Properties, Structure And Morphology Of Recycled Brick Concrete Coarse Aggregates Based On Micro And Nano Particle Reconstruction

The use of construction and demolition waste for the preparation of recycled aggregates is an important way to realise the "resourcefulness,reduction and harmlessness" of construction solid waste.It is also an effective means to alleviate the shortage of natural aggregate reserves.However,the resource utilization of recycled aggregates is extremely difficult due to the deficiencies in performance.Compared with recycled concrete aggregates,the performance of recycled brick concrete aggregates obtained from the demolition of old buildings in China is further deteriorated.This paper presents a comprehensive comparative study of two types of recycled brick concrete aggregate matrix before and after strengthening in terms of performance,structure and morphology based on the micro-nano-particle reconstruction.Finally,a regression equation for the performance of recycled aggregates was proposed.The results of the study can provide directional recommendations for the production and strengthening methods research of recycled brick concrete aggregates.The main research elements of this paper are described as follows:(1)Two main components of recycled brick concrete coarse aggregates: recycled concrete coarse aggregate and recycled brick coarse aggregate were used as research objects.Five different ratios of micro-nano slurry were used to strengthen the recycled aggregate particles.The reconstructed aggregate’s physical and mechanical properties and structural characteristics were tested.The results show that the reconstruction slurry with both mineral admixtures and nano-calcium carbonate has the best strengthening effect on the recycled concrete aggregates and that the nano-materials can give full play to their filling and nucleation effects,densifying the interfacial structure and thus achieving improved performance.For the recycled brick aggregate,all groups of slurry with nano-calcium carbonate have a good strengthening effect,with the interfacial transition zone showing good microscopic morphology and a reduction in the total porosity of the aggregate.(2)Based on the non-destructive XCT structural testing technique and the calculation of CT data by Avizo software,the structural change of different recycled brick concrete coarse aggregate matrices reconstructed by different ratios of modified slurry were analysed.The results show that when used for reconstructed recycled concrete aggregates,the micro-nano reconstruction slurry needs to be mixed with mineral admixtures to improve its permeability.The effect of the nanomaterials is mainly reflected in the filling of fine pore structures by the reconstructed slurry.The refinement of the internal structure can also be seen in the grouping of cement slurry only,as the recycled brick aggregate has a large volume of crack networks distributed on its surface.(3)Combined with MATLAB programming and profiling of recycled aggregates varying from the micron,to the millimetre,to the centimetre scale,a rapid and effective characterisation of their morphological features can be achieved.The results show that the two main matrix materials of recycled brick concrete aggregates have different morphological characteristics: the recycled concrete aggregates have a rougher surface and a more complex angular structure.The surface roughness of the reconstructed recycled aggregate is reduced and the angular structure is simpler due to the combined effects of the thickness of the coating layer,the original morphological characteristics of the aggregate matrix and the type of reconstruction slurry.(4)Combining Pearson correlation coefficient and multiple linear stepwise regression methods,correlation analysis and stepwise regression modelling were conducted on the property,structure and morphological parameters of the two recycled brick concrete coarse aggregate matrixes.The results show that the reconstruction slurry mixed with mineral admixtures and nano calcium carbonate has the best strengthening effect on the recycled aggregates.The different penetration depths of the reconstituted slurry into the two different recycled brick aggregate matrices are the main reasons for the different strengthening effects of the two recycled aggregate matrices.In addition,the increased particle surface roughness and overall morphological irregularity are morphological explanations for the enhanced physical and mechanical properties of the recycled aggregates.