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2015SpringShotcreteEMag

Fig. 1: Deterioration mechanism of a water contact environment growing random fashion would be diffusion. In sorption and capillary action. Sorption is the Fig. 2, an 8 in. (200 mm) pre-saturated concrete transport of water, moisture, and material in solu- cylinder is placed in a bucket with 9 in. (230 mm) tion by the combination of absorption and adsorp- of standing water. The resulting convection transport tion (refer to Fig. 2). Absorption is the permeation mechanism is due to concentration gradient of (x) of water or moisture and material in solution into ions. Subsequent random spreading of the (x) ions a dry or under-saturated cementitious matrix. This is diffusion due to a chemical concentration gradient. process can also be reversed, from a wet cementi- tious material to a dry or under-saturated soil. Wicking Adsorption is the physical adhesion of atoms, Wicking is the movement of water or moisture ions, or molecules to the compounds and solid and the transport of the material in solution by surfaces within the cementitious matrix. MASS TRANSPORT Wicking requires a lack of water or moisture Convection requires sufficient water or moisture to be (moisture gradient to be present somewhere in present throughout the system and some other gradient the system in order to facilitate the transport (chemical, temperature, electrical, etc.) that facilitates of water or moisture (and matter in solution). the transport of matter from one place to another. Fig. 2: Deterioration—transport mechanisms Shotcrete • Spring 2015 9


2015SpringShotcreteEMag
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