Pozzolanic cement is a powdered material with astringent properties, it is based on clinker with various additives. The mass acquires a plastic structure upon contact with water and hardens upon drying.
Production
Lime-pozzolanic cement is produced at specialized plants, the production of which requires a complete technological cycle. The difference between such industrial facilities is that they have a grinding compartment used for grinding and drying additives. Mineral natural substances act as them - glizh, diatomite, it is also possible to use by-products of energy production.
There are many additional substances in a material such as pozzolanic cement. The composition and ratio of ingredients affect performance. To change the solidification period during grinding, gypsum is added, while its amount should not be more than 3% of the totalmasses.
Structure
Total grinding, which is the most popular technique for the manufacture of lime-pozzolanic cement, has a distinctive feature in the form of grinding clinker together with gypsum and mineral active elements in a special multi-chamber mill. Before this, the ingredients are crushed and brought to the required moisture level in the dryer drum. It should be noted that an increase in the share ratio of additives helps to reduce the cost of the 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 solidification. The process practically stops if the ambient temperature is 5 degrees. Because of this, the use of the material in the cold season in open space becomes much more difficult.
At the same time, pozzolanic cement sets much faster at high temperatures and even exceeds the usual Portland cement. To increase the performance of manufactured elements, they can be subjected to additional heat treatment at a temperature in the range of 80-90 degrees.
Pros and cons
Pozzolanic cement, whose properties allow the formation of substances such as calcium hydroaluminate and hydrosilicate during solidification, which are less active than those formed in ordinary cement, provides greater resistance to the influence of mineralized and fresh water. Amongmerits worth noting the following:
- pozzolanic cement has fewer cracks;
- high level of adhesion with reinforced concrete reinforcing elements;
- easy handling;
- excellent binding characteristics;
- pozzolanic mixture forms more concrete or mortar at the same consumption of this material and mixtures of other types.
But not without flaws:
- the need to use more water for mixing;
- prolonged storage reduces the activity of the substances contained.
What you need to know
Not a single building project can do without cement, 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 the composition contains an additive in the form of silicon dioxide. The basis of cement is clinker, which consists of lime and clay that have been fired. Infusor earth acts as an impurity. Formed during production and use, cement dust, with prolonged exposure, causes the development of bronchitis and, in rare cases, pneumoconiosis, provided that the level of silicon dioxide that pozzolanic cement contains is exceeded.
Silicosis is a severe form of pneumoconiosis and has become most widespread during the active development of engineering and mining due to the fact thatthat the working composition is affected by a large amount of quartz dust. This disease is most common in people involved in 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 at factories, but also at the construction sites themselves using grinding and drying plants. Mineral additives are dried in them, ground and mixed with the main mass, it is also possible to simultaneously grind all the ingredients. Due to this, traffic congestion is reduced, only 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 using fillers. But the use of specialized installations is justified only for large volumes of construction.
Pozzolanic cement: application
The material has become most widespread in the creation of reinforced concrete and concrete objects for underground and underwater purposes, which interact with sulfate and fresh waters. It can be used for mortars and structural elements, the ambient conditions of which are characterized by a high level of humidity. It is also widely used in hydraulic structures as part of intramassive concrete.
Use in concrete ground structures is limited due to low frost resistance characteristics, especially under the condition of air curing. This is justified by rapid drying, which can stop the curing process and lead to significant shrinkage. It is also undesirable to create structural elements from pozzolanic cement if they are operated under conditions of periodic thawing and freezing, drying and moistening.
Strength
Pozzolanic cement, composition, properties, the use of which provides the distinctive strength of the finished elements, durable, this is due to the amount of calcium hydrosilicate formed. The material is characterized by a long-term increase in strength due to a decrease in the total mass of pure cement, it's all about the added additional ingredients. Hardening acceleration is noted when calcium oxide hydrate and active silica interact, as a result, the material acquires strength similar to other cement mortars. Therefore, a longer stay in a humid environment is required.
Water demand
Pozzolanic cement, which is based on diatomites and tripoli, is characterized by increased water demand, leading to a slowdown in the onset of final hardening. To form a cement paste, the required amount of liquid also increases depending on the mineral active elements used. Its decrease is noted in the presence of tuff and trass in the composition.
Increasewater demand is undesirable because it contributes to a greater consumption of cement of this type compared to others. The addition of fly ash does not change the amount of mixing fluid needed. It can be mixed both with the concrete mixture and with the cement itself. At the same time, the quality of the material does not decrease, even if part of it is replaced with ash.
