92
3220.051
Howell, K.W.
File R 3746-7-8
Paper
Underwriters' Laboratories, Inc. and ESCSI
1970
March 2
1-4 +test,photo
N
The subject of this report is the fire resistance classification of unreinforced load bearing walls consisting of nominal 8 in. thick concrete masonry units made with expanded shale aggregate produced by the rotary kiln process. The concrete blocks were made with a cement-aggregate proportion of 1:10.The purpose of the investigation was to determine the equivalent thickness (amount of solid material) required of the 8 in. blocks to obtain 2, 3, and 4 hr fire resistant walls.
As a result of previous tests conducted on 8 in. concrete masonry units made with expanded shale (rotary kiln process) with a cement-aggregate proportion of 1:9, it was established that concrete units with an equivalent thickness of 4.20 in. would provide a 2 hr rating; units with an equivalent thickness of 4.85 in. would provide a 3 hr rating; and units with an equivalent thickness of 5.35 in. would provide a 4 hr rating. The above points were determined by plotting the test data from various fire tests on a log-log graph paper and connecting the test points by means of a straight line. The test points were plotted on log-log graph paper because previous plots of equivalent thickness versus fire resistance ratings have shown a straight line relationship on that type of graph. Table II of the Standard for Concrete Masonry Units, UL 618, presently shows the above equivalent thickness requirements.
The submittor proposed to show that the minimum equivalent thickness for 2, 3, and 4 hr units and the cement to aggregate proportion could be reduced as a result of improvements made over the past years in block forming machines and in the selection of block aggregates. In addition, the development of humidity measuring equipment now makes it possible to test concrete block walls at a more uniform equilibrium relative humidity value, thereby improving the reliability of a graphical analysis.