Material of self compacting concrete

Civil Concrete Engineering

 

hello friends we study about introduction and other two material in part one. other renaming material is given below

Water

Water is the readily available most important component of SCC. The hydration of cement can take place only in the presence of water. Adequate water is required for the hydration of cement, leading to the formation of paste to bind the aggregates. In addition, water is required in conjunction with HRWR to achieve the self-consolidation capacity of SCC. It contributes to attain good flowing ability of SCC by lubricating the fine and coarse aggregates. Here in the study tap drinkable water was used.

Rice husk ash

Rice milling generates a by-products know as husk. This surrounds the paddy grain. During milling of paddy about 78 % of weight is received as rice, broken rice and bran .Rest 22 % of the weight of paddy is received as husk. This husk is used as fuel in the rice mills to generate steam for the parboiling process. This husk contains about 75 % organic volatile matter and the balance 25 % of the weight of this husk is converted into ash during the firing process, is known as rice husk ash (RHA). This RHA in turn contains around 85 % – 90 % amorphous silica.

Rice husk ash

The main objective of this work is to study the suitability of the rice husk ash as a pozzolanic material for cement replacement in concrete. However it is expected that the use of rice husk ash in concrete improve the strength properties of concrete. Also it is an attempt made to develop the concrete using rice husk ash as a source material for partial replacement of cement, which satisfies the various structural properties of concrete like compressive strength
and Flexural strength.

Pozzolanic activity of rice husk ash (RHA) depends on (i) silica content, (ii) silica Crystallization phase, and (iii) size and surface area of ash particles. In addition, ash must contain only a small amount of carbon. RHA that has amorphous silica content and large surface area can be produced by combustion of rice husk at controlled temperature. Rice Husk Ash is a Pozzolanic material. It is having different physical & chemical properties. The product obtained from R.H.A. is identified by trade name Silpoz which is much finer than cement.

Super plasticizer 

High-range water reducer, also known as super plasticizer, has made a breakthrough in concrete industry. It is an essential material component that must be used to produce SCC. The HRWRs improve the flowing ability of SCC by their liquefying and dispersing actions. They reduce the yield stress and plastic viscosity of concrete by their liquefying action and thus provide a good flowing ability in SCC. In addition, the HRWRs deflocculated the cement particles and free the trapped water by their dispersing action, and hence enhance the flowing ability of SCC. In dispersing action, the inter-particle friction and thus the flow resistance are also decreased, and therefore the flowing ability of concrete is improved.

Super plasticizer

High-range water reducers can either increase the strength by lowering the quantity of mixing water for a given flowing ability, or reduce both cement and water contents to achieve a given strength and flowing ability. They contribute to achieve denser packing and lower porosity in concrete by increasing the flowing ability and improving the hydration through greater dispersion of the cement particles, and thus assist in producing high strength and good durability.

Viscosity modifying admixture

Rixom and Mailvaganam (1999) have categorized the VMAs into five classes based on their physical actions in concrete. The classification is as follows: Class A: Water-soluble synthetic and natural organic polymers, which increase the viscosity of concrete by increasing the viscosity of mixing water.

Viscosity modifying admixture

Class B: Organic water-soluble flocculants, which increase the viscosity of concrete by enhancing interparticle attraction between, cement particles.

Class C: Emulsions of various organic materials, which improve the viscosity of concrete by increasing interparticle attraction and supplying additional superfine particles in the cement paste.

Class D: Water-swellable inorganic materials of high surface area that improve the viscosity of concrete by increasing the water-retaining capacity of the concrete.

Class E: Inorganic materials of high surface area that improve the viscosity of concrete by increasing the content of fine particles in concrete, and thereby resulting in greater viscosity. Most widely used VEAs for concrete are of Class A. The VEAs under this class can be further subdivided into natural, semi-synthetic and synthetic polymers

Viscosity-modifying admixture is relatively a new addition to the family of admixtures for cement paste, mortar and concrete. The common application of VEA is to produce non-dispersible underwater concrete and SCC. VMA improves the viscosity and cohesion of fresh concrete, and thus reduces the bleeding, surface settlement and aggregate sedimentation resulting in a more stable and uniform fresh concrete. In addition, VMA makes the fresh concrete more robust and less sensitive to the small variations in the conditions and proportions of other constituent materials.

 

 

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