Investigating the application of biochar, bentonite clay and polyvinyl acetate polymer on some mechanical properties of sand deposits

Investigating the application of biochar, bentonite clay and polyvinyl acetate polymer on some mechanical properties of sand deposits
Introduction Wind erosion seriously threatens bare soils and is recognized as a global environmental problem; however, little is known about this process in comparison to rainfall or tillage erosion. Due to the heavy costs of controlling wind erosion and the difficulty of detecting which control measure is the most effective, the correct selection of technical methods is indispensable for a suitable land management. Since the last decades, the methods of sand stabilization studied are diverse, but basically based on wind speed reduction by including chemical, mechanical and biological methods. One of the most important methods of stabilizing sandy soils is the use of mulches. In recent years, due to the disproportionate development of residential in peri-urban areas, humans use polymeric and oil mulches to stabilize sandy soils. Therefore, in this research, the effects of bentonite clay, polyvinyl acetate and palm biochar on reducing soil erosion by wind in peri-urban areas were investigated. Methods and Materials
Three selected treatments were compared with a control plot without any treatment: palm biochar, polyvinyl acetate and bentonite clay. In order to prepare the palm biochar, palm remnants including the trunk, foliage and palm leaves were poured into the mill and turned into small pieces. The fragments were passed through a 2 mm sieve. The remnants transmitted from the sieve were poured into the trays of the discharger unit and placed inside a discharger at 350°C for 4 hours, and the biochemicals were prepared to the extent necessary for this research. Polyvinyl acetate treatment was provided by Isfahan Resin Co. and the bentonite clay by the Derin Kashan enterprise (both of them from Isfahan, Iran). To apply the treatments, each of them was mixed with a certain proportion of water per m2: i) 20 g l-1of palm biochar treatments; ii) 7 g l-1 of polyvinyl acetate treatment; and, iii) 20 g l-1 of bentonite clay.In order to apply the treatments, 36 galvanized trays with a same size (5×35×105 cm) were prepared and filled up from the air to the top edge with sand. After 1, 2, 4, 10 and 20 weeks some mechanical and physical properties were measured in laboratory. Results and Discussion A significant difference was observed among different treatments in terms of the impact on aggregates formations and stabilities at different moments. The application of bentonite clay treatment significantly increased the stability of formed aggregates compared to control treatment. The rest of treatments showed lower aggregability. The mean weigh diameter (MDW) for the control plot was 0.28 mm. The lowest MWD was obtained by the palm biochar treatment, which increased by 20.1, 14.9, 9, 2.5 and 1.6% after the first, second, fourth, tenth and twentieth weeks of application, respectively. Polyvinyl acetate treatment increased MDW by 65.1, 61.6, 58.8, 41.9 and 31.5% after the first, second, fourth, tenth and twentieth weeks, respectively. The highest MWD was obtained by bentonite clay treatment, which generated an increase by 77.8, 71, 65.1, 59.9 and 49.7% in the first, second, fourth, tenth and twentieth weeks, respectively). The images from thin sections of bentonite clay and polyvinyl acetate treatments showed that soil particles were joined to form larger aggregates in all of cases.
No significant differences was observed for hydraulic conductivity at different times were observed. There was a significant difference among different treatments at different monitoring periods. The application of bentonite clay significantly reduced the fractal dimension. On the contrary, the lowest effect was registered for the palm biochar treatment. The effect of bentonite clay treatment on soils was higher than other selected treatments showing a reduction by 10.6, 9.7, 8.7 6.7 and 6.3% in the first, second, fourth, tenth and twentieth weeks, respectively.
The impact of different treatments on shear resistance showed that the application of the selected treatments significantly increased the shear strength in all the cases. Among the selected treatments, the effect of bentonite clay treatment on shear resistance was higher than other treatments. The lowest and the highest shear resistance were registered for the palm biochar and bentointe clay, respectively. Palm biochar increased shear resistance by 9.3, 9.3, 8, 5.3 and 3.3% compared to the control plot in the first, second, fourth, tenth and twentieth weeks after its application. On the other, bentonite clay registered the highest improvement in shear resistance by 44.7, 44.7, 42.7, 37.3 and 31.3% in the first, second, fourth, tenth and twentieth weeks, respectively.
Keywords: Mulches, Bentonite, Clay, Biochar, Palm, Mechanical properties