Contributions of the Soil Scientist to Soil‐Cement Paving

SINCE the development of portland cement in England in the last century, engineers have been interested in finding ways of mixing soil and cement together to produce a structural material. This objective was stimulated by the obvious reductions in construction costs that would result from using 'soils occurring on the site. A brief history of the subject and the high-lights of soil-cement paving will show that its development and use has hinged on the mass of knowledge already accumulated by soil scientists and engineers. With the development of automobiles and extensive improved roads, the highway -engineer became particularly interested in the possibilities of mixing soil and cement to produce a low cost road. Field experiments of this-nature were tried in the 2o's and continued sporadically. The state highway departments of California, Iowa, North Dakota, Ohio, and finally South Carolina made road field installations of mixtures of soil and cement to determine their charac• teristics ,and possible practical applications. While each trial added to the little known relations of soil and cement, the. field results were not particularly promising until the South Carolina State Highway Department built five short • sections totaling 1.02 miles in 1933 and 1934. The results of this work were most stimulating since, although the results were unpredictable and no system or theory of control was used, the projects carried traffic successfully and indicated that it might be possible to develop scientific methods for mixing soil and cement to produce a practical, low cost road. The promise held forth by the South' Carolina results prompted the Portland Cement Association to set up a project in the Development Department at the beginning of 1935, under the direction of Frank T. Sheets, to conduct research and tests on soilcement mixtures with a view of producing a low cost, structural material suitable for use for light traffic roads and streets that could be controlled by scientific methods and whose performance could be foretold and thus warrant expenditures. The project was assigned to the writer and the first step was the careful review of'all literature on soils arid previous tests on mixtures of soil and cement. At the conclusion of the study of soil literature, it seemed that the work of R. R. Proctor, Field Engineer, Bureau of Waterworks and Supply, Los Angeles, Calif., offered worthwhile possibilities for investigating the influence of cement in soil-cement mixtures. He developed a field test method for determining the moisture content that a soil should contain so that it could be compacted in the field with sheepsfoot rollers to give the highest density and stability possible to obtain with these field construction methods. His article (9)* brought national attention to the principle that a direct relation exists between the moisture content of a soil, the degree of compaction, and the resulting density and stability. These principles were uncovered by the Materials and Research Division of the California State Highway Commission (12). With the moisture-density relations of soils as a beginning, laboratory tests were started on soilcement mixtures. It was proved soon that these same relations also prevailed for soil-cement mixtures before cement hydration, and they then served as the basis of an extended series of research projects and tests that culminated .in a scientific series of laboratory and field tests for predicting and controlling soilcement mixtures suitable for light traffic paving. The basic tests are now Standard ASTM Tests : 0558-44, 0559-44, d 0560-44. Details of soil-cement research and development in the United States are given in the Proceedings of the Highway Research Board from 1936 to the present time. The detail research data of the Portland Cement Association were published (2, 3) in 1937 and 1940.