Technology and pigments

Products, such as concrete roofing, paving tiles, kerbstones etc. are manufactured of wet concrete. The concrete is formed by means of vibropressing equipment with a die and ages on the bottom of the form. Products of larger sizes, such as shaped concrete bricks, are mainly manufactured and stored directly on the floor, where the manufacturing equipment moves. Products of various shapes and for various usage, such as formed parts for pavement tiles, are made by casting from soft or liquid concrete in plastics, metallic forms. When they are made compact on a vibrating equipment they age. Forms are usually removed after 24 hours from the casting.

Technological discipline
When manufacturing concrete, it is strictly necessary to keep to verified (suitable) recipes for the manufacture of the corresponding concrete. It is especially valid for the manufacture of wet concrete. Its ability to be processed influences the success of the manufacture of final concrete products. Quality and uniform manufacture of concrete presumes a verification of suitability of the recipe used with focusing together on properties of fresh concrete and final products. On the base of gained results a recipe is determined, where doses of input materials are given. Technological discipline is joined with the most accurate determination of the recipe. Manufacture without stipulated rules can seldom bring uniform quality of products.

Quality, suitability and way of storing of input materials for the production
•Cements with class of strength of 42.5 or 52.5 are suitable to be applied for concrete and prefabricated products with class of strength above B 35. Cements available on market generally meet requests of technical standards. Cement packed in bags is necessary to be stored on a place, where it cannot be damaged with moisture or penetration of foreign bodies. It is recommended to give palettes under bags. As to cement stored in bulk, it is suitable to store it in silos determined for this purpose. Recommended time of storage is three months from the time of manufacture.
•Powder and liquid pigments. When powder pigments are stored, it is necessary to keep to the same rules as those for cement storage. Liquid pigments are necessary to be stored at temperatures above 5°C.
•Aggregates represent about 70 to 80% of the weight of concrete. They carry the decisive properties of fresh and hard concrete. Classified and from a part crushed compact mined aggregates are the most suitable for the manufacture of wet concrete. Dolomite aggregates are not suitable, but in some cases they can be used for the core of the product. Compact, mined, classified aggregates are also the most suitable for the manufacture of concrete within soft to liquid consistence. Crushed aggregates, such as andesite and melaphyre can also be used. Aggregates of dolomite origin cannot usually ensure a necessary resistance to abrasion, frost and due to this also a necessary lifetime of concrete products. It is suitable to use compact aggregates mined from rivers for fractions up to 4 mm. For larger fractions above 4 mm, also crushed aggregates can be used. Crushed small aggregates (up to 2 mm) are not suitable, above all due to high content of dust particles, which appear during the manufacture and are cumulated in the finest fractions. High content of such particles increase the consumption of batch water and by this way also indirectly increase shrinking of concrete and its resistance to aggressive compounds. As to storage of aggregates, it is necessary to ensure that individual fractions cannot be mixed together, the ground bottom of storage rooms should be hard (covered with concrete) in order to avoid contaminating with foreign materials (soil during handling).
•Water always has to be clean, the manufacturer of concrete has to verify content of soluble salts. Drinking water can also be applied, but it is necessary to test if it is suitable for manufacturing concrete.
•Chemical ingredients are mostly in liquid phase. In principle, there is a rule - protect the ingredients from frost and contaminating with foreign compounds. It is necessary to keep recommendations by manufacturers stated in the technical data sheets.

Information has been developed by PRECHEZA a.s.