184 REIBLING AND REYES. 
A. The effects of anhydrous free lime: 
(a) Lime which fails to slake before the cement has set is the 
usual cause of disintegration or weakness. 
(6) Lime burned at a white heat hydrates much more slowly and 
expands approximately 50 per cent more than lime burned 
at a low heat. 5 
(c) Owing to the impermeable nature of indurated neat cement, 
the expansion due to free lime will not develop equally in 
specimens of different shape, size, volume, or density. 
(d) The expansive force manifests itself less in lean than in 
rich mortars and the action of free lime is rendered less 
harmful by using sands containing pozzuolana. 
(e) When cement is submerged in cold water “this disruptive 
force may not develop its full value in a month or a 
year.” 
(f) In air, sintered lime slakes much more slowly than in water. 
(g) Owing to the impermeable coating of slag and calcium 
carbonate, boiling water may fail immediately to attack 
the free lime in aérated cement unless it has been ground 
to extreme fineness. 
(h) The force which operates to cause cements and mortars to 
disintegrate does not become apparent to the eye until 
it has overcome the strength of cohesion developed by 
other constituents in the cement. 
(2) If anhydrous free lime is present in a hardened cement and 
is allowed to slake, it will weaken the latter. 
B. The effects of slaked lime: 
(a) Its influence upon the strength depends upon the nature of 
the cement, and the manner in which it is used. 
(b) Slaked lime does not possess the ability to harden in water, 
but hydraulicity may be slowly imparted to it by the 
presence of pulverized pozzuolana. 
(c) If permitted to absorb carbon dioxide, it has cementive prop- 
erties of its own, but the process of induration is slow and 
confined more or less to exposed surfaces. 
(d) The presence of slaked lime may affect the strength of a 
cement in a mechanical manner, because it shrinks very 
much if permitted to dry, increases the plasticity, and in 
certain conditions decreases the permeability. 
C. The effects upon the strength of various combinations of calcium 
oxide with silica, alumina, or iron oxide: 
(a) The pulverized, fused, or perfectly sintered calcium com- 
pounds in calcareous cements possess the property of 
hardening under water without an appreciable change in 
volume and without the necessity of preliminary curing. 
(b) With proper mixtures, the nearer we approach a thoroughly 
combined and fused clinker, the less the expansion of the 
resulting cement. 
