Marine clay stabilization enhancement using calcined shale and pofa

The abundance of marine clay in Malaysia increased the concerns among engineers about any development to be constructed on this type of soil because marine clay is usually regarded as problematic soil. Treatment with calcium-based binders and the inclusion of reinforcement material such as ash have gained popularity for improving marine clay due to their easy adaptability and robustness. Although the use of cement and lime has many benefits, many shortcomings are caused by these materials for the environment and engineering structures, such as carbon dioxide (CO2) emissions and sulfate attacks. As a result, the partial and full replacement of calcium-based binders with sustainable materials is necessary for soil stabilization. Many attempts have been made to address this issue, including using metakaolin. However, the use of metakaolin is limited due to its high cost. By contrast, low-cost natural pozzolana (calcined shale CS) has been proven beneficial for concrete construction. Previous research showed that CS improves the strength and reduces the corrosion resistance coefficient of cement. The performance of CS is comparable with that of metakaolin in cementitious mixtures. However, the review of previous research shows that CS has not yet been employed in soil stabilization. Therefore, this study focused on developing a new soil matrix by combining calcined shale and palm oil fuel ash (POFA) to optimize the improvement of lime-treated marine clay and an attempt to use CS as a partial replacement for lime in soil stabilization, thus reducing the use of potentially harmful lime in soft soil stabilization. Two cases were conducted. Case 1: The physical, mechanical, and microstructural behavior of POFA-lime-treated marine clay was studied to evaluate the optimum percentage of POFA that can be used in lime-treated marine clay. Case 2: The physical characteristics, mechanical properties, and microstructural behavior of the CS-POFA-lime-treated marine clay composite were assessed by many tests after 7, 28, and 90 days to obtain the optimum ternary blending mixture. In addition, the performance of this ternary blending mixture as a platform layer in a pile-supported earth platform physical model over soft soil was evaluated. The results of Case 1 showed that the addition of lime and POFA to marine clay caused a decrease in its plasticity and compressibility while improving its strength behavior and the optimum proportion of POFA is 5%, which gives the highest strength; therefore, 5% POFA was used in Case 2 as the optimum percentage of POFA. Adding CS to the optimum mixture in Case 1 was highly effective in enhancing the compaction properties and compressibility behavior of lime-treated marine clay and gave it a higher strength than using lime-POFA alone. Adding CS decreases plasticity properties such as LL, PI, SL, and OWC, while MDD increases. LL was reduced by 27%, PI reduced by 75%, and SL reduced by46% with the addition of 10%CS in the S+5%L+5%POFA mixture, while the MDD increased by 1.06 times. Similar behavior was observed when replacing 5% lime with 3% or 1% lime. Furthermore, a significant increment was observed in UCS, peak flexural load, Young’s modulus, and flexural strength with the addition of CS to POFA-Lime-treated marine clay at 7 days of the curing period, particularly with 10% CS. The increment is higher as the stabilizer content and curing increase. The UCS of S+5%Lime+5%POFA+10%CS increased 3.98 times more than the untreated marine clay. While the UCS of S+3%Lime+5%POFA+10% CS increased 2.3 times, the flexural strength and Young's modulus increased by 1.78 and 1.73 times more than the untreated marine clay. Also, results showed that adding CS gives higher resistance to the cycles of wetting/drying and sulfate attack than the lime-POFA/soil and lime/soil specimens. These findings can be confirmed with the micrograph results from FESEM and EDX, where adding CS shows compact clay matrices and the microstructure becomes more continuous, less open, and denser. Also, TGA and electrical resistivity results supported the formation of the cementitious gel. The curing periods contributed to the continuing and increasing formation of cementitious products. Based on these findings, the optimum ternary blending mixture is a combination of 3% and 15% pozzolan (10% calcined shale and 5% POFA), which is the most effective combination for stabilizing marine clay. Using CS and POFA as partial replacements will reduce construction costs, reduce the sulfate attack, and be more environmentally friendly. Finally, the physical model analyses illustrate the significance of the mechanical characteristics of the treated marine clay, where using S+3%L+5%POFA+10% significantly reduced the settlement and the differential settlements at the ground surfaces and above the pile heads. It was reduced by 36% compared to the untreated platform marine clay layer. Furthermore, increasing the height of the platform layer causes an increase in the efficiency of arching mechanisms and decreases the differential settlement of soft soil by up to 50% when the earth platform height used is 0.25 m.

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