Que4.29. What’s loss of concrete? Explain about bracket of loss.
1. loss of concrete is the time-dependent strain measured in an disburdened and unrestrained instance at constant temperature.
2. loss is shortening of concrete due to drying and is independent of applied loads.
Types of Shrinkage Following are the colorful types of loss
1. Plastic loss Plastic loss occurs veritably soon after pouring the concrete in the forms. ii. The hydration of cement results in a reduction in the volume of concrete due to evaporation from the face of concrete, which leads to cracking.
2. Drying loss i. The loss that appears after the setting and hardening of the concrete admixture due to loss of capillary water is known as drying loss. ii. Drying loss generally occurs in the first many months and decreases with time.
3. Carbonation loss Carbonation loss occurs due to the response of carbon dioxide CO2) with the doused cement minerals, carbonating Ca( OH) 2 to CaCO3. ii. The carbonation sluggishly penetrates the external face of the concrete. iii. This type of loss substantially occurs at medium moisture and results increased strength and reduced permeability.
4. Autogenous loss Autogenous loss occurs due to no humidity movement from concrete paste under constant temperature. ii. It’s a minor problem of concrete and can be ignored.
Que4.30. What are the different factors affecting of loss.
Answer Affecting Factors of loss
1. Drying Conditions i. The most important factor is the drying condition or the moisture in the atmosphere. ii. No loss will do if the concrete is placed in one hundred percent relative moisture.
2. Time i. The loss rate will drop fleetly with time. ii. It has been proved that 14 to 34 of the 20 time loss will do within two weeks of it being poured. iii. Within one time of the concrete being poured, loss will be about to 85 of the 20 time loss.
3. Water Cement rate i. The water to cement rate will impact the quantum of loss that occurs. ii. The concrete’s uproariousness also affects the loss. iii. The process of swelling and also drying affects the concrete’s integrity and the loss.
Que4.31. What are the effect of loss on concrete and how is it reduces?
Answer goods of Shrinkage Following are the goods of loss on concrete
1. loss of concrete between movement joints causes joints to open or makes it wider. thus joints must be designed to accommodate the widening caused by loss.
2. Where other accoutrements , similar as ceramic penstocks, are fixed on top of concrete face, loss of the concrete causes relative movement between the different accoutrements . The performing stresses can beget failure at the interface.
3. still, the concrete is put into pressure and when If loss isrestrained.tensile stress becomes equal to tensile strength, the concrete cracks.
4. loss of the concrete causes the concrete to grip buttressing bars more tightly. This increases disunion between concrete and sword and so improves bond strength, especially for plain bars . The deviation of flexural members is increased by loss. This is because the smoothly corroborated contraction zone is free to shrink further than heavily corroborated pressure zone.
6. loss causes a reduction in pre stressing force.
Prevention of Shrinkage Following are the measures to be taken to reduced loss
1. give sun tones in case of arbor construction to control the face temperature.
2. Dampen the subgrade of concrete before placement it’s liable to water immersion but shouldn’t over damp.
3. Try to start the curing soon after finishing.
4. Use chemical cocktails to accelerate the setting time of concrete.
Que4.33. Define continuity of concrete. bandy the factor affecting concrete continuity.
1. The continuity of concrete is defined as its capability to repel riding action, chemical attack, bruise, or any other process of deterioration.
2. Durable concrete will retain its original form, quality, and utility when exposed to terrain.
Factors Affecting continuity Following are the factors affecting the continuity of concrete
1. Physical Factors Temperature Unfavourable temperature conditions can lead to loss cracks and volume changes. Variation in temperature changes beget secondary stresses in structures.
ii. humidity humidity induces erosion in sword. humidity also acts as a carrier of chemicals inside the body of concrete. humidity can also beget efflorescence on structural shells. Seepage/ Leakages beget vexation to inhabitants and deteriorates structures due to passable concrete.
iii. indurating and Deliquescing Leads to expansion of concrete and cracking.
2. Chemical Factors
i. When we’re dealing with continuity, chemical attack which results in volume change, cracking and consequent deterioration of concrete come a major cause of concern.
ii. Ice- melting mariners beget corrosion of concrete.
3. Cement Content and w/ c rate of Concrete Volume change affect in cracks and cracks are responsible for decomposition of concrete.
4. Workmanship Batching, mixing, transportation, placing, contraction and curing bear proper workmanship for a durable concrete.
5. Cover to Bedded sword( As per IS 4562000) i. For main underpinning up to 12 mm dia bar for mild exposures, the nominal cover may be reduced by 5 mm ii. Unless specified else, factual concrete cover shouldn’t diverge from the needed nominal cover by 10 mm.
6. Mineral Oil generally goods only fresh concrete in their hardening process( petrol, petroleum distillates etc) .
Organic acid has sharp effect.
8. Vegetable and beast canvases and fats beget deterioration of concrete shells due to their sharp action.
9. Action of sugar has braking effect on fresh concrete and has gradational sharp effect on hardened concrete.
10. Action of Sewage Concrete seamsters running full remain innocent; but in incompletely filled seamsters where hydrogen sulphide gas is evolved and sulphuric acid is formed, concrete above sewage