# Influence of Five Additives on No Loading Swelling Potential of Red Clay
## 1 Introduction
Cement has been used in improving the water stability of expansive soil, and the UCS tests and swelling potential tests show that the addition of cement can significantly improve the strength of soil and modify the swelling and shrinkage properties [7; 8]. Steel slag is a common solid waste produced by steel-making, and its output accounts for 15-20% of the total crude steel production [9]. In 2020, Chinese crude steel production was 1053 million tons, accounting for 56.5% of global production [10]. Massive quantities of steel slag are discarded because it cannot be effectively utilized, which has a negative effect on the environment. The efficient utilization of steel slag has become an urgent problem to be solved. Previous studies have shown that steel slag has a similar chemical and mineral composition to that of Portland cement. In many cases, steel slag can be used as an additive for soil modification, so as to save resources and reduce carbon emission in cement production. [PERSON] conducted field experiments to study the engineering properties of a steel slag mixed soil embankment. The Cone Penetration Test (CPT) results of the studied embankment with different steel slag contents showed that the average tip resistance of the test embankment improved by steel slag was greatly improved, and there was no expansion and heavy metal leaching in the experiment [11]. [PERSON] found that the swelling properties and long-term strength of soil treated with basic oxygen steel slag were better than those treated with lime [12]. [PERSON] proposed that the cation exchange between soil and steel slag is the main factor affecting the modification of soil engineering properties by steel slag. The addition of steel slag reduces the diffusion water layer and agglomerates the clay particles in the soil-slag mixture, to improve the strength and plasticity of the soil [13]. Thermal power generation results in large quantities of coal ash. Fly ash, which is produced from the combustion of pulverized coal, has an important place among industrial by-products. A large amount of fly ash cannot be used effectively, which results in environmental problems. [PERSON] and [PERSON] pointed out that the addition of fly ash to clayey soils significantly reduces their swelling due to the reduction in plastic fines of clay by non-plastic fines of fly ash. The swell potential decreases significantly as the percentage of fly ash increases [14; 15]. [PERSON] and [PERSON] investigated the influence of fly ash on the free swell index of expansive soil. The differential free swell was reduced by 28.3% with 20% fly ash as a replacement in the expansive clay [16]. Zeolite and other pozzolanic materials may catalyze the occurrence of pozzolanic reactions due to their high SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) content. The addition of natural zeolite to cement kiln dust-stabilized expansive clayey soil has been proven to greatly improve the strength of the stabilized soil [17; 18]. In the current study, paper, cement, zeolite powder, and three industrial by-products (blast furnace slag, steel slag, and fly ash) were selected as additives. The swelling potential of mixed specimens with different additive contents at different curing ages was tested through no loading swelling tests. The no loading swelling test measures the ratio of the unidirectional expansion in the height direction of the specimen after immersion in water to the original height value under the condition of no-load and side limit. This ratio is called the expansion rate and is expressed by a dial indicator. It is suitable for measuring the no loading swelling rate of undisturbed soil and compacted soil specimens, which can be used as a reference for evaluating the expansion potential energy of cohesive soil. Specimens with significantly reduced expansion potential were selected.