Effect of moisture content of concrete on water uptake
- Concrete Concepts Ingenieurgesellschaft mbH Brandes, Lay, Rucker, Fraunhoferstrasse 30b, 80469 Muenchen (Germany)
The penetration of water and non-polar hexane in Portland cement mortar prisms with different initial moisture contents was investigated using nuclear magnetic resonance ({sup 1}H NMR). The amount of water in gel pores strongly affects the penetration of water in much larger capillary pores. Water penetration is reduced by the self-sealing effect as characterized by non-sq roott dependence of capillary uptake and penetration depth. This is explained by the ongoing redistribution of water from capillaries into gel pores which results in internal swelling and loss of continuity of the capillary pore system; a correlation was observed between the amount of redistributed water and departure from sq roott behaviour. A descriptive model is used to explain the dependence of water uptake and penetration on moisture content. For increasing initial moisture contents up to a critical value equivalent to equilibrium with a relative humidity between 65 and 80%, less penetrating water is able to redistribute. Thus more penetrating water is in larger capillaries with less viscous resistance; uptake and penetration depth increase. Above the critical initial moisture content, uptake and penetration depth decrease towards zero. This is explained by (a) an overall reduction in capillary pressure because transport takes places in fewer and larger pores and (b) an increase in viscous resistance due to the connection of penetrating capillary water with pores already containing water. Less capillary pore space is available for transport. The surface region of concrete placed in contact with water is not instantaneously saturated. Water content increases with time depending on the degree of surface saturation. A new transition coefficient for capillary suction gamma is defined for the calculation of surface flux.
- OSTI ID:
- 21344740
- Journal Information:
- Cement and Concrete Research, Vol. 40, Issue 1; Other Information: DOI: 10.1016/j.cemconres.2009.09.001; PII: S0008-8846(09)00241-5; Copyright (c) 2009 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0008-8846
- Country of Publication:
- United States
- Language:
- English
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CONCRETES
HEXANE
HUMIDITY
MORTARS
NUCLEAR MAGNETIC RESONANCE
PENETRATION DEPTH
PERMEABILITY
PORTLAND CEMENT
SURFACES
SWELLING
WATER
ALKANES
BUILDING MATERIALS
CEMENTS
DEFORMATION
HYDROCARBONS
HYDROGEN COMPOUNDS
MAGNETIC RESONANCE
MATERIALS
MOISTURE
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
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