Autoclave and non-autoclave aerated concrete 

Aerated concrete is a type of blown-out concrete. Aerated concrete is artificial stone with spherical pores evenly distributed throughout its volume.  Aerated concrete is obtained from a mixture of binding, siliceous component and water with adding of gas-forming and modifying agents.

Portland cement and limestone (gas silicate) are commonly used as binding component. CHP ash, granulated blast furnace slag and silica sand are commonly used as siliceous component. As a rule, aluminum powder works as gas forming agent. Adding of aluminum powder to the mixture causes a chemical change which leads to hydrogen evolution.  In its turn, hydrogen forms pores. Regulators of structure formation and plastic strength development, hardeners and plasticizers are used as modifying agents.   

Aerated concrete types

There are many different types of aerated concrete which are classified according to the following criteria:

1. By functionality:

• structural;
• structural and heat insulating;
• heat insulating.

2. By curing conditions:

• autoclave (synthetic hardening) — hardening in saturated steam media at pressure above atmospheric;  
• non-autoclave (hydration hardening) — hardening  under natural conditions with electrical heating, in saturated steam media at atmospheric pressure. 

3. By type of binding component:

• limestone;
• cement;
• mixed;
• slag;
• ash;

4. By type of siliceous component:

• natural materials: floured silica sand and other kinds of sand; 
•  secondary products of industry: CHP fly ash,  hydro removal ash, afterproducts of different ores, ferroalloys waste and etc. 

Main characteristics of aerated concrete

Types of autoclave and non-autoclave aerated concrete strength are specified by classes according to compression strength, due to ST SEV 1406.

For aerated concrete the following classes are specified : В0,5; В0,75; В1; В1,5; В2; В2,5; В3,5; В5; В7,5; В10; В12,5; В15.

For constructions designed without taking into account requirements of ST SEV 1406 compression strength indexes of aerated concrete are characterized by marks: М7,5; М10; М15; М25; М35; М50; М75; М100; М150; М200.

By average density the following marks of aerated concrete in dry condition are specified: D300; D350; D400; D500; D600; D700; D800; D900; D1000; D1100; D1200.

The physical and mechanical properties of concrete types are given in Table 1.

Table 1 - The physical and mechanical properties of concrete types

  Drying shrinkage of aerated concrete should be not more than 3,0 mm/m for non-autoclave concrete of marks D600—D1200. Heat-conductivity coefficients of aerated concrete should not exceed the values given in the Table 2 in more than 20%.

Table 2- Regulated physical and technical properties of aerated concrete types