RVH f 2w - By replacing coarse aggregate by porous or cellular aggregate. The concrete produced is
known as cellular concrete which is further classified as follows:
f2
2w 2w
—classified as foam concrete and gas concrete.
f2
22
2f 2w —classified as gas and foam concrete (Portland cement),
gas and foam concrete (lime and sand), gas slag and foam slag concretes (lime and finely
divided blast furnance slag or fly ash).
p
2g
is obtained by mixing cement paste or mortar with stabilized foam. After
hardening, the foam cells form concrete of a cellular structure. The foam is obtained by stirring
a mixture of resin soap and animal glue. The best foaming agents are alumino sulpho napthene
compounds and hydrolysed slaughter blood. This concrete is very suitable for heat insulation
purposes.
r2 22 is cast into blocks measuring 100 × 50 × 50 cm and over, which,
once hardened, can be sawn into slabs of 100 × 50 × 50 to 100 × 50 × 12 cm. Heat insulating foam
concrete has a strength of up to 2.5 N/mm^2 and a coefficient of heat conductivity of 0.10–0.20
k Cal/m.h.°C. This kind of foam concrete is used as heat insulating material for reinforced
concrete floors, partitions, etc.
E E2 22 has a strength of 2.5 – 7.5 N/mm^2 and a
coefficient of heat conductivity of 0.20–0.40kCal/m.h.°C and is used for exterior walls.
22 is used to make reinforced floor components, the items being
reinforced by two wire meshes from wires of 3–5 mm thick. Structural foam concrete has a
strength up to 15 N/mm^2 and a coefficient of heat conductivity of 0.40–0.60 kCal/m.h°C. Heat
insulating foam concrete is widely used in three-layer exterior walls of heated buildings.
q2g
is manufactured by expanding the binding material paste, which may or may
not include aggregates. It is also known as aerated concrete. The mix is expanded by gas
forming substances, but care should be taken to synchronize the end of gas formation with the
beginning of mix setting. The setting time of cement may be regulated with the aid of accelerators
(such as dihydrate gypsum) or retarders (such as industrial sugar, or molasses, introduced in
amounts from 0.1 to 2.5 kg/m^3 ).
The approximate relative proportions of gas concrete ingredients are as follows: 90% Portland
cement, 9.75% powdered lime, 0.25% aluminium power (for a water to cement ratio of 0.55–
0.65). About 2/3 of sand are ground in a wet state. The basic considerations in choosing the
proportion of light weight concrete are economy consistent with placability and adequate
strength, and attainment of specified bulk density with the lowest consumption of cement.
Lime for preparing gas concrete should be of the top grade, quick-slaking and low-magnesium
variety. In sand intended for gas concrete, the content of clay impurities should not exceed
1.5% by weight, since the impurities lower the strength and slow down gas evacuation and
concrete expansion. The gas forming agent used is finely ground aluminium powder. The
evolving hydrogen produced during the chemical reaction between hydrate calcium oxide and
aluminium according to the equation
2Al + 3Ca(OH) 2 + 6 H 2 O = 3 CaO.Al 2 O 3 .6H 2 O + 3H 2expands the cement paste which retains its porous structure as it hardens.