摘要
为研究氯盐浸泡液pH值、激发剂种类对碱激发矿渣(AAS)净浆氯离子固化量的影响规律,采用氯盐暴露-平衡法、X射线衍射(XRD)、热分析(TGA‑DSC)、扫描电镜(SEM)等分析了AAS净浆在氯盐浸泡前后的水化产物种类及微观形貌,同时对AAS净浆固化氯离子中的物理吸附和化学结合作用进行了量化评价.结果表明:AAS净浆的氯离子固化量随着氯盐浸泡液pH值的增大而降低;水玻璃激发矿渣(WAS)净浆固化氯离子的能力大于NaOH激发矿渣(NAS)净浆;AAS净浆对氯离子的固化作用不仅包括物理吸附作用,还包括少量化学结合作用;氯离子固化过程中的物理吸附作用在NAS、WAS和普通硅酸盐水泥净浆中均占50%以上.
土木工程领域中,氯盐侵入引起的钢筋锈蚀是导致混凝土结构耐久性劣化乃至失效的重要原因之一.引起钢筋锈蚀的并非只有进入混凝土内部的氯离
碱激发矿渣(AAS)是一种由碱性物质激发高炉矿渣而制成的绿色胶凝材料,其氯离子固化能力受到学者的关注.AAS主要水化产物为含铝相的 C‑S‑H(C‑A‑S‑H),其次是微纳米级水滑石(也被称为Mg‑Al层状双氢氧化物)和AFm型相混合
碱激发矿渣混凝土固化氯离子规律及其对氯离子传输性能影响效应的研究仍有较大空间.为此,本文研究了在不同激发剂种类和碱当量(质量分数,文中涉及的当量、含量等均为质量分数)、氯盐浸泡液pH值条件下AAS净浆氯离子固化能力的变化规律.通过X射线衍射(XRD)、热分析(TGA‑DSC)、扫描电镜(SEM),研究了氯盐浸泡前后AAS净浆的水化产物种类以及微观形貌,以期更深入地探究AAS净浆对氯离子的固化行为及其机理.
矿渣为青岛中矿宏远工贸有限公司提供的S95矿渣,颜色为灰白色;水泥为山东山铝水泥有限公司产P·I 42.5普通硅酸盐水泥;NaOH采用上海埃彼化学试剂有限公司产分析纯,含量≥96%,外观为白色结晶片状;水玻璃原液来自临沂绿森化工有限公司,外观为透明黏稠液体,模数3.2~3.4,制备试件时将水玻璃模数调配至1.8;用于配制氯盐浸泡液的NaCl来自上海埃彼化学试剂有限公司,分析纯,含量≥96%;试验用水均采用去离子水.胶凝材料的化学组成见
考虑激发剂种类(NaOH和水玻璃)和碱当量的影响,共设计6种配合比的AAS净浆试件,另外还制备了1组普通硅酸盐水泥净浆试件,用于对比.各试件尺寸均为40 mm×40 mm×160 mm,其配合比见
试件脱模后,放入(20±1)℃的去离子水中养护28 d;取出破碎后,取样置于无水乙醇中浸泡3 d;之后放入干燥箱中以65 ℃真空烘干至恒重,终止试样水化并防止碳化发生;再将烘干好的样品在手套箱中磨粉过74 μm筛,放入密封袋中干燥保存,分别用于氯盐溶液浸泡和微观测试.
采用平衡法原理试验评价试样的氯离子固化量.氯盐浸泡液选用浓度为1 mol/L的NaCl溶液.首先用NaOH将氯盐浸泡液的pH值分别调节为11.0、11.5、12.0、12.5、13.0和13.5,并用pH计测量确定;然后将3 g待测粉末样品置于40 mL的NaCl溶液中浸泡14 d;最后提取250 μL上清液,稀释100倍后,采用ICS‑1500离子色谱仪测量其氯离子浓度,以确定试样对氯离子的固化量.每组数据为3个平行样结果的平均值.随后过滤粉末样品,真空烘干,密封保存以备微观测试.
将氯盐浸泡前后的AAS粉末在65 ℃下真空干燥48 h,采用XRD技术分析氯盐浸泡前后AAS的晶相变化.粉末样品在10°~70°内连续扫描,扫描步宽为0.02°,扫描速度为0.02(°)/s.
采用美国TA公司产SC‑TGA Q600同步热分析仪测试氯盐浸泡前后AAS粉末的TGA‑DSC曲线.取8 mg左右的粉末置于陶瓷坩埚中,进行热分析测试.升温区间为室温~800 °C,加热速率为10 °C/min,氮气作为保护气,其流量为20 mL/min.
采用日立S‑3500N型SEM,结合能谱仪研究氯盐浸泡对AAS形貌的影响.先将样品粉末用导电胶粘到铜片上,并用真空镀膜仪对其进行镀膜处理,使之具有导电性,然后开机观察.能谱分析(EDS)采用面扫描方式.

图1 AAS净浆氯离子固化量与氯盐浸泡液pH值之间的关系
Fig.1 Relationship between chloride binding amount of AAS pastes and pH value of chloride immersion solution

图2 各AAS净浆及PC净浆的氯离子固化量
Fig.2 Chloride binding amount of AAS pastes and PC pastes

图3 NAS、WAS和PC净浆经氯盐溶液浸泡14 d前后的XRD图谱
Fig.3 XRD patterns of NAS,WAS and PC pastes before and after 14 d of immersion in chloride solution
由

图4 AAS(N3、W3)和PC净浆的TGA‑DSC曲线
Fig.4 TGA‑DSC curves of AAS(N3, W3) and PC pastes
由
(1) |
式中:为主层水在Friedel盐中的质量损失率,%;和分别为Friedel盐和水的摩尔质量,本文分别取为561.30、18.02 g/mol.
由TGA测定的Friedel盐的质量分数来计算化学结合氯离子量(mg/g),其计算式为:
(2) |
式中:MCl为氯的摩尔质量,本文取为35.45 g/mol;20为Friedel盐中氯的摩尔浓度(2 mol Cl/1 mol Friedel’s salt)、与单位转换的影响因数.
C‑(A)‑S‑H凝胶物理吸附氯离子量 (mg/g)可通过从固化氯离子总量减去化学结合氯离子量来计算:
(3) |

图5 NAS、WAS和PC净浆的物理吸附和化学结合氯离子量
Fig.5 Physical adsorption and chemical binding chloride amount of NAS, WAS and PC pastes
图

图6 NAS净浆在氯盐溶液中浸泡前后的SEM‑EDS分析
Fig.6 SEM‑EDS analysis of NAS pastes before and after immersion in chloride solution

图7 WAS净浆在氯盐溶液中浸泡前后的SEM‑EDS分析
Fig.7 SEM‑EDS analysis of WAS pastes before and after immersion in chloride solution
Note: ‑1 refers to the samples before chlorine solution immersion; ‑2 refers to the samples after chlorine solution immersion
由

图8 经氯盐溶液浸泡后AAS中Friedel盐的SEM照片
Fig.8 SEM photos of Friedel’s salt in AAS after chloride solution immersion
(1)在氯盐浸泡液pH值为11.0~13.5时,AAS净浆对氯离子的固化能力随着氯盐浸泡液pH值的增大而降低.AAS净浆所固化的氯离子量普遍高于PC净浆.其中WAS净浆固化氯离子的能力大于NAS.
(2)NAS、WAS和PC净浆对氯离子的固化作用中物理吸附作用均占50 %以上,其中,WAS的化学结合氯离子量最少,物理吸附氯离子量最多.
(3)经氯盐溶液浸泡后,AAS与氯离子反应生成一部分Friedel盐.AAS净浆对氯离子的固化作用不仅包括物理吸附作用,还包括少量化学结合作用.
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