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Subhead 4.0 focuses on the materials, preparation, and specifications of various types of concrete used in construction. Below is a detailed explanation of each section along with examples.
Concrete work includes the use of various materials such as water, cement, fine aggregate, coarse aggregate, surkhi, and fly ash. These materials must meet specific standards and guidelines as outlined in the respective sections.
Example: Using 20 mm stone aggregate in reinforced concrete to ensure structural strength and durability.
Concrete is classified into different grades based on its compressive strength, such as M10, M15, M20, M25, etc.
Example: Using M25 grade concrete for constructing a multi-story building foundation to ensure it can withstand the load.
The concrete mix should be workable enough to be placed and compacted properly. The degree of workability is measured in terms of slump, with different ranges specified for various applications.
Example: For mass concrete in lightly reinforced sections, a slump range of 25-75 mm ensures proper compaction and placement.
Concrete mix proportions should be determined by mass, and the mixing should ensure uniformity in the mix.
Example: Proportioning a concrete mix for M20 grade with a cement content of 300 kg/m³ and a water-cement ratio of 0.55.
Batching involves measuring the quantity of each material by mass to ensure accuracy and consistency in the mix.
Example: Using a batching plant to measure and mix concrete for a large infrastructure project.
Concrete should be mixed in mechanical mixers conforming to IS 1791 standards. Hand mixing may be allowed with specific permission and requires adding 10% extra cement.
Example: Mixing concrete using a mechanical batch type mixer to achieve uniform consistency and strength.
Concrete should be deposited as near as possible to its final position and should be compacted before setting commences.
Example: Placing concrete for a slab using proper vibratory techniques to ensure it is free from air pockets.
Concrete must be thoroughly compacted using mechanical vibrators to ensure it is dense and free from voids.
Example: Compacting concrete with a mechanical vibrator to achieve the desired density and strength.
Construction joints should be planned and kept to a minimum. They must be prepared properly when resuming work.
Example: Preparing a construction joint by roughening the surface and applying cement slurry before resuming concreting.
Specific procedures must be followed for concreting under extreme weather, underwater, or in sea water.
Example: Using special admixtures and techniques for concreting in cold weather to prevent frost damage.
Curing involves maintaining moisture in the concrete to ensure proper hydration and strength development.
Example: Curing concrete slabs by covering them with wet hessian cloth for at least 7 days.
Concrete should be tested for various parameters as specified in the R.C.C. chapter.
Example: Conducting a slump test to measure the workability of fresh concrete on site.
Form work should be designed to maintain the shape and alignment of concrete structures until they gain sufficient strength.
Example: Using steel form work for casting columns to ensure a smooth finish and accurate dimensions.
Finishes such as plastering or special treatments must be specified and executed separately unless otherwise stated.
Example: Applying a special finish to exposed concrete surfaces for aesthetic purposes.
Concrete must be durable to perform satisfactorily under expected exposure conditions. Factors affecting durability include the environment, cover to embedded steel, type and quality of materials, cement content, water-cement ratio, and workmanship.
Example: Using M30 grade concrete with a water-cement ratio of 0.45 for a structure exposed to severe environmental conditions to ensure longevity.
Fly ash concrete is prepared by mixing coarse aggregate, fine aggregate, ordinary Portland cement, and fly ash in specified proportions.
Example: Using a 1:4:8 mix of cement, fly ash, and sand for a lean concrete base.
The damp proof course involves laying a cement concrete layer with specified proportions and curing it properly to prevent moisture ingress.
Example: Applying a damp proof course on a brick masonry wall to prevent rising dampness.
Subhead 4.0 provides comprehensive guidelines for the materials, preparation, mixing, placing, and curing of concrete in construction projects. It emphasizes the importance of quality control, proper proportioning, and adherence to standards to ensure the durability and performance of concrete structures.
Wed Jul 3, 2024
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