This standard outlines the criteria for coarse aggregates intended for use in Water Bound Macadam (WBM) road layers, covering materials like natural stones, slag, and crushed bricks. It details essential attributes such as particle size, grading, durability, water absorption, and mechanical performance to guarantee suitability for wearing, base, and sub-base courses. It is a crucial reference for professionals engaged in the construction and upkeep of roads utilizing WBM techniques.
Overview
This standard outlines the criteria for coarse aggregates intended for use in Water Bound Macadam (WBM) road layers, covering materials like natural stones, slag, and crushed bricks. It details essential attributes such as particle size, grading, durability, water absorption, and mechanical performance to guarantee suitability for wearing, base, and sub-base courses. It is a crucial reference for professionals engaged in the construction and upkeep of roads utilizing WBM techniques.
Audience
Contents
Structure
This section defines the applicable size ranges and grading requirements for coarse aggregates in WBM construction, referencing specific sieve sizes and percentage passing limits as outlined in a grading table. The grading must conform to standard sieve designations, and includes parameters such as abrasion resistance, impact value, flakiness index, and water absorption limits with rounding conventions followed as per relevant IS standards.
Describes the types of aggregates permitted for WBM including crushed rock, slag, and broken brick, emphasizing physical properties such as hardness, durability, and cleanliness. It also discusses potential variations in grading based on aggregate degradation tendencies and reinforces the importance of adhering to standard sieve sizes.
Details the required size distributions, physical soundness assessed via sulfate resistance tests, and procedural guidelines for sampling and conformity assessments in compliance with IS standards. It also includes permissible limits for material degradation and essential testing methodologies.
Presents comprehensive tables and explanations regarding sieve sizes and the percentage passing criteria for different grading categories, highlighting the importance of avoiding contaminants and weak particles to ensure aggregate strength and durability in WBM layers.
Focuses on mechanical tests such as abrasion (Los Angeles test), impact resistance, flakiness index, and water absorption rates. It outlines the formulas used to calculate these parameters and their significance in determining the aggregate’s suitability for various pavement courses.
Explains the standardized sampling protocols and conformity criteria to be followed, including soundness testing for freeze-thaw conditions. It also clarifies the allocation of testing costs based on compliance outcomes and references relevant IS codes for detailed procedures.
Describes the supplier’s obligations to certify aggregate compliance with the standard and provide test materials at no charge. It also specifies the cost-bearing responsibilities depending on whether the material meets or fails the prescribed requirements, supported by a summary flowchart.
Frequently Asked
As per the standard, coarse aggregates suitable for WBM include crushed or broken natural rock, crushed slag, and broken brick aggregates. These materials collectively make up about 75% of the total volume and weight of WBM layers. The aggregates must be hard, durable, and free from impurities to ensure structural integrity and longevity.
The standard specifies different water absorption thresholds based on environmental conditions: aggregates used in wearing surface, base, and sub-base courses located in freezing and thawing regions must not exceed 1.5% water absorption, whereas in other regions, the maximum permissible absorption is 2.0%. These limits help maintain durability and reduce frost-related damage.
Abrasion resistance is measured using the Los Angeles Abrasion test following the IS 2386 (Part IV) procedure. Aggregates are tumbled in a rotating drum with steel balls, and the percentage of wear is quantified by weight loss. The permissible maximum abrasion values are 40% for wearing surfaces, 50% for base courses, and 60% for sub-base courses, ensuring adequate resistance to surface wear.
Coarse aggregates must comply with specific grading requirements outlined in the standard’s grading table, which details percentage passing for various sieve sizes across three grading categories. Additionally, aggregates should be robust, free from excessive flat or elongated particles, and devoid of dirt or weak materials. Adjustments to grading may apply if aggregates are susceptible to crushing under compaction.
Suppliers are responsible for certifying that the aggregates conform to the standard’s specifications and must provide a certificate of conformity upon request. They must supply test samples at no cost. If testing reveals non-compliance, the supplier bears the cost of testing; if compliant, the purchaser assumes the cost. This process ensures quality assurance and accountability.
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