粉煤灰对水泥与减水剂相容性的影响研究

影响混凝土外加剂与水泥相容性问题的因素很多,混和材的种类和掺量是其中之一。以减水剂为例,其在水泥混凝土应用中存在饱和点,通过饱和点的变化可判定水泥与减水剂的相容性好坏,采用不同混和材掺量、不同高效减水剂掺量的水泥净浆试验,进行5 min、30 min、60 min的净浆流动度的测试及饱和点的确定,结果表明,加入混合材后改善了水泥与高效减水剂之间的相容性,少量粉煤灰可以提高浆体的初始流动度,改善流动度经时损失。     

矿物掺和料与高效减水剂对浆体流变性的影响

采用净浆流动度与NXS-11A型旋转粘度计对掺有矿物掺和料、聚羧酸高效减水剂的水泥浆体进行塑性粘度、屈服剪切应力试验，结果随着FA⊥、矿粉掺量的增加，水泥浆体的流动性变好，塑性粘度、屈服剪切应力均减小，且浆体的流动度经时损失得到显著地改善。     

不同黏土对掺减水剂水泥净浆流动度影响

目的 研究4种不同黏土对掺聚羧酸减水剂及萘系减水剂水泥净浆流动度的影响规律并从黏土的吸附性能角度探究其影响机理.方法 采用水泥净浆流动度试验方法比较了4种黏土对掺聚羧酸减水剂水泥净浆流动度的影响,通过TOC总有机碳测试仪测定了4种黏土对聚羧酸减水剂的吸附量.结果 4种黏土对水泥净浆流动度的影响差异较大,其中钙基蒙脱土和钠基蒙脱土的掺量为2％时,掺聚羧酸减水剂水泥净浆已基本没有流动度,掺萘系减水剂的水泥净浆流动度也有所下降,但降幅稍小,而伊利土和高岭土对掺减水剂水泥净浆流动度无明显负面影响;钙基蒙脱土和钠基蒙脱土对聚羧酸减水剂的吸附量较大,伊利土、高岭土对聚羧酸减水剂的吸附能力和水泥相当.结论蒙脱土对掺聚羧酸减水剂水泥净浆流动度负面影响极为严重,而伊利土和高岭土对掺减水剂水泥净浆基本没有负面影响.     

基于分形维数确定高效减水剂饱和掺量

通过测试掺加高效减水剂的水泥絮凝颗粒粒度分布,分析了絮凝颗粒的分形特征,探讨分形维数(Df)与高效减水剂掺量间的关系.结果发现,当减水剂掺量达某范围,分形维数出现突变,突变处对应的减水剂掺量与净浆流动度测定减水剂饱和掺量吻合良好.因此可采用分形维数来确定高效减水剂在水泥净浆中的饱和掺量.     

功能调整材料对水泥浆体流动性影响

使用自行研制的H管分别研究了不同功能调整材料对水泥浆体流动性的影响,得到不同种类矿物掺合料和增稠剂对水泥浆体流动性改性规律:粉煤灰掺量的增加引起浆体流动性先增加后减小;矿粉掺量越大,浆体流动性越大;硅灰和增稠剂掺量越大,浆体流动性越差。H管对水泥浆体流动性变化十分敏感,可以准确快速评价不同功能调整材料对水泥浆体流动性影响。     

粉煤灰、减水剂对水泥浆体相容性影响的试验研究

通过调整萘系和聚羧酸系减水剂的含量,观察水泥浆体的流动性和流动性经时损失的变化,由此确定减水剂的饱和点和减水剂对水泥相容性影响;减水剂在饱和点掺量时,调整粉煤灰掺量,研究粉煤灰掺量对水泥相容性的影响.结果表明:水泥浆体的流动度随减水剂掺量的增加而增大;萘系减水剂的饱和点掺量为0.8%,聚羧酸系减水剂的饱和点掺量为1.4%;在减水剂饱和点附近,静置35 min、60 min,萘系、聚系减水剂流动度经时损失分别为65%和39%,且聚羧酸系减水剂具有滞后性;聚系减水剂与水泥的相容性优于萘系高效减水剂;在减水剂饱和点掺量处,随着粉煤灰含量的增加,水泥浆体的流动度增大.     

水泥浆体性能对再生骨料透水混凝土成型和透水性能的影响

利用减水剂调整水泥净浆流动度,研究了再生骨料透水混凝土(RPC)在理论容重的情况下,流动度和目标孔隙率(15%、20%、25%)对RPC的影响,主要研究水泥浆体性能(流动性、粘聚性)对RPC成型方法和透水性能(孔隙率、透水性能)的影响。结果表明:随着减水剂掺量的增加,新拌水泥浆体的流动度不断提高,粘度不断降低;RPC成型时振动时间不断减少;有效孔隙率在相同质量情况下变化不大;流动度在70～230 mm的范围内,随着流动度的增加,目标孔隙率15%的RPC透水系数不断降低直至无法透水,目标孔隙率20%的RPC透水系数先增加后降低,目标孔隙率25%的RPC系数不断增加,并得出了RPC成型的有效流动度范围。     

基于后掺法的混凝土坍落度恢复技术研究

通过水泥对减水剂的吸附、水泥浆溶液Zeta电位、净浆流动度和混凝土坍落度等试验,分析了后掺聚羧酸减水剂量和添加时间对水泥净浆流动性、混凝土工作性能的影响及其相互关系,在此基础上提出了恢复混凝土坍落度的技术方法。结果表明:后掺法通过降低水泥颗粒对减水剂的吸附和减小颗粒的Zeta电位,能够有效避免早期水化产物对减水剂的吸附包裹,提高减水剂的有效分散能力;减水剂后掺的量与时间的合理匹配,可在一定时间内恢复混凝土坍落度,当先掺80%、后掺20%的减水剂时,在2h内可以显著地改善坍落度损失。     

新型羧酸盐高效减水剂的合成试验

根据混凝土外加剂分子设计理论，试验采用了自制丙烯酸聚乙二醇单酯、丙烯酸钠盐和二乙烯三胺通过Michael加成制得一种新型羧酸盐高效减水剂．对该新型减水剂进行了水泥净浆流动度测试，结果表明该减水剂具有良好的分散能力与流动保持性，其掺量的质量分数为1．5％，水灰质量比为0．29时，水泥净浆流动度达218mm。     

循环流化床灰对聚羧酸减水剂竞争吸附的影响研究

为研究循环流化床灰对聚羧酸减水剂竞争吸附的影响,通过在Ⅱ级粉煤灰中掺加无水硫酸纳、二水硫酸钙和氧化铁的方式来改变粉煤灰中三氧化硫和氧化铁含量,使其化学成分接近循环流化床灰,利用成分单因素分析的方法,测试减水剂水泥浆体的净浆流动度、zeta电位和混凝土性能.研究结果表明循环流化床灰中的三氧化硫和氧化铁对聚羧酸减水剂的吸附有明显负面影响,当可溶性硫酸盐掺量达到胶凝材料的3%、氧化铁掺量达到6%时,相应浆体均失去流动性.Zeta电位试验表明随着无水硫酸钠和氧化铁掺量的增大,Zeta电位绝对值越小,粒子间相互斥力越弱,分散性越差,分散体系就越不稳定.混凝土性能试验表明无水硫酸钠和氧化铁的掺入使得混凝土的流动性和抗压强度均变小,坍落度由220 mm降至125 mm,强度降低幅度最高达45%.     

聚羧酸系高效减水剂PC的合成及性能研究

以甲基丙烯酸、聚乙二醇1000、对甲苯磺酸、对苯二酚、过硫酸铵和甲基丙烯磺酸钠为原料,采用两步法合成出新型聚羧酸系高效减水剂(简称PC)。将合成的PC与目前广泛使用的萘系高效减水剂(简称FDN)相比,具有更加优异的性能,具体表现为:在掺量很少情况下,水泥净浆就具有较高的流动度;当掺量相同时,其对水泥净浆流动度远超FDN。此外,它与水泥的相容性好,具有缓凝及明显抑制水泥净浆流动度经时损失性能,对混凝土也能表现出显著的减水增强性,是一种性能优良,适合于配制高强、超高强混凝土的高效减水剂。     

Adsorption mechanism of polycarboxylate-based superplasticizer in CFBC ash-Portland cement paste

Circulating fluidized bed combustion （CFBC） ash exhibits the desirable pozzolanic activity which makes it a potential supplementary cementitious material to replace cement for concrete production. However, the high unburnt carbon content and porous surface structure of CFBC ash may adsorb water reducer and thereby significantly reduce the efficiency of water-reducing agents. The adsorption mechanism of polycarboxylate superplasticizer in CFBC ash-Portland cement paste was investigated by ultraviolet-visible spectrophotometer, and the conception of ＂invalid adsorption site＂ of CFBC ash was presented. The results show that the adsorption behavior of polycarboxylate superplasticizer in coal ash-Portland cement paste can be described by Langmuir isothermal adsorption equation. The adsorption capacity of CFBC ash-Portland cement paste is higher than that of pulverized coal combustion （PCC） fly ash-Portland cement paste. Moreover, the adsorption amount of polycarboxylate superplasticizer increases with the ratio of ash-to-cement in the paste. At last, the fluidity of CFBC ash-Portland cement paste is lower than that of the PCC fly ash paste. This work suggests that when CFBC ash is used as concrete admixture, the poor flowability of the cementitious system due to the high adsorption of water and water-reducing agent should be taken into consideration.     

Influence of Polycarboxylate Superplasticizer on Rheological Behavior in Cement Paste

Molecular structures of polycarboxylate(PCE) superplasticizer significantly affect the rheological properties of cement paste. Consequently, we employed self-synthesized PCE copolymers with different carboxylic densities to investigate their influence on the rheological behavior of cement paste. Three typical rheological models were applied to analyze the rheological properties, including Power-law model, Bingham model as well as Herschel-Buikley model. In addition, the thixotropical performances of cement paste in the presence of PCE with different carboxylic densities were investigated. The results show that the carboxylic density of PCE greatly influences the dispersing performance of PCE superplasticizers. As carboxylic density increases, the dispersing capability of PCE improves, and P(PEG1-AA6) possesses the strongest dispersing capability, the initial fluidity and 1 h fluidity of cement paste are both the highest, and cement paste has the lowest viscosity and the smallest hysteresis loop.     

氨基磺酸盐系高效减水剂的改性研究

氨基磺酸盐系减水剂具有高减水率、抑制混凝土塌落度经时损失等优点,但泌水严重,限制了其在混凝土中的应用。本文根据“分子设计”原则,通过单体A和单体U引入适当的官能团,对传统氨基磺酸盐系高效减水剂进行改性,测试了产品对水泥净浆流动度、流动度经时损失和泌水率的影响。试验表明,单体A的改性效果优于单体U,以9%的单体A改性后,减水剂的分散性和分散保持性能好,泌水率显著降低。     

The influence of steel slag with high Al2O3 content on the initial hydration of cement

The initial hydration of steel slag with high Al₂O₃ content and its influence on the initial hydration of cement were investigated in this study. Steel slag with high Al₂O₃ content may contain much calcium aluminate mineral but very little gypsum. The steel slag hydrates much more quickly than cement in the initial hydration period, producing many flake products which have a great influence on the fluidity, initial setting time, and adsorption level of superplasticizer of paste. Replacing part of cement by steel slag with high Al₂O₃ content can change the hydration condition of calcium aluminate mineral of the cement by decreasing the gypsum to calcium aluminate mineral ratio, resulting in accelerating the hydration rate of calcium aluminate mineral in the initial hydration period. Paste containing steel slag with high Al₂O₃ content has a shorter initial setting time, higher adsorption level of superplasticizer, and greater loss in fluidity than the pure cement paste.     

磺化淀粉-聚羧酸复合减水剂的制备与表征

由于保护环境的原因,以天然高分子为原料来合成高效减水剂已经成为混凝土外加剂研究领域的新热点.本文研究了采用磺化糊精取代部分功能大单体来合成复合聚羧酸减水剂的方法.结果显示:当磺化糊精取代功能单体40%、复合聚羧酸减水剂掺量为0.5%时,水泥净浆的初始流动度达255,mm,1,h 后其流动度仍为250,mm.淀粉酸解后,增加亲水的羟基基团导致初期水化缓慢,而增加 Zeta 电位使水泥颗粒更易于分散.在复合减水剂中,长链 Starch 与短链的聚羧酸减水剂主链将被吸附于水泥颗粒表面上,交替发生静电与空间位阻作用,起到了增加减水率和降低缓凝的效果.     

Effect of competitive adsorption between sodium tripolyphosphate and naphthalene superplasticizer on fluidity of cement paste

The adsorption amount, ζ-potential of cement particles and fluidity of cement paste were tested to research the competitive adsorption between naphthalene superplasticizer(FDN) and STPP. The experimental results showed that the presence of STPP could significantly improve the fluidity of cement paste and reduce the fluidity loss with FDN. There existed a competitive adsorption between STPP and FDN. STPP and calcium ions formed complexes; they preferentially adsorbed onto surface of cement particles and preempt adsorption points of FDN; and it reduced adsorption amount of FDN. In the absence of STPP, saturation adsorption amount of FDN was 5.93 mg/g; but when the dosage of STPP was 0.1%, it reduced to 4.3 mg/g(about 72.5%). The adsorption amount of FDN was reduced by STPP, but ζ-potential of cement particles enhanced and fluidity of cement paste increased because of strong negative charge effect of the complexes. Adsorption of the complexes would delay Ca2+ into liquid and inhibit formation of active adsorption points. Then, content of FDN in liquid increased with the addition of STPP and ζ-potential of cement particles became stable. In this way, fluidity loss of cement paste reduced.     

Probing development of microstructure of early cement paste using 1H low-field NMR

Development of microstructure of early cement paste (0–6 h) was investigated with ¹H low-field NMR. It was found that T ₂ (transverse relaxation time) distributions of fresh cement paste were bimodal and two peaks were ‘long component’ and ‘short component’. Separation degree of two peaks was a sign of exchange of water within flocculation and outside flocculation. Factors such as water cement ratio, specific surface area and dosage of superplasticizer had influences on the separation degree: the separation degree increased with the water cement ratio; the separation degree of cement paste prepared with cement with a high specific surface area was zero; dosage of superplasticizer will decrease separation degree. Results also suggested that T ₂ distribution gradually moved to the left and T ₂ of long component and initial fluidity were linearly correlated.