Different Methods for producing Blocks of air-cured Cellular Lightweight Concrete (CLC)

Applicable Standards:
DIN 4232, 4219 Lightweight Concrete
DIN 1048 Testing Methods
DIN 4164, 4165, 4166 ACC/CLC 4223, 4226, 18 152
DIN 4102 Fire Rating
DIN 4108, 52.612 Thermal insulation
DIN 4149 Seismic
DIN 18.152 Solid Blocks
DIN 50.017 Water Condensation…
DIN 52.104 Freece-Thaw-Cycle
DIN52.615 Water Vapor Permeab.
DIN 53.420, 50.014 Determ. of Density

For the production of blocks in air-cured cellular concrete Neopor recommends a mini-mum density of 1.000 kg/m³ (oven-dry). This is to safeguard that the blocks produced offer:

• Sufficient strength
• Affordable shrinkage
• Affordable strength
• Affordable water absorption

Utmost care has to be taken on the only solid used in CLC (besides binder), namely the sand. As ruled in general standards for any type of concrete, it has to be free of any con-taminationand in sieve according to our attached sample. Generally it is recommen-ded not to use crushed sand, which tends to crush the foam when agitated (mixed). A special method of even using crushed sand has been patented and is under trial.

To warrant best distribution of the foam in the shortest possible time, the use of gravity mixers is recommended, ensuring, that the mix is more than 60% of the total volum of its total capacity after adding the foam. To ensure optimum strength, it is recommende to first charge the mixer with sand, until the remaining mix/water left from the previous mix has been absorbed, before adding cement. When a homogeneous dry mix had been obtained, the recommended amount of water is been added.

Make sure, that sufficient water had been added, as otherwise the cement in the mix will draw its shortcomings from the water in the foam, causing the latter to collapse partly or totally. There is no fear of taking too much water, as the W/C ratio does not play the role as in conventional concrete, reducing the strength. Too much water in CLC prima-rily prolongs the hydration process but has no negative reaction on the strength to be achieved.

Moulds used have to be waxed/oiled befor pouring CLC to allow easy stripping and smooth surfaces. Care has to be taken in selecting the most suitable wax/oil to allow ad-hesion of later-on painting or plastering. Where “green-strength” of CLC is required to cut larger cakes into desired dimensions, a special tool is available to mechanically de-termine the suitable time of cutting by wires.

A typical mix design per 1 m³ of CLC for blocks in density 1.000 kg/m³ (oven-dry) is as follows:

Sand up to 1mm, maximum 2 mm : 560 kg
Cement (Portland) : 350 kg
Water in mix : 120 ltrs +
Stable Foam : (560 ltrs)
Water in foam ( use potable water for ~) : 5 ltrs

Wet density : 1.075 kg/m³
Oven-dry density : 1.000 kg/m³

Acceleration: Hydration/hardening of CLC can be reduced by either using high early strength cement, warm water (heat, steam) or else chemistry.

Stripping: If not accelerated (see above), the moulds are normally stripped the day after pouring, cleaned, assembled and waxed/oiled, before pouring again.

Treatment: Curing/herdening after stripping is best done by keeping the blocks moist for minimum 7 days after, preferably even longer, storing the stripped blocks under canvas, which is constantly kept moist. It is recommended alternatively, to wrap the stack of blocks into plastic foil immediately after demoulding ((if possible use shrink foil), to keep the moist-ure within as long as possible, keeping hydrating /crystal-lizing/hardening.

Paint/Plaster (Stucco):

When using paint only, we recommend a water repelling quality. Otherwise, different methos are been applied in different countries. Mortars are prepared in a variety of qualities as for instance:

• Combination mortar of cement plus lime plus sand ( 1 : 1 : 6)
• Or else 0,8 parts of cement – 0,2 parts of fly-ash plus 6 parts of sand -
• Or else cement plus sand mortar reinforced with say 0,5 kg/m³ of polypropylene fibres.

Some also use ladder reinforcement every alternate layer of partition wall masonry.

Others consider it best, if the joint line between the structural frame columns and beams is defined after plastering work, as this is the location where cracks, if any, appar later-on. The joint under the beam and the top of the masonry wall should prefearably be sealed with some kind of sealant after the total structural elements are fully loaded with masonry walls from above (the next floor).

Generally care has to be taken, that the mortar used will develop less strength than the blocks to be layed on mortar.

Further details are available to our clients upon request.