【作者】 邓最亮；

【导师】 路贵民；

【作者基本信息】 华东理工大学 ， 环境科学与工程， 2021， 博士

【摘要】 砂石料是世界第二大消耗的自然资源,其在混凝土之中占比高达70%。随着基础建设的蓬勃发展,砂石开采带来的环境污染、河流生态环境破坏等问题日益凸显,机制砂替代天然河砂已成趋势。机制砂由岩石破碎而成,岩石特性和砂所含层状粘土杂质均会影响混凝土的工作性。非洲为“一带一路”倡议重要节点,基础设施建设项目蓬勃发展,随之催生了巨大的混凝土需求。非洲就地取材的粗骨料品质不容乐观,其吸水率通常为2%～5%,远大于国标对吸水率指标(小于2%)的要求。大吸水率粗骨料和伴生的层状粘土往往会严重影响聚羧酸减水剂对胶凝材料的分散效果进而影响新拌混凝土的工作性能,为工程施工及硬化服役过程埋下了隐患。为解决多孔大吸水率粗骨料和层状粘土引起的混凝土工作性问题,本文以大吸水率粗骨料制备的大吸水率石粉(LBSP)和层状膨润土为研究对象,系统研究聚羧酸减水剂PCE-1对两种吸附性粉体的吸附行为和流变行为的影响,PCE-1为丙烯酸和甲基烯丙基聚氧乙烯醚聚合物,单体摩尔比为3.2:1,结合砂浆应用性能研究,系统分析聚羧酸减水剂与多孔和层状骨料的适应性问题。论文主要研究结果如下:(1)PCE-1在LBSP上的吸附量随温度升高而增加,等温吸附曲线符合Langmuir模型。随着时间延长,LBSP对PCE-1的吸附量先增大后减小,30min时趋于平衡。LBSP多孔结构是吸水和吸附聚羧酸减水剂的主要原因,吸附聚羧酸减水剂后,LBSP的孔容和孔径减小。热重分析结果佐证了聚羧酸减水剂分子吸附在LBSP中。(2)掺LBSP的水泥砂浆符合非牛顿流体特征。LBSP会使砂浆粘度增大,PCE-1则会降低砂浆表观粘度,2-丙烯酰胺-2-甲基丙磺酸-N,N-二甲基丙烯酰胺(简称AMPS)可改善易沉底的砂浆粘度。水化时间越长,砂浆粘度越大。流变模型拟合结果表明:LBSP和AMPS可使屈服应力增大;PCE-1则会降低屈服应力。(3)PCE-1在膨润土上的吸附量随温度升高而增加,Langmuir模型可以较好地描述吸附等温线,吸附过程符合准二级动力学模型。膨润土的Zeta电位随PCE-1浓度和聚乙烯醇(PVA)浓度的增大而减小;X射线衍射结果表明,仅吸附聚羧酸减水剂的膨润土(001)晶面间距从1.24nm增大至1.65nm,而吸附聚羧酸减水剂和聚乙烯醇两种聚合物的膨润土(001)晶面间距仅为1.55nm,表明聚乙烯醇可以抑制聚羧酸减水剂的插层作用。(4)掺膨润土的砂浆符合非牛顿流体的特性。膨润土会增加架桥结构,导致砂浆体系粘度随掺量增加而增大;聚羧酸减水剂的分散作用使砂浆粘度减小;聚乙烯醇浓度增加时,砂浆粘度先略有增加后下降。三种模型拟合得到的流变参数表明,屈服应力随膨润土掺量增加或水化时间延长而增大,随聚羧酸减水剂或聚乙烯醇掺量增大而减小。(5)LBSP和膨润土两种吸附性粉体材料会降低砂浆的初始流动度,减小砂浆对水或聚羧酸减水剂的敏感度。膨润土对砂浆性能的影响比LBSP更为显著,膨润土的掺量为LBSP的1/6～1/10时即可以达到与其相近的影响,原因在于膨润土对聚羧酸减水剂的吸附量远大于LBSP。提高聚羧酸减水剂的掺量或掺加PVA可以降低掺加膨润土砂浆的流动度经时损失速率。屈服应力越大则流动度越小、砂浆流速越慢;流速与屈服应力和粘度的相关性比流动度更好,流速更能表达砂浆的流变性。AMPS可以抑制LBSP替代率高时引起的砂浆泌水性,可以有效降低含膨润土砂浆的收缩率。设计合成聚羧酸减水剂PCE-2和PCE-3,其中PCE-2为丙烯酸和甲基烯丙基聚氧乙烯醚按单体摩尔比为2:1聚合,PCE-3为马来酸和异戊烯醇聚氧乙烯醚按单体摩尔比为1:1聚合。与PCE-1相比,PCE-2和PCE-3的酸醚比更低,侧链密度更高。PCE-2和PCE-3的水力学直径都大于PCE-1,在LBSP上的吸附量均减小;PCE-3静电斥力比PCE-1更明显,其在膨润土表面的吸附量更低。酸醚比低的聚羧酸减水剂在掺吸附性粉体砂浆中分散能力减弱,经时流动度保持能力增加。利用不同酸醚比聚羧酸减水剂的配合,可以降低聚羧酸减水剂掺量、提高经时流动度保持能力,具有较强的实用性。更多还原

【Abstract】 Aggregate is the second largest consumption of natural resources globally,which takes more than 70%of parts in concrete mix.With the rapid development of infrastructure construction,environmental pollution and river ecological environment damage caused by mining are increasingly prominent,the replacement of natural river sand by manufactured sand has become a trend.Manufactured made sand is made from broken rock.The characteristics of rock and the layered clay impurities in sand will affect the workability of concrete.As an important node of China’s "One Belt And One Road" strategy,Africa has witnessed a boom in infrastructure construction projects,which has generated a huge demand for concrete.The quality of local coarse aggregate is unsatisfactory,of which the water absorption rate is about 2%～5%which far exceeds the requirement of national standard(<2%).Large bibulous coarse aggregate and layered clay have a strong impact on the dispersion effect of polycarboxylate superplasticizer(PCE)to the binding materials and lead to a negative effect on concrete workability,even leaving serious hazards on the quality of the project.Adsorption of polycarboxylate water reducer PCE-1 onto porous and layered aggregates and rheological properties of mortar were researched to solve the concrete workability problems caused by porous and layered aggregates.PCE-1 was synthesized via copolymerization using acrylic acid(AA)and acrylic methyl allyl polyoxyethylene ether(HPEG),n(AA):n(HPEG)was 3.2:1.The adaptive problem between PCE and LBSP was analyzed systematically by mortar performance.Main research results and contents of this paper as below:(1)The adsorption isotherm of PCE-1 on the surface of LBSP could be described well by Langmuir model that rising temperature was favorable for adsorption.The adsorption capacity increased first and then decreased with the extension of time and tended to balance at 30min.The adsorption behavior of PCE-1 on the surface of LBSP was proved by pore structure analysis and thermo gravimetric analysis.The PCE/LBSP compound showed a reduction of both pore diameter and pore size due to the presence of PCE in the LBSP pores.(2)The mortar pastes mixed LBSP displayed the typical character of non-Newtonian fluid.LBSP increased slurry viscosity.However,PCE-1 reduced slurry’s apparent viscosity.The viscosity of mortar with sinked particles could be improved by AMPS-NNDMA.The viscosity of mortar increased with the prolonging of hydration time.Rheological models displayed that the yield stress was increased by increasing the dosage of LBSP and AMPS-NNDMA copolymer,while decreased by PCE-1.(3)The adsorption isotherm curve was better in line with the Langmuir model,which means raised temperature was favorable for adsorption.The adsorption process of PCE-1 on the surface of the bentonite conformed to the Pseudo-second-order model.The Zeta potential of bentonite decreased with the concentration increased of PCE-1 and poly(vinyl alcohol).X-ray diffraction(XRD)results showed that(001)layer spacing of bentonite changed from 1.24 nm to 1.65 nm after mixed PCE,the(001)layer spacing of bentonite absorbed both PCE-1 and PVA become 1.55 mm.It demonstrated that the intercalation between PCE-1 and bentonite could be prevented by PVA.(4)The mortar containing bentonite was in accordance with the characteristics of non-Newtonian fluid.The viscosity of mortar showed increment by increasing the dosage of bentonite caused by the bridging effect from bentonite particles.It was got opposite results when adding PCE-1 to the slurry mortar due to its dispersibility.Slurry viscosity slightly increased at first then decreased with the concentration of poly(vinyl alcohol)increase.After fitting three kinds of model rheological parameter,the result showed that the yield stress of cement mortar increased as the dosage of bentonite increased and the hydration time extended,while decreased by an incremental dosage of PCE-1 and poly(vinyl alcohol).(5)LBSP and bentonite could reduce the initial fluidity of mortar and reduce the sensitivity of mortar to water and PCE-1.The effect of bentonite on mortar performance was more significant than LBSP.Bentonite only needed 1/6～1/10 dosage of LBSP to get the same effect due to the adsorption amount of bentonite on PCE-1 higher than LBSP.The fluidity loss ratio of mortar with bentonite could be reduced by increasing the dosage of PCE-1 or poly(vinyl alcohol).Fluidity increased and flow rate decreased while yield stress increased.The correlation between flow rate and rheological parameters such as yield stress and viscosity was better than fluidity.AMPS-NNDMA copolymer could inhibit bleeding in mortar with high replacement LBSP,and could effectively reduce the shrinkage of mortar containing bentonite.Polycarboxylate water reducers named PCE-2 and PCE-3 were designed and synthesized,PCE-2 was synthesized via copolymerization using AA and HPEG,n(AA):n(HPEG)was 3.2:1,PCE-3 was synthesized via copolymerization using maleic acid(MA)and isopentenol polyoxyethylene ether(TPEG),n(MA):n(TPEG)was 1:1.Compared with PCE-1,PCE-2 and PCE-3 owned a denser side chain and lower acid to ether ratio.The adsorption capacities of PCE-2 and PCE-3 on LBSP were decreased due to that the hydrodynamic diameters of both polymers were bigger than PCE-1.The adsorption capacity of PCE-3 on bentonite was lower than PCE-1 caused by higher electrostatic repulsion.The dispersion ability of polycarboxylate water reducer with low acid to ether ratio in mortar mixed with adsorptive powder was weakened,and the fluidity retention ability increased.With the combination of polycarboxylate water reducer with different acid to ether ratio,the dosage of polycarboxylate water reducer was decreased,and the fluidity retention ability was improved,which has strong practicability.更多还原