The effect of thermal history on thermo-mechanical behavior of bentonite-sand mixture

Bentonite-sand mixture is one of the most important candidates for engineering buffer element in nuclear waste repositories;so the analysis of its thermo-hydro-mechanical behavior is important for design purposes.An innovative setup of classic oedometer was used for swelling and compression study at high temperatures in this research. A fully calibration program was utilized to include high temperature effects on measurements. This research shows that the elevation of temperature from 25 to 90?C in 1:1bentonite-sand mixture in distilled water reduces free swelling potential and strain about 20 percent. The required time for equalization of swelling is less in high temperature due to increasing in permeability. Also, the high temperature causes increasing in compressibility rate and quantity for this buffer. For detection of this effect, XRD analysis showed that an increase in temperature causes a decrease in basal spacing. So, the particles can come near to each other more than lower temperatures and the amount of absorbed water in the microstructure of the clay is smaller.The effect of thermal history on behavior of bentonitesand mixture has been showed and tried to clarify it. At similar stress-temperature states, thermal history causes different deformation in samples. The highest temperature that bentonite has been experienced, controls its behavior in the next thermal cycles.