8 
COLORADO EXPERIMENT STATION 
per cent, of the water free decomposition product, while they amount to 
only about i.o per cent, each in the original cement. 
That the magnesic sulfate also participates in producing the deteriora¬ 
tion is indicated by its presence in the altered cement to the extent of about 
five times the amount present in the original; i.e. 7.46 per cent, in the water 
free alteration product against 1.75 per cent, in the original. 
The changes effected in this case are quite consonant with the view^s 
quoted excepting the formation of so large a proportion of carbonate, evi¬ 
dently calcic carbonate due to the action of the sodic carbonate in the 
ground water. The presence of sodic carbonate in a solution so rich in lime 
may seem improbable, but this has been shown to be not only possible, but 
a fact. 
This alteration product differs materially from those produced by the 
action of sea water on the works at Aberdeen and analyzed by Prof. Brazier 
(Redgrave and Spackman, Calcareous Cements, p. 285.) according to which 
the chief decomposition products were calcic carbonate with calcic and 
magnesic hydrates, while the amount of the sulphuric acid was scarcely 
altered at all. The analyses indicate a removal of the ferric and aluminic 
oxids from the interior portions of the work, and an increase of them in the 
outer portions. The authors after giving the analyses justly make the 
following statement: “We may observe with respect to these analyses that 
both in the case of the original cement and the deteriorated concrete, there 
are many matters which we are quite unable to reconcile.” 
The action of the ground waters seems to have been one of chemical 
change converting the lime of the cement into a sulfate and carbonate ac¬ 
companied by the removal of silicic acid, alumina and lime and totally des¬ 
troying the cohesiveness of the concrete., 
The samples of deteriorated tiles sent to me do not justify any infer¬ 
ences whatever in regard to the part that may have been played by the ex¬ 
pansive force of newly formed crystallizable compounds. The thickness of 
the tile and the amount of material involved is so small that this factor is 
negligible and the results presented are probably wholly due to chemical 
action. 
This subject is of some importance as concrete structures, bridges, 
culverts,.foundations, etc., are being erected in places where they will be 
subjected to the action of such waters. 
Most of the cretaceous shales are, so far as my observation goes, rich 
in alkalies, calcic sulfate, etc., and concrete foundations laid in these may 
be acted on prejudiciously. 
As the work in this article was about completed, I received Bulletin 69 
of the Montana Experiment Station. The attention of the writers of this 
bulletin, E. Tappan Sannatt, and Edmund Burke, was called to the deterior¬ 
ation of the cement mortar used in the construction of the sewer system of 
Great Falls, Montana, by the City Engineer, C. W^. Swearinger. 
This bulletin gives some excellent illustrations of deteriorated mortar 
and a general description of the conditions as they found them, also some 
suggestions relative to their local conditions and recommendations in re¬ 
gard to foundations and other structures made of concrete, but there is no 
chemical work done on the cement and the products of its alteration. Such 
work is promised for some future time. 
