Aggregates play a crucial role in the production of concrete as they are the inert granular materials that form the bulk of the mixture. These aggregates can be sourced from various materials such as gravel, crushed stone, sand, slag, recycled concrete, and geosynthetic aggregates. They are typically granular and do not react chemically with the other components of concrete. Aggregates used in concrete can be classified as natural, manufactured, or recycled, depending on their origin. Natural aggregates are obtained from naturally occurring sources, while manufactured aggregates are artificially produced, and recycled aggregates are obtained from previously used concrete or other materials. All these types of aggregates are used in the production of concrete to provide strength, durability, and stability to the final product.
Fig 1: Fine and Coarse Aggregate.
The geometrical characteristics of aggregates, including size, grading, shape, shell content, fine content, and quality, are important considerations in the production of concrete according to the European Standards (EN-12620). These requirements ensure that the aggregates used in concrete meet specific standards set by EN-12620. The size of aggregates refers to the dimensions of the particles, while grading refers to the distribution of different particle sizes in the aggregate mixture. The shape of aggregates refers to their physical form, such as angular or rounded particles. The shell content refers to the presence of shells or other organic materials in the aggregates, which can affect the quality of the concrete. The fine content refers to the proportion of fine particles in the aggregates, which can impact the workability and strength of the concrete. Finally, the quality of aggregates refers to their overall characteristics, including durability, strength, and resistance to environmental factors. All of these geometrical requirements play a crucial role in ensuring that the aggregates used in concrete production meet the necessary standards for quality and performance as per EN-12620.
1. Aggregate Size
The given context pertains to the designation of aggregate sizes using a pair of sieve sizes selected from the basic sieve or the basic set plus set 1 or set 3, as specified in table 1. According to the guidelines, the aggregate sizes should have D/d values that are not less than 1.4. It is important to note that a combination of sizes from set 1 and 2 is not allowed under any circumstance.
Table 1: Sieve sizes for specifying aggregate sizes.
2. Aggregate Grading
The grading of aggregates must adhere to the specifications outlined in EN 933-1 and must meet the standards specified in the accompanying tables.
1. Coarse Aggregate
The statement pertains to the adherence of the coarse aggregate to the grading requirement specified in Table 2, which is deemed appropriate for their respective size designation d/D and selected categories. In simpler terms, it is necessary for the coarse aggregate to meet the grading requirement specified in Table 2, which is based on their size designation and chosen category.
Table 2: Grading requirement for coarse aggregate.
The specified requirements for graded coarse aggregates depend on the values of D and d. If D is greater than 11.2 mm and D/d is greater than 2, or if D is less than or equal to 11.2 mm and D/d is greater than 4, additional requirements must be met for the percentage passing the mid-size sieve.
For such graded coarse aggregates, two conditions must be satisfied. Firstly, the overall grading of all the fractions must comply with the limits given in Table 3. Secondly, the producer is responsible for documenting and declaring the typical grading passing the mid-size sieve and the tolerance selected from the categories specified in Table 3. These requirements apply to ensure the quality of the graded coarse aggregates.
Table 3: Overall limit and tolerances for coarse aggregate grading at mid-size sieves.
The requirement for single size coarse aggregates can be classified into two cases. In the first case, if the diameter (D) of the coarse aggregate is greater than 11.2 mm and the ratio of D to the minimum dimension (d) of the particle is less than or equal to 2, then there is no need for any additional requirement beyond what is specified in Table 2. Similarly, in the second case, if the diameter (D) of the coarse aggregate is less than or equal to 11.2 mm and the ratio of D to the minimum dimension (d) of the particle is less than or equal to 4, then there is no need for any extra requirement beyond what is mentioned in Table 2.
Therefore, if the above conditions are met, the coarse aggregates do not require any further specifications apart from those listed in Table 2.
2. Fine Aggregate
The specified general grading requirement in Table 2 for fine aggregates must be met, based on their upper sieve size D. In addition to this, there are further requirements that need to be met to control the variability of the fine aggregate. The typical grading of the fine aggregate is expressed as a percentage by mass of aggregate that passes through the sieve sizes listed in Table 4. These requirements are necessary to ensure consistency and quality in the fine aggregate used.
Table 4: Tolerance on producer’s declared typical grading for general use fine aggregates.
3. Natural Graded 0/8 mm Aggregate
Natural graded 0/8 mm aggregate is subject to certain requirements to ensure its quality. Firstly, it must meet the general grading requirement stated in Table 2. However, to further control the variability of this type of aggregate, an additional requirement must be met.
The producer of the natural graded 0/8 mm aggregate must document and be prepared to declare the typical grading for each aggregate that they produce, upon request. This serves as a means of ensuring that the aggregate is of a consistent quality.
In addition to documenting and declaring the typical grading, the grading of the natural graded 0/8 mm aggregate must also comply with the tolerance specified in Table 5. This is necessary to maintain a consistent level of quality in the aggregate and prevent unacceptable variability.
Table 5: Tolerance on producer’s declared typical grading for natural graded 0/8 mm aggregate.
4. All-in Aggregate
The specification requires that the all-in aggregate be supplied as a mixture of coarse and fine aggregate. The maximum particle size of the aggregate should be 45 mm or less, and there should be no particles smaller than 0 mm. The aggregate mixture must also meet the general grading requirements for the category selected from Table 2.
Furthermore, the all-in aggregates must comply with the percentage passing requirements for the two intermediate sieves specified in Table 6. The percentage passing requirements in Table 6 are appropriate to the size of the aggregate being used. It is important that the all-in aggregate meets all of these requirements to ensure that it is suitable for its intended use.
Table 6: Grading requirement for all-in aggregates.
5. Filler Aggregate
According to EN 933-10, the assessment of filler aggregate grading must comply with the restrictions outlined in Table 7.
Table 7: Grading requirement for filler aggregate.
6. Special use Aggregate
For specific applications of concrete, special aggregate gradings may be necessary. In these cases, specific grading envelopes must be established using the R 20 series of sieves outlined in ISO 565:1990. These envelopes should incorporate the appropriate sieves ranging in size from 0.063 mm to 63 mm, including 0.125 mm, 0.250 mm, 0.500 mm, 1 mm, 2 mm, 4 mm, 8 mm, 16 mm, and 31.5 mm. By using these particular sieves, a specialized grading system can be developed to suit the particular needs of the end use of the concrete.
3. Shape
In some cases, special aggregate gradings are necessary for specific applications of concrete. To establish these gradings, it is important to use the R 20 series of sieves outlined in ISO 565:1990. This series includes sieves ranging in size from 0.063 mm to 63 mm, with sizes such as 0.125 mm, 0.250 mm, 0.500 mm, 1 mm, 2 mm, 4 mm, 8 mm, 16 mm, and 31.5 mm included. By utilizing these specific sieves, it becomes possible to create specialized grading envelopes that meet the needs of the concrete’s intended end use. These envelopes can be tailored to the requirements of the application, ensuring that the concrete will perform optimally in its designated role.
Table 8: Categories for maximum values of flakiness index.
The shape Index, as determined by EN 933-4, must be declared according to the appropriate category in Table 9 for the specific application or end-use. This declaration is necessary wherever it is required. The shape Index is an important parameter that helps in understanding the characteristics of the material being used. It provides information about the shape of the particles and can be used to determine how the material will perform in certain applications. The EN 933-4 standard provides guidelines for measuring and determining the shape Index of materials. It is important to follow these guidelines to ensure accuracy and consistency in the declaration of the shape Index. Once the shape Index has been determined, it can be compared to the categories in Table 9 to determine the appropriate declaration for the specific application or end-use.
Table 9: Categories for maximum values of shape index.
4. Shell Content of Coarse Aggregate
According to EN 933-7, the determination of shell content for coarse aggregate is required. This determination is made in accordance with the guidelines set forth in the standard. The results of this determination must be declared using the relevant category specified in Table 10. The declaration of the shell content must follow the guidelines outlined in the standard in order to ensure accuracy and consistency. Table 10 provides categories for the declaration of shell content that are relevant to the specific characteristics of the coarse aggregate being tested. By following the guidelines and using the appropriate category from Table 10, the shell content of coarse aggregate can be accurately determined and declared.
Table 10: Category for maximum value of shell content of coarse aggregate.
5. Fines Content
According to the standard EN 933-1, the fines content of the aggregate needs to be determined and declared based on the relevant category specified in Table 11. The declaration should be made in accordance with this table.
If the aggregate is being used as filler, then its fines content needs to comply with the requirements specified in Table 7. This is particularly important when it comes to filler aggregate. The fines content needs to meet the standards set in Table 7 in order to ensure that the aggregate is suitable for use.
Table 11: Categories for maximum values of fines content
6. Fines Quantity
Aggregates play a crucial role in determining the properties of concrete. The composition, shape, and size of the aggregate used in the concrete have a significant impact on the workability, durability, strength, weight, and shrinkage of the final product. Thus, the selection of the right type of aggregate is critical in ensuring the desired characteristics of the concrete.
In the production of concrete, a specific size of coarse aggregate is generally preferred. Typically, aggregate that passes the sieve of 20mm and retains the sieve of 12.5mm is used. This size of aggregate is ideal for achieving the desired properties of the concrete.
It should be noted that the harmfulness of fines in the fine aggregate, including filler aggregate, should be assessed in accordance with Annex D of EN 12620. This assessment is crucial in ensuring that the aggregate used in the concrete does not negatively impact the final product.