摘要
以粉煤灰、矿粉、石英砂为主要原材料,无水硅酸钠为碱激发剂,硅酸镁铝为专用外加剂,制备了粉煤灰基3D打印地聚合物砂浆(以下简称地聚合物砂浆),研究了硅酸镁铝掺量及静置时间对其流变性能的影响,并在最佳硅酸镁铝掺量和最适合静置时间条件下进行了3D打印上机试验.结果表明:地聚合物砂浆的流变性能随着硅酸镁铝掺量的增加而增加,且随着静置时间的增加总体呈增长趋势;采用宾汉(Bingham)流体模型和赫切尔-巴尔克(Herschel‑Bulkley)流体模型拟合地聚合物砂浆的流变曲线后发现,上述2种模型的拟合度
建筑3D打印技术是将3D打印与建筑施工有机结合的一种新型建筑技术.与传统浇筑成型施工工艺相比,建筑3D打印技术具有节约人工成本、提高施工效率等优势,且能够打印出其他方式难以建造的高成本曲线建筑.近十年来,世界各国已有30多个研究团体从事相关研究,并取得了快速发
地聚合物是一种新型的碱激发无机胶凝材料,其早期强度高、硬化快的特点在一定程度上可以满足建筑3D打印技术的需
鉴于此,本文基于前期粉煤灰基3D打印地聚合物砂浆的合适配合比(胶凝材料种类和掺
胶凝材料粉煤灰、矿粉均从郑州恒诺滤料有限公司采购,其化学组成见
为研究硅酸镁铝掺量对地聚合物砂浆流变性能的影响,设计了0%、0.5%和1.0%这3种硅酸镁铝掺量的地聚合物砂浆试样.另外,以试样FAS1.0‑new为基准,研究了静置时间对地聚合物砂浆流变性能的影响.各试样具体配合比如
将粉煤灰、矿粉、碱激发剂和石英砂倒入搅拌锅,先低速搅拌1 min,使固体混合物混合均匀;然后缓慢添加硅酸镁铝专用外加剂与水的混合溶液(空白试样仅添加水),再次低速搅拌1 min;最后将混合料高速搅拌2~3 min,以保证混合料充分拌和,此时开始计时静置时间.需要说明的是,对于掺有硅酸镁铝专用外加剂的试样,须确保外加剂与水较好混合,即先将硅酸镁铝专用外加剂倒入水中,搅拌1 min至水中无明显沉淀,得到其与水的混合溶液后,再添加至其他原材料中.
采用RVDV‑2型旋转黏度计测定地聚合物砂浆的流变性能.砂浆的表观黏度和触变性能数据根据黏度计的默认设置直接测得,其塑性黏度和屈服应力通过试验数据计算得出.
表观黏度是指在一定速度梯度下,用相应的剪切应力除以剪切速率所得的
触变性能的一个重要标志就是浆体流动性恢复的可逆过程.触变性流
BH模型和H‑B模型是常用的水泥基材料流变曲线本构模
BH模型的表达式如
τ=τ0+ηγ | (1) |
H‑B模型的表达式如
τ=τ0+m | (2) |
Larrard
(3) |
式(
为了分析不同流变模型对地聚合物砂浆流变曲线方程的适用性,本文基于BH模型及H‑B模型,采用分析法将试验数据与流变相关参数进行拟合.基于BH模型进行拟合时,将“下行曲线”中每个剪切速率与剪切应力的对应值代入

图1 硅酸镁铝掺量对地聚合物砂浆流变性能的影响
Fig.1 Effect of magnesium aluminum silicate dosages on rheological properties of geopolymer mortar
以FAS1.0‑new试样的触变环面积为基准,分析了外加剂掺量对地聚合物砂浆触变性能的影响.由
廖洪
由
为了更好地阐明硅酸镁铝掺量对地聚合物砂浆的影响,运用分析法得到不同硅酸镁铝掺量地聚合物砂浆的塑性黏度和屈服应力,其中塑性黏度由公式计算得
不同硅酸镁铝掺量对地聚合物砂浆凝结时间的影响如
结合以上分析可知,硅酸镁铝专用外加剂的掺入有利于改善地聚合物砂浆的流变性能,且硅酸镁铝的适宜掺量为1.0%.
一般而言,屈服应力分为静态屈服应力与动态屈服应力.使砂浆开始流动的最小剪切应力为静态屈服应力;而维持材料流动的剪切应力为动态屈服应力,且后者较前者稍

图2 静置时间对地聚合物砂浆流变性能的影响
Fig.2 Effect of different rest time on rheological properties of geopolymer mortars
由
由
为了更好地研究静置时间对地聚合物砂浆的影响,分析比较了静置时间对地聚合物砂浆塑性黏度和屈服应力的影响,结果见
由此可见:当静置时间较短时,2种流变模型的拟合优度
前文从流变性能的角度研究了硅酸镁铝专用外加剂掺量和静置时间对地聚合物砂浆的影响,然而,地聚合物砂浆配合比设计和打印工艺参数是否适用于实际3D打印尚需上机验证.结合流变性能试验结果与实际上机试验发现:本试验条件下,适宜的静置时间约为10 min,可根据不同程序、打印时间等具体情况需要进行适当调整;当静置时间超过30 min时,地聚合物砂浆屈服应力过高,砂浆无法从打印喷头中挤出,可以大致估算出材料的开放时

图3 地聚合物砂浆的3D打印
Fig.3 3D printing of geopolymer mortars
(1)地聚合物砂浆的表观黏度、触变性能、塑性黏度和屈服应力均随着硅酸镁铝掺量的增加而增加;地聚合物砂浆的屈服应力和触变性能随着静置时间的增加而增加,其表观黏度和塑性黏度虽有所波动,但仍呈现增长趋势.
(2)采用BH模型与H‑B模型来拟合地聚合物砂浆的流变性能,当外加剂掺量和静置时间合理时,2种模型的拟合度高,其中H‑B模型略优于BH模型;但当静置时间接近初凝时间时,基于H‑B模型分析得到的砂浆屈服应力有较大偏差.综上,BH模型比H‑B模型更具有优越性.
(3)本试验条件下,在粉煤灰基地聚合物砂浆体系中,硅酸镁铝专用外加剂的适宜掺量为1.0%,适宜的静置时间约为10 min.在适宜外加剂掺量和静置时间条件下,地聚合物砂浆具有较好的可打印性能,且打印效果良好.
参 考 文 献
LOWKE D, DINI E, PERROT A, et al. Particle‑bed 3D printing in concrete construction-Possibilities and challenges[J]. Cement and Concrete Research , 2018, 112:50‑65. [百度学术]
PEGNA J. Exploratory investigation of solid freeform construction[J]. Automation in Construction, 1997, 5(5):427‑437. [百度学术]
GARG A, VIJAYARAGHAVAN V, ZHANG J, et al. Robust model design for evaluation of power characteristics of the cleaner energy system[J]. Renewable Energy, 2017, 112:302‑313. [百度学术]
KAUR M, SINGH J, KAUR M. Synthesis of fly ash based geopolymer mortar considering different concentrations and combinations of alkaline activator solution[J]. Ceramics International, 2018, 44(2):1534‑1537. [百度学术]
GARG A, LI J, HOU J, et al. A new computational approach for estimation of wilting point for green infrastructure[J]. Measurement, 2017, 111:351‑358. [百度学术]
张大旺, 王栋民. 3D打印地质聚合物材料的早期工作性研究[J]. 混凝土世界, 2018, 37(9):64‑68. [百度学术]
ZHANG Dawang, WANG Dongmin. Early workability of 3D printing geopolymer materials [J]. Concrete World, 2018, 37(9):64‑68.(in Chinese) [百度学术]
SINGH N B, SAXENA S K, KUMAR M, et al. Geopolymer cement:Synthesis, characterization, properties and applications[J]. Materials Today:Proceedings, 2019, 15:364‑370. [百度学术]
PANDA B, PAUL S C, HUI L J, et al. Additive manufacturing of geopolymer for sustainable built environment[J]. Journal of Cleaner Production, 2017, 167:281‑288. [百度学术]
PANDA B, PAUL S C, TAN M J. Anisotropic mechanical performance of 3D printed fiber reinforced sustainable construction material[J]. Materials Letters, 2017, 209:146‑149. [百度学术]
PANDA B, UNLUER C, TAN M J. Investigation of the rheology and strength of geopolymer mixtures for extrusion‑based 3D printing[J]. Cement and Concrete Composites, 2018, 94:307‑314. [百度学术]
LIM J H, PANDA B, PHAM Q C. Improving flexural characteristics of 3D printed geopolymer composites with in‑process steel cable reinforcement[J]. Construction and Building Materials, 2018, 178:32‑41. [百度学术]
MA G, LI Z, WANG L, et al. Micro‑cable reinforced geopolymer composite for extrusion‑based 3D printing[J]. Materials Letters, 2019, 235:144‑147. [百度学术]
张大旺, 王栋民, 朴春爱,等. 钢渣掺量对3D打印地质聚合物材料新拌浆体流变性的影响[J]. 应用基础与工程科学学报, 2018, 26(3):596‑604. [百度学术]
ZHANG Dawang, WANG Dongmin, PU Chun'ai, et al. Effect of steel slag content on the rheological of 3D printing geopolymer pastes [J]. Journal of Applied Foundation and Engineering Science, 2018, 26(3):596‑604. (in Chinese) [百度学术]
MA G, LI Z, WANG L. Printable properties of cementitious material containing copper tailings for extrusion based 3D printing[J]. Construction and Building Materials, 2018, 162:613‑627. [百度学术]
REINHARDT H W, GROSSE C U. Continuous monitoring of setting and hardening of mortar and concrete[J]. Construction and Building Materials, 2004, 18(3):145‑154. [百度学术]
GUO X L, YANG J Y, XIONG G Y. Influence of supplementary cementitious materials on rheological properties of 3D printed fly ash based geopolymer[J]. Cement and Concrete Composites, 2020, 114(9),1‑9. [百度学术]
LI H, LIU S, LIN L. Rheological study on 3D printability of alginate hydrogel and effect of graphene oxide[J]. International Journal of Bioprinting, 2016, 2(2):54‑66. [百度学术]
PANDA B, TAN M J. Experimental study on mix proportion and fresh properties of fly ash based geopolymer for 3D concrete printing[J]. Ceramics International, 2018, 44(9):10258‑10265. [百度学术]
CHHABRA R P, RICHARDSON J F. Non‑Newtonian flow and applied rheology:Engineering applications[M]. Oxford:Butterworth‑Heinemann, 2011:1‑54. [百度学术]
LIPSCOMB G G, DENN M M. Flow of Bingham fluids in complex geometries[J]. Journal of Non‑newtonian Fluid Mechanics, 1984, 14:337‑346. [百度学术]
DE LARRARD F, FERRARIS C F, SEDRAN T. Fresh concrete:A Herschel‑Bulkley material[J]. Materials and Structures, 1998, 31(7):494‑498. [百度学术]
廖洪涛. XVT凝胶的胶体性能研究[J]. 日用化学工业, 1992, 3(6):51‑54. [百度学术]
LIAO Hongtao. Colloidal properties of XVT gels [J]. China Surfactant Detergent & Cosmetics, 1992, 3(6):51‑54. (in Chinese) [百度学术]
陶晡, 康占海, 张金林. 硅酸镁铝及其与黄原胶协同使用对30%辛硫磷微囊悬浮剂贮存物理稳定性的影响[J]. 农药学学报, 2012, 14(5):574‑578. [百度学术]
TAO Bu, KANG Zhanhai, ZHANG Jinlin. Study on influence of veegum and the coordination of veegum with xanthan gum to physical stability of phoxim 300 capsule suspension[J]. China Journal of Pestic Science, 2012, 14(5):574‑578. (in Chinese) [百度学术]
PANDA B, UNLUER C, TAN M J. Extrusion and rheology characterization of geopolymer nanocomposites used in 3D printing[J]. Composites Part B:Engineering, 2019, 176:107290. [百度学术]
蔺喜强, 张涛, 霍亮, 等.水泥基建筑3D打印材料的制备及应用研究[J]. 混凝土, 2016(6):141‑144. [百度学术]
LIN Xiqiang, ZHANG Tao, HUO Liang, et al. Preparation and application of 3D printing materials in construction[J]. Concrete, 2016 (6):141‑144. (in Chinese) [百度学术]
马国伟,王里. 水泥基材料3D打印关键技术[M]. 北京:中国建材工业出版社,2020:165‑170. [百度学术]
MA Guowei, WANG Li. 3D Printing key technologies for cementitious materials[M]. Beijing:China Building Materials Industry Press, 2020:165‑170. (in Chinese) [百度学术]
LE T T, AUSTIN S A, LIM S, et al. Mix design and fresh properties for high‑performance printing concrete[J]. Materials and Structures, 2012, 45(8):1221‑1232. [百度学术]