Experimental Study on the Strengthening Mechanism of Modified Coal Gangue Concrete and Mechanical Properties of Hollow Block Masonry

To enhance the utilization efficiency of coal gangue aggregate, coarse aggregates are chemically modified with 5% sodium silicate solution. The effects of this modification on the compressive strength and microstructural characteristics of concrete are systematically investigated through integrated macro-testing and micro-characterization. By evaluating the compressive performance of modified coal gangue concrete blocks, the optimal mix ratio of each strength grade of blocks is determined. Experimental results indicate that the apparent density, water absorption, and crushing index of the modified coal gangue coarse aggregate exhibit better mechanical properties than the control group. The modified coal gangue coarse aggregate demonstrates improved mechanical performance, with the compressive strength of 28-day concrete showing a 15.3% increase relative to the control group. Furthermore, using a sodium silicate solution effectively enhances the interface transition zone’s performance between coal gangue coarse aggregate and cement mortar, improving the compactness of this interface. The modified coal gangue concrete blocks exhibit higher compressive strength than the original material. When the substitution rate remains constant, the compressive strength of modified coal gangue concrete decreases with increasing water–cement ratio. Similarly, at a constant water–binder ratio, compressive strength decreases with higher modified gangue aggregate replacement. Finally, compressive tests are conducted on masonry constructed with hollow blocks of strength grades MU7.5, MU10, and MU15. Then, a calculation model for the average compressive strength of modified coal gangue concrete hollow block masonry is proposed, providing theoretical support for its engineering application.