| abstract |
The invention provides a setable composition consisting of a bonding material (e.g. cement) and an aggregate which aggregate contains a quantity of relatively large electrically conductive particulate material and a quantity of relatively small electrically conductive particulate material. In one form the conductive material is gap-graded. In this form if calcined oil coke and acetylene black is used concretes of resistivities of the order of 25Ω ohm-centimeter may be obtained. In another form, the conductive material includes quantities of conductive material ranging in size between the relatively large and the relatively small conductive material. In this form, where the conductive material is calcined oil coke forming the entire aggregate and the size distribution of the coke is such that the spectrum of size is in accordance with one of the National Standards relating to the spectrum of particle sizes recommended for conventional aggregates in cementitious compositions, concretes having resistivities at least as low as 2Ω centimeter may be obtained, whilst still providing satisfactory mechanical strengths. |