This paper presents details of a study that deals with determination of engineering properties, identification of phases of major hydration products, and microstructural characteristics of a zinc-contaminated (referred to as Zn-contaminated in this paper) kaolin clay when it is stabilized by a cement additive. Investigations were carried out with respect to the effect of the level of zinc (Zn) concentration on the overall soil properties including Atterberg limits, water content, pH, stress–strain characteristics, unconfined compressive strength, and secant modulus. In addition, X-ray diffraction, scanning electron microscopy, and mercury intrusion porosimetry studies were conducted to understand the mechanisms controlling the changes in engineering properties of the stabilized kaolin clay. The study reveals that the level of Zn concentration has a considerable influence on the engineering properties, phases of hydration products formed, and microstructural characteristics of the stabilized kaolin clay. These changes are attributed to the retardant effect of Zn on the hydration and pozzolanic reactions, which in turn alters the phases of hydration products and cementation structure – bonding of the soils. Theoretical simulation of the pore-size distribution curves demonstrates that the cement-stabilized kaolin exhibits bimodal type when the Zn concentration is less than 2%, whereas it displays unimodal type when the Zn concentration is 2%. With an increase in the Zn concentration, the characteristics of the interaggregate pores in terms of volume and mean diameter change considerably, whereas those of intra-aggregate pores remain nearly unchanged.

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Seepage-induced internal erosion in earth-filled embankment dams has been attracting attentions of civil engineering researchers and practitioners for decades.Microbially induce carbonate precipitation (MICP), due to its proved performance in soil enhancement and permeability control, can be potentially used for internal erosion control. This paper examines the applicability of MICP for internal erosion control in gravel-sand mixtures using a large one-dimensional column test apparatus which incorporates the implementation of MICP. Visual obersverations, erosion characteristics and hydromechanical behaviours of Non-MICP and MICP treated gravel-sand mixtures were investigated through a series of constant-pressure erosion tests. Test results confirm that MICP treatment can reduce the cumulative erosion weight, erosion rate and axial strain relative to Non-MICP soil. The magnitudes of hydraulic conductivity for all tested samples before erosion process fall into a range from 5.5×10 -5 to 8.0×10 -3 m/s. After erosion process, Non-MICP soils and MICP treated soils with low cementation concentrations experience a significant increase in the hydraulic conductivity. Furthermore, the hydro-mechanical coupling analysis was conducted and different erosion modes were identified for low and high concentrations of cementation solution, respectively. Fundamentally, the efficiency of internal erosion reduction is controlled by the calcium carbonate precipitation content within the tested soils. Higher precipitation content can facilitate the formation of larger clusters of cemented sand particles, thus reducing the likelihood of erosion.

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Earth embankment dams are one of the most commonly constructed hydraulic infrastructures worldwide. One mode of dam failure is piping through the embankment, which is initiated by internal erosion of soil particles inside dams. In this study, the applicability of microbially induced carbonate precipitation (MICP) for internal erosion control is examined in the laboratory using sand-kaolin mixtures of different particle sizes. A series of internal erosion tests are conducted using a newly designed rigid-wall column erosion test apparatus, which allows independent control of MICP treatment. Erosion rate/coefficient, volumetric change and permeability are characterized during the internal erosion process. It is found that MICP treatment facilitates the reduction of erosion and volumetric contraction of sand-clay mixtures investigated in the current study. Carbonate precipitation increases the erosion resistance of sand-clay mixtures by absorbing/coating fine particles directly and bridging the contacts of coarse particles. An improved effectiveness of internal erosion control is observed in the sandclay mixture having a higher gap ratio. This observation is due to the inherently large porosity, which hosts more carbonate precipitation. The difficulty of bacteria and chemical injection in sand-clay mixtures triggers the flushing of produced calcium carbonate, which reduces the overall carbonate content and MICP treatment efficiency. The spatial distribution of precipitation within the soil is also altered.

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Physical, hydraulic, and mechanical properties of clayey soil stabilized by Physical, hydraulic, and mechanical properties of clayey soil stabilized by lightweight alkali-activated slag geopolymer lightweight alkali-activated slag geopolymer Abstract Abstract Lightweight cement materials are extensively used in the infrastructure construction. Geopolymer is a low-carbon and environmentally friendly cementitious material. This paper presents an investigation on the physical, hydraulic, and mechanical characteristics of lightweight geopolymer stabilized soil (LGSS) and a comparison with lightweight cement stabilized soil (LCSS). Measurements of volumetric absorption (VA) of water, hydraulic conductivity (k), and unconfined compressive strength (qu), scanning electron microscope (SEM) observation, mercury intrusion porosimetry (MIP) test, and thermogravimetric analysis (TGA) are conducted. The results show that LGSS has higher VA than LCSS. The k of LGSS is one order of magnitude higher than that of LCSS. The qu of LGSS is 2-3.5 times of that of LCSS. Microstructurally, the VA and k of LGSS are found to be positively correlated with the volume of large air pores (>10 μm). Higher qu of LGSS than LCSS is attributed to more hydration products that fill up the voids of soil. It is concluded that LGSS gives better engineering performances than LCSS in terms of water absorption, permeability, and strength characteristics. Abstract: Lightweight cement materialsare extensively used in the infrastructure 5