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Pull and Creep Tests on Gypsum-bonded Roof Bolts.

Hansen JS; Gerdemann SJ
MISSING :36 pages
To improve mine safety, the Bureau of Mines has conducted a search for better materials and systems to anchor roof bolts. This report describes a study on the ability of a gypsum-based anchoring medium to withstand short- and long-term loads. Results showed that 2-ft- long bolts anchored with gypsum that was injected as plaster slurry at a 0.370 Water-cement ratio and cured for 10 min sustained pull test loads equal to the ultimate strength of the bolt steel (about 37,000 lb). For comparison, the minimum required capacity is 17,600 lb. Long-term loads of 15,500 lb were sustained with estimated 10- yr movement of less than 1/2 in. Two-foot-long bolts anchored with gypsum installed in a cartridge in which the water was contained in tiny capsules sustained a pull test load of about 30,300 lb at a 0.319 Water-cement ratio, load capacity was about 37,000 lb. The lower capacities of cartridge-installed bolts resulted primarily from the remnants of the water-wax capsules. Above 10,000 lb, creep movement of cartridge-grouted bolts appears excessive, but longer bolts may be capable of resisting creep better.
Publication Date
Document Type
IH; Report of Investigations
Fiscal Year
Identifying No.
RI 8937
NIOSH Division
Source Name
Page last reviewed: November 12, 2021
Content source: National Institute for Occupational Safety and Health Education and Information Division