چكيده به لاتين
Lots of undesirable properties associated with soft soils, including low bearing capacity and high compressibility, make it necessary for project sites to use a proper stabilization technique to meet engineering requirements. Chemical stabilization with lime and cement is a common method used for soft soil improvement. However, cement production is responsible for lots of destructive environmental impacts, such as high CO_2 emission, considerable energy consuming and accelerating the depletion of natural resources. All of the drawbacks above made us to investigate the possibility of using environmentally friendly materials as an alternative for traditional binders. An attempt in this study has been made to examine the feasibility of using VA-GGBS based geopolymers as a sustainable binder to stabilize clayey soil. The influence of different percentages of VA replaced by GGBS, activator/binder ratio, curing temperature, and curing time on compressive strength are investigated. The Unconfined Compressive Strength (UCS), freeze-thaw and wet-dry durability tests, X-ray diffraction (XRD), FESEM-EDS-Mapping and FTIR analysis have been utilized to study the mechanical, durability and microstructural properties of the geopolymer stabilized soil respectively. The results demonstrated that as volcanic ash requires elevated heat to be activated while, GGBS has a good reactivity at ambient temperature, utilizing a mixture of these two materials enables them to be applicable in wider ranges of temperatures which resulted in gaining desirable strengths in both curing conditions of OC and DC, however for all of the samples the curing condition of DC brought about higher strengths which was due to the better dissolution of aluminosilicates. Moreover, since volcanic ash is relatively high in silica and alumina but deficient in calcium oxide, while GGBS is rich in calcium oxide, the coexistence of these two materials in geopolymer was more efficient, which was due to the synergic formation of N-A-S-H and C-A-S-H gels. Investigating Lots of undesirable properties associated with soft soils, including low bearing capacity and high compressibility, make it necessary for project sites to use a proper stabilization technique to meet engineering requirements. Chemical stabilization with lime and cement is a common method used for soft soil improvement. However, cement production is responsible for lots of destructive environmental impacts, such as high CO_2 emission, considerable energy consuming and accelerating the depletion of natural resources. All of the drawbacks above made us to investigate the possibility of using environmentally friendly materials as an alternative for traditional binders. An attempt in this study has been made to examine the feasibility of using VA-GGBS based geopolymers as a sustainable binder to stabilize clayey soil. The influence of different percentages of VA replaced by GGBS, activator/binder ratio, curing temperature, and curing time on compressive strength are investigated. The Unconfined Compressive Strength (UCS), freeze-thaw and wet-dry durability tests, X-ray diffraction (XRD), FESEM-EDS-Mapping and FTIR analysis have been utilized to study the mechanical, durability and microstructural properties of the geopolymer stabilized soil respectively. The results demonstrated that as volcanic ash requires elevated heat to be activated while, GGBS has a good reactivity at ambient temperature, utilizing a mixture of these two materials enables them to be applicable in wider ranges of temperatures which resulted in gaining desirable strengths in both curing conditions of OC and DC, however for all of the samples the curing condition of DC brought about higher strengths which was due to the better dissolution of aluminosilicates. Moreover, since volcanic ash is relatively high in silica and alumina but deficient in calcium oxide, while GGBS is rich in calcium oxide, the coexistence of these two materials in geopolymer was more efficient, which was due to the synergic formation of N-A-S-H and C-A-S-H gels. Investigating different activator/binder ratios of 1.2, 1.4 and 1.6 demonstrated that for the samples cured in OC condition with 90 days of curing and those cured in DC condition with 28 days of curing increasing the ratio from 1.2 to 1.4 and further increase from 1.4 to 1.6, enhanced the mechanical strength, while for all of the samples the optimum ratio was 1.4. Additionally, the results of durability tests outline that geopolymer stabilized soil has a better performance against freeze-thaw cycles compared with wet-dry cycles. The samples containing 30% GGBS experienced a fewer strength reduction during durability tests in comparison with those with 0% GGBS, which sheds light on the positive effect of using GGBS to gain better performance against wet-dry and freeze-thaw cycles. Moreover, all of the microstructural analysises support the mechanical results.
