Reception of the ready-mixed concrete: check first!
The success of a concrete structure depends not only on the proper use of the material, but also on the ordering of the concrete made by the company to its supplier. It is still necessary to check that the concrete delivered complies with the request and the delivery note…
Any structural work company is, according to the NF EN 206-1 standard, responsible for placing the concrete in the structure, and therefore for carrying out the work in accordance with the rules of the Art (NF DTU 21, NF DTU 13.3, etc.). Compliance with these allows it to limit the appearance of defects in the building (such as cracking of the concrete) provided that the concrete used has the specifications satisfying the type of sites and the climatic and environmental conditions of the destination structure.
This is how the relationship between the structural work company and its concrete supplier becomes a fundamental element of the durability of a structure. It will make it possible to establish the order of the right concrete for the work in question. However, certain rules, enacted in standard NF EN 206-1 and re-specified in this article, must be followed to ensure the smooth delivery of the concrete.
Before receiving the concrete...
The user must agree with his producer on the date, time and rate of delivery of the concrete. If necessary, the company also informs its supplier about the special transport on the site, the special installation methods and the limitation on the type of delivery vehicle to be used (type, need for agitation or not, height, height or total weight).
In return, always before delivery and if the structural work company requires it when ordering, the concrete producer gives information concerning the composition of the concrete such as the type and strength class of the cement, the type of aggregates , the type of additives or even the water/cement ratio targeted, the evolution of the resistance or the origins of the constituents.
Finally, according to the provisions in force, the producer must inform the user of the health risks to which he is exposed by handling the fresh concrete.
Upon receipt of the concrete, the structural work company must carry out various checks aimed at validating, in a timely manner, that the concrete delivered, intended for the work in question, "can be presumed to meet the market requirements of work” (NF DTU 21). Two types of controls:
Depending on the categories of site and the types of concrete, these checks are to be carried out according to a frequency specified in NF DTU 21 and listed in the table below:
In the event of detection of any non-conformity of the concrete delivered with respect to the request and/or the delivery note, the company must not hesitate to return the non-conforming mixer or to apply the conditions provided for in this case in the contract. with the producer (for example, admixture on site).
Full delivery note required
In addition, the delivery note must provide the following details:
Sign the delivery note only after receipt of the product and implementation, not before!
What categories of construction sites?
The categories of sites are defined in such a way as to be able to ensure increasing levels of control with the importance of the works and the presence of any special works. In the absence of prescriptions in the contract for the construction of the work, these categories are defined as follows :
Category A: These are small worksites that meet the following conditions:
This category concerns in particular single-detached, semi-detached houses, in small numbers.
Category B: This concerns medium-sized worksites, comprising only elements of standard dimensions and normally stressed. It targets in particular buildings of at most 16 levels, a large residential complex or common industrial construction. The quantity of concrete used for this category of site does not exceed 5,000 m 3 .
Category C: This category concerns construction sites of great importance, comprising only elements of common dimensions and normally stressed. It applies in particular to buildings with more than 16 floors, industrial warehouses with heavy loads or large sports complexes.
Specific works PA, PB and PC of category A, B and C worksites:
These are works such as:
Concrete is a very commonly used construction material, it makes the job easy and quick. It is also a natural and harmless material in the hardened state. The risks of using concrete in its fresh state have been known for a long time and mainly concern the eyes and the skin. They come in the form of burns, allergies or redness.
Elementary precautions must therefore be taken when mixing and placing concrete:
Handling concrete with bare hands, smoothing concrete with your fingers, picking up a trowel handle covered in fresh concrete with your bare hands or even kneeling in a humid environment containing fresh concrete must be prohibited from working methods.
In the event of direct contact with the skin or eyes, here are the first steps to take:
Promptly remove clothing that has been soaked in fresh concrete and launder. If, despite all these precautions, irritation or pain persists, consult a doctor without delay.
* These precautions are taken from the “Vicat Concrete advice sheets”.
Consistency measurement of fresh concrete
First of all, the fresh concrete must be sampled according to standard NF EN 12350-1. Next, the most commonly used test in France is the so-called sag test, or Abrams cone test. It is carried out in 4 steps according to standard NF EN 12350-2:
Other measurements can be made by one of the following tests:
Compressive strength measurement of hardened concrete
Resistance measurements are obtained from compression tests carried out, in France, on cylinders, 160 mm in diameter and 320 mm in height, crushed at 28 days (unless otherwise specified) in accordance with standard NF EN 12390-3 .
Samples of fresh concrete are taken according to standard NF EN 12350-1 or the documentation P 18 - 457 (which provides, for example, in its text, the taking of samples on Fridays with conservation of the specimens until Monday ). They are carried out on site immediately before the concrete is placed. Each sample is taken from a single batch, or load, and the latter can only give rise to a single sample. It includes a volume of concrete at least equal to 1.5 times (approximately) the volume required for the tests. The results of all these measurements are recorded and their interpretation is made in accordance with appendix A of NF DTU 21.
The characteristic strength of the concrete must be equal to or greater than the minimum characteristic strength for the strength class specified. For any construction site, the various parties can agree in the Special Contract Documents (DPM) to reinforce the means of controlling the concrete.
The ready-mixed concrete memorandum of understanding
In order to improve the quality of concrete delivered to the site, a memorandum of understanding on ready-mixed concrete was created in 1995 between UMGO, EGF-BTP, FNTP and SNBPE.
Updated in 2009 due to changes in standards and the general context, and signed on October 14, 2009, it provides details on the charter for relations between BPE suppliers and customers, namely:
The NF DTU and standards are available in the bookstore of our shop