مطالعه آزمايشگاهي رفتار مكانيكي مخلوط ماسه و لاستيك

گسترش صنعت خودرو سبب شده است كه انباشت حجم لاستيك‌هاي فرسوده به ‌عنوان زباله‌هاي شهري به يك مشكل بزرگ اقتصادي، زيست محيطي و اجتماعي تبديل شود. مخلوط كردن خرده‌هاي لاستيك با ماسه و استفاده از آن به ‌عنوان مصالح سبك‌ وزن يكي از گزينه‌هاي ممكن براي جلوگيري از انباشت آنها در محيط زيست مي­باشد. در اين تحقيق براي اولين بار دانه‌هاي ماسه و خرده‌هاي لاستيك با منحني دانه‌بندي يكسان مخلوط شده است. اين كار به جهت به حداقل رساندن تفاوت اندازه‌ي بين دانه‌هاي مخلوط انجام پذيرفته است؛ بنابراين، رفتار مكانيكي مخلوط بدست‌آمده، تنها بر پايه نسبت حجمي آن و ساز و كار داخلي بين دانه‌هاي لاستيك و ماسه استوارمي­باشد. به منظور بررسي رفتار مكانيكي مخلوط، آزمايش‌هاي سه محوري زهكشي شده فشاري و كششي تحت تنش‌هاي همه‌جانبه 50، 100 و 200 كيلو پاسكال انجام شده است. نتايج اين تحقيق نشان مي‌دهد كه سهم حجم ذرات لاستيك بر رفتار فشاري و كششي مخلوط قابل‌توجه مي باشد. درواقع، دانه‌هاي لاستيك به‌عنوان يك ساز و كار داخلي، پارامترهايي چون؛ حداكثر تنش انحرافي، سختي اوليه نمونه‌ها، مدول الاستيسيته، كرنش شعاعي، زاويه اصطكاك، اتساع و زاويه اتساع نمونه‌ها را كاهش مي‌دهند و در عين حال باعث افزايش كرنش متناظر با تنش انحرافي حداكثر، شكل‌پذيري نمونه‌ها، كرنش محوري، چسبندگي، مقادير و و شيبِ خطِ حالتِ بحراني مي‌شوند. رفتار تنش-كرنش مخلوط‌هاي ماسه و لاستيك نشان مي‌دهد كه با افزايش نسبت اختلاط لاستيك به بيش از 20 درصد، در تمامي تنش‌هاي همه‌جانبه، نقطه حداكثري مشخصي در نمودار تنش-كرنش وجود ندارد. درنهايت چنين بدست آمد كه، رفتار مكانيكي مخلوط‌ خرده لاستيك‌هاي دانه‌اي و ماسه با منحني دانه‌بندي يكسان براي نسبت اختلاط لاستيك كمتر از 20 درصد، توسط ماسه و براي نسبت اختلاط بيشتر از 30 درصد، توسط لاستيك كنترل مي‌شود.

The number of scrap tires is increasing rapidly in both developed and developing countries due to the steady rise in the number of vehicles. Scrap tires accumulation in the environment causes several social, economical and environmental issues all around the world. Recent studies showed that this material can be considered as an alternative for some conventional materials in construction industries. Scrap tires are used as a whole or in processed pieces in geotechnical engineering to help reducing the disposal effects and improve mechanical characteristics of soils. It is becoming quite common to mix soils and processed rubber particles in different civil and geotechnical constructions like lightweight backfill, road subbase, embankment fills, slopes, asphalt construction, sound barriers, rail construction and foundation reinforcement. However, the employment of these mixtures in real scale projects requires a better understanding of the mechanical performance of the mixtures. The mechanical response of sand-rubber mixtures, initial fabric skeleton and interaction mechanism between constituents depend on several factors such as volume proportions of the mixtures, confinement stress and size ratio between constituent’s grains. The idea of mixing sand and rubber particles with the same particle size distribution was employed in this study to minimize size contrast effect between the grains. Therefore, the mechanical behavior of the mixtures is only based on the volume proportions of the mixtures and internal mechanism between sand and rubber particles. To do so, drained triaxial compression and extension tests were conducted in conventional triaxial apparatus on sand-rubber mixtures. The triaxial samples were made using moist tamping method in three successive layers to avoid high segregation between rubber and sand particles. The effect of rubber particles was significant on drained mechanical response of sand-rubber mixtures. Peak strength reduction followed by axial strain increase corresponding to the peak strength were observed by increasing the rubber fractions of the mixtures. Consequently the initial elastic modulus of sand-rubber mixtures reduces by increasing the rubber proportions of the mixtures. The contribution of volume proportions of the rubber particles inside the mixtures was found to be significant on the deformation behavior of the mixtures. The volumetric response of sand-rubber mixtures shows that increasing the rubber proportions of the mixtures increases the compressibility tendency of the mixtures which reduces the dilatancy of the mixtures. The angle of friction and intercept cohesion reduces and increases by increasing the rubber fractions of sand-rubber mixtures which are consistent with what have been observed by the previous investigations in the literature. The critical state line parameters of the mixtures were highly dependent on rubber proportions of the mixtures as the slope of critical state line increases by increasing the rubber fraction of the mixtures. The radial strain of the mixtures decreases by increasing the rubber proportions of the mixtures which could be the effect of replacing sand particles by rubber particles in force chains. In general, the mechanical response of sand-rubber mixtures was mostly controlled by sand particles where FR ≤ 20% and by rubber particles where FR > 30%.