Table of Contents
Overview
Course Aggregate is major construction material used in preparation of concrete both plain cement concrete (PCC) and reinforced cement concrete (RCC). It consists of crushed or broken stone, gravel or other inert material with similar characteristics or a combination. It shall be of uniform grading with max size as required for various types / classes of concrete meeting the grading requirements, when tested in accordance with ASTM C 117 & C 136, as given in Picture-1:
Properties of Aggregates
- Los Angeles Abrasion Value should be 40% (max) as per ASTM C 131
- Loss of weight when immersed in Na2SO4 should be 12% (max) as per AASHTO T-104
- Weight of material passing #200 sieve by washing should be One (1)% (max)
Selection of Max Size of Aggregate
Max Size of Aggregate to be selected for use in various types of construction is given in Table-1:
TABLE-1
| Type of Construction | Max Size of Aggregate (mm) | Max Size of Aggregate (in) |
|---|---|---|
| Plain Footings, caissons and Sub structure walls | 50 | 2 |
| Reinforced Foundation Walls and footings | 37.5 | 1-1/2 |
| Beams and Reinforced walls | 25 | 1 |
| Columns | 25 | 1 |
| Pavements and Slabs | 19 | 3/4 |
| Mass Concrete | >50 | 2 |
Note: The Max Size of Aggregate is subject to condition that Concrete shall not contain any aggregate greater in size than 1/5 of the narrowest dimension between sides of the forms, nor 1/3 of the least dimension of the concrete nor ¾ of the min clear spacing between the individual reinforcing bars or wires, bundles of bars, individual tendons, bundled tendons or ducts.
Characteristics of Good Quality Aggregate
- Natural aggregates shall be clean, round and smooth
- Aggregate should not have flaky shape
- Aggregate should not be having sandy characteristics
- Coarse aggregates shall be crushed aggregate from suitable sources and conform to quality requirements mentioned in Picture-1. If allowed for a specific work, ballast, gravel or shingle may be used, mixed with sand to various proportions. However, these materials must conform to strength and gradation requirements.
- Alternative aggregates of hard broken bricks and broken CC will NOT be used in RCC and Pre-stressed concrete in any position.
- Mixed aggregates are not required to be uniformly graded and shall be known as Mixed Aggregate. The size shall be specified in terms of the largest gauge required, but not exceed 50 mm and shall consist of various gauges.
