When producing concrete, the primary materials used are inert granular substances such as sand, gravel, crushed stone, slag, recycled concrete, and geosynthetic aggregates. These materials can be classified as natural, manufactured, or recycled. The size of the aggregates determines their classification into two types: fine and coarse.
In accordance with American Standards (ASTM- C33/C33M), the properties of standard aggregates used in concrete production are of great importance. Fine aggregates typically consist of natural sand or crushed stone sand, whereas coarse aggregates are made up of gravel or crushed stone. The quality of the aggregates used can greatly affect the strength and durability of the resulting concrete structure.
It is essential to ensure that the aggregates used meet the necessary standards for particle size distribution, cleanliness, and other physical properties. Testing is carried out to determine the aggregate’s specific gravity, absorption, abrasion resistance, and soundness. Only after passing these tests can aggregates be considered suitable for use in concrete production.
Overall, the choice of aggregates is crucial in determining the quality of the concrete produced. Therefore, selecting high-quality, standard aggregates is crucial to achieving a durable and structurally sound end product.
Fine Aggregate
The provided text specifies that the fine aggregate to be used should be either natural sand, manufactured sand, or a combination of both. This indicates that any of these materials can be utilized for this purpose, as long as they meet the necessary specifications and requirements. The use of natural sand may be preferred in some cases, while manufactured sand may be more suitable in others. Additionally, the option to combine these materials provides flexibility and may offer advantages such as improved durability or reduced cost. Ultimately, the choice of fine aggregate will depend on various factors such as availability, cost, and the intended use of the concrete or other construction material.
1. Grading
The specifications state that the fine aggregate must not pass more than 45% from a single sieve and must be retained on the next consecutive sieve, as per the values presented in Table-1. Additionally, the fineness modulus of the fine aggregate must be within the range of 2.3 to 3.1, and it should not deviate more than 0.20 from this range. This means that the fineness modulus of the fine aggregate should be consistent and fall within the specified range, without exceeding the maximum deviation allowed. Overall, these specifications aim to ensure that the fine aggregate used in construction meets certain quality standards and is suitable for its intended purpose.
Table 1: Sieve Size and Passing Percentage of Aggregates.
| Sieve | Percent Passing |
| 9.5-mm (3/8-in.) | 100 |
| 4.75-mm (No. 4) | 95 to 100 |
| 2.36-mm (No. 8) | 80 to 100 |
| 1.18-mm (No. 16) | 50 to 85 |
| 600-µm (No. 30) | 25 to 60 |
| 300-µm (No. 50) | 5 to 30 |
| 150-µm (No. 100) | 0 to 10 |
2. Deleterious Substances
According to ASTM standards, the acceptable levels of harmful substances in fine aggregate are outlined in Table-2 below. This table provides the permissible range of deleterious substances that are allowed in fine aggregate, as specified by ASTM guidelines. Compliance with these standards ensures that the fine aggregate used in construction meets the required quality criteria, and that the levels of harmful substances present are within acceptable limits. Adhering to these guidelines helps to maintain the safety and quality of fine aggregate used in various construction applications, ensuring that it does not pose any risks or negative impacts on the performance or durability of the finished construction product.
Table 2: Deleterious Substance in Fine Aggregate
The context provided relates to the testing of aggregates for organic impurities. Specifically, it states that if the amount of organic impurities in the aggregates exceeds the prescribed limits, a test for organic contaminants must be conducted. If the color of the aggregates is darker than the standard, and this discoloration is caused by coal, lignite, or similar particles, the aggregates shall be rejected.
It is worth noting that if the fine aggregate fails the organic impurities test, it is not prohibited. However, the aggregate must undergo further testing to determine its effect on the strength of mortar. Specifically, the relative strength at seven days must be calculated in accordance with the ASTM-C87 test method. If the relative strength is not less than 95%, the aggregate is deemed acceptable despite having failed the organic impurities test.
3. Soundness
The requirement for the fine aggregate is that it must undergo five cycles of the soundness test. The weighted average loss must not exceed 10% and 15% when sodium sulfate and magnesium sulfate are used, respectively. If the fine aggregate sample does not meet the soundness test criteria, it is still acceptable to use the same fine aggregate for making concrete. However, the concrete must undergo freezing and thawing tests in accordance with ASTM C666/C666M.
Coarse Aggregate
The given context describes the requirements for the coarse aggregate used in construction. It specifies that the aggregate can be made up of several materials, including gravel, crushed gravel, crushed stone, air-cooled blast furnace slag, or crushed hydraulic-cement concrete. Additionally, the aggregate must conform to the provided specification.
1. Grading
The given statement specifies that the coarse aggregates must meet the requirements listed in Table 3 for the particular size number indicated. This implies that the coarse aggregates should satisfy the standards mentioned in the table for their respective sizes.
It is essential to adhere to these specifications to ensure that the coarse aggregates utilized in the construction project are of the required quality. Non-compliance with the prescribed requirements could lead to problems such as reduced strength and durability of the resulting structure.
Therefore, it is crucial to carefully select and verify the quality of coarse aggregates before using them in construction activities to ensure the longevity and stability of the final product.
Table 3: Grading Requirement of Coarse Aggregate
2. Deleterious Substances
The paragraph states that there are limits for deleterious substances in coarse aggregates, which must fall within a certain range as specified in Table 4. The paragraph does not provide any further information regarding what these limits are or why they are important.
Table 4: Deleterious Substance in Coarse Aggregate
The figure below depicts the requirements for weathering regions categorized as severe, moderate, and negligible. In cases where the class is not specified, the requirements for Class 3S, 3M, or 1N shall apply in severe, moderate, and negligible weathering regions, respectively.
Fig 2: Weathering Regions in America
The coarse aggregate utilized in concrete must be able to withstand wetting, prolonged exposure to humid conditions, or contact with moist ground without containing any materials that could react deleteriously with the alkalies present in the cement. Such reactions, if they occur, could lead to excessive expansion of mortar or concrete, resulting in undesirable consequences for the structural integrity of the construction. Therefore, it is imperative to carefully select coarse aggregates that do not pose a risk of detrimental alkali-aggregate reactions when used in concrete mixtures. This precautionary measure ensures that the performance and durability of the concrete are not compromised, and the desired quality of the final construction is achieved.
Methods of Sampling and Testing
The methods for sampling and testing fine and coarse aggregates must follow the guidelines outlined below, unless otherwise specified in this specification.
It is permitted to use the same test specimen for both sieve analysis and determining the amount of material that is finer than the 75-µm (No.200) sieve.
If using separated sizes from the sieve analysis for soundness or abrasion tests, it is acceptable. However, additional preparation of test specimens is necessary.
For all other test procedures and the evaluation of potential alkali reactivity, independent test specimens are required, as specified.
Sampling of Aggregate
The sentence states that the sampling method used for aggregates must follow the guidelines set out in Practice D75 and Practice D3665. These two practices likely outline specific procedures and protocols that should be followed to ensure that the sampling process is standardized and produces reliable results. It is important to adhere to these guidelines to maintain consistency and accuracy in the sampling process.
Testing of Aggregate
The types of tests on aggregate shall be as tabulated in the table below-
Table 5: Recommended Test for the Aggregates as per ASTM
| Name of Test on Aggregate | ASTM Reference |
| Grading and Fineness Modulus | ASTM C136 – Test Method for Sieve Analysis of Fine and Coarse Aggregates. |
| Amount of Material Finer than 75-µm (No. 200)Sieve | ASTM C117 – Test Method for Materials Finer than 75-µm (No. 200) Sieve in Mineral Aggregates by Washing. |
| Organic Impurities | ASTM C40 – Test Method for Organic Impurities in Fine Aggregates Concrete. |
| Effect of Organic Impurities on Strength | ASTM C87- Test Method for Effect of Organic Impurities in Fine Aggregate on Strength of Mortar. |
| Soundness | ASTM C88 – Test Method for Soundness of Aggregates by Use of Sodium Sulfate or Magnesium Sulfate. |
| Clay Lumps and Friable Particles | ASTM C142 – Test Method for Clay Lumps and Friable Particles in Aggregates. |
| Coal and Lignite | ASTM C123 – Test Method for Lightweight Particles in Aggregate. |
| Bulk Density of Slag | ASTM C29/C29M – Test Method for Bulk Density and Voids in Aggregate. |
| Abrasion of Coarse Aggregate | 1. ASTM C131 –Test Method for Resistance to Degradation of SmallSize Coarse Aggregate by abrasion and Impact in the Los Angeles Machine. 2. ASTM C535 – Test Method for Resistance to Degradation of LargeSize Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine. |
| Reactive Aggregates | Appendix X1 of ASTM C33/C33M – Methods for Evaluating Potential for Deleterious Expansion due to Alkali Reactivity of an Aggregate. |
| Freezing and Thawing | ASTM C666/C666M – Test Method for Resistance of Concrete to Rapid Freezing and Thawing. |
| Chert | 1. ASTM C123 – Test Method for Lightweight Particles in Aggregate (used to identify particles in a sample of coarse aggregate lighter than 2.40 specific gravity). 2. Guide C295 – Guide for Petrographic Examination of Aggregates for Concrete (to identify which of the particles in the light fraction are chert). |
1. What is the importance of aggregates in concrete?
The quality of concrete, including its workability, durability, strength, weight, and shrinkage, is significantly impacted by the properties of the aggregate used in its composition. The physical characteristics of the aggregate, such as its size, shape, and composition, can greatly affect the overall properties of the concrete.
Workability, for example, refers to the ease with which the concrete can be mixed, transported, placed, and compacted. This factor is heavily influenced by the size and shape of the aggregate particles. The use of a well-graded aggregate with a range of particle sizes can result in improved workability of the concrete.
Durability is another crucial property of concrete, as it determines its ability to resist wear, weathering, and other environmental factors. The selection of a durable aggregate can enhance the durability of the concrete, as it can resist degradation over time.
Strength is a critical factor in determining the load-bearing capacity of the concrete. The strength of the concrete is largely influenced by the strength of the aggregate particles used in its composition. The use of high-strength aggregate can significantly increase the overall strength of the concrete.
Weight is another key consideration in the selection of aggregate for concrete production. The use of lightweight aggregate can reduce the weight of the concrete, making it easier to handle and transport, and potentially reducing overall construction costs.
Finally, shrinkage is an important property that can impact the overall performance of the concrete. Shrinkage refers to the contraction of the concrete as it cures and dries. The use of low-shrinkage aggregate can reduce the amount of shrinkage and cracking that may occur in the concrete over time.
2. Which size of coarse aggregate is generally used in the production of concrete?
When it comes to producing concrete, it is generally preferred to use aggregate that passes through a 20mm sieve and is retained by a 12.5mm sieve. This specific range of aggregate size has been found to be optimal for creating concrete with desirable properties.
The size of the fine aggregate used in the mix design of concrete can greatly impact the final product. Fine aggregate, also known as sand, is typically added to concrete in a certain proportion to improve workability and durability. If the sand is too fine, it can lead to a lack of cohesion within the concrete and make it more difficult to work with. On the other hand, if the sand is too coarse, it can result in a less smooth surface finish and a reduction in the strength of the concrete.
Similarly, the coarse aggregate used in the mix design of concrete can also have a significant impact on the final product. Coarse aggregate, which is typically made up of gravel or crushed stone, is added to the concrete mix to provide bulk and strength. If the coarse aggregate is too small, it can lead to a reduction in the strength of the concrete and make it more prone to cracking. Conversely, if the coarse aggregate is too large, it can lead to difficulty in achieving proper workability and can result in a less smooth surface finish.
Overall, using aggregate that falls within the preferred size range of passing through a 20mm sieve and being retained by a 12.5mm sieve can help ensure that the concrete produced has the desired strength, workability, and surface finish.