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217
point of view very little advantage would be derived to Fulham; that is, of
course, assuming that Artificial Stone is not more durable than York; but to
assist you in arriving at this point, I wish to lay the following observations
before you.
Artificial Stones are composed chiefly of granite and Portland cement, mixed
together in the form of concrete, and placed into moulds until set. Granite is
a very hard and durable material, and will resist abrasion about three times as
well as the hardest sandstones, and when cemented together with a matrix
of Portland cement it presents a very hard and homogeneous mass.
The quality of the cement is an important point in the manufacture of these
stones, and under certain conditions may be such as to cause very serious
results.
The process of manufacturing cement is as follows: Clay and chalk are mixed
together and ground in a pug mill, burnt to a clinker, and finally ground as
cement.
Cement used immediately after grinding is very dangerous, being hot and
subject to expand considerably. For instance, new cement when spread and
subjected to a process of aeration will increase in bulk at least 5 per cent. If
stones are manufactured with such cement, they will blow and crack; experience
has also proved that cement increases in strength with age, and therefore, stone
manufactured with it will also increase in the same ratio, and again, Dykerhoff
has shown* that slow setting cement had an average expansive power of .0734
per cent., and quick setting .2019 per cent. over a period of twelve months.
From these observations it will be seen that this stone will not only increase
in bulk, but also in strength with age; it would, therefore, be necessary to obtain
the very oldest stones in stock.
I do not adduce the above arguments against this stone, for I contend that
both the aggregate and the matrix of Artificial Stones are far harder and more
durable than those of York Stone. I merely make this observation to show
how necessary it will be to subject these stones to such tests as to satisfy
ourselves as to their quality, and further to point out that if a firm were
very busy, and that stones were sent out immediately after their manufacture,
the results might be serious.
Artificial Stones have now been used by almost every Yestry and District
Board in the Metropolis, and, from testimonials, it would appear that they have
given every satisfaction.
A portion of Victoria Stone was laid in Piccadilly, in 1872, and is said to be
in good condition still, having been laid 19 years.
In 1869, the approach to Blackfriars Bridge was paved with Victoria Stone,
and 6 years later, Mr. Carr, the Engineer, said the surface was perfect, and the
wear decidedly less than the York Stone contiguous. This stone has also been
laid in Holborn, where the traffic is estimated at 88,355 daily, and Aldgate
High Street, where the traffic is estimated at 79,048 daily. Portions of the
stone were taken up after 5 years, and the wear was found to be so slight as to
be scarcely measurable.
Imperial Stone has also been largely used throughout the metropolis, and
appears to have given every satisfaction.
There are many other good stones in the market, of which I append a list,
showing their cost, tensile and compressive strains, &c., as given by the respective
firms.
* Strachan on Footpaths, Congress of Municipal and Sanitary Engineers, Leicester.