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Technical Tip Fig. 2(a and b): Newly placed precast stone pavers Fig. 3: Aged concrete slab deterioration is a normal occurrence within hydraulic cement. Over time, ongoing hydration tends to densify the matrix of the structure, which seals shut much of the spacial interconnectivity and confines the CH. Carbonation of the upper surface also tends to densify and seal the surface of the structure over time. Prior to this, however, if sufficient moisture is introduced to the structure, CH can be taken into solution and transported from within the structure to the upper surface, forming efflorescence. Alkalis (Na, K) may also be present in various components of the mixture design in minor amounts, but significantly more concentrated amounts of alkali (Na, K) are often found to originate from the soil, water, or other materials in contact with the structure. Supply of Moisture Efflorescence cannot form without sufficient Fig. 4: Efflorescence buildup that caused delamination of tiles; more than moisture. It is important, during construction, to just an aesthetic problem incorporate a means of removing or diverting moisture away from the structure whenever pos- sible, allowing water to drain away from the structure quickly and unimpeded. Structures in constant water or saturated soil contact on one side, and an evaporation front on the other, are of primary concern. Such conditions often exist with retaining walls, negative edge or above- ground walls of swimming pools, basements, and tunnels. In this case, measures should be taken that essentially render the structure water- tight (water resistant). Constant single-direct transport of water through cementitious materials increases the leaching of the calcium compo- nents, or the influx of deleterious ions into the structure from the saturated side, or a combina- tion both, resulting in severe deterioration of the structure over time. Such structures, designed to be viewed on the “evaporation front” or “nega- Fig. 5: Efflorescence caused by water in transit Shotcrete • Summer 2015 45


2015SummerShotcreteEMag
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