Cause of errors in flat concrete surface

While concreting is going on the job site, construction errors may happen because of failure to certain methods, improper practice as well as casual attitude.

All of these errors do not contribute to failure or impairment of concrete, but they may provide harmful effect on the structure in due course.

These errors are not present throughout new construction, but also occur throughout repair or recondition works.

Given below, mostly found inappropriate finishing methods which can significantly affect the strength of flat concrete surface:

a. Adding water to the surface: It is found that the water is included to the surface and it is verified with the existence of a large paint brush, together with the other finishing tools. The brush is soaked in water and water is heaved onto the surface that is already completed.

b. Timing of finishing: Final finishing operations should be carried on as soon as the concrete has accommodated its initial set and bleeding does not occur. The waiting period is based on the amounts of water, cement, and admixtures in the mixture but mainly the temperature of the concrete surface. On a incompletely shaded slab, the portion in the sun will normally be prepared to finish prior to the part in the shade.

c. Inclusion of cement to the surface: It is frequently performed to dehydrate bleed water so that finishing can be started and it produces a thin cement-rich coating to craze or flake off easily.

e. Use of tamper: A tamper or “jitterbug” is utilized on several jobs needlessly. This tool drives the coarse aggregate far from the surface and the finishing becomes smooth. This method, however, forms a cement-rich mortar surface layer having the ability for scale or craze. A jitterbug should be un-allowed with a well designed mixture. If it is required to complete a rough mixture, a jitterbug could be useful by applying it sensibly.

e. Jointing: If the joints are placed and located improperly, it may lead to cracking in flatwork frequently.



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Published By
Rajib Dey
www.constructioncost.co
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Details of Cracking in Concrete

If cracks occur in concrete on regular basis, the appearance of the concrete becomes unpleasant as well as the structure of the concrete becomes feeble.

The cracking can be managed with reinforcement and joints. With foul cracking, the reinforcement is uncovered to air and moisture which may cause rust as well as reduce the strength.

Types of Cracks: Two types of cracks occur in reinforced concrete

Pre-Setting Cracks: It develops prior to solidification of concrete whereas it is still executable.

Hardened Cracking: Here, crack develops as soon as the concrete gets solidified.

Pre-Setting Cracks: Pre-setting cracks mainly develop at the time of placing, compaction and finishing resulting from movement of concrete prior to it gets dried.

The following types of pre-setting cracks mainly exist:

Plastic Settlement cracks
Plastic Shrinkage cracks
Cracks resulting from Movement of The Formwork.

When pre-setting cracks occur, examine them carefully so that they can be easily restrained whereas the concrete is still setting.

If these are identified at the initial stage, fixing is done easily with re-compacting, re-trowelling or re-floating the concrete surface.

Plastic Settlement Cracks: These types of cracks develop once the concrete is arranged, whereas it is still plastic. They become larger as concrete dries and shrinks and like to follow the lines of reinforcement.

Prevention
Re-vibrate the concrete.
Re-trowel the surface.

Search for cracks when the concrete is setting. At this stage, these can be easily settled.

Plastic Shrinkage Cracks: Usually cracking occurs in summer but it may also happen throughout winter. Plastic shrinkage cracks become visible in lines, roughly parallel or in a crazed haphazard way. They are generally 300–600 mm long but may be among 25 mm and 2 m in length.

Prevention: Moisten the subgrade and forms and safeguard concrete from the wind. Retain all materials cool on hot days.

Set, compact and cure in quickest possible time on hot days in order that concrete won’t dry out.

As soon as the concrete is condensed, screeded and floated, use a consistent spray film of EVAPORATIVE RETARDANT (Aliphatic Alcohol) to avoid quick loss of surface moisture, then continue with finishing.

It is recommended to set concrete at the cooler times of the day.

Repair Cracks is closed with alteration in the plastic concrete.

For more information, go through the following link onlinecivilforum.com



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Published By
Rajib Dey
www.constructioncost.co
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