Experimental study on mechanical properties of coal gangue base geopolymer recycled aggregate concrete reinforced by steel fiber and nano-Al2O3

Using recycled aggregates to prepare geopolymer concrete plays an essential role in reducing dependence on natural resources and solving the problem of waste accumulation. However, the application of geopolymer recycled aggregate concrete (GRC) has been greatly limited due to the defects in the quality of recycled aggregates and the limitations of the brittleness of concrete materials. Therefore, the work is dedicated to improving GRC properties and exploring the mechanism of action of steel fiber (SF) and nano-Al2O3. In this study, calcined gangue, slag, fly ash, and recycled aggregate were used as raw materials, the influence of SFs (0-1.25 vol%) was first explored by single factor analysis, and on this basis, the effect of nano-Al2O3 (NA) (0-2 wt%) on the GPC performance of SF was studied. The microstructure of GRC was analyzed by scanning electron microscopy. The test results showed that adding SF could significantly improve the splitting tensile and flexural strength of GRC, among which 0.75 vol% is the most excellent. However, the increase in compressive strength could be more apparent. The addition of NA can make up for the lack of SF in improving compressive performance. When NA content is 1 wt%, the version of GRC is most apparent. Adding 1% NA has the most significant advance in GRC performance. The microstructure analysis showed that the NA could promote the polymerization reaction, generate more gel, and make the contact interface between SF and matrix more compact, thus improving the strength of GRC.