Aggregates play a crucial role in concrete production, providing the necessary granular materials for its composition. These materials can be natural, manufactured, or recycled, encompassing a variety of options such as gravel, crushed stone, sand, slag, recycled concrete, and geosynthetic aggregates.
Continuation from Previous Articles: This discussion follows our exploration of geometrical and physical requirements in aggregates, building upon the standards set by the European Union (EN – 12620). In this installment, we delve into the chemical requirements, focusing on chloride, sulfur content, and other constituents specified in EN – 12620.
The concentration of water-soluble chloride ions in concrete aggregates is a critical factor. According to EN 1744-1:1998, clause 7, producers must declare this content upon request. If the chloride ion content is known to be minimal (e.g., 0.01% or lower), this value can be used in concrete chloride content calculations.
The acid-soluble sulfate content of aggregates and filler aggregates for concrete, determined per EN 1744-1:1998, clause 12, is categorized and declared according to Table 20.
| Category | Maximum Value |
|---|---|
| A | X1 |
| B | X2 |
| … | … |
EN 1744-1:1998, clause 11, establishes limits for total sulfur content:
Special precautions apply if pyrrhotite is present, limiting the total sulfur content to 0.1% as S.
Aggregates with substances altering concrete setting and hardening undergo assessment. EN 1744-1:1998, 15.3 outlines criteria ensuring they do not adversely impact stiffening time or compressive strength.
Organic Matter Determination: EN 1744-1:1998, 15.1 and 15.2 determine organic matter presence, considering humus content and fulvic acids. Lightweight or organic contaminator presence is tested per EN 1744-1:1998, 14.2.
Air-cooled blast furnace slag aggregates must be free from dicalcium silicate and iron disintegration, as per EN 1744-1:1998, 19.1 and 19.2, respectively.
Controlling carbonate content in fine aggregates for concrete surface courses is vital. Determination, as specified in EN 196-21:1989, clause 5, and declaration of results following EN 1744-1:1998, ensure compliance.
Aggregates significantly influence concrete properties like workability, durability, strength, weight, and shrinkage. Their composition, shape, and size play a pivotal role.
Generally, for concrete production, aggregates passing a 20mm sieve and retained on a 12.5mm sieve are preferred.
Understanding and adhering to these chemical requirements ensures the production of high-quality concrete, meeting European Standards and delivering robust structural performance.