石粉作为机制砂生产过程中的副产品,是机制砂区别于天然砂的主要特征之一.本文在结合现有规范的基础上,提出将机制砂中石粉含量纳入胶凝体系的配合比设计,系统开展了两种岩性(石灰岩、花岗岩)石粉及其在不同含量条件下的室内混凝土物理力学性能试验,并结合X射线衍射仪(XRD)、扫描电镜(SEM)、红外光谱(FTIR)、热重分析仪(TGA)等测试手段深入分析石粉对混凝土的微观作用机理.试验结果表明:在按照试验设计的混凝土配合比,随着机制砂中石粉含量的增加,混凝土的抗压强度、劈裂强度均呈先增大后减小的趋势.微观机理分析表明,机制砂中的石粉大多是惰性的,仅微量石灰岩石粉存在有限的化学活性,促进早期水泥水合作用,进而加快混凝土早期强度的发展.综上,机制砂中的石粉在混凝土中主要发挥物理填充作用,其含量保持在16%~19%时,能发挥良好的微集料填充效应而提升混凝土力学性能;超过该范围则导致稀释效应而降低混凝土力学性能.在石粉含量相同的情况下,花岗岩石粉组混凝土试样的整体微观结构相较于石灰岩石粉组更为致密,从而导致花岗岩石粉组的混凝土宏观力学性能强于石灰岩石粉组.相比于同类研究,本文获得的最优石粉含量处于较高范围,可为高石粉含量的机制砂混凝土的配合比设计及机制砂石骨料制作过程中的石粉含量控制提供参考依据.
As a by-product in the process of manufactured sand production,stone powder is one of the main characteristics that is different from natural sand.Based on the existing specifications,a design method of mixing ratio of stone powder in manufactured sand into the cementation system was proposed.The physical and mechanical properties of concrete with two lithology(limestone,granite)powders and their different con-tents were systematically tested.The microscopic action mechanism of stone powder on concrete was analyzed by X-ray diffraction(XRD),scan-ning electron microscopy(SEM),infrared spectroscopy(FTIR),and thermogravimetric analyzer(TGA).The results showed that the compressive strength and splitting strength of concrete increased first and then decreased with the increase of the stone powder content when the stone powder was used to replace manufactured sand in accordance with the mix ratio of concrete in this test.Microscopic mechanism analysis showed that most of the stone powder in the manufactured sand was inert,and only a small amount of limestone stone powder which had limited chemical activity could promote the early hydration of cement and accelerate the development of the early strength of concrete.Stone powder in manufac-tured sand mainly played a physical filling role in concrete.When stone powder's content was kept at 16%~19%,it could play a good micro-ag-gregate filling effect to improve the mechanical properties of concrete.When the content exceeded this range,the dilution effect would reduce the mechanical properties of concrete.In the case of the same content of stone powder,the overall microstructure of concrete samples in the granite stone powder group was denser than that in the limestone stone powder group,resulting in the macroscopic mechanical properties of concrete in the granite stone powder group was stronger than that in limestone stone powder group.Compared with similar studies,the optimal stone powder content obtained in this study was in a higher range.This study can provide a scientific basis for the mix ratio design of manufactured sand con-crete with high stone powder content and the control of stone powder content in the process of making manufactured sand aggregate.