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The aggregates used in the production of concrete are inert granular materials such as gravel, crushed stone, sand, slag, recycled concrete, and geosynthetic aggregates. The aggregates may be natural, manufactured, or recycled.

This article is in continuation of the article: Geometrical Requirement of Aggregates as per European Standards [PDF] and Physical Requirement of Aggregates as per European Standards

Aggregate used in the concrete
Fig 1: Aggregate used in the concrete.

In this article, we discuss the chemical requirement of the aggregates such as chloride, sulfur content, and other chemical constituents as per the European Standards (EN – 12620).

1. Chlorides Content

The water-soluble chloride ion content of aggregates for concrete shall be determined in accordance with EN 1744-1:1998, clause 7, and shall, on request, be declared by the producer.

If the water-soluble chloride ion content of the combined aggregate is known to be 0.01 % or lower (e.g., for extracted from most inland quarries), this value can be used in the calculation of the chloride content of concrete.

2. Sulfur Compounds

2.1 Acid Soluble Sulfate

The acid-soluble sulfate content of the aggregates and filler aggregates for concrete determined in accordance with EN 1744-1:1998, clause 12, shall be declared in accordance with the relevant category specified in Table 20.

Table 20 – Categories for maximum values of acid-soluble sulfate content

Categories for maximum values of acid-soluble sulfate content

2.2 Total Sulfur

The total sulfur content of the aggregates and filler aggregates, determined in accordance with EN 1744-1:1998, clause 11, shall not exceed:

  1. 2% S by mass for air-cooled blast furnace slag.
  2. 1 % S by mass for aggregates other than air-cooled blast furnace slag.

Special precautions are necessary if pyrrhotite, (an unstable form of iron sulfide FeS), is present in the aggregate. If this mineral is known to be present, a maximum total sulfur content of 0,1 % as S shall apply.

3. Other Constituents

3.1 Constituents which alter the rate of setting and hardening of concrete

The aggregates and filler aggregates that contain organic or other substances in proportions that alter the rate of setting and hardening of concrete shall be assessed for the effect on stiffening time and compressive strength in accordance with EN 1744-1: 1998, 15.3.

The proportions of such materials shall be such that they do not:

  1. Increase the stiffening time of mortar test specimens by more than 120 min.
  2. Decrease the compressive strength of mortar test specimens by more than 20 % at 28 days.

The presence of organic matter shall be determined in accordance with EN 1744-1: 1998,15.1 (determination of humus content). If the results indicate a high humus content, the presence of fulvic acids shall be determined in accordance with EN 1744-1: 1998, 15.2. If the supernatant liquid in these tests is lighter than the standard colors, the aggregates shall be considered to be free from organic matter.

If required, the presence of lightweight of organic contaminator shall be tested in accordance with EN 1744-1: 1998 14.2, and the results shall be declared.

3.2 Constituents which affect the volume stability of air-cooled blast furnace slag

The air-cooled blast furnace slag aggregate shall be free from dicalcium silicate disintegration when tested in accordance with EN 1744-1: 1998, 19.1. The air-cooled blast furnace slag aggregate shall be free from iron disintegration when tested in accordance with EN 1744-1: 1998, 19.2.

4. Carbonate content of fine aggregates for concrete pavement surface

When it is required to control the carbonate content in fine aggregates for use in concrete surface courses, the carbonate content shall be determined as specified in EN 196-21:1989, clause 5, with the test portion being prepared in accordance with EN 1744-1: 1998123 and the results declared.

1. What is the importance of aggregates in concrete?

The properties of concrete such as workability, durability, strength, weight, and, shrinkage are governed by the properties (composition, shape, and size) of aggregate used in the concrete.

2. Which size of coarse aggregate is generally used in the production of concrete?

Generally, aggregate passing the sieve of 20mm and retaining the sieve of 12.5mm is preferred for the production of concrete.

Read More:
1. Physical Requirement of Aggregates as per European Standards
2. Geometrical Requirement of Aggregates as per European Standards

Fasi Ur Rahman

Fasi Ur Rahman

EDITOR
Fasi is a Civil Engineer associated with Project Management Consultant for Tumkur Smart City Project in Karnataka, India. He is the author, editor, and partner at theconstructor.org

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