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2015SummerShotcreteEMag

Technical Tip tive pressure” side and aesthetic appearance is combination, are effective at reducing or stop- of primary importance, should incorporate a ping the movement of water or moisture through method of densification or waterproofing of the the structure. structure that inhibits any moisture migration (moisture resistant). Efflorescence and Durability Typically, efflorescence is more of a cosmetic Permeability eyesore, and less of a durability concern. The There are several effective ways to inhibit the intended finish is merely altered by the unsightly mobility of water or moisture through a cementi- deposition of salts. In such cases, new efflores- tious structure: cence (also known as “bloom”) can generally be 1. Solid waterproof membranes can be placed removed from the structure with little to no that inhibit water from entering into the cemen- damage to the surface. This efflorescence typically titious structure; consists of many small individual grains or crys- 2. Pozzolan can be incorporated into the mix- tals. A bristle brush and water will often remove ture design, which combines with CH to such efflorescence that is days old. However, these form insoluble compounds and further den- crystalline deposits can build up and carbonate sify the matrix; from either CO in air or CO in water. If allowed 2 3 3. Polymers can be incorporated into the mix- to form into a hardened dense deposit, removal ture design to densify the matrix, or to form a can be very difficult. co-matrix with cement; A similar buildup, known as sub-efflorescence, 4. Reducing the water-cement ratio (w/c), or the can develop at the interface of the structure sur- use of a water reducer, can reduce permeability; face and surface coatings, tile, or other coverings; 5. Integral waterproofing or water-resistive addi- or just below the upper finished surface of the tives can be incorporated into the mixture design; structure. If this buildup continues unimpeded, a 6. Efflorescence-reducing additive (ERA) can form of salt attack can cause the deterioration and be incorporated into the mixture design; weakening of the binder system. Ultimately, this 7. Integral waterproofing or other densifiers can may lead to a complete failure of the binder be sprayed on, or applied as a slurry coat, to system, causing the debonding of the coating or the surface of the cementitious structure; and covering from the substrate, or the delamination 8. Incorporating methods of application, finishing, or peeling away of the upper surface of the and curing that optimize consolidation of the cementitious structure. Structures such as swim- matrix and produce a dense upper surface. ming pool vanishing edges, retaining walls, base- Each of these, whether individually or in ments, and tanks can be especially vulnerable. Methods of preventing the migration of moisture, as mentioned previously, should be considered in the initial design and construction. Penetrations (for example, pipes, lights, or joints) or abnormalities (such as holes and cracks) within the structure can create open pathways, allowing the facilitated transport of salt-laden solutions to the surface. Small overlooked holes or gaps during application, or certain cracks (shrinkage, autogenous, or plastic), may often simply be plugged or patched. Structural move- ment cracks, or cracking due to some internal stress mechanism within the structure, require a more in-depth investigation be undertaken and evaluation as to cause and remedy be determined. Applying non-breathable paints, sealers, and other coatings onto the surface of a surface expe- riencing efflorescence is to be avoided. Such coatings, which are less permeable than the cementitious structure, do not allow moisture to escape at the same rate. This impedance of mois- Fig. 6: Example of spray-applied densifier ture can create a buildup of moisture, pressure, 46 Shotcrete • Summer 2015


2015SummerShotcreteEMag
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