Why curing of concrete is important?

Curing offers the following functionalities :

1. Resist the concrete from getting dried throughout hydration. If this happens, the strength of the concrete is reduced significantly. The damage can’t be recovered. If concrete is dried, the cement grains will produce an impervious layer of hydration product around them, and it will resist recurring of hydration, though several occasion it is dampened again.

2. To maintain heat at the surface.

Curing is carried out for the following purposes :-

a. To get rid of frost damage (under 5°C, 40°F)
b. To raise initial strength
c. To minimize temperature gradients

When low temperatures decrease initial strength, the effect does not remain for a long time in case the concrete has not frozen, and it is consequently retained at higher temperatures. As a result, a sample that is retained at 5°C (40°F) will not completely hydrate (specifically if there exist a pozzolan in it), but even after a number of months it will hydrate again with higher temperature.

Since hydration occurs more slowly, cements containing pozzolans and GGBS normally need longer curing. It is therefore necessary that these concretes should be recognized on site, and cured sufficiently. The pozzolanic reaction will then produce extra hydration products to block some of the pores among the cement grains, and attain good strength.

Given below, some recognized process of curing :

• Cover materials (e.g., columns) in polythene once the shutters are detached.
• Spray with curing membrane as soon as detachment of shutters.
• Wrap slabs with polythene (and pour ground slabs on polythene).
• For heat retention, the polystyrene should be utilized on the back of shutters (particularly, steel ones)
• Just leave shutters in exact position for a few extra days (particularly wooden ones).
• 50 mm of sand is well suited on slabs.
• Ponding (i.e., developing a pool on the concrete surface) will be definitely most suitable.

Note about curing:

• Ensure that curing is provided immediately as possible. A few hours may provide significant effect.
• Spray-on curing membranes are less effective, and in windy conditions they should not be used. On complicated areas (like columns), they should be used as there is no other options.
• Keep in mind that PFA, GGBS and, especially, CSF requires much better curing (frequently 5 days, in spite of 3 days).
• Allowing the bleed water to dry off will lead to more bleeding, and plastic cracking.
• Slabs on ground should contain a polythene sheet that is arranged under them, to get rid of excessive water absorption with dry soils.



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Published By
Rajib Dey
www.constructioncost.co
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Difference Between Flexible Pavement and Rigid Pavement

The pavement designing is complicated task in Transportation Engineering. The most recognized methods for pavement design are Rigid pavement and Flexible pavement. The pavement surface has good longevity and it can resist the load operating from the wheel tyres.

Given below, the functional requirement of highway pavements :-

1. Flexible pavement and Rigid pavement contain superior riding quality
2. It should be less slippery
3. It should be rigid
4. It should contain adequate friction keeping the power of the vehicle unchanged.

Variation among Rigid Pavement and Flexible Pavement

1. Flexible Pavement

a. Load is transmitted from grain to grain to the lower layers
b. The design is totally based on the subgrade strength.
c. IRC 37-2012 code is applied for making the design of flexible pavement
d. The strength of flexible pavement is influenced by the aggregate interlock, particle friction and cohesion.
e. Flexible pavement demonstrates the deflection of subgrade at the surface of the pavement.
f. Design life lasts for 15 years.

Rigid Pavement:

1. Rigid pavement contains a strong flexural strength that is considered as the vital factor of design.
2. Rigid pavement contains a concrete layer at the top, the base course and soil subgrade remain underneath.
3. Rigid pavement disperses the load over a broad area due to its high flexural strength.
4. Load is transmitted through slab action.
5. The total thickness of the pavement remains under flexible pavement.
6. IRC: 58-2011 is utilized for making the designing of Rigid pavement.
7. Design life extends for 30 years



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Published By
Rajib Dey
www.constructioncost.co
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Variations among Wet, Moist, and Damp Subgrade

Subgrade is taken as the most vital element of the pavement structure as it functions as a foundation for other pavement elements which are developed upon it and resist detrimental influences of weather and various traffic loads.

The performance of subgrades is significantly impacted with unstable water content. Hence, it is essential to examine the behaviour of subgrade under several conditions. Under this condition, wet, moist, and damp subgrade are identified on the basis of the water quantity in the subgrade components.

The concerned engineers should have clear conceptions on the variations among wet, moist, and damp condition and how the strength of pavement structure is influenced by them. The bearing strength, shrinkage, and swelling of subgrade are mostly affected by the moisture content. Given below, the detail information about the variations among wet, moist, and damp subgrade.

Wet Subgrade

1. As per ACI 116R-90, wet condition happens when the material comprises of apparent free moisture.
2. It is the indication of maximum level of moisture.
3. Wet subgrade is majorly damaged under loads.
4. Wet subgrade tolerates severe swelling and shrinkage and due to this pavement deforms and cracks.
5. Wet subgrade is not recommended for pavement construction. Therefore, so it should be upgraded with proper method.
6. When the roads are built up on such subgrade devoid of correct advancement, then future maintenance work is necessary.

Moist subgrade

1. As per ACI 116R-90, if the material is mildly coated with moisture, the moist condition occurs.
2. There is mild moisture among wet and dump.
3. Bearing strength performance is superior as compared to wet subgrade but lower than damp subgrade.
4. Swelling and shrinkage of moist subgrade and flaws of pavement above occurs to some extent among damp and wet subgrade.
5. It is suitable for pavement construction but a slight advancement is required.
6. Less costly improvement is applied to get rid of future maintenance.

Damp subgrade

1. As per ACI 116R-90, damp condition happens if the material is marginally dump but not gets dry to the touch Specifies lowest level of moisture.
2. Damp subgrade functions well with regard to load bearing strength as compared to wet and moist subgrade.
3. It is not affected with swelling and shrinkage significantly, and therefore the damage is not adequate to the pavement.
4. It is ideal for pavement construction.
5. It does not need any improvement and future maintenance is inexpensive.

To get more detail, go through the following link theconstructor.org

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Published By

Rajib Dey

www.constructioncost.co

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