Sprayed coatings shrinkage

In order to minimize rebound, thorough blending of the ingredients should be done. The aggregate should be well coated with the cement in the dry-mix process. Since shotcrete admixtures promote shrinkage, it is essential that the sprayed surfaces be kept moist for at least 7 days. Ambient temperature conditions should be maintained at a level so that air in contact with the shotcrete surface is above freezing - at least for 7 days [106, 115]. 

CCCs are not heat-tolerant [151, 152]. Exposure to elevated temperature accelerates dehydration, consolidation of the Cr(III) backbone, and losses in properties described above. Losses in CCC corrosion protection, Cr(VI) leaching, and increases in shrinkage cracking are profound when coatings are subject to temperatures in excess of 60 °C. Corrosion resistance in salt spray exposure testing and electrochemical testing can be completely lost when CCCs are heated for more than 15 min at temperatures in excess of 60 C [133]. 

As mentioned by Devahastin [4], more recently flash dryers consisting of inert media have been employed at pilot scales to dry slurries and suspensions, which are sprayed onto than. The partides are coated thinly by the slurry and dried rapidly as a thin film. Due to particle-particle interactions, particle collisions, and shrinkage of the film in the drying process, the powda from the slurry is produced. 

When the gelled materials dry, capillary forces cause shrinkage of the flexible skeleton. The skeleton stiffens as it shrinks until the gel can withstand capillary pressures at which point the pores empty, leaving a microporous solid xerogel. Gel films can be formed on a substrate by two methods, immersion and non-immersion (spray, dip, spinon, etc.) Sol-gel based coatings must be designed to contain and deliver soluble non-chrome inhibitors at a rate to maintain effective concentrations in the coating system. ... 

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