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This study focuses on the shear-strength properties of polyurethane polymer–treated sand stored at different temperatures. The triaxial test was performed at unconsolidated and undrained conditions on the specimen after 2 days of curing at room temperature and 1 day of curing at various temperatures. The effects of polymer content and dry density on strength properties were also considered. Polymer reinforcement mechanism was analyzed using scanning electron microscope images. Results indicated that the stress-strain relationship exhibited increasing ductility as temperature increased; the shear strength, energy absorption, and cohesion tended to decrease initially and then increase, while the friction angle remained stable at approximately 30°. The strength properties were in proportion to an increment in polymer content, and the trend became more apparent in a warmer environment. The shear strength, energy absorption, and cohesion increased up to about 2.4 MPa, 65 kPa, and 400 kPa, respectively. A higher dry density resulted in significant improvement in strength properties, except for a slight reduction in ductility, no matter the temperature. The presence of a polymer matrix formed a honeycomb and special net structures among sand via coating, bridging, and filling effects; hence, the treated sand turned into a whole system exhibiting favorable strength properties. This reinforcement effectiveness depended on polymer content, dry density, ambient temperature, soil grain, and polymer characteristics. [ABSTRACT FROM AUTHOR]

Weak water stability of soil is one of the prime causes of soil erosion and slope damage. To understand the improvement on the water stability of sand by a soluble organic polymer (polyurethane, PU), we have conducted a series of water-stability and turbidity tests to evaluate the effects of different polymer content, densities, and immersion times. The mechanism of the improvements is investigated based on scanning electron and digital microscopes. Our results reveal that the polymer can effectively improve the water stability of sand, where the water-stability coefficient enhanced from zero to 100. The turbidity of the water after oscillation was determined, and its value reduced from 84.5 to 10 and kept stable, which further proved the PU improvement on the water stability of sand. The results can be considered as the reference for construction and management of riverbanks and drainage ditches. [ABSTRACT FROM AUTHOR]

There has been a growing interest in polymer applied for soil reinforcement in recent years. However, there little attention has been paid to the effects of polymer on soil cracking behavior, and cracks significantly change soil strength and hydraulic properties and alter reinforcement effectiveness. This study investigated the desiccation cracking behavior of polyurethane (PU) and polyacrylamide (PAM) admixed clayey soils with different polymer concentrations by performing desiccation cracking tests. Scanning electron microscope (SEM) observation was also carried out to obtain the internal structure of these soils. The results show that PU and PAM addition both prolonged the initial evaporation stage, accelerated later evaporation processes, and the effects were related to polymer concentration. Final cracks morphology analyses show that PAM addition slightly reduced the cracking and crushing degree and kept the soil relatively intact, while PU addition slightly enhanced the cracking and crushing degree of soil. In addition, PU and PAM addition both increased the width and length of cracks. The scanning electron microscopy (SEM) analyses show that the effects of polymer on soil evaporation and cracking could be concluded as: (1) storing water in voids, (2) influencing water immigration channel, (3) providing space for soil shrinkage, and (4) enhancing the connection between aggregates, which did not fully come into play because of the existence of hydrogel form. These achievements provide a certain basis for the research of desiccation cracking behavior of polymer treated soil and make significant sense for the safe and effective running of related projects. [ABSTRACT FROM AUTHOR]

[Display omitted] • The mechanical properties of PU treated sand enhance with PU content and dry density at different temperatures. • Positive and negative temperatures both make positive effect on PU treatment. • PU coats sand grains and bonds them together. • PU bonding effect depends on PU content, dry density and temperature. In this study, the mechanical behavior of a polyurethane (PU) polymer-sand mixture was investigated by performing a series of uniaxial compression (UC) and direct tensile (DT) tests at different polyurethane polymer contents (PUC), dry densities (DD) and temperatures (TP). Results show that the axial stress–strain relationship depends on PUC, DD and TP, in particular, the failure mode gradually changes from fragile to ductile feature; the uniaxial compressive strength (UCS), secant modulus (E 50) and tensile strength (TS) all linearly increase with increasing PUC and DD at different TPs. Positive and negative temperatures (i.e., 35℃ and 50℃, −20℃ and − 10℃) both make positive effect on PU treatment since the UCS ratio, E 50 ratio and TS ratio all are higher than unity. Positive temperature significantly increases the strength and ductility, while negative temperature obviously affects the strength and modulus. Linear relationships of E 50 -UCS, UCS-TS are obtained, and these relationships depend on temperature. Scanning electron microscope (SEM) observation reveals that the presence of PU additive links adjacent grains together, improving the mechanical properties of the mixture. As this bonding effect is expected to be dependent on PUC, DD and TP, the strength, ductility and stiffness are different in different scenarios. [ABSTRACT FROM AUTHOR]