ON THE SELECTION OF MATERIAL FOR THE MANUFACTURE OF PORTLAND CEMENT.

South Canterbury Times, Issue 2584, 2 July 1881, Page 2

ON THE SELECTION OF MATERIAL FOR THE MANUFACTURE OF PORTLAND CEMENT.

SECOND EDITION

By J. Brough Stansell,

The manufacture of Portland cement is possible wherever chalk, mountain limestone, clay, decomposed basalt, shales, or slate are found in sufficient quantity, or can be cheaply procured. Raw materials are most suitable for cement making, when their simple constituents have already become partially united, »nd when, in their original position, they have been exposed to the weather and the action of water.

A coarse or fine-grained crystalline texgreat or less degree of hardness,give raw materials very different properties, so that, although they are sometimes identical in chemical composition, yet possess different values for cement making, and require different treatment and proportions. During the early period of Portland cement making, none but the softest and most plastic clays were used, but through the introduction and development of the modern dry process, shales, slates, and basalts have been used with very considerable success. In making cement from the mountain limestone it must be reduced by special machinery or by decarbonisation or conversion into lime; the latter is the better method for a thorough amalgamation of the raw material, but the choice must depend upon the relative expense of the methods.

The following analyses of the Medway clay—which may be taken as the readiest and best of clays for cement purposes, being constant in its composition—basalt, slate, and shales, will show by comparison their suitability for the manufacture of cement; —

1, Medway Clay ;2, Basalt; 3, Slate ; 4, Shales.

* Pyrites. The. above analysis of Med way clay by Feichtenger differs somewhat from that given in the second paper on this subject. It will serve as an illustration of the variableness of the same material at various times, and shew the necessity for cuution in selecting and dealing with the various materials used in this manufacture. Shale is of varied character, frequently impregnated with iron : pyrates and sulphur, caution is therefore requisite in their use, the sulphur being detrimental to the formation of Portland cement. Shale of fine and even texture is the most suitable for the purposeIn South Canterbury abundance of all the material for making cement exists, only requiring skill and capital to establish a very important industry. In Oaraaru it is believed large quantities of decomposed basalt are being used to reclaim land from the sea, whilst at Malvern Hills almost inexhaustible quantities of shale may be found. In the Valley of Kakahu, mountain limestono containing about 95 per cent, of carbonate of lime exists in abundance, while clay and slate are found in close proximity, and probably shale may be found on the ground of the proposed Kakahu Colliery Company To utilise these materials a number of experiments would require to be made, (

and the fact of Hoffman’s ring kiln being built would point to this site as the most suitable for such experiments to be made, or a small kiln of the ordinary type of Portland cement kiln of say 18 to 24 inches internal diameter, could be erected at a small expense, and would answer for some time until the question of proper proportions could bo ascertained (for these the reader is referred to former articles upon this subject published in this journal.) In making investigations into the various material indicated, the ingredients to be determined are—in limestone the per centage of carbonate of lime and silica, and in clays the per centage of alumina, silica, iron, and alkali.

It is to be hoped these remarks will incite those most interested in this locality to endeavor to utilise the treasures lying within their reach. . In the manufacture of Portland cement from any of the materials indicated, the dry process only would be suitable.

1. 2. 3. 4. Silica . • 68.45 48.0 60.27 57.00 Alumina .. 11.64 16.0 18.48 (24.33* ( 2.86* Oxide of Iron 14.80 16.0 7.13 „ Manganese . . — — 5.17 — Lime 0.75 9.0 0.89 1.88 Potash .. 1.10 — — — Soda 2.90 4.0 — — Magnesia .. — — 3.62 2.10 Water — 5.0 4.45 12-27