The production of concrete relies on the use of inert granular materials, known as aggregates. These aggregates can be sourced from various materials, including gravel, crushed stone, sand, slag, recycled concrete, and geosynthetic aggregates. They are chosen for their stability and lack of chemical reactivity in the concrete mixture.
In accordance with European Standards, aggregates must meet specific geometrical requirements. These requirements ensure that the aggregates used in concrete production have the appropriate size, shape, and surface texture for optimal performance. The geometrical characteristics of aggregates are crucial in determining the overall strength, durability, and workability of the concrete.
In addition to geometrical requirements, aggregates must also meet physical requirements as per European Standards. These physical requirements include properties such as particle size distribution, particle density, water absorption, and abrasion resistance. These physical properties are essential in determining the performance and quality of the aggregates in concrete production.
Furthermore, aggregates used in concrete production can be categorized as natural, manufactured, or recycled. Natural aggregates are obtained from naturally occurring sources such as rivers, quarries, or mines. Manufactured aggregates are produced through industrial processes, such as crushing, grinding, or screening of raw materials. Recycled aggregates are obtained from the recycling of construction and demolition waste materials.
The use of aggregates in concrete production is regulated by European Standards to ensure that the aggregates used meet the necessary requirements for quality, performance, and sustainability. Adhering to these standards helps to ensure that the resulting concrete is of high quality, durable, and safe for use in various construction applications.
Fig 1: Aggregate used in the concrete.
The chemical requirements of aggregates, as per the European Standards (EN – 12620), include parameters such as chloride and sulfur content, along with other chemical constituents. These standards outline the specifications for aggregates used in construction, particularly in concrete production. Compliance with these requirements ensures that aggregates meet the necessary chemical properties for safe and reliable use in construction applications. These chemical requirements are an important aspect of quality control in the production and use of aggregates in accordance with European Standards.
1. Chlorides Content
According to EN 1744-1:1998, clause 7, the determination of the water-soluble chloride ion content of aggregates for concrete is necessary. Moreover, the producer must declare this information upon request. If the combined aggregate’s water-soluble chloride ion content is established to be 0.01% or less, which is typical for extracted materials from most inland quarries, this value can be utilized in calculating the chloride content of the concrete.
2. Sulfur Compounds
2.1 Acid Soluble Sulfate
In accordance with EN 1744-1:1998, clause 12, the acid-soluble sulfate content of the aggregates and filler aggregates for concrete must be determined. The results of this determination should be declared according to the relevant category specified in Table 20.
Table 20 – Categories for maximum values of acid-soluble sulfate content
2.2 Total Sulfur
The regulation outlined in EN 1744-1:1998, clause 11, stipulates that the total sulfur content of both aggregates and filler aggregates must not surpass certain limits. Specifically, air-cooled blast furnace slag aggregates must not exceed 2% sulfur by mass, while all other aggregates, excluding air-cooled blast furnace slag, must not exceed 1% sulfur by mass. It is important to take extra care when dealing with aggregates containing pyrrhotite, an unstable form of iron sulfide FeS. If pyrrhotite is present in the aggregate, a maximum total sulfur content of 0.1% as S must be enforced.
3. Other Constituents
3.1 Constituents which alter the rate of setting and hardening of concrete
According to EN 1744-1: 1998, the aggregates and filler aggregates that contain organic or other substances in proportions that can affect the rate of setting and hardening of concrete need to be evaluated. This evaluation should be done to determine their effect on stiffening time and compressive strength.
To assess their impact, the stiffening time of mortar test specimens should not be increased by more than 120 minutes, and the compressive strength of mortar test specimens should not be reduced by more than 20% at 28 days. The proportions of these materials should be adjusted accordingly to ensure that these criteria are met.
To determine the presence of organic matter in the aggregates, EN 1744-1: 1998 recommends conducting a test to determine the humus content using method 15.1. If the results show a high humus content, then the presence of fulvic acids should be determined using method 15.2. If the supernatant liquid in these tests is lighter than the standard colors, the aggregates can be considered free from organic matter.
If required, the presence of lightweight or organic contaminants can be tested in accordance with EN 1744-1: 1998 method 14.2, and the results of these tests should be declared. These steps ensure that the aggregates used in concrete do not negatively impact the setting and hardening process, as well as the compressive strength of the final product.
3.2 Constituents which affect the volume stability of air-cooled blast furnace slag
According to EN 1744-1:1998, 19.1, air-cooled blast furnace slag aggregate must not have any dicalcium silicate disintegration. Similarly, when tested in accordance with EN 1744-1:1998, 19.2, the aggregate must also be free from iron disintegration. It is imperative that the air-cooled blast furnace slag aggregate meets these requirements to ensure its quality and suitability for use.
4. Carbonate content of fine aggregates for concrete pavement surface
Aggregates play a crucial role in the properties of concrete, including workability, durability, strength, weight, and shrinkage. The composition, shape, and size of the aggregate used in the concrete govern these properties. Therefore, it is essential to select the right type of aggregate based on the intended use of the concrete.
The size of the coarse aggregate used in concrete production is generally between 20mm and 12.5mm. The aggregate passing through the sieve of 20mm and retained on the sieve of 12.5mm is preferred for making concrete. The selection of the right size of coarse aggregate is important to ensure that the concrete has the desired strength and durability.
When using fine aggregates in concrete surface courses, it is necessary to control the carbonate content. The carbonate content is determined according to EN 196-21:1989, clause 5, with the test portion prepared as per EN 1744-1:1998. The results of the test are declared to ensure that the carbonate content is within the specified limits. This is important to ensure that the concrete surface course has the desired properties and is suitable for its intended use.