United States Department of Transportation
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Abstract:Soil-cement base course materials design in Louisiana is based upon durability and compressive strength criteria, with the compressive strength requirements being the controlling factor in 95 percent of the designs. The findings to data have provided reasonable verification that the previous design strength of 300 psi was being achieved in the field on-the-average. However, definite indications are that excessive variability existed in the former design system, and variability exists in the quality of the final product in the field.
A system for recommending the percent of cement for soil-cement has been developed which virtually eliminates the majority of problems associated with testing variability. This variability was inherent in the procedure and not due to careless testing techniques. in addition, compressive strength test reproducibility has been improved by strictly controlling the cement used for testing, slaking in water overnight just prior to molding specimens, closely controlling the temperature of the ingredients during the molding of specimens and increasing the number of specimens per test.
According to the mean of all the data, the construction projects reasonably met the design criteria of 300 psi at 28 days; indications suggest that some projects are poor in quality, better quality soil-cement can be constructed since approximately half of the projects investigated developed properties in excess of, or equal to, the design criteria. Excessive variability in cement content frequently exists in the finished soil-cement. It appears that the average cement content in the field ends up approximately 1 1/2 percent less than the design percentage. In addition, the present method of field density control has several undesirable features. When using this method there is an implication of greater density than actually achieved. a different method of field density control should be considered. The specifications should disallow the use of overweight construction traffic at all time.
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