Investigation of concrete in absorbing formwork

1.	Absorbing formwork has a substantial effect on concrete quality for concretes with W/C0.365.
2.	The concrete surface quality depends on the quality of the absorbing formwork materials used.
3.	The possible amount of water removed from the concrete by means of the absorbing (vacuum) formwork was 2.4–3.57 kg/m2.
4.	Before the start of hardening of the concrete, its water content decreases by 20–30% at a depth to 15 cm from the absorbing formwork. During hardening of concrete, its water content equalizes over the entire length of the specimen (thickness of the block), and under these conditions the W/C ratio of the concrete near the formwork is not more than 1% below the initial.
5.	According to the results of testing the concrete for cavitation resistance, the best indices were noted for formwork containing ensonite. In this case, the cavitation resistance of the concrete was increased up to 1.4 times. The latter circumstance permits recommending for use as formwork absorbing material fine-porous paperboard of the ensonite type (with pore sizes 20–100 Å), which freely passes water molecules but retains cement particles.

Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 11, pp. 39–41, November, 1989.