Physical And Mechanical Properties Of Biochar-cement Soil

In recent years,with the introduction and gradual advancement of the national "dual carbon" strategy,the green transformation of the industrial construction industry is imminent,and green and low-carbon building materials have become an important boost for carbon sequestration and emission reduction in civil engineering.Cement-soil is one of the more mature and widely used geotechnical materials,which provides cost-effective engineering solutions for foundation treatment,subgrade compaction,slope reinforcement and anti-seepage curtains in soft soil areas.However,traditional cement-soil materials have been unable to meet the carbon emission reduction requirements for green building materials in the new development environment.In this regard,in this paper,a high-efficiency carbon-fixing material,biochar,is used as an admixture of cement-based materials,and is incorporated into soft clay with high water content to prepare biochar-cement soil composites,test and analyze its important physical properties and mechanical performance,the effects of biochar content,biochar particle size and biochar type on the physical and mechanical performance of cement-soil were studied,and the micro-consolidation mechanism of biochar-cement soil was explored.Based on these work,the following conclusions are drawn:(1)With the increase of biochar content,the density of biochar-cement soil decreases linearly,and the porosity gradually increases,but the water absorption rate of biochar-cement soil increases linearly to a certain value at first,and then does not continue to increase.With the increase of biochar particle size,the density of cement-soil before curing increases first and then decreases.The density of cement-soil with a particle size of 0.075 mm biochar is higher,and the density of cement-soil after curing gradually decreases.On the contrary,with the increase of biochar particle size,the porosity first decreased and then increased,and the porosity of cement soil with a biochar particle size of 0.075 mm has a lower level.The increase in the particle size of biochar will lead to a gradual increase in the water absorption of the cement-soil.Among the four kinds of biochar-cement soils,YBC-cement soil has lower porosity and higher water absorption,NBC-cement soil has higher porosity and lower water absorption,the performance of wood chip biochar and rice husk biochar is between the first two(2)The addition of biochar is beneficial to improve the unconfined compressive strength of cement-soil,up to 1.76 times.With the increase of biochar content,the maximum dry density and optimal moisture content of biochar-cement soil after compaction increased slightly.The ultimate stress peak value of the unconfined compressive test of cement-soil increases noteworthy,and the strength significantly enhance.The larger the particle size of biochar,the greater the early stress of the cement-soil,and the steeper the ascending segment of the stress-strain curve,the lower the unconfined compressive strength of the cement-soil specimens.The mechanical performance of NBC-cement soil is slightly better than the other three kinds of biochar-cement soil,and its unconfined compressive strength is higher(3)The micro-consolidation model of biochar-cement soil can be approximated and simplified to a chain rod cementation model,that is to say that can be considered that the large agglomerates formed by biochar and clay particles and the biochar cement particles are used as the skeleton,and the hard cement hydration products are used as the chain rods.Biochar enters between clays by filling,have reinforced the strength of clay aggregates and cement stone,and as a stable solid,it plays an inner filling role,which have strengthened the structural compactness of cement-soil,the mechanical performance of biochar-cement soil was improved preferably.