Mix design and properties of lean concrete for sub-bases

The principal criteria applicable to the mix design and the properties of lean concrete are: - splitting tensile strength in the region of 1.7 MFa and compressive strength in the region of 15 MPa at 28 days; - good erosion resistance; - lowest possible modulus of deformation; - possibility of using substandard aggregates and binders produced wich low energy input. The main results obtained on the basis of these criteria and of investigations carried out in the laboratory, chiefly on siliceous aggregates, are as follows: The conventional cement content of 150 - 160 kg/m3 can be si~nificantly reduced to 110 kg/m3 while nevertheless retaining a sUfficiently high content of fine particles. The use of cements of type CLK 45 (clinker-slag cements) or of mixtures of standard cements with active additives such as ground blastfurnace slag ensures the required mechanical strengths and the non-erodability of the sub-base. The use of substantial amounts of air-entraining agent (so that upwards of 10% of air is entrained in the concrete) appreciably reduces the deformation modulus from 25,000 MPa to below 20,000 MFa, but the mechanical performance characteristics are impaired.