Microstructure Development in Artificially Cemented, Fine-Grained Soils

Abstract

Fine-grained sedimentary deposits can bear an increased risk for building settlements due to their moderate stiffness and strength properties, as well as high groundwater tables. However, some buildings, e.g., situated on shallow foundations in Alpine basins, show only relatively small settlements because the formation of carbonate cement can create bridging bonds between the detrital soil particles, leading to increased stiffness. These weak bonds can be damaged through dynamic loads and high static loads, causing a weakening of the soil’s microstructure and resulting in large settlements in several cases. However, the environmental controls and mechanistic processes underlying the formation versus damaging of microstructure in fine-grained, postglacial sediments are, to date, poorly understood. In the present study, fine-grained sediments are artificially cemented by calcium carbonates (CaCO3) to investigate (i) the influence of a mild and sustainable cementation process on the stress–strain behavior of silicate- and carbonate-rich soils and (ii) the possibilities and limitations of artificial microstructure development for soil stabilization. Incremental load oedometer testing (IL), bender element testing (BE), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) specific surface area (SSA) measurements are used to characterize the development of cementation and to elucidate the improvements in the soil mechanical properties. It is shown that cementation induced by CaCO3 mineralization (by 5–15% replacement) leads to an increased stiffness (factor ≈ 5–7) and shear wave velocity (factor ≈ 1.1), caused by the formation of nanocrystalline, particle-binding CaCO3 cements. The improvement of soil stiffness is dependent on the CaCO3 replacement level, reaction time and primary soil mineralogical composition.

Hydration of MgO: Reaction Kinetics and pH Control on Brucite Crystal Morphology

“…Further details about BET theory are provided elsewhere. 34 Powdered samples were used to record X-ray diffraction (XRD) patterns using a PANalytical X'Pert PRO diffractometer (Co−Kα radiation; 40 mA, 40 kV) in the range from 5°to 85°2θ with a step size of 0.017°2θ and a count time of 15 s per step for each scan, for the identification of the mineralogical composition of the MgO raw materials and its reaction products. For mineral identification and quantification, the PANalytical X'Pert Highscore Plus software (version 3.0.4) and the ICSD database were used, with an analytical error of <3 wt %.…”

“…The samples were predried by heating to 105 °C under vacuum for 24 h. The analytical error of the BET measurements is approximately ±10%. Further details about BET theory are provided elsewhere …”

Comparison of preloading by fill surcharge and ground water lowering based on a case study

“…As the pools are very sensitive to settlements, especially to differential settlements, such vertical deformations must be minimized to a certain magnitude, where no restrictions in use occur. Due to a possible negative effect on the behavior of the low silt layer [4], a foundation with elements reaching layer C was excluded.…”

Investigating the Consolidation Behaviour of Cement-Bentonite Barrier Materials Containing PFA and GGBS

“…Since both CB and cemented soils contain cementitious elements, a comparison between the two may be more apt. [18][19][20][21][22][23][24] studied the extent to which the incorporation of cementitious material into the soil improved the consolidation behaviour of clay. According to the majority of past studies, the addition of cement contributed by making the material become less consolidated and by leading to an increase in preconsolidation pressure [18,21,24].…”

“…[18][19][20][21][22][23][24] studied the extent to which the incorporation of cementitious material into the soil improved the consolidation behaviour of clay. According to the majority of past studies, the addition of cement contributed by making the material become less consolidated and by leading to an increase in preconsolidation pressure [18,21,24]. Cai et al [23] also claimed that the temperature at which the cement was cured and the method by which it was cured could contribute to an improvement in the compressibility characteristic of cemented soil.…”