In the field of soil stabilization, only calcium silicate hydrate(CSH) and ettringite(AFt) as hydration products have been reported to directly contribute to the strength enhancement of the soil. A chloride dredger fi...In the field of soil stabilization, only calcium silicate hydrate(CSH) and ettringite(AFt) as hydration products have been reported to directly contribute to the strength enhancement of the soil. A chloride dredger fill, an artificial chloride saline soil, and a non-saline soil were stabilized by Portland cement(PC) and PC with Ca(OH)_2(CH) with different contents. A series of unconfined compressive strength(UCS) tests of stabilized soil specimen after curing for 7 d and 28 d were carried out, and the hydration products and microstructure of the specimens were observed by X-ray diffractometry(XRD), scanning electronic microscopy(SEM), and energy-dispersive X-ray analysis(EDXA). The results showed that the strengths of PC+CH-stabilized chloride saline soils were much higher than those of PC-stabilized soils. A new hydration product of calcium aluminate chloride hydrate, also known as Friedel's salt, appeared in the PC+CH-stabilized chloride saline soils. The solid-phase volume of Friedel's salt expanded during the formation of the hydrate; this volume filled the pores in the stabilized soil. This pore-filling effect was the most important contribution to the significantly enhanced strength of the PC+CH-stabilized chloride saline soils. On the basis of this understanding, a new optimized stabilizer was designed according to the concept that the chloride in saline soil could be utilized as a component of the stabilizer. The strength of the chloride saline soils stabilized by the optimized stabilizer was even further increased compared with that of the PC+CH-stabilized soils.展开更多
The synthesis of Friedel＇s salt （FS： 3CaO·Al2O3·CaCl2·10H2O） by the reaction of calcium chloride with sodium aluminate was investigated. Factors affecting the preparation of Friedel＇s salt, such as...The synthesis of Friedel＇s salt （FS： 3CaO·Al2O3·CaCl2·10H2O） by the reaction of calcium chloride with sodium aluminate was investigated. Factors affecting the preparation of Friedel＇s salt, such as reaction temperature, initial concentration, titration speed, aging time and molar Ca/Al ratio were studied in detail. XRD, SEM images and particle size distribution show that the reaction temperature, aging time and molar Ca/Al ratio have significant effect on the composition, crystal morphology, and average particle size of the obtained samples. In addition, the initial CaCl2 concentration and NaAlO2 titration speed do not significantly influence the morphology and particle size distribution of Friedel＇s salt. With the optimization of the operating conditions, the crystals can grow up to a average size of about 28 μm, showing flat hexagonal （or pseudo- hexagonal） crystal morphology. Moreover, two potential mechanisms of Friedel＇s salt formation including adsorption mechanism and anion-exchange mechanism were discussed. In the adsorption mechanism, Friedel＇s salt forms due to the adsorption of the bulk C1- ions present in the solution into the interlayers of the principal layers, [Ca2Al（OH-）6·2H2O]＋, in order to balance the charge. In the anion-exchange mechanism, the freechloride ions bind with the AFro （a family of hydrated compounds found in cement） hydrates to form Friedel＇s salt by anion-exchange with the ions present in the interlayers of the principal layer, [Ca2Al（OH-）6. 2H2O]＋- OH-.展开更多
基金Project(51008007)supported by the National Natural Science Foundation of ChinaProject(2013318J01100)supported by the Science and Technology Project of Ministry of Communications,China
文摘In the field of soil stabilization, only calcium silicate hydrate(CSH) and ettringite(AFt) as hydration products have been reported to directly contribute to the strength enhancement of the soil. A chloride dredger fill, an artificial chloride saline soil, and a non-saline soil were stabilized by Portland cement(PC) and PC with Ca(OH)_2(CH) with different contents. A series of unconfined compressive strength(UCS) tests of stabilized soil specimen after curing for 7 d and 28 d were carried out, and the hydration products and microstructure of the specimens were observed by X-ray diffractometry(XRD), scanning electronic microscopy(SEM), and energy-dispersive X-ray analysis(EDXA). The results showed that the strengths of PC+CH-stabilized chloride saline soils were much higher than those of PC-stabilized soils. A new hydration product of calcium aluminate chloride hydrate, also known as Friedel's salt, appeared in the PC+CH-stabilized chloride saline soils. The solid-phase volume of Friedel's salt expanded during the formation of the hydrate; this volume filled the pores in the stabilized soil. This pore-filling effect was the most important contribution to the significantly enhanced strength of the PC+CH-stabilized chloride saline soils. On the basis of this understanding, a new optimized stabilizer was designed according to the concept that the chloride in saline soil could be utilized as a component of the stabilizer. The strength of the chloride saline soils stabilized by the optimized stabilizer was even further increased compared with that of the PC+CH-stabilized soils.
基金Funded by International Science&Technology Cooperation Program of China(No.2013DFB70220)the National Natural Science Foundation of China(No.21076212)the Natural Science Foundation of Guizhou Province of China(No.[2014]2003)
文摘The synthesis of Friedel＇s salt （FS： 3CaO·Al2O3·CaCl2·10H2O） by the reaction of calcium chloride with sodium aluminate was investigated. Factors affecting the preparation of Friedel＇s salt, such as reaction temperature, initial concentration, titration speed, aging time and molar Ca/Al ratio were studied in detail. XRD, SEM images and particle size distribution show that the reaction temperature, aging time and molar Ca/Al ratio have significant effect on the composition, crystal morphology, and average particle size of the obtained samples. In addition, the initial CaCl2 concentration and NaAlO2 titration speed do not significantly influence the morphology and particle size distribution of Friedel＇s salt. With the optimization of the operating conditions, the crystals can grow up to a average size of about 28 μm, showing flat hexagonal （or pseudo- hexagonal） crystal morphology. Moreover, two potential mechanisms of Friedel＇s salt formation including adsorption mechanism and anion-exchange mechanism were discussed. In the adsorption mechanism, Friedel＇s salt forms due to the adsorption of the bulk C1- ions present in the solution into the interlayers of the principal layers, [Ca2Al（OH-）6·2H2O]＋, in order to balance the charge. In the anion-exchange mechanism, the freechloride ions bind with the AFro （a family of hydrated compounds found in cement） hydrates to form Friedel＇s salt by anion-exchange with the ions present in the interlayers of the principal layer, [Ca2Al（OH-）6. 2H2O]＋- OH-.
