# Experimental Study on the Workability and Stability of Steel Slag Self-Compacting Concrete
## 1 Introduction  
In the process of iron and steel smelting, as one of the by-products, steel slag emission is about 15%-20% of the total crude steel production and is increasing rapidly along with the increase of steel production in the world. Taking China as an example, according to the China economic network, crude steel output in 2018 was 928 million tons, and the steel slag output was about 150 million tons. As a kind of solid waste, steel slag stacking not only takes up land, but also brings a series of ecological environmental pollution problems, and also causes the waste of precious resources to a certain extent. With the increase in its total amount, it has greatly hindered the sustainable development of the environment. Self-compacting concrete (SCC) is one of the key research directions of the high-performance concrete industry because it flows under its own weight, can completely fill the formwork without mechanical compaction, and has the advantages of fast construction, easy pouring, high efficiency, etc. The research and application of SCC have attracted attention all over the world [1; 2; 3]. The concept ofSCC and related scientific tests were first proposed and tested in Tokyo University, Japan, by [PERSON] et al. [4; 5], and they also started to analyze and study the design method of SCC mix proportion through conducting a lot of experimental research. This mix proportion design method of SCC is called the 'Japanese prototype method' or'step-by-step method'. In this method, the target performance of SCC is determined, firstly, by the mix proportion of the mixture being initially designed, secondly after selecting the raw materials required in construction, and then the mix proportion is adjusted to meet the performance and construction requirements according to the related experiment. [PERSON] et al. [6; 7] proposed the liquid criterion theory and blocking criterion theory, based on the interaction between aggregate particle system and cement paste in SCC, to design the mix proportion of SCC. [PERSON] et al. [8] proposed the SCC mix proportion design method based on the compactness between aggregates by introducing an aggregate compaction factor. Moreover, other SCC design methods have been proposed including the fixed aggregate content method [9], the computer-aided design method [10; 11], and the mathematical statistics factor method [12], etc. It is difficult to use a single index or test method to assess the workability of fresh SCC mixture comprehensively. Generally, the workability of SCC mainly comprises filling ability, passing ability, and segregation resistance. The segregation resistance is often considered as the index of stability of SCC, which also can be classified as static stability and dynamic stability. At present, the evaluation and test methods of the workability of SCC mainly includes a slump flow (SF) test incorporating slump flow time (T500) measurements [13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 26], a V-funnel test [14; 15; 17; 19; 20; 21; 22; 24; 26], a L-box test [13; 15; 19; 21; 23; 24; 26], a U-shape meter test [14; 17; 22], and a J-ring test [15; 16; 17; 18; 19; 24; 25], etc. Stability tests conducted for SCC mixture involved a sieve analysis test [15; 17; 20; 25], flow table test [27], segregation probe test [20], and static settlement column test [20; 23], etc. [PERSON] et al. [13] studied the influence of manufactured sand and lightweight sand on the workability of fresh self-compacting lightweight concrete (SCLC) by the slump flow test incorporating T500 measurement and the L-box test. The experimental results indicated that higher manufactured sand and lightweight sand ratios can reduce the flowing ability of SCC. [PERSON] et al. [27] used a flow table test to investigate the self-compacting properties and the consistency of fresh SCC using air-cooled blast furnace slag to replace coarse and fine natural aggregate.