This standard defines uniform procedures to evaluate the mortar-making characteristics of fine aggregates utilized in concrete. It covers the preparation of mortar mixes, flow consistency testing, specimen molding and curing, and compressive strength measurement to assess fine aggregate suitability. It is crucial for professionals ensuring the quality and durability of concrete mixtures.
Overview
This standard defines uniform procedures to evaluate the mortar-making characteristics of fine aggregates utilized in concrete. It covers the preparation of mortar mixes, flow consistency testing, specimen molding and curing, and compressive strength measurement to assess fine aggregate suitability. It is crucial for professionals ensuring the quality and durability of concrete mixtures.
Audience
Contents
Structure
This section delineates the purpose of the standard in assessing mortar-forming qualities of fine aggregates for concrete use. It references flow table and mould dimensions aligned with IS 1727:1960, highlighting adjustments such as the 50 mm diameter for the flow table. Details about the tamping bar include material properties and dimensions to ensure consistent compaction.
Outlines the necessary equipment including flow tables and flow moulds conforming to IS 1727:1960 standards. Emphasizes temperature control for mixing water, moist closets, and storage tanks maintained at 27 ± 2°C. Specifies fine aggregate gradation and cement type used in mortar preparation.
Describes mortar mixing steps with a water-cement ratio of 0.6 by weight. Details the sequence of cement and water mixing, addition of saturated surface-dry sand, and adjustment to achieve target flow of 100 ± 5%. Provides typical material quantities and criteria for mortar flow acceptance.
Presents the procedure for conducting the flow test including mould filling in layers, tamping strokes, mould removal timing, dropping the flow table, and measuring spread diameters. Explains calculation of flow percentage and criteria for acceptance or adjustment.
Specifies mould sizes (7.06 cm cubes), layering and tamping technique, flow table drop details, and surface finishing of specimens. Includes instructions on surface-drying, removal of loose particles, flatness verification, and grinding procedures if necessary.
Details curing in moist closets for 3-4 hours, striking off surfaces, demoulding after 20-24 hours, and subsequent storage under water at controlled temperature (27 ± 2°C). Describes handling before testing to maintain specimen integrity.
Explains surface preparation of specimens prior to testing, loading procedures including initial preload for high expected loads, continuous loading to failure within 20 to 80 seconds, and prohibition of load adjustments during failure. Emphasizes accurate compressive strength measurement.
Mandates testing a minimum of three specimens, reporting average compressive strength with specimen age, and following specified loading rates. Reinforces standardized reporting to ensure reproducibility and reliability.
Frequently Asked
The standard prescribes assessing mortar-making properties by preparing mortar with a specific cement-to-aggregate ratio (commonly 1:3 by weight) and a water-cement ratio of 0.6. Cement and fine aggregate are initially mixed dry, followed by gradual water addition to achieve workable consistency. The mortar is then placed into standard 50 mm cube moulds, compacted using prescribed tamping methods to avoid air voids, cured in a moist environment at 27 ± 2°C for 24 hours, demoulded, and further cured under water. Finally, the mortar properties such as compressive strength and consistency are tested to evaluate aggregate quality.
The flow test involves placing a 25 mm layer of freshly mixed mortar into the flow mould, tamping it 20 times with controlled pressure, then adding a second layer with similar tamping. The surface is leveled flush with the mould top. One minute after mixing completion, the mould is lifted vertically, and the flow table is dropped 10 times from a height of 12.5 mm within 15 seconds. The spread diameter is measured in at least four directions to calculate the flow percentage. If the flow deviates beyond 100 ± 5%, adjustments are made by adding sand or retesting, ensuring consistent mortar workability.
Moulds are standardized at 7.06 cm cubes used for specimen formation. The tamping bar must be made of non-absorbent, abrasion-resistant, and non-brittle materials such as rubber compound with Shore A hardness of 80 ± 10 or seasoned teak wood treated with paraffin. Its cross-sectional dimensions are 12.5 mm by 25 mm with a length ranging from 125 to 150 mm, featuring a flat tamping face perpendicular to its length. Additionally, a tamping rod about 10 mm in diameter and 100 mm long with a hemispherical tip is used for compaction.
Specimens are initially cured in a moist closet for 3 to 4 hours after moulding, with surfaces struck off to a smooth finish. They are demoulded after 20 to 24 hours and then stored fully immersed in water maintained at 27 ± 2°C. Testing of 24-hour specimens should occur immediately after removal from the moist closet, while other specimens are tested immediately after removal from water storage. When multiple specimens are handled simultaneously, 24-hour specimens are kept covered with a damp cloth, and others remain immersed until testing. Specimens must be surface-dried and cleaned of loose particles prior to testing.
For comparison, at least three specimens each from untreated and chemically treated fine aggregates (treated by repeated washing in 3% sodium hydroxide until visibly lighter) are prepared and tested under uniform conditions. The average compressive strength is calculated for both sets. The untreated fine aggregate strength is then expressed as a percentage of the treated aggregate strength. A lower percentage indicates the presence of harmful impurities in the untreated aggregate affecting mortar strength, thus providing insight into the benefits of treatment.
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