CO_(2)碳化水泥土抗压强度与微观机制研究

Compressive strength and micro-mechanisms of CO_(2) carbonated cement-solidified soils

CO_(2)碳化与水泥水化协同加固技术是兼具固化增强和实现CO_(2)永久封存的新方法。目前关于CO_(2)碳化水泥固化土抗压强度、耐久性及微观机制的研究尚不深入。通过抗压强度、扫描电镜、长期浸水、干湿循环和冻融循环等试验,依据表观形貌、抗压强度和强度软化系数等指标,全面评价了CO_(2)碳化水泥土的力学表现和耐久性。结果表明:水泥掺量增加促使试样抗压强度持续增长,碳化试样抗压强度高于标准养护试样,最佳水泥掺量为25%;CO_(2)浓度增大可加快CO_(2)扩散速率和碳化反应进度,试样碳化深度和抗压强度随之增加,碳化试样抗压强度高于标准养护试样;生成的方解石和霰石是CO_(2)碳化水泥固化土强度显著增长的根本原因;标准养护水泥固化试样抵抗浸水软化、干湿循环和冻融循环破坏的能力高于碳化试样;碳化3 d试样抗冻融循环等耐久性最差,试样表面出现大范围块体剥落;标准养护7 d碳化1 d试样具有良好耐久性;短期浸水时,碳化试样抗压强度高于标准养护试样;干湿循环时,碳化固化试样强度软化系数保持在0.8以上,最高达0.9且抗压强度超过5.5 MPa;冻融循环时,碳化的固化土试样抗压强度高于标准养护试样。研究成果可为CO_(2)碳化与水泥水化协同加固地基土技术的研发及工程应用提供参考。

The combined technology of CO_(2) carbonation and cement hydration is a novel approach for soil solidification and CO_(2) permanent storage.Until now,there are few reports on the strength,durability and micro-mechanisms of CO_(2) carbonated cement-solidified soils.By using compressive strength,scanning electron microscopy,water immersion,cyclic dry-wet and cyclic freeze-thaw tests etc.,the strength and durability of CO_(2) carbonated solidified soil is evaluated according to the morphology,compressive strength and strength softening coefficient.The compressive strength of solidified sample tends to grow with increasing cement content,while the strength of carbonated sample is higher than that of standard curing sample and the optimal cement content is 25%.An increase in CO_(2) concentration can accelerate the diffusion rate of CO_(2) and carbonation degree,and it can induce an increase in carbonation depth and compressive strength of carbonated sample,and the strength of carbonated sample is greater than that under standard curing.The formation of calcite and aragonite crystals is the intrinsic reason that the compressive strength of carbonated sample significantly increases.From the viewpoint of strength softening coefficient,the resistance of solidified sample to water immersion,cyclic dry-wet and cyclic freeze-thaw is higher than that of carbonated sample.The durability of freezing resist of 3-day carbonated sample is the worst,and the large-scale block spalling appears on the sample surface after testing.The 7-day standard curing and 1-day carbonated samples have good durability.For the short-term immersion,the strength of carbonated sample is higher than that of standard curing sample.For the cyclic dry-wet tests,the softening coefficient of carbonated solidified sample remains above 0.8(maximum 0.9)and the strength exceeds 5.5 MPa.For the cyclic freeze-thaw tests,the strength of carbonated solidified sample is higher than that of standard curing sample.The obtained results provide a theoretical basis for the development and engineering application of combined solidification technology based on CO_(2) carbonation and cement hydration for ground reinforcement.