Bentonite and marconite for electrical grounding applications from geotechnical engineering perspective

2019 
Bentonite and marconite are commonly used as soil substitute and filler material for electrical grounding applications in trouble environments. Bentonite is a fine grained highly plastic clay derived from volcanic formation, whereas Marconite is an engineered material in the form of super conductive aggregate derived from coal power production. Both material are used to reduce the electrical resistance between the soil and earth-electrode rod. In this study, a sodium based bentonite, namely MX80 bentonite and Marconite aggregates were characterized and tested to perform as grounding material under varying water contents. After each test, the resistivity of each specimens were measured using a Nelsson 2-point resistivity meter. In addition, aluminum discs were inserted into the specimens to measure the effect of wetting and corrosion induced by both material. Test results indicated that the resistivity behavior of bentonite is greater than that of Marconite. On the contrary, the resistivity of Marconite is far lower than that of MX80 bentonite. The lowest resistivity achieved by Andrassy bentonite was found to be 2.4 Ωm under very wet conditions as compared to 0.44 Ωm in Marconite. Based on the tests results, the resistivity behavior of bentonite is governed by the water content. Water within the pores acts as particle bridging for electrical currents to pass through the bentonite. The resistivity values is lower under liquid state as compared to under plastic or solid state. On the hand, Marconite resistivity behavior remained somewhat unchanged under both dry and wet conditions indicating that interparticle contact is more dominant. Higher corrosion was observed on aluminum discs placed within bentonite specimens due to the availability of water.
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