摘要
研究了高低黏度羟丙基甲基纤维素(HPMC)对硅酸盐水泥(PC)-硫铝酸盐水泥(CSA)复合浆体流变性的影响及其机理.结果表明:HPMC在水泥颗粒表面的吸附及其对孔溶液动力黏度的提高阻碍了颗粒的迁移,进而增加了复合浆体的初始表观黏度;HPMC掺量越大,初始表观黏度越高,且高黏度HPMC改性浆体的初始表观黏度比低黏度HPMC改性浆体更高;随着时间的推移,HPMC逐渐吸水膨胀,导致其改性浆体的表观黏度也逐渐增大;HPMC的吸水效果受孔溶液性质的影响,低黏度、低掺量HPMC改性浆体孔溶液的动力黏度较小,溶液在孔隙中的传输阻力也较小,HPMC更容易吸水;高黏度、高掺量HPMC改性浆体孔溶液的动力黏度较大,溶液在孔隙中的传输阻力也随之增大,从而阻碍了HPMC的吸水.
近年来,硅酸盐水泥(PC)-硫铝酸盐水泥(CSA)作为一种复合胶凝材料受到了广泛的关注,这主要源于二者的复合能够充分发挥各自的特点,比如缩短凝结时间、增加早期强度、抵抗收缩、优化耐久性以及降低碳排放
胶凝材料为P∙Ⅱ 52.5R硅酸盐水泥、硫铝酸盐水泥和无水石膏(C),其氧化物组成(质量分数,文中涉及的掺量、比值均为质量分数或质量比)见
Material | CaO | SiO2 | Fe2O3 | Al2O3 | SO3 |
---|---|---|---|---|---|
PC | 72.2 | 12.9 | 4.5 | 4.3 | 2.4 |
CSA | 43.1 | 7.7 | 1.9 | 33.6 | 9.3 |
C | 42.1 | 0.1 | 57.7 |
净浆水胶比为0.4,胶凝材料PC、CSA和C的质量比为92.50∶7.50∶0.75.设置HPMC的掺量wHPMC为0.1%、0.3%,采用高黏度和低黏度HPMC制备的对应样品分别记为H1、H3和L1、L3.为了对比,制备了不掺HPMC(wHPMC=0%)的样品,记为R.
样品的制备过程为:称量一定质量的减水剂,在搅拌锅里与水混合均匀;将拌和好的干混材料倒入搅拌锅搅拌,先慢速搅拌120 s、停15 s、再快速搅拌120 s.得到的浆体用于流变性
为方便得到更多孔溶液,将水胶比增大为5.0.采用高速离心机制备浆体的孔溶液,首先将水泥与水充分混合5 min,随后将离心管放入离心机离心5 min,转速设定为4 000 r/min,旋转后取其上清液作为孔溶液,测定其表面张力和动力黏度.
流变性测试参考课题组前期研
孔溶液表面张力参照GB/T 8077—2023《混凝土外加剂匀质性试验方法》,采用上海衡平BZY‑2全自动界面张力仪进行测试.
孔溶液动力黏度的测试参照GB/T 265—1988《石油产品运动黏度测定法和动力黏度计算法》,采用毛细管内径为1 mm的乌氏黏度计,测试孔溶液的流出时间.孔溶液的动力黏度ηt为:
(1) |
式中:ρt为样品在测定温度t下的密度,g/c
样品表观黏度随静置时间的变化见

图1 样品表观黏度随静置时间的变化
Fig.1 Change of apparent viscosity of samples with resting time
需要说明的是,在实际施工过程中,为了避免因设备剪切速率而导致的复合浆体表观黏度不稳定现象,一般选择较高的剪切速率以获取稳定表观黏度的浆体,因此本文选择高剪切速率下的剪切应力进行分析.为了量化样品在不同静置时间下的流变行为,给出了其在高剪切速率下的剪切应力,结果见

图2 样品在不同静置时间下剪切应力的拟合结果
Fig.2 Fitting results of shear stress of samples at different resting time
为了更直接地说明HPMC对浆体流变性的影响,引入宾汉姆模型来拟合剪切应力和剪切速率的关系.宾汉姆模型的数学表达式为:
(2) |
式中:τ0为屈服应力,Pa;η为塑性黏度,Pa∙s.
依据宾汉姆模型,样品在不同静置时间下剪切应力的拟合结果见

图3 样品屈服应力和塑性黏度随静置时间的变化
Fig.3 Variation of yield stress and plastic viscosity with resting time for samples
在本研究中,由于样品R在前60 min的屈服应力和塑性黏度并没有太大改变,这说明复合体系水泥颗粒在前60 min发生水化反应的程度并不深,可能更多的只是溶解.另外,较多文
样品在不同静置时间下的T2分布图见

图4 样品在不同静置时间下的T2分布图
Fig.4 T2 distribution diagrams of samples at different resting time
为了便于分析,绘制了HPMC吸水峰积分强度(峰面积)随静置时间的变化情况,结果见

图5 HPMC吸水峰积分强度随静置时间的变化
Fig.5 Change of HPMC water absorption peak integral intensity with resting time
HPMC既有表面活性剂的性质又属于黏度改性剂,其掺入很大可能将改变新拌浆体中孔溶液的性质,比如表面张力和动力黏度.而对于多孔介质,溶液在孔隙中的迁移速率可能受到孔溶液表面张力和动力黏度的影响,CE具有表面活性剂的性质,它能够降低孔溶液的表面张力,使得浆体在搅拌的过程中容易引入气泡.在这种情况下,CE在气孔界面积累,从而可以稳定气
为此,测试并计算了孔溶液的表面张力和动力黏度,结果见

图6 孔溶液表面张力和动力黏度随HPMC掺量的变化
Fig.6 Changes of surface tension and dynamic viscosity of pore solution with HPMC dosages
由
综上,HPMC的掺入降低了孔溶液的表面张力,增加了其动力黏度,这在一定程度上增加了溶液迁移过程中的阻力;HPMC掺量越高,阻力越大;相同掺量下,HPMC‑H改性体系的阻力高于HPMC‑L改性体系.
HPMC的掺入增加了PC‑CSA复合胶凝体系的静态黏度(初始表观黏度).主要原因有2个:一是HPMC在水泥颗粒表面的吸附,增加了水泥颗粒迁移的阻力;二是HPMC增大了孔溶液的动力黏度,进而增加了各种粒子之间的迁移阻力,这均源于HPMC分子的链状结构.
HPMC的掺入使得PC‑CSA复合胶凝体系的表观黏度随时间发生了有规律的变化,这取决于HPMC的吸水效果.HPMC吸水产生溶胀,进而增大胶凝体系的表观黏度,而HPMC的吸水效果又受孔溶液性质的影响.当孔溶液易于传输时,HPMC对水的吸收能力决定了其吸水效果,掺量越高,吸水效果越明显(对比试件L1和L3);在相同掺量下,高黏度HPMC吸水效果更好(对比试件L1和H1).但是,当孔溶液的传输所受阻力较大时,HPMC的吸水效果就会变慢(对比试件L3和H3).
(1)羟丙基甲基纤维素(HPMC)在水泥颗粒表面的吸附及其对孔溶液黏度的提高,阻碍了颗粒的迁移,从而增加了硅酸盐水泥-硫铝酸盐水泥(PC‑CSA)复合浆体的初始表观黏度,且HPMC掺量越大,初始表观黏度越高,且高黏度HPMC改性浆体的初始表观黏度比低黏度HPMC改性浆体更高.
(2)随着时间的推移,HPMC逐渐吸水膨胀,导致其改性浆体的表观黏度也逐渐增加.HPMC的掺入使得PC‑CSA复合浆体的表观黏度随时间发生了有规律的变化:HPMC掺量越高,浆体表观黏度随时间增长的幅度越大;对于不同黏度HPMC,低掺量(0.1%)时,高黏度HPMC改性浆体的表观黏度随时间增长的幅度高于低黏度HPMC改性浆体,当掺量达到0.3%时,低黏度HPMC改性浆体的表观黏度随时间增长的幅度高于高黏度HPMC改性浆体.
(3)HPMC的吸水效果受孔溶液性质的影响,低黏度、低掺量HPMC改性浆体孔溶液动力黏度较小,溶液在孔隙中的传输阻力较小,HPMC容易吸水;高黏度、高掺量HPMC改性浆体孔溶液动力黏度较大,溶液在孔隙中的传输阻力也随之增大,从而阻碍HPMC的吸水.
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