As you know, according to the decree of the Government of the Republic of Kazakhstan dated 20.04.2005 No. 367, the list of products subject to mandatory certification was approved. Only for those products prescribed in this resolution, the contractor must provide certificates of conformity. Certificates of conformity for products are issued by an accredited organization on the basis of test reports of samples provided by the supplier. The validity period of the certificate is mainly in the range of 1-3 years. However, the presence of certificates does not mean that high-quality material was delivered to the facility. That is, participation in the input control of materials by technical supervision should not end only with checking the availability of certificates.
According to the legislation of the Republic of Kazakhstan, regulatory and technical documents (GOST) have been developed for each building material, where the item "Acceptance Rules" is provided. In this paragraph, it is prescribed that the manufacturer must accompany each batch of products with a document on the quality of the established sample, indicating the appropriate controlled indicators. It is also indicated that the consumer (customer) has the right, and in some cases is obliged to take a sample during a control check with the receipt of a test report.
Let's analyze one building material, for example cement. How will you check the quality of cement when it is received at the construction site?
It is important to check the quality of cement when it is received at the construction site to ensure that there are no failures and stops in the project due to poor-quality cement.
Cement is transported in bags and bunkers.
When the cement arrives at the site, check the following to make sure that the cement is of good quality or not:
1.Check the marking on the cement bag (this indicates that the brand is standard and complies with the product quality assurance instructions, and in such cases a third-party test report is not required. But you can perform a lab test if the client requires or you want to test).
2.Check the cement production information printed on the side of the bag, indicating the week, month and year of manufacture.
3.After checking the manufacturing details, check how old the cement is. It is recommended to use cement within 3 months from the date of manufacture. Because no one knows the conditions in which cement is stored by the supplier/trader. Insist that your company buys cement directly from the manufacturer, this ensures that you get fresh cement and no changes or damage to the cement due to the storage location of the supplier/merchant.
4.Do not accept cement that is more than a month old (make sure you specify this item in the purchase order to avoid disputes in the future).
5.Check the weight of cement bags randomly (Sample testing). When unloading cement at the unloading point at the railway station, the movers begin to shift these bags with an iron hook. No quality specialist or technical supervisor will object to such damage to the packaging by these unskilled workers. Of course, no manufacturer is able to replace these local workers at every station.
But manufacturers can change the design and replace bags with bags, for example, instead of trying to replace labor, which is impossible. As technical supervision engineers, we should contact cement manufacturers to do something to ensure the safety of handling cement.
Getting back to the point, due to improper handling of bags of cement and puncturing them in several places, there is a possibility that the cement in the bags will not weigh exactly or more than 50 kg. Therefore, it is important to make sure that the weight of the bag exceeds or equals 50 kg in order to avoid concrete destruction, since someone can use a bag weighing less than 50 kg as a full bag and make concrete that greatly changes the proportion of composition and chemistry of the resulting concrete.
6.Check the temperature of the cement in the bag. Sometimes you can get hot cement in a bag, this does not mean that the hydration process is started in it. When the cement is loaded directly after manufacture, it can be hot up to 50 degrees, in such cases, store the cement for 2-3 days before use to allow it to cool down. This happens when the order exceeds the supply of cement. If we use hot cement, false setting may occur in the concrete obtained with its help. This means that the concrete will become rigid after mixing, in order to restore plasticity, it is necessary to re-mix or increase the mixing time of such concrete.
7.Checking physical properties:
The color of the cement. It depends mainly on the color of the lime stone, which is used to produce the same and other additives that increase productivity. A dirty-white cement does not mean that it is bad or contains more fly ash or any other additives (for example, AAC cement - it has a whitish calcareous stone, so the color is slightly weaker than the gray shade). The color of the cement as a whole from a shade of gray may be dark or may be pale. You should know why it is dim or dark (ask your company to arrange a visit to the manufacturer to better understand the manufacturing process. such visits are organized by the manufacturer free of charge at the request of customers).
Smoothness. When you take a little cement in your fingers and rub it, it will seem silky smooth because of the fineness of the cement. If the grinding is not done properly, you will feel roughness in it. If roughness is observed, check the fineness of the cement.
Lumps in bags. Lumps form in bags because of the dead weight on them, called a soft lump, which breaks when we roll up the bag. Solid lumps - formed due to hydration of cement due to contact with moisture or direct contact with water during transportation, for example, due to rainwater entering the bag. In this case, cement should not be taken.
Pollution. Take a handful of cement and throw it into the water, it should float for a while and then sink into the water. If it is directly immersed in water, it shows that the cement has been modified after being shipped from the factory and can lead to destruction (in such cases, the cubes should be cast and tested for strength within 1 day, if it does not withstand, the cement should be rejected).
Consistency. This shows in general the need for cement in water, the more it is required, the higher the water consumption for cement, and vice versa. In general, the standard consistency ranges from 27 to 34%. Old cement may have less need for water due to partial hydration of cement. In addition, less fine cement typically requires less water (coarser material has a smaller surface area than finer material).
Compressive strength. A good technical supervision engineer always checks the compressive strength of cement for each batch of cement received, this ensures that there are no failures in real work. Since laboratory conditions are not standard for most facilities, the engineer can compare his results with previous results of the same cement under the same conditions.
Cement obtained in tanks. Bulk cement sent in bunkers does not have production data printed on it. You need to confirm this by reading the information provided in the quality document. Before opening the seals on all holes, make sure that the numbers written on the seal and the quality document match.
After checking, follow the same process that we use to check the bag cement.
Saving a sample from each batch
The resulting cement sample should be stored in an airtight bag or container with all the details about this batch. this will help in resolving a dispute in the future that may arise due to the failure of concrete on the project, and will also help you blacklist the manufacturer if he does not recognize the refusal.
The saved sample will give you the exact result of the actual cement production.
Concrete destruction can occur for many reasons, such as:
Cement storage conditions on the construction site.
Concrete batching conditions.
Errors can occur at the factory.
Sampling errors, etc.
If you have any questions about this or a request for technical supervision, please contact us.