The Effect of Ulexite Additive on the Engineering Properties of Sand-Bentonite Mixtures

Öz

Bentonites and sand-bentonite mixtures are usually used for impervious barriers at nuclear waste repositories, municipal solid waste landfill liners, etc. These mixtures should be able to perform for a long time without changing their strength and hydraulic conductivity properties. The literature studies have shown that high temperature and thermal cycles have negative effects on the hydraulic conductivity and strength of soils. For example, hydraulic conductivity increases in the presence of high temperature. For that reason, the resistivity of bentonites and sand-bentonite mixtures should be increased against high temperatures when they are used in liners. Boron minerals are used in order to increase the thermal resistivity of materials in industry. Hence the boron mineral namely; ulexite can be added to the sand-bentonite mixtures in order to improve strength and hydraulic conductivity properties of these mixtures against high temperature or thermal cycles. In this study, the compaction, consolidation, hydraulic conductivity and shear strength properties of ulexite added sand-bentonite mixtures were investigated at room temperature. Additionally, the shear strength behavior of ulexite added sand-bentonite mixtures was investigated under high temperature (80°C). The sand-bentonite mixtures were prepared which contains 10% bentonite by weight. The 10% and 20% ulexite were added to these mixtures. The mixtures were prepared according to the compaction test results (dry unit weight and optimum water content+2%). According to the test results, as the ulexite additive decreased the optimum water content value and increased the maximum dry unit weight. When the ulexite was added to the sand-bentonite mixtures, amount of the total vertical strain (compressibility) increased as the ulexite percentage increased. The maximum shear stress value of sand-bentonite mixtures in the presence of ulexite at 80°C was generally higher than those of at room temperature.

Anahtar Kelimeler

• Boron,shear strength,consolidation,compaction,temperature

Üleksit Katkısının Kum-Bentonit Karışımlarının Mühendislik Özelliklerine Etkisi

Öz

Bentonit ve kum-bentonit karışımları genellikle nükleer atık depolama sahaları, kentsel katı atık depolama alanlarında geçirimsiz bariyer uygulamalarında kullanılırlar. Bu zemin karışımlarının dayanım ve hidrolik iletkenlik gibi mühendislik özellikleri tasarım aşamasındaki değerlerde çok uzun süre değişmeden kalmalıdır. Literatür çalışmaları, yüksek sıcaklık ve termal döngülerin, zeminlerin hidrolik iletkenlik, hacimsel deformasyon ve dayanımı üzerinde olumsuz etkileri olduğunu göstermiştir. Endüstride, malzemelerin termal direncini arttırmak için bor mineralleri kullanılmaktadır. Bu nedenle bir bor minerali olan üleksit, zemin karışımlarının yüksek sıcaklık veya termal döngülere karşı dayanım ve hidrolik iletkenlik özelliklerini geliştirmek için bentonit veya kum-bentonit karışımlarına eklenebilir. Bu çalışmada, üleksit katkılı kum-bentonit karışımlarının kompaksiyon, konsolidasyon, hidrolik iletkenlik ve kayma dayanımı özellikleri oda sıcaklığında, ayrıca üleksit ilave edilmiş kum-bentonit karışımlarının kayma dayanımı davranışı yüksek sıcaklık varlığında (80°C) incelenmiştir. Deneylerde %10 bentonit içeren kum-bentonit karışımlarına %10 ve %20 oranlarında üleksit eklenmiştir. Elde edilen sonuçlara göre, üleksit katkısı kum-bentonit karışımlarının optimum su içeriği değerini düşürürken, maksimum kuru birim hacim ağırlık değerini arttırmıştır. Üleksit yüzdesi arttıkça toplam düşey deformasyon (sıkışabilirlik) miktarı artmıştır. Üleksit varlığında kum-bentonit karışımlarının 80°C'de maksimum kayma gerilmesi değeri, genellikle oda sıcaklığındaki değerlerden daha yüksek elde edilmiştir.

Anahtar Kelimeler

• Bor,kayma dayanımı,konsolidasyon,kompaksiyon,sıcaklık

Kaynakça

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