| There are lots of red clay of Quaternary from alluvial-diluvial in WuHan City. The mail components of clay mineral are kaolinite and illite, also small amount of chlorite and vermiculite; the non-clay minerals are quartz, feldspar and mica. Because of containing hematite, the red clay's color is red. This type of red clay is characterized by medium-porosity, high-plasticity, medium-water content, medium-low compression, medium-weak expansion. With the rapid development of China's economy, red clay was used as construction materials and foundation. However, when the village dirt roads, temporary roads, building sites, anti-seepage projects of red clay meet rain, bad road traffic is too bad to use. When the weather is fine, the original road surface has changed dramatically. In addition, the red clay softened by the water has also arisen lot of project diseases, for example, because of fracture of red clay, the red clay swells when meeting water, which will cause inhomogeneous subsidence damage and infrastructure faults; when surface water flows into cracks of red clay, it will soften the soil, decrease the work performance; the foundation and slope of crack red clay are prone to collapse, landslides. At the long-term of soil-reinforcement project, taking into account the resource conservation and environmental protection, people gradually realized that the use of cement, lime, fly ash and other traditional soil-reinforcement material have a lot of shortage, which can not meet the needs of social development.The study shows that the conflict between the adverse physical properties and good mechanical properties of red clay mainly depends on the thickness of adsorbed water film of red clay granules. The property, type and thickness of adsorbed water film of red clay not only has correlation with plasticity index, hydration-expansion, shrinkage, specific surface area, pore structure, micro-structure, soil-water characteristic curve and shear strength etc. physical and mechanical properties, but also pH, conductivity rate, absorption, Zeta potential, cation exchange capacity and exchangeable cation etc. electrochemical properties. At the same time the adsorbed water of red clay is an essential factor to trigger geological disasters and environmental damage. Therefore, research on the adsorbed water of red clay is very necessary and urgent. In order to reduce the thickness of adsorbed water film. Ion Soil Stabilizer (ISS) is used to deal with red clay. ISS is a complex of ion surfactant. The hydrophilic group and hydrophobic group of ISS can significantly reduce the surface tension of water. Added into the red clay, ISS can not only occupy and wet the surface of soil and capillary, but also exist on the surface and capillary. ISS can exchange with polarity water molecules and exchangeable cations of the red clay surface, thus ISS can decrease the charge of the soil particle surface, thin the thickness of diffusion layer, improve water stability and the intensity of red clay. ISS reinforces the red clay, which has the characteristics of low cost, easy construction, environmental protection, high intensity and small amount of shrinkage. For China to build a resource-saving and environment-friendly society, to improve rural living and ecological environment, to promote rural economic development and the establishment of a harmonious society is an important practical significance.At present, the study of red clay adsorbed water have made some progress, but the study of mechanism of ISS with red clay adsorbed water is relatively low and there are some storages such as following: First of all, the water nature, existence boundary and thickness of red clay adsorbed water before and after treating with ISS. In the past it has not been a unified understanding, the majority of scholars believe that the main mineral compositions of red clay are kaolinite and illite, so its adsorbed water is strong adsorbed water. In the role of free iron oxide, it is very stable in nature. Adsorbed water is not easy to break away from the red clay and the thickness is several layers of water molecules only. This conclusion is very vague, and did not explain that non-swelling clay mineral composition of the red clay, in the role of strong adsorbed water, how the free-swell reaches nearly 50%. After treatment with the ISS, the free expansion rate decreased significantly. What water ISS remove, what is the existence forms, exist boundary and the thickness? Secondly, the problem of quantitative measurement of red clay adsorbed water after treatment with ISS. In the past, the guessing results of increase or decrease the adsorbed water film according to the physical and mechanical properties and electrochemical properties is clearly unscientific. After joining ISS, what is the number of weight loss of adsorbed water, how the hydration behavior impact on the project property. In order to resolve this problem, it is necessary to set up adsorbed water test method of quantitative measurement. Once again, the problem of research on the mechanism of ISS with red clay adsorbed water. After ISS reinforcing the red clay, if not set up a mechod from a macro to micro-research, the research will remain at the surface hydration and penetration. Therefore, in order to research on the nature, existence limit and thichness of red clay adsorbed water film, to study of Zeta potential, the type and quantity of cation exchange, combination of physical and mechanical properties, electric chemical nature and micro-test results are necessary to analysis the mechanism of ISS-reinforcing adsorbed water of red clay.In view of the above analysis, in order to research on the mechanism of ISS treating adsorbed water, the article firstly revolutionary carry on the following physical, mechanical and electrochemical properties test of red clay treated by ISS, for example, plastic, hydration expansion, shrinkage, specific surface area and pore size distribution, micro-structural characteristics, soil-water characteristic curve, shear strength, cation exchange capacity, exchangeable cation and Zeta potential, etc. ,from the macro to micro-mechanism to give preliminary explanation. On this basis, the mechods of quantitative analysis of red clay adsorbed water was established, that is thermogravimetry, differential scanning Calorimetry and infrared spectroscopy; use of the flat model of red clay particle to calculate the adsorbed water with the quantitative method. Finally the model of ISS-reinforcing red clay is set up to analysis the nature and distribution of red clay adsorbed water. The reaction mechanism of 1SS with adsorbed water is analyzed from cation exchange capacity, double-layer changes and thickness of adsorbed water.In this paper, the following research works have been done.First of all, physical and mechanical properties test of a different ratio of ISS on red clay was carried on, the test results show:①Different proportions of ISS added, red clay can be found the minimum plastic index that can be used as the optimal ratio of reinforcing red clay;②X-ray diffraction and chemical composition analysis results show, after adding ISS, there is no new mineral or crystal, only small distances of crystalline surface changes. The chemical composition of red clay adding ISS has no change; the H2O content is 1.88 times than the unreinforcement soil. That is to say ISS will not only be able to get rid of or reduce the thickness of adsorbed water of red clay, but also to reduce the number of interlayer water of halloysite;③The red clay added ISS can improve the shear strength, but no contribution to the sliding friction and occlusion friction, mainly enhance original cohesion and reinforcing cohesion of soil particles;④ISS can replace the exchangeable cation and the polar water molecules of particle surface, thereby reducing the the expansion and shringkage of red clay. Red clay with a shrinkage, the main reasons is not fully explained of free iron oxide, halloysite's inter layer water must have the contribution;⑤Kaolinite crystals, exchangeable cation, free iron oxide and hydrophilic group (negative) of ISS, in the role of a strong ionic bond, can form a larger aggregates and stacked body. By this way, the specific surface area of red clay treated by ISS will be reduced;⑥The cumulative pore volume decreased with average pore diameter decreased of red clay treated with ISS. Using ISS to deal with red clay, only the pore size is less than the size of large pores can by decrease;⑦Liquid nitrogen freeze- vacuum drying can avoid the crystallization of water into ice and will not appear about 9% of the volume expansion to prevent destroy the structure of soil. After adding ISS, it can be seen that micro-structure of red clay is face to face and the edge to face aggregates. Some particles are flat and like-hexahedron kaolinite particles, the stack is very compaction. Cementation material of surface is free oxides and ISS's polymer chain;⑧After added ISS, the red clay's water-holding capacity increase with the matrix suction increase. At 500kPa, the water content of reinforced red clay is less than the non-reinforcement red clay. Standard moisture absorption water content of red clay reinforced by ISS is less than the non-reinforcement red clay.Secondly, The electrochemical properties test was carried on a different ratio of ISS, and the results analysis is as following:①The net charge of red clay's clay minerals is negative charge, ISS can replace cation and the polar water molecules, after that, the red clay particle still show the negative charge;②After ion exchange of ISS with the red clay, the pH of red clay solution decrease, and the conductivity of ISS solution increase;③The adsorption of red clay from solution have to consider three types of force: the red clay with ISS, red clay and water, ISS and water;④After treatment with ISS, the cation exchange capacity of red clay decrease, which will indicate its negative electricity decrease, the hydration, swelling and dispersion decline, the thickness of adsorbed water film thin. The exchangeable cation of red clay decrease with the time increase, which indicates the cation exchange capacity is different in the surface and interlayer. The surface can be instantaneous exchange; on the interlayer surface, it wil take a long time to achieve the required balance, because the exchangable ions before arrival at the purpose will move in the interlayer. Constrained by the laws of ion diffusion, it often requires a long time to achieve balance.⑤From the results of cation exchange of four components, the exchangeable cation of the red clay is mainly Ca2+, and the total amount of exchangeable cations is lower or much lower than the cation exchange capacity. Because red clay is alluvial-diluvial, in the process of laterization, the ion of K+, Na+, Ca2+, Mg2+ has been filtered, and has little effect on the thickness of adsorbed water film, but free iron oxide, silicon, aluminum ion and its interaction with the red clay have great impact on adsorbed water;⑥ISS solution contains a large number of high charge cation which can exchange the cation in the red clay and make the thickness of adsorbed water film thin, Zeta potential drop. That will open the force between soil and water molecules, and make the water molecules leave from the soil surface into the surrounding water freely. At last, most of the adsorbed water of soil can become discharged from the soil into free water.Thirdly, the thermogravimetric analysis, differential scanning Calorimetry and Fourier transform infrared spectroscopy technology is use to quantitative analysis the adsorbed water of the red clay , the results show:①The combination of thermogravimetric analysis and differential scanning Calorimetry to quantitatively calculate the adsorbed water, and Fourier transform infrared spectroscopy to determine the nature, type and limit of adsorbed water of red clay surface are feasible.②The TG / DSC curves of air-dried red clay show that ISS can significantly reduce the weak adsorbed water of the red clay, from 0.58 percent to 0.42 percent down, lower by 28%; strong adsorbed water also can be reduced from 0.57 percent to 0.45 percent, lower by 21%.③The interlayer water of halloysite is reduced after adding ISS.④At high step of infrared spectra there are three typical absorption bands, 3700cm-1, 3650cm-1 and 3620cm-1, whose transmission intensity decrease one by one. The characteristics of red clay spectroscopy show it is not well-crystalline kaolinite, similar to halloysite. Adding ISS, the internal OH and OH in the structure surface has not changed. The rate of absorption peak of adsorbed water and Si-0 bond decrease, that is to say adsorbed water in the red clay reduce, but ISS can not completely replace the strong adsorbed water of red clay surface.⑤According to the formula for calculating the thickness of weak adsorbed water before and after adding ISS. In the status of liquid limit, the thickness of weak adsorbed water film of red clay is 112.97nm, after treatment with ISS, the thickness of weak adsorbed water film of red clay can be reduced to76.74nm, 20% decline.Through the above analysis, the mechanism of ISS-reinforece red clay can be described as following:①The hydrophilic-group of ISS can combine with red clay particle, but the hydrophobic-group outward from the surface of clay particles to form a reservoir to protect the red clay. In this way, the adsorbed water of red clay surface can be forced out by hydrophobic-group.②ISS can reduce the surface tension of solution. When ISS occupy the location of red clay surface, moisten the surface of particle, decrease the surface tension of adsorbed water, in the role of hydrophobic, the surface adsorbed water will be replaced.③The adsorbed water and exchangeable cation of red clay can be replaced and form free water after adding ISS. That make the thickness of adsorbed water film thin and density of red clay increase, also make the physical and mechanical properties improved. This organic red clay has the property of hydrocarbons of hydrophobic on the surface, is often water resistant property.④ISS can make the solution high ion concentrations, and exchange the exchangeable cation and polar water molecules on the surface. The result of exchange is to enable the exchangeable cation and polarity water molecules separate from the red clay particle, thereby reducing the Zeta potential of red clay, make the thickness of adsorbed water thin. At the same time, ISS can increase the concentration of electrolyte solution, in the role of penetration, the adsorbed water diffuse to solution, the electric double layer and adsorbed water thinning. Although ISS and replace the exchangeable cation and polar water molecules of the surface of red clay, make the electric double layer thin, make the thickness of adsorbed water reduce, but ISS can not change the structure of electric double layer. Zeta potential of red clay still exists. |
