溶胶-凝胶法制备具有碱激发活性的无定形Al2O3-2SiO2粉体

以正硅酸乙酯（TEOS）和水合硝酸铝（ANN）为原料，采用溶胶-凝胶法合成了无定形Al2O3-2SiO2粉体。通过XRD与FT-IR对其无定形相结构进行了表征，发现其结构与偏高岭土相似。为了考察粉体的碱激发活性，用SiO2／Na2O摩尔比为1．2的硅酸钠溶液对其进行碱激发试验，结果表明合成的无定形Al2O3-2SiO2粉体具有碱激活性，3d抗压强度达到24MPa。     

Nanoindentation characteristics of calcium hydroxide-metakaolin blended with sodium hydroxide solutions

In order to determine the active mechanism of metakaolin (MK) as partial replacement of cement in concrete from the nanoscale structure perspective, nanoindentation characteristics of calcium hydroxide (CH)-MK blended with 5 M sodium hydroxide (NaOH) solutions simulating the condition of MK in concrete has been studied. The results indicate that three distinct phases are found by the nanoindentation and BSE tests, such as HD C-S-H gel, LD C-S-H gel and the reaction products with the network structure, the residual unreacted MK and CH, respectively. The volume fraction of HD C-S-H gel is about 96% of all reaction product phases. This means that the use of MK in concrete can increase the volume fraction of HD C-S-H gel and thus will improve the properties of concrete.     

偏高岭土高性能混凝土的轴压应力-应变关系

采用美国产MTS试验机,研究了掺偏高岭土(Melakaolin,MK)的混凝土轴压应力-应变关系．试验结果表明,随着MK掺量的增加,混凝土的抗压强度随之提高,特别是早期强度提高更为显著．弹性模量略有提高,但幅度明显小于强度提高值．混凝土的韧性得到改善．此外,MK对混凝土的流动性影响较小,且能显著改善粘聚性和保水性．因此,偏高岭土是一种优异的高强高性能混凝土掺合料．     

Effect of particle size distribution of metakaolin on hydration kinetics of tricalcium silicate

The focus of this study is to elucidate the role of particle size distribution (PSD) of metakaolin (MK) on hydration kinetics of tricalcium silicate (C₃S–T₁) pastes. Investigations were carried out utilizing both physical experiments and phase boundary nucleation and growth (pBNG) simulations. [C₃S + MK] pastes, prepared using 8%_mass or 30%_mass MK, were investigated. Three different PSDs of MK were used: fine MK, with particulate sizes <20 µm; intermediate MK, with particulate sizes between 20 and 32 µm; and coarse MK, with particulate sizes >32 µm. Results show that the correlation between specific surface area (SSA) of MK's particulates and the consequent alteration in hydration behavior of C₃S in first 72 hours is nonlinear and nonmonotonic. At low replacement of C₃S (ie, at 8% _mass), fine MK, and, to some extent, coarse MK act as fillers, and facilitate additional nucleation and growth of calcium silicate hydrate (C–S–H). When C₃S replacement increases to 30% _mass, the filler effects of both fine and coarse MK are reversed, leading to suppression of C–S–H nucleation and growth. Such reversal of filler effect is also observed in the case of intermediate MK; but unlike the other PSDs, the intermediate MK shows reversal at both low and high replacement levels. This is due to the ability of intermediate MK to dissolve rapidly—with faster kinetics compared to both coarse and fine MK—which results in faster release of aluminate [Al(OH)₄⁻] ions in the solution. The aluminate ions adsorb onto C₃S and MK particulates and suppress C₃S hydration by blocking C₃S dissolution sites and C–S–H nucleation sites on the substrates’ surfaces and suppressing the post-nucleation growth of C–S–H. Overall, the results suggest that grinding-based enhancement in SSA of MK particulates does not necessarily enhance early-age hydration of C₃S.     

偏高岭土对水化硅酸镁水泥结构与性能的影响

将偏高岭土引入水化硅酸镁水泥中并测定其抗压强度、pH值,同时研究其物相组成和微观结构.结果表明:偏高岭土掺量小于10％时,可以提高水化硅酸镁水泥的28 d抗压强度,其中偏高岭土掺量为8％时,水化硅酸镁水泥的28 d抗压强度提高了60.9％;偏高岭土中的Al2O3参与了反应,导致体系的水化程度增大,偏高岭土掺量为8％时体...     

基于NMR的地聚合物水泥土孔隙结构与动态力学特性研究

为研究养护龄期和偏高岭土(MK)掺量对地聚合物水泥土孔隙结构和动态力学特性的影响,借助分离式Hopkinson压杆(SHPB)试验系统开展了地聚合物水泥土动态单轴冲击压缩试验,并结合核磁共振(NMR)和扫描电镜(SEM)等分析手段研究了地聚合物水泥土的孔径分布和微观形貌变化特征。结果表明:地聚合物水泥土的动态抗压强度随MK掺量的增加呈现先增大后减小的变化趋势,在MK掺量为2%时出现峰值;其动态抗压强度在7~14 d内增长较缓;地聚合物水泥土的T2分布曲线呈双峰型,以主峰所占面积为主,掺2%的MK能够有效改善孔隙分布,促进小孔隙向微孔隙转化;随着孔隙率的增加,地聚合物水泥土的动态抗压强度呈指数下降;MK掺量为2%时,地聚合物水泥土内部孔隙大幅度降低,水化产生的胶凝材料能够起到填充孔隙和连接土颗粒的作用。     

偏高岭土地质聚合物仿瓷材料的试验研究

以偏高岭土为原料,水玻璃为激发剂制备了地质聚合物材料,研究了激发剂的模数、掺量、水土比及养护方式对地质聚合物抗压强度的影响,确定了此类地质聚合物的最佳制备条件为水玻璃模数1.0,碱掺量10%,水土比0.25,自然条件下养护,并探讨了地质聚合物的开裂和气泡问题,从而制备了性能优良的地质聚合物仿瓷材料。     

偏高岭土对混凝土性能影响的研究进展

介绍了偏高岭土的火山灰活性,以及偏高岭土对混凝土工作性能、力学性能及耐久性等方面影响的研究进展。有关研究结果表明,掺入偏高岭土可改善混凝土的工作性,提高混凝土的力学性能和抗渗性以及抗耐蚀能力,能够有效抑制碱集料反应,是一种极具开发和应用价值的活性掺合料。     

低水胶比偏高岭土混凝土的强度和细观结构的分形特征

为探明低水胶比偏高岭土混凝土的力学性能,以及定量表征掺入偏高岭土后混凝土内部细观结构的变化规律,测试了不同偏高岭土掺量混凝土的抗压、劈裂和弯折强度;利用扫描电镜拍摄了混凝土水化产物微结构的SEM图像;运用分形理论计算分析了SEM图像的分形维数及其变化规律;并研究探讨了分形维数和强度的关系。研究表明：偏高岭土可以有效提高和改善混凝土的力学性能和细观结构;分形方法能够定量分析偏高岭土混凝土内部细观结构的变化特征,分形维数随着偏高岭土掺量的增加呈现降低趋势;抗压强度和分形维数存在良好的指数负相关性,抗压强度随分形维数的增大而减小。     

偏高岭土水热合成Y型分子筛的晶体成核研究

本文采用偏高岭土水热合成NaY分子筛,用TEM、XRD、BET、SEM分析了其晶体成核过程.结果表明:偏高岭土水热合成Y型分子筛的成核过程属于非均相成核,受扩散过程控制.