CFB灰渣对水泥稳定红砂岩集料的增强改性作用

Reinforcement and Modification Effect of CFB Fly Ash and Bottom Ash on Cement Stabilized Red Sandstone Aggregate

针对红砂岩均质性差,红砂岩集料性能和水泥稳定红砂岩集料路用性能不明确的问题,以水泥稳定石灰岩集料为对照,分别研究了红砂岩粗、细集料取代率。研究了循环流化床(CFB)炉渣、CFB飞灰掺量对水泥稳定红砂岩集料7 d无侧限抗压强度、长期强度、抗干缩性能和抗冻性能的影响规律。采用SEM揭示了CFB灰渣对水泥稳定红砂岩集料的改性作用机理。结果表明:红砂岩集料的组成成分和物理性能与粒径大小存在明显相关性,集料粒径越小,集料中的黏土矿物含量越高,压碎值越低,塑性指数越高,表明可以通过破碎筛分将不同类型红砂岩分离,提高红砂岩集料均质性。水泥稳定红砂岩集料的强度、抗裂性能、抗冻性受红砂岩粗集料替代率影响小,受红砂岩细集料替代率影响大。采用CFB炉渣和CFB飞灰作复合细集料可显著提高水泥稳定红砂岩集料的路用性能。与同水泥掺量水泥稳定石灰石集料相比,经改性后的水泥稳定红砂岩集料7 d无侧限抗压强度高0.8 MPa,干缩应变低49.5%,抗冻性持平。从SEM的试验结果中可以观察到针棒状钙矾石和絮状C—S—H凝胶,这表明CFB灰渣的水化产物起到了胶结增强作用,针棒状钙矾石形成产生的膨胀与CFB炉渣的多孔“内养生”作用可协同降低干缩、防止冻融破坏。

The homogeneity of red sandstone is poor,meanwhile the performance of red sandstone aggregate and cement stabilized red sandstone aggregate are not clear.Based on cement stabilized limestone aggregate,the substitution rates of coarse and fine red sandstones are studied respectively.The influence rules of circulating fluidized bed(CFB)bottom ash and fly ash contents on 7 d unconfined compressive strength,long-term strength,drying shrinkage resistance and frost resistance of cement stabilized red sandstone aggregate are studied.In addition,SEM is used to reveal the modification mechanism of CFB bottom ash and fly ash on cement stabilized red sandstone aggregate.The result indicates that there is a significant correlation between the composition and physical properties of red sandstone aggregate and its particle size.The smaller the aggregate particle size is,the higher the clay mineral content is.The lower the crushing value is,the higher the plasticity index is,which indicates that the different types of red sandstone can be separated by crushing and screening for improving the homogeneity of red sandstone aggregate.The compressive strength,crack resistance and frost resistance of cement stabilized red sandstone are less affected by the replacement rate of red sandstone coarse aggregate,but greatly affected by the replacement rate of red sandstone fine aggregate.Using CFB bottom ash and fly ash as composite fine aggregate can significantly improve the road performance of cement stabilized red sandstone aggregate.Compared with the cement stabilized limestone aggregate with the same cement content,the 7 d unconfined compressive strength of modified cement stabilized red sandstone aggregate is 0.8 MPa higher,the drying shrinkage strain is 49.5%lower,and the frost resistance is equal.With the SEM test result,needle-like ettringite and flocculent C—S—H gel can be observed,which indicate that the hydration products of CFB bottom ash and fly ash play a role in cementing enhancement.The expansion caused by needle-like ettringite formation and the porous internal curing effect of CFB bottom ash can synergistically reduce drying shrinkage and prevent freeze-thaw damage.