聚羧酸减水剂对水泥水化的影响及相关机理研究

发布时间：2018-09-03 20:07

【摘要】：水泥及其外加剂化学是设计和改善混凝土各种性能的理论基础。本论文以凝胶渗透色谱、ζ电位分析、X-射线衍射、差示扫描量热分析以及扫描电镜等,研究了聚羧酸减水剂对水泥水化的影响及其作用机理,并探讨了减水剂对水化产物结晶习性和微观形貌的影响。研究以聚羧酸减水剂的吸附为重要线索,将水泥水化研究和单矿水化研究相结合。主要研究内容及创新点如下:1.研究了不同结构的聚羧酸减水剂在水泥单矿C3S表面及其水化产物Ca(OH)2表面的吸附以及对C3S水化的影响。结果表明,水化60 min,C3S对聚羧酸减水剂的吸附量为5.5~6.5 mg/g,相应的ζ电位为-3.2 mV。此时,Ca(OH)2的吸附量为1.9 mg/g,相应的ζ电位为-4.32 mV。综合数据研究表明,C3S对减水剂的吸附发生在C3S及其水化层表面,并对C3S水化产生重要影响。诱导前期,减水剂的吸附增大C3S水化放热量,促进C3S表面Ca2+溶解;诱导期和减速期,放热滞后,C3S水化延迟,且水化相分布、形貌也发生明显变化,Ca(OH)2晶粒明显细小。减水剂掺量越高,分子羧基密度越大,C3S水化延缓的效应越明显。模拟的Ca(OH)2晶体合成实验表明,不掺聚羧酸减水剂的Ca(OH)2晶粒尺寸约为0.5~1μm,而掺0.2%聚羧酸减水剂的Ca(OH)2晶粒尺寸仅为0.2~0.5μm。上述研究表明,在硅酸盐水泥浆体中,聚羧酸减水剂不仅起到高效减水和改善混凝土气孔结构的作用,而且通过吸附影响到C3S的水化及其水化相形态。这为聚羧酸减水剂提高混凝土密实性和力学性能提供了新的依据。2.研究了不同结构的聚羧酸减水剂在C3A、Ca2SO4·2H2O及其水化产物AFt表面的吸附以及对C3A水化的影响。结果表明,C3A、AFt和Ca2SO4·2H2O的ζ电位分别为+12、+4.1和-0.6 mV。水化60 min,C3A对三种聚羧酸减水剂的吸附量在9~12 mg/g,此时AFt和Ca2SO4·2H2O对聚羧酸减水剂的吸附量分别为13~15 mg/g和0.21 mg/g左右。减水剂主要吸附在C3A和AFt的表面,羧基密度越大,吸附量相对越高。聚羧酸减水剂吸附对C3A水化产生重要影响。诱导前期,C3A和Ca2SO4·2H2O的溶解均受到减缓,从而使诱导期被延长1~2 h,并抑制了加速期AFt向AFm的转化,低羧基密度的聚羧酸减水剂对C3A水化的抑制作用表现得更加强烈。AFt对聚羧酸减水剂较强的吸附作用导致其晶体的生长、形貌及其分布形态受到严重影响。溶液结晶法模拟实验制备的AFt为2μm左右针状晶体,且相互聚集。但聚羧酸减水剂存在条件下得到的AFt晶体外形为1μm左右长的棒状,分散且生成量大。3.研究了不同结构聚羧酸减水剂在水泥颗粒表面的吸附及其对水泥水化的影响。结果表明,聚羧酸减水剂在水泥颗粒表面的吸附量随时间延长逐渐增大。水化60 min,水泥颗粒对聚羧酸减水剂的吸附量为1.3~1.6 mg/g之间,吸附平衡的ζ电位在-9~-12 mV范围。这一吸附量虽然比上述C3S和C3A单矿的吸附量都低,但却与混凝土工程中聚羧酸减水剂的常规掺量相一致,原因可能与水泥中C2S的矿物含量以及水泥中的助磨剂有关。聚羧酸减水剂对水泥水化的影响是:诱导期延长,水化速率减慢;减水剂掺量增加,诱导期延长越明显,这与C3S和C3A单矿的水化情况相一致。另外,由于水化相中Ca(OH)2、AFt被C-S-H凝胶所覆盖,其形貌特征不明显。但从聚羧酸减水剂影响单矿水化产物Ca(OH)2、AFt的结果来看,聚羧酸减水剂可以细化AFt、Ca(OH)2的晶粒,因此会对水泥石的强度产生贡献。4.为了进一步验证吸附是影响水泥及其单矿水化的主要原因,本论文还研究了有机膦酸HEDP在水泥表面的吸附及其对水泥水化的影响。结果表明,HEDP的吸附能力比聚羧酸减水剂强,在掺量0.02~0.2%的范围,吸附率达到掺量的98%以上且未达到饱和。0.2%掺量时水泥水化温峰出现时间也从正常的11 h延长至50 h。HEDP掺量越大,其水化诱导期越长。进一步的岩相研究表明,HEDP的吸附明显抑制了AFt和Ca(OH)2的形成与生长,得到的水化产物由正常的短纤维状变为独特的毛绒状。HEDP的缓凝机理可被认为是通过“吸附”和“螯合沉淀”使水泥水化受到抑制作用。
[Abstract]:Chemistry of cement and its admixtures is the theoretical basis for designing and improving various properties of concrete. In this paper, the effects of polycarboxylic superplasticizer on cement hydration and its mechanism are studied by gel permeation chromatography, zeta potential analysis, X-ray diffraction, differential scanning calorimetry and scanning electron microscopy, and the bonding of hydration products is also discussed. The main research contents and innovations are as follows: 1. The adsorption of polycarboxylic acid superplasticizers on the surface of C3S and its hydrated product Ca (OH) 2, and the adsorption of C3S water on the surface of C3S were studied. The results show that the adsorption capacity of C3S on polycarboxylic superplasticizer is 5.5-6.5 mg/g and the corresponding_potential is - 3.2 mV at 60 min of hydration. At this time, the adsorption capacity of Ca (OH) 2 is 1.9 mg/g and the corresponding_potential is - 4.32 mV. In the early stage of induction, the adsorption of water reducer increases the heat release of C3S hydration and promotes the dissolution of Ca2+ on the surface of C3S; in the induction and deceleration stages, the heat release lags, the hydration delay of C3S, and the distribution of hydration phases and morphology of Ca (OH) 2 grains are obviously changed. The higher the dosage of water reducer, the higher the molecular carboxyl density, the more obvious the effect of C3S hydration retardation. The experimental results of Ca(OH)2 crystal synthesis show that the grain size of Ca(OH)2 without polycarboxylic acid superplasticizer is about 0.5-1 micron, while that of Ca(OH)2 with 0.2% polycarboxylic acid superplasticizer is only 0.2-0.5 micron. The above studies show that the polycarboxylic acid superplasticizer not only plays an important role in reducing water and improving the pore structure of concrete, but also plays an important role in the Portland cement paste. Adsorption of polycarboxylic acid superplasticizers on the surface of C3A, Ca2SO4.2H2O and its hydration products AFt and their effects on the hydration of C3A were studied. The_potential of H2O is +12, +4.1 and -0.6 mV, respectively. The adsorption capacity of C3A to the three polycarboxylic superplasticizers is 9-12 mg/g after 60 min of hydration. At this time, the adsorption capacity of AFt and Ca2SO4.2H2O to the polycarboxylic superplasticizers is about 13-15 mg/g and 0.21 mg/g respectively. The superplasticizer is mainly adsorbed on the surface of C3A and AFt. The higher the density of carboxyl group is, the higher the adsorption capacity is. The solubility of C3A and Ca2SO4.2H2O was slowed down at the early stage of induction, which prolonged the induction period by 1-2 hours and inhibited the transformation of AFt to AFm. The inhibition of polycarboxylic acid superplasticizer with low carboxyl density on the hydration of C3A was stronger. The growth, morphology and distribution of AFt crystals are seriously affected by the action. The AFt crystals prepared by solution crystallization method are about 2 micron acicular crystals and aggregate with each other. However, the AFt crystals obtained in the presence of polycarboxylic acid superplasticizer have a rod shape of about 1 micron long, dispersed and produced a large amount of AFt crystals. The results show that the adsorption capacity of polycarboxylic superplasticizer on the surface of cement particles increases with time. The adsorption capacity of cement particles on the surface of polycarboxylic superplasticizer is between 1.3 mg/g and 1.6 mg/g after 60 min of hydration, and the zeta potential of adsorption equilibrium is between - 9 mV and - 12 mV. However, the adsorption capacity of C3S and C3A is lower than that of C3S and C3A, but it is consistent with the conventional dosage of polycarboxylate superplasticizer in concrete engineering. The reason may be related to the mineral content of C2S in cement and the grinding aids in cement. In addition, the morphology of AFt covered by C-S-H gel is not obvious because of Ca (OH) 2 in the hydration phase. But from the results of polycarboxylic acid superplasticizer affecting Ca (OH) 2, AFt can refine the grain of AFt and Ca (OH) 2 in cement. In order to further verify that adsorption is the main factor affecting the hydration of cement and its single mineral, this paper also studies the adsorption of organic phosphonic acid HEDP on cement surface and its effect on cement hydration. When the content of HEDP is more than 98% and less than 0.2%, the occurrence time of hydration temperature peak is prolonged from 11 h to 50 H. The larger the content of HEDP, the longer the hydration induction period. Further lithofacies studies show that the adsorption of HEDP obviously inhibits the formation and growth of AFt and Ca (OH) 2, and the hydration products are changed from short fibrillar to independent. The retarding mechanism of HEDP can be considered as the inhibition of cement hydration by "adsorption" and "chelating precipitation".
【学位授予单位】：武汉理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ172.1

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