Incorporation of a nanotechnology-based additive in cementitious products for clay stabilisation

The mechanical performances and water retention characteristics of clays, stabilised by partial substitution of cement with by-products and inclusion of a nanotechnology-based additive called RoadCem (RC), are studied in this research. The unconfined compression tests and one-dimensional oedometer swelling were performed after 7 d of curing to understand the influence of addition of 1% of RC material in the stabilised soils with the cement partially replaced by 49%, 59% and 69% of ground granulated blast furnace slag (GBBS) or pulverised fuel ash (PFA). The moisture retention capacity of the stabilised clays was also explored using the soil-water retention curve (SWRC) from the measured suctions. Results confirmed an obvious effect of the use of RC with the obtained strength and swell properties of the stabilised clays suitable for road application at 50% replacement of cement. This outcome is associated with the in-depth and penetrating hydration of the cementitious materials by the RC and water which results in the production of needle-like matrix with interlocking filaments – a phenomenon referred to as the ‘wrapping’ effect. On the other hand, the SWRC used to describe the water holding capacity and corresponding swell mechanism of clays stabilised by a proportion of RC showed a satisfactory response. The moisture retention of the RC-modified clays was initially higher but reduced subsequently as the saturation level increased with decreasing suction. This phenomenon confirmed that clays stabilised by including the RC are water-proof in nature, thus ensuring reduced porosity and suction even at reduced water content. Overall, the stabilised clays with the combination of cement, GGBS and RC showed a better performance compared to those with the PFA included.     

分散性粘土判别试验研究

应用碎块、针孔、双比重计、孔隙水可溶盐和交换性钠百分比等五种试验方法,结合物理化学性质和矿物成分分析,对西郊、三坪两水库大坝心墙土样进行了多种方案的分散性试验及长期渗流条件下的渗透变形试验和盐分运移试验。认为三坪土样中钠离子的分散作用小于西郊土样,钙镁离子的抑制分散作用大于西郊土样,并且三坪土样中的蒙脱石含量低于西郊土样,因此三坪土样属于非分散性土,西郊土样属于过渡型土。土样施工用水对土样的分散性鉴定结果影响较小,而冲蚀用水对土样的分散性鉴定结果产生大的影响。在长期的渗流条件下土样中钠离子随水流易迁移,河水中的钙离子含量大,进入土体后能抑制土样的分散性,促使土体向非散性的方向发展。结果表明土样中钠离子和钙镁离子含量多寡和相对含量对粘土分散性具有重要的作用,蒙脱石的存在是粘土分散性的重要因素,河水对粘土分散性能将产生显著影响。     

A cids as chemical stabilizers of clay soils

Summary 1. In the acid stabilization of clay soils the aluminosilicate nucleus of the clay minerals is attacked. This process is accompanied by the escape of primarily the aluminum ion from the crystal lattice and the formation of depolymerized silicic acid. As the acid medium is neutralized to pH>3, the latter is condensed into an acid, highly hydrated silica gel, which cements the soil.2. The aluminum and, to a lesser extent, iron, calcium, and magnesium salts formed as a result of exchange reactions play a secondary role in the chemical stabilization process.3. Fluosilicic and phosphoric acids are most effective for treating clay soils. However, treatment with acids does not achieve the long-term stabilization of the surface horizons of soils subject to periodic freezing and thawing or wetting and drying out. Soils stabilized with phosphoric acid are biologically unstable.4. A serious disadvantage of the acid stabilization of clay soils is the technical difficulties associated with the need to mix acid with the soil and the impossibility of its injection into practically impermeable soils. This is an obstacle to the use of acid stabilization in foundation building.Scientific-Research Institute of Foundations. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 22–23, July–August, 1973.     

黏土中多离子体系的扩散机理研究

黏土微观结构、颗粒表面电场以及黏土孔隙液中离子之间相互作用对离子运移有着重要的影响,但如何考虑上述因素对离子运移的影响一直是个没有解决的难题。针对黏土颗粒表面电场对离子运移影响这一核心问题,从微观角度(纳米级)采用Nernst-Planck方程和Poisson方程描述离子在带电黏土多孔介质中的运移。在参考已有实验成果的基础上,建立了黏土中微观多离子运移数值分析模型,采用多场耦合分析有限元软件Comsol Multiphysics求解。数值分析表明:由于黏土颗粒表面负电荷的作用,阳离子浓度明显升高,阴离子浓度则明显降低;不考虑颗粒带电,阳离子和阴离子浓度分布相同。在颗粒表面形成明显的双电层,浓度越高,双电层厚度越小;浓度越低,双电层厚度越大。研究成果将有助于深入理解离子在黏土垫层中的扩散运移机理,为进一步宏观分析提供详尽的基础数据。     

粘性土层井孔抽水试验的参数识别

粘性土层属于弱透水层,其水流、溶质运移和地球化学过程对于水文地质条件和环境变化具有重要意义.通过抽水试验来获取粘性土原位水力学参数是对粘性土水文地质问题进行研究的必要手段,但由于其渗透性很小,不能采用和常规含水层一样的方法求参.粘性土中的单孔抽水试验与一般含水层中的微水试验具有较大的相似性,因此可以借用微水试验的计算公...     

Assessment of clay soils and clay-rich rock for clogging of TBMs

Shield tunnel drives in both, overconsolidated clays soils and sedimentary rock with clay minerals, frequently suffer extremely from hindrance due to clogging. The problem of clogging can have varying degrees, from locally blocked disk cutter housings to completely clogged excavation chambers with a blocked cutterhead. The clogging risk depends on multiple mineralogical and soil-mechanical parameters. The authors have more than 15 years of experience in practice and scientific research with the problem of clay clogging of TBMs. The paper shows the occurrence and risk for clogging in varying ground types and for different machine components, summarizes the available characterization methods for the stickiness of the ground, discusses a variety of laboratory tests for the assessment of clogging potential, explains a recently developed diagram for the assessment of clogging risks for all types of tunnelling machines, and introduces a new testing scheme for the evaluation of sedimentary rocks regarding clogging.