PLACING AND CURING

After mixing, latex-modified mortar and concrete are placed and finished in almost the same manner as ordinary cement mortar and concrete. The latex-modified mortar and concrete have a shorter working time than the cement mortar and concrete. Although the working time depends on the ambient temperature, the latex-modified mortar and concrete should be placed and finished within about one hour after mixing. 

Because they have an excellent adhesion to various materials, even to metals, all the equipment and tools such as mixers, trowels, and vibrators should be washed down or cleaned immediately after use. It also is advisable to use the most effective mold-release agents, e.g., silicone wax or grease. 

The choice of a latex-modified mortar or concrete depends on the thickness of the overlay or coating to be applied. Generally, the modified mortar can be reconnnended for thicknesses of 30 mm or less, and the modified concrete for the thickness exceeding 30 mm. 

Latex-modified mortar and concrete should never be placed at temperatures lower than 5°C or higher than 30°C. Adequate care should be talmn to prevent floating the polymer solids to the finished surfaces due to wetting by water or rainfall immediately after placing. It is desirable that the surfaces are promptly covered with wet burlap or polyethylene sheets. In 

Generally, polymer latexes used as cement modifiers are not toxic, and are safe materials to handle. Consequently, they require no special precautions. 

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In the production of foundry sand concrete, conventional mixing, placing, and curing are easily referable. 

The effects on other properties of both plastic and hardened mortar or concrete have not been investigated. Furthermore, since the studies have been done on a laboratory scale, no information pertaining to effects of placing and curing under normal or varied environmental conditions is available. 

Haddad, J.G. (1975). Conditions for the Production, Placing, and Curing of Winter Concrete, ACI Chapter Meeting, Ottawa. 

Concrete Microsiructure. Documents the investigation of variables which control cement hydration and microstructural development during the mixing, placing and curing of concrete. 179 pages. SHRP-C-340, 15... 

The optimization approach to any activity in technology, economics or other fields is aimed at finding methods of determining the best solutions in an objective way. In particular, optimization of composite materials deals with problems of the selection of the values of several variables, which determine their composition and internal structure. Other variables that describe the conditions of mixing, vibration, placing and curing may also be included. 

Blocks made from the cement mixed with seawater cracked and disintegrated. Blocks made from cement mixed with fresh water performed very well, however, even when placed and cured in seawater [9]. While natural cement mortars mixed with seawater have not displayed this same tendency to disintegrate rapidly, these results did guide later concrete work. 

To speed up the molding process, the required amount of molding powder or granules is often pressed iato a block and prewarmed before placing it ia the mold. Rapid and uniform heating is accompHshed ia a high frequency preheater essentially an iadustrial microwave oven. The prewarmed block is then transferred to the hot mold, pressed iato shape, and cured. 

Resins are also used for permanent tooth-colored veneers on fixed prostheses, ie, crown and bridges. Compositions for this application include acryflcs, vinyl—acryflcs, and dimethacrylates, as well as silica- or quartz-microfilled composites. The resins are placed on the metallic substrates of the prostheses and cured by heat or light. These resins are inexpensive, easy to fabricate, and can be matched to the color of tooth stmcture. Acrylic facings do not chemically adhere to the metals and are retained only by curing the resin into mechanical undercuts designed into the metal substrate. They have relatively low mechanical strength and color stability, and poor abrasion and strain resistance they also deform more under the stress of mastication than porcelain veneers or facings. 

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