微纳米Ca(OH)_(2)加固遗址土室内试验研究

Laboratory test of micro-nano Ca(OH)_(2) reinforced earthen sites

无机材料以兼容性强、耐久性好等特点被广泛应用于土遗址加固,特别疏松结构土遗址加固一直是学界关注的焦点,微纳米Ca(OH)_(2)具有分子结构小、加固效果显著和耐久性好等特点。以世界文化遗产锁阳城为代表,制备密度为1.5 g/cm^(3)的疏松土样,采用浓度为5%、7.5%和10%微纳米Ca(OH)_(2)的悬浊液滴渗加固,通过透气性、色差、无侧限抗压强度和抗剪强度测试发现,透气性下降值均在2%以内,5%和7.5%微纳米Ca(OH)_(2)加固后色差ΔEab*均小于4,在一定范围内可接受;其中用浓度为7.5%微纳米Ca(OH)_(2)加固3次后抗压强度和抗剪强度均有提高,无侧限抗压强度增长率为9.8%,土的黏聚力增加了34%,内摩擦角提高了9°;土-水特征曲线表明,微纳米Ca(OH)_(2)对土的体积收缩率具有较好的抑制作用。扫描电镜、X射线衍射和热重分析发现,微纳米Ca(OH)_(2)渗透加固后,在碱性环境下发生了的物理化学反应,在物理层面主要通过填充、包裹和镶嵌等使得疏松体更加密实,化学层面主要通过氢氧化钙的碳酸化反应形成新的钙质胶结物,这是其强度提高的主要原因。研究表明,微纳米Ca(OH)_(2)在土遗址防风化加固方面具有潜在应用价值。

Inorganic materials with strong compatibility and durability are widely used in the conservation of earthen sites,and those with especially loose structure has been the research focus of earthen sites reinforcement.Micro-nano Ca(OH)_(2) has a range of characteristics,including small molecular structure,significant reinforcement effect and good durability.Take the UNESCO world heritage site at Suoyang City as an example,we prepared the loose soil samples with the density of 1.5 g/cm^(3),then,the samples are enforced by micro-nano Ca(OH)_(2) suspension with concentration of 5%,7.5%and 10%,respectively.Through the tests of air permeability,color difference,unconfined compressive strength and shear strength,it is found that the decrease value of air permeability is within 2%,and the color difference(ΔEab*)treated by 5%and 7.5%micro-nano Ca(OH)_(2) suspension is less than 4,to certain degree,which is acceptable.The compressive strength and shear strength are improved after three rounds of reinforcement using the suspension with concentration of 7.5%.Meanwhile,the unconfined compressive strength increases by 9.8%,and the cohesion of soil increases by 34%.The internal friction angle grows up by 9°.The soil-water characteristic curve shows that micro-nano Ca(OH)_(2) has a good inhibitory effect on the volumetric shrinkage of soil samples.The reinforcement mechanism is revealed by scanning electron microscopy(SEM),X-ray diffraction(XRD),and thermogravimetric analysis.It is found a series of physicochemical reactions occurred in the alkaline environment after the treatment of micro-nano Ca(OH)_(2).From the physical perspective,loose samples are enhanced by filling,wrapping,and mosaic.In terms of chemical perspective,the carbonation of calcium hydroxide forms new calcareous cements,which is the primary reason of reinforcement.This study reveals that micro-nano Ca(OH)_(2) has potential for the anti-weathering and reinforcement of earthen sites.