A Process for the Production of Portland Cement from Blast Furnace Slag and Lime and the like.
Year: 1899

page_text: Date of Application, 5th Aug., 1899-Accepted, 9th Dec., 1899
COMPLETE SPECIFICATION.
A Process for the Production of Portland Cement from Blast Furnace
Slag and Lime and the like.
I, CARL VON FORELL, of No. 3, Liebigstrasse, Giessen, in the German Empire,
Manager of a Factory, do hereby declare the nature of this invention and in what
manner the same is to be performed to be particularly described and ascertained
in and by the following statement:―
In the manufacture of Portland cement from blast furnace slag it has hitherto
been usual to dry the powdered or granulated slag and limestone under natural
conditions, to grind and then to work them up together with hydraulic fluxes,
such as hydrate of lime, clayey substances, bauxite clay and the like, into bricks,
to burn same to a hard cinder, and finally to grind it whereupon the cement is
ready for the market. By my invention however, the heavy grinding processes
and the making of bricks are dispensed with, both of which processes necessitate
the expenditure of much time and money, and a perfectly intimate and uniform
admixture of the materials (the lime and the slag) is obtained in a pulverised
form in the kiln or oven that both materials are burnt together at a high tem-
perature before the grinding.
By this preceding burning process, granulated slag (which by reason of the
internal cementition is very tough and difficult to grind) is brought into molecular
disintegration, or crumbles on the extraction of the chemically inherent water
in the same way as does slag when heaped up in the open, which slag through
the influence of air and moisture and in consequence of its hydraulic properties
has become conglomerated into large blocks, whilst the slag which has crumbled
to dust in the air (the so-called slag sand or slag powder) is, chemically,
entirely decomposed inasmuch as the free lime contained therein is changed into
caustic lime or hydrate of lime.
The silicic acid in the slag is moreover set at liberty from the slag by the
burning process so that during the subsequent process of calcination it combines
more readily with the lime.
The lime itself and especially hard limestone undergoes a loosening of its
texture during the giving off of carbonic acid gas, that is to say, there is a
structural alteration which diminishes its molecular density and materially facili-
tates its reduction. In the case of chalkmarl or fresh water limestone the
chemically contained water is driven off by the calcination and organic substances
are burnt so that a loosening of the texture or increased sponginess is also pro-
moted hereby, the grinding is facilitated and a more intimate and denser mixture
is obtained.
The proportions of the mixture of slag and lime depend upon the nature of
the slag. The finished burnt product must be of such a nature that the proportion
of united silicates to that of lime is nearly as 1:2 that is to say to 1 part of the
silicates there should be 2 parts of lime.
With regard to the different steps in the process, the raw materials, slag and
lime are first rendered friable by heat at high temperature, then ground and then.
in the form of powder burnt together to ashes The clinkers thus formed are
ground and powdered Portland cement is thus obtained.

page_text: The essential feature of the foregoing process accordingly consists herein that
the raw materials, in their natural condition, upon being heated to a clear red
heat, undergo a loosening of their texture which essentially facilitates their reduc-
tion, and permits a quicker calcination to the form of powder during the sub-
sequent burning process, whereby an economy in time and money is effected and
the possibility attained of making into cement materials hitherto useless, such
as heaps of blast furnace slag and the like.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is:-
1. A process for the manufacture of Portland cement from slag and lime
consisting in subjecting. the. raw materials namely slag and lime such as lime-
stone chalk, marl, freshwater limestone or the like, in their natural condition
to a high temperature, by which the structure of the slag is altered or its texture
is rendered more open the silicic acid is set at liberty therefrom and is free to
.combine with the lime and the structure of the lime is also altered by losing the
carbonic acid contained therein.
i
2. The process for the manufacture of Portland cement substantially as
described.
JENSEN & SON,
77, Chancery Lane, London, W.C.,
Patent Agents.