The IS 5640:1970 standard outlines a specialized procedure to measure the aggregate impact value (AIV) specifically for soft coarse aggregates such as laterite, kankar, and shale. This method evaluates their mechanical strength under saturated conditions, ensuring their suitability for use in road bases and sub-bases where moisture exposure may weaken the aggregates. It is an important guideline for assessing durability and impact resistance in infrastructure construction.
Overview
The IS 5640:1970 standard outlines a specialized procedure to measure the aggregate impact value (AIV) specifically for soft coarse aggregates such as laterite, kankar, and shale. This method evaluates their mechanical strength under saturated conditions, ensuring their suitability for use in road bases and sub-bases where moisture exposure may weaken the aggregates. It is an important guideline for assessing durability and impact resistance in infrastructure construction.
Audience
Contents
Structure
The standard, developed with insights from Road Research Monograph No. 5 by the Central Road Research Institute, New Delhi, details the equipment and methodology for determining the impact value of soft coarse aggregates. Apparatus dimensions and properties are standardized to ensure consistent test results. The test results are reported as the average of two trials, representing the Aggregate Impact Value (wet).
The key apparatus includes:
Aggregates passing through a 12.5 mm IS sieve but retained on a 10 mm IS sieve are selected. The sample is oven-dried at 105 to 110°C for a minimum of 4 hours until a constant weight is achieved, then cooled. The dried aggregate is filled into the case-hardened steel cup in three layers, each tamped 25 times using the rounded end of a tamping rod, to ensure uniform compaction.
The saturated test sample is placed into the cylindrical steel cup secured at the base of the impact testing machine. The hammer, weighing between 13.5 and 14.0 kg, is raised to a height of 380 ± 5 mm and allowed to fall freely to impact the sample. The test is performed twice, and the results averaged. Final values are rounded following IS 2:1960 guidelines.
The Aggregate Impact Value (AIV) is calculated as the percentage ratio of the weight of fines passing a 2.36 mm sieve to the total oven-dried sample weight, using the formula: AIV = (Weight of fines / Oven-dried sample weight) × 100. Lower AIV indicates stronger aggregates with better impact resistance.
The reported Aggregate Impact Value is the mean of two test values obtained from identical samples tested under saturated conditions. Results are expressed as percentages, rounded according to IS 2:1960. Proper documentation ensures standardized communication of aggregate impact resistance.
This standard incorporates modifications to the conventional aggregate impact value test to accommodate soft aggregates sensitive to moisture. It specifies apparatus details and reporting methods consistent with other IS codes for aggregate mechanical properties. The procedure is also applicable to brick aggregates, broadening its utility.
Frequently Asked
To prepare the aggregate sample following IS 5640, select aggregates that pass through a 12.5 mm IS sieve and are retained on a 10 mm IS sieve. Oven-dry the sample at 105 to 110°C for at least 4 hours or until reaching constant weight, then allow it to cool. Fill the cylindrical measure in three layers, tamping each layer 25 times with the rounded end of the tamping rod to ensure a compacted, representative sample. This procedure guarantees consistent sample conditions for the impact test.
The impact testing machine should weigh between 45 and 60 kg, with a base weighing 22 to 30 kg and a flat lower surface at least 30 cm in diameter. It must be firmly mounted on a level concrete or stone block no less than 45 cm thick to prevent movement. The hammer, weighing 13.5 to 14.0 kg, is raised to a height of 380 ± 5 mm and released to fall freely, striking the sample contained in the cylindrical steel cup. The hammer guides must be vertical to ensure accurate impacts. The machine may include features to support the hammer during cup changes and record the number of blows automatically.
IS 5640 modifies the traditional impact value test by introducing a saturation step for soft coarse aggregates such as laterite, kankar, and shale. Instead of testing dry samples, the aggregates are fully saturated with water before impact testing to simulate actual conditions where moisture weakens the materials. This approach results in a more realistic assessment of the aggregates' mechanical strength and durability when used in road pavement layers exposed to moisture.
The Aggregate Impact Value (AIV) is determined by calculating the percentage of the weight of fines passing a 2.36 mm sieve relative to the total oven-dried weight of the sample, using the formula: AIV = (Weight of fines / Oven-dried sample weight) × 100. Results are recorded to one decimal place. A lower AIV indicates greater resistance to impact and thus a tougher, more durable aggregate. Typical thresholds classify aggregates with AIV less than 30% as good quality, 30-35% as moderate, and above 35% as poor.
Yes, the IS 5640 testing method for Aggregate Impact Value is explicitly applicable to brick aggregates as well. The test evaluates their mechanical strength using the same procedures and sample sizes as for natural aggregates, ensuring the suitability of brick aggregates for use in road construction. The standardized method involves drying, layering, tamping, impact testing, and calculation of fines to quantify their impact resistance.
Ask AI about any clause, requirement, or provision in IS 5640. Get instant, clause-cited responses powered by our indexed library.
Free tier includes 150 queries (50 AI + 100 Reference) · No credit card required