Fiber reinforcement technology has become one of the effective ways to improve the mechanical properties and deformation capacity of concrete. This study investigated the effects of single-doped and blended-doped basalt fiber (BF) and polyethylene fiber (PEF) on the drying shrinkage and mechanical strength of mortars. Meanwhile, the microstructure and reinforcement mechanism of single-doped and blended-doped BF and PEF mortars were studied. The results show that the mortar with a single-doped 6 mm PEF has the strongest resistance to drying shrinkage, and that blended fibers also effectively enhance the resistance to drying shrinkage of mortars. The compressive strength and flexural strength of the blended-fiber mortars are both higher than those of the single-fiber mortar. When the fiber length was 12 mm and the BF/PEF was 1:1, the compressive strength and flexural strength of the mortar at 28 d were respectively 18.6% and 56.1% higher than those of the mortar without fiber. Furthermore, when the fiber lengths were both 12 mm and 18 mm, the splitting tensile strength of the blended-fiber mortar at 28 d was higher than that of the single-fiber mortar and the mortar without fiber. When the fiber length was 12 mm and the BF/PEF was 1:1, the splitting tensile strength of the blended-fiber mortar was 103.3% higher than that of the mortar without fiber. The BF is randomly distributed in the mortar in the form of single filaments, and it exhibits brittle fracture when the mortar fails. When the mortar is damaged, PEF exhibits the phenomenon that the fibers are pulled out, and its surface is covered with hydration products, demonstrating excellent interfacial bonding performance. BF and PEF can interlock and intertwin with each other, forming a three-dimensional network structure in mortar, and jointly exert a complementary reinforcing effect of rigidity and flexibility.

The particle size of aggregate is a key factor affecting the mechanical properties and deformation capacity of cemented gangue filling body. In this study, coal gangue with a particle size range of (0.05, 20) mm was sieved into six groups of aggregate particles. Based on the Talbot gradation theory, cubic specimens with gradation indices n = 0.3, 0.4, 0.5, 0.6, and 0.7 were prepared for acoustic emission (AE) monitoring tests. The microstructure of the filling body was analyzed, and the failure characteristics and damage evolution laws of the cemented gangue filling body with different gradation indices were explored. The results show that the compressive strength reaches its maximum when n = 0.5. As the gradation index increases, the compressive strength of the specimens first increases and then decreases, and the specimens shift from primarily experiencing cleavage failure to shear failure. The curve of cumulative AE ringing count shows a bimodal distribution pattern, with both surge points and fracture points coexisting. The surge points can be regarded as precursor signals of backfill failure. The spatiotemporal evolution of AE events exhibits complex phased changes. An excessively small gradation index tends to form micropores and striped microcracks, reducing the compactness of the microstructure. An excessively large gradation index can lead to the formation of penetrative weak channels. A reasonable gradation index enables the mutual interlocking of aggregate particles, constructing a stable three-dimensional spatial skeleton structure. The dynamic trend of damage in the filling body can be captured based on AE analysis, and reverse guidance can be provided for parameter optimization of Talbot gradation, achieving a dynamic closed loop of “gradation design-AE monitoring-damage assessment-parameter optimization”. This not only enriches the application scenarios of acoustic emission analysis in graded materials, but also provides a new research approach and technical method for gradation design and safety assessment in scenarios where particle sizes are missing in practical engineering.

In order to improve the utilization rate of coal gangue as aggregate in concrete, based on the orthogonal experimental design method, the L16 (4⁵) orthogonal table was used to initially prepare the mix ratio, and the concrete compressive specimens were poured, and their compressive strength was tested after standard curing for 7 days. The significance of the three factors of coal gangue ratio, coal gangue-sand ratio and water-binder ratio on strength was preliminarily understood. Then adjust the factor levels, use the L9 (3⁴) orthogonal table to arrange the factor levels, formulate the mix ratio, test its strength after curing under the same conditions, and finally analyze that the optimal mix ratio of high-volume coal gangue concrete is 90% of coal gangue. Coal gangue sand accounts for 60% of the total sand, the water-binder ratio is 0.4, the sand rate is 35%, and the amount of cement per cubic meter is 350 kg. This mix ratio can use a large amount of coal gangue as a concrete cushion or sub-base in road engineering. Keywords Coal gangue concrete Orthogonal test design Mix ratio Compressive strength