The material is mixed in the following proportions: One measure of Portland Cement and three measures of Mountsorrel Granite, together with sufficient washed sand added to fill up all interstices. _
The Cement is of our own manufacture and guaranteed to withstand a tensile strain of from 600-lb. to 700-lb. on a 1-in. section at seven days, and conforms in every respect to the British Standard Specification.
The Granite is crushed, washed, and passed through a t-in. mesh.
The Tubes are made in vertical steel moulds and the concrete filled-in in thin layers, each layer being thoroughly rammed and consolidated with a heavy machine-driven rammer. The Tubes are left in the moulds for three days, after which they are placed in the open air for six months. The tubes are not at any time during the course of manufacture subjected to heat or other artificial means of maturing.
The Tubes are made both with and without steel ribs; stock is kept of each description. The Steel-Ribbed Tubes are reinforced with i-in. welded steel rings placed in the centre of material, 12·in. apart.
THE MINISTRY OF HEALTH WILL SANCTION LOANS TO LOCAL COUNCILS FOR THE FULL TERM OF THIRTY YEARS FOR WORK IN WHICH OUR GRANITE CONCRETE SEWER TUBES ARE TO BE USED.