摘要
利用工业废弃物赤泥、电石渣和脱硫石膏组成的赤泥复合固化剂对低液限粉土进行固化,探究了固化粉土的力学性能(无侧限抗压强度和劈裂强度)和耐久性(水稳定性和干湿循环),并采用扫描电镜(SEM)和X射线衍射仪(XRD)分析赤泥复合固化剂的固化机理.结果表明:固化粉土的无侧限抗压强度和劈裂强度随着赤泥复合固化剂掺量的增加和养护龄期的延长而提高;当赤泥复合固化剂掺量由8%增至24%且养护龄期由7 d延至28 d时,固化粉土的水稳系数由69.5%提高到82.4%;干湿循环12次后,固化粉土的强度损失率为35.14%.赤泥复合固化剂掺入粉土中发生水化反应,生成具有胶凝作用的水化硅酸钙(C‑S‑H)和水化铝酸钙(C‑A‑H)凝胶,同时C‑A‑H与CaSO4生成钙矾石(AFt)晶体;C‑S‑H和C‑A‑H包裹并填充着土颗粒,AFt晶体穿插在土颗粒间,使其成为一个整体,有效提高了固化粉土的路用性能.
粉土因具有级配差、整体结构松散、强度低等特点,不宜直接作为路基材料.为实现对粉土的有效利用,采用固化剂来固化粉土已成为一种常见的处理方
考虑到电石渣和脱硫石膏可以组成复合激发剂,在一定程度上能够提高反应环境的pH值,有助于硅铝酸盐的溶解.本试验选用由工业废弃物赤泥、电石渣和脱硫石膏组成的赤泥复合固化剂,对河南地区高速路段低液限粉土进行固化,研究赤泥复合固化剂对粉土的固化效果及其固化机理.
试验用土取自河南安鹤高速工程现场地下150 cm深处土体.根据JTG 3430—2020《公路土工试验规程》测定土样的基本物理指标. 由于粒径小于75 μm的土样占比(质量分数,文中涉及的占比、组成等均为质量分数)为60.2%,故判定其为低液限粉土,基本物理指标见
Natural moisture (by mass)/% | Plastic limit(by mass)/% | Liquid limit(by mass)/% | Plasticity index | Maximum dry density/ (g∙c | Optimal moisture(by mass)/% |
---|---|---|---|---|---|
13.3 | 17.2 | 26.2 | 9 | 1.96 | 11.2 |
试验用赤泥为河南恒源新材料有限公司生产的烧结法赤泥,脱硫石膏购于河南锦源环保技有限公司,电石渣购于武汉华英新世纪环保设备有限公司.3种固化剂的化学组成及X射线衍射(XRD)图谱见
Material | CaO | SiO2 | Al2O3 | Fe2O3 | MgO | Na2O | SO3 |
---|---|---|---|---|---|---|---|
Red mud | 34.38 | 25.61 | 7.84 | 9.43 | 2.99 | 0.31 | |
Carbide slag | 84.30 | 3.40 | 0.18 | 0.23 | 0.79 | 0.11 | |
Desulfurization gypsum | 45.06 | 1.08 | 0.78 | 0.46 | 0.11 | 32.14 |

图1 3种固化剂的XRD图谱
Fig.1 XRD patterns of three kinds of solidification agents
试样制备参照JTG E51—2009《公路工程无机结合料稳定材料试验规程》与JTG 3430—2020进行.将赤泥复合固化剂按设计掺量(w)掺入粉土中,设置赤泥复合固化粉土(以下简称固化粉土)含水率为最佳含水率11.2%,压实度为98%.采用静力压实法制备尺寸为ϕ50×50 mm的圆柱试样,每组6个,试验值取其平均值.
固化粉土的耐久性通过水稳定性试验和干湿循环试验进行评价.采用5种掺量(8%、12%、16%、20%和24%)的赤泥复合固化剂,通过水稳系数K(%)表征固化粉土的水稳定性.K的计算式为:
(1) |
式中: Rw为试样浸泡24 h的无侧限抗压强度,MPa;R0为试样养护至规定龄期的无侧限抗压强度,MPa.
干湿循环试验采用掺量为16%的赤泥复合固化剂,固化粉土养护28 d后分别进行1、3、6、9、12次干湿循环过程,以试验前后试样的质量、体积和强度变化来评价固化粉土的抗干湿循环能力.
为研究固化粉土的固化机理,选取3种典型试样(未掺固化剂的粉土,单掺赤泥的粉土和复掺赤泥、电石渣、脱硫石膏的粉土)进行扫描电镜(SEM)试验和XRD试验.固化粉土微观试验方案见
Sample name | w(solidification agent)/% | Curing age/d | Experimental project | ||
---|---|---|---|---|---|
Red mud | Carbide slag | Desulfurized gypsum | |||
Silt | 0 | 0 | 0 | 7/28 | SEM/XRD |
Silt of single‑doped red mud | 15.84 | 0 | 0 | ||
Red mud composite solidified silt | 15.84 | 14.32 | 7.32 |

图2 固化粉土无侧限抗压强度随赤泥复合固化剂掺量和养护龄期的变化
Fig.2 Variation of unconfined compressive strength of solidified silts with red mud composite solidification agent content and curing age

图3 固化粉土劈裂强度随赤泥复合固化剂掺量和养护龄期的变化
Fig.3 Variation of splitting strength of solidified silts with red mud composite solidification agent content and curing age

图4 固化粉土水稳系数随赤泥复合固化剂掺量和养护龄期的变化
Fig.4 Variation of water stability coefficient of solidified silts with red mud solidification agent content and curing age

图5 固化粉土(赤泥复合固化剂掺量为16%)质量损失率和体积膨胀率随干湿循环次数的变化
Fig.5 Variation of mass loss rate and volume expansion rate of solidified silts(red mud solidification agent content is 16% ) with number of dry‑wet cycle

图6 固化粉土(赤泥复合固化剂掺量为16%)无侧限抗压强度随干湿循环次数的变化
Fig.6 Variation of unconfined compressive strength of solidified silts(red mud solidification agent content is 16% ) with number of dry‑wet cycle

图7 3种典型试样的XRD图谱
Fig.7 XRD patterns of three kinds of typical samples

图8 3种典型试样的SEM照片
Fig.8 SEM images of three kinds of typical samples
对比
(2) |
(3) |
(4) |
(5) |
对比
(6) |
对比
赤泥的主要成分为CaO、SiO2、Al2O3和Fe2O3.当其掺入粉土后首先发生水化反应,生成的Ca(OH)2激发粉土中的SiO2、Al2O3,生成C‑S‑H和C‑A‑H等凝胶物质.这些凝胶物质不断连接土颗粒并填充土颗粒间的孔隙,有效提高了土体强度.
随着电石渣和脱硫石膏的掺入,电石渣中大量的Ca(OH)2不仅提高了土体的pH值,更好地激发了土颗粒和赤泥中SiO2和Al2O3的活性,还参与反应生成更多的凝胶物质.这些凝胶物质进一步与CaSO4反应生成AFt,C‑S‑H和C‑A‑H凝胶物质包裹着土颗粒,填充着土颗粒间的空隙,AFt晶体穿插在土颗粒中,使其成为一个整体,提高了固化粉土整体强度.
粉土表面吸附着的N
(1)赤泥复合固化剂对粉土力学性能有显著改善作用.固化粉土的无侧限抗压强度和劈裂强度随着赤泥复合固化剂掺量的增加和养护龄期的延长而提高.当赤泥复合固化剂掺量由8%增至24%,且养护龄期由7 d延至28 d时,固化粉土的水稳系数由69.5%提高到82.4%.干湿循环12次后,固化粉土的强度损失率达到35.14%.
(2)赤泥复合固化剂掺入粉土中会激发其中不稳定的SiO2和Al2O3水解生成[SiO(OH)3
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