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How to mix concrete
Fri 19 Feb, 13:26
Concrete - a material used to construct buildings. It is used for construct the foundation, walls and roofs. Even the erection of a wooden building is not without pouring the foundation. Small artificial objects such as paving slabs, garden vases, urns, baluster, and sometimes even countertops for kitchen tables, make concrete also. It is important to know how to perform calculations of concrete.
Modern technology make the concrete very high quality. This artificial material in terms of its strength is along with natural marble and granite. Although it is not as aesthetic as natural materials from it, unlike natural stones, not out background radiation, and beautiful appearance, grant using the newest processing technologies. During construction you can make concrete with their hands or buy construction materials to finished composition. Plants for the manufacture of concrete using different proportions of concrete for the foundation and its species - lightweight concrete, heavy and in some cases, especially heavy concrete. If you want to make concrete, you need to understand in what proportions to mix components.
In general, the composition of concrete is a mixture of cement and filler. So the main ingredients are:
- Cement;
- Sand;
- Filling (gravel, slag, pebbles, etc.).
Modern technology involving the use of special additives to provide concrete some unique properties.
Creep
Tue 2 Apr, 16:21
Creep is the continuous deformation of a member under sustained load. It is a phenomenon associated with many materials, but it is particularly evident with concrete. The precise behaviour of a particular concrete depends on the aggregates and the mix design as well as the ambient humidity, member cross-section, and age at first loading, but the general pattern is illustrated by considering a member subjected to axial compression. For such a member, a typical variation of deformation with time is shown by the curve in figure.
The characteristics of creep are:
1. The final deformation of the member can be three to four times the short-term elastic deformation.
2. The deformation is roughly proportional to the intensity of loading and to the inverse of the concrete strength.
3. If the load is removed, only the instantaneous elastic deformation will recover - the plastic deformation will not.
4. There is a redistribution of load between the concrete and any steel present.
The redistribution of load is caused by the changes in compressive strains being transferred to the reinforcing steel. Thus the compressive stresses in the steel are increased so that the steel takes a larger proportion of the load.
The effects of creep are particularly important in beams, where the increased deflections may cause the opening of cracks, damage to finishes, and the non-alignment of mechanical equipment. Redistribution of stress between concrete and steel occurs primarily in the uncracked compressive zone of a flexural member, however, often helps to restrain the deflections due to creep.
