If you burn the pieces of limestone on high heat, the stone sequentially release water and carbon dioxide forming carbon dioxide acid, as the temperature rise. At about 900°C, limestone represents anhydrous product of calcium oxide – white pieces of quicklime. This is the first conversion of limestone.
You should be very careful with these white stones as quicklime can eat away your hands, clothes and shoes. It ‘eats’ everything like sulfuric acid. If a pile of lime stones is watered it will hiss and boil, and bulges will rise above it. White pieces of lime quickly turn into a fine powder. A minute later the boiling stops. Thus lime is transformed in the so-called ‘hydrated lime’.
Dry hydrate is a dry powder to the touch. Poured on quicklime water got bound with it and the second transformation of limestone took place.
When you mix lime powder with water it won’t boil, but it will turn into dough with the technical name of the calcium hydroxide. The more water added to it, the more liquid it becomes. If the dough is tightly closed on top with soil, it will not harden for decades and still becomes very ductile. If the dough is left in the air, it will soon be covered with a hard crust and gradually turn into stone. Batter is the third conversion of limestone. It is almost ready to glue. The word ‘almost’ means that such dough can not be good to glue the bricks or stones as pure lime putty quickly dries and cracks. To avoid this, you need to have the dough mixed with sand. This mixture is called mortar and mortar transition into the solid stone – the fourth and fifth steps of limestone conversion. This is the most important and difficult stage of lime hardening.
A transition of mortar or concrete in a stone-limestone or calcium carbonate is known as hardening of the carbonate of lime binders. At ordinary temperatures it is made up of two simultaneous processes: evaporation of water from the lime paste (fourth conversion), with the gradual formation of a crystalline skeleton of calcium hydroxide (fifth conversion).
The process of crystallisation of calcium hydroxide is very slow. Evaporation of water causes gradual crystallisation and coalescence of its smallest particles into larger ones and. Growing crystals are fused together, forming limestone skeleton that surrounds the particles of sand. These two processes take place almost simultaneously and tested intensively for the presence of moisture and carbon dioxide.
The film of calcium carbonate formed during the initial period of hardening of the solution on its surface, impedes ingress of carbon dioxide into the inner layers of calcium hydroxide. As a result of the carbonisation process it is almost suspended and the hardening of the stone is mainly due to crystallisation, where necessary reduced humidity and positive temperature.
As a result of the formation of crystalline aggregates the strength of mortar air lime is very weak, and only after 28 days the hardening of 0.5 MPa is formed. Of course, the technical conditions no longer fit the concept of modern construction – these processes are speeded up and the companies like Telling, a largest UK construction agency widely applying hydraulic lime and lime mortar solutions, take advantage of artificial speeding methods. Back to the process, the resulting compound is not stable to water and frost. However, as a result of the ongoing process of carbonation, the strength of the mortar and concrete is increased by 5-7 times or more, but the process is very slow – for tens and hundreds of years.