## 1 Introduction  
Countries all over the world are eager to research the reuse of industrial waste, turning industrial waste into reusable resources and, at the same time, moving towards the goal of carbon reduction. This research follows the principles of waste reduction, resource reuse, and a safe economy. Therefore, the application of silicic acid slag to controllable low-strength materials is discussed to effectively control the generation of waste, properly handle it, and make up for the shortage of sand. Global steel production peaked in 2014, reaching 1.6 billion tons, of which Asian production accounted for 60% of the total production; China's production accounted for 800 million tons of total production. Japan, India, the United States, South Korea, and Russia are also the largest producers. The global output of 1.6 billion tons of steel produces about 250 million tons of slag. Now, the annual output of desulfurized slag from the Taiwan Iron and Steel Company is about 300,000 tons [1]. Desulfurization slag (DS) is the solid waste generated in the molten iron desulfurization process by the desulfurization agent in the blast furnace. Therefore, it is a product produced during the high-temperature melting process. Its physical properties are tolerant to high temperatures and are less influenced by climate change. Its chemical properties are very stable and safe, and the mobility of heavy metals is low. It can also partially replace limestone or be used as a backfill material for soil and stone during the cement clinker firing process [1]. The molten iron in blast furnace steel contains sulfur; it is hot. After the torpedo car, the sulfur is removed by a desulfurizing agent, and the obtained slag body is discharged into the torpedo car and then slowly cooled to a fine granular shape, and because of the high content of SiO\({}_{2}\) in the components thereof, it is also called the sulfur residue. Since the desulfurized slag still contains a part of the slag, after subsequent processing, such as magnetic partition, crushing, and smashing, the slag can be recovered, which improves the purity and utilization value of the desulfurized slag [2]. In recent years, some studies have been carried out to replace part of the natural coarse aggregate and fine aggregate with desulfurized slag in the design of concrete mix ratio and applied to cement mortar [1; 2; 3; 4; 5; 6; 7]. From the study of [PERSON] and [PERSON] (2014) [2], it was found that desulfurized slag can be used to replace the natural sand in the cement mortar mixture, and it was pointed out that, if the mortar solidified at a high temperature and the desulfurized slag replacement rate increased, the mortar volumetric expansion tended to increase, and the rate of volumetric expansion increased. Additionally, as the desulfurization slag replacement rate increases, the compressive strength tends to decrease [5; 6; 7; 8]. In recent years, countries and regions around the world, such as the United States, Canada, Europe, Israel, Japan, and other countries, have developed a highly mobile to improve the quality of backfill engineering, reduce costs, reduce manpower, and reduce the impact of traffic. Controlled low-strength materials (CLSM) has been widely used in foundations, roads, and pipeline-backfilling projects. It is a new type of cementitious material that replaces traditional backfilling materials and can be applied to solve the problem of pipeline excavation. The lack of artificial compaction leads to the loss of road surface subsidence, cracks, and road surface flaking and reduces the noise caused by the use of a large number of tamping workers and construction [9; 10]. Additionally, CLSM has no special restrictions on the requirements of aggregates. Recycled aggregates such as abandoned masonry, concrete, and cast sand are also ideal materials for CLSM. The water-binder ratio of CLSM is between 1 and 1.5, which is much higher than the water-binder ratio of 0.4-0.55 for general concrete.