Although this article refers to a specific location, it is provided as a general example of the early history of the often-difficult adaptation of Blue Lias lime plants to the production of Portland cement.
This is taken from Reid's book, pp 168-172. Henry Reid was taken on as a consultant by G H Walker, the owner of the Rugby Blue Lias Lime and Cement Co. Ltd, during the period 1869-71. His initial visit to the Rugby plant resulted in a damning report, the flavour of which can be seen in the following text. This was accepted, and he was taken on, on a part-time basis, as manager with the brief of "turning the plant around" and establishing genuine Portland cement production. This he certainly achieved, but his contract was terminated early, following disagreements among the owners. It seems likely that Reid's main transgression was in "buying off" (at considerable expense) complaints about the company's earlier products in his attempts to get customers to try the new product. The ensuing litigation put Reid very much on the defensive, and his writings in his 1877 book have to be seen in this context. He paints a no doubt unfairly bad picture of the early plant, but it is fair to assume that many of the practices described were not unknown in all those areas where Portland cement was being introduced (with little technical understanding) alongside "traditional" hydraulic lime products.
OWING to the imperfect and careless manner formerly adopted in the blue lias districts, very unsatisfactory products were placed in the market, having a most damaging effect on the reputation of such cements. Before and during the year 1868, the author in common with most engineers looked upon “Portland cement” from Warwickshire and Somersetshire (the more important seats of such manufacture) with much suspicion, and generally characterized it as worthless and false. Its sale was limited and confined to small consumers, to whom its best recommendation was cheapness, and within so circumscribed a limit of intelligence the damage sustained was not of a very serious character. In the early part of the year 1869 the author was consulted as to the best method of extricating the Rugby cement works from a dead-lock caused by misunderstanding in the management. On visiting these works he found that raw materials of a valuable character were in abundance, but a total absence of the necessary technical skill for their proper and profitable conversion. There was no Portland cement made there at that time, and the following prescribed formula will show that its production under such conditions was impossible.
For the manufacture of best Portland the prescription was:
| Material | In Winter | In Summer |
|---|---|---|
| Stone | 5 | 1 |
| Clay | 4 | 1 |
These proportions were roughly mingled by the workman as they came from the quarry.
There was also produced what was termed light Portland cement by the following mixtures:
| Material | In Summer | In Winter |
|---|---|---|
| Burnt Shale | 6 | 6 |
| Best Portland | 2 | 2 |
| Light Brick | 2 | 3 |
| Foundry Coke | 3 | 3 |
And for heavy natural cement:
| Material | Amount |
|---|---|
| Heavy Natural Stone | 9 |
| Burnt Shale | 3 |
| Best Portland | 2 |
| Light Brick | 2 |
Lias cement again was made of:
| Material | Amount |
|---|---|
| Burnt Shale | 3 |
| Best Portland | 1 |
| Light Brick | 1 |
while “Roman cement” was produced from:
| Material | Amount |
|---|---|
| Burnt Shale | 3 |
| Colouring Stone | 1 |
| Light Brick | 1 |
The manipulation of these several materials to realize the various results was performed in the most careless manner, and under no special measures of capacity except the ordinary and irregular sized wagons of about one cubic yard in volume used for general purposes at the works.
We will explain a little more fully the nature of these several materials.
“Stone”. Containing about 80 per cent carbonate of lime.
“Clay”. Disintegrated shale, generally containing about 20 per cent carbonate of lime, about 60 per cent silica, and 10 per cent alumina.
“Shale”. One of the beds of indurated shale, containing about the same proportions as the clay.
“Best Portland”. Clinker taken from the kiln when the best Portland cement was burnt.
“Light brick”. The yellow or slightly burnt bricks from the same source as the last mentioned.
“Foundry coke”. The best coke, as commonly used in the cupola of an iron foundry.
“Heavy natural stone”. A bed of stone approaching in chemical value to the proportions required to make a Portland cement.
“Burnt shale”. Shale specially burned for the purpose of these mixtures.
“Colouring stone”. An imported material, obtained from the deposits of argillaceous ironstone in the neighbouring Northamptonshire oolitic deposits.
Such a jumble of mixtures and proportions clearly indicated that the management had no reliable knowledge of the true constituents of a good and honest Portland cement. The author had some difficulty, even after he was invested by the partners of the works with full authority, in upsetting this ignorant and damaging process of manufacture, and directed his attention to the more simple process of making a good Portland cement. The materials were carefully examined and analyzed as well as the circumstances of the works permitted, for it should be mentioned that these were originally used for making bricks from the clays and shales. It was not long before a good heavy cement was produced by the following process:
The raw materials (stone and best shales) were accurately mixed in their rough condition, passed through toothed rollers, and thence to the horizontal millstones, from the spouts of which the finely ground powder was elevated to the dust-room. The next part of the process was that of passing the dust by double worms or creepers descending a shoot, where it received the necessary amount of water to render it sufficiently plastic for the pug-mill brick-making machine, through the dies of which it rolled on to trays which were passed into flues constructed on “Beart's patent principle”. After being sufficiently desiccated, the bricks were pushed through these ovens and burnt in the old brick-kiln without cover of any kind. The kilns were oblong in form, and about 10 or 12 feet high. The bricks were built in layers, having placed between each course (as is done in other kilns) the necessary quantity of fuel in the shape of gas coke. The bricks were well clinkered, and, much to the author's satisfaction, produced really a good heavy cement. The kilns had underneath the common “dead horses” or arches, which were used to light it up. These kilns were unusually extravagant in the cost of fuel, but owing to the difficulty attending the building of new and appropriate ones, their service was continued, and, considering the circumstances, with much success.
As may well be supposed, works producing (under the old system) such a medley of cements, created amongst the customers who were confiding enough to purchase its products much eventual dissatisfaction and distrust. Under such circumstances the author pressed on the market of Lancashire a good Portland cement, the acceptance of which was difficult, but owing to confidence in the writer as an acknowledged authority on Portland cement, and to his selling conditionally that if not good no charge was to be made, he eventually succeeded. It was necessary also to sell, for some time at least, this good cement at the same price as was formerly charged for the previously prepared rubbish.
In addition to the difficulties of such damaging reputation, the author had to contend with a large list of old claims for damages, which were ultimately met.
The quality proved to be as good as represented, and the reputation of cement made from blue lias materials was established. The cement continues to maintain its reputation, and can hold its own against the best-known London cement, unless where ignorance and prejudice stand in the way.
These remarks are perhaps of greater length than the subject may appear to warrant, but the author is desirous that a cement-making source of so valuable a character especially in Warwickshire should not suffer from the misrepresentation of its interested opponents. The products of the Warwickshire cement works find their natural outlet in a northern direction, for the cost of carriage to London operates against them entering into any large successful competition with the Thames and Medway cements. In the northern counties, however, a large and increasing trade is done, and with a daily improving reputation, proving that in one inland district at least a good Portland cement can be made, equal in every respect to the best and oldest established London cements.