PHYSICAL AND CHEMICAL PROPERTIES. PARTS IV, V. ]4] 
to the slaking of free lime, and much depends upon the con- 
dition of the free lime and upon the influences to which the 
cement is subjected before and after it has set as to whether 
its presence will cause disintegration or weakness. 
It is the lime which fails to slake before the cement has set 
that tends to cause disintegration. Lime which has been burned 
at a low heat and then finely ground hydrates within a very 
few minutes after being brought in contact with water. On 
the other hand, lime which has been burned at the white heat 
of the Portland cement kiln hydrates much more slowly and 
expands much more than lime burned at a low red heat. Con- 
sequently, a large quantity of anhydrous free lime may not cause 
natural cements to warp or crack, whereas as little as 1 or 2 
per cent in hard-burned Portland cement is apt to cause dis- 
integration. 
The evil effect which free lime is capable of producing also 
depends more or less for its development upon the manner in 
which the cement is used and exposed. In general it may be 
stated that the expansion due to free lime in indurated Port- 
land cement occurs within a few hours when it is submerged 
in boiling water or steam. Under water, at ordinary tem- 
peratures, it occurs mostly during the first seven days and is 
apparently complete by the end of two months. It is still slower 
when exposed to the air. 
These observations are based upon the action of small exper- 
imental specimens. The ability of water or air to attack free 
lime in cement depends upon the density and volume of the 
mortar or concrete. Neat cement is almost impervious when 
it has hardened without cracking, and so also is a 1:1 or even 
a1: 2 well-mixed and indurated quartz-sand mortar. Therefore, 
the expansion due to free lime will not develop equally on 
specimens of different shape, volume, or density. It would 
manifest itself less in lean than in rich mortars, and the action 
of the lime will be rendered less harmful in natural sands 
containing pozzuolana than in the coarse, standard, quartz, test- 
ing sand. ; 
It is the object of the boiling or steam tests to determine the 
presence of slow-slaking lime. If a Portland cement passes 
the hot test, it may be used immediately with reasonable cer- 
tainty of its ultimate soundness. McCready ™ has called atten- 
tion to the fact that the destructive force due to free lime 
and manifested in the boiling test “may not develop its full 
™ Loe. cit. 
