Two types of expiration dates
Each package of material indicates the date of manufacture and the guaranteed duration of storage of cement under normal conditions. However, if the climate in the warehouse is not observed, the properties of cement change even within the period specified by the manufacturer. For this reason, it is better to choose a dry binder personally, making sure that it has not turned into stone or crumpled due to dampness or depressurization of the bag.
In unfavorable conditions, cement can be stored, but not for long, and this is the second type of shelf life - real. You should not count on it, because there is a high risk of receiving a low-quality product with reduced strength.
The guaranteed shelf life of Portland cement in bags according to GOST 10178-85 for quick-hardening binder is 45 days after shipment, for other types - 60 days.
Cement storage rules
The standard set of protective measures consists of sealing the bags and selecting the correct location for their placement. Any mistake leads to hardening of the material inside the package or a decrease in its grade.
It is best to accurately calculate the amount of the required composition and not buy excess, because it is very difficult to create the necessary conditions for preserving the substance at home.
Cement is not left on the street; even during concreting, the bags are placed under a canopy. The storage room must be dry, heated in winter and ventilated. This is explained by the fact that dampness and carbon dioxide accumulate in a closed space; sub-zero temperatures, in turn, accelerate the process of quality loss. Basements are absolutely not suitable; attics or warehouses are more suitable, provided they are heated. It is believed that cement in bags can be stored in winter at a temperature not lower than +5 °C. If there is no ventilation, the room must be ventilated.
There are also rules for the placement location: under no circumstances should cement be laid on bare ground or even on film. It will be possible to save it only by organizing a ventilated pallet; the top of the bags is covered with a tarpaulin or 2-3 layers of polyethylene. But they are not completely sealed; two sides remain open (ideally towards the air flow).
In order for the building material to be suitable for use for as long as possible, the bags must be placed horizontally on special wooden pallets at a distance of at least 30 cm from the floor. To preserve the quality of the product, it is recommended to wrap each bag hermetically in thick polyethylene. The room where the building material will be placed must be dry and frequently ventilated.
It is much more difficult to maintain the activity of Portland cement in big bags than when packaged in ordinary bags, so it is better to use such packaging immediately.
In case of purchasing bulk cement, two options are possible: packaging in bags and proceeding according to the same scheme or filling into a barrel. You will need a large storage container (from 200 liters), wooden or plastic, with special latches. But reviews about this method are contradictory; theoretically, bulk cement cannot be stored for more than two months. Again, installing the barrel will require a special room; exposure to sub-zero temperatures and dampness is difficult to prevent.
Factors affecting shelf life
Air temperature and humidity conditions determine how long the binder will be stored.
- Humidity is the main enemy of dry cement, because the powder reacts with water from the air and premature hardening processes begin. The optimal level is 50-60%. When stored in silos, the humidity level is regulated by automatic settings, which practically do not allow failures.
- The temperature for storing paper bags should not be lower than +5°C. It is not advisable to store cement in unheated hangars in winter; the properties of the material are no longer restored.
Package
The shelf life of cement depends on the type of packaging. GOST 22237-85 “Cements. Packaging, labeling, transportation and storage" allows cement to be packaged and stored in the following types of containers:
- 5 and 6-layer paper bags of domestic and imported production with a capacity of 50, 20 kg;
- plastic bags and cans for small retail packaging.
The main requirement for packaging is to maintain tightness to prevent moisture from entering the binder.
The shelf life of cement in paper bags and polyethylene is different: the polymer creates an absolutely sealed environment, but bags made from it are more fragile, and the integrity of the container is compromised due to packaging and transportation errors. Paper is much more reliable in this regard.
Concreting methods
In the summer season, when in the central and southern regions of Russia the outside air temperature can go beyond 30 degrees, the technology of concrete work has its own characteristics, since the rapid dehydration of concrete in such an environment slows down and even stops the processes of cement hydration. This is not the only problem. intense evaporation of free water from concrete increases its porosity, reduces frost resistance and water resistance. What should summer concreting be like, what are the roles of transportation, hardening, and the use of additives - these and other questions became the topics of the round table, in which Natalya Boroulya, head of the testing laboratory of SUPERPLAST Trading House LLC, Vladimir, took part; Irina Aubakirova, Ph.D. tech. Sciences, Deputy head of testing, St. Petersburg; Elena Goryainova, Head of Quality Control Department of Tsentrmonolitstroy LLC, Penza; Irina Skripnik, head of the central production line of Kuznetsovsky Reinforced Concrete Products Plant LLC, Ramenskoye.
– What is the shelf life of the concrete mixture that is actually required for its transportation and placement? How justified are the requirements for maintaining mobility for 6-10 hours?
Irina Skripnik: The optimal time required for transporting and laying the concrete mixture, based on the experience of the concrete mixture manufacturer, is 2-3 hours. Longer delivery times, as a rule, cause a negative reaction from buyers (in this case, questions may arise regarding the quality of the concrete mixture and chemical additives used in its production). In laboratory conditions, we managed to achieve shelf life of the concrete mixture for 10-13 hours, but, at first glance, such success had a negative impact on the further development of concrete strength. At the age of 3 days, the concrete showed 10% of the required strength; 7 days - 37-40% of the required strength, for 28 days 95-97% of the required strength. It seemed like a good result, but I was concerned about the appearance of the 10x10x10 cube samples, which caused the buyer to refuse to supply BSG. Natalia Borowlya: In real conditions, it is difficult to clearly determine the time frame for maintaining the technological properties of a concrete mixture. There are objects that really require a long time to maintain the mobility of the concrete mixture. In particular, this is due to the presence of specific requirements and some technological nuances during production, for example, for massive structures, hydraulic concrete, densely reinforced structures and structures of complex configuration. In addition, this is due to such factors as the remoteness of the objects under construction from the production sites, low standards of construction work - untimely laying of the concrete mixture, unprepared equipment for continuous concreting, lack of responsibility for the quality of the work performed, and low qualifications of the performers. Taking into account such peculiarities of construction in our country, when designing and producing concrete mixtures, it is necessary to ensure that the time for maintaining their technological properties is 20-30% higher than required. For this purpose, low-heat cements and chemical additives that combine the properties of plasticizers, mobility regulators and hardening retarders are used in the production of concrete. For ordinary civil construction projects, it is usually sufficient to ensure that the mobility of the mixture is maintained at a level of 2-4 hours, taking into account the time of transportation and installation. Irina Aubakirova: The real time for maintaining mobility is determined by the specific construction conditions: the duration of transportation in a metropolis or a small village, the quality of the road, the volume and speed of concreting, the project requirements for the presence or absence of “cold” joints, the continuity of the process, the qualifications of concrete workers, environmental conditions ( heat, rain, wind, frost), quality of materials, etc. I consider the requirement of 6-10 hours to be excessive; it can only be justified when transporting concrete from Vladimir to Moscow or due to a transport collapse on the Ring Road. Elena Goryainova: Our organization Tsentrmonolitstroy LLC produces ready-to-use concrete and mortar mixtures and delivers them to the consumer by concrete trucks. Transportation of freshly prepared mixture, depending on the distance of the construction site from the RBU, can take from 20 minutes to 5 hours. Then the mixture must be placed into the structure. This process, as practice shows, can take another 1-2 hours. This depends on the concreting method and the accessibility of the areas to be concreted. Therefore, we consider each application individually.
Prices for concrete from our production
CONCRETE TECHNOLOGY No. 8, 2013
More details about deadlines
Even under normal storage conditions, cement loses its original properties over time. The average rate of deterioration in its quality is about 15% per 3 months or one position in the brand. That is, the M500 material will turn into M400 in 3 months, which must be taken into account. Experts recommend choosing material that has not yet been stored in the supplier’s warehouse. Only in this case will concrete of the expected grade be obtained.
So, the shelf life of M500 cement in bags is 6 months, but the initial storage strength properties are available only for 3 months. By the end of the warranty period read “M400”.
The situation is similar with the M400 material - it can be kept in sealed packaging for only 6 months, after which it can only be disposed of.
Expert advice on cement storage
When using material that has survived the winter, the inevitable decrease in quality is taken into account. Even if all storage rules are followed, next year the cement will lose its properties. In practice, this means an increase in its total proportion in the solution (up to 1.5 times). That is, when preparing concrete in the spring from M500 Portland cement purchased in winter or autumn, proportions for M400 or lower are used.
It is not recommended to store paper bags of cement with different grades of strength next to each other: in their normal state, they contain different amounts of moisture and negatively affect each other.
The motionless powder hardens, so it is advisable to turn over even securely packed cement in plastic bags every 2-3 months.
You can check the safety of the material by touch. High-quality cement does not contain lumps and flows between your fingers like dry sand. The binder cannot be used to prepare concrete after its expiration date.
If you doubt the quality of Portland cement, it is recommended to make a test batch of concrete and evaluate its strength and hardening time.
How long can an opened package of cement be stored?
In private home construction or during repairs, situations arise when only a little powder is needed from the bag for mixing. What to do with the rest of the cement? It is correct to store it in a tightly (if possible) sealed bag in a cool, dry place. Fold the free edge several times and seal with tape.
But even in such conditions, the previous shelf life is no longer relevant - the remaining binder can only be used within a few days.
It is no longer possible to use such a “stale” component for the manufacture of load-bearing and structural elements. In addition, before removing any leftovers from the package, evaluate their suitability: the powder should be dry and free-flowing without the slightest sign of moisture. This is suitable for preparing plaster, creating bedding layers and solving other auxiliary tasks.
