Although tar-Macadam may be somewhat ambitious for mofussil municipalities, an abstract of the specification for MacCabe’s tar-Macadam, which was kindly supplied to me by the Chief Engineer of the Calcutta Corporation, is of interest, see specification Appendix H, page [75]. The cost of a road so laid is Rs. 2–2–0 per square yard, and although sufficient experience is not available to predict its life, some has been down for 3 years and is still good. The materials consist of two parts Pakoor Stone metal, MacCabe’s patent Bituminous binder of Gas Co.’s Coal-tar, and Stagg brand English coal-pitch, in the proportion of 1 of tar to 3 of pitch by weight, with stone chipping, and sand as a top binder.
Kunkar Metal.
All kunkar metal required for metalling or repair work should be collected, screened, and stacked by the middle of May at latest; screening must be done in the dry weather, otherwise the meshes of the screen soon clog up when the kunkar is damp, and the operation is more or less a farce. A specification for this is given below:—
(1) All kunkar must be washed, cleaned, and screened during the dry weather months; and must be of such quality that, being re-washed and rescreened through an expanded metal screen of ⅜″ mesh, set at an angle of 45°, shall leave a residue of 80 per cent. pure kunkar. If kunkar of a lower standard is stacked it must either be rejected, or the cost of bringing the metal up to specification, deducted from the price paid.
(2) No kunkar should be measured after the 1st June. All kunkar collection must be completed by 15th May.
Brick Metal.
Brick metalled roads are rarely successful owing to the difficulty of ensuring that the metal is of equal hardness throughout, and especially so in a dry climate, as under heavy traffic the metal soon wears into brick dust, which either blows away in the dry season in the form of dust, or is washed away in the rains; on no account should jhama, or vitrified brick, and red brick metal be mixed, as their degree of hardness is so different.
Morhum & Kutcha Roads.
It is of great importance that excessive slope be not given in morhum or kutcha roads, otherwise they will rapidly gutter during heavy rain. A rise of 1 in 50 to the centre of the road will generally be found to be ample.
Stacking Metal.