基于稳态流变测试的水泥浆体剪切模式研究

采用RHEORIAB QC型旋转黏度计测定不同剪切方式下水泥浆体稳态流变曲线,并用修正宾汉姆流变模型对其进行拟合,研究了剪切方式对水泥浆体稳态流变测试的影响.结果表明:预剪切对水泥浆体动态屈服应力和塑性黏度影响不大.恒定剪切变形速率小于、等于、大于、偏大于水泥浆体结构抗剪切破坏能力时,剪切应力随时间分别先线性增加接着保持同一值、直接保持恒定值、先减小接着保持同一值、轻微增加后达到平衡.随剪切速率增加,水泥浆体在0.1～100 s-1、100～400 s-1、400～600 s-1三个区段依次呈现出剪切变稀、宾汉姆流体、剪切增稠的流变行为.剪切速率变化范围向剪切变稀或剪切增稠段移动,水泥浆体动态屈服应力减小、塑性黏度增大;单个剪切速率的剪切时间越长,水泥浆体动态屈服应力、塑性黏度均越小.     

水泥-白云石粉浆体流变性能研究

试验采用旋转黏度计测定了水泥-白云石粉浆体剪切应力和塑性黏度随剪切速率变化的规律,对所测浆体T-γ曲线采用Bingham流体模型进行拟合,得到浆体屈服应力和塑性黏度,采用Power Law流体模型拟合出浆体的流变指数,并用触变环面积表征浆体的触变性.研究结果表明:在0 ～ 30％掺量范围内,随白云石粉掺量的增大,水泥浆体的屈服应力、塑性黏度和触变性均逐渐增加;白云石粉细度对浆体屈服应力和塑性黏度影响较小.     

使用同轴双圆柱流变仪获取Bingham流体流变参数

分析了使用同轴双圆柱流变仪测试Bingham流体流变参数(屈服应力和塑性黏度)时,非剪切区对转速–扭矩曲线的非线性和连续性的影响,以及非剪切区对Bingham流体剪切应变速率的影响。对使用转速–扭矩曲线的线性段来获取Bingham流体流变参数的可行性进行了分析,提出了使用同轴双圆柱流变仪,在考虑非剪切区存在与否的情况下,利用剪切应力–剪切应变速率曲线获取Bingham流体流变参数的方法。同时,提出了剪切应力–剪切应变速率计算过程中的去噪声方法,实现了剪切应力–剪切应变速率曲线的高精度获取。     

矿物掺合料对胶凝材料浆体流变性能和触变性的影响

基于大流态混凝土配合比,研究了各种矿物掺合料对胶凝材料浆体的流变性能和触变性的影响。结果表明:通过流变仪转速阶梯变化制度构建稳定的浆体流动状态,并利用转换方程可进行浆体流变性能参数的有效测量和计算。胶凝材料浆体的流变性能符合Bingham模型。粉煤灰和粉煤灰微珠均能降低浆体的屈服应力、塑性黏度和触变性,粉煤灰微珠作用效果更为明显;硅灰能增大浆体的屈服应力、塑性黏度和触变性;磨细矿渣粉会降低浆体的屈服应力和触变性,提高浆体的塑性黏度。在进行大流态混凝土配合比设计时应综合考虑矿物掺合料对新拌混凝土流变性能的影响。     

剪切速率和温度对低水胶比水泥浆流变性能的影响

水泥浆体的流变性能不仅与材料本身有关,还受环境及外部作用影响。本文针对水泥基材料实际工程中存在的主要外部影响因素,即剪切作用与环境温度,研究了两者对低水胶比水泥浆流变性能的耦合作用。结果表明:水泥浆体在剪切过程中的流变行为与所施加的预剪切有关,水泥浆体的屈服应力随预剪切速率的增大而减小,剪切增稠的程度随预剪切速率的增大而增大;温度升高,水泥颗粒对减水剂的吸附量增加,浆体在不同剪切速率下的平衡表观黏度减小;温度和剪切速率对水泥浆平衡表观黏度的影响具有耦合效应,剪切速率越高,温度的影响越小,反之亦然,并建立了不同温度和剪切速率下平衡表观黏度的数学关系。     

大理石粉颗粒丛特性对水泥浆体流变性能影响

试验研究了水泥-大理石粉浆体剪切应力和塑性黏度随剪切速率变化的规律,使用Bingham流体模型和PowerLaw流体模型分别对浆体低剪切速率和高剪切速率阶段的剪切应力进行拟合,得到浆体屈服应力,塑性黏度系数.探究了水泥-大理石粉颗粒丛特性即颗粒分布宽度、颗粒数密度、总比表面积和Zeta电位与浆体屈服应力和塑性黏度的关系.研究结果表明:大理石粉比表面积小于640m2/kg时,起到稀化浆体的作用,大于640m2/kg时起稠化作用,且稀化或稠化的作用随其掺量的增加而增大.浆体中颗粒间接触点数量和固-液相接触面积增大使浆体屈服应力,塑性黏度提高.大理石粉降低了水泥浆体Zeta电位,浆体中粒子间静电作用力减弱,对流动性起到削弱作用.     

水泥-石灰石粉浆体流变经时行为研究

研究了水泥-石灰石粉浆体流变参数随水化时间的变化,采取RHEORIAB QC型旋转黏度计测定水泥-石灰石粉浆体流变,采用Herschel-Bulkley模型拟合浆体曲线得到相关流变参数,分别利用Roussel和Philippe提出的模型对水泥-石灰石粉浆体的动态屈服应力和稠度进行拟合。结果表明：水泥浆体动态屈服应力比石灰石粉浆体小,稠度比石灰石粉浆体大;水泥-石灰石粉浆体动态屈服应力、稠度随水化时间线性增大,随石灰石粉掺量增加,增大速率线性减小,其初始动态屈服应力线性增大,初始稠度按二次抛物线先增大后减小。     

纳米SiO2对新拌水泥浆体流变性能的影响

选用RHEOLAB QC型旋转黏度计,分别测试了内掺水泥质量分数0.0％、1.0％、2.0％与3.0％纳米SiO2的水泥浆体在5℃、20℃、30℃时的稳态流变曲线、静态屈服应力、恒定速率剪切下的表观黏度与剪切应力,系统研究了不同环境温度时纳米SiO2对新拌水泥浆体流变性能的影响.结果表明:随纳米SiO2掺量增加,水泥浆体的动态屈服应力与稠度系数均显著增大;随温度升高,掺纳米SiO2的水泥浆体的稠度系数均增大,纳米SiO2掺量为0％与1.0％的水泥浆体的动态屈服应力增大,而纳米SiO2掺量为2.0％、3.0％的水泥浆体的动态屈服应力基本不变;随纳米SiO2掺量增加,水泥浆体的静态屈服应力与其在10～120 min的增长速率均增大;20℃、30℃时,随纳米SiO2掺量增加,水泥浆体的剪切变稀程度增大;5℃与30℃时,随纳米SiO2掺量增加,水泥浆体的触变指数增大;当纳米SiO2掺量为1.0％时,水泥浆体的活化能低,温度敏感性弱,热稳定性好.     

水泥-粉煤灰-石灰石粉复合浆体的流变性能

采用Rheolab QC型旋转黏度计研究了水泥–粉煤灰–石灰石粉复合浆体的流变性能,分析了不同粉体含量以及石灰石粉颗粒粒径对复合浆体屈服应力、塑性黏度以及触变性的影响。结果表明:复合浆体中石灰石粉掺量增大或颗粒粒径减小,浆体屈服应力、塑性黏度和触变性均增大;随剪切速率增大,水泥–粉煤灰–石灰石粉复合浆体发生显著的剪切稀化现象,随后塑性黏度渐趋稳定,掺入石灰石粉后,提高了浆体由剪切稀化向塑性黏度逐渐稳定时需要的剪切速率;在水泥–粉煤灰体系浆体中掺入质量分数为20%～40%石灰石粉能够显著改善浆体的流变性能,提高浆体的稳定性。     

乳胶粉掺量对纤维素醚改性水泥浆体流变性能的影响

采用Anton Paar MCR 302型流变仪研究了乳胶粉掺量对纤维素醚改性水泥浆体流变性能和触变性的影响。结果表明,掺入乳胶粉的纤维素醚改性水泥浆体表现为剪切稀化的流变特性,当剪切速率较小时,浆体黏度下降显著。乳胶粉掺量越大,浆体基于Herschel-Bulkey模型拟合得到的屈服应力和黏度系数均越大。并且乳胶粉能够增大浆体的触变滞后环面积和三段式触变测试的结构恢复率。掺入乳胶粉和纤维素醚的水泥浆体屈服应力和触变环面积呈正向线性关系。     

Method for calculating dynamic yield stress of fresh cement pastes using a coaxial cylinder system

The calculation of the rheological parameters of fresh cement pastes plays a key role in understanding the rheology of cement-based mixes. Because cement paste is not a simple Bingham fluid, a suitable nonlinear model must be found for characterizing its flow. A test system in which the rotational speed or shear rate can be changed in multiple steps is regarded as a suitable rheological test protocol because the paste reaches a steady state. Furthermore, theoretical derivations show that the solution of the Couette inverse problem corresponding to the modified Bingham model and the Herschel–Bulkley (H-B) model is complex. However, a comparative analysis revealed that the yield stress of fresh paste could easily be obtained through a calculation process based on a Parabolic model. This study presents the complete calculation procedure for this model. The influence of the plug flow is considered, and test points with low minimum shear stress (τ_min) are excluded. Finally, the accuracy of the proposed method is verified through comparisons with the results obtained using mini-cone slump tests. These results show that the dynamic yield stress calculated using the expression of the Couette inverse problem based on the Parabolic model in consideration of the plug flow is very close to the yield stress obtained using the mini-cone slump flow test. This proves that the proposed method could precisely characterize the dynamic yield stress of cement pastes.     

超细粉体对水泥净浆流变行为影响研究

采用截锥圆模法测定不同掺量超细粉体水泥复合浆液的流动度.采用ZNN-D6B型旋转黏度计研究超细玻璃粉和偏高岭土两种超细粉体对水泥净浆流变行为的影响,得到了剪切速率-剪切应力(γ-τ)曲线和剪切速率-表观粘度(γ-μa)曲线,并分别采用宾汉姆模型和赫-巴模型对γ-τ流变曲线进行拟合,得到不同掺量超细玻璃粉-水泥(GP-C)复合浆液和偏高岭土-水泥(MK-C)复合浆液的动切力、塑性粘度、稠度系数和流性指数等流变参数.结果表明:超细粉体的加入降低了复合浆液的流动度.随着掺量的增加,两种复合浆液的宾汉动切力τ0、塑性粘度η、赫-巴动切力τy均逐渐增大,MK-C复合浆液的稠度系数K和流性指数n逐渐减小,GP-C复合浆液的稠度系数K呈现增大-减小-增大的趋势,而流性指数n呈现减小-增大-减小的趋势.所有样本表观粘度μa都随着剪切速率的增大而减小,呈现剪切稀释现象.     

硅微粉对水泥浆体流变性能的影响

运用水化热测定仪、流变仪、以及Dinger-Funk紧密堆积等方法,研究了硅微粉掺入水泥中对复合浆体的流变性能的影响,比较了不同硅微粉掺量对复合浆体的早期水化放热、紧密堆积程度、屈服应力和塑性粘度的作用.结果显示:硅微粉取代水泥后,降低浆体水化热放热量,提高了体系紧密堆积程度;Bingham流体仍适用于硅微粉-水泥复合浆体,取代5%、10%、15%水泥的复合浆体,屈服应力和塑性粘度在0、60 min时都小于纯水泥浆体,并且取代10%水泥的复合浆体,其屈服应力和塑性粘度在0、60 min时都最小,流变性能最好.     

Estimating rheological properties of cement pastes using various rheological models for different test geometry, gap and surface friction

Shear stress-shear rate flow tests were carried out on various cement pastes incorporating different mineral additions and chemical admixtures using various test geometries. Different gaps and friction capacity of shearing surfaces of the test geometries were employed in the flow tests. Rheological properties of cement pastes were calculated from the resulting flow curves using various rheological models. The Bingham, Modified Bingham, Herchel-Bulkley and Casson models were used to estimate yield stress. Plastic viscosity was estimated by the Bingham, Modified Bingham and Casson models, while the Williamson and Sisko models were used to estimate the theoretical viscosity at zero and infinite shear rates. It was observed that the rheological properties of cement pastes varied with the change of the test geometries and rheological models used for their calculation. The performance of rheological models in estimating the rheological properties of cement pastes, as expressed by a standard error, varied with the test geometries as well as with the composition of cement pastes. The paper highlights the difficulty in reconciling rheological results from different sources and the need for standardizing rheological test methods for rheological interlaboratory results to be critically analyzed and compared.     

Effects of purification process on rheological properties of catfish oil

Effects of oil refining steps (degumming, neutralizing, bleaching, and deodorizing) on rheological properties of catfish oil were investigated. Four rheological models (Newtonian, Bingham, Herschel-Bulkley, and Casson) were used to fit the experimental data. Refined catfish oil behaves like a Newtonian fluid. Based on the Casson model, the yield stress values of oils gradually decreased after each refining step. The highest shear rate index (0.904) was observed in the deodorized oil. The Casson model was used to predict rheological properties because it works well at both lower and higher shear rates.     

旋转黏度计测定水泥浆体静态屈服应力和黏弹性研究

采用旋转黏度计进行了恒定剪切速率、应力松弛、蠕变试验,研究了水泥浆体的静态屈服应力和黏弹性.结果表明:新拌水泥浆体属于带有屈服应力的黏弹性流体,其静态屈服应力为弹性向黏性转变时所对应的剪切应力;恒定剪切速率、应力松弛、蠕变试验均能测试出水泥浆体屈服应力和黏弹性.在恒定剪切速率试验中,新拌水泥浆体的屈服应力测试依赖于测试时剪切速率的选择,剪切速率过小,水泥浆体不出现静态屈服应力,剪切速率过大,测试的静态屈服应力较小;在应力松弛和蠕变试验中,测试出的水泥浆体静态屈服应力较恒定剪切速率试验的精确.对于一个静态屈服应力未知的新拌水泥浆体,可先采用恒定剪切速率试验粗略选择剪切速率和剪切应力范围,之后采用应力松弛或蠕变试验进行精确测试其静态屈服应力.