机制砂中石粉对混凝土物理力学性能的宏细观影响机制研究

石粉作为机制砂生产过程中的副产品，是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之上，提出了将机制砂中石粉纳入胶凝体系的配合比设计方法，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（FT-IR）、热重分析仪（TGA）等测试手段深入分析了石粉对混凝土的微观作用机理。研究结果表明：当按照本试验混凝土配合比，以石粉替代机制砂的情况下，随着石粉含量的增加，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，进而加快混凝土的早期强度的发展。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提升混凝土力学性能，超过该范围则导致稀释效应降低混凝土力学性能。在石粉含量相同的情况下，由于花岗岩石粉组的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，本研究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科学依据。

Macro-micro mechanisms for the effects of stone powder in manufactured sand on physical and mechanical properties of concrete

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. On the basis of the existing specifications, this paper proposes a design method of mixing ratio of stone powder in manufactured sand into the cementation system. And the physical and mechanical properties of concrete with two lithology (limestone, granite) powders and their different contents are systematically tested. The microscopic action mechanism of stone powder on concrete was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (FT-IR) and thermogravimetric analyzer (TGA). The results show that the compressive strength and splitting strength of concrete increase first and then decrease with the increase of the stone powder content when stone powder is used to replacing manufactured sand in accordance with the mix ratio of concrete in this test. Microscopic mechanism analysis shows that most of the stone powder in the manufactured sand is inert, and only a small amount of limestone stone powder which has limited chemical activity can promote the early hydration of cement and accelerate the development of the early strength of concrete. Stone powder in manufactured sand mainly plays a physical filling role in concrete. When its content is kept at 16%-19%, it can play a good micro-aggregate filling effect to improve the mechanical properties of concrete. When the content exceeds this range, the dilution effect will reduce the mechanical properties of concrete. In the case of the same content of stone powder, the overall microstructure of concrete samples in granite stone powder group is more dense than that in limestone stone powder group, resulting in the macroscopic mechanical properties of concrete in granite stone powder group is stronger than that in limestone stone powder group. Compared with similar studies, the optimal stone powder content obtained in this study is in a higher range. This study can provide a scientific basis for the mix ratio design of manufactured sand concrete with high stone powder content and the control of stone powder content in the process of making manufactured sand aggregate.