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2020, April 13 NU now

Innovative and environmentally friendly - research project of NU scientists on soil improvement technology

2020, April 13

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There is a growing concern about ecological sustainability and mitigating potential human impact on our planet’s environment.  Scientific communities around the world want to create eco-friendly products that will help reduce risk in a variety of industries, and NU researchers are no exception.   Currently, an assistant professor at Nazarbayev University, School of Engineering and Digital Science, Sung-Woo Moon is conducting a research-based project in "Development of the sustainable and innovative ground improvement technique via environmentally friendly low-carbon rapid-hardening cement in Kazakhstan".  This project has significant implications for using a new alternative to traditional cement to reduce the carbon footprint in geotechnical soil improvements and other projects. 

“Cementation, either by a natural or artificial process, even in small amounts, tends to alter characteristics of soil behaviors and improve the strength of the soil. Artificial cementation carried out by in-situ soil mixing can significantly improve the properties of the soft soil. For example, it has been applied for soil stabilization, column type reinforcement in soft soils, as gravity composite structures, liquefaction mitigation and in-place barriers for cutting off seepage. Cementation studies in the laboratory are usually carried out to either understand the effect of natural cementation in the field or to establish design criteria for cement stabilization. Hence, cementation effects need to be considered while designing the foundation, analysis of the dynamic response of the subsurface, and evaluation of stability problems” says the assistant professor.

Assistant professor Sung explains that Ordinary Portland Cement (OPC) is the most commonly used binding material as extensive research has been conducted to study the behavior of the cementing agent. OPC treated sand shows higher strength, improved liquefaction resistance, reduced permeability and compressibility. The mechanical properties of the soil are improved by the hydration of OPC with water available around and in the voids of geomaterial. The hydration of OPC involves converting calcium silicates to calcium silicate hydrates (CSH) and calcium hydroxide (Ca(OH)2), with CSH responsible for long term strength and also converting calcium aluminates to calcium aluminate hydrates (CAH), responsible for short term strength and dimensional stability (Taylor 1997). These cementitious materials bind the soil grains to improve shear strength, permeability and compressibility of soil mixtures. The carbon footprint of conventional OPC, however, can have a significant effect on the environment.  For this reason, it is necessary for researchers to discover an alternative binding admixture environment to reduce this environmental impact. To meet its obligations under the Kyoto Protocol Kazakhstan has agreed to reduce carbon emissions by 15% by 2020 and by 25% by 2050 compared to its 1992 level (National concept transition to green economy up to 2050, 2013). Calcium Sulfo aluminate (CSA) is a new alternative which has been studied with respect to concrete technology applications. The use of CSA for geotechnical soil improvement has not yet been explored. Compared to concrete technology applications, geotechnical applications such as ground improvement or land reclamation require generally much higher water to cement ratio. Apart from the eco-friendly characteristics, it is also expected that CSA-treated soil will have a higher initial strength gain than conventional OPC due to the compositional characteristic of CSA. In the long term, the use of CSA in geotechnical projects would help us move towards a more sustainable approach in reducing the carbon footprint.

Impact on science

Construction projects today often need to use tunnelling and or other underground works.   Especially in places where there is high population density compared to available land such as in Singapore.  Additional difficulties are encountered when there are unfavorable soil conditions. For instance, Singapore has extensive coverage of soft clay, mainly marine clay deposit, which is characterized by low strength and high compressibility. Cement stabilization is one of the most common ways to improve the ground. Even in places where there is more available land for construction, like Kazakhstan, underground works in unfavorable soil conditions make cement stabilization necessary. Kazakhstan has designed and constructed numerous underground space works which can lead to ground deformations, large settlements and foundation collapse, especially in soft soils. Severe ground movements may not only impact the structure that it supports but might also affect surrounding buildings due to close proximity of construction. Therefore, binding admixtures are generally used to improve marine clay deposits. In addition, a loose sand deposit can be also improved by artificial cementation, which is targeted to avoid any failure related to slope stability and soil liquefaction.

The goal of the research is to examine the effectiveness of Calcium Sulfoaluminate (CSA) in geotechnical applications, especially targeting cement-treated ground improvement. The carbon footprint of the widely used Ordinary Portland Cement (OPC) is much higher than CSA, which is examined as a new alternative with a lesser carbon footprint concerning global warming and climate change.

 

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