The main difference between Portland cement and pozzolanic cement is in the composition, because the latter also contains volcanic lapilli.
Portland and pozzolanic cement, two cementitious binders
I cements I am a family of highly hydraulic binders obtained from the cooking at very high temperatures (between approximately 1200 and 1450 °C) of calcari vanity or specially designed artificial mixtures normally consisting of silica, aluminum oxide, iron oxide and calcium oxide.
Among them we find the Portland cement and that pozzolanicothe fundamental difference between the two it concerns the compositionbecause pozzolanic cement is essentially made up of Portland cement, gypsum and natural pozzolana or calcined in variable proportions.
Various samples of cement mortar, by Cementi Rossi
Over the years, with the understanding of the characteristics chemical, physical and mechanical properties of the various types of cement, the improvement of the production processes and above all the loss of profitability of the cave from which rocks were extracted for the production of natural cements, artificial mixtures have become absolutely prevalent.
Mixing of raw materials for cement production, by Cementi Rossi
Their design, called mix designin fact guarantees numerous advantagesbecause many types of cements can be created, each of which is particularly suitable for specific applications: the Portland cement and the pozzolanic cement there are exactly two of these.
What is Portland Cement?
The first binder quite similar to today’s cements was discovered in 1824 by Joseph Aspdin, and renamed by him Portland Cementwhy the hardened mortar it took on an appearance similar to that of the rocks of the English peninsula of the same name.
The first real one modern concrete However, it was produced in 1844 da Isaac Charles Johnson.
Il Portland cement today it is very different from the one from the beginning of the 19th century which bore the same name; productive process It also includes various phases.
A modern cement production plant, by Cementir Holding
First of all we proceed to the mixing of raw materials.
These may consist of natural minerals (including for example ground limestone, clay or shale) extracted from quarries or deposits, or from so-called dry flours made from chemical elements such as calcium, silica, alumina or iron, coming from other production processes.
These flours are inserted in industrial ovens specific, and then heated to approximately 1400 °C to get the clinkerwhich appears in the form of small blackish spheres with a glassy appearance.
Silos for raw materials for cement production, by Cementir Holding
Once out of the kiln, the clinker is cold to safeguard its hydraulic properties, and subsequently stored in special silos.
We then move on to the production of the actual cement, through the mix design and grinding. The clinker is in fact mixed with the other components, which obviously vary according to the type of cement to be produced, and then ground in special mills to obtain a very fine powder and homogeneous, to default grain size.
The cement production process, by Cementir Holding
L’last phase of the process involves the execution of checks and quality testl’packaging (usually in paper bags), and finally storage before shipping.
Uses of Portland Cement
Portland cement can be used for thebrick laying or masonry blocks or for the production of plasterseven if its use is not recommended in the interventions on historical buildings due to its much higher mechanical resistance compared to historical mortars and its excessive content of soluble salts harmful.
Portland cement almost always appears as a impalpable dust with an unmistakable cold colour in shades of grey-bluealthough there are also some versions of it White colorwith a different composition from the basic formulation.
Portland cement mallet. Photo Getty Images
To prepare the cement mortar (which sometimes also has, although to a lesser extent, the same blue-grey colour) it is sufficient to add the sand and water, normally following a proportion of 4 parts of sand and 1 of water for each part of cement.
Likely Portland cement concrete. Photo Getty Images
Portland cement is also one of the fundamental components of the concrete for the structural ones reinforced concrete. It is also used to produce the underlay screeds of common floors, the industrial floors monolithic and a vast series of prefabricated elements such as manholes, covers, pipes and so on.
Classification of cement binders
There are several versions of Portland cement (all available in the catalogues of specialist companies such as Cementir Holding Nv o Red cement), classified by UNI EN 197-1 standard depending on chemical composition and of their clinker content in five different classes.
The first, called CEM Ihas a clinker content greater than 95% and corresponds to real Portland cement.
The second class, CEM IIinstead concerns the Portland cement compositeconsisting of at least 65% clinker and 45% other componentssuch as limestone, blast furnace slag, shale, pozzolana or silica fume.
Given the variability of the composition, these cements are further subdivided into 19 subclasses.
Cement mortar. Getty Images photo
The classes CEM III and CEM IV instead they concern respectively the blast furnace cement (made up of basic granulated blast furnace slag and a percentage of clinker not exceeding 64%) and the pozzolanic cement.
The last class, the CEM Vfinally corresponds to the composite concrete.
What is pozzolanic cement?
Il pozzolanic cement It corresponds to CEM class IV and it has this name because of its high content of pozzolanaa natural material made of ash e volcanic lapilli ground according to predefined granulometry.
There are four main varieties, respectively black, greyish-white, yellow and red-purple in colour.
Pozzolanic cements have a high pozzolana content. Photo Getty Images
Furthermore, although they are widespread in all areas with volcanic phenomena, those considered to be better quality were imported from Santorini in Greece and from the Campanian city of Pozzuoli (hence the name pozzolana).
Pozzolana reacts with thecalcium hydroxide (or slaked lime) contained in Portland cement, reducing its quantity within the mortar or concrete.
Consequently, since calcium hydroxide is particularly vulnerable to the action of aggressive waters rich in sulphates and/or carbon dioxide combined in various compounds such as carbonic acid, pozzolanic cement resists their action very well.
Natural red pozzolana. Photo Getty Images
The result is a binder that is particularly suitable for use in aggressive environments (for example with acid rain or prolonged exposure to salt).
The composition of pozzolanic cement is however quite variable depending on its typology: it is in fact divided into two subclasses based on pozzolana content.
The composition of the subclass IV/A in fact, it provides for a percentage of Portland cement clinker and pozzolana of between 65 and 89% and between 11 and 35% respectively; while in the subclass IV/B Pozzolana varies between 36 and 55% of the total, with a proportionally lower percentage of Portland cement.
Finally, in both subclasses there is also a small percentage of gessonot exceeding 2-4% of the total.
Source: www.lavorincasa.it
