## 1 Introduction  
With the development of the iron industry, the utilization of its by-product, namely, ground granulated blast furnace slag (GGBFS), has been a problem that needs to be addressed. China, for example, produces over 2.4 million tonnes of such slag per year, the common use of which is as an admixture in Portland cement. However, only 20-30% of slag can be used effectively [1]. At the same time, Portland cement used in the construction industry consumes large amounts of energy [2] and releases a large amount of CO\({}_{2}\) in its production process [3], contributing to global warming. Given that the world is facing energy shortages and serious environmental problems, the use of alkali-activated slag (AAS) as a cementitious binder and an alternative to Portland cement in certain areas may be advantageous. In recent decades, alkali-activated materials have been applied in increasing numbers of practical engineering projects around the world [4, 5]. Compared to Portland cement, AAS has obvious advantages in its resistance to a chemical attack [6, 7] and frost [8, 9]. Creep is an important long-term characteristic of concrete, particularly in large-scale structures in which its presence may intensify the occurrence of cracks and deformations. In turn, such conditions deteriorate the resistance to a chemical attack and frost. AAS materials have a high early strength [10, 11],which may make them suitable for application in pre-stressed engineering. Prior to such application, the procedure of calculating the stress loss is bounded with the creep property [12]. However, compared with concrete made of ordinary Portland cement (OPC), only a few studies on the creep occurring in alkali-activated slag (AAS) concrete have been conducted. In 1999, [PERSON] and [PERSON] [13] studied the creep in AAS for a period of 112 days, which to the best of the authors' knowledge was the first experiment on AAS creep. They found that AAS concrete has higher creep and a lower elastic modulus than OPC concrete. Nevertheless, only one stress-strength ratio (0.4) for each sample was applied and the creep test time was short. In general, creep should be tested for a period of approximately 200-300 days [14; 15] and even up to 1000 days [16]. [PERSON] and [PERSON] [17] investigated the creep in AAS concrete with two different stress-strength ratios (0.35 and 0.5) under different conditions of relative humidity (65% and sealed) for approximately 180 days. More laudably, they compared the test results with the creep model of CEB-FIP 2010 [18], and found that the experimentally determined creep coefficient of AAS concrete is higher than predicted. Unfortunately, they did not compare the test value with more models or discuss the effects of the stress-strength ratio. To the best of the authors' knowledge, there have been no more studies on the creep property of AAS concrete. The stress-strength ratio is one of the most important parameters of creep strain. How does the stress-strength ratio affect the creep of AAS concrete, and is it similar with OPC concrete? Several mature code models have already been developed to calculate the creep strain of OPC concrete, and whether they are suitable for AAS concrete should be determined. If not, the ways in which they can be adjusted for AAS concrete should be studied. Such gaps in knowledge have blocked the further practical applications of AAS concrete. Thus, the creep property of AAS concrete requires further study. Based on the facts above, this study focuses on the creep of AAS concrete under a stress-strength ratio of 0.15-0.75. Five groups of AAS concrete with different stress-strength ratios (0.15, 0.3, 0.45, 0.6, and 0.75) were tested. After the tests, we analyzed the results from three perspectives (stress-dependent strain, specific creep, and creep coefficient). We then compared the curves with the current models (ACI 209R-92 [19], B3 [20], CEB-FIP 2010 [18], and GL2000 [21]) and discussed the applicability of such models.