The interfacial transition zone (ITZ) has long been considered as a zone of weakness in concrete. Many scholars have carried out relatively scattered tentative explorations to improve the performance of ITZ. The application of nanomaterials to enhance ITZ in concrete is a promising research. In order to further study the basic principles and practical applications of this field, it is urgent to systematically sort out the existing results. In this study, the nano-modification of ITZ in concrete is systematically reviewed and summarized. First, this study reviews the microscopic characterization of ITZ, including hydration products, porosity, and microhardness. Then, the influence of nanomaterials on ITZ is reviewed from the view of the above three aspects. Finally, the method and mechanism of the ITZ modified by nanomaterials were preliminarily clarified, which provided theoretical and empirical data support for the team’s next experimental work. A large number of research results show that nanomaterials improve the mechanical properties and microstructure of the ITZ, thus enhancing the mechanical properties and durability of concrete. The results of this article will provide source materials for the development of this field, a broader research basis for peer research, and a basis for further development of green engineering materials.

In the global construction industry, with the growth of population, two important construction problems have to be faced, namely, the excessive consumption of non-renewable resources and the massive accumulation of construction waste. In order to solve these problems, geopolymer recycled aggregate concrete (GRAC) arises at the historic moment. On the one hand, using geopolymers produced by industrial wastes to completely or partially replace cement can reduce cement consumption, thus reducing CO₂ emissions. On the other hand, recycled concrete made of recycled aggregate can consume accumulated construction waste and save non-renewable materials and land resources. The combination of the two materials can protect the environment to the greatest extent and save resources. This article reviews the current research on the mechanical properties of GRAC, makes a systematic analysis of GRAC materials, reaction mechanisms, and evaluation indicators, and also discusses the application prospects of GRAC, and strives to make contributions to the field and industry.

The raw materials of geopolymer come from industrial wastes, which have the advantages of lower carbon emissions and less energy consumption compared with traditional cement products. However, it still has the disadvantages of low strength, easy cracking, and low production efficiency, which limit its engineering application and development. At present, with the application and development of nanotechnology in the field of materials, it is found that nanomaterials have a good filling effect on composites, which greatly improves the integrity of the composites. It has become a very popular research direction to optimize and improve the engineering application performance of geopolymer concrete (GPC) by nanomaterials. The modification of nanomaterials can further improve the properties of GPC and expand its application fields in engineering and life. Based on people’s strong interest in nanomaterial-modified GPC and providing the latest and complete research status for further related work, this paper summarized the key technical problems in the field of nanomaterials-modified GPC in the past decade. Those include the modification mechanism, dispersion mode, and mechanical properties of nanomaterials. At the same time, the application bottlenecks and key problems of nanomaterials-modified GPC are comprehensively analyzed. Finally, the prospects and challenges of future work in this field are discussed.

Geopolymer cementitious materials and recycled aggregate are typical representatives of material innovation research in the engineering field. In this study, we experimentally investigated a method to improve the performance of geopolymer-recycled aggregate concrete (GRAC). The recycled concrete aggregates and steel fiber (SF), fly ash (FA), metakaolin (MK), and sodium silicate solution were used as the main raw materials to prepare fiber-reinforced geopolymer-recycled aggregate concrete (FRGRAC). First, the orthogonal test was carried out to study the GRAC, and the optimal mix proportion was found. Second, building on the optimal mix proportion, the effects of the SF content on the slump, 7 and 28 days compressive strength, tensile strength, and flexural strength of FRGRAC were further studied. Finally, the microscopic mechanism of FRGRAC was studied by scanning electron microscopy (SEM). The study results indicate that the slump continues to decrease as the fiber content increases, but the compressive strength, tensile strength, and flexural strength increase to a certain extent. Through SEM analysis, it is found that SF restrains the development of cracks and improves the strength of concrete.