Do not buy a pig in a poke, or markings on the bags of cement

Many years ago, not everyone cement, which was on the market, wore the name "Portland". The name was wearing only cements "clean", ie without additives, while others - adequately to the composition: fly ash, slag, pozzolanic and so on.

Currently, beginning a few years, each cement is called "Portland", also referred to letters and Roman numerals, which for the most part buyers are a strange and incomprehensible codes.

1. CEM - the abbreviation of cement.Each cement regardless of what is in it, includes the name that part.

2. I, II, III, IV, V - the Roman numbers in a fairly exact approximately determine the "purity" of the cement, or the contents of other additives, which are in addition to cement clinker. The lower the number, the fewer of them. The so-called "type one" (ie, CEM I) is cement (in theory) without additives. The following codes of different types of cement

• CEM I - portland cement
  
• CEM II - portland cement multicomponent
  
• CEM III - blast furnace cement
  
• CEM IV - pozzolanic cement
  
• CEM V - cement multicomponent
  

3.Another element of the name is (usually because it cements indicated with the number I do not contain) the letter A, B or C. It happens that such a letter means that the amount of clinker in cement is basically vestigial ...

• CEM I - no letters, according to the standards of the amount of minerals in weight should not exceed 5%
  
  
• CEM II/A - the amount of minerals is in the range 6-20%
  
• CEM II/B - the amount of minerals is in the range 21-35%
  
  
• CEM III/A - the amount of minerals is in the range 36-65%
  
• CEM III/B - the amount of minerals is in the range 66-80%
  
• CEM III/C - the amount of minerals is in the range 81-95%
  
  
• CEM IV/A - the amount of minerals is in the range 11-35%
  
• CEM IV/B - the amount of minerals is in the range 36-55%
  
  
• CEM V/A - the amount of minerals is in the range 36-60%
  
• CEM V/B - the amount of minerals is in the range 61-80%
  
  
• Apart from them, they are or may be the so-called secondary components, whose number in the cement does not exceed 5% (see explanation of the composition of the CEM I)
  

4.Subsequent letters characterize the extras that are included in the cement, or replacement of clinker, which should be the most important component of cement. You can meet, among others:

• K - portland cement clinker (that is, from what it should do cement)
  
• D - dust volatile silica (silica portland cement)
  
• S - granulated blast furnace slag (slag portland cement)
  
• P - natural pozzolan (portland cement pozzolanic)
  
• Q - natural pozzolan fired
  
• V - fly ash silica (portland cement fly ash)
  
• W - fly ash limestone
  
• L - limestone powder (cement portland limestone)
  
• LL - limestone powder with a organic carbon content below 0.2%
  
• T - slate burned
  
• M - designation of all the constituents other than clinker, none of which dominates (Portland-composite cement)
  

5.Other letter codes located on the bags usually refer to special or specific properties of the type of cement. Usually the result of the type used in the additives, sometimes directly - with their absence.

• R - cement with high initial strength increase of (early)
  
• L - blast furnace cement with high initial strength increase of (early)
  
• N - cement normal increase of initial strength (early)
  
• MSR - average (medium) resistance to sulphates
  
• HSR - high resistance to sulphates
  
• LH - cement, low heat of hydration
  
• NA - cement with low alkali content
  

High early strength development and initial mean that cement compressive strength (measured in MPa or psi) is growing rapidly in the first few days, or even hours, sometimes reaching almost a half of the maximum value within the first three days of binding. Typically, it involves high heat of hydration - the fact that the setting time of concrete gives a lot of heat (in the colder days can be simply seen as concrete "steams").Covering such a concrete or polystyrene nieoddychajšcym material helps further this process, allowing in many cases for concreting during light frosts. Cement the just warms himself

Cement resistant sulfates are typically used in situations where the concrete, which was used in the manufacture of such cement, must be resistant to the aggressive environment (eg. sewage treatment plants, sea water etc.).

Cements with a low alkali content - for each of the types of cement is another - are used in situations where the concrete mix are added to alkali-sensitive ingredients, or compounds of an alkaline. Part of the cement meets the conditions cements niskoalkalicznych (see white cement), but for various reasons those are the signs do not wear. The standards refer to the following upper limit values for the determination NA:

• CEM I, CEM II, CEM III. CEM IV, CEM V - less than 0,6% alkali
  
• CEM II/B, CEM III/A, CEM III/B, CEM III/C - less than 0,7% alkali
  
• CEM III/A containing less than 49% of blast furnace slag - not more than 0.95% alkali
  
• CEM III/A containing more than 50% of blast furnace slag - no more than 1.1% alkali
  
• CEM III/B and CEM III/C containing blast furnace slag - no more than 2.0% alkali
  

This brief enumeration means really to see, with which cement we have to do and that is something that the manufacturer does not provide (because for him certain things arise from the knowledge of the subject and knowledge through it possessed), it is necessary to simply download technical data the type of cement.

6. Strength class is the last but one of the most important parameters of cement. Currently, we distinguish basically three types of strength classes: 32,5, 42,5 and 52,5. These are the absolute values of the compressive strength in MPa after 28 days. Yes, there are a lot of cements with higher strength (from 62.5 and above, and even well above 100), but they are basically special cements, used relatively rarely. If the cement used by us, despite such. Declared class of strength 52.5 achieved such. 70, or instead of 42.5 - more than 54, it means that in fact use cements class better than would be the result of the determinations. This demonstrates the best of the manufacturer of such cement. The exact value of research are given by the manufacturers and posted on their websites.

7. Additional comments

However, for ordinary construction works normally sufficient cement of inferior quality, but note that their composition affects not only the more or less desirable characteristics to facilitate our work (eg. setting time, price, cramps etc.), but also on the visual effects and external what we do with them. Plaster precious minerals produced (or rather should produce a), whether the manufacturer or on site, on the basis of white or gray cement without the addition of a low alkali content, because then we can really achieve a satisfactory outcome of our work. The same thing applies in the case of renovation plasters, terrazzo, concrete, architectural sculptures, artificial stone, masonry natural stone or brick. Wherever the most important features of the cement is not price or this or cramps, but the fact that the cement used reduces the risk of efflorescence (which are directly related to the alkali content in the cement), the possibility of obtaining a coloring mortar or concrete (cement color). Other equally important features is the reproducibility of batches of cement stability of its physico-chemical composition, and hence also its properties. In all these and many other cases, we must first be able to understand what is in the bag, then to make the right buying decision.

CSome of the additives described previously tends to come up to the surface, while others, despite small fluctuations, even complying with the standards, which are used by the manufacturer, can make the added chemicals, amending even the parameters mortar or concrete will react very unevenly, causing us extra trouble ..

Interestingly, some of the described parameters is not, or need not be mandatory investigated by the manufacturer, which makes that they are not given in the technical data sheet published on the website. Such parameters are eg. strength after 24 hours and the alkali content - they allow you to appreciate and understand of how good (or as weak) the product we have to do.