Düzenli depolama tesislerinde kullanılmak üzere kum-bentonit karışımlarının kireç ve yüksek fırın cürufu katkısı ile iyileştirilmesi
Investigation of lime and blast furnace slag treated sand-bentonite mixtures to be used in waste disposal facilities
Yazar: AYŞE NEVA İNCESU
Danışman: YRD. DOÇ. DR. BERRAK TEYMÜR
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Zemin Mekaniği ve Geoteknik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2012
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Atık yönetimi, günümüzde kontrolsüz nüfus artışı, endüstriyel gelişmeler ve buna bağlı olarak artan atık miktarı nedeni ile oldukça önem kazanmış durumdadır. Atıkların düzenli depolanması, gelişmiş ülkelerde uygulama kolaylığı ve kalıcı çözüm sağlaması açısından yaygın olarak tercih edilmekte olan bir bertaraf yöntemidir. Ancak düzenli depolama tesisi tasarımında belirli kriterler dikkate alınmadığı takdirde atıkların doğaya ve insan sağlığına zarar vermesi kaçınılmazdır. Sahanın hazırlanması, geçirimsiz tabaka oluşturulması, atıkların serilmesi ve sahanın örtülmesi gibi temel aşamalardan oluşan düzenli depolama tesisi tasarımında tabanda geçirimsizlik oluşturulması, sızıntı sularının yeraltı suyuna karışmasını önlemek amacı ile özellikle önem arz etmektedir. Yapılan çalışmada, endüstriyel atık olarak ortaya çıkan malzemelerin düzenli depolama tesislerinin inşasında kullanımının uygunluğu araştırılmış, bu sayede depo tabanını meydana getiren malzeme özelliklerinin iyileştirilmesinin yanı sıra mevcut endüstriyel atık miktarının azaltılması planlanmıştır. Bu amaç doğrultusunda belirli oranlarda hazırlanan kum ve bentonit karışımlarına kireç ve yüksek fırın cürufu (YFC) ilave edilerek karışımlar hazırlanmış ve kompaksiyon, konsolidasyon ile serbest basınç deneylerine tabi tutularak malzemelerin oturma, geçirimlilik ve mukavemet özellikleri incelenmiştir. Çalışmada % 116 likit limit değerine sahip CH sınıfı bentonit kullanılmıştır. Kum ve YFC malzemeleri, karışımlarda üniformluk sağlamak amacı ile 40 numaralı elekten elenerek yalnızca elek altında kalan malzeme kullanılmıştır. YFC, Ereğli Demir Çelik Fabrikası'ndan temin edilmiş, kireç olarak ticari paket kireç kullanılmıştır. Çalışmalar öncelikle en uygun bentonit miktarını belirlemek üzere % 40, % 50 ve % 60 bentonit içerikli kum ve bentonit karışımları üzerinde yapılmış ve uygun oran % 50 bentonit - % 50 kum olarak belirlenmiştir. Karışım içerisindeki bentonit miktarındaki artışın geçirimlilikte azalmaya neden olduğu anlaşılmıştır. Mukavemet ve birim deformasyon özellikleri üzerinde bentonitin önemli ölçüde etkisi görülmemiştir. Kireç içeriği ise % 2 ile % 6 aralığında çalışılmış, % 50 bentonit oranı sabit tutularak % 2, % 4 ve % 6 oranında kireç içeren karışımlar hazırlanmıştır. Çalışmalar sonucunda kireç katkısının geçirimliliği azaltarak basınç dayanımını kum ve bentonit karışımlarına oranla artırdığı görülmüştür. Genel anlamda malzeme özelliklerini düzenli depolama tesislerinde kullanımının uygunluğu açısından olumlu yönde etkilediği kanaatine varılmıştır. Kireç etkisinin araştırılması sonucu yüksek fırın cürufu katkısının % 6 kireç içerikli malzemeye yapılmasına karar verilmiştir. % 50 Bentonit ve % 6 kireç oranı sabit tutularak, % 1, % 2 ve % 3 oranında cüruf katkısının, karışımların mukavemet ve geçirimlilik özellikleri üzerindeki etkileri incelenmiştir. YFC katkısı % 1 oranında katıldığında geçirimliliği önemli ölçüde azaltmış ancak artan katkı miktarı ile geçirimlilikte artış gözlenmiştir. Basınç dayanımını ise önemli ölçüde artırdığı belirgin şekilde anlaşılmaktadır. Yapılan çalışmalar sonucunda kireç ve yüksek fırın cürufu katkısının kum-bentonit karışımlarının özelliklerini düzenli depolama tesislerinde uygulanabilirliği açısından olumlu yönde etkilediği anlaşılmıştır.

Abstract:
Ascending life standards worldwide bring out the consequences to deal with, as the effect of human on nature grows with all technological and industrial improvements. As amount of products used increase and the term of usage decrease, consumption rate cannot get as fast as production, resulting in excess amount of waste products and consequently waste management becomes one of the most serious issues. Disposing of waste in a landfill is the most applicable and preferred method in developed countries since the method does not bring out new waste products and is a permanent solution. However when application is not right, there is a big chance of serious danger for the environment to occur, thus it is important to design the landfill area in the manner that soil, air and underground water is not affected from contamination. It is essential to control the interaction between environment and waste material; especially to prevent underground water from contamination should be considered before designing the landfill. Therefore, an impermeable layer at the base of disposal area is constructed with various materials. Properties of the material to be used as barrier in waste disposal areas are determined by regulations. Generally proposed hydraulic conductivity value is not bigger than 1x10-8 m/s, which may differ for various types of waste products and territories. Clay is frequently preferred due to low permeability characteristics and is generally applied with other natural or produced materials. Usage of bentonite and sand mixtures has became widely preferred within last years, with alternatives of geosynthetic clay liners or geomembranes. In this study, the material to be treated is chosen to be natural or naturally produced without bringing out any new waste products. The aim of this study is to investigate the improvement of bentonite-sand mixtures through laboratory tests to be used as barrier material in waste disposal areas considering the usage of industrial waste materials in order to reduce the amount of waste products and increase the barrier material properties.In this study, lime only (BESL) and lime with blast furnace slag (BFS) treatments are applied on sand-bentonite (BES) mixtures in order to determine settlement, strength and permeability characteristics. Bentonite clay classified as CH according to ASTM with a liquid limit of 116 and unit weight of 25.7 kN/m3 is used in the mixtures with sand, lime and blast furnace slag (BFS). Sand and BFS used is sieved from standard #40 sieve to eliminate finer grains and to acquire more uniform mixtures. Specific gravities of sand including mixtures showed that sand addition increased the unit weight of the mixtures. Swelling of the bentonite is investigated before experimenting the properties of the mixtures and results showed that swelling amount is insignificantly low.Standard proctor tests are done in order to obtain maximum dry unit weights and optimum water contents and to prepare consolidation test samples. Apart from 100 % bentonite, no distinct changes occur in maximum dry unit weights and optimum water contents with any bentonite, lime nor BFS treatment.Consolidation tests are done in order to investigate settlement and permeability of prepared samples to analyse applicability as barrier materials. Mixtures are prepared progressively to determine suitable percentages of bentonite and lime. First series of the mixtures consist of 100 % bentonite (B), 60 % bentonite ? 40 % sand (BES40) , 50 % bentonite ? 50 % sand (BES50), 40 % bentonite ? 60 % sand (BES60) in order to determine proper bentonite amount in barrier material. After standard proctor test results, specimens for odometer tests are prepared compacted with water content of about 2 % above the optimum. Standard proctor test results showed that bentonite-sand ratio is not significantly effective on compressibility of the mixtures between 40 to 60 percent.Using oedometer test results, settlement and hydraulic conductivities of the mixtures are calculated. Results of each BES mixture can be defined similar since there is no significant change in hydraulic conductivities with changing bentonite amount between the ranges of 40 to 60 percent, also it can be stated that increasing bentonite amount decreases hydraulic conductivity depending on test results. BES50 with 50 % bentonite content and 100 % bentonite gave nearly equal results, and it can be stated that bentonite amount above 50 % causes the material to behave like bentonite. Hydraulic conductivity value of B ( 100 % bentonite) is calculated 6.41x10-9 m/s on average for each loading stage. BES50 has nearly the same hydraulic conductivity as B which is 6.98x10-9 m/s. Depending on test results, BES50 is chosen to be treated with lime based on low hydraulic conductivity properties, low settlement capacity and relatively consistent behavior without unexpected rises nor falls.Unconfined compression tests are done in order to determine strain and strength of the mixtures. BES40 with 60 % bentonite content showed maximum strength. There was no direct correlation determined between increasing bentonite content and strength.Mixtures with constant 50 % bentonite by weight and 2 % lime (BESL2), 4 % lime (BESL4) and 6 % lime (BESL6) by weight and sand are prepared. Results are compared with BES50 in order to investigate the lime effect. Effect of lime treatment is obvious from standard proctor tests in both optimum water content and maximum dry unit weight values when compared with BES50. Adding 2 % lime in bentonite-sand mixtures increase maximum dry unit weight and increase optimum water content but increasing lime amount to above 4 % resulted in decreasing maximum dry unit weight and increasing optimum water content.Hydraulic conductivities are calculated using the same method as BES mixtures and compared with BES50 and each other. For BESL2 with 2 % lime by weight, hydraulic conductivity value is calculated as 3.01x10-9 m/s, which is lower than BES50 with 6.98x10-9 m/s value. BESL4 consolidation test results are not very different from BESL2 with hydraulic conductivity of 2.28x10-9 m/s. Settlements of the 20mm thick samples are 1.10mm, 0.73mm for BESL2 and BESL4 respectively. Compared with BES50, the effect of lime treatment decreases settlement that the samples undergoes and the hydraulic conductivity decreases. Depending on unconfined compression test results, it can be stated that lime addition increases strength of bentonite-sand mixtures and decreases settlement.Keeping 50 % bentonite and 6 % lime content constant, mixtures containing 1 % (BFS1), 2 % (BFS2) and 3 % (BFS3) blast furnace slag by weight are prepared. Results are compared with BES50 and BESL6 to compare results with lime additive only and lime+BFS additive effects. Proctor test results showed 1 % BFS addition to BESL6 decreases optium water content and increases maximum dry unit weight, while adding more BFS does not effect optimum water content or maximum dry unit weight values much. BEFS2 has nearly the same values with BESL6, while BEFS3 had optimum water content-maximum dry density values between the values of BEFS1 and BEFS2. The situation may have been caused due to the properties of BFS which have materials with various particle sizes.According to consolidation test results, permeability seriously decreases with 1 % lime additive but when 2 % and 3 % BFS is added permeability increases respectively. Still not more than 4,82 x 10-9 m/s is gathered, which is inside the limits for usage in waste disposal facilities. The decrease may depend on uniformity and homogenity of the mixtures and also on compaction properties which are related to the force applied.Unconfined compression tests are done on samples compacted with constant 32 % water content since water content plays a significant role in compression test results. Results showed that BFS significantly increases the strength of the material, and similar results are gathered for all BEFS1, BEFS2 and BEFS3. Unit strain of the samples are very low compared with BESL and BES mixtures.Lime stabilised bentonite-sand mixtures resulted in lower hydraulic conductivity values and lower volumetric change with respect to bentonite-sand mixtures. Compared with previous studies, calculated hydraulic conductivity values for sand-bentonite mixtures are not as low. This situation is related with the type and index properties of the bentonite used. Effect of lime in decreasing hydraulic conductivity is obvious when compacted 2 % above optimum water content, giving the lowest value at 4 % lime content. Unlike previous studies mostly stating lime treatment increase hydraulic conductivity at lower percentages, but decrease it when added above a certain amount, 2 % lime content lowered hydraulic conductivity value from 6.98x10-9 m/s to 3.01x10-9 m/s, when adding more lime similarly caused hydraulic conductivity to continue to decrease. Settlement properties also gave better results when lime treated, decreasing amount of volumetric change. Generally, lime treated sand-bentonite mixtures gave hydraulic conductivity results within determined limits and is considered appropriate to be used as barrier materials in waste disposal areas.Industrial waste lime generally improves engineering properties of soils and is applicable for roads and earth fills thus usage of lime in waste disposal areas as barrier material would not just improve properties of barrier material but also reduce the amount of waste products, reducing waste product amount when lime is considered as industrial waste product.BFS treated mixtures gave even better results compared with lime treated mixtures to be used in waste disposal areas. Permeability values of each sample prepared was below the limit determined as 1 x 10-8 m/s, and the effect on increasing compression strength is obvious. Generally, it can be stated that lime and BFS treatment improves the properties of sand-bentonite mixtures to be used as impermeable layer in waste disposal areas.