Que4.10. bandy the factors affecting the bleeding of concrete.
Answer Factors Affecting Bleeding of Concrete Following are the factors that affecting the bleeding of concrete
1. Water Content and Water Cement rate Any increase in the quantum of water or water- to- cementitious material rate results in more available water for bleeding.
ii. A one- fifth increase in water content of a normal concrete admixture can increase bleeding rate further than two and a half times.
2. Cement
i. The type, content and fineness of cement can prompt bleeding. As the fineness of the cement increases, the quantum of bleeding diminishments. ii. Increases in cement content, reduces the water- cement rate, and also reduces bleeding.
3. Supplementary Cementing Accoutrements Fly ash, sediment, silica cloud, rice cocoon ash and natural pozzolanas can reduce bleeding by their essential parcels and by adding the quantum of cementitious accoutrements in a admixture.
4. Aggregate total that contain a high quantum of ground, complexion or other material passing the75 μm sieve can have a significant effect in reducing bleeding.
5. Chemical amalgamation Air- enplaning agents have been used largely because the air bubbles appear to keep the solid patches in suspense.
ii. Water reducers also reduce the quantum of bleeding because they release trapped water in admixture.
Que4.11. How would you reduce bleeding from concrete?
Answer Controlling Measures of Bleeding Following are the controlling measures of bleeding from concrete
1. Proper proportioning of concrete.
2. A complete and invariant mixing of concrete.
3. still, the If we can increase the traveling length of water to bebleeded.bleeding can be reduced vastly. For this purpose we can use finely divided pozzolanic accoutrements
4. An preface of air- entrainment by using air enplaning agent can reduce bleeding.
5. The use of finer cement. 6. By using of a rich blend rather than spare blend.
7. Controlled vibration can reduce bleeding.
Que4.12. What are the goods of bleeding on concrete parcels?
Answer Following are the goods of bleeding on concrete parcels 1. Due to bleeding concrete losses its unity.
2. Bleeding is responsible for causing permeability in concrete.
3. This accumulation of water creates a water voids and reduces bond between the total and cement history. So the strength of concrete reduces.
4. Water that accumulates below the buttressing bars, particularly below the cranked bars, reduces the bond between the underpinning and concrete.
5. The bleeding water flows at over the unsubstantiated side of pavement which causes collapsing of sides.
6. In pavement construction bleeding water detainments face finishing and operation of curing emulsion.
7. Bleeding causes of ‘ Laitance in concrete ’. Due to the conformation of Laitance, structures may lose its wearing capacity and decreases its life.
8. Water while moving from bottom to the top, forms nonstop channels. Due to this channel, concrete becomes passable and allow water to move, which forms water voids in the matrix and reduces the bond between total and the cement paste.
Que4.13. Describe the curing and significance of curing. Explain the different styles of curing.
Answer Curing It’s a procedure that’s espoused to promote the hardening of concrete under conditions of moisture and temperature which are conducive to the progressive and proper setting of the constituent cement. Importance of Curing Following are the significance of curing of concrete
1. To maintain humidity content in the blend for complete hydration of concrete.
2. To maintain invariant temperature of the concrete.
3. To save the parcels of concrete, similar as impermeability, continuity and strength.
4. To reduce the loss of the concrete. styles of Curing of Concrete Following are the styles of curing
1. Ponding of Water over the Concrete face after it has Set This is the most common system of curing the concrete arbor or pavements and consists of storing the water to a depth of 50 mm on the face by constructing small billabong complexion bunds each around.
2. Covering the Concrete with Wet Straw or Damp Earth In this system the damp earth or beach in layers of 50 mm height are spread over the face of concrete pavements. The material is kept wettish by journal smattering of water.
3. Covering the Concrete with Wet Burlap The concrete is covered with burlap( coarse jute or hemp) as soon as possible after placing, and the material is kept continuously wettish for the curing period.
4. smattering of Water
i. This is a useful system for curing perpendicular or inclined shells of concrete.
ii. The spraying can be done in fine aqueducts through snoots fixed to a pipe spaced at set intervals.
iii. Flogging is done in the same way except that the flogging snoots produce a mist- suchlike effect, whereas scattering snoots exfoliate out fine spray.
5. Covering the face with Leakproof Paper Leakproof paper prevents loss of water in concrete and protects the face from damage.
ii. A good quality paper can be frequently reused. The paper is generally made of two wastes struck together by rubber latex composition.
6. Leaving the Shuttering or Formwork The thick watertight formwork also prevents the loss of humidity in concrete and helps in curing the sides and the base of the concrete.
7. Membrane Curing of the Concrete
i. The process of applying a membrane forming emulsion on concrete face is nominated membrane curing.
ii. frequently, the term membrane is used not only to relate to liquid membranes but also to a solid sheeting used to cover the concrete face.
iii. The curing membrane serves as a physical hedge to help loss of humidity from the concrete to be cured.
iv. A curing liquid membrane should dry within 3 to 4 hours to form a nonstop coherent tenacious film free from perforations and have no injurious effect on concrete.
8. Chemical Curing Chemical curing is fulfilled by scattering the sodium silicate( water glass) result on concrete face.
ii. About 500 g of sodium silicate mixed with water can cover 1 m2 of face and from a hard and undoable calcium silicate film.
iii. It actually acts as a case hardener and curing agent.