This study advances the use of elemental sulfur in structural materials by demonstrating its value in bonding high-strength, well- graded basalt aggregates to form sulfur-basalt concretes. Sulfur is an excellent bonding agent, and the strength of a thermoplastic sulfur-aggregate mixture depends, to a large degree, on the strength and grain-size distribution of the aggregate used. A 3-cubic-foot, electrically powered mixer with heat applied to the barrel was used to mix the sulfur and aggregate. Sulfur content of several mixtures was varied to obtain the best workability with a minimum of sulfur in excess of that necessary to fill the voids. The average grain sizes and grain-size distributions were also varied to determine their effects on strength. Unconfined compression tests of forty- five 6- by 12-inch cylinders yielded average strengths of 3,348 psi to 10,398 psi. The highest strength single cylinder was 10,717 psi. The cylinders were tested from 24 hours to 6 days after pouring; after 24 hours the rise in strength was very slight. The results obtained suggest that sulfur can be a useful construction material. An evaluation was also made of a high-vacuum application for sulfur concrete. Sulfur has a high vapor pressure at elevated temperatures, 50 deg. to 100 deg. C; consequently, significant losses by sublimation can be expected. At lower temperatures the losses are not significant; however, this factor will limit its use at a higher temperature.