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This study investigated the strength behaviors of dredged clays treated with metakaolin (MK) and fly ash (FA). A series of laboratory tests including direct shear and unconfined compressive strength tests were performed on MK and FA-treated dredged clay at various MK contents and different curing times. The direct shear test results showed that the shear stress and displacement curves for all specimens tested are strain-softening types and influenced by MK content and curing time. The variation curve at a higher MK content or higher curing time is always higher than that at a lower one. The shear strength from the direct shear test at a given vertical stress consistently increases linearly with the increase of MK content while increasing parabolically with curing time. This indicates both curing time and MK content contribute to the development of the shear strength. Both strength parameters c and φ grow with increasing MK content and curing time. Unconfined compressive strength test results show the strain-softening behavior for all tested specimens. Compared with adding FA alone or MK alone, adding both fly ash and MK exhibited a better treatment effect in the unconfined compressive strength, which increases with increasing MK content and curing time. [ABSTRACT FROM AUTHOR]

This study presents an experimental investigation of the interface behaviors of recycled asphalt pavement (RAP) reinforced with biaxial geogrid. A series of direct shear tests were conducted on compacted RAP specimens with or without geogrid under different normal stresses (50, 75, and 100 kPa) and test temperatures (0, 20, and 35°C) using an improved temperature-controlled direct shear apparatus. The effect of test temperature on interface shear strength and strength parameters was systematically examined. Test results showed that shear stress versus shear displacement curves of RAP specimens with or without geogrid show strain-softening characteristics. Under the same normal stress, the curve of the reinforced RAP sample with a high temperature is always below that with a low temperature, which indicates the test temperature has an adverse effect on the strength of the reinforced RAP sample. The shear strength consistently increases linearly with the increase of applied normal stress for all RAP samples. The shear strength with geogrid is greater than pure RAP under a given test temperature and normal stress. The shear strength of RAP samples at lower test temperatures is higher than that at a higher temperature. Both apparent adhesion intercept of RAP-geogrid and cohesion of RAP show a decreasing trend with the increase of the test temperature and tend to be stable with increasing temperature. Both the interface friction angle of RAP-geogrid and the internal friction angle of RAP slightly decrease with the increase of test temperature. For RAP-geogrid, the value of the apparent adhesion intercept is higher than that for sand and gravel with geosynthetics. The interface friction angle is close to that of sand and gravel with geosynthetics. Therefore, RAP material can be well used as alternative backfill materials in lieu of natural aggregates such as gravel and sand in geotechnical applications. [ABSTRACT FROM AUTHOR]

This study experimentally investigated the strength characteristics of metakaolin (MK) and sodium silicate (SS) treated dredged clay at high water content for use as construction fills. A series of laboratory tests including direct shear tests, unconfined compression tests, SEM and XRD tests were carried out to systematically evaluate the effects of water content, sodium silicate modulus, curing agent content, and curing time on the strength behavior of MK and SS treated dredged clay samples. The direct shear test results showed that the shear strength at a given vertical stress consistently increases with the increase of curing agent content and curing time while decreasing with the modulus of SS. Both cohesion and friction angle increase with increasing curing agent content and curing time, while reducing with the increasing modulus of SS. Unconfined compression test results showed that all samples tested exhibit a strain-softening behavior. The value of unconfined compressive strength increases with the increase of curing agent content and curing time but decreases with the increase of water content and modulus of SS. The optimal dosage combination is a sodium silicate modulus of 0.9, curing agent content of 12%, and curing time of 28d. SEM test confirmed the formation of gels in the treated soil sample, the dredged clay showed a more uniform and denser microstructure after treatment. Through XRD analysis, it is not easy to generate direct chemical reactions with no new mineral components generated in the sample. For high-water content dredged clay, it is recommended to use an optimum dosage combination of MK and SS to achieve a better treatment effect for use as construction fills. [Display omitted] • The strength properties of MK and SS treated dredged clay sample were optimized. • The UCS of treated clay samples at different initial water contents were compared. • The microscopic mechanism of MK and SS treated dredged clay sample was revealed. [ABSTRACT FROM AUTHOR]