Concrete Quality Control in 15 Minutes

By
KAUSHAL KISHORE
Materials Engineer, Roorkee

The time lag (usually 3 to 28 days) between concrete placement and the evaluation of cube strength is a primary deficiency of the current quality control method used in concrete construction. The development of accelerated curing techniques have reduced the lag time to 24 to 48 hours. But even the 24 hours time is sufficient to allow the concrete to set and harden in the form prior to the testing of the accelerated cubes. This paper describes the method for determination of water-cement ratio of the mix discharged from the mixer and conjunction with air-content tests can predict 28-days strength of concrete in 15 minutes, so that any mix found sub-standard should not be allowed for placement.

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28-Days Strength of Concrete in 15 Minutes

By
KAUSHAL KISHORE
Materials Engineer, Roorkee

Determination of compressive strength of concrete, either accelerated or normal 28-days, takes such a long time that remedial action for defective concrete cannot be under-taken at an early stage. By the time cube strength results indicate low strength, it is too late to do any remedy for the defective concrete which has already set in the form, Further in whole day of concreting work, cubes are filled from only a few batches of concrete which do not actually represent the strength of the entire concrete mass being used in the construction. This shows the limitations of cube strength test for the quality control of concrete.

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The GANGES CANAL

By
KAUSHAL KISHORE
Materials Engineer, Roorkee

UPPER AND LOWER GANGES CANAL
The upper ganges canal is the original ganges canal, which starts at the Bhimgoda Barrage near Har Ki Puri at Haridwar, running at the centre of Roorkee, at right bank of canal is Roorkee city and at left bank is Civil Lines, IIT, Roorkee, Bengal Sappers and Minors, traverses Meerut and Bulandshahr and continues to Nanu in Aligarh district, where it bifurcates into the Kanpur and Etawah branches.

A channel from a barrage at Narora intersects the canal system 48 km downstream from Nanu, and continues past the sengar river and Sersa River past Shikohabad in Mainpuri district to become the Bhognipur branch which was uponed in 1880. This Bhognipur branch, together with the Kanpur and Etawah branches, is known as the lower ganges canal. The canal is administratively divided into the upper Ganges canal from Haridwar to Aligarh, with some branches, and the lower Ganges Canal which constitutes several branches below Aligarh.

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Dusting of Concrete Slab Surface

By
KAUSHAL KISHORE
Materials Engineer, Roorkee

It is supposed that concrete should give satisfactory service to its entire life. However problems arises, if care is not taken during construction blemish appears on the surface of a concrete slab, it will likely to be one of these: bilisters, cracking, crazing, curling, delamination, discoloration. DUSTING, efflorescence, low spots, popouts, scaling or spelling. This paper will give the details about dusting.

DUSTING
Formation of loose powder resulting from disintegration of surface of hardened concrete is called dusting or chalking and this is composed of water, cement and fine particles. The concrete surface powder under any kind of traffic, and also surface can be easily scratched with nail or even by sweeping.
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Capping Concrete Specimens For Compression Testing

By
KAUSHAL KISHORE
Materials Engineer, Roorkee

CAPPING THE CYLINDERS
It is required that the cylinders ends must be plane within 0.050 mm. The most common way of achieving this planeness requirement is to cap the ends of the cylinder as per ASTM C6176 with suitable materials. Three different capping materials are permitted (a) A thin layer of stiff Portland cement paste may be used on freshly molded specimens. (b) on hardened cylinders, either high-strength gypsum plaster or sulfur mortar may be used (c) A third method is, an elastomeric pad is placed within a metal retaining ring, and the assembly is then placed over the specimen end. The pad conforms to the shape of the cylinder end, but is prevented from spreading laterally by the metal retaining ring. This provides a uniform load across the specimen ends.

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