This standard outlines the specifications and design requirements for pressure meters used to measure the air content in freshly mixed concrete. It covers details on construction materials, calibration procedures, and component markings to ensure precise evaluation of entrained air, which is vital for concrete quality assurance. The guidelines are critical for professionals involved in concrete testing and equipment manufacturing.
Overview
This standard outlines the specifications and design requirements for pressure meters used to measure the air content in freshly mixed concrete. It covers details on construction materials, calibration procedures, and component markings to ensure precise evaluation of entrained air, which is vital for concrete quality assurance. The guidelines are critical for professionals involved in concrete testing and equipment manufacturing.
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Contents
Structure
This section defines the scope of the standard, detailing the requirements for pressure meters employed to determine the air content in fresh concrete. It includes guidelines on rounding off numerical test outcomes according to IS 2-1960 and aligns the standard with international methods adapted for Indian conditions. It also specifies the measuring bowl design — a flanged cylindrical container made from steel, cast iron, brass, or other cement-resistant metals with machine-finished surfaces — and details nominal capacities matched to maximum aggregate sizes (38 mm: 0.005 m³, 75 mm: 0.01 m³, 150 mm: 0.10 m³) to ensure precise air measurement.
This section describes the essential parts and supplementary equipment of the pressure meter. It covers materials and finishes for measuring bowls, capacities in relation to aggregate sizes, and includes flowcharts illustrating component relationships. It emphasizes that proper selection and manufacturing of parts like the measuring bowl, conical cover, calibration cylinder, and accessories are crucial for accurate air content determination.
Defines the specifications for the measuring bowl, including material choices (steel, cast iron, brass, or other hard metals resistant to cement), machine-finished surfaces for accuracy, and flanged cylindrical shape. The section also specifies the nominal capacities corresponding to maximum aggregate sizes and introduces calibration cylinder requirements and the design of the conical cover assembly, including interior slope and pressure-tight fitting.
Details the construction of the conical cover assembly, specifying materials such as steel, cast iron, brass, or other hard, corrosion-resistant metals. It mandates an interior slope of at least 30° from the flange surface to ensure a tight, rigid seal with the measuring bowl. The section also describes stand pipe features, including graduated precision bore glass or uniform metal tubes with water gauges, required graduations, accuracy, and sealing methods using valves, clamps, and O-rings.
Outlines the calibration cylinder's volume, set between 3% to 6% of the measuring bowl's volume, constructed from No. 16 gauge brass tubing with one end sealed by a 6 mm thick brass disc. The section includes details on the coil spring used to hold the cylinder in place and the stand pipe equipped with graduations and a pressure gauge to ensure precise calibration.
Specifies the pressure gauge dimensions and operational range, highlighting a 75 mm diameter gauge capable of measuring twice the normal working pressure (e.g., from 0.05 to 20 N/mm²). The gauge must have clearly marked graduations with at least 2 mm divisions and an accuracy of ±0.1%, connected to the air chamber above the water column to monitor applied pressure during measurement.
Describes the tamping rod dimensions and material requirements: a 16 mm diameter, 230 mm length steel rod with a circular cross-section and one rounded end, conforming to IS 7320-1974. The tamping rod is used for compacting concrete samples uniformly during slump tests, ensuring consistency and preventing damage to aggregates.
Covers the specifications for the mallet and trowel used with the pressure meter. The trowel is a standard brick mason’s type, while the mallet is wooden with a rubber or rawhide head weighing between 250 to 500 grams depending on bowl size. Additional tools include the tamping rod and rubber padding, with precise dimensional references provided.
Mandates clear, permanent, and indelible marking on each apparatus part, including the manufacturer’s name or trademark and the date of manufacture. Markings must not impair functionality or safety. The section also discusses adherence to IS 2-1960 for rounding numerical test results to maintain standard compliance and quality control.
Explains the assembly process for the pressure meter components, emphasizing the materials, design features, and fittings for the conical cover, stand pipe with graduated water gauge, pressure gauge, and sealing elements such as rubber padding and clamps. It includes typical dimension references and diagrams to ensure correct setup, facilitating accurate air content measurement.
Describes calibration procedures for the apparatus, including the use of a calibration cylinder sized between 3% to 6% of the measuring bowl volume, and a graduated stand pipe with ±0.1% accuracy. The section highlights the importance of proper calibration to ensure precise air content determination, including rounding rules per IS 2-1960 and formulae for air content calculation.
Provides guidance on maintaining the pressure meter, such as keeping the measuring bowl clean to avoid cement residue, regularly calibrating the stand pipe and pressure gauge, and checking for equipment accuracy before use. Proper maintenance extends the apparatus’s lifespan and ensures reliable concrete air content measurements.
Details the rounding off of test or analysis results in accordance with IS 2-1960, ensuring the number of significant digits matches those specified in the standard. It explains rounding conventions and includes bowl capacity tables correlating with aggregate sizes to maintain consistency and precision in reporting.
Frequently Asked
Per IS 9799, the pressure meter components must be made from materials that ensure durability and resistance to cement attack. The measuring bowl should be constructed from rigid materials capable of forming a pressure-tight assembly, typically steel, cast iron, brass, or other hard, corrosion-resistant metals. The conical cover assembly must be made from steel, cast iron, brass, or similar non-corrosive hard metals with an interior slope of at least 30°. The stand pipe is either a graduated precision bore glass tube or a uniform bore metal tube equipped with a glass water gauge, facilitating accurate air content measurement.
The measuring bowl's nominal capacity is selected based on the maximum nominal size of the concrete aggregate to ensure representative sampling and accurate air content measurement. According to IS 9799, for aggregates up to 38 mm, a bowl capacity of 0.005 m³ is used; for aggregates up to 75 mm, 0.01 m³; and for aggregates up to 150 mm, the capacity is 0.10 m³. The bowl is a flanged cylindrical container made of materials resistant to cement corrosion with machine-finished internal surfaces.
The pressure gauge specified in IS 9799 should have a diameter of 75 mm and a measuring range approximately double the expected working pressure, commonly from 0.05 to 20 N/mm². It must feature a clearly graduated scale with divisions at least 2 mm wide and an accuracy of ±0.1%. The gauge is connected to the air chamber located above the water column in the stand pipe to accurately reflect the pressure applied during air content measurements.
Calibration involves using a calibration cylinder with a volume between 3% and 6% of the measuring bowl's volume, made from No. 16 gauge brass tubing with one end sealed by a 6 mm thick brass disc. The stand pipe, a graduated precision bore glass or metal tube with a glass water gauge, must have graduations with a minimum 2 mm width and an accuracy of ±0.1%. Calibration is performed by applying known air pressures, observing the water column displacement, and adjusting the graduations accordingly to reflect accurate air content values, with a pressure gauge monitoring the applied pressure throughout the process.
Each part of the apparatus must be permanently and clearly marked with the manufacturer's name or registered trademark and the date of manufacture, as stipulated in Clause 3.1 of IS 9799. These markings should be indelible and positioned so they do not interfere with the apparatus's performance or safety. Optionally, components may bear the ISI Certification Mark, indicating compliance with Indian standards and quality assurance requirements.
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