Portland cement - what is it? Brands, technical characteristics

One of the most common types of binder for concrete mixes is Portland cement. What is it, how it is used, what properties it possesses, consider these and other questions further.

Composition

As with any building material, high demands are placed on the components from which Portland cement is produced. GOST 10178-85 "Portland cement and slag Portland cement" regulates the composition and quality of ingredients for this type of binder:

• Cement clinker with a mass fraction of silicon oxide is not more than 5%.
• Gypsum, corresponding to GOST 4013-82. The presence of phosphorus, boron and fluorine compounds in the amount not contradicting the normative documentation is allowed.
• Mineral additives of a certain property necessary to create mixtures of the desired kind.

All components are co-grinded to a homogeneous state.

For different types of portland cement, various components can be used, which are also subject to certain technical requirements prescribed in the GOST.

At factories where production is conducted, all components undergo the necessary tests for compliance, the proportions of the creation of dry and working mixtures are strictly observed.

Portable cement GOST and its designation contains on the packaging and in the accompanying documentation. If there is none, the product is manufactured according to the specifications, its properties may differ from those generally accepted.

Production

To understand Portland cement - what is it, it is worth considering the process of its production, which consists of several stages:

1. Extraction of limestone greenish or yellow. It lies at a depth of up to 10 meters in layers, so they seize it in an open way at geological development sites.
2. Preparation. First, the raw material is subjected to drying and primary grinding with the use of some additives to obtain a working mixture. To find out what size of the mass fraction of impurities contains an astringent, it is enough to look at the marking: the PC400 D20 has 20% improvers in its volume, and the PC500 D0 does not have them at all. After the initial grinding, the mixture is baked in special powerful furnaces. So it turns out cement clinker - the main component of Portland cement.
3. Finishing. At this stage, the clinker is dried and ground into a working fraction together with limestone stone and special additives for each type of Portland cement. Further, the mixtures are packed in bags of 30, 40, 50 kg and sent to warehouses of construction sites, shops.

Production features

All types of Portland cement (PC) are made from different raw materials, the common component for all is only cement clinker. The other components can have different properties: moisture, strength, mineral composition. Given these factors, it is impossible to process all types of raw materials in one way, so there are several ways to implement the second stage of production:

• A wet method involves grinding the components in water. This is done with chalk and clay iron containing additives. For them, there are norms of humidity: clay - 20%, chalk - 29%. The resulting emulsion has a moisture content of 50% and is sent to the kiln as such. In the process of heat treatment, clinker balls are formed, which are subsequently ground into a finished binder.
• The dry method does not imply the moistening of the raw material: it enters the furnace in a dry form. The cost of cement produced in this way is lower, since energy consumption for drying is not required.
• The combined method combines wet and dry. The slurry (raw mix) is ground in water. Further, with the use of the filter, more moisture is eliminated, the mixture enters the kiln with a moisture content of up to 18%.

Properties

As already mentioned, concrete acquires certain qualities, when one or another portland cement is added to it. The characteristics of each of them are unique in their own way, but there are common parameters for all:

• Absolute density within 3050-3150 kg / m ³ , bulk for different types of PC will be different.
• The fineness of Portland cement grinding should be determined by sieve No. 008 by the permeability of the powder to at least 85%.
• Specific surface area after screening is 2500-3000 cm ² / g.
• Setting time: the beginning - 45 minutes, the end - 12 hours. Determine the Vita scale.

Strength is measured by testing samples with dimensions 4x4x16 cm, made of a cement-sand mortar in a ratio of 1: 3 at a water to cement ratio of 0.4, after 28 days of hardening. The finished prisms are subjected to bending and compression, determining their significance and conformity to the indices of the brand.

Kinds

Depending on the type of additives used, Portland cement may have several varieties:

• Fast hardening;
• Sulfate-resistant;
• hydrophobic;
• Plasticized;
• With moderate exothermia;
• Slag Portland cement;
• Acid-resistant;
• aluminous;
• White and color;
• Pozzolanic.

Each of the species endows concrete stone with certain properties necessary for application in a particular place or area.

Fast-hardening PC contains a large number of calcium compounds and is capable of intensively increasing the hardening strength.

Sulfate-resistant Portland cement contains additives that increase the resistance of concrete to the effects of chemical aggressive substances.

The hydrophobic appearance of the binder contains additives that promote the slow evaporation of water, which makes it suitable for use in arid areas where gradual hardening of the stone is necessary without loss of strength.

Plastified form of binder, introduced into the concrete mix, increases its plasticity and workability.

Portland cement with moderate exothermia during hydration produces relatively small amounts of heat.

Slag Portland cement contains blast-furnace slag, which significantly reduces its cost.

Acid-resistant PC has in the composition pure quartz sand and sodium silicofluoride, resistant to aggressive chemical media;

Alumina Portland cement contains a high concentration of aluminum oxide, which contributes to fast hardening.

Pozzolanic PC is enriched with mineral additives of volcanic and sedimentary origin (up to 40% of the total mass). They increase the waterproofness and do not form efflorescence on the surface of the finished concrete.

White and colored types of binder contain various metal compounds, capable of staining the stone in certain colors.

Classification by strength

Portland cement is divided into brands, based on the index of its activity - the tensile strength at axial compression of half of samples with the age of 28 days. Accordingly, distinguish marks 400, 500, 550, 600.

Any kind of portland cement grade 400 is used to create conventional and standard structures that are not subject to increased loads.

Higher values of brands are much more expensive, they are used for responsible structures and their elements.

Application

Portland cement - what is it? This is an improved type of binder for concrete. Accordingly, depending on the type of filler, the stone has some reinforced characteristics. For example, the fast-hardening Portland cement 500 and 600 is characterized by a high curing speed, because it is added to concrete for the production of critical and massive structures of both underground and land structures. Also, it is often used in those cases where there is a need for a fast set of strength, for example, for pouring the foundation formwork.

The most common is Portland cement 400. It is universal in application: to create monolithic and prefabricated reinforced concrete elements with increased strength requirements, while not significantly inferior to the characteristics of the PC500, but it has a lower cost.

The sulfate-resistant type of binder is used to prepare mixtures that participate in the construction of underwater structures. Such are most susceptible to the destructive effects of aggressive sulfate waters.

Plasticised Portland cement 300-600 significantly improves the plastic properties of the solution, its strength characteristics, allows you to save 5-8% of the binder, compared with conventional cement.

Special types of PCs are rarely used in small construction, since such raw materials have a high cost, and not every philistine knows about this kind of active substance. More often Portland cement is used for concrete mixtures used in especially large and critical facilities.

When to use it is not necessary

Portland cement is an active component that gives concrete special properties. But no kind of it should not be used in highly flowing river beds, in saline water bodies, in water with a high content of minerals. The sulfate-resistant species under these conditions does not cope with its functions, it is designed to work in static moderate waters. For the construction of dams, dams, hydraulic structures, which serve in the environment of water pressure, use special types of cements.

How to choose and buy

At purchase it is necessary to understand, portland cement - what is it? First of all, an astringent for creating a concrete mix. Like ordinary cement, it is sold in packing bags, paper bags of 50 kg, sometimes 30, 40.

When selecting, pay attention to the symbols on the package. Must be indicated type (Portland cement, slag Portland cement, etc.), compliance with GOST or TU, the number of mineral additives. Also you need to pay attention to the date of manufacture: the fresh raw materials, the better its quality.

The cost of special cement can be influenced by both the producer and the reseller. The same manufacturing technology does not imply a big difference in price. Therefore, choose the material of the plant you trust, which one has the best reputation.

How much is portland cement? The price for the most popular P 400 per bag of 50 kg starts from 200 rubles., PC500 (50 kg) - from 230 rubles. It would seem that the difference is small, but a large amount of a mixture, based on the astringent, is required to create the designs. As a result, an error in the choice can cost a considerable penny.