This code of practice outlines detailed procedures for the production, placement, curing, and testing of plain and reinforced concrete used in dams and other colossal structures. It ensures the structural soundness, longevity, and quality of concrete works by specifying material standards, mixing proportions, construction techniques, and quality control measures. The standard is indispensable for professionals engaged in the engineering and construction of large-scale concrete projects.
Overview
This code of practice outlines detailed procedures for the production, placement, curing, and testing of plain and reinforced concrete used in dams and other colossal structures. It ensures the structural soundness, longevity, and quality of concrete works by specifying material standards, mixing proportions, construction techniques, and quality control measures. The standard is indispensable for professionals engaged in the engineering and construction of large-scale concrete projects.
Audience
Contents
Structure
This introductory section sets forth the scope, references, unit systems, and rounding conventions. It emphasizes the primary focus on quality control of materials and concrete handling practices, excluding contractual details. It also summarizes key aspects such as raw materials, mixing, placing, curing, formwork, and testing procedures, providing foundational knowledge for quality assurance.
Defines the extent of the code, covering specifications for plain and reinforced concrete in massive structures, including material standards, mix designs, placement, compaction, curing, jointing, formwork, and testing. It outlines the relevant clauses governing these aspects, ensuring comprehensive coverage for large concrete works.
Details the standards and specifications for cement, admixtures, water, aggregates, and reinforcement materials. It includes guidelines for accurate measurement and typical mix proportions, emphasizing the importance of material quality and consistency to achieve desired concrete performance.
Describes the procedure for determining mix proportions based on laboratory tests, establishing water-cement ratio versus strength curves, and adjusting mixes for workability and durability. It also covers conversion between weight and volume batching and outlines steps for preparing suitable concrete mixes.
Specifies correct methods for material measurement, mixing durations, placing, handling, compaction using vibrators, and curing. It also includes requirements for formwork strength and removal timing to ensure structural integrity and surface quality.
Explains the design and construction of forms to shape and support concrete, including strength, rigidity, surface finish, alignment, use of ties and linings, and safe removal practices. It provides guidance on resisting pressures from fresh concrete and maintaining quality finishes.
Covers procedures for preparing horizontal joints, cleaning and bonding new concrete to existing placements, shear resistance provisions, curing of joints, timing between successive pours, and handling emergency joints. It ensures watertightness and bond strength in massive structures.
Outlines field and laboratory testing requirements including slump, temperature, air content tests on fresh concrete, and compression and flexure tests on hardened specimens. It details specimen sizes, testing ages, equipment standards, record keeping, and consistency assessment methods.
Describes the classification and specifications of finishes for both formed and unformed concrete surfaces, including permissible surface irregularities, treatment methods like sack rubbing, and curing practices to achieve desired aesthetics and durability.
Specifies timely repair procedures for damaged or honeycombed concrete including removal, surface preparation, bonding treatments, type of repair mortar, layering and compaction techniques, and finishing to restore structural and surface quality.
Details approved methods for depositing concrete under water such as tremie pipes, drop bottom buckets, and bag placement. It includes equipment requirements, procedural controls to prevent segregation and washout, and conditions when underwater placing is permissible.
Provides guidance for transporting concrete maintaining uniform flow without segregation, use of covered belt conveyors, discharge methods to prevent damage or uneven placement, and preparation for efficient concrete placement.
Specifies curing durations, protection measures against drying and heat, recommended curing techniques such as water sprinkling or wet coverings, procedures for joints, and temperature control measures to ensure concrete strength and durability.
Details the sizes and molding procedures for test specimens, measurement precision, consistency tests using Vee-Bee consistometer, and careful extraction and curing of hardened samples to ensure reliable quality control results.
Includes additional information such as consistency measurement scales, specimen securing guidelines, flexural strength test formulae, and compressive strength correction factors, enriching the understanding and application of the code.
Frequently Asked
The code permits the use of Portland Cement conforming to IS 269, Portland Blast Furnace Slag Cement as per IS 455, and specialized cements as specified for mass concrete applications. Admixtures like pozzolanic materials, air-entraining agents, and wetting agents can only be incorporated with prior approval from the engineer-in-charge. These additives must demonstrate proven benefits without adverse effects, and their proportions and application methods should be clearly defined by the supervising engineer.
Concrete underwater placement must be continuous and avoid seams, employing techniques such as the tremie method using a pipe of at least 20 cm diameter with submerged outlet and controlled flow, drop bottom buckets lowered slowly and dumped only when resting on the deposit surface, and interlocked placement of jute or coarse cloth bags filled two-thirds full. The area should be dewatered if possible; otherwise, these approved methods should be used under engineer supervision to prevent segregation and washout.
For formed surfaces, finishes range from F1 for surfaces in contact with backfill requiring minimal treatment, to F4 for absorptive form-lined surfaces needing only cleaning. Permanently exposed formed surfaces typically have F2 or F3 finishes, with F3 involving sack rubbing mortar and moist curing for smoothness. Unformed surfaces include U1 screeded finishes under backfill, U2 floated finishes for floors and sidewalks, and U3 steel trowelled finishes for slabs under roofing and stair treads. Each finish category specifies acceptable limits for surface irregularities and treatment methods.
Repairs should be executed promptly, preferably within 24 hours post form removal. Defective concrete such as honeycombed or fractured areas must be removed by chipping or wet sand blasting. Surfaces are then cleaned thoroughly with high-pressure air or water jets and wire brushing. Bonding new concrete involves applying a dense cement grout to all hollows. Dry-patching mortar with a 1:2 cement to sand ratio is placed in 2.5 cm layers, tamped thoroughly, and finished smoothly to match the surrounding surface. Bulges in certain finishes are reduced by bush-hammering and grinding.
Concrete workability is controlled by maintaining an appropriate slump at the point of placement, consistent with the water-cement ratio specified. The slump test, conducted as per IS 456 appendix, measures subsidence of fresh concrete in a standard cone. For very low or zero slump mixes, the Vee-Bee consistometer is used to evaluate consistency based on the time taken for concrete to assume a specific shape. Any modifications in slump or consistency require approval from the engineer-in-charge to ensure proper placement and compaction.
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