低需水的新拌水泥浆体流变性研究

在对水泥浆体流变模型和流变性能影响因素分析的基础上，研究了外加剂掺量、SO3含量、矿渣掺量等对新拌水泥浆流变性能的影响。用旋转粘度计对新拌水泥浆进行了动态检测，低需水量水泥的新拌水泥浆具有良好的流变性能，同时它的流变模型符合宾汉姆流变模型。     

矿渣对新拌水泥浆体流变性能的影响

通过对掺有矿渣的新拌水泥浆体流变曲线、流变参数、标准稠度需水量和胶砂流动度的测定,研究了矿渣的化学组成、掺加量和细度等对新拌水泥浆体流变性能的影响。     

水胶比和硅灰掺量对灌浆水泥浆体流变性的影响

为了研究水胶比和硅灰掺量对改性超细灌浆水泥浆体流变特性的影响,采用旋转粘度计和马氏漏斗粘度计法对不同水胶比(0.6,0.7,0.8,1.0,1.5和2.0)的新拌水泥浆体进行流变性能试验研究,其中硅灰掺量分别为0%,3%,5%,7%和10%.结果表明,新拌水泥浆体的塑性黏度和屈服应力随着水胶比的增大而减小;掺有硅灰的改性超细灌浆水泥在水胶比大于1.5时,流变性能变化不大,反之则变化较大;硅灰的掺量对改性超细灌浆水泥浆体的流变性影响较大,随着掺量增加浆体流动性变差,但在水胶比为1.0左右时,存在最优掺量,约5%.通过将马氏试验中时间指标转化为流速指标,可以有效拓展高黏度浆体的流变性能测试.     

聚合物改性超细水泥灌浆材料性能研究

研究了聚合物对超细水泥浆体工作性能的影响,探讨了聚合物改性超细水泥灌浆材料的水化硬化程度.结果表明:当P/C 15%时,聚合物本身具有的自分散性能和表面活性减小了改性超细水泥浆体屈服应力τ0和塑性粘度η0,使得流动速率B和灌入量qb增加,从而显著地改善了超细水泥浆体的可灌性.     

纳米C—S—H/PCE对硅酸盐-硫铝酸盐复合水泥凝结硬化的影响

研究了纳米C—S—H/PCE对硅酸盐-硫铝酸盐复合水泥凝结时间、早期水化历程及抗压强度的影响,采用XRD、TG、pH计和SEM等分析测试手段对早龄期水化产物和液相碱度等进行表征,探讨了纳米C—S—H/PCE对硅酸盐-硫铝酸盐复合水泥的增强机理。结果表明：掺加纳米C—S—H/PCE能有效缩短硅酸盐-硫铝酸盐复合水泥浆体初凝及终凝时间,当C—S—H掺量≥1.0%时,硅酸盐-硫铝酸盐复合水泥的初、终凝时间差明显缩短。纳米C—S—H/PCE加快了硅酸盐-硫铝酸盐复合水泥水化放热速率,提高了总的水化放热量,早期水化产物生成数量多,但对水泥水化产物类型没有影响,硅酸盐-硫铝酸盐复合水泥体系8、12、16 h的抗压强度显著提高。     

掺HRA对蔗糖超缓凝水泥基材料性能的影响

研究了掺水化恢复外加剂(HRA)对蔗糖超缓凝水泥基材料性能的影响,结果表明:在蔗糖超缓凝水泥基材料中掺入HRA可有效缓解蔗糖的严重缓凝作用,使水泥开始加速水化时间大幅提前.蔗糖掺量为0.20%时,未掺HRA的水泥浆体放热温升峰值出现时间长达64.6h,同掺2.0%HRA时,开始水化时间提前至20h;后掺时间为24h时,2h内水泥净浆即开始加速水化.掺加一定量HRA导致水泥胶砂抗折和抗压强度略有下降,原因可能是掺加胶态HRA导致水泥胶砂水灰比略有增大所致.     

聚羧酸超塑化剂的性能研究

研究了含有亲水性羧基、酸酐基团、磺酸基、聚环氧乙烷侧链的三种羧酸类共聚物对水泥浆体流变性能和水泥粒子表面Zeta电位的影响,并与萘系高效减水剂进行了对比.在改善水泥浆体的流变性能方面,三种聚羧酸超塑化剂的最佳掺量和饱和掺量均为0.3%～0.45%;对水泥粒子表面Zeta电位的影响方面聚羧酸超塑化剂远小于萘系高效减水剂,证实了两类减水剂的分散作用机理的区别.     

聚合物干粉改性水泥砂浆性能及应用研究

研究了掺羟乙基甲基纤维素醚和乙烯-醋酸乙烯酯共聚物乳胶粉的改性水泥砂浆的各项物理性能及其断面形貌。试验结果表明,2种聚合物均具有很好的保水功能,能使砂浆的水分更多、更长时间地保留在水泥浆体中,从而保证了水泥砂浆的充分水化,减少了浆体的分层离析现象,使砂浆具有良好的施工和易性;聚合物的引气功能,使新拌水泥砂浆的体积密度下降,且引入的空气在硬化砂浆中形成孔径小且分布均匀的微孔,因而改性砂浆的抗吸水能力提高;聚合物的种类、掺量对砂浆的各项性能有很大的影响,复掺能充分发挥不同聚合物对砂浆的改性作用,且聚合物间存在一个合适的掺量范围。聚合物改性水泥砂浆适合商品化生产,通过改变聚合物的掺量可满足现代施工对砂浆不同功能的需求。     

基于水膜厚度假设分析磨细高炉矿渣对水泥浆性能影响

为探索磨细高炉矿渣对水泥浆性能及其水膜厚度的影响,研究测量了30组不同水胶比、不同磨细高炉矿渣掺量的水泥–;矿渣复合浆体的流动性能、黏聚性和抗压强度.为探索浆体的流变性能控制机理,进一步测量了5组不同磨细高炉矿渣掺量水泥–;矿渣复合浆体的填充密度,并基于填充密度测量结果计算出各浆体试样配比的水膜厚度,探索水膜厚度对水泥–;矿渣复合浆体流变性能的影响.实验结果表明,适量磨细高炉矿渣的掺入能提高浆体的流动性能和抗压强度,黏聚性些许减弱,最优配比磨细高炉矿渣掺量为5%,此时水泥–;矿渣复合浆体综合性能最好.磨细高炉矿渣掺入能提高胶凝材料的填充密度,水膜厚度为流动性主要控制因素,水泥浆的流动性能随水膜厚度增大而增大.     

萘系减水剂不同掺加方法的作用机理的研究

本文通过水泥和水泥熟料矿物对减水剂的吸附及电化学测定,认为萘系减水剂不同掺法的作用机理主要与减水剂的吸附平恒浓度及水泥颗粒的ζ-电位有关,而这两者又取决于水泥中各熟料矿物的水化程度和电性质。本文还通过化学结合水和水化热以及流变参数等的测定,探讨了减水剂不同掺法对水泥浆体水化动力学过程和流变性能的影响,并提出了减水剂后掺—分两次加水的新方法。     

Rheological behaviors of fresh cement pastes with polycarboxylate superplasticizer

The rheologicalbehaviors of fresh cement paste with polycarboxylate superplasticizer were systematically investigated.Influentialfactors including superplasticizer to cement ratio(Sp/C),water to cement ratio(w/c),temperature,and time were discussed.Fresh cement pastes with Sp/Cs in the range of 0 to 2.0% and varied W/Cs from 0.25 to 0.5 were prepared and tested at 0,20 and 40 °C,respectively.Flowability and rheologicaltests on cement pastes were conducted to characterize the development of the rheologicalbehavior of fresh cement pastes over time.The exprimentalresults indicate that the initialflowability and flowability retention over shelf time increase with the growth in superplasticizer dosage due to the plasticizing effect and retardation effect of superplasticizer.Higher temperature usually leads to a sharper drop in initialflowability and flowability retention.However,for the cement paste with high Sp/C or w/c,the flowability is slightly affected by temperature.Yield stress and plastic viscosity show similar variation trends to the flowability under the abovementioned influentialfactors at low Sp/C.In the case of high Sp/C,yield stress and plastic viscosity start to decline over shelf time and the decreasing rate descends at elevated temperature.Moreover,two equations to roughly predict yield stress and plastic viscosity of the fresh cement pastes incorporating Sp/C,w/c,temperature and time are developed on the basis of the existing models,in which experimentalconstants can be extracted from a database created by the rheologicaltest results.     

Effect of Fly Ash on Rheological Properties of Cement Paste

This paper is aimed to study the factors influencing rheological properties of cement paste with fly ash,including the quantity of cement replaced by fly ash,types of the fly ash,degree of cement hydration and the microstructure of cement paste. By changing the water-cement ratio,mixing different amounts of fly ash,adding different types fly ash,the rheological parameters of cement paste are measured with a rheometer,and the needle penetration are tested by Vical needle. A ultrasound velocity test was aslo employed to monitor hydration of paste at early ages. Combinations of different factors on the rheological properties of cement paste are studied. The objective is to reveal the effect mechanism of material nature and proportion of each component on the rheological properties of cement paste with fly ash.     

Effect of borax on hydration and hardening properties of magnesium and pottassium phosphate cement pastes

Magnesium and potassium phosphate cement (MKPC) sample were prepared by mixing dead burnt MgO powder, potassium phosphate and different dosages of retarder borax to investigate the effect of borax on its hydration and hardening characteristics. The pH value, fluidity, hydration temperature and strength development of MKPC paste were investigated, and the mineralogical composition and microstructural morphology of its hydration products were analyzed. The experimental results indicated that, within a certain dosage, borax caused an endothermal effect for MKPC paste, which decreased the early hydration rate of MKPC paste, increased the fluidity of MKPC paste. Thus, strength and micro-morphology of hardened MKPC are affected. It can be concluded that borax in MKPC paste retards the early hydration rate of MKPC paste by forming a film onto surface of MgO, decreasing the temperature and increasing the pH value of the system. As borax dosage varying, different factors may dorminate the effects.     

Influence of Nano-SiO_2 Addition on Properties of Sulphoaluminate Cement Based Material

The influences of different nano-SiO_2(NS) contents on the mechanical properties and rheological behavior of sulfoaluminate cement(SAC) based composite materials were studied.Results show that with increasing content of NS,the apparent viscosity,and shearing strength of fresh paste gradually increase but the fluidity decreases.With a dosage of 3.0%NS,the tensile and flexural strengths of mortars at 56 days were increased by 87.0%and 84.6%,respectively,compared with that in the absence of NS,indicating that the toughness of hardened mortars is significantly improved.Besides,the exothermic peaks of hydration are obviously increased and will earlier occur,and the second and the third peaks appear 2.61 hours and 2.56 hours earlier,respectively than that in the absence of NS,and the hydration of SAC before 8 hours is accelerated.The forming mechanism of strengths was revealed by scanning electron microscopy(SEM),hydration heat,X-ray diffraction(XRD) and derivative thermogravimetry(DTG).The micro-aggregate filling effect and nucleation effect at early age and weak pozzolanic effect at late age of NS make the microstructure more compact,which obviously enhances the strength of SAC mortars.     

Hydration kinetics of phosphorus slag-cement paste

Hydration characteristics of Portland cement paste with phosphorus slag powder incorporated and hydration kinetics was investigated with SEM, X-ray diffraction, DTA-TG and calorimeter II 80. Results showed that phosphorus slag powder could reduce total amount of hydration products yet had little influence on the type of hydration products. The total amount of heat of hydration was decreased by 49.11% and the final setting was postponed by 2.28 h when phosphorus slag powder substituted 35% Portland cement by mass. The accelerating stage of this composite paste was controlled by catalysis, decreasing stage controlled by both catalysis and diffusion while stabilizing stage by diffusion alone. Hydration resistance and activation energy were reduced and hydration speed was accelerated.     

Early age hydration of cement paste monitored with ultrasonic velocity and numerical simulation

Early age hydration of cement paste was investigated by monitoring the ultrasonic propagation velocity and simulated with the numerical model CEMHYD3D. The ultrasonic velocity of the P-wave was recorded during the first 24 hours of the hydration process and its evolution was analyzed. It is shown that the UPV method is an effective, accurate and non-destructive method for monitoring the early age hydration process of cement paste. The early age hydration process can be classified as four periods, which are the dormant period, acceleration period, deceleration period and stabilization period. Higher w/c ratios result in lower UPV, and delay initial setting time due to the decreased solid volume. The change of UPV is clearly related to the hydration degree of cement particles.     

基于水化动力学模型的水泥基材料温度效应

为探究温度对水泥浆水化过程的影响,采用等温量热仪测试了水泥浆样品在20,30和40 ℃的水化放热量和水化放热速率,获得了水化度α和表观活化能Ea并利用Krstulovic-Dabic模型计算了相应阶段动力学参数K和n,探讨不同温度的水泥浆体的水化机理。结果表明,水化动力学参数随温度升高显著增大,水泥浆在20~40 ℃的水化表观活化能Ea为37.63 kJ/mol,且升高温度促进0~72 h内水泥水化度的增长。20 ℃下的水泥浆具有NG-I-D过程,而30 ℃和40 ℃下的水泥浆只具有NG-D过程,表明升高温度使水化阶段的持续时间缩短,且反应速率加快。研究可为水泥基材料在不同环境温度下施工时控制浇筑时间以及掌握强度的发展趋势,提供一定的理论依据。     

外加剂对水泥净浆水化热的影响

采用直接测定法测试了矿物、化学外加剂对水泥净浆的水化热的影响，并对外加剂降低或提高水化物的原理作了一些探讨。结果表明，粉煤灰和矿渣等矿物外加剂能明显在降低水泥净浆的水化热和温升。FDN-5型减水剂、糖密缓凝剂等化学外加剂能不同程度地降低水泥净浆的水化热和温升，推迟热峰出现时间。Na2SO4早强剂会提高水化热和温升，且使热峰出现时间提前。松香引气剂对水化热和温升影响不明显。     

Ultra high early strength self-compacting mortar based on sulfoaluminate cement and silica fume

The influences of silica fume and aluminum sulfate on hydration process of sulfoaluminate cement were carried out by ring flow, setting time, hydration heat, XRD and DTG analyses. In addition, mortar mixtures with different functional additives have been studied through compressive strength, flexural strength, volume stability at early age and porosity characterization tests. The results show that the addition of silica fume and aluminum sulfate reduces the fluidity and shortens the setting time of sulfoaluminate cement paste, promoting hydration process and increasing hydration products at early age. In the case of appropriate proportion of mortar, the inclusion of hydroxy propyl methyl cellulose, dispersible polypropylene fiber and organic silicon kind of defoamer can control segregation and bleeding, improve mechanical strength and volume stability at early age, and modify the pore distribution of sulfoaluminate cement mortar, respectively. The sulfoaluminate cement mortar can carry out gravitational grouting in the absence of outside force, the compressive strength of 2 hours and 24 hours have reached 26 and 58 MPa respectively, and have good microexpansion and tiny pore distribution characterization.