Excessivly wet soil is difficult to mix and pulverize. Experience has 

 shown that cement can be mixed with sandy soils when the moisture content 

 is as high as 2 percent above optimum. For clayey soils the moisture 

 content should be below optimum for efficient mixing. 



d. Curing. Compacted and finished soil-cement contains sufficient 

 moisture for adequate cement hydration. A moisture- retaining cover must be 

 placed over the soil-cement soon after completion to retain this moisture 

 and permit the cement to hydrate. Materials such as waterproof paper or 

 plastic sheets, wet straw or sand, wet burlap or cotton mats are entirely 

 satisfactory. 



e. Engineering Properties of Soil Cement . During construction the 

 soil-cement is compacted to a high density. As the cement hydrates, the 

 mixture hardens in this dense state to produce a structural slablike 

 material, and thus possesses engineering properties. The magnitude of 

 these properties depends primarily on the type of soil, age and curing 

 conditions . 



Depending on soil type, 7-day compressive strength of saturated speci- 

 mens of the minimum cement content meeting soil-cement criteria is generally 

 higher than 2.1 megapascals (300 pounds per square inch). The 28-day 

 flexural strength is approximately 20 percent of the compressive strength, 

 and the modulus of elasticity about 6 900 megapascals (1 million pounds per 

 square inch) . Soil cement tends to be brittle, cracking under impact and 

 temperature stresses. 



f. Functions of Soil-Cement . Soil-cement is used primarily as a base 

 course for stabilizing and compacting soils for foundations, bank protection 

 and subbase construction. It has been used for earth dam cores, reservoir 

 linings, and slope protection. 



5 . Sulfur Cement Concrete and Grouts . 



a. Introduction. The past 15 to 20 years have seen a rapid increase 

 in research and development work on sulfur, and two factors have been the 

 cause of this increase. In the early 1960's, large quantities of sulfur 

 were beginning to be recovered from sour natural gas and petroleum. Sulfur 

 producers realized the necessity of creating new end-use markets to absorb 

 this sulfur, and sponsored research to that purpose. As a result of this 

 research, sulfur was discovered, or in some cases rediscovered, to have a 

 number of interesting mechanical properties. Research workers who originally 

 had envisioned sulfur as a substitute material now discovered that sulfur 

 had properties superior to some conventionally used materials and that it 

 could outperform such material both technologically and economically. These 

 initial discoveries stimulated additional research in many aspects of 

 sulfur. Many interesting new uses for sulfur in construction have been 

 discovered. Some of the more promising are: 



(1) Sulfur asphalt paving materials, 



(2J sulfur concretes, 

 (3) sulfur coatings, 



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