## 1 Introduction
There were popular additives, such as magnesium oxide [38], calcium oxide [39], gypsum [40], expansion agent [41] and absorbent polymer materials [42]. [PERSON] et al. [43] found that increasing the curing temperature is another measure to reduce the drying shrinkage of geopolymers. [PERSON] et al. [44] found that the drying shrinkage of geopolymer can also be reduced by increasing the curing humidity. However, the chemical nature of recycled fine powders differs significantly from that of other types of precursor materials, and it remains unknown whether these strategies will be effective in reducing the drying shrinkage of recycled fine powder-based geopolymers. In geopolymer systems, efflorescence is mainly caused by alkali metal cations freeing to the surface of the material and reacting with carbon dioxide to form substances such as sodium carbonate and sodium bicarbonate [45; 46]. The highly alkaline reaction conditions of geopolymers will inevitably result in a much higher degree of efflorescence than that of OPC. Efflorescence not only affects the esthetics of the building material, but also reduces the strength of the material and affects the durability of the structure. The efflorescence of alkali-activated binders severely limits their practical engineering applications [47; 48; 49]. Therefore, it is crucial to limit the efflorescence of geopolymers. [PERSON] et al. [50] found that the addition of 20% slag to fly ash-based cementitious materials were able to reduce the rate of efflorescence in specimens, while efflorescence could also be inhibited by high-temperature curing. A similar result was found by [PERSON] et al. [51], who showed that the addition of alumina-rich precursors or the addition of slag was effective in inhibiting alkali efflorescence. In contrast, [PERSON] et al. [52] found that the addition of less than 50% mass of slag to fly ash did not significantly change the degree of efflorescence in the specimens, which showed higher levels of efflorescence with slag content above 50%. Therefore, the relationship between the amount of slag and efflorescence is not entirely positive. [PERSON] et al. [50] found that soluble silica reduced the porosity of the specimens to inhibit efflorescence at the same alkali equivalent, and also pointed out that the efflorescence degree of NaOH-activated geopolymers was lower than that of sodium silicate-activated geopolymers. With regard to the effect of alkali equivalent on the efflorescence properties, [PERSON] et al. [53] concluded that reducing the alkali equivalent would reduce the degree of efflorescence, but when the alkali equivalent was less, it would again affect the strength of the specimen, so a relative compromise was needed. [PERSON] et al. [54] suggested that water evaporation is an important factor affecting the efflorescence of fly ash-based geopolymers. [PERSON] et al. [55] first investigated efflorescence mitigation in recycled fine powder-based geopolymers and demonstrated that both slag and metakaolin could mitigate the degree of efflorescence in recycled fine powder based-geopolymers. As can be seen from the above, recycled fine powder-based geopolymers have great potential to replace OPC. However, little research has been reported on the durability of recycled fine powder-based geopolymers in terms of drying shrinkage and efflorescence, which restricts the promotion and application of recycled fine powder-based geopolymers. In this paper, recycled brick and concrete fine powder-slag-based geopolymer (RPSG) was prepared by using recycled brick and concrete fine powder (RP) and slag. The effects of different slag contents, alkali equivalents and moduli on drying shrinkage and efflorescence were studied. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG) and scanning electron microscope (SEM) were used to analyze the hydration products and their microstructure.