Only at a laboratory that operates in each large company is it feasible to know precisely some mixing characteristics. After all, the M350 or M400 concretes look almost the same as the M100. The customer must rely on the passport and other paperwork for the required cement test apparatus delivery when placing an order for a batch. Review the offered certificates in detail to accomplish this.
The cement testing machine manufacturers suggested brand and the date the invoices were issued are the next two things you should pay attention to.
Consistency of cement for testing
- Pay particular attention to the colour of the mixture. Light brown denotes too much sand, whereas reddish denotes clay or slag additives. The answer needs to be homogeneous and grey in hue. However, the addition of different additives may affect how the combination changes colour.
- If you pour a portion of concrete into a different container, you may assess the quality of the material (bucket, moistened mold). The solution shouldn’t contain any water puddles. Delamination and fissures shouldn’t appear on the surface after pouring.
- If the cement slurry runs independently and the concrete crumbles like a cake, the given mix may not have been of sufficient quality.
However, the concrete mixture can only be accurately tested under controlled laboratory circumstances and most frequently after curing. As a result, the main base must be poured into 100x100x100 mm cubes and let to harden under normal circumstances.
How can the quality of hardened concrete be assessed?
- Thoroughly examine the base or product’s finished surface. Smooth concrete without pores or layers is a sign of high-quality construction. Winter pouring at low temperatures shouldn’t result in the surface showing distinctive patterns that indicate the mixture has frozen. Patterns indicate freezing during pouring and reduce the grade of concrete by 70 to 100 points (from M300 to M200-250);
- Use a hammer no heavier than 500g to strike the base after the concrete has reached 70% of its strength characteristics. A resonant sound is required. If hammer marks from a blow that made a ringing sound remain on the surface, concrete has a density of 150–200 kg/cm2. A low-grade mixture produces a dull sound, which implies that its strength is less than 100 kg/cm2. Additionally, it is advised to fix any surface fractures or crumbling caused by impact.
You can also assess the calibre of concrete by striking it with a hammer that only weighs between 300 and 400 grams. It’s important to assess how deeply the chisel penetrates the concrete under medium force hits.
- The grade is less than M70 if the tip dips deeply and readily without touching gravel or crushed stone.
- The marking is thought to be equivalent to M70-M100 with an immersion depth of up to 5 mm.
It can be assumed that the grade of the concrete is greater than M200 if there is no trace of the chisel or only a slight trace and there are no delaminations. When concrete of the M100-M200 grade is hit with a chisel, small, thin layers only separate on the surface.
But each of these approaches only provides a rough estimate. The reliability of the structure and the calibre of the poured concrete can only be reliably determined by laboratory tests. In this instance, specialised tools, measuring instruments, and cement testing equipment are used. There are numerous non-destructive methods to check the quality of the mixture, including ultrasonography, shock pulses, and other control devices and procedures, in addition to testing molten control samples (a cube with a 10 cm rim). The aforementioned techniques are “popular” but do not guarantee great accuracy. The master’s experience in attempting to identify the concrete brand also affects how reliable the determination is.