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CEMENT--RETARDED SETS.
RETARDED SETS.
These results comprise tests of cements which were mixed with water and allowed to remain different intervals of time, subjected to different treatment during those intervals, finally tamping the material into the molds where it hardened undisturbed, and subsequently determining the compressive strength of the samples.
There were experiments in which the cement, after initially adding the water, was allowed to remain at rest excepting such times as material for samples was withdrawn, when the whole mass was worked over and restored to its primitive consistency by the addition of water, and so continuing until the whole quantity of material was exhausted. In other cases the cement was kept in a state of nearly constant agitation in the mixing bed by the continuous use of the hoe, adding water from time to time in order to keep the material at the desired consistency, taking out samples at regular intervals. In still other cases only the material withdrawn at intervals for samples was regauged with water, allowing the main body to remain undisturbed in the mixing bed. After aging in the air the several samples were tested for strength under loads of compression.
The figures in the first columns of the tables indicate the time, in hours, intervening between mixing and putting the material into the molds.
Alpha Portland Cement.
retarded set series.
Samples taken out at 2-hour intervals. Main batch of cement allowed to rest undisturbed in the mixing bed between the times of taking out samples or when regauging. Age when tested, 30 days.
Original quantities:	Pounds.
Cement.................................................................... 105.5
Water.........................................................26.1 per cent= 27.5
Water added to the main batch as follows:
Interval after mixing, hours.	Water used.	
	Pounds.	Percent, approxi- mate.
Initial mixing		27.5	26.1
2		.25	26.4
6		.12	26.7
Hours.	Dimensions.			Sectional area.	First crack.	Compressive strength.		Remarks.
	Height.	Compressed surface.				Total.	Per square inch.	
	Inches.	Inches.	Inches.	Sq.'inches.	Pounds.	Pounds.	Pounds.	
0	5.99	6.03	5.95	35.88	249,000	256,500	7,148	
0	6.00	6.02	5.98	36.00	253,000	266,800	7,411	
2	6.00	6.05	5.95	35.40	217,000	218,400	6,169	
4	6.02	5.99	6.06	36.30	211,000	272,000	7,493	
4	6.02	6.00	5.98	.35.88	231,000	244,000	6,800	
6	6.04	5.99	6.04	36.18	243,000	245,100	6,774	
8	6.03	5.98	6.01	35.93	198,000	254,500	7,083	
8	4.07	4.03	4.00	16.12	92,000	104,200	6,464	
8	4.06	4.03	4.02	16.20	104,000	110,300	6,808	
8	1.99	2.01	2.05	4.12	22,500	23,900	5,800	
H. Doc. 508----32