Pozzolanic cement is a powdery material with astringent properties, it is based on clinker with various additives. The mass acquires a plastic structure upon contact with water and solidifies upon drying.
Production
Specialized factories produce lime-pozzolanic cement, the production of which requires a full 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, and the use of by-products of energy production is also possible.
Contains many additional substances in a material such as pozzolanic cement. The composition and ratio of ingredients affect performance. To change the pour point during grinding, gypsum is added, while its amount should not be more than 3% of the total mass.
Structure
General grinding, which is the most popular method for manufacturing lime-pozzolanic cement, has a distinctive feature in the form of clinker grinding 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 dryer drum. It is worth noting that an increase in the proportion of additives contributes to a reduction in the cost of the material.
Lime-pozzolanic cement has a hardening process that is sensitive to temperature extremes. At temperatures up to 14 degrees, the mixture has 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 the open space is greatly complicated.
In this case, pozzolanic cement sets much faster at high temperatures and even exceeds the usual Portland cement. To increase the operational characteristics of the manufactured elements, they can be subjected to additional heat treatment at a temperature in the range of 80-90 degrees.
Advantages and disadvantages
Pozzolanic cement, whose properties allow to form during hardening such substances as calcium hydroaluminate and hydrosilicate, which have a lesser effect than those formed in ordinary cement, provides greater resistance to the influence of mineralized and fresh waters. Among the advantages, it is worth noting the following:
- pozzolanic cement is characterized by the formation of fewer cracks;
- high level of adhesion with reinforced concrete reinforcing elements;
- easy handling;
- excellent binding characteristics;
- the pozzolanic mixture forms a greater amount of concrete or mortar at the same flow rate of this 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
Not a single construction object can do without cement, while Russia occupies a leading position in the manufacture of this material. Any of its varieties, by their chemical structure formation, belong to the category of silicates, while in the composition there is an additive in the form of silicon dioxide. The basis of cement is clinker, which consists of lime and clay that have been fired. Cuspidal earth acts as an impurity. Cement dust formed during production and use during 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 that a large amount of quartz dust affects the working composition. This disease is most often found in people related to the processing of granite, the development of tunnels, the manufacture of ceramic and refractory compositions.
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 using grinding and drying plants. Mineral additives are dried in them, grinded and mixed with the bulk, it is also possible to grind all the ingredients at the same time. Due to this, transport 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 made material using fillers. But the use of specialized installations is justified only on large volumes of construction.
Pozzolanic cement: application
The material is most widely used in the creation of reinforced concrete and concrete objects of underground and underwater purposes, which interact with sulfate and fresh waters. It can be used for solutions and structural elements, the environmental conditions of which are characterized by a high level of humidity. Also widespread use in hydraulic structures as part of intramassive concrete.
Use in concrete ground structures is limited due to low frost resistance characteristics, especially when air cured. This is justified by quick drying, which can stop the solidification 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 out and moistening.
Strength
Pozzolanic cement, the composition, properties, the use of which provide the distinctive strength of the finished elements, is 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 is all about the added additives. Acceleration of hardening is noted during the interaction of calcium oxide hydrate and active silica, as a result, the material acquires a 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, which leads to a delay in the onset of final hardening. For the formation of 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 road in the additives.
An increase in water demand is undesirable because it contributes to a greater consumption of cement of this type compared to others. Adding fly ash does not change the amount of fluid needed for mixing. It can be mixed with both concrete mix and cement itself. At the same time, the quality of the material does not decrease, even if part of it is replaced with ash.