--- title: "Aggregate impact value test" subject: "Transportation Engineering I" chapter: 6 key: "semester_6/transportation_engineering_i:impact-value" source: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/impact-value site: BCT Engineering --- # Aggregate impact value test Transportation Engineering I · Chapter 6: Highway Materials - Asked in: 2075 Bhadra; 2075 Baisakh; 2068 Magh (old course), 8 marks (asked 3 times) - Video: [Aggregate Impact Test | Aggregate Impact Value | Impact Test on Aggregates by Impact Testing Machine](https://www.youtube.com/watch?v=W9Xvc-5UEKc) — All About Structural Analysis and Design - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/impact-value - Whole chapter: https://www.bctengineer.com/md/semester_6/transportation_engineering_i/chapter-6 ## Question Describe briefly the laboratory test procedure to determine the impact value of aggregate. ## Short answer Aggregate impact value (AIV) measures resistance to sudden shock as percentage of fines passing 2.36mm sieve after 15 blows of a 14kg hammer falling 380mm on aggregate passing 12.5mm retained on 10mm. Procedure: fill cup in three layers with 25 tamps each, apply 15 blows, sieve and weigh fines. AIV ≤30% for wearing course, ≤35-45% for base. ## Answer The **aggregate impact value (AIV)** measures the resistance of an aggregate to sudden shock or impact (toughness). It is the percentage of fines (passing 2.36 mm) produced when the sample is subjected to 15 blows of a standard hammer (IS:2386 Part IV). #### Apparatus - Impact testing machine: a metal base, a steel cup (102 mm inside diameter, 50 mm deep), and a hammer of **13.5-14 kg** (usually 14 kg) with a free fall of **380 mm**. - Cylindrical measure (75 mm diameter, 50 mm deep), tamping rod (10 mm diameter, 230 mm long), IS sieves 12.5, 10 and 2.36 mm, balance. ```text | hammer 14 kg | falls 380 mm ___v___ | cup | <- aggregate in 1 layer |_______| base ``` #### Procedure 1. Take dry aggregate **passing the 12.5 mm and retained on the 10 mm** sieve (about 300-400 g, enough to fill the measure in three layers). 2. Fill the cylindrical measure in **three layers**, tamping each layer with **25 strokes**; weigh the sample ($W_1$). 3. Transfer it to the cup of the machine (fixed on the base) in a single layer and tamp it 25 times. 4. Raise the hammer to 380 mm and let it fall freely; give **15 blows**, each at an interval of not less than 1 second. 5. Remove the crushed material and sieve it through the **2.36 mm** sieve. Weigh the passing portion ($W_2$) and the retained portion ($W_3$); $W_2 + W_3$ should not differ from $W_1$ by more than 1 g. $$ \text{AIV} = \frac{W_2}{W_1} \times 100\% $$ Report the mean of two tests. #### Interpretation - Below 10%: exceptionally strong; 10-20%: strong; 20-30%: satisfactory for road surfacing; above 35%: weak. - Limits (IRC/NRS 2070): **not more than 30%** for the wearing course and **not more than 35-45%** for bituminous base and WBM. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What property of aggregate does the aggregate impact value measure? A. Hardness: resistance to wear by rubbing B. Strength under slowly applied compressive load C. Toughness: resistance to sudden shock or impact D. Resistance to weathering by salt solutions Answer: C. AIV is the percentage of fines produced under repeated hammer blows, so it shows toughness against sudden impact. (Key point: What AIV measures) 2. Which size fraction of aggregate is used for the impact test? A. Passing 20 mm and retained on 12.5 mm B. Passing 10 mm and retained on 6.3 mm C. Passing 2.36 mm and retained on 1.7 mm D. Passing 12.5 mm and retained on 10 mm Answer: D. The test sample is passing 12.5 mm sieve and retained on 10 mm sieve. (Key point: Sample size) 3. How is the impact applied in the standard test? A. 15 blows of a 14 kg hammer falling freely through 380 mm B. 500 blows of a 4.5 kg hammer falling 457 mm C. 25 blows of a 2.6 kg rammer falling 310 mm D. A steady 40 t load applied over 10 minutes Answer: A. The standard hammer (13.5-14 kg) falls 380 mm, 15 times at intervals of at least 1 second. (Key point: Test conditions) 4. How is AIV calculated? A. (W1 - W2)/W1 x 100 using the 1.7 mm sieve B. W2/W1 x 100, where W2 is the portion passing the 2.36 mm sieve C. W3/W1 x 100, the portion retained on 2.36 mm D. W2/W3 x 100 as a ratio of fines to retained Answer: B. AIV is the percentage by weight of fines passing 2.36 mm relative to the original sample weight W1. 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