随着我国旧城改造及城市更新的不断发展需要拆除大量的旧建筑物，导致建筑垃圾日益增多，并带来了“垃圾围城”等一系列的环境问题，如何有效的资源化利用建筑垃圾已迫在眉睫。混凝土和砖是我国村镇建筑的主要材料，建筑垃圾的主要组成部分是废混凝土与废砖且难以完全分离，因此对再生砖混骨料混凝土（Recycled Mixed Brickbat and Concrete Aggregate, RMBCA）的力学性能及耐久性进行研究，对提高建筑垃圾资源化水平和节能减排具有重要意义。本文采用理论分析与试验分析相结合的方法，研究再生砖及再生混凝土的取代率对RMBCA混凝土性能的影响并确定最优配合比，并对其在荷载-冻融环境耦合作用下劣化规律及机理进行研究，具有一定的社会意义与工程意义。

本文选取再生砖骨料（Recycled Brickbat Aggregate, RBA）与再生混凝土骨料（Recycled Concrete Aggregate, RCA）的比例为1：1，并将再生砖混骨料以5种取代率（20%、30%、40%、50%、60%）取代天然骨料（Natural Aggregate），选取一种特定取代率，并将RBA与RCA按照五种比例进行混合（0：1、3：7、1：1、7：3、1：0），得出最优配合比后采取不同弯曲应力水平（0、0.2、0.4、0.6）、不同冻融次数进行荷载-冻融耦合环境下的耐久性试验，分析RMBCA混凝土的抗冻性能变化规律。得到的主要结论有：

（1）RMBCA的宏观破坏模式与普通混凝土较为类似，但因其RBA的强度较低，则破坏面贯穿RBA内部，抗压强度随RMBCA的掺量逐渐降低，抗折强度和劈裂抗拉强度与RMBCA的掺量的相关性不显著，经试验结果得出，RMBCA的取代率为30%，且RBA与RCA的比例为1：1时，试件性能相对较好。

（2）RMBCA混凝土中加入RBA和RCA后，界面过渡区种类增加，建立了多重界面过渡区模型，RBA与新砂浆界面区性能优于旧砂浆界面区，RCA与旧界面性能优于新界面性能。

（3）RMBCA混凝土经荷载-冻融试验后，根据抗压强度、相对动弹模、质量损失率及损伤层厚度变化可知，随着冻融次数及应力水平的逐渐增大，试件的力学性能及抗冻性逐渐降低。当弯曲应力比小于0.6时，试件的失效形式为动弹模下降到临界值来评定，弯曲应力比大于0.6时，因RMBCA混凝土自身受冻融影响使自身的承载能力下降，过大的应力水平使试件发生脆性断裂。

（4）由显微硬度试验及扫描电镜可知，多重界面过渡区均随着冻融循环次数的增加以及应力水平的升高使界面过渡区的显微硬度值降低，以及界面区厚度加宽，均为由低应力少冻融次数时的细微裂缝，至高应力多冻融次数下的界面区裂缝加宽，骨料与砂浆基体脱粘，从而降低试件的性能。

（5）根据核磁共振结果来看，得到RMBCA混凝土的孔隙结构随冻融次数及应力水平不断变化，冻融次数越大，应力水平越高，导致试件总孔隙增多，胶凝孔占比逐渐减少，大孔数量增加。但施加适当的弯曲荷载会对质地疏松的RMBCA混凝土的孔隙产生一定的挤密作用，使得抗冻性小幅提升，应力水平较高时，则会使小孔隙逐渐劣化，孔隙与孔隙之间连通，增大冻胀力，降低试件的抗冻性。

With the continuous development of China's old city reconstruction and urban renewal, a large number of old buildings need to be demolished, resulting in an increasing number of construction waste, and bringing a series of environmental problems such as ' garbage siege '. How to effectively utilize construction waste is imminent. Concrete and brick are the main materials of rural buildings in China. The main components of construction waste are waste concrete and waste brick, which are difficult to be completely separated. Therefore, it is of great significance to study the mechanical properties and durability of Recycled Mixed Brickbat and Concrete Aggregate (Recycled Mixed Brickbat and Concrete Aggregate Concrete, RMBCA) to improve the level of construction waste recycling and energy saving and emission reduction. In this paper, the method of combining theoretical analysis and experimental analysis is used to study the influence of the replacement rate of recycled brick and recycled concrete on the performance of RMBCA concrete and determine the optimal mix ratio, and study its deterioration law and mechanism under the coupling effect of load-freeze-thaw environment, which has certain social significance and engineering significance.

In this paper, the ratio of recycled brick aggregate (Recycled Brickbat Aggregate, RBA) to recycled concrete aggregate (Recycled Concrete Aggregate, RCA) is 1:1, and the recycled brick aggregate is replaced with five kinds of replacement rates (20%, 30%, 40%, 50%, 60%) to replace the natural aggregate. A specific replacement rate is selected, and RBA and RCA are mixed according to five ratios (0:1, 3:7, 1:1, 7:3, 1:0 ). After the optimal mix ratio is obtained, different bending stress levels (0, 0.2, 0.4, 0.6) and different freeze-thaw cycles are used to carry out the durability test under the load-freeze-thaw coupling environment. The macro and mcro properties and frost resistance of RMBCA were analyzed. The main conclusions are as follows :

The macroscopic damage pattern of RMBCA is more similar to that of ordinary concrete, but because of its lower strength of RBA, then the damage surface penetrates inside RBA, the compressive strength decreases gradually with the amount of RMBCA admixture, the correlation between flexural strength and splitting tensile strength and the amount of RMBCA admixture is not significant, and it is concluded from the test results that the specimen performance is relatively good when the replacement ratio of RMBCA is 30% and the ratio of RBA to RCA is 1:1.

After adding RBA and RCA to RMBCA concrete, the type of interfacial transition zone increases, and a multiple interfacial transition zone model is established. The performance of RBA and new mortar interface area is better than that of old mortar interface area, and the performance of RCA and old interface is better than that of new interface.

(3) RMBCA concrete by load - freeze-thaw test, according to the compressive strength, relative dynamic elastic modulus, mass loss rate and damage layer thickness changes can be seen, with the number of freeze-thaw and stress level gradually increased, the mechanical properties of the test specimen and frost resistance gradually reduced. When the bending stress ratio is less than 0.6, the failure of the specimen in the form of dynamic-elastic mode drops to a critical value to assess, the bending stress ratio is greater than 0.6, because RMBCA concrete itself by the freeze-thaw influence to make its own load-bearing capacity decreases, excessive stress levels make the specimen brittle fracture.

(4) From the microhardness test and scanning electron microscopy, it can be seen that the multiple interface transition zone are with the increase of the number of freeze-thaw cycles and the increase of the stress level to reduce the microhardness value of the interface transition zone, as well as the widening of the thickness of the interface zone, are from the fine cracks at low stress less freeze-thaw times, to the widening of the interface zone cracks at high stress more freeze-thaw times, the aggregate and mortar matrix debonding, thus reducing the performance of the specimen.

(5) According to the NMR results, the pore structure of RMBCA concrete was obtained to change continuously with the number of freeze-thaws and stress levels, and the higher the number of freeze-thaws, the higher the stress level, leading to an increase in the total pores of the specimens, a gradual decrease in the percentage of colloidal pores, and an increase in the number of large pores. However, the application of appropriate bending load will produce a certain crowding effect on the pores of RMBCA concrete with loose texture, which makes a small increase in the freezing resistance, and the higher stress level will cause a gradual deterioration of small pores and a connection between pores, which increases the freezing and swelling force and reduces the freezing resistance of the specimens.

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