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The physical and chemical composition of caliche soils of the Tucson, Ariz. area were investigated to determine the compressive strength of indurated and crushed calcisols. The results of stabilization of crushed calcisols with portland cement additive were determined and the soil-cement reaction products were investigated.
Soil minerals were identified by X-ray diffraction analysis. The calcisols were found to consist mainly of feldspar and randomly oriented microcrystalline calcite with lesser amounts of quartz and clay minerals.
The strength of the calcisols was found to be inversely related to their clay content, with unconfined compressive strengths varying from less than 1.03 MPa (150 psi) to more than 20.67 MPa (3000 psi). When the indurated caliche was crushed it behaved as an inert granular material with no immediate recementation when compacted.
It was shown that a loss of compressive strength generally occurred in the remolded soil-cement mixtures after 28 days of curing, the maximum 28-day compressive strength, using 10 percent portland cement, varying from 2.51 to 7.80 MPa (364 to 1132 psi). The compressive strength was a function of the amount of portland cement added and of the combined feldspar-calcite content of the soil.
The feldspars of the Tucson basin were found to consist mainly of intermediate microcline with lesser amounts of orthoclase and oligoclase. The weak soil-cement bonding strengths appear to be due to the feldspars and the strength losses which occur are the result of the chemical interaction of the calcite and alkali feldspars with the portland cement in an aqueous environment. Portland cement is an unreliable additive for the effective stabilization of crushed calcisols.
calcareous soils, compressive strength, mineralogy, portland cement treatment
Professor, California State University, Sacramento, Calif.