Pozzolanic Cement CP40

CP40 is a hydraulic binder produced from the mixture of a material known as Pozzolana and finely ground Calcium Hydrate. This binder is of low mechanical strength and its setting speed is a little bit slower than Portland Cement. Because of this, it can be considered as a cement for masonry applications. Lime-pozzolana binders had their origin in the constructions made by the Romans. Even today the ruins of great buildings made with this material are still preserved.

What is meant by pozzolanas?

The ASTM code (1992 in the definition 618-78 states the following: “pozzolanas are siliceous or alumino-siliceous materials which have little or no cementing value by themselves, but when finely ground and in the presence of water, they chemically react with calcium hydroxide at room temperature in order to form compounds with cementing properties”.

What are the main types of pozzolanas?

Volcanic rocks, in which the amorphous constituent is glass produced from the sudden cooling of lava. For example, volcanic ashes, pumice, tufa, slags and obsidian. Rocks or soils in which the siliceous constituent contains opal, either by siliceous precipitation from a solution or from the residues of organisms, such as diatom earths or clays naturally calcinated from the action of heat or from a lava flow.

Artificial pozzolanas:
Flying ashes: the ashes produced during the mineral carbon combustion (lignite), mainly in thermal plants that generate electricity.
Activated or artificially burnt clays: for example, residues from burning clay bricks as well as other types of clays subjected to temperatures higher than 800 °C.
Slags: mainly from ferrous alloys in blast furnaces. These slags must be violently cooled so that they an amorphous structure can be formed.
Ashes from agricultural residues: rice shell ash, bagasse ash and sugar cane straw. When conveniently burnt, a mineral residue rich in silica and alumina, whose structure depends on the combustion temperature, is obtained.

How can the properties of the pozzolanas used be improved?

The properties of pozzolanas depend upon the chemical composition and the internal structure. Pozzolanas with a chemical composition in which the presence of the three main oxides (SiO2, AL2O3, Fe2O3) is greater than 70% are preferred. The objective is to have pozzolanas with an amorphous structure. In the case of pozzolanas obtained from agricultural wastes (sugar can and rice ashes), the most viable way to improve their properties is through controlled burning in simple incinerators where the temperature and time of residence of the material are controlled. If the biomass burning temperature falls in the range of 400-760 Celsius the silica occurs in amorphous phases that are likely more reactive. For higher temperatures, crystalline phases of silica, little reactive at room temperature, begin to form.

How is CP40 produced?

CP40 is produced from a mixture of very fine lime hydrate and pozzolana powders with an average proportion of 70% pozzolana and 30% lime. The material obtained demands a fineness similar to that of common Portland Cement (250-300 m2/kg Blaine Test).

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Marcelino Castro
Civil Engineer (MSc)
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