摘要
在2种类型石膏(无水石膏和半水石膏)情况下,研究了三乙醇胺(TEA)对掺偏高岭土水泥(MKC)水化进程及其硫酸盐平衡的影响,并与自配硅酸盐水泥(APC)进行对比.结果表明:无TEA加入时,MKC中偏高岭土(MK)的存在可延长水泥的水化诱导期并加快硫酸盐的消耗,2种类型石膏表现基本一致;TEA的加入能够显著促进水泥中铝相矿物的水化,增加硫酸盐平衡所需石膏掺量,同时石膏类型对水泥水化进程与硫酸盐平衡影响显著;对于APC与MKC,在TEA作用下能有效维持其硫酸盐平衡的石膏类型分别为无水石膏与半水石膏,这与水泥中硫酸根离子溶出-吸附-沉淀的动态平衡密切相关.
煅烧黏土水泥具有原料充足、低碳环保等突出优点,被视为应用前景广阔的新型低碳胶凝材
硫酸盐平衡是水泥凝结硬化性能的关键因素,可通过调控水泥中的石膏掺量实
考虑到煅烧黏土中的主要矿物为偏高岭土(MK).为简化试验变量,本文使用MK替代煅烧黏土,将其与水泥熟料及石膏混合,制备得到掺偏高岭土水泥.通过改变石膏类型及掺量,系统研究不同石膏类型情况下TEA对掺偏高岭土水泥水化进程与硫酸盐平衡的影响,分析了内在反应机制,以期为煅烧黏土水泥更加广泛的应用提供一定理论指导.
水泥熟料为灵寿县岩行矿产品贸易有限公司产P·Ⅰ 42.5普通硅酸盐水泥熟料;偏高岭土(MK)为河南焦作煜坤矿业有限公司产偏高岭土;半水石膏(Hem)、无水石膏(Ahy)及氢氧化钠(NaOH)由国药集团化学试剂有限公司提供,分析纯;三乙醇胺(TEA)由国药集团提供,分析纯,掺量(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)为0%、0.1%和0.5%(以水泥质量计).水泥熟料和偏高岭土的化学组成如
Material | Al2O3 | CaO | Fe2O3 | TiO2 | MgO | SiO2 | IL |
---|---|---|---|---|---|---|---|
Cement clinker | 6.60 | 56.40 | 4.37 | 0.36 | 5.10 | 24.03 | 0.41 |
Metakaolin | 48.59 | 0.63 | 5.46 | 3.39 | 0.23 | 40.91 | 0.11 |
C3S | C2S | C3A (cub) | C3A (ortho) | C4AF | Arcanite |
---|---|---|---|---|---|
65.50 | 13.50 | 5.20 | 2.10 | 12.80 | 0.90 |
试验用硅酸盐水泥(APC)与掺偏高岭土水泥(MKC)由实验室自配,两者的BET比表面积均控制在1.41
No. | MK | Hem | Ahy | Clinker |
---|---|---|---|---|
APC‑Ahy | 0 | 0 | 1.5/3.0/5.0/7.0 | 98.5/97.0/95.0/93.0 |
MKC‑Ahy | 30.0 | 0 | 1.5/3.0/5.0/7.0 | 68.5/67.0/65.0/63.0 |
APC‑Hem | 0 | 1.5/3.0/5.0/7.0 | 0 | 98.5/97.0/95.0/93.0 |
MKC‑Hem | 30.0 | 1.5/3.0/5.0/7.0 | 0 | 68.5/67.0/65.0/63.0 |
为保证各组分充分混合,先将水泥熟料、石膏及偏高岭土在vortex‑2型漩涡混匀仪中搅拌24 h,搅拌速率为1 500 r/min;再在25 ℃下将去离子水或TEA溶液与上述原材料搅拌1 min制得水泥浆体.采用TAM Air八通道等温量热仪测试浆体的水化放热数据,测试温度为25 ℃,放热速率与放热量试验值基于胶材总量进行归一化处理.依照GB/T 17671—2021《水泥胶砂强度检验方法(ISO法)》测试水泥浆体在3、7、28 d时的抗压强度,重复测试3次,取其平均值作为试验值.采用梅特勒Five Easy Plus测定2种类型石膏在溶液中的电导率,以表征其溶解速率,具体步骤如下:将25.00 mg Ahy或26.65 mg Hem分别加到100 g NaOH(pH值为11)与TEA的混合溶液,其中TEA质量为0、1.25 g(对应水泥浆体中TEA掺量为0%和0.5%).待石膏加入上述混合溶液后即开始记录数据,初始5 min,每30 s记录1次;5~30 min时,每1 min记录1次;30 min后,每5 min记录1次.测试过程中对溶液进行持续搅拌,搅拌速率为1 000 r/min.

图1 无TEA作用时不同类型石膏对APC和MKC水化进程的影响
Fig.1 Effect of different types of sulfate carriers on APC and MKC hydration process without presence of TEA
由

图2 TEA作用下不同类型石膏对APC水化进程的影响
Fig.2 Effect of different types of sulfate carriers on APC hydration process in the presence of TEA

图3 TEA作用下不同类型石膏对MKC水化进程的影响
Fig.3 Effect of different types of sulfate carriers on MKC hydration process in the presence of TEA
强度测试是检验水泥硫酸盐平衡的重要手段.

图4 TEA作用下不同类型石膏对MKC抗压强度的影响
Fig.4 Effect of different types of sulfate carriers on compressive strength of MKC in the presence of TEA
相较传统的强度测试方法,通过水化放热量判断水泥的硫酸盐平衡更加快捷有

图5 TEA作用下不同类型石膏对APC及MKC 48 h放热量的影响
Fig.5 Effect of different types of sulfate carriers on heat released within 48 h of APC and MKC in the presence of TEA
由
由
由
上述研究表明,在无TEA加入情况下,不同类型石膏对APC水化进程影响有限,而MK的引入能够促进体系中铝相矿物的水化反应,出现明显放热峰肩.由于水泥中铝相矿物二次反应的出现为石膏耗尽后硫酸根离子在铝酸三钙(C3A)表面的脱附所致,因此放热峰肩的出现说明MK的引入可加速水泥中硫酸根离子的消
当TEA掺量为0.1%时,不同类型石膏对APC与MKC水化进程的影响与无TEA加入情况下类似.对于TEA掺量为0.5%时的APC体系,相较半水石膏,APC中无水石膏掺量的增加可显著缩短水泥的水化诱导期,更能有效抑制水泥中铝相矿物的快速水化反应.

图6 不同TEA掺量下不同类型石膏溶液电导率
Fig.6 Conductivity of sulfate solution prepared at different TEA dosages
对于TEA掺量为0.5%时的MKC体系,当MKC体系中石膏掺量不足(1.5%或3.0%)且石膏类型相同时,MKC水化诱导期显著长于APC,这可能源于MK通过溶出铝酸根离子或吸附硫酸根离子,加速了水泥浆液相中硫酸根离子的消耗,促进了铝相矿物的水化,进而抑制了硅相矿物水化.与APC相似,MKC体系中无水石膏由于溶解速率缓慢,可持续提供硫酸根离子,当其掺量增加时,能够显著缩短诱导期,但半水石膏在此掺量下影响有限.当石膏掺量大于5.0%时,APC‑Ahy诱导期仍略短于MKC‑Ahy,这与MK促进铝相矿物水化规律一致.但MKC‑Hem的诱导期较APC‑Hem显著缩短,并且铝相矿物的二次水化峰更为延迟,这说明当半水石膏掺量充足时(大于等于5.0%),MK的引入反而会抑制铝相矿物的水化,从而降低了达到体系硫酸盐平衡时所需的石膏掺量.
(1)在无三乙醇胺(TEA)加入情况下,不同类型石膏对自配硅酸盐水泥(APC)的水化进程影响有限.偏高岭土(MK)的加入会促进体系中铝相矿物的水化反应,改变APC中原有的硫酸盐平衡并延缓硅相矿物水化.
(2)由于TEA的加入会促进水泥中铝酸盐相及石膏的溶解,需要更高的石膏掺量以维持体系内硫酸盐平衡.同时,石膏类型与掺量的变化将通过改变水泥中硫酸根离子溶出-吸附-沉淀的动态平衡,对APC和掺偏高岭土水泥(MKC)的水化进程及硫酸盐平衡产生显著影响.
(3)对于APC,当TEA掺量为0.5%时,相较半水石膏,无水石膏掺量的增加可显著缩短水泥水化诱导期,更能有效抑制水泥中铝相矿物的快速水化反应,减缓铝酸根离子对硅相矿物水化进程的抑制作用,可能是由于无水石膏较低的溶解速率使体系中一直有硫酸根离子的溶出,进而更能有效抑制水泥中铝相矿物的反应.对于MKC,当石膏掺量大于5.0%时,相较无水石膏,半水石膏更有助于抑制铝相矿物的水化.这可能是由于半水石膏快速溶出的硫酸根离子不仅可形成水化产物,还可吸附在MK表面,作为硫酸根离子供给源,在水化后期脱附进入液相,能够持续抑制水泥中铝相矿物反应.
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