate of fluid flow, ν the viscosity of the fluid, ∆ Hthe pressure gradient, A the surface area, and L the thickness of the solid.
Dq/dt = K ( ∆ H A)/(Lν )
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Permeability
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
Permeability of the paste
the mixing water is indirectly responsible for permeabilityof the hydrated cement paste because its contentdetermines first the total space and subsequently theunfilled space after the water is consumed by eithercement hydration reactions or evaporation to theenvironment.
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Permeability
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
Age (days) Permeability (cm/s 10 -11 )
Fresh 20,000,000
5 4,000
6 1,000
8 400
13 50
24 10ultimate 6
Permeability of Cement Paste
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b l
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Permeability
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
Permeability of Aggregate
Compared to 30 to 40 percent capillary porosity of typicalcement pastes in hardened concrete, the volume of poresin most natural aggregates is usually under 3 percent, andit rarely exceeds 10 percent.
P bili
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Permeability
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
Permeability of Aggregate
However, the coefficient of permeability of aggregates areas variable as those of hydrated cement pastes ofwater/cement ratios in the range 0.38 to 0.71
P bili
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Permeability
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
Reason
The reason some aggregates give much higherpermeability than the cement paste is that the size ofcapillary pores in aggregate is usually much larger.
Most of the capillary porosity in a mature cement paste
lies in the range 10 to 100 nm, while pore size inaggregates are, on the average, larger than 10 microns.
P bili
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Permeability
P K Mehta and P J M Monteiro Concrete: Microstructure Properties and Materials
Permeability of Aggregates
Type of Rock permeability (cm/sec )
dense trap 2.47 x 10 -12
quartz diorite 8.24 x 10 -12
marble 2.39 x 10 -10
granite 5.35 x 10 -9
sandstone 1.23 x 10 -8