偏高岭土增强石灰-水泥固化淤泥的耐久性研究

Enhancing durability of lime-cement solidified sludge with metakaolin

淤泥富含有机质,分解后产生腐殖酸,进而影响淤泥固化效果。仅掺入12%水泥固化淤泥,当标准养护期超过60 d,其强度不增反减。联合掺入3%石灰和12%水泥,固化淤泥的pH值持续180 d处于10.5以上;无侧限抗压强度由750 kPa(养护期28 d)提升到1500 kPa(120 d),说明借助石灰营造强碱性环境,可以提高水泥固化淤泥的强度;但养护到180 d后,其强度又降到1250k Pa;钙离子浓度变化规律表明,这是由于腐殖酸溶蚀水泥和石灰的水化胶结物所致。借助偏高岭土卓越的火山灰反应能力,掺入3.0%偏高岭土,提升石灰(3%)-水泥(12%)固化淤泥的耐久性,发现180 d养护期内,其强度始终处于增长趋势,究其原因是偏高岭土富含无定形硅、铝氧化物,具有快速捕获氢氧化钙溶液中钙离子的能力,形成稳定的胶结物,而且不易受腐殖酸的侵蚀作用,证明偏高岭土能够有效提升石灰-水泥固化淤泥长期强度。

Sludge is rich in organic matter,which would generate humic acid after decomposition.Humic acid will affect the reaction process and strength of cement-treated soil.The unconfined compressive strength(UCS)of sludge treated with 12%cement may decrease after 60 days curing.If adding both of lime(3%)and cement(12%)into sludge,the pH value of treated soils is higher than 10.5 after 180 days curing,and the UCS increases from 750 kPa(cured 28 d)to 1500 kPa(cured 120 d),which indicates that lime can improve the UCS of treated sludge significantly through establishing suitable strong alkaline environment.However,the UCS of treated sludge reduces to 1250 kPa after 180 days curing,which may ascribe to humic acid dissolving hydration products of lime and/or cement.The calcium ion concentration increases with the elapsing of curing period,which could explain the behavior of humic acid attacking to hydration products.Metakaolin contains lots of amorphous silicon and aluminum oxides,with the addition of 3%metakaolin into sludge based on mixing with lime(3%)and cement(12%),the UCS increases in the whole curing period(180 d).The results show that metakaolin can capture the calcium ion in short time and form stable cementitious materials in solidified soils.And these cementitious materials have strong anti-erosion capacity to humic acid effect.These above findings prove that metakaolin can improve the long-term performance of cement treated sludge.