تاثير سرباره‌هاي صنعت فولادسازي بر خصوصيات ژيوتكنيكي و مشخصات كاني‌ساخت رس متورم‌شونده اسمكتيت

Effect of iron industry slags on the geotechnical properties and mineralogy characteristics of expansive clayey soils

هدف از پژوهش حاضر بررسي قابليت كاربرد تركيبات زايد صنعت فولادسازي ازجمله سرباره كوره بلند (GBFS) و سرباره ساخت فولاد (BOS)، در اصلاح رفتار خاك هاي متورم شونده است. بدين منظور در شرايط آزمايشگاهي مقادير صفر تا 30 درصد وزني، GBFS و BOS به رس تورمي اسمكتيت اضافه و پس از عمل آوري در چندين بازه زماني مختلف (2 ساعت تا 90 روز)، مجموعه اي از آزمايش هاي ژيوتكنيكي و ريزساختار شامل حدود اتربرگ، تعيين هدايت الكتريكي و pH، اندازه گيري تورم، مقاومت فشاري محدود نشده و تهيه طيف پراش اشعه ايكس، در راستاي تجزيه و تحليل اندركنش خاك با سرباره ها انجام شد. آهك نيز به عنوان يك ماده افزودني متداول و با هدف ارزيابي عملكرد GBFS و BOS، به صورت مجزا مورد استفاده قرار گرفت. نتايج نشان مي دهد در زمان هاي كم عمل آوري و با افزودن حدود %20 سرباره، بيشتر ناشي از انجام واكنش هاي كوتاه مدت شامل تبادل كاتيوني و افزايش فشار اسمز، تورم خاك كنترل مي-شود. از طرفي بر اساس طيف هاي اشعه ايكس مشخص شد با عمل آوري مناسب (بيش از 7 روز) و به دليل رشد تركيبات سيماني به ويژه در نمونه هاي حاوي BOS، مصرف سرباره لازم براي كنترل تورم تا 4 برابر كاهش خواهد يافت. اضافه كردن سرباره و افزايش زمان نگهداري، مانند حضور آهك باعث بهبود خصوصيات مقاومتي خاك نيز مي‌شود. به گونه‌اي كه مقاومت فشاري نمونه اسمكتيت همراه 30 درصد BOS پس از 90 روز نگهداري، تقريباً 12 برابر نسبت به نمونه اوليه افزايش مي يابد. اگر چه در حضور GBFS به دليل قابليت انحلال كمتر و درنتيجه محدوديت فعاليت پوزولاني، تغييرات كمتري مشاهده شد. در مجموع نتايج به دست آمده از اين مطالعه بيانگر آن است كه استفاده از زباله هاي صنعت فولادسازي به ويژه BOS، جايگزين مناسبي براي آهك در تثبيت خاك هاي رسي مسيله دار بوده كه علاوه بر كاهش هزينه هاي اجرايي، كمك موثري در مديريت پسمانداري اين تركيبات و حفظ محيط زيست خواهد كرد

Expansive clayey soils, which are predominantly distributed in different countries such as Iran, have a complicated behavior depending on the soil mineralogy and the pore fluid chemistry. Heaving and settling in these type of soils may pose considerable problems and severe damage to geotechnical structures and geo-environmental projects that come into their contact or constructed out of them and consequent distress to people if not adequately taken care of. On the other hand, the proper disposal of by-product materials and industrials wastes that are produced in the large amount throughout the world is one of the major issues for environmentalists since leaving them to the environment directly may cause considerable health problems. Hence, the aim of this study is to evaluate and investigate the effects of two type of iron industry slags on the on the geotechnical properties and mineralogy characteristics of expansive clayey soils. To achieve the objectives, the admixtures were added to the soil samples in proportion of zero to 30 percent by weight and tests of the pH value, electrical conductivity (EC) measurement, consistency limits, swelling, unconfined compression strength (UCS) and micro level analysis were performed on those samples at different curing period (i.e. 1, 3, 7, 14, 28, 45 and 90 days). The obtained results revealed that under the limited curing condition (i.e. less than 3 days) and with the addition of appropriate amount of slag, the swelling potential of soil samples could be completely eliminated. This is mainly due to the short term reactions (i.e. cation exchange and osmotic pressure increasing) as confirmed by pysicho-chemicals experiments. Based on the micro level tests, it was found that with enough time of curing of soil samples (more than 7 days) and due to the growth of the cementation compounds such as calcium silicate hydrates (CSH) and calcium aluminate hydrates (CAH), especially in samples containing converter, the needed admixture to control heave potential of soil will be declined up to 4 times. The presented results indicate that highly expansive clayey soils can also be treated satisfactorily by calcium hydroxide and following adequate curing due to development of the pozzolanic reactions. However, with a further increase in the content of latter additive, the pozzolanic activity cannot continuously take place and the excessive addition of additive caused a reduction in the strength improvement factor (SIF), which negatively affect the geo-mechanical performance of modified soil. Such an undesirable effect was not observed in case of the slags. The samples containing slags show a continuously decrease in the swelling potential and a progressive increase in the compression strength with increasing the additive content and curing time that could overcome the difficulties associated with the expansive clays. For example, the compression strength of soil sample with 30% slag and after 90 days of curing was almost 12 times higher than the untreated sample. The macro and micro level test results of this study indicate that the utilization of iron slags, especially converter, is a good alternative for soil stabilization which reduces the cost of soil treatment and help the management of these by-products