Aggregates play a crucial role in the production of concrete, as they are inert granular materials that are added to the mixture. These materials include gravel, crushed stone, sand, slag, recycled concrete, and geosynthetic aggregates, and can be either natural, manufactured, or recycled. In order to ensure that the aggregates are suitable for use in concrete, they must meet certain physical requirements as specified by the European Standards (EN – 12620).
One important physical requirement of aggregates is their resistance to fragmentation. This refers to their ability to resist breaking or shattering under load. In addition, the aggregates must also be able to withstand wear, polishing, and abrasion, as these factors can impact the strength and durability of the concrete.
Another key physical requirement is particle density, which is the mass per unit volume of the individual particles. This is important because it can affect the strength and workability of the concrete mixture. The bulk density of the aggregates is also important, as it can impact the volume of concrete produced per unit of weight.
Finally, the durability of the aggregates is also an important consideration. This refers to their ability to resist the effects of weathering, chemical attack, and other environmental factors over time. By meeting these physical requirements, aggregates can help ensure that the resulting concrete is strong, durable, and able to withstand the demands of its intended use.
1. Resistance to Fragmentation of Coarse Aggregate
In order to determine the resistance to fragmentation, the Los Angeles test method should be used as a reference. This test method is specified in clause 5 of the EN 1097-2:1998 standard. The Los Angeles coefficient obtained from this test should be declared in accordance with the relevant category specified in Table 12. This is important in determining the appropriate application or end-use for the material being tested.
Table 12 – Categories for maximum values of Los Angeles coefficients
The declaration of the impact value determined in accordance with EN 1097-2:1998, clause 6, should be made according to the relevant category specified in Table 13, depending on the specific application or end-use. This means that when declaring the impact value, it is necessary to consider the particular purpose or function of the material in question and assign it to the appropriate category listed in Table 13.
The determination of impact value is an important factor in assessing the performance of a material in different applications. However, the impact value alone may not provide enough information on the suitability of the material for a specific use. Hence, it is essential to consider the end-use requirements and choose the relevant category from Table 13 to make an informed declaration.
By following the guidelines provided in EN 1097-2:1998, clause 6, and Table 13, manufacturers and users can ensure that the impact value of the material is declared accurately and appropriately. This helps in selecting the right material for a specific application, which can improve the overall performance and longevity of the product.
Table 13: Categories for maximum values of resistance to impact
2. Resistance to Wear of Coarse Aggregate
In order to determine the resistance to wear of coarse aggregate, the procedure specified in EN 1097-1 shall be followed. After conducting the test, the micro-deval coefficient value shall be declared. The declared value must correspond to the relevant categories specified in Table 14. The appropriate category must be chosen based on the particular application or end-use of the aggregate.
Table 14: Categories of maximum values of resistance to wear
3. Resistance to Polishing
In order to determine the resistance to polishing of coarse aggregate to be used for surface courses, the procedure outlined in EN 1097-8 must be followed. The resistance to polishing, also known as the polished stone value (PSV), is an important characteristic that must be declared in accordance with the relevant category specified in Table 15. This ensures that the coarse aggregate meets the required standards for use in surface courses. The resistance to polishing is a crucial factor in determining the durability and skid resistance of the surface course, which is vital for ensuring the safety of the users of the surface. Therefore, it is important to accurately determine the resistance to polishing of coarse aggregate and declare it in accordance with the specified category in Table 15.
Table 15 – Categories for minimum values of resistance to polishing
4. Resistance to Surface Abrasion
According to the given requirements, the determination of the resistance to surface abrasion, also known as the aggregate abrasion value (AAV), should follow the guidelines specified in Annex A of the EN 1097-8:1999 standard.
Furthermore, the declared resistance to surface abrasion should correspond to the relevant category indicated in Table 16. This table contains specific criteria that define the appropriate level of resistance based on the intended use of the aggregate material.
Therefore, it is crucial to adhere to these standards to ensure that the aggregate material meets the necessary requirements for its intended application and can withstand the expected level of surface abrasion.
Table 16: Categories for maximum values of resistance to surface abrasion
5. Resistance to Abrasion from Studded Tires
In order to determine the resistance to abrasion from studded tires, the Nordic abrasion value, known as An, must be measured according to the guidelines outlined in EN 1097-9. The resulting level of resistance should then be declared using the appropriate category specified in Table 17.
Table 17 – Categories for maximum values of resistance to abrasion from studded tires
6. Particle Density and Water Absorption
To determine particle density and water absorption, the EN 1097-6 standard must be followed. Upon request, the results of these tests should be disclosed along with the methods of determination and calculations used.
7. Bulk Density
As per the given requirements, the determination of bulk density must be carried out in accordance with EN 1097-3. This process needs to be followed when it is deemed necessary and the results obtained should be declared whenever requested. The method specified by EN 1097-3 must be used for the determination of bulk density, and the results should be made available upon request. The declaration of the results is necessary and should be done whenever required. The EN 1097-3 guidelines need to be followed strictly for this determination process.
8. Durability
8.1 Freeze and Thaw Resistance of Coarse Aggregate
The specified testing standards for aggregates in freezing and thawing environments are outlined in EN 1367-1 or EN 1367-2, based on the relevant category specified in either Table 18 or Table 19. It is necessary to follow these guidelines to properly test the aggregates for their ability to withstand freezing and thawing conditions.
Table 18: Categories of maximum values of freeze-thaw resistance.
Table 19: Categories of maximum Magnesium sulfate soundness
8.2 Volume Stability – Drying Shrinkage
When concrete experiences disruptive shrinkage cracking as a result of aggregate properties, it is necessary to limit the drying shrinkage associated with the aggregates used in structural concrete. The maximum allowed drying shrinkage, which must be declared in test results according to EN 1367-4, is 0.075%. This limit is imposed to prevent further instances of disruptive shrinkage cracking in the future.
8.3 Alkali-Silica Reactivity
Aggregates play a vital role in determining the properties of concrete such as its workability, strength, weight, durability, and shrinkage. The composition, shape, and size of the aggregate used in the concrete directly affect these properties. Therefore, it is essential to assess the alkali-silica reactivity of aggregates in accordance with the provisions valid in the place of use, and declare the results to ensure the quality of concrete.
When it comes to the size of the coarse aggregate used in the production of concrete, it is commonly preferred that the aggregate should pass through a sieve of 20mm and retain a sieve of 12.5mm. This size of aggregate has been found to be suitable for producing concrete with desired properties. However, the assessment of the aggregates’ properties should be in accordance with the relevant standards, such as the Geometrical Requirement of Aggregates as per European Standards or Aggregates for Concrete as per American Standards – ASTM, to ensure that the quality of the concrete is maintained.