SHEAR STRENGTH OF CEMENT-BENTONITE MIXTURES AN EXPERIMENTAL STUDY

Abstract

An experimental program was conducted using the unconfined compressive strength test apparatus and the triaxial test apparatus to study the shear strength and the deformation properties of cement-bentonite mixtures. Bentonite-cement ratio, curing time, initial water content, curing environment, confining pressure and sand content were the main parameters that were varied in this research. Preliminary tests were carried out to characterize the used materials: bentonite, cement and sand (sieve analysis, Atterburg limits, X-ray diffraction and chemical analysis).

Test results show that the value of the unconfined compressive strength increases as curing progresses. The increase in qu varied between 175% and 328% for specimens cured in salty water, while the increase ranged between 210% and 350% for specimens cured in potable water. In addition, the shear strength parameters c and and the value of E 50 increase with the increase in curing time. Test results also indicate that the addition of sand results in an increase in the unconfined compression strength only when the sand­ cement ratio is 1:1. Furthermore, the existence of sulfate ions in the curing environment decreases the shear strength of cement bentonite mixtures and also causes swelling corrosion for mixtures having low water contents and high cement contents. It can also be concluded that the increase of the initial mixing water content increases the workability while decreases the shear strength. Moreover, the comparison between measured values of the unconfined compression strength for specimens cured in salty water and specimens cured in potable water shows that only the outer surface is damaged while the inner core remains intact.