Table 82. Regaging Natural Cement Mortar

Age of all briquets, 1 year.

Treatment

a — Mortar molded as soon as gaged.

b — Mortar let stand 1 hour, regaged at intervals of 1/2 hour ; total number of gagings, 3. c —Mortar let stand 2 hours, regaged and briquets made; total number of gagings, 2. d — Mortar let stand 2 hours, regaged at intervals of 1/2 hour; total number of gagings, 6. e — Mortar let stand 4 hours, regaged at intervals of 1/2 hour; total number of gagings, 9. f — Same as b, except water added in regaging to restore consistency of mortar. g — Same as c, except water added in regaging to restore consistency of mortar. h — Same as d, except water added in regaging to restore consistency of mortar. i — Same as e, except water added in regaging to restore consistency of mortar. k — Mortar let stand 1 hour, regaged and briquets made.

l — Mortar let stand 4 hours, regaged at intervals of 1 hour; total number of gagings, 5.

Neat cement mortars of these two brands appeared more plastic when they were re tempered with more water after standing one hour (column f), but if allowed to stand three hours (column i), they had then become quite hard set. Mortars containing two parts sand that had stood sixty to ninety minutes with intermediate retempering, showed a slight increase in tensile strength, but more severe treatment was deleterious.

In Table 82 the mortars all contain two parts sand to one of cement,by weight. The only cases of any serious results of retempering are for mortars standing four hours and regaged, at intervals of one-half hour or one hour, with no water added to the original mortar. Briquets made from mortar that had been gaged every half hour, and was molded two hours after first mixed, showed a somewhat higher strength than briquets made of fresh mortar.

Table 83 shows that the behavior of regaged natural cement mortars, as shown in the preceding tables, is not an eccentricity of one or two brands. Mortars containing two parts sand do not appear to suffer in tensile strength by being allowed to stand two hours if regaged hourly.

Table 83. Effect Of Regaging On Tensile Strength. Five Brands Natural Cement

Notes: —Sand, Point aux Pins, passing No. 10 sieve.

In general, each result mean of five briquets. All briquets made by one molder and stored in one tank. All mortars appeared about same consistency when molded. No water added in regaging except Brand Kn, 1 to 2 mortar, standing two hours.

368. Conclusions

The conclusions to be drawn from these tests appear to be as follows: The cohesive strength of mortars of neat cement is appreciably diminished if they are allowed to stand a considerable length of time after gaging before they are used. Sand mortars, especially of Portland cement, usually develop a higher tensile strength under moderate treatment of this kind; and if regaged frequently, with sufficient water added to keep them plastic, mortars of slow setting cements may be used several hours after made without serious detriment to the tensile strength. Portland cements withstand severe treatment better than natural cements.

The effect of regaging on the adhesive strength is shown in Table 117, § 405. These tests were quite severe and pointed to the conclusion that the adhesive strength is diminished by standing and regaging, rich mortars and natural cement mortars being most affected.

The effect of regaging on a given sample should be investigated before it is permitted to any great extent, or in the most careful work. Regaged mortars are said not to give good results in sea water, and it may be expected that quick setting cement will be injured by regaging.