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8. Transverse rupture testing of sulfur concrete......

9. Modulus of elasticity of sulfur concrete.......... 10. Sulfur concrete beam data..... 11. Sulfur concrete wall demonstration, test data...

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The Bureau of Mines investigated modified sulfur concretes as one part of a program for utilizing sulfur in construction materials. The use of modified sulfur was studied as a means of preventing the stressing action in the concretes caused by the allotropic transformation of sulfur on solidification. Unmodified sulfur concretes have been prepared that have compression, flexural, and tensile strengths equivalent or better than Portland concretes. However, most of these concretes have been vulnerable to deterioration by weathering, temperature fluctuations, and freeze-thaw cycling. The sulfur was modified by reaction with dicyclopentadiene or dipentene before use as an aggregate binder. Sulfur concretes and modified sulfur concretes were prepared from acidic and basic type aggregates. Physical properties of the optimum mixtures were determined and compared with each other and with Portland cement concretes. The best results were obtained by reacting sulfur with 5 pct dicyclopentadiene to prepare modified sulfur concretes. Field testing of the concretes are in progress. Present results show that modified sulfur concretes are superior to unmodified sulfur concretes and equal or better than Portland concretes in compressive, flexural, and tensile strengths. Long-term aging characteristics of both modified and unmodified sulfur concretes are being determined.

INTRODUCTION

A Sulfur Utilization Program was initiated by the Bureau of Mines in 1972 to develop new uses for sulfur to take advantage of a projecte d sulfur surplus in the 1980's (22).3 Part of that program was to investigate concrete-type materials using sulfur instead of Portland cement as the binder for aggregate. Sulfur-aggregate concrete has been described by Dale and Ludwig as a thermoplastic mixture of sulfur, fine aggregate, and coarse aggregate that is heated to above the melting point of sulfur (240° F) and then cooled and allowed to solidify into a rigid, concretelike material (11). There are many potential speciality uses for sulfur concretes. As a corrosion resistant

Research chemist. 2 Metallurgist. Underlined numbers in parentheses refer to items in the list of references.

material, it can be used for acid-proof leach tanks, reaction vessels, thickeners, sumps, and for handling sewage and wastes that contain acid and salts. Since the material is thermoplastic, it can be placed in freezing temperatures without damage. Sulfur concrete attains 90 pct of its ultimate strength within a few hours after solidifying and would be useful in the paving industry for base or surface material which can be placed in service quickly. It is also resistant to salt solutions that damage normal concrete paving. While sulfur concretes have advantages in selected application, the replace. ment of cement by sulfur in all concrete is not feasible on a resource basis alone as the production of cement is roughly 10 times that of sulfur. Cement production in 1974 declined 8 pct principally from shortages of natural gas, low-sulfur coal, and modernization and improvements of dust collection facilities to conform to environmental pollution standards. Saving of cement and of the energy used in its production will result by utilizing sulfur for preparing concretes.

The projected use of sulfur as a construction material is not new. During World War I the demand for sulfur grew enormous ly and led to development of the Texas sulfur deposits. This resulted in more than a doubling of the U.S. annual sulfur production. A potential surplus of sulfur similar to the present day situation existed at the end of the war. At that time, Bacon and Davis reported on projected use of sulfur in the construction industry (2). They found that many additives had been suggested to modify the sulfur to enhance its properties and tested most of the proposed additives and found them unsuitable. They did, however, develop an acid-resistant mortar containing 40 pct sulfur and 60 pct sand, and it was this work that led to the industrial production of acid-resistant sulfur mortar for the chemical industry. Duecker, in 1934, found that the sulfur mortars grew on the rmal cycling with a loss of flexural strength which resulted in failure of the mortars (14). He modified the sulfur cements by the addition of an olefin polysulfide to the sulfur. This resulted in retarding both the tendency to grow and the loss in flexural strength on thermal cycling of the mortar. The use of additives to modify the sulfur to prepare more stable mortars led to industrial acceptance of the material.

Dale and Ludwig's research work on the physical properties of sulfur has led to a better understanding of its potential use in construction materials (5-13, 16-17). Their work using sulfur as a binder for aggregate to prepare concretes showed that such materials could be prepared having compressive, flexure, and tensile strengths comparable to Portland cement concretes, which for building purposes average 2,500 to 3,500 psi compressive strengths and when prestressed will average up to twice these values. For pavements, Portland concretes are used with compressive strengths of 3,000 to 4,000 psi. In general, these concretes have flexural strengths of 10 to 15 pct and tensile strength of 10 pct of their compressive strengths. Sulfur concretes of various strengths have been prepared by using various aggregates and mix designs (10-11). Crow and Bates used sulfur and basalt aggregates to prepare high-strength sulfur concretes with compressive strengths ranging to 10,000 psi (4). Malhotra, in 1973, reported that elemental sulfur could be combined with mineral aggregate to produce high-strength concrete (18).

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