What is used to indicate the thickness of mechanism sand? What is the impact on concrete?

The thickness of mechanism sand, which is also known as manufactured sand or artificial sand, is typically indicated by the sieve analysis of the sand. This involves passing the sand through a series of standardized sieves with different mesh sizes to determine the distribution of particle sizes. The percentage of sand that passes through each sieve is recorded, and this data is used to create a particle size distribution curve.

The particle size distribution is important because it affects the workability, strength, and durability of concrete. Here's how it impacts concrete:

1. **Workability**: Sand with a well-graded particle size distribution (meaning it contains a mix of particle sizes) helps to improve the workability of concrete. This is because smaller particles can fill the gaps between larger particles, creating a more cohesive mix that is easier to pour, place, and finish.

2. **Strength**: Concrete made with mechanism sand can have similar strength to that made with natural sand, provided that the particle size distribution is appropriate. The shape and surface texture of the sand particles can also affect the bond with the cement paste, which in turn affects the concrete's strength.

3. **Durability**: The particle size distribution of sand can influence the concrete's resistance to abrasion, wear, and chemical attack. Well-graded sand can help to reduce the potential for voids and improve the concrete's overall durability.

4. **Shrinkage and Cracking**: Concrete with an excessive fine aggregate content (too many small particles) can be more prone to shrinkage and cracking. On the other hand, too few fines can lead to a less cohesive mix and potential segregation of aggregates.

5. **Cementitious reaction**: The surface area of the sand particles can affect the rate of cement hydration, which is the chemical reaction that transforms cement into concrete. Finer sand particles have a higher surface area, which can lead to faster hydration and setting times.

6. **Aggregate-Cement bond**: The particle size and shape of the sand can affect the bond between the aggregate and the cement paste. Aggregates that are too fine may not bond as well, leading to weaker concrete.

In summary, the thickness or particle size distribution of mechanism sand is indicated by sieve analysis, and it has a significant impact on the properties of concrete. The selection of sand with the appropriate particle size distribution is crucial for achieving the desired workability, strength, and durability in concrete construction.