Strength properties and microstructural characteristics of clay treated with alkali activated mortar and fiber.

• Conducting a set of tests to investigate the effect of basalt fibers, wollastonite and alkaline active solution on clay. • Increasing the compressive and tensile strength by basalt fibers, wollastonite and alkaline activator and ductile failure of samples. • The compressive and tensile strength of alkali-activated mortar soil increases with curing time. • According to SEM and XRD, CSH and CASH are produced from chemical reactions between wollastonite, KOH and clay. Chemical stabilization, along with strengthening and reinforcing the soil with the use of fibers are among the methods employed for soil improvement. In recent years, the application of alkali-activated mortars has received considerable attention due to less CO 2 emissions along with no need to precure the pozzolans used to make the mortar. Application of fibers in addition to chemical stabilizers can be effective to increase the ductility and tensile strength of improved soils and delay the rupture process. Basalt fibers, which are of natural origin and have very high resistance in acidic, alkaline, and saline environments, are considered as suitable options for reinforcement of alkali-activated mortars. In the present study, the improvement of a type of clay has been examined using basalt fibers and the alkali-activated mortar. To investigate the strength parameters of the improved clay soil, a combination of basalt fibers and alkali-activated mortar (Clay improved with 3% wollastonite and 16% potassium hydroxide alkaline solution) was prepared and was then subjected to uniaxial compressive strength and indirect tensile strength tests after curing times of 7, 14, 28 and 90 days. Also, electron microscope images (SEM) and EDX analyses were performed on the samples to interpret the results. The results showed that in samples improved with alkali-activated mortars, the formation of calcium silicate hydrate(C-S-H) and calcium aluminosilicate hydrate (C-A-S-H) gels and their polymerization after the curing time increased the compressive and tensile strengths. In the samples improved with alkali-activated mortars reinforced with basalt fibers, the ductility of the samples also increased in addition to the increase in the compressive and tensile strengths as the gels formed were interlocked among the fibers. [ABSTRACT FROM AUTHOR]