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2015SpringShotcreteEMag

Capillary action is the transport of water or (protecting) or breaking down (destroying) the moisture and material in solution by the forces of passivity layer on and around all embedded steel capillary motion and capillary rise. In general, this reinforcement. Except for the electrochemical is the ability of water or moisture and material in migration associated with steel reinforcement, solution to transport through narrow passages electrochemical gradients within cementitious without the assistance of gravity or bulk motion. In materials typically cause migration of material in Fig. 2, an 8 in. (200 mm) dry concrete cylinder is solution on the scale of millimeters. placed in a bucket with 4 in. (100 mm) of standing water; the water is wicked into the cementitious Other Terms and Definitions matrix. This is mainly due to sorptivity. The water • Decompose—break down into components, or or moisture and material in solution, however, con- to separate into constituents or elements tinue to slowly climb upward against gravity; this • Deteriorate—to decompose, decay, breakdown, upward permeation is mainly due to capillary action. or crumble Combined Mechanisms • entially remove material into a solution -Dissolution—to extract chemically or prefer Not all attacks on concrete or shotcrete include • Dissolve—to disintegrate a material chemically mass transport as a contributing factor. While into a solution, or to break apart physical gradients, chemical gradients, electrical • Etch—to physically or chemically carve or gradients, and combinations of these were placed engrave into the surface of a material within the overall sphere of mass transport deterio- • Leach—the loss of mineral and organic solutes ration mechanisms (refer to Fig. 1), this may not due to percolation from a material always be technically correct. For example, freezing • Migration—a motion of material in solution, and thawing could be considered solely a physical distinct from diffusion, due to an electrical- deterioration, and a sphere could be added to the applied force or electrical gradient diagram that is outside of (but still linked with) the mass transport sphere. However, for cementitious materials exposed to water or moisture contact, mass transport mechanisms often initiate, facilitate, and govern the rate at which deterioration proceeds. Jonathan E. Dongell is current In other words, if there was no water or moisture Director of Research & Dev- present, there would be no mass transport mecha- elopment, Pebble Technologies, nism, and there would be no deterioration. Scottsdale, AZ. Dongell has worked in concrete construction Physicochemical and with cementitious materials Deterioration caused by the physical action of spanning over 30 years. His roles erosion, weathering, or decomposition does not have included technician, super- require a mass transport mechanism to proceed. intendent, manager, contractor, and President. He However, a cementitious material placed in a water- was Past President, Whitestone Cement Company, contact environment or exposed to cycles of wet- Scottsdale, AZ (1998-2005) and Universal White ting and drying can experience a physicochemical Cement Co, Inc., Glendale, AZ (1992-1998). He is attack. The combination of physical attack (abra- a member and past Chair of ACI Committee 524, sion, weathering, and so on) and chemical attack Plastering, and is a member of ACI Committees 201, (leaching, dissolution, dissolving, or formation of Durability of Concrete; 225, Hydraulic Cements; concentrated areas of salts or alkalis) is facilitated 232, Fly Ash in Concrete; 308, Curing Concrete; by mass transport mechanisms. With salt weath- 350, Environmental Engineering Concrete Struc- ering, for example, there is mass transport of salts tures; and 555, Concrete with Recycled Materials. into a cementitious matrix, but the attack may be Dongell also serves on the ACI Concrete Research considered strictly a physical attack as it results Council (CRC) and the ASA Pool & Recreational from the precipitation of salts within the matrix Shotcrete Committee. He is a voting member of without necessarily the dissolution of the cementi- ASTM International main committees and several tious components to drive the degradation. In either subcommittees, including C4.01, Cement, Lime, instance, a mass transport mechanism facilitates Gypsum, and C4.02, Concrete and Aggregates. the attack. The attack is considered a “physical salt Dongell is the author of several books, including attack” form of deterioration, made possible by a The Durability of Cementitious Materials in a Water physicochemical transport mechanism. Contact Environment. He is an inventor and holds three patents on cementitious materials. Dongell Electrochemical is a designated expert witness in the fields of cement, Electrochemical transport is a migration of concrete, stucco/plaster, and water chemistry. He electrons or ions through solution. This mecha- was the recipient of the Del Bloem Distinguished nism plays an important role in maintaining Service Award in 2008. 10 Shotcrete • Spring 2015


2015SpringShotcreteEMag
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