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- Title
Improving resilient modulus and cyclic crack restriction of preloaded expansive subgrade treated with nano-geopolymer binder.
- Authors
Ikechukwu, Aneke Frank; Chibuzor, Onyelowe Kennedy
- Abstract
This study investigated the synergy effects of precompression pressures on expansive subgrade treated with a nano-geopolymer binder (NGB). A moderate aqueous potassium hydroxide (KOH) of 10 M concentration was synthesized with nanoscale fly ash (α-FA) to develop the NGB. The specimens used for this study were subjected to precompression pressures equivalent to 10 kPa and 20 kPa after 12 h of specimen fabrication to achieve the desired stiffness capable of resisting cyclic cracks. A series of zero swelling tests, unconfined compressive strength (UCS) tests, split tensile strength (STS) tests, and resilient modulus tests were conducted to evaluate the synergic effects of preloading and NGB on the expansive subgrade. Additionally, the cohesive zone theorem was used for the crack analysis of the subgrades through discrete fracture mechanics. The test results showed that the 10 kPa preloaded subgrade treated with 5%, 15%, and 20% of NGB developed low strength of 1.4 MPa, 3.8 MPa, and 4.3 MPa respectively. Compared to their counterpart, 20 kPa preloaded pressures rendered an increase in strength equivalent to 4.6 MPa, 7.3 MPa, and 10.12 MPa. The trend of strength development was mobilized by precompression pressures and inclusion of NGB which triggered polycondensation reactions, which trigged at 28 days under ambient conditions of 40 °C. Furthermore, the results revealed that the un-preloaded geo-composite specimens were severely cracked at high cyclic energy. The cohesive zone analysis confirmed that the synergy effects of preloading pressure and inclusion of NGB fostered the required resistance against cyclic stress at low strain energy due to the high stiffness of the treated subgrade, which was mobilized by the geo-polymerisation reaction between the aqueous alkaline and clay minerals. At high cyclic stress, cracks were observed, suggesting that the coupling effects of applied treatment were more effective at low cyclic stress. The failure of the preloading pressure and NGB application to sustain cyclic stress in subgrade was due to the high brittleness characterized by the nano-geopolymer-treated subgrade. The failure could be attributed to the breakdown of the inter-particles of the treated preloaded specimens at high strain energy. This study concluded that increasing the stiffness of subgrades through nanotechnology and preloading pressure effectively reduced crack formation on the subgrade.
- Publication
Arabian Journal of Geosciences, 2022, Vol 15, Issue 15, p1
- ISSN
1866-7511
- Publication type
Article
- DOI
10.1007/s12517-022-10629-x