Rheological properties of laponite and chemically modified laponite suspenisons

Meng Shen, Purdue University

Abstract

This research investigates the rheological properties of concentrated laponite RD suspensions modified through the addition of laponite RDS and sodium pyrophosphate (SPP). The work is aimed at establishing the possible suitability of these materials for treating liquefaction susceptible sands. This application requires that a laponite suspension initially exhibits liquid like behavior and low viscosity that allow its delivery into the pore space of a sand, but that over time the suspension develop a gel structure with solid like behavior that can serve to restrict sand particle mobility during earthquake shaking. The experimental program made use of a Physica MCR 301 Rheometer, a fully automated, air bearing apparatus controlled stress apparatus. Controlled shear rate tests (CSR) and amplitude sweep tests (AS) were performed to determine the flow and the viscoelastic behavior of 30 different clay suspensions as a function of time (from immediately after mixing to after 4 months). The concentration of laponite RD was varied between 3% and 9% by mass of water, while the dosages of the modifiers ranged between 1.5% and 6% by mass of water in the case of laponite RDS, and between 1.5% and 8.0% by mass of laponite RD, in the case of the SPP. The test results demonstrate that the addition of RDS and SPP impacts the rheology of the laponite RD suspensions, and that the effects are more marked when the concentration of RDS and SPP increases. For suspensions with the same RD %, at early aging times the addition of RDS or SPP causes a reduction in viscosity, yield stress and storage modulus. For sufficiently high dosages of RDS or SPP a Newtonian response is observed immediately after mixing. Both CSR and AS tests show a significant evolution in the rheological behavior of all RDS and SPP modified suspensions. Over time all suspensions display an increase in viscosity, yield stress and storage modulus, and a reduction in the phase angle measured in the LVE region. These effects reflect the transition of all suspensions from sols to gels. This transition is delayed for increasing concentration of RDS or SPP. After 2 weeks of aging all the suspensions examined in its research display phase angle less than 10°, indicating the formation of a gel-like structure with solid like behavior. While the viscosity measured at a reference shear rate of 1000/s is found to reach a "steady state" after ∼ 1 week of aging, the storage modulus of all suspensions continues to increase with time 3-4 months after mixing. Beyond 20-50 hours, the storage modulus increases with the total laponite concentration (RD plus RDS) and decreases with increasing SPP%. Based on the tests conducted, two suspensions (5% RD suspension modified with 4% RDS and 9% RD suspension modified with 7% SPP) are identified as potentially suitable permeation materials to treat sands susceptible to liquefaction.

Degree

M.S.C.E.

Advisors

Bobet, Purdue University.

Subject Area

Geotechnology|Civil engineering

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