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Concrete Strength Acceptance Criteria IRC:15-2011

By
KAUSHAL KISHORE
Materials Engineer, Roorkee

For concrete roads, flexural strength of concrete is the design criteria. For all major projects, flexural strength of the mix shall be determine by third point loading of flexural beams size 150 mm x 150 mm x 700 mm as per IS: 516. Determination of flexural strength by correlating with cube strength (compressive strength) shall not be allowed for major projects, as the correlation is not well established.

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Concrete Strength Acceptance Criteria IS:456-2000

By
KAUSHAL KISHORE
Materials Engineer, Roorkee

Strength of concrete is commonly considered its most valuable property, although in many practical cases, other characteristics, such as durability and permeability, may in fact be more important. However, the strength of concrete is almost invariably a vital element of structural design and is specified for compliance purposes.

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Mix Design and Pumped Concrete

By
KAUSHAL KISHORE
Materials Engineer, Roorkee

A simple method of concrete mix design for pumpable concrete based on an estimated weight of the concrete per unit volume is described in the paper. The tables and figures presented are worked out by the author from a wide range of Indian materials. The method is suitable for normal weight concrete with admixture.

INTRODUCTION
Pumped concrete may be defined as concrete that is conveyed by pressure through either rigid pipe or flexible hose and discharged directly into the desired area. Pumping may be used for most all concrete construction, but is especially useful where space or access for construction equipment is limited.
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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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