RESUMO
Cement-improved loess (CIL) is used as a common filler for subgrade construction projects in loess areas. The freeze-thaw (F-T) conditions have a significant effect on the stability of cement-improved loess subgrades in seasonally frozen regions. In this paper, the CIL samples, experiencing different numbers of F-T cycles at varying freezing temperatures, were used in consolidated undrained triaxial compression tests to investigate the effect of F-T conditions on the mechanical properties of CIL. The results show the stress-strain curves of CIL are of a strain-softening type with strong elastic brittleness. The initial tangent modulus of CIL increases with the growing confining pressure and gradually decreases with the increase in the F-T cycle number and the decreasing freezing temperature. It loses 46.4% of its original value after the twelfth F-T cycle with the confining pressure of 150 kPa and at the freezing temperature of -15 °C. The strength of CIL decreases with the increasing F-T cycle number, but it gradually tends to keep stable after the sixth F-T cycle. The strength also decreases with the reduction in the freezing temperature. It loses 37.7% of its original value after the twelfth F-T cycle with the confining pressure of 150 kPa and the freezing temperature of -15 °C. To express the nonlinearity correlation between the strength and confining pressure under F-T conditions, the Weibull function was applied and a nonlinear Mohr-Coulomb strength criterion was proposed. Through introducing a breakage rate function and a local strain coefficient, a binary-medium constitutive model consisting of bonded elements (soil-particle cohesion) and frictional elements (soil particles or soil aggregations) was established to describe the stress-strain relationships of CIL under F-T conditions. The test results indicated that the model can well describe the strain-softening phenomenon of the stress-strain curve of CIL and reflect the breakage mechanism of CIL.
RESUMO
One major defect in paper adhesives is that it is difficult to remove the adhesive in waste paper. These adhesives can easily adhere to paper-making equipment, which hampers recycling. Herein, the hyperbranched polyester H102 is used to act as dispersant, and grafting copolymerization of lignin onto the starch backbone was carried out by initiation of free radicals to prepare a bio-based paper adhesive in water. The results show that the adhesive can achieve the best adhesion properties under m(H2O)/m(St) = 15:1, m(SLS)/m(St) = 0.15:1, m(APS)/m(St) = 0.02:1, and pH = 4 at 80 °C for 6 h. The addition of H102 stabilizes the performance of the adhesive and extends the shelf life. The feasibility was verified by Fourier transform infrared spectroscopy (FT-IR), Ultraviolet-visible Spectrophotometry (UV-vis), Thermogravimetric analysis (TG), X-ray diffraction (XRD) and rheological property analysis. Moreover, the as-prepared adhesive can be dissolved in H2O by heating, which is beneficial to improve the recovery and recycling of waste paper compared with the traditional adhesives.