Since 1999 the company has been active on an industrial level with the production, transport and paving of ready-mix concrete and cement products, by establishing an industrial production unit in its facilities in the Industrial Zone of Herakleio Crete. However, its engagement with this sector dates back to its establishment, due to the execution of a big number of public and private works, which makes it one of the most experienced and reliable companies in this field.
The raw materials used for the production of ready-mix concrete are the following:
- Aggregates (sand, coarse gravel, crushed stone)
- Additional concrete chemicals (retardants, superfluidizers)
All different categories of concrete are created from the different composition ratio of the aforementioned raw materials (composition study). The company’s ready-mix concrete composition studies are certified by an external accredited laboratory, according to the specifications of Concrete Technology Regulation and taking into account the constant changes and improvements the Regulation is at times subject to. The main and most common categories are presented in the following table:
|READY-MIX CONCRETE CATEGORY|
|1.||C12/15 (Gros Béton)|
|3.||C16/20 (Road concreting)|
|4.||C20/25 (Building projects)|
|5.||C25/30 (Buildings, bridges)|
|6.||C30/37 (Special applications)|
All the aforementioned categories of concrete are also produced in the form of grained concrete with a maximum grain size smaller than 16mm (Dmax < 16mm), as well as than 8mm (Dmax < 16mm) for cases that demand a finer grained aggregate mixture (e.g. in case of extremely dense reinforced concrete, use of concrete pump for concreting with grid, forming smoother surfaces, etc.)
TRANSPORT AND PAVING OF CONCRETE
The ready-mix concrete -immediately after production- is placed in special trucks with agitators (barrels) and then transferred to the customer. During transport and until paving, concrete is protected against water (e.g. rain) or admixture with foreign materials, while its temperature is monitored so as to not exceed the allowable limits, as defined in ELOT 346. This ensures that the quality of the finished concrete remains unchanged, from production to paving. Our company has barrels with a maximum capacity of 8 m3, as well as concrete pumps (presses), the largest of which can concrete surfaces up to 42 meters high.
CONCRETE QUALITY ASSURANCE
The quality control of the produced material is conducted in four phases:
- Quality control of raw materials
- Monitoring during the production process
- Laboratory testing of the material produced
- Traceability of the material produced
A. Quality control of raw materials
All raw materials used for the production of concrete are certified and appropriately marked. Aggregates come from a certified quarry and, additionally, are granulometrically monitored on a daily basis. The cement comes from the local warehouses of certified cement supply companies. In each case, the results of the inspections carried out by the supplier are requested and taken into account.
Β. Monitoring during the production process
Monitoring during the production process includes:
- Visual appearance
- Concrete slump
- Sand moisture
Production is monitored at all times by the mixer operator, who monitors through the PC the quantities fed in the mixer. The system self-checks the specifications and detects any deviations, and if they exceed the specifications determined it stops automatically and the quantity produced is discarded.
C. Laboratory testing of the material produced
The quality control of the ready-mix concrete includes measuring of the following parameters:
- Concrete slump
- Compression strength 7 and 28 days
- Visual appearance
From all of the above, the slump test is carried out at the construction site, while the strength of 7 and 28 days on a uniaxial compression is carried out using the company lab’s calibrated crushing press for concrete specimens. The maintenance of the specimens to determine their compressive strength is also carried out in a certified test chamber at 20o C and a humidity level of 95 to 100%. Also performed in the lab on a daily basis are all the necessary tests (granulometric aggregate grading, sand equivalent, sand moisture, etc.) through appropriately calibrated and certified laboratory equipment.
Regardless of the tests carried out using the lab equipment, the company also collects as many as possible quality testing results for the final product performed at external laboratories by the customers of MARMI S.A.
D. Traceability of the material produced
All the data related to the customer’s details, the production conditions, sampling and quality control are recorded in the Registry-Logbook of each one by the Production Manager. It should be noted that the production of ready-mix concrete is daily and autonomous and is accompanied by a logger, a balance record and the Dispatch Note.
Based on the above, it is possible and easy to detect or trace any produced material in case it was found it does not meet the requirements and criteria of the CTR. Evidence of compliance with the acceptance criteria is kept in the relevant records of the department