GFRC is a composite material that combines the high compressive strength of cement mortars with significantly increased impact, flexural and tensile strengths imparted by the glass fiber reinforcement. According to the particular product and the engineering design, GFRC formulation materials are normally involved with the following:
Alkali Resistant (AR) Glass Fibre Products AR glassfiber is specially formulated to have a high degree of resistance to alkali attack and high durability in cement. Laboratory testing shows that at least 16% zirconia content is required for adequate alkali resistance. AR glassfibers are available in roving, chopped strand, net and mat forms. The use of roving for hand spray including auto spray and chopped strands for premix are most common, with scrim being used in areas of high stress concentrations and mat for the similar application although more successful in floor screeding.
Cement Ordinary Portland Cement (OPC), Rapid hardening Portland Cement (RHPC), Calcium Sulphoaluminate Cement (CSA) and White Portland Cement are the most commonly used cements. They should conform to the relevant National or International Standards. CSA cement is widely used in the Far East due to its low alkalinity and rapid hardening properties, which consequently reduces the corrosion of fibers and speeds up the mould turnover. White Portland Cement is used in GFRC where a white or light coloured finish is required.
Sand Properly graded silica sand is recommended. The particle shape is preferably round or irregular but having a smooth surface without honeycombing. For spray GFRC, the maximum particle size is generally limited to 1.2 mm; for premix GFRC, the maximum particle size may be 2.4 mm. Sand other than silica sands may be used but the producer should provide evidence of their suitability.
Pozzolanic materials PFA, GGBS, Metakaolin, Microsilica and ground glass powder are a range of pozzolanic materials that can be used to partially replace cement either to have a beneficial effect on the properties of GFRC or for the environmental concerns. They work by reacting with the free lime produced during the hydration process to form further hydration products.
Sand and aggregate for facing When a facing mix is used to produce an architectural finish special aggregates and sand may be required. They should be clean, hard, strong, durable and inert, and free of staining or deleterious material. Crushed and graded hard rocks like limestone, granite, spar, calcite or marble are particularly suitable.
Admixtures Admixtures such as water reducers, accelerators, retarders and air entraining agents may be used to impart specific properties to GFRC. They can be standard concrete admixtures or those specially formulated for GFRC manufacture.
Polymer Acrylic thermalplastic polymer is added to the GFRC mix to allow for a subsequent dry cure and for property enhancement, particularly the reduction of surface crazing. It is particularly favoured, when white cement is used, to avoid the possible water stain from wet cure.
Pigments Powder pigments or dispersions may be used to achieve specific colour effect. They are normally iron oxide based and should be harmless to concrete strength and set, temperature stable, non-fading and alkali resistant. The dosage should not exceed 10% of amount of cement.
Paints and sealers Paints and sealers may be applied to GFRC. Latex masonry paints and water resistant stains in a methylemethacrylate base offer a wide range of colour choices. A clear coating of silane or siloxane may be applied to the face and back surfaces of a panel to reduce moisture movement and efflorescence.
If you happen to be a geologist, the raw materials quarry is probably the most interesting part of a cement works, maybe unless you view the clinkering process as igneous rocks in the making.The most common raw rock types used in cement production are:
Quarry management is an art; most quarries will probably have "good material" from which cement can easily be made. They may also have some material that is not as good. This might be harder to grind, or be of less convenient composition.
If the 'good stuff' is all used up first, it may be more difficult to make cement out of what is left. Careful selection on a day-to-day basis is needed to make the best use of all the materials available.Raw materials are extracted from the quarry, then crushed and ground as necessary to provide a fine material for blending. Most of the material is usually ground finer than 90 microns - the fineness is often expressed in terms of the percentage retained on a 90 micron sieve.Once the the raw materials are ground fine enough, they are blended in the proportions required to produce clinker of the desired composition.The blended raw materials are stored in a silo before being fed into the kiln. The silo stores several days' supply of material to provide a buffer against any glitches in the supply of raw material from the quarry.Technically, a cement producer can have almost complete control over clinker composition by blending raw materials of different compositions to produce the desired result. In practice, however, clinker composition is largely determined by the compositions of the locally-available raw materials which make up the bulk of the raw meal.Supplementary materials are used to adjust the composition of the raw meal but cost and availability are likely to determine the extent to which they are used. Transport costs in particular become significant in view of the large quantities of materials used in making cement.
Articles like this one can provide a lot of useful material. However, reading an article or two is perhaps not the best way to get a clear picture of a complex process like cement production. To get a more complete and integrated understanding of how cement is made, do have a look at the Understanding Cement book or ebook. This easy-to-read and concise book also contains much more detail on concrete chemistry and deleterious processes in concrete compared with the website.
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Each of these materials has different grinding coefficient. The higher grinding coefficient, the more grinding of this material. The grinding factors for base raw materials in cement production are given in table below.
Corrective additives are added in cases where the chemical composition of the raw mix does not meet the established requirements. For example, sand, tripoli are used to increase silica. With a lack of iron oxide to reduce the clinker sintering temperature and increase the saturation coefficient, add pyrites cinder, iron ore. This results in saving gas during burning. Carbonate and clay components are used to provide the necessary content of CaCO3. They have different carbonate components of CaCO3 (titer).The carbonate component contains up to 97% CaCO3, clay contains about 10%. It is necessary to achieve, for example, a titer of 80%. Therefore, there are sludge pools with high and low titer content on cement plants. The sludge from pools is mixed in certain proportions.
That is why high quality grinding balls with high hardness over the entire section are used during grinding materials in tube mills in this industry. During 10 years Company Energosteel has been supplying grinding balls to cement plants not only in Ukraine, but also abroad.