Brief Information of Reinforced Concrete
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Classification of Building Mortars
Building mortar is the name of a mixture containing a binding agent, water and fine aggregate acquiring a stone-like monolithic structure as a result of hardening. Prior to hardening a building mortar is called a building mix. Building mortars often contain different additions – dispersed (clay), hydraulic and surface-active.
By composition and properties building mortars are similar to concrete, but they contain no coarse aggregates.
Building mortars are intended for filling joints and as a binder in free-stone and brick masonry, for the preparation of decorative and protective plasters and production of small-size articles (brick, tile, etc.).
Building mortars are made with different properties and composition depending on application.
In respect to binding agents and additions there are cement, lime, lime-cement and cement-clay mortars.
In respect to the properties of the binding agent mortars are divided into air-setting, incorporating air-setting binding agents and hydraulic mortars made with hydraulic agents.
In respect to aggregates mortars are classified as heavy, incorporating ordinary sand and light, having porous aggregates (pumice, sands, etc.).
By composition mortars are classified as: simple including one binding agent (cement, lime, etc.) and combined including two or three binding agents (cement-lime, lime-gypsum, etc.).
Air-setting building mortars are used in structures serving in dry environments and hydraulic mortars – in moist environments.
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Placing and Curing of Concrete and Quality Checking
The placing of the concrete mix and its distribution in the form or mould is one of the most labour-consuming operations of concreting.
At present placing and distribution of concrete are mechanized and the operations are carried out with the aid of concrete placers or machines of a simpler construction-concrete distributors. Concrete placers differ from concrete distributors in that they permit the processes of both placing concrete and its distribution to be mechanized in a great measure.
The quality of placing concrete is a very important factor in building durable concrete or reinforced-concrete structures.
The concrete mix must be placed in the form in a manner that no air be entrained in the mass; corners and restrictions in the form must be filled with most care. Placement and leveling of the concrete mix are followed by compacting.
The methods of compacting concrete manually by rodding or with the aid of tampers are almost obsolete now.
Mechanized placing and compacting of the concrete mix by vibrating, vibrostamping, centrifuging, vacuum treatment, rolling and vibrolling are widely practiced.
Vibration consists in uninterrupted positive shaking of the concrete mix by imparting frequent vibratory motion to the entire mass to ensure good compacting.
Vibrostamping. In this method of compacting the treated concrete mass is subjected to the simultaneous action of the oscillatory motion of the vibrator and the load exerted by the stamp, i.e. the method ensures vibration under pressure permitting the outlines of the stamp or dye to be reproduced on the surface of the product being treated.
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Brief Information of Reinforced Concrete
Reinforced concrete is a building material in which the joint functions of concrete and steel are advantageously utilized.
The idea of combining these two materials extremely differing in mechanical properties in one monolith departs from the following premise. Like any other stone material concrete offers a good resistance to compressive loads but it is brittle and poorly withstands, therefore, tensile stresses. The tensile strength of concrete is about 10-15 times inferior to compressive strength. As a result of such anisotropy of mechanical properties concrete cannot be used in structures to be subjected to tensile stresses under load. But if steel possessing a high tensile strength is introduced into concrete, the steel will take over the tensile stresses appearing in the loaded reinforced-concrete element.
It is the most advantageous to employ reinforced concrete in structural elements subjected to bending. In service two oppositely directed stresses appear in such elements – tensile and compressive. In this case the steel reinforcement takes over the first and concrete – the second kind of stress and the entire reinforced-concrete element successfully withstands bending loads.
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