Use of Retarders with Cement Treated Soils: Final Report

About the report:

The purpose of this study was to investigate various set retarding admixtures for possible use as an economical method of allowing long delay periods between the mixing of cement, soil and water and remixing. Three types of retarders were used in preliminary tests, from which one, a sugar and lime combination, was chosen for all further work. The study comprised four phases. Phase I concentrated on the selection of a suitable test for determining retardation and the selection of the most suitable and economical retarder. As a result of this phase, a procedure based on a penetration test was developed; and sugar-lime combination was selected as the retarder to be used in the rest of the study. Phase II was conducted to supply some basic information about the effect of the sugar-lime mixture on the hydration of cement paste. Using an X-ray diffraction technique an attempt was made to determine if any key compounds of hydration formed that could be used as indicators of the effective end of retardation. The results showed that the sugar-lime retarded cement paste did not develop Ca(OH)2 reflections until set occurred, which was at a much later time than it occurred in the retarded soil-cement specimens. In addition, the variability of the test results was very high, apparently because of the extreme sensitivity of cement to sugar. Study of the retarded soil-cement system is further complicated by the possibility that the clay in the soil will adsorb some of the retardant. Phase III investigated the effects of the sugar-lime retarder on the durability of soil-cement mixtures as measured by freezing and thawing tests. It was concluded that there was no harmful effect. The last phase was a field project to determine the feasibility of using the sugar-lime retarder in the field. In this phase two experimental sections were constructed incorporating several variables. As a result of this phase, it was concluded that the properties of cement treated soils will not be impaired if the compaction is delayed for 6 hours, or if the mixture is remixed and compacted at 6 hours and if the mixture is compacted immediately and not remixed. It was also concluded that strength development might be decreased about 50% if compaction of the mixture is delayed for 18 hours or if the mixture is remixed and recompacted after a delay of 18 hours.

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