Abstract
The proper design of protective structures may start from improving the characteristics of soils. In order to obtain reasonable safety criteria, several research studies have recently been dedicated to enhancing complex civil engineering structural systems with the use of nanotechnology. Thus, the following paper investigates the effect of nanospheres, including nanosilica (nano-SiO2) and nano zinc oxide (nano-ZnO), on lime-stabilized high-plasticity clay soil. For this purpose, unconfined compressive strength (UCS) and California bearing ratio (CBR) tests were performed on samples. The results showed that the use of the selected nanospheres greatly increased the UCS of the samples compared to untreated soil. The UCS value of samples containing 6% lime and 1.5% nano-ZnO after 28 days of treatment increased by 5-fold compared to the UCS of untreated samples. In addition, the samples containing 6% lime and 2% nano-SiO2, with similar curing conditions, experienced a 5.3-fold increase in their UCS value compared to the untreated samples. These compounds were considered as the optimal amounts and showed the highest mechanical strength in both UCS and CBR tests. The same trend was achieved in the CBR test, in which the CBR value for the optimal mixtures containing nano-ZnO and nano-SiO2 was 14.8 and 16.6 times higher than that of high-plasticity clay soil, respectively. Finally, the results obtained from scanning electron microscopy (SEM) analysis revealed that the nanospheres caused a dense and compact matrix to form in the soil, which led to the enhancement of the mechanical strength of the treated samples.
Highlights
When designing protective structures, high-plasticity clay soils, which are widely scattered throughout the world, are very problematic. is is mainly due to the fact that they are highly sensitive after being exposed to moisture. e presence of these soils in construction projects should be addressed and treated if necessary due to their undesirable behaviour such as swelling, shrinkage, dispersion, low mechanical strength, and high level of settlement [1,2,3]
To carry out the unsoaked California bearing ratio (CBR) test according to ASTM D1883-16 [47], the dry soil and additives were mixed for each sample individually and water was added to them to achieve the optimum moisture content
The unconfined compressive strength (UCS) increased and reached its maximum resistance with the addition of lime of up to 6%, whereas the UCS value was reduced for higher amounts of lime. e presence of lime in the samples increased the pH value of the soil and provided the conditions for long-term pozzolanic reactions
Summary
High-plasticity clay soils, which are widely scattered throughout the world, are very problematic. is is mainly due to the fact that they are highly sensitive after being exposed to moisture. e presence of these soils in construction projects should be addressed and treated if necessary due to their undesirable behaviour such as swelling, shrinkage, dispersion, low mechanical strength, and high level of settlement [1,2,3]. Ese methods can lead to increased mechanical strength, reduced settlement, and controlled swelling or shrinking of soils, as well as providing a suitable site for the construction of structures Among these methods, stabilization with the use of chemical additives, most notably lime and cement, is considered as one of the most effective techniques to improve the characteristics of soil [15,16,17,18]. The effect of nano-SiO2 and nano-ZnO on the mechanical strength parameters of high-plasticity clay soil stabilized with lime was investigated and their microstructural changes were carefully considered. For this purpose, unconfined compressive strength (UCS) and California bearing ratio (CBR) tests were performed on samples. Scanning electron microscopy (SEM) analysis was applied to observe the microstructural properties
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