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2015SummerShotcreteEMag

Technical Tip Controlling Efflorescence By Jonathan E. Dongell and Jerry B. Werner EIts occurrence may be of little consequence 2. A sufficient supply of moisture to transport theAn available supply of soluble salt-formingcomponents;1.fflorescence typically manifests itself as awhite salt deposit on the surface of a material. or may be a sign of significant internal distress. salt-forming components in solution; and It may appear as a white powdery dusting across 3. Sufficient permeability, or spacial interconnec- the surface or as a thick hardened white crust tivity, within the structure to allow the transport exuding from cracks. It may intensify in wet of the salt-forming solution to the surface. periods and diminish in dry periods. It may The mechanisms that create efflorescence are encompass a large majority of the surface or may evaporation and precipitation. However, other be confined to small areas of the surface. transport mechanism(s) are typically present, This article is an introduction to the topic of allowing the overall process to proceed. These are efflorescence. Various mechanisms and factors the driving forces that move moisture into, that facilitate the formation of efflorescence and through, and/or upward to the surface of the methods for reducing or eliminating its occurrence structure (a more detailed discussion on these are introduced. Consideration for the aesthetic transport mechanisms can be found in “Durability and Exposure Conditions of Cementitious Mate- ramifications, and structural implications, of the rials,” Shotcrete magazine, Spring 2015). presence of efflorescence is offered. Of course, Knowing that the aforementioned factors and every structure is unique. Therefore, having a mechanisms are necessary for efflorescence to thorough understanding of the facts and condi- form allows insight into measures that might be tions for a specific project (mixture design, appli- taken to reduce or stop its occurrence. cation, and placement environment) is necessary to determine a preferred course of action. Salt-Forming Components A primary source of efflorescence-forming Mechanism material derives from the abundance of calcium Assuming there is an evaporation front on at hydroxide (CH) that is liberated during the hydra- least one surface of the structure, three other fac- tion of cement. A majority of this CH is liberated tors must be present for efflorescence to form: early on, when a structure is young. CH formation Fig. 1: Infinity edge (water-retaining wall) of swimming pool—2-year-old pool with no specific integral waterproofing or densifier controls 44 Shotcrete • Summer 2015


2015SummerShotcreteEMag
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