Lime-pozzolanic cement: production and use

Pozzolanic cement is a powder-like material with astringent properties, it is based on clinker with various additives. The mass acquires a plastic structure upon contact with water and freezes when it dries.

Production

Specialized plants produce lime-pozzolanic cement, the production of which requires the presence of a technological full cycle. The difference between these industrial objects is that they have a grinding compartment used for grinding and drying additives. They act in the role of mineral natural substances - gliae, diatomite, it is also possible to use by-products of energy production.

Contains many additional substances in a material such as pozzolanic cement. The composition and the ratio of the ingredients affect the performance characteristics. To change the period of hardening during the grinding process, gypsum is added, and its quantity should not be more than 3% of the total mass.

Structure

The common grinding, which is the most popular technique for making lime-pozzolan cement, has a distinctive feature in the form of grinding clinker together with gypsum and mineral active elements in a multi-chamber special mill. Before this, the ingredients are crushed and brought to the required moisture level in the drying drum. It is worth noting that increasing the proportion of additives contributes to a reduction in the cost of material.

Lime-pozzolanic cement has a hardening process that is sensitive to temperature changes. At temperatures up to 14 degrees, the mixture is characterized by a slower cure. The process practically stops when the ambient temperature is 5 degrees. Because of this, the use of material in the cold season in an open space is made much more difficult.

In this case, pozzolanic cement sets much faster at high temperatures and even exceeds the parameters of the usual Portland cement. To increase the performance characteristics of the manufactured elements, they can be subjected to additional heat treatment at a temperature within the range of 80-90 degrees.

Advantages and disadvantages

Pozzolanic cement, whose properties make it possible to form, when solidified, substances such as calcium hydroaluminate and hydrosilicate, which have a smaller effect than those that are formed in ordinary cement, provides greater resistance to the influence of mineralized and fresh waters. Among the advantages is the following:

• Pozzolanic cement is characterized by the formation of fewer cracks;
• High level of adhesion with reinforced concrete reinforcing elements;
• Easy processing;
• Excellent binding characteristics;
• The pozzolanic mixture forms a larger quantity of concrete or mortar at the same consumption of the material and mixtures of other types.

But there were some shortcomings:

• The need to use more water for mixing;
• Prolonged storage reduces the activity of the substances contained.

What you need to know

Without cement, not a single building object, while Russia occupies a leading position in the manufacture of this material. Any of its varieties in their chemical structure formation belong to the category of silicates, while in the composition there is an additive in the form of silica. The clinker is used as the basis of cement, which consists of lime and clay that have been fired. Infusional ground acts as an impurity. The cement dust produced during production and use with prolonged exposure causes the development of bronchitis and, in rare cases, pneumoconiosis, provided that the level of silica that contains pozzolanic cement is exceeded.

Silicosis is a severe form of pneumoconiosis and has become most widespread during the active development of machine building and mining industry due to the fact that a large amount of quartz dust affects the working composition. This disease most often occurs in people related to the processing of granite, the development of tunnels, the manufacture of ceramic and refractory compounds.

Other production methods

Pozzolanic cement, whose properties also depend on the technological process, can be produced not only in factories, but also on the construction sites themselves with the help of grinding-drying plants. They dry mineral additives, grind and mix with the main mass, it is also possible to crush all the ingredients at the same time. Due to this the transport load is reduced, only the clinker is transported, and the mineral elements themselves are mined in the construction region. Among the advantages of this technique, it is worth noting the possibility of changing the composition of freshly prepared material with fillers. But the use of specialized installations is justified only at large volumes of construction.

Pozzolan cement: application

The most widespread material was acquired in the creation of reinforced concrete and concrete objects of underground and underwater use, which interact with sulphate and fresh waters. It is possible to use for solutions and structural elements, the surrounding conditions of which are characterized by a high level of humidity. It is also common to use in hydraulic engineering structures as part of intramassive concrete.

The use in concrete ground structures is limited due to low frost resistance characteristics, especially if air congealed. This is justified by rapid drying, which can stop the hardening process and lead to substantial shrinkage. It is also undesirable to create structural elements from pozzolanic cement if they are used in the conditions of periodic thawing and freezing, drying and moistening.

Strength

Pozzolanic cement, composition, properties, the use of which ensure the distinctive strength of the finished elements, is long-lived, this is due to the amount of calcium hydrosilicate formed. The material is characterized by a prolonged increase in strength due to a reduction in the total mass of pure cement, it is all about the added additional ingredients. Acceleration of hardening is noted when the calcium hydroxide hydrate and active silica react, resulting in the material acquiring a strength similar to other cement slurries. Therefore, a longer stay in a humid environment is required.

Water requirement

Pozzolanic cement, which is based on diatomite and trefoil, is characterized by increased water demand, which leads to a delay in the time for the onset of final hardening. To form a cement test, the required amount of liquid also increases, depending on the mineral active elements used. Its decrease is noted in the presence of additives in the tuff and route.

The increase in water demand is undesirable because it contributes to a higher consumption of cement of this type in comparison with others. The addition of fly ash does not change the amount of liquid required for mixing. It can be mixed with both the concrete mix and with the cement itself. In this case, the quality of the material does not decrease, even if the ash is replaced by its part.