偏高岭土协同石灰抑制红黏土收缩的行为与机制

Behavior and mechanism of laterite shrinkage inhibition with lime and meta-kaolin mixture

红黏土失水易收缩开裂而诱发工程灾害,为抑制或缓减红黏土的收缩特征,添加4%偏高岭土和5%石灰改善其水敏性。按照最优含水率制备压实试样,养护180 d后抽真空饱和,脱湿到预定含水率,随后开展收缩、无侧限抗压强度、吸力和孔隙分析等试验。结果表明,压实红黏土随着含水率降低,其无侧限抗压强度呈现先增大后减少的变化规律,这是脱湿导致的红黏土衍生微裂隙,进而引起结构性损伤所致。红黏土掺入石灰,尤其是掺入石灰-偏高岭土后,虽然脱湿也会引起强度减小,但接近完全干燥时,其强度又会增大。由此说明,偏高岭土协同石灰可以更加有效地抑制红黏土收缩效应,提高其整体强度。究其原因,是偏高岭土含有大量无定形硅、铝氧化物,且呈现边-面"搭接"的独特结构形态,使其能够快速捕获氢氧化钙溶液中的钙离子,在红黏土团(颗)粒间形成了胶结性水化物。

The laterite is prone to shrinkage and crack due to dehydration, which may result numerous engineering disasters. Lime(5%) and meta-kaolin(4%) were added into laterite for mitigating their shrinkage behavior through improving moisture sensitivity. The samples were compacted at optimal water content and cured for 180 days. And then, samples were vacuumed and saturated immediately. After that, the saturated samples were dehydrated to predetermined moisture content for conducting a series of tests such as shrinkage, unconfined compressive strength, suction and pore analysis. The results showed that compressive strength of laterite increased at first and then decreased with moisture content reducing, which may be caused by micro-cracks derived ascribing to dehumidification. However, the strength of laterite adding with lime, especially lime and meat-kaolinite mixture, would increase with approaching to dry status, even if which has a slight reduction during drying process. This proved that meta-kaolin and lime were able to inhibit the shrinkage effect of laterite, and increase their overall strength. This may be ascribed to the following reasons, meta-kaolin contains lots of amorphous silicon and aluminum oxides and has an edge-surface contacted structure, both enable meta-kaolin to quickly capture calcium ions in calcium hydroxide solution and form cementation hydrates between grains or particles of laterite.