Damage of saline intact loess after dry-wet and its interpretation based on SEM and NMR

X-ray diffraction (XRD) technique was adopted to test the mineral composition of quicklime-solidified loess with different lime-adding rates at different curing periods. Scanning electron microscopy (SEM) and nitrogen adsorption were used to analyze the microporous structure of the solidified loess. The unconfined compressive strength and limit moisture content of solidified loess were combined to analyze the evolution mechanism of mineral composition and microstructure of solidified loess with the change of curing period and clarify the mechanism of quicklime-solidified loess. The results showed reduced content of clay minerals and decrease in the number of large pores due to increase of hydrates and pozzolanic products during extended curing period. The solidified soil fabric transformed from a compact structure into a mesh structure composing of acicular crystal and cementation. The main reasons for strength increase and change of liquid and plastic limits with the lime-solidified loess after extended curing are the change of the substance and the microstructure.

Section: Discussionmentioning

confidence: 99%

Study on the Mechanism of Stabilizing Loess with Lime: Analysis of Mineral and Microstructure Evolution

Chen

2021

“…e T 2 distribution of the inversion curve generated by NMR analysis can be used to estimate the pore size distribution. e soil pores are assumed as ideal spheres; then, the diameter of the pore is proportional to T 2 [31].…”

Section: Testing Methodsmentioning

confidence: 99%

Durability Analysis of Sludge Solidified with Soda Residue Subjected to Dry‐Wet and Freeze‐Thaw Cycles

Zhang

2021

Soda residue (SR), ground-granulated blast-furnace slag (GGBS), and quicklime (QL) were employed for solidifying sewage sludge, which is a technique for sustainable development by transforming industrial solid waste and sludge into engineering fill material such as backfill material in mine or abandoned caverns. The durability of solidified sludge against dry-wet and freeze-thaw cycles was investigated by unconfined compressive strength (UCS), X-ray diffraction, scanning electron microscopy, and nuclear magnetic resonance tests. The results demonstrated that the SR-GGBS-QL solidified sludge had good dry-wet and freeze-thaw durability. In general, UCS increased at first, but then it decreased to some degree with the increase in dry-wet and freeze-thaw cycles. The cycle number for peak UCS depended on the durability test types and SR content. The UCS values after seven dry-wet cycles or ten freeze-thaw cycles were higher than the initial values before cycles. The main products detected in SR-GGBS-QL solidified sludge were ettringite, hydroaluminite, and calcium silicate hydrate (C-S-H). In addition, some pollutants such as copper, arsenic, and chromium were stabilized. The weakening effect on the microstructure of the solidified sludge occurred after dry-wet or freeze-thaw cycles. However, the hydration reaction continued with the increase of dry-wet and freeze-thaw cycles, leading to an increase in the amount of hydration products (especially C-S-H) and compact microstructure. These contributed to high UCS values and good dry-wet and freeze-thaw durability. The strength and failure strain of solidified sludge still met the requirement of filling materials after dry-wet or freeze-thaw cycles.

“…Salt weathering is a frequently encountered phenomenon in the loess region, developed in the loess in different stratigraphic ages, paleosol and compacted loess. Induced by both dry-wet cycles and salt weathering, the natural environment of the loess region, which is already very fragile, is easy to form a gradual stripping of surface soils of the slope and even leads to landslides [4,5].…”

Section: Introductionmentioning

confidence: 99%

Permeability and Microstructure of a Saline Intact Loess after Dry‐Wet Cycles

Ren

Wang

et al. 2021

Self Cite

Influenced by both dry-wet cycles and salt weathering, the loess will exhibit significant changes in microstructure and permeability, which threatens the stability of loess slopes. Triaxial permeability tests and industrial computed tomography (CT) scans were carried out on saline intact loess with sodium sulfate. The relationship between permeability and pore structure of the loess after dry-wet cycles was discussed. Results show that the permeability coefficient of loess increases after dry-wet cycles, with the increment declining. After specified dry-wet cycles, the permeability coefficient increases approximately linearly with sodium sulfate content. However, the permeability coefficient significantly declines at higher confining pressures, while its attenuation rate decreases. An empirical relationship based on log 10 1 + e − log 10 k was proposed to estimate the permeability coefficient of saline intact loess considering dry-wet cycles and salt content. Comparisons of measured and calculated results proved its rationality. CT scan images imply the damage to soil microstructure induced by dry-wet cycles and salt weathering, corresponding to the decline of the mean CT value (ME) and the increase of both crack ratio and fractal dimension of crack network.