新型缓凝剂对建筑石膏性能的影响及机理研究

研究了一种新型缓凝剂—羟基羧酸化合物(KH-PT),对建筑石膏的凝结时间2、8 d强度等性能的影响,并通过无极电阻率测定仪、扫描电镜等测试手段进行了水化进程、晶体形貌变化的研究。结果表明,建筑石膏的凝结时间随着改性剂掺量的增加而延长,在改性剂掺量为0.05%时,不但对建筑石膏具有一定的缓凝效果,而且可使建筑石膏的强度有一定量的增加,在参量为0.10%时,即可使建筑石膏的初凝时间达到近1 h,并随改性剂掺量的增加,建筑石膏水化电阻率的突变段会向后延迟,水化稳定电阻率值也随着减小,而晶体的形貌则随之变粗大,长径比减小。     

黄姜废渣对硅酸盐水泥水化和力学性能的影响

研究不同掺量的黄姜废渣对普通硅酸盐水泥标稠需水量、凝结时间、水化热、化学收缩、力学强度等影响。结果表明,对比空白水泥试样,掺加RT的水泥标准稠度需水量有所减少,试样的初凝和终凝时间随RT掺量的增加而延长。当RT掺量为15%时,水化热的峰值明显低于空白样,水化热的峰值出现的时间明显延迟。掺加RT后的试样,7d内水泥浆体的化学收缩有所减小。掺量为7%RT的水泥净浆强度最大。     

缓凝剂对建筑石膏结构与强度的负面影响

利用SEM扫描电镜、MIP压汞测孔技术等测试手段．系统深入地研究了柠檬酸、多聚磷酸钠、骨胶3类常用典型缓凝剂对建筑石膏水化早期液相过饱和度、晶体形貌以及硬化体孔结构的影响,研究了石膏强度损失的内在原因和机制．结果表明：缓凝剂降低了胶凝材水化早期液相过饱和度,改变了二水石膏结晶习性和晶体形貌,晶体明显粗化,晶形也由针状转变为短柱状,大大削弱了晶体间的搭接,硬化体孔径增大,大孔比例明显增加,孔结构劣化,并最终导致建筑石膏强度的大幅度降低．强度损失与其缓凝效果基本成正比,掺量越高,缓凝时间越长,强度损失越大．     

多元复合缓凝剂制备及其对磷酸镁水泥性能的影响

以硼砂、十二水合磷酸氢二钠、氯化钙为原料制备了复合缓凝剂,利用水化热、XRD、SEM等手段,对比研究了复合缓凝剂与硼砂对磷酸镁水泥主要性能的影响。结果表明:对于掺复合缓凝剂的磷酸镁水泥,其流动性降低,水化放热更迟,放热速率更低,凝结时间更长;其水化产物中除了鸟粪石(KMgPO4·6H2O),还存在少量氯化钾,且水化产物的结晶度和微裂纹也得到了一定改善;复合缓凝剂掺量在一定范围内(≤8%)时,其凝结时间显著延长,且后期强度优于掺10%(常规掺量)硼砂的磷酸镁水泥。因此,在满足凝结时间的条件下,多元复合缓凝剂更有利于改善磷酸镁水泥的整体性能。     

柠檬酸对石膏析晶过饱和度和微结构的影响

利用SEM扫描电镜、MIP压汞测孔技术和原子吸收光谱等测试手段，系统研究了柠檬酸对建筑石膏水化进程、液相离子浓度与过饱和度、二水石膏晶体形貌、硬化体结构的影响。结果表明：柠檬酸是建筑石膏的高效缓凝剂，它使建筑石膏水化进程减慢，水化诱导期延长，早期水化率降低；柠檬酸使早期液相离子浓度和过饱和度降低，使二水石膏晶体尺度增大，并改变二水石膏晶体生长习性，使晶形由针状转变为短柱状；柠檬酸使石膏硬化体大孔增加，孔径分布粗化。     

磷酸盐对α半水脱硫石膏凝结硬化的作用机理

研究磷酸盐对α半水脱硫石膏水化反应进程、液相离子浓度与过饱和度以及水化产物形貌与硬化体强度的影响,结合X光电子能谱分析技术对磷酸盐缓凝机理进行分析.结果表明,磷酸盐抑制α半水脱硫石膏早期水化,使水化放热减缓,早期水化速率降低,凝结时间延长;磷酸盐改变了二水石膏晶体生长习性,晶形由长棒状转化为板状,并使晶体粗化,硬化体强度降低;磷酸盐通过化学作用吸附在二水石膏晶体表面,抑制离子扩散和晶面生长,这是二水石膏缓凝的内因,对晶面的选择性吸附改变了二水石膏晶体生长习性和形貌,是硬化体强度降低的原因所在.     

柠檬酸对建筑石膏缓凝作用影响因素的研究

研究了柠檬酸对建筑石膏凝结时间与流动度经时性的影响,以及建筑石膏细度、相组成、pH值、水化温度对柠檬酸缓凝性的影响。结果表明:柠檬酸是建筑石膏高效缓凝剂,可有效抑制其流动度经时损失;Ⅲ型无水石膏和二水石膏削弱柠檬酸的缓凝效果,比表面积增加,凝结时间缩短;柠檬酸在弱碱性条件下缓凝效果最好;柠檬酸的缓凝效果对温度很敏感,温度升高,缓凝性降低。     

高性能胶凝材料中石膏的优化

高性能胶凝材料主要用于高性能混凝土,具有强度高、需水量小、水化垫低和收缩小等特点。按掺高效减水剂的胶凝材料的流变性能来优化石膏的掺量是高性能胶凝材料的特有技术之一。试验研究了石膏的掺量对高性能胶凝材料的需水量、凝结时间、强度、收缩性的影响,以此作为优化石膏掺量的依据。     

大掺量粉煤灰路面基层专用水泥的制备与性能

研究了一种大掺量的具有缓凝微膨胀性的路面基层稳定专用水泥,分析了石膏掺量、粉煤灰掺量对该种水泥的强度和凝结时间的影响。研究表明:这种水泥具有凝结时间长的特点,随着石膏掺量的增加,水泥的凝结时间和强度都有一个最大值,石膏的用量控制在SO3含量4.0%左右为宜,粉煤灰掺量增加,水泥的凝结间延长,强度逐渐降低,当掺量大于50%后,水泥的水化过程明显延缓。这种水泥的胶砂强度比32.5级水泥略低,但采用这种水泥稳定粒料的强度比采用通用水泥稳定粒料的强度有明显提高,达到相同的设计强度可以节省水泥用量15%左右。     

高效减水剂与缓凝剂复掺对三元胶凝体系流动性和强度的影响

针对掺萘系高效减水剂(BNS)的硅酸盐水泥-铝酸盐水泥-石膏三元胶凝体系浆体流动性小、流动性经时损失大、凝结时间短等这些问题,采用了BNS与缓凝剂柠檬酸(CA)、葡萄糖酸钠(SG)复掺的方式来予以解决,同时研究了外加剂复掺对三元胶凝体系1 d、7 d、28 d强度的影响.研究结果表明:随着CA和SG掺量的增加,三元胶凝体系浆体的流动度增大、凝结时间明显延长,且SG的作用效果较CA更加显著;CA和SG均使胶砂试件早期抗压强度小幅度降低,后期强度略有增加.     

Effect of calcium aluminate cement variety on the hydration of portland cement in blended system

Two kinds of CACs with different monocalcium aluminate（CA） contents were used in the PC/CAC（PAC） mixtures. Effects of CA and CACs on the properties of PAC were analyzed by setting times and the compressive strength tests, and also by means of calorimetry, XRD, DTA-TG and ESEM. The experimental results show that the compressive strength of the PAC mortars decreases with increasing content of CAC while it declines sharply with a higher content of CA in CAC. Compared with neat PC paste, the content of calcium hydroxide in hydrates of PAC paste decreases significantly, and the hydration time of PC is prominently prolonged. Additionally, the higher the content of CA in CAC, the more obviously the hydration of PC is delayed, confi rming that the CA phase in CAC plays an important role in the delay of PC hydration.     

Effects of citric acid on hydration process and mechanical properties of thermal decomposed magnesium oxychloride cement

In order to make full use of salt lake magnesium resources and improve the strength of the thermal decomposed magnesium oxychloride cement(TDMOC), the effects of citric acid on the hydration process and mechanical properties of TDMOC was studied. The hydration heat release at initial 24 h and strengths at 3, 7, and 28 days of TDMOC specimens were conducted. The hydration products and paste microstructure were analyzed by XRD, FT-IR and SEM, respectively. The results showed that citric acid can not only reduce the 24 h hydration heat release and delay the occurring time of second peak of TDMOC, but also produce more 5Mg(OH)2·MgCl 2·8H2O and less Mg(OH)2 in hydration process of TDMOC. More perfect and slender crystals were observed in the microstructure of the TDMOC pastes with citric acid. The results demonstrated that citric acid as an additive of TDMOC can decrease the hydration heat release and increase the compressive strength and flexural strength of TDMOC. The possible mechanism for the strength enhancement was discussed.     

Effect of compounding of sodium tripolyphosphate and super plasticizers on the hydration of α-calcium sulfate hemihydrate

The inhibition and its mechanism of sodium tripolyphosphate (STP) composited with super plasticizers (SPs) on hydration of α-calcium sulfate hemihydrate were studied by setting time, strength, hydration heat, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electronic probe micro analysis (EPMA), scanning electron microscopy (SEM) and differential scanning calorimeter (DSC) measurements. The experimental results show that compared with STP addition, compositing STP with polycarboxylate (PC) plasticizer, the final setting time is prolonged from 0.5h to 2hs. While formulating STP with naphthalene-based plasticizer (NAP) or sulfonate melamine formaldehyde plasticizer (SMF), the final setting time is reduced to quarter of an hour. Similar changes can also be found in the rate of exothermic hydration and hydration degree. Formulating STP with suitable addition of PC can enhance the strength, while compositing STP and NAP or SMF weakens the strength. Besides, adding STP or STP and SMF, obvious movement (more than 1ev) of binding energy of Ca2p1/2 and Ca2p3/2 is detected. Compared with STP addition, content of the characteristic element (P) of STP is cut down form 1.1% to 0.49% by compositing STP with SMF. Furthermore, as hydration age increases, hydration inhibition in the presence of admixtures weakens and even disappears within 56 h.     

Compressive strength development and microstructure of cement-asphalt mortar

The compressive strength developing process and the microstructure of cement-asphalt mortar (CA mortar) were investigated. The fluidity of CA mortar has a great influence on its strength. The optimum value of spread diameter of slump flow test is in the range of 300 to 400 mm. The compressive strength of CA mortar keeps a relatively high growth rate in 56 days and grows slowly afterwards. The residual water of hydration in CA mortar freezes under minus environmental temperature which can lead to a significant reduction of the strength of CA mortar. Increasing A/C retards asphalt emulsion splitting and thus prolongs the setting process of CA mortar. The hydration products of cement form the major structural framework of hardened CA mortar and asphalt is a weak phase in the framework but improves the viscoelastic behavior of CA mortar. Therefore, asphalt emulsion should be used as much as possible on the condition that essential performance criterions of CA mortar are satisfied.     

水玻璃激发碱-矿渣水泥的水化放热和凝结性能

水玻璃模数和碱当量对碱-矿渣水泥的水化放热和凝结性能有重要影响。该文系统地探讨了水玻璃模数和碱当量对碱-矿渣水泥水化放热和浆体凝结时间及抗压强度的影响规律。结果表明：随模数的增加,水化热降低,凝结时间延长,抗压强度先增加,随后降低;随碱当量的增加,水化热增加,凝结时间稍有延长,强度增加。比较合理的水玻璃模数Ms在1.0~2.0,碱当量为矿渣质量的3%~6%。     

Effects of Rice Straw Fibres on the Mechanical Properties and Hydration of Cements

The purpose of this research is to study the effects of rice straw fibres (RSF) on the setting time,heat of hydration,hydration products (XRD),mechanical properties for cements. Three types of the cements (P.I.52.5,P.O.42.5,sulphate aluminium) are used in this test. Results show that with the addition of RSF,the setting times for these three kinds of cements are delayed. According to P.O.42.5 cement,The max temperatures of exothermic peak (Tmax) decrease,exothermic peak times (tmax) are delayed and the mechanical strengths generally drop as RSF concentration is increased. XRD test shows that the RSF hinder the formation of Ca(OH)2 phase and hydration of cement (C3S,C2S,C4AF),which resulted in the delay of setting time and hydration reaction.     

建筑石膏制品的防火性能及应用

为解决建筑材料的防火问题,讨论了目前流行的建筑石膏制品的防火机理、耐火极限及其防火应用,并与其它建筑材料的防火性能进行比较,结果表明建筑石膏制品因其优良的防火性能可广泛应用于各种重要建筑物上．     

Effect of Waste Paper Fiber on Properties of Cementbased Mortar and Relative Mechanism

The aim of this work was to investigate the effect of waste paper fiber on the properties of cement-based mortar and the relative mechanism. The cement-based mortars with various contents and mixing way of waste paper fibers were prepared and the slump flow, setting time and strength developments of all mortars were tested. Besides, Ca(OH)_2 content in hardened pastes at different ages and the microstructures of all mortar at 90 d were observed by scanning electron microscopy. The experimental results showed that in the process of mixing, more superplastizier was consumed to maintain the workability because of the absorption of water and superplastizer on waste paper fiber. With more waste paper fiber being added, longer setting time is available for the pastes with it because of the carbohydrate dissolving and its retarding to the cement hydration. Waste paper fiber is adverse to the early and later strength of cement-based mortar, but it increases the mortar strengths at 7 and 28 d. The strength, Ca(OH)_2 content and microstructure are related to the content and mixing way of waste paper fiber. Waste paper fiber helps produce the Ca(OH)_2 at 7 and 28 d, but this case is reverse at ages of 1 and 3 d. Overall, waste paper fiber leads to the appearance of more pores in the hardened paste. However, it increases the toughness of cement-based mortar.