A Comprehensive Review of Biochar Utilization for Low-Carbon Flexible Asphalt Pavements

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Abstract

A large amount of biomass waste is produced globally, and its production and improper management are major environmental issues. Pavement industries consume large amounts of natural resources and adversely impact the environment. Thus, the utilization of waste materials, such as biochar from biomass, has been prioritized as an innovative and sustainable strategy. However, there is currently a paucity of knowledge regarding the utilization and performance of biochar in flexible asphalt pavements. Thus, the purpose of this study was to provide a comprehensive literature review of studies conducted between 2010 and 2022 on the advancement and application of biochar in flexible asphalt pavement production. This review also highlights biochar production materials (feedstocks) and processes. This review further evaluates the viability of biochar as a carbon-neutral material utilized in producing asphalt pavements. Owing to its exceptional and variable physicochemical properties, biochar has demonstrated improved performance for a variety of applications in flexible asphalt pavements. According to the review, for optimum performance, a particle size < 75 µm is recommended as a modifier for asphalt binders and mixtures with a content range of 5–10 wt.% of the binder, while a particle size of 1–5 mm is recommended as a filter layer. In addition, the review concluded that as a carbon-neutral material, biochar has many possibilities that can aid in reducing CO2 emissions. The challenges and future perspectives, underlying study niches, and future research suggestions for biochar application in the flexible asphalt pavement industry are also highlighted. As a result, this review will contribute to the increased sustainability and eco-friendliness of flexible asphalt pavements by encouraging the transition to carbon-negative and emission-reducing pavements. The current review will assist researchers in identifying research gaps that will encourage the high-potential, sustainable, and multifaceted application of biochar in the pavement industry for greater environmental benefits.

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Influence of pyrolysis temperature on characteristics and heavy metal adsorptive performance of biochar derived from municipal sewage sludge.

Tan Chen, Yaxin Zhang, Hongtao Wang … (2014)

To investigate systematically the influence of pyrolysis temperature on properties and heavy metal adsorption potential of municipal sludge biochar, biophysical dried sludge was pyrolyzed under temperature varying from 500°C to 900°C. The biochar yield decreased with the increase in pyrolysis temperature, while the ash content retained mostly, thus transforming the biochars into alkaline. The structure became porous as the temperature increased, and the concentrations of surface functional group elements remained low. Despite the comparatively high content of heavy metal in the biochar, the leaching toxicity of biochars was no more than 20% of the Chinese standard. In the batch experiments of cadmium(II) adsorption, the removal capacity of biochars improved under higher temperature, especially at 800°C and 900°C even one order of magnitude higher than that of the commercial activated carbon. For both energy recovery and heavy metal removal, the optimal pyrolysis temperature is 900°C.