Field to laboratory shear strength ratio for clays stabilized with low-carbon binders

The carbon dioxide emissions of a low-carbon deep mixing binder can be up to 80-90% lower compared with, for example, lime-cement binder emissions. The transition to low-carbon binders is ongoing in deep mixing, and thus studying the curing and optimization of the binder content of clay stabilized with low-carbon binders is necessary to develop design processes. In Finland, since 2001, a field to laboratory strength ratio is used to determine the design strength of stabilized clay if quality control (QC) soundings of the earlier representative columns are not available. The objective of this study was to determine field to laboratory strength ratios for low-carbon binders based on laboratory stabilization tests and QC soundings. The data consist of six stabilization test sites implemented with 11 different low-carbon binders and lime-cements. The laboratory specimens were made with the same clay, binder recipe, and curing time as the test columns. The binders discussed in this study are divided into four groups on the basis of their raw material compositions: Calcareous, gypsum, blast furnace slag, and fly ash. The results showed that when the laboratory shear strength is low, the field-to-laboratory strength ratio is higher than when laboratory shear strength is high. Further, with gypsum-, blast furnace slag-, and fly ash-containing binders, higher shear strengths were often achieved in the laboratory than in the test columns. With calcareous binders, higher strengths were frequently achieved in the test columns than in the laboratory. The extensive data were used to derive trendlines (laboratory shear strength versus field to laboratory strength ratio) for the four binder types. Trendlines can be used to predict the characteristic shear strength value of stabilized clay from laboratory strength. In addition, the uncertainty related to the prediction was quantified. These trendlines for low-carbon binders will be used in the revision of the Finnish guidelines.