Abstract: The rice husk charcoal (RHC) and lime, by-products from biomass gasification, were used to conduct composite modification of roadbed soil. The unconfined compressive strength and dynamic rebound modulus of RHC-lime composite soil was tested, and its strength characteristics and mechanism were analyzed by Fourier transform infrared spectroscopy (FTIR), XRD, and SEM. The results show that the addition of rice husk charcoal significantly improves the unconfined compressive strength of soil. The strength of composite soil with different rice husk charcoal and lime dosages varies significantly, and the combined addition of rice husk charcoal and lime is superior to the addition of rice husk charcoal alone. According to the strength, energy-saving and carbon reduction effects, the recommended dosage of rice husk charcoal+lime is 2%+2% (2L+2R). Composite soil exhibits early strength, with slow later improvement. The predictive formula for compressive strength changing with age has been derived. Rice husk charcoal enhances the toughness of composite soil, and as the dosage increases, the failure mode transitions gradually from brittle to plastic. Additionally, the dynamic rebound modulus of the composite soil positively correlates with confining pressure, cyclic stress, and age. The addition of rice husk charcoal increases the dynamic rebound modulus of composite soil, and the established multi-state dynamic rebound modulus prediction model exhibits high accuracy. It is revealed that the volcanic ash reaction between SiO2 and lime in rice husk charcoal is the main reason for the rapid increase in the strength of composite soil, and age-related strength variations stem from the quantity and form of C-S-H generation.

Key words: highway engineering; composite soil of rice husk charcoal and lime; compressive strength; dynamic rebound modulus; micro-mechanism

摘要： 采用生物质气化的副产品稻壳炭和石灰对路基土进行复合改性，测试稻壳炭-石灰复合土的无侧限抗压强度及动态回弹模量，采用傅里叶红外光谱、XRD及SEM分析其强度特性机理。结果表明：加入稻壳炭可以显著提高土的无侧限抗压强度，不同稻壳炭、石灰掺量的复合土强度差异明显,稻壳炭、石灰复掺优于稻壳炭单掺,根据强度及节能降碳效果，推荐稻壳炭＋石灰的掺量为2%+2%（2L+2R）；复合土具有早强性，其后期强度提升缓慢，获得了抗压强度随龄期变化的预测公式；稻壳炭可以增强复合土的韧性，复合土的破坏形态随掺量的增加逐渐由脆性向塑性转变；复合土的动态回弹模量与围压、循环应力、龄期呈正相关，加入稻壳炭，复合土的动态回弹模量增大，建立的多状态动态回弹模量预估模型具有较高的精度；稻壳炭中活性SiO2与石灰的火山灰反应是复合土强度迅速提升的主要原因，不同龄期的强度差异源自于C—S—H生成的数量和存在形式。

关键词: 道路工程；稻壳炭-石灰复合土；抗压强度；动态回弹模量；微观机理