519
CEMENT--RETARDED SETS.
Whitehall Portland Cement.
RETARDED SET SERIES.
Samples taken out at intervals, the main hatch remaining undisturbed in the mixing bed after the initial gauging. The cement was mixed with 25.6 per cent water by weight. Lots of two 6-inch cubes were taken out immediately after gauging, and 2 hours and 4 hours later. The material for the second and third lots was regauged with 0.25 pound and 1.75 pounds of water, respectively. In subsequent lots the cement had set very hard in the mixing bed and required to be broken up with a pickax and reground in a mortar before regauging. This was reground to pass a 100-mesh sieve. About 40 per cent of water additional was used in regauging the material 24, 48, and 146 hours retarded.
The results show the cement retained its strength practically unchanged after an interval of 4 hours in the mixing bed, and that even 6 days thereafter the indurated material can be broken up, reground and regauged, and then reacquire a certain compressive strength. The samples were tested when 35 days old from the time of initial gauging.
	Dimensions.					Compressive strength.		
Hours.	Height.	Compressed surface.		Sectional area.	First crack.	Total.	Per square inch.	Remarks.
0	Inches. 6.07	Inches. 6.03	Inches. 5.98	Sq. inches. 36.06	Pounds. 165,000	Pounds. 214,100	Pounds. 5,940	
0	6.12	6.00	6.03	36.18	202,000	251,400	6,950	
2	6.24	6.00	6.05	36.30	236,000	245,100	6,750	
2	6.22	6.00	6.01	36.06	126,000	209,900	5,820	
4	6.02	5.99	6.14	36.78	196,000	249,900	6,790	
4	6.00	6.00	6.17	37.02	231,000	235,000	6,350	Dark colored
								fragments.
24	4.06	4.04	3.87	15.63		17,800	1,140	Light colored fragments.
								
24	4.03	4.05	3.90	15.80		18,100	1,150	
24	3.85	4.10	4.08	16.73	19,100	20,700	1,240	Seam across
								middle normal to applied stress.
48	4.09	4.09	3.90	15.95		11,500	721	
48	4.09	4.03	3.96	15.96		10,500	658	
146	4.07	4.01	4.00	16.04		11,200	698	
146	4.09	4.03	3.97	16.00		10,500	656	
146	4.01	4.04	4.05	16.36		10,900	666	
146	4.10	4.04	4.04	16.32		11,700	717	
A number of grouts were mixed in the afternoon, allowed to remain at rest in the mixing bed over night, a period of 15 to 16 hours, reworked in the morning, adding water if necessary to establish such a consistency as common in mortar for stone masonry or removing surplus water at this time, after which the material was put into molds. After setting about 30 days or more in the air, tests on compressive strength were made as follows: