摘要
研究了羟乙基纤维素(HEC)和高低取代度羟乙基甲基纤维素(H‑HMEC、L‑HEMC)对硫铝酸盐(CSA)水泥早期水化进程和水化产物的影响.结果表明:不同掺量L‑HEMC均可促进CSA水泥在45.0 min~10.0 h内的水化;3种纤维素醚均先延缓CSA水泥溶解及其转化阶段的水化,后促进2.0~10.0 h内的水化;甲基的引入增强了含羟乙基纤维素醚对CSA水泥水化的促进作用,L‑HEMC的促进作用最强;不同取代基和取代度的纤维素醚对水化前12.0 h内水化产物生成量的影响存在显著差异,HEMC对水化产物的促进作用强于HEC,L‑HEMC改性CSA水泥浆体在水化2.0、4.0 h时生成钙钒石和铝胶的量最多.
以无水硫铝酸钙(C4A3Š)和硅酸二钙(C2S)为主要熟料矿物的硫铝酸盐(CSA)水泥具有快硬早强、抗冻抗渗、碱度低等优
然而,目前关于不同取代基及取代度的CE对CSA水泥早期水化影响的对比研究尚不充分.本文研究了不同掺量、取代基和取代度的含羟乙基纤维素醚对CSA水泥早期水化的影响,着重分析了12 h内含羟乙基纤维素醚改性CSA水泥的水化放热规律,并定量分析了其水化产物.
水泥为42.5级快硬CSA水泥,初、终凝时间分别为28、50 min,其化学组成和矿物组成(质量分数,文中涉及的掺量、水灰比等均为质量分数或质量比)见
固定水灰比为0.54,L‑HEMC的掺量(文中掺量均以水泥的质量计)wL=0%、0.1%、0.2%、0.3%、0.4%、0.5%,HEC和H‑HEMC的掺量均为0.5%.文中:L‑HEMC‑0.1为wL=0.1%的L‑HEMC改性CSA水泥,其他类推;CSA为纯CSA水泥;HEC改性CSA水泥、L‑HEMC改性CSA水泥、H‑HEMC改性CSA水泥分别记为HCSA、LHCSA、HHCSA.
水化热测试采用八通道等温微量热仪,量程为600 mW.试验前将仪器在(20±2) ℃、相对湿度RH=(60±5)%下稳定6.0~8.0 h,按配合比将CSA水泥、CE及拌和水,以600 r/min的转速电动拌制1 min后,立即称量(10.0±0.1) g浆体装入安瓿瓶中,将安瓿瓶放入仪器中并开始计时测试,水化温度为20 ℃,每隔1 min记录1次数据,测试至12.0 h.
热重(TG)分析:根据ISO 9597—2008《Cement—Test methods—Determination of setting time and soundness》制备得到水泥浆体.将拌制好的水泥浆体装入20 mm×20 mm×20 mm的试模中,人工振动10次后,置于(20±2) ℃、RH=(60±5)%下养护,分别在龄期t=2.0、4.0、12.0 h时取出试样.去除试样表层(≥1 mm)后将其破碎成小块浸泡在异丙醇中,连续7 d每隔1 d更换1次异丙醇,以确保水化反应完全中止,并在40 ℃下烘干至恒重.称取(75±2) mg样品放入坩埚中,绝热条件下,在氮气氛围中,以20 ℃/min的升温速率将样品从30 ℃加热至1 000 ℃.CSA水泥水化产物的热分解主要发生在50~550 ℃,通过计算该范围内样品的质量损失率可以得到其化学结合水的含量;钙钒石(AFt)在50~180 ℃受热分解失去20个结晶水,铝胶(AH3)在230~300 ℃受热分解失去3个结晶水,根据TG曲线可计算得到各水化产物的含

图1 不同掺量L‑HEMC改性CSA水泥浆体的水化放热曲线
Fig.1 Hydration heat release curves of L‑HEMC modified CSA cement pastes with different wL
L‑HEMC掺量对CSA水泥水化溶解和转化阶段的影响各异:当L‑HEMC掺量较低时,L‑HEMC改性CSA水泥浆体第2水化放热峰的出现时间略提前,其放热速率和放热峰峰值明显高于纯CSA水泥浆体;随着L‑HEMC掺量的增加,L‑HEMC改性CSA水泥浆体的放热速率逐渐降低,并低于纯CSA水泥浆体.L‑HEMC‑0.1的水化放热曲线放热峰数量与纯CSA水泥浆体相同,但其第3、4水化放热峰分别提前至42.0 min和2.3 h,且相比于纯CSA水泥浆体的33.5、9.0 mW/g,其放热峰峰值分别提高到36.9、10.5 mW/g,这表明0.1%掺量L‑HEMC加速且加强了L‑HEMC改性CSA水泥相应阶段的水化;而L‑HEMC掺量为0.2%~0.5%时,L‑HEMC改性CSA水泥的加速减速阶段逐渐合二为一,即第4放热峰提前并与第3放热峰合并,中间的动态平衡阶段不再出现,L‑HEMC对CSA水泥水化的促进作用更显著.
由
3种CE改性CSA水泥浆体的水化放热曲线见

图2 3种CE改性CSA水泥浆体的水化放热曲线
Fig.2 Hydration heat release curves of three kinds of CE modified CSA cement pastes
CE的化学结构对其在水泥颗粒表面的吸附作用有很大影响,尤其是取代度和取代基的类
不同掺量L‑HEMC改性CSA水泥浆体的TG‑DTG曲线见

图3 不同掺量L‑HEMC改性CSA水泥浆体的TG‑DTG曲线
Fig.3 TG‑DTG curves of L‑HEMC modified CSA cement pastes with different wL

图4 不同掺量L‑HEMC改性CSA水泥浆体化学结合水及水化产物AFt、AH3的含量
Fig.4 ww、wAFt and of L‑HEMC modified CSA cement pastes with different wL
3种CE改性CSA水泥浆体的TG‑DTG曲线见

图5 3种CE改性CSA水泥浆体的TG‑DTG曲线
Fig.5 TG‑DTG curves of three kinds of CE modified CSA cement pastes

图6 3种CE改性CSA水泥浆体化学结合水及水化产物AFt、AH3的含量
Fig.6 ww、wAFt and of three kinds of CE modified CSA cement pastes
由图
(1)不同掺量低取代度羟乙基甲基纤维素(L‑HEMC)均可促进硫铝酸盐(CSA)水泥在45.0 min~10.0 h内的水化.
(2)羟乙基纤维素(HEC)、高取代度羟乙基甲基纤维素(H‑HEMC)、L‑HEMC这3种含羟乙基纤维素醚(CE)均对CSA水泥水化的溶解和转化阶段具有延缓作用,对2.0~10.0 h的水化具有促进作用.
(3)含羟乙基CE中引入甲基能显著增强其对CSA水泥2.0~5.0 h内水化的促进作用,L‑HEMC对CSA水泥水化的促进作用强于H‑HEMC.
(4)当CE掺量为0.5%时,L‑HEMC改性CSA水泥浆体在水化2.0、4.0 h时生成的钙矾石(AFt)和铝胶(AH3)的量均最多,其促进水化的作用最显著;H‑HEMC和HEC改性CSA水泥浆体仅在水化4.0 h时生成的AFt和AH3含量高于纯CSA水泥浆体.水化12.0 h时,3种CE对CSA水泥水化产物生成量的影响不再显著.
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