煤矸石是采煤选煤过程中产生的主要固体废弃物，其资源化利用已成为煤炭行业关注的热点问题。利用煤矸石替代天然骨料制备混凝土不仅可以解决煤矸石带来的环境问题，还可以减少砂石骨料开采带来的环境问题，满足建筑行业可持续发展的需求，是煤矸石有效的资源化利用方式。然而煤矸石混凝土的力学性能和耐久性能仍存在不足，相关研究表明，在煤矸石混凝土中掺加粉煤灰，不仅能减少其带来的环境问题，还能有效改善煤矸石混凝土的性能。目前对于粉煤灰在煤矸石混凝土的应用主要集中在粉煤灰掺量对其宏观性能的影响上，缺乏对其微观改性机理的探究。因此，本文采用理论分析与试验研究相结合的方法，开展粉煤灰对煤矸石混凝土的改性效应及改性机理的研究，具有重要的社会、环保与经济意义。

课题组前期研究表明，煤矸石取代率40%的混凝土具有相对较好的力学性能及耐久性能，因此本文在40%取代率的煤矸石混凝土中以0%、10%、20%、30%、40%等梯度的粉煤灰掺量替换水泥制备试块，分别对其进行力学性能、抗冻性能及微观性能试验，分析研究粉煤灰掺量对于煤矸石混凝土宏观性能的影响规律和微观结构的作用机理。得到的主要研究结论有：

（1）粉煤灰掺量过多或过少都会对煤矸石混凝土力学强度造成不利影响，适当掺量的粉煤灰替代水泥，能够改善煤矸石混凝土的力学性能；粉煤灰能够降低煤矸石混凝土损伤演化的速度，但掺量过多则改性效果变差，冻融环境下的煤矸石混凝土粉煤灰掺量建议为20%-30%。

（2）粉煤灰对煤矸石混凝土的性能和砂浆区孔隙结构具有双重改善效应，其可以有效地改善煤矸石砂浆区的孔隙结构，提高砂浆的密实均匀度，且有效地减少界面过渡区（ITZ）的厚度，且掺入30%粉煤灰后，煤矸石混凝土的孔隙级配最好。虽然粉煤灰掺量达到40%时，骨料附近砂浆区的多害孔隙占比减小的幅度最大，但其孔隙率增量相对过大，对有害孔细化的优势并不能抵消整体孔隙率增多带来的消极影响，总体仍会对煤矸石混凝土宏观性能产生不利影响。

（3）粉煤灰对煤矸石骨料ITZ的改善效果更好。粉煤灰掺量为30%的试块煤矸石骨料附近的多害孔减少的幅度相差不大，而在碎石骨料附近多害孔减少的幅度出现明显递增，这是因为煤矸石集料表面较为粗糙，粉煤灰中的珠状颗粒容易优先富集在其周围，随着掺量的增加，煤矸石骨料附近的大孔隙优先得到细化，小孔隙优先得到填充。

（4）粉煤灰对煤矸石混凝土强度改性机理表现在三个方面。第一，适量粉煤灰使得其自身的“火山灰效应”得以充分发挥，改善了煤矸石混凝土的孔径结构。第二，粉煤灰颗粒物在砂浆中可以发挥“微集料填充”的作用，贡献其强度。第三，粉煤灰的大量掺入，改变了煤矸石骨料界面的物理化学性质，减少了界面过渡区的孔洞和裂缝宽度，增大了界面的粘结力，从而增加了煤矸石混凝土的劈裂抗拉强度。

（5）粉煤灰的加入能够有效地减少有害孔增加的速率，从而提高煤矸石混凝土的抗冻耐久性能。本文建立了考虑冻融次数和粉煤灰掺量的冻融损伤方程，可以为寒冷地区粉煤灰煤矸石混凝土的应用提供一定的理论参考。

Coal gangue is the main solid waste produced in coal mining and preparation, and its resource utilization has become a hot issue in countries that use coal as the main source of energy. An effective resource utilization method is using coal gangue instead of crushed stone to prepare concrete, which can not only solve the environmental problems caused by the waste of coal gangue, but also meet the requirements of sustainable development in the construction industry. Although the mechanical properties and durability of coal gangue concrete exhibit poor performance, relevant studies have reported that adding fly ash to concrete can help improve concrete performance. However, the mechanical properties and durability of gangue concrete are still insufficient. Correlativity researches indicate that adding fly ash to coal gangue concrete can not only reduce the environmental problems caused by coal-based solid waste but also help improve the performance of coal gangue concrete. Currently, relevant studies on the application of fly ash in coal gangue concretes mainly focuses on the macro performance. Few studies have focused on the microinterface characteristics. Therefore, theoretical analysis and experimental research are combined to study the modification effect and mechanism of fly ash on coal gangue concrete in this research, which has multiple meanings of environmental protection, economy and resource recycling.

Research by the research group shows that concrete with a 40% replacement rate of coal gangue has a certain promotion value. Therefore, this paper replaces cement with 0%, 10%, 20%, 30%, 40% isocratic fly ash content in the coal gangue concrete with 40% replacement rate to prepare test blocks, and the mechanical performance test, freeze-thaw cycle test, and micro test were carried out to analyze the modification effect and mechanism of fly ash content on coal gangue concrete respectively. The main research conclusions are as follows :

(1) Too much or too little fly ash will have an adverse impact on the mechanical strength of coal gangue concrete, the appropriate amount of fly ash instead of cement can improve the mechanical properties of coal gangue concrete; fly ash reduces the speed of damage development of coal gangue concrete, but the improvement performance becomes worse with too much fly ash, 20% - 30% fly ash can be considered when using coal gangue concrete in cold environment.

(2) Adding fly ash into coal gangue concrete should consider its dual improvement effect on ITZ performance and pore structure of mortar area, and the pore gradation of coal gangue concrete is the best after 30% fly ash is mixed. Although the proportion of harmful pores in the mortar area near the aggregate decreases the most when the fly ash content reaches 40%, the porosity increment is relatively large, which can not offset the negative impact of the increase of overall porosity, and will still have an adverse impact on the macro performance of coal gangue concrete.

(3) The improvement effect of fly ash on ITZ of coal gangue aggregate is better. When the content of fly ash is less than 30%, the reduction range of multi harmful pores near the coal gangue aggregate is similar, but the reduction range of multi harmful pores near the crushed stone aggregate increases obviously. This is because the surface of coal gangue aggregate is relatively rough, and the bead particles in fly ash are easy to be preferentially enriched around it. With the increase of the content, the macro pores near the coal gangue aggregate are preferentially enrichet to refine, small pores are filled preferentially.

(4) The strength modification mechanism of fly ash to gangue concrete is shown in three aspects. First, the proper amount of fly ash can bring the "pozzolanic effect" of fly ash into full play, improve the pore structure of coal gangue concrete, and make the structure of cement stone more compact. Secondly, fly ash particles play the role of "micro aggregate filling" in mortar and contribute to its strength. Thirdly, the addition of fly ash changes the physical and chemical properties of the interface of coal gangue aggregate, reduces the width of holes and cracks in the interface transition zone, increases the bonding force of the interface, and thus increases the splitting tensile strength of coal gangue concrete.

(5) The addition of fly ash can effectively reduce the rate of harmful pore increase, so as to improve the frost resistance and durability of gangue concrete. In this paper, the freeze-thaw damage equation considering freeze-thaw times and fly ash content is established, which can provide a theoretical reference for the application of fly ash gangue concrete in cold areas.