Selection of cement-based grouts for soil treatment

The design of high performance grouts for soil treatment requires consideration of many aspects of the grouting mixture including the selection of the binder (composition and fineness), the admixture (e.g. type and dosage of superplasticizer), and the water-binder ratio. This paper describes the results of a laboratory program conducted to establish criteria for cement-based grout design. Grouts were manufactured employing three pozzolanic microcements, identical in composition? but different in fineness (D-98 = 9, 17, 20 mu m) and an acrylic-based superplasticizing admixture( Grout injectability was evaluated through laboratory injection tests:performed on columns of four different sands with hydraulic conductivity ranging from 2.1x10(-4) to 1.2 x 10(-3) mts. Compression tests on specimens of the grouted sand indicated the effectiveness of the treatment. In addition, mercury intrusion porosimetry was employed to characterize the microstructure of the impregnated soil. Results indicate that by minimizing the water-cement ratio of the grout the effectiveness of the treatment, in terms of higher strength and smaller void size of the grouted medium, is greatly enhanced. The minimum water-cement:ratio that guarantees successful permeation of the soil varies greatly depending on the properties of the porous medium (permeability) and of the grout (fineness of the binder, use of superplasticizing admixture). Curves relating the composition of the grout to the permeability of the untreated soil and to the desired properties (strength and void size) of the treated medium were also obtained. These curves may be used to select the most appropriate grout for a given soil, based on the required strength of the grouted medium.