The Washington herald., 1912-03-20

country districts of Italy.
shown merely to indicate the durability
OF constructions of this character, and
will not be specifically referred TO. 1t
must be remembered. however. that much
Of the destruction noted has been the
willful work OF man. and not all due TO
the action Of time and the elements We
win be indeed fortunate IL our concrete
construction Of to-day will appear as well
to the students OF cementitious materials
two thousand years hence.
With the growth OF wealth of Rome-to
ionsbie ambition; old structures were torn
down. and the constant search for the
new and costly led to the destruction OF
AUGUSTUS boosted that 'he found Rome
of brick and left II of MARBLE In this
transformation concrete suffered as well
as brick, and IL is in the smaller towns
that We find the best examples OF the
use Of concrete.
As shown by analysis of mortar from
the amphitheater at Cubbio, the eharac-
teristic n the Cementing material used by
the Romans in massive construction, such
as that In which We would now use Port
land cement, was its low lime content.
In this these mortars differ radically from
Portland cement. The analysis was made
to determine as nearly as possible the
composition of the cement itself, ana
care was taken to exclude pieces OF stone
and coarse sand. -
Mixed with Beer. ~.
There are frequent instances jim me-
dieval writing of the addition TO rnortars
of various substances. such as beer,
blood. wakes. white of eggs, milk. sugar.
rye flour, sc. The action of any such
| additions was either to retard the set
II the base of the mortar was gypsum,
or TO supply carbonic acid by decompo-
sition to the interior OF the walls IL the
base was lime The effect of the addition
of sugar, however, which was common
10, 49, d
! recognized that lines are much more
/ soluble in sugar solutions thaD In pure
water, and that Capitalization OF car
Donates OF lime precipitated from aqueous
adhere better TO sand than where the
| carbonation of lime takes place when the
lime is in a mechanically dry state.
While lime Is the essential ingredient
\ In all structural cements and forms alone
very durable mortar hardening in air.
through the absorption OF carbonic acid
and reversion to carbonate OF lime, the
| conditions are different when the harden
ing depends largely on the formation OF
| new chemical compounds through COM
bination with silica or other acid acting
material The production of maximum
| durability under these conditions reQutr-
| ing that there shall be certain definite
| the, ideal cement being one so .propor-
| toned that all OF the lime after complete
setting would be combined with the clay
material present.: and none Of 1t left in
! All cements used for structural pur-
poses are produced by exposure OF the
crude or raw material to the action OF
heat, which causes certain chemical
changes and supplies the energy required
to bring about setting, which reaction is
exothermic: they all contain lime and re;
lquire presence OF water before setting VIII
take place
In Three Glasses.
Clements generally used for structural
| may ha divided fnfO fhref
classes:
Reyertive-This class includes those
which, on hardening. revert to the same
chemical composition as the raw ma.
terials from which they are produced
natural natl material to heat, the effect oi
which is to drive OF one OF the constitu-
ents, the process of setting being simply
sbsorpticn Of the element driven on. This
group is exemplified by lines and gypsum
Metafhetie-ThIs class includes thos,
cementing materials whose hardening
properties are due to the decomposition
Of the original raw material and the
formation of new chemical compound
through the action Of heat. the cement
differing, both before and after setting
in chemical cor position from the raw
materials from which II was produced
various components on each other. 'Thi,
group is exemplifed by natural and Port
land cements.
synthetie-This class includes thos,
: | cementing materials which are formed
by mixing or blending together, withou
subsequent exposure to heat. two or mort
cementitious or cement forming materials
: The set of these synthetic or composite
: cements may partake Of the characters
: tics of both groups. This group is eX
emplified by hydraulic lines, puZZolan ce
, ments and Alca lines.
The word Time" as used in the build
. ing trade is applied loosely to any mix
ture of caustic oxides formed by the cal
: cination of calcium or magnesium car
) oxide to cause the material to slake OF
: exposure to moisture. The chemical com
( Positions Of lines very largely from com
: paratively pure calcium oxides to dolo
mitic lines containing so per cent calcium
7 oxide and 45 per cent magnesium oxide
! Lines may also contain silica and alum
: ina without detriment, but where thes
, elements are present to any marked ex
: tent, the character Of the lime is changed
. | and II Possesses hydraulic properties. ant
i comes under the classification Of the syn
) thetic group. Lines suitable for ordi
T nary use in building construction shoul'
: contain not less than 90 per cent OF OK
ides of calcium and magnesium.
| Upon calcination at temperatures suf
/ flcient to drive OF the carbonic acid gas
the resulting oxide will, upon contac
: With euflcient water, slake or break dow
Into a smooth paste, which paste has tn
. property OF hardening on drying throug
! 1.-THE absorption of carbonlc acid For thl
; reason lime was probably the first trul
cementitious material used by man, 70
: we cannot consider as a cement mu
! which hardens only through desiccatio
and softens on becoming wet, The prop
r erty of oxide of lime Of hydrating. an
Z subsequently crystallizing on combinatio
4 with acid acting elements, forms the basi
1 of all our structural cements, and tn
/ lime of to-day differs IN no essential O
: its chemical composition. burning. slak
E ing, or use. from that of two or thre
thousand years ago.
Physical Characteristfcs Vary.
Lines of the same general chemica
composition even when produced undo
/. the same treatment vary largely IN thei
. physical characteristics on being mad
: into mortar The reason for this is nc
! well understood, but II Is due probabl
! 70 physical differences In the stone be
: fore calcination. such as crystalline struC
a lure. honogeneity, character Of impur
s | ties, and the condition In which the
= are present namely. uniformity of dii
4 tribution and size Of Particles of thes
: in1purifies. SC II rs. however, general
= recognized that for the production {
Il good lime. assuming the stone to
: OF proper quality. the foiowing require
{ ments must be met:
Z F1rst-Complete calcination, that Is, II
' lime must be so burned that PRACTICAL
\ no calcium carbonate Is present. but
Il the same time the temperature must NJ
; be carried to such point as TO fuse II
lime and fiux 7 with any impurities pre-
: second-Thoroush hydration or slakini
9 otherwise. any urslaked particles In q
S lime may slake after the mortar h