--- title: "Mechanical properties of aggregates" subject: "Concrete Technology and Masonry Structure" chapter: 1 key: "semester_5/concrete_technology_and_masonry_structure:aggregate-mechanical-properties" source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/aggregate-mechanical-properties site: BCT Engineering --- # Mechanical properties of aggregates Concrete Technology and Masonry Structure · Chapter 1: Introduction to concrete and concrete materials - Asked in: 2076 Ashwin, 4 marks; 2072 Kartik, 6 marks (asked 2 times) - Video: [Classification and Properties of Aggregates](https://www.youtube.com/watch?v=q6Aytex3bgY) — Ekeeda - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/aggregate-mechanical-properties - Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-1 ## Question Describe the mechanical properties of aggregates (state briefly four mechanical properties of aggregate). ## Short answer Four key mechanical properties: crushing value (resistance to compression; limit 45% general, 30% for wearing surfaces), impact value (toughness under shock; same limits), Los Angeles abrasion value (wear resistance; ≤30% for wearing surfaces), and rock strength (parent rock compressive strength should not be less than required concrete strength). ## Answer Mechanical properties show how the aggregate resists loads and wear. Four main properties are: #### 1. Crushing value (IS 2386 Part 4) Resistance to crushing under a gradually applied compressive load. A 12.5-10 mm sample of mass $W_1$ in a steel cylinder is loaded to 400 kN in 10 minutes; the fines passing the 2.36 mm sieve ($W_2$) are weighed. $$ \text{ACV} = \frac{W_2}{W_1} \times 100\ \% $$ Limit: not more than 45% for concrete in general and 30% for wearing surfaces such as runways, roads and pavements (IS 383). #### 2. Impact value (IS 2386 Part 4) Toughness under sudden shock. A 12.5-10 mm sample is given 15 blows from a 13.5-14 kg hammer falling 380 mm; the fines passing 2.36 mm as a percentage of the total is the AIV. Limit (IS 383): 45% for concrete other than wearing surfaces and 30% for wearing surfaces. #### 3. Abrasion value (Los Angeles, IS 2386 Part 4) Resistance to wear. The sample is rotated with steel balls in a drum for 500 revolutions at 30-33 rpm; the percentage passing the 1.70 mm sieve is the abrasion value. Limit: 30% for wearing surfaces and 50% for others. #### 4. Hardness / toughness (and strength) Hardness is the resistance to scratching (Mohs scale); the strength of the parent rock is tested on cores or cubes. Granite is usually 100-250 MPa; the rock strength should not be less than the required concrete strength. Lower crushing, impact and abrasion values mean a stronger, tougher and more durable aggregate. Weak aggregates cannot make strong concrete, since high-strength concrete fails through the aggregate. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Aggregate crushing value is based on: A. Weight lost after 500 revolutions B. Hammer blow count C. Water absorbed D. Fines passing 2.36 mm after 400 kN load Answer: D. ACV = W2/W1 x 100. (Key point: Crushing) 2. Impact test uses: A. 15 blows of a 13.5-14 kg hammer from 380 mm B. 500 revolutions C. 400 kN load D. Sulphate immersion Answer: A. It measures toughness against shock. (Key point: Impact) 3. Los Angeles abrasion value is the percentage passing: A. 2.36 mm sieve B. 1.70 mm sieve after 500 revolutions C. 4.75 mm sieve D. 150 micron sieve Answer: B. Steel balls in a rotating drum measure wear. (Key point: Abrasion) 4. A lower crushing/impact/abrasion value means: A. Weaker aggregate B. Finer aggregate C. Stronger, tougher aggregate D. More porous Answer: C. Less fines produced means better resistance. 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