煤系偏高岭土对混凝土力学性能及微观结构的影响机理

Influence Mechanism of Coal-Series Metakaolin on Mechanical Properties and Microstructure of Concrete

将600目(23μm)和1000目(13μm)煤系偏高岭土按照0%、5%、10%、15%(质量分数)的掺量分别掺入混凝土,通过强度测试、XRD、TG-DTG、SEM-EDS和氮吸附试验等研究了煤系偏高岭土细度和掺量对混凝土力学性能和微观结构的影响。结果表明:偏高岭土的掺入显著提高了混凝土的力学性能,当偏高岭土细度为1000目、掺量为15%时,混凝土的抗压强度最大,90 d抗压强度达到了81 MPa;水化产物主要由氢氧化钙、钙矾石、类水滑石及水化硅酸钙(C-S-H)凝胶等组成,掺入偏高岭土并未改变水化产物种类,但是增加了水化产物中C-S-H凝胶的产生量,同时降低了氢氧化钙的含量。偏高岭土与水泥水化产物氢氧化钙发生二次水化生成C-S-H凝胶,提高混凝土致密性,这是偏高岭土能够增强混凝土力学性能的主要原因。

Coal-series metakaolin of 600 mesh(23μm)and 1000 mesh(13μm)was tested according to the concentration of 0%,5%,10% and 15%(mass fraction)mix into concrete,and the influences of coal-series metakaolin fineness and content on the mechanical properties and microstructure of concrete were studied by strength,XRD,TG-DTG,SEM-EDS and nitrogen adsorption tests.The results show that the incorporation of metakaolin significantly improves the mechanical properties of concrete.When the fineness of metakaolin is 1000 mesh and the content is 15%,the compressive strength of concrete is the largest,and the 90 d compressive strength reaches 81 MPa.The hydration products are mainly composed of calcium hydroxide,ettringite,hydrotalcite and calcium silicate hydrate(C-S-H)gel,etc.The addition of metakaolin do not change the type of hydration product,but increases the content of C-S-H gel in the hydration product,while reduces the content of calcium hydroxide.Metakaolin and cement hydration product calcium hydroxide undergo secondary hydration to form C-S-H gel and improve the compactness of concrete,which is the main reason that metakaolin can enhance the mechanical properties of concrete.