Mechanical Characteristics of Lime-Treated Subgrade Soil Improved by Polypropylene Fiber and Class F Fly Ash.

To improve the limitations of lime-treated subgrade soil (LS), a series of unconsolidated and undrained triaxial tests were conducted to investigate the improvement effect of fiber modified lime-treated soil (PLS) and fly ash modified lime-treated soil (FLS). The test results showed that (1) The deviatoric stress-strain curves of LS, PLS, and FLS were basically of the softening type. (2) The addition of fiber and fly ash improved the ductility and stiffness of LS. The ductility of PLS increased by 134% compared with LS, while the mechanical strength of FLS increased by 53%. (3) The microscopic tests showed that a denser skeleton structure was generated inside LS with the addition of fiber and fly ash. (4) The deviatoric stress-strain curves of LS, PLS, and FLS under different confining pressures were better characterized with the CES curve model. The above results indicate that fiber and fly ash can effectively improve the mechanical characteristics of lime-treated subgrade soil.

A novel acidic phosphoric-based geopolymer binder for lead solidification/stabilization.

Many contaminated sites are acidic and the existing binders are mainly alkaline materials. Alkaline binders are used to treat contaminated sites in acidic environments and the solidification/stabilization (S/S) effect is affected by acid corrosion. Therefore, good application prospects exist in developing a binder suitable for the treatment of acidic contaminated sites. In this paper, a new acidic phosphoric-based geopolymer (named APG binder) was synthesized with fly ash as a raw material and aluminum dihydrogen phosphate as the reactant, and the APG binder was used for Pb2+ S/S for the first time. The pH of the APG binder with Pb2+ ranged from 2.56 to 4.09 during 7-28 days of curing, and its compressive strength with Pb2+ exceeded 10 MPa at 28 days. Moreover, Pb2+ had a significant impact on the APG binder compressive strength, and when the Pb2+ content was 0.6%, the APG binder yielded a maximum compressive strength of 6.5, 9.1 and 14.28 MPa at 7, 14, and 28 days, respectively. Furthermore, the compressive strength correlated well with pH and electrical conductivity. The proposed APG binder had a better S/S effect on Pb2+ than that of cement and alkali-activated geopolymers in acidic environments. The stabilization mechanism of the APG binder for Pb2+ included chemical precipitation, physical adsorption and encapsulation.

Microscopic and mechanical properties of undistributed and remoulded red clay from Guiyang, China.

Unconsolidated-undrained (UU) tests were conducted to investigate the mechanical and morphological properties of undisturbed and remoulded red clay, with the microscopic characteristics determined by scanning electron microscopy (SEM). The microanalysis showed that the red clay aggregate was granular, curved-slice and thin layered and flower-shaped ellipsoid, with X and Y-type cracks and pores in the undisturbed red clay. Moreover, the contact modes of red clay aggregates were point contact, line contact, surface contact and mosaic contact. In addition, the main microstructure red clay was flocculation, honeycomb and pseudosphere structures. The pores in undisturbed soil were arranged in one direction, with no obvious directionality in remoulded red clay. The pore area, perimeter and maximum length of undisturbed red clay were smaller than those of remoulded red clay, with a larger probability entropy, probability distribution index and fractal dimension of pore distribution of undisturbed red clay than remoulded red clay. UU tests showed that the shear strength of undisturbed red clay was higher than that of remoulded red clay.