Page 46

2016SpringShotcreteEMag

Pool & Recreational Shotcrete Corner When proper practices are pursued in the drymix process, one member of the crew will predampen the dry material when using pre-bagged concrete mixtures to reduce dust and waste while another is normally stationed alongside the nozzle operator to gather and shovel away any rebound or overspray. This clears the way for application of high-quality, paste-rich concrete material to build out the structure. The fact is, however, that the ignorant or unscrupulous contractor will save a great deal in labor and materials by skipping these crucial steps. The in-place material may incorrectly be said to conform to the norm or the standard, despite the fact that best practice would definitively classify the end product as substandard. Curing Another prime example of broad-scale deviation from good practice that cropped up on the 1950s (and persists in some quarters to this day) is the ill-advised tendency some contractors have to skip the curing step. Even in today’s shotcrete industry, there are contractors who have apparently never been introduced to this concept or have an imperfect understanding of its importance. Beyond question, curing is among the most important factors involved in ensuring proper strength gain in concrete. The key is maintaining an adequate level of surface moisture: This prevents evaporation of the mix water from within the hydrating concrete, allowing the chemical processes that are taking place between the water and the cement to continue and increase strength gain. Without a wet cure or the use of a curing agent, the hydration process will halt early, and the concrete will often not reach its target strength. A properly cured structure with proper concrete mixture proportions, for example, will easily attain compressive strength values of 5000 to 6000 psi (35 to 41 MPa). The same structure, uncured, may not reach half that level. A Troubled Process The result of this ongoing lack of proper material selection and application standards was the development of an industry that performed poorly and had a worsening reputation into the 1970s and even into the ’80s. The strange outcome here was the creation of another subtrade of contractors who compensated for the poor performance of shotcrete crews by applying waterproofing materials to concrete Fig. 3: Shotcrete sprayed at proper velocities results in compacted material with well-encapsulated steel reinforcing bar Fig. 4: A free-form pool with a perimeter overflow edge and complex step detail is executed with the shotcrete process 44 Shotcrete • Spring 2016


2016SpringShotcreteEMag
To see the actual publication please follow the link above