摘要
基于紧密堆积级配模型,研究了级配分布模数对复合胶凝材料浆体流变性能的影响.结果表明:Dinger‑Funk模型级配分布模数对不同复合胶凝材料的屈服应力和塑性黏度具有不同的影响规律;浆体流变性能与湿堆积密实度存在一定的相关性,而水膜厚度是级配分布模数影响浆体流变性能的关键因素;随着水膜厚度的增加,复合胶凝材料浆体的屈服应力和塑性黏度呈幂指数型下降趋势,这一影响可通过简化YODEL模型和Ahmadah模型体现.
水泥混凝土是世界上用量最大的人造建筑材料,每使用1 kg水泥需要排放0.6 kg以上的CO2,对全球温室效应造成显著影
胶凝材料的流变性能影响新拌水泥基材料的施工性能,成为当代混凝土结构更复杂发展趋势下的重要性能.颗粒级配影响拌和物中粗细颗粒的比例,是影响流变性能的重要因素.当前级配分布模数对混凝土流变性能影响的研究主要集中在骨料层次,如Dinger‑Funk模型已应用于自密实混凝土和超高性能混凝土
本文基于Dinger‑Funk模型,设计了水泥与辅助性胶凝材料的配合比,研究了级配分布模数对复合胶凝材料浆体流变性能的影响规律,通过堆积密实度、水膜厚度等物理特征,探究其对屈服应力、塑性黏度的影响机理,以期为流变性能调控以及基于流变性能需求的复合胶凝材料设计提供理论基础.
水泥为P·O 52.5普通硅酸盐水泥(C),选用硅灰(SF)、矿粉(SL)、粉煤灰(FA)和石灰石粉(LP)作为辅助性胶凝材料,制备的水泥-硅灰、水泥-矿粉、水泥-粉煤灰和水泥-石灰石粉分别记为C‑SF、C‑SL、C‑FA和C‑LP.使用激光粒度仪测试胶凝材料的粒径分布,结果见

图1 胶凝材料粒径分布
Fig.1 Particle distribution of cementitious materials
Material | Specific surface area/( | Apparent density/(kg· | d5/μm | d95/μm |
---|---|---|---|---|
C | 355.1 | 3 147.1 | 2.21 | 27.39 |
SF | 15 738.4 | 2 153.3 | 0.10 | 5.61 |
FA | 1 886.7 | 2 508.2 | 1.26 | 33.01 |
SL | 428.0 | 2 844.0 | 1.38 | 43.67 |
LP | 364.9 | 2 688.0 | 2.66 | 110.98 |
采用Dinger‑Funk模型设计级配(见
(1) |
式中:为粒径小于的理想累计体积分数,%;为材料第i个粒级的粒径,μm.
复合胶凝材料实际累计分数与有差距,用激光粒度仪所测数据进行计算:
(2) |
式中:为第k种胶凝材料的体积分数,%;j为胶凝材料的种类;为第k种胶凝材料中粒径小于的累计体积分数,%.
借助solver tool实现与的偏差最小化,可得胶凝材料的体积分数,其求解过程包含目标值、调控值和边界条
(3) |
(4) |
式中:n为粒级总数.
调控值是复合胶凝材料中各材料的占比,影响总胶凝材料的级配,通过调控实现最小,达到级配优化的效果.复合胶凝材料在不同值下的配合比见
Group | q value | Mix proportion/(kg· | |||||
---|---|---|---|---|---|---|---|
C | FA | SL | SF | LP | |||
C‑FA‑0.10 | 0.10 | 2 328.8 | 652.1 | 1.19 | |||
C‑FA‑0.15 | 0.15 | 2 457.8 | 549.3 | 1.20 | |||
C‑FA‑0.20 | 0.20 | 2 590.0 | 443.9 | 1.21 | |||
C‑FA‑0.25 | 0.25 | 2 715.9 | 343.6 | 1.22 | |||
C‑FA‑0.30 | 0.30 | 2 841.7 | 243.3 | 1.23 | |||
C‑FA‑0.35 | 0.35 | 2 961.3 | 148.0 | 1.24 | |||
C‑FA‑0.40 | 0.40 | 3 080.9 | 52.7 | 1.25 | |||
C‑SL‑0.10 | 0.10 | 1 973.2 | 1 060.8 | 1.21 | |||
C‑SL‑0.15 | 0.15 | 1 712.0 | 1 296.9 | 1.20 | |||
C‑SL‑0.20 | 0.20 | 1 447.6 | 1 535.8 | 1.19 | |||
C‑SL‑0.25 | 0.25 | 1 183.3 | 1 774.7 | 1.18 | |||
C‑SL‑0.30 | 0.30 | 912.6 | 2 019.2 | 1.17 | |||
C‑SL‑0.35 | 0.35 | 642.0 | 2 263.8 | 1.16 | |||
C‑SL‑0.40 | 0.40 | 371.3 | 2 508.4 | 1.15 | |||
C‑SF‑0.10 | 0.10 | 1 595.5 | 1 061.4 | 2.13 | |||
C‑SF‑0.15 | 0.15 | 1 734.0 | 966.7 | 2.16 | |||
C‑SF‑0.20 | 0.20 | 1 869.3 | 874.1 | 2.19 | |||
C‑SF‑0.25 | 0.25 | 1 998.3 | 828.9 | 2.23 | |||
C‑SF‑0.30 | 0.30 | 2 124.2 | 699.7 | 2.26 | |||
C‑SF‑0.35 | 0.35 | 2 243.8 | 617.9 | 2.29 | |||
C‑SF‑0.40 | 0.40 | 2 360.3 | 538.3 | 2.32 | |||
C‑LP‑0.10 | 0.10 | 1 076.3 | 1 768.7 | 1.14 | |||
C‑LP‑0.15 | 0.15 | 909.5 | 1 911.2 | 1.13 | |||
C‑LP‑0.20 | 0.20 | 739.5 | 2 056.3 | 1.12 | |||
C‑LP‑0.25 | 0.25 | 575.9 | 2 196.1 | 1.11 | |||
C‑LP‑0.30 | 0.30 | 412.3 | 2 335.9 | 1.10 | |||
C‑LP‑0.35 | 0.35 | 248.6 | 2 475.6 | 1.09 | |||
C‑LP‑0.40 | 0.40 | 91.3 | 2 610.0 | 1.08 |
流变试验中,水泥-硅灰浆体在水胶比0.4下的剪切应力和塑性黏度较大,超出流变仪测量范围,因此将其水胶比调整为0.8.动态剪切流变测试(DSR)分为预剪切、剪切速率增大和剪切速率减小3个阶段,其剪切速率γ随时间的变化见

图2 动态剪切流变测试中剪切速率随时间的变化
Fig.2 Change of shear rate with time in DSR
(5) |
式中:为剪切应力,Pa;为屈服应力,Pa;为塑性黏度,Pa·s;为二阶参数,Pa·
在特定水胶比下,将胶凝材料达到的最大堆积密实度作为湿堆积密实
(6) |
(7) |
(8) |
(9) |
式中:为容器的体积,
浆体的剪切应力-剪切速率曲线见

图3 浆体的剪切应力-剪切速率的曲线
Fig.3 Shear stress‑shear rate of pastes
浆体的拟合屈服应力和塑性黏度见

图4 浆体的拟合屈服应力和塑性黏度
Fig.4 Fitted yield stress and plastic viscosity of pastes
水泥-粉煤灰浆体的湿堆积密实度见

图5 水泥-粉煤灰浆体的湿堆积密实度
Fig.5 Wet packing density of C‑FA pastes
复合胶凝材料浆体的湿堆积密实度见

图6 复合胶凝材料浆体的湿堆积密实度
Fig.6 Wet packing density of composite cementitous materils pastes
综上,当值取0.15~0.25时,浆体湿堆积密实度较高,且与其组成无关.
浆体的水膜厚度主要受到比表面积、水胶比等的影响.浆体的水膜厚度见

图8 浆体的水膜厚度
Fig.8 Water film thickness of pastes
浆体流变性能与水膜厚度的关系见

图9 浆体流变性能与水膜厚度的关系
Fig.9 Relationship between rheological properties and water film thickness of pastes
YODEL模
(14) |
式中:为粒径分布函数;为颗粒半径的中位值,m;为颗粒间距,取2倍水膜厚度,m;为固体体积分数,%.
利用简化YODEL模型可建立浆体屈服应力与胶凝材料物理特征的关

图10 浆体屈服应力与胶凝材料物理特征的关系
Fig.10 Relationship between yield stress of pastes and physical characteristics of cementitious materials
浆体的塑性黏度与颗粒间流体动力相互作用、颗粒接触作用有关联,可通过颗粒间距、粒径、湿堆积密实度等参数进行表
式中:为颗粒平均粒径,取50%累计粒度分布粒径值,m;为浆体间隙液黏度与接触点曲率半径有关的系数.
浆体的塑性黏度与胶凝材料物理特征的关系见

图11 浆体塑性黏度与胶凝材料物理特征的关系
Fig.11 Relationship between plastic viscosity of pastes and physical characteristics of cementitious materials
(1)不同组成的复合胶凝材料的流变性能随级配分布模数值的变化趋势不一致.随着值的增加,水泥-粉煤灰和水泥-硅灰浆体的屈服应力先增大后减小,塑性黏度呈下降趋势;水泥-石粉浆体的屈服应力随值增加而减小,塑性黏度保持不变;水泥-矿粉的流变性能受值的影响较小.
(2)通过研究值对湿堆积密实度的影响,建议值取0.15~0.25,用于Dinger‑Funk模型设计复合胶凝材料的配合比,以实现浆体较高的湿堆积密实度.
(3)湿堆积密实度对流变性能有一定的影响,但水膜厚度是值影响流变性能的关键因素,其屈服应力和塑性黏度与水膜厚度呈幂指数型下降关系.
(4)值影响复合胶凝材料的粒径分布、湿堆积密实度、水膜厚度等物理特征.通过简化YODEL模型和Ahmadah模型可建立复合胶凝材料浆体流变性能与物理特征的相关性.
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