Influence of feedstock type and particle size on efficiency of biochar in improving tensile crack resistance and shear strength in lean clayey soil

Abstract

The development of tensile stress can cause desiccation cracks, further increasing infiltration and inducing instability in green infrastructure (slopes and landfill liners). Recent research has promoted the use of biochar (i.e., stable carbon with a life period of more than 500 years) as an eco-friendly material that can provide simultaneous benefits in reducing tensile stresses and crack development, aiming to enhance landfill cover longevity. However, there is a lack of guidelines and criteria for selecting biochar (feedstock type and particle size) as landfill cover material. This study aims to investigate the effects of biochar particle size and feedstock type on cracking of soil. Two contrasting feedstock types (i.e., pig manure-based and wood-based) have been selected for amendment on lean clay soil. Laboratory experiments were conducted to monitor the cracks. The results show that wood biochar (WB) is more efficient in crack reduction than pig manure biochar (PMB). Moreover, it has been observed that fine-grained biochar is more suspectable to cracks formation regardless of biochar type. The cohesion and internal friction angle of biochar are dependent on the surface morphology of biochar. WB has more angularity and sharp edges, which can increase interlocking in soil, thereby enhancing shear resistance and, hence, soil stability. The comprehensive study can help narrow down the selectivity of biochar and its specifications to mitigate cracks and enhance the strength of landfill cover.

Influence of Sustainable Biochars Produced from Kitchen Waste, Pig Manure, and Wood on Soil Erosion

“…Historically, erosion studies about soil-biochar composite mainly discuss the influence of biochar characteristics, such as biochar percentage [49,53] and biochar particle size [56]. There are studies that exist on studying the influence of the type of biochar on the performance of green infrastructure, including water retention [57,58], nutrient leaching mitigation [59], and pollutant removal from runoff [60]. However, few studies have documented the effects of different types of biochar on erosion, runoff, and infiltration [61,62].…”

Effect of biochar on desiccation of marine soils under constant and cyclic temperatures

“…Hussain et al [20] stated that biochar intra-pores (micropores located within biochar particles) merely served as ''storage regions'' for the water molecules while the hydrophilic functional groups absorbed and retained the water molecules inside the pores. Kumar et al [25] attributed the interaction between water molecules and hydrophilic functional groups to the wellknown ''hydrogen bonding'' mechanism. Accordingly, Fig.…”

“…Accordingly, Fig. 3 was developed to illustrate the potential ways that hydrogen bonds could form between the identified hydrophilic functional groups in biochar and its surrounding water molecules which would lead to the water retention within biochar [25,43]. In Fig.…”

“…Presence of a high quantity of narrow pores (mesopores and micropores) within the BAS matrix would have limited the volume contraction by limiting the escape/loss of water during drying. Strong forces that resulted from capillarity together with the functional group effect would have held water tightly within narrow pores and not allowed it to escape easily during desiccation [20,25]. Moreover, the lower thermal conductivity of BAS compared to that of natural soil would have led to attenuated heat transfer across the BAS matrix, which in turn would have lowered water evaporation and resulted in reduced shrinkage.…”

“…Firstly, as mentioned earlier in this paper, the addition of fine biochar would have clogged and reduced the size of coarse pores (macropores) present within the natural soil matrix which would have in turn increased the quantity of micropores present within the BAS matrix. Such narrow pores would have held the water molecules tightly and limited their escape owing to the functional group effect and forces resulting from capillarity [20,25,57]. Secondly, the clogging of wide pores by fine biochar would have evidently reduced the formation of effective water migration channels and hindered the water flow up to the surface for evaporation [9,30,65].…”