Que4.5. Mention the different tests which are generally acclimated to measure plasticity and explain any one test in detail. Answer Test for Measure Plasticity Following are the test used for measure plasticity Depression test. ii. Compacting factor test. iii. Vee- Bee test. Concrete Depression Test Procedure 1. originally, the internal face of the mould is gutted precisely. oil painting can be applied on the face. 2. The mould is also placed on a base plate. 3. The mould is filled with fresh concrete in three layers. Each subcaste is tamped 25 times with a sword rod. 4. After filling the mould, redundant concrete should be removed and the face should be leveled. 5. also the mould is lifted gently in the perpendicular direction and also unsubstantiated concrete will slump. The drop in height at the centre point is measured to nearest 5 mm or0.25 inch and it’s known as ‘ depression ’. Que4.6. How do you conduct compacting factor test in laboratory. Answer contraction Factor Test 1. The contraction factor test gives the geste
of fresh concrete under the action of external force. 2. In this test, the contraction achieved through a free fall of concrete determines its plasticity. contraction Factor Test Procedure 1. The concrete sample is placed in the upper hopper. 2. also the door of hopper is opened. The sample drops into lower hopper filling it to overflowing. 3. The trap door of the lower hopper is also opened and the sample falls into the cylinder which is also filled to overflowing. 4. The fat concrete is removed from the top of the cylinder with the help of a trowel. 5. The outside face of cylinder is wiped and gutted. 6. The cylinder is also counted and it’s recorded as weight of incompletely compacted concrete. 7. The cylinder is again filled with concrete in layers not exceeding 50 mm in consistence. Each subcaste is completely compacted with tamping rod. 8. The cylinder is again counted after wiping and drawing the outside face of cylinder. This weight is recorded as the weight of completely compacted concrete. 9. The compacting factor is also calculated from the formula Compacting factor = Weight of incompletely compacted concrete/ Weight of completely compacted concrete. Que4.7. Explain the Vee- Bee test of determining plasticity with neat sketch. Answer 1. The test is suitable for stiff concrete mixes having low or veritably low plasticity. 2. Compared to the depression and compacting factor tests, the Vee- Bee test has the advantage that the concrete in the test receives a treatment analogous to what it would in factual practice. 3. The test consists of moulding a fresh concrete cone in a spherical vessel mounted on a wobbling table(Fig.4.7.1). 4. When the concrete cone is subordinated to vibration using a standard vibrator, it starts to enthrall the spherical vessel by way of getting remoulded. 5. The remoulding is considered complete when the concrete face becomes vertical. 6. The time( in seconds) needed for the complete remoulding is considered as a measure of plasticity and is expressed as the number of Vee- Bee seconds. 7. The end point of the test, when the concrete face becomes vertical, has to be caught on visually. 4.7.1. Vee- Bee outfit. Glass plate rider Que4.8. What’s the effect of time and temperature on plasticity? Answer Effect of Time on Workability 1. lately mixed concrete stiffens with the passage of time. This is different from the hardening of the blend. 2. As time passes, water is lost due to immersion by summations if they are not formerly impregnated. Some water is lost due to evaporation, especially if the concrete is exposed to hot rainfall and wind also plasticity drop. Effect of Temperature on Plasticity 1. When temperature increases, also in the same proportion plasticity of fresh concrete diminishments. 2. The reason that stands before is “ when temperature increases also evaporation rate also increases due to that hydration rate diminishments and hence, concrete will gain strength before ”. 3. Due to fast hydration of concrete, a hardening comes in concrete and that decreases the plasticity of fresh concrete. Que4.9. Write about isolation and its causes. How reduce isolation of concrete? Answer isolation It’s defined as the separation of the ingredients of a homogeneous admixture of concrete. It’s caused by the differences in sizes and weights of the constituent patches. Causes of isolation in Concrete 1. Transporting concrete composites for long distances. 2. inadequately proportioned blend, where sufficient matrix isn’t there to bind the summations. 3. Dropping concrete from further than 1m. 4. wobbling concrete for a long time. Remedial Measures To reduce isolation, well canted summations are used and concrete is placed with enough contraction. ii. The concrete shouldn’t be dropped from a height of further than1.5m. Que4.10. bandy the factors affecting bleeding of concrete. Concrete Technology 4 – 11 D( CE- Sem- 5) 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. Concrete product, Properties & Testing 4 – 12 D( CE- Sem- 5) . 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 Concrete Technology 4 – 13 D( CE- Sem- 5) 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.