كليدواژه :
رس متورم شونده , آهك , نانوذرات سيليكا , دما , فعاليت پوزولاني , خصوصيات مهندسي
چكيده فارسي :
در پژوهش حاضر بطور همزمان تاثير دماي عمل آوري و افزودن نانوذرات سيليكا (NS) بر عملكرد آهك در اصلاح خصوصيات مهندسي خاك تورمي از طريق انجام آزمايش هاي مختلف بزرگ ساختاري و ريزساختاري تجزيه و تحليل شد. نتايج بدست آمده نشان ميدهد با كاهش دما (به ويژه دماي زير C° 20 و در زمان هاي نگهداري كمتر از 28 روز)، فعاليت پوزولاني و رشد تركيبات سيماني (مانند نانوساختارهاي CSH و CAH) دچار اختلال شده و فرآيند اصلاح خاك بعد از افزودن آهك عمدتاً ناشي از واكنشهاي كوتاه مدت (تبادل كاتيوني و افزايش فشار اسمز) رخ ميدهد. در اين شرايط علاوه بر افزايش مقدار افزودني لازم براي كنترل تورم، مشخص شد بهبود ساير پارامترهاي ژئومكانيكي خاك (ازجمله ظرفيت باربري و پتانسيل نشست پذيري) بسيار اندك ميباشد. از طرفي، نتايج بيانگر آنست كه در حضور تركيب آهك-نانوذرات سيليكا (LNS) اثر نامطلوب افت دما بر مشخصات مهندسي نمونه ها كاهش يافته و بر خلاف محدوديت عملكرد آهك، مقاومت فشاري نمونه هاي اصلاح شده با LNS متناسب با افزايش ماده افزودني روند كاملاً صعودي دارد. بر اساس طيفهاي پراش اشعه ايكس و تصاوير SEM، علت حساسيت كمتر نمونه هاي حاوي LNS به دما و زمان نگهداري و رفتار بهتر در مقايسه با آهك تنها، به دليل انجام سريعتر و بيشتر واكنشهاي پوزولاني و افزايش تراكم ساختار ارزيابي شد. بر پايه نتايج اين مطالعه، استفاده از LNS (به خصوص در هواي سرد و زمانهاي محدود عمل آوري) ضمن شدت بخشي تاثير آهك، مصرف افزودني را تا 50 درصد كاهش خواهد داد.
چكيده لاتين :
Expansive clayey soils can undergo periodic volumetric changes in the form of ground heave and settlement when subjected to moisture fluctuations. Such changes exert stress and serious problems to geotechnical structures, if not adequately taken care of. Lime continues to be commonly used for treatment of these soil types; however, some restrictions are associated with its application. In the present study, series of macro and micro level tests are carried out to assess the effects of environmental condition and SiO2-nanoparticles (NS) on the performance of lime treatment. Tests include swelling potential, unconfined compression strength (UCS), consolidation, pH and electrical conductivity (EC), adsorption, X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses and are performed at various curing periods (1, 7, 28 and 90 days) and different temperatures (10, 20, and 40 °C). To achieve the stated aim, lime and lime/NS (LNS) mixtures are separately added to highly expandable clay at wide ranges from 0% to 30% by mass, respectively. The results show that temperature, especially in the initial time of curing, has a prominent role on the geo-mechanical properties of lime treated soil samples. It is also found out that the reduction in the temperature -particularly at inadequate curing (lower than 28 days)- provides a deleterious impact on the pozzolanic activity and decreases the formation of cementing compounds such as Calcium-Silicate-Hydrate (CSH) and Calcium-Aluminate-Hydrate (CAH) gels. In this case, the process of soil modification is mainly due to the short-term reactions (i.e. cation exchange and increase in osmotic pressure), increasing the amount of additives (up to two times) to control the swelling power. On the other hand, corporation of SiO2-nanoparticles in the binder system causes a reduction in the detrimental effects of low temperature on the engineering parameters of lime-treated products and decreases their sensitivity to the time of curing. The samples amended with the LNS blend exhibit a continuous development of soil mechanical capacity as the additive content increased. They are less deformable and show a decrease in their compression index by nearly 40% as compared to sole lime. Based on the XRD and SEM test results, the superior influences of LNS are mainly ascribed to the higher and faster formation of cementitious compounds. In fact, at the presence of LNS, the silicate gel can be immediately formed to coat and bind the clay particles together; as a result of direct interaction of lime and silica from NS. Whereas, by addition of lime alone, the gel is produced only by the removal of silica from the clay minerals that needs further time to complete its formation; thus, the lower modification is occurred, especially at curing times shorter than 28 days. Moreover, NS reduces the pore sizes and serves to distribute the new crystalline phase (e.g. CSH gel) in a more homogenous fashion in the available space. This micro-structural reorganization - due to the LNS treatment - could rapidly block off the soil voids and greatly interlock the clay particles together. This will provide higher environmentally-stable materials with lower cost and energy as compared to standalone lime. According to the results and discussions, utilization of LNS mixture gives a promising way for increasing the efficiency of lime stabilization and decreasing additive consumption.
