materials Article Applicability of Additives for Ground Improvement Utilizing Fine Powder of Waste Glass Shinya Inazumi 1, * , Ryo Hashimoto 2 , Takashi Shinsaka 3 , Supakij Nontananandh 4 and Susit Chaiprakaikeow 4   Citation: Inazumi, S.; Hashimoto, R.; Shinsaka, T.; Nontananandh, S.; Chaiprakaikeow, S. Applicability of Additives for Ground Improvement Utilizing Fine Powder of Waste Glass. Materials 2021, 14, 5169. https:// doi.org/10.3390/ma14185169 Received: 3 August 2021 Accepted: 7 September 2021 Published: 9 September 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional afﬁl- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Civil Engineering, Shibaura Institute of Technology, Toyosu Campus, Tokyo 135-8548, Japan 2 Doboku Chishitsu Co. Ltd., Sendai 981-3107, Japan; rhashimoto@geoce.co.jp 3 Sanshin Corporation, Tokyo 111-0052, Japan; shinsaka@sanshin-corp.co.jp 4 Department of Civil Engineering, Kasetsart University, Chatuchak, Bangkok 10900, Thailand; fengskn@ku.ac.th (S.N.); fengssck@ku.ac.th (S.C.) * Correspondence: inazumi@shibaura-it.ac.jp; Tel.: +81-358598360; Fax: +81-358598401 Abstract: As a solidifying material for ground improvement using inorganic waste as a raw material, the authors have been developing an additive mixture of the ﬁne powder of waste glass containing a large amount of silica generated during the production of glass cullet and an alkaline aid (heat- treating type of “Earth-Silica; ES” additive). Furthermore, a solidifying material that solidiﬁes by mixing this additive with the ﬁne powder of blast furnace slag, which is a by-product of steel production, is also being developed. In this study, the authors reviewed the mixing process of the solidiﬁed materials, especially the one made with the heat-treating type of ES additive, omitting the heat treatment of the ﬁne powder of waste glass and the alkaline aid and applying only the mixing treatment. As a result, a mixing type of ES additive was manufactured to simplify the manufacturing process, and the difference in the performance of the solidifying material, depending on the presence or absence of the heat-treating process during the additive manufacturing, was veriﬁed in terms of the effect on the solidifying action. Speciﬁcally, the solidifying materials to which the heat-treating type of ES additive and the mixing type of ES additive were added, respectively, were applied to the high-pressure injection stirring method, one of the ground-improvement methods. Various tests clariﬁed the changes in viscosity of these solidifying materials over time and the acceleration of their solidifying rates when adding ordinary Portland cement separately. Keywords: additive; ﬁne powder of blast furnace slag; ﬁne powder of waste glass; ground improve- ment; solidifying material 1. Introduction The sustainable development of industries is desired in modern society, and giving consideration to the environment is becoming more and more important with the progress of technologies. In the case of glass, one kind of industrial product, it is collected after its use and reused as a raw material for glass, but the ﬁne powder generated during the production of glass cullet is landﬁlled as general waste [1–3]. As a result, in Japan alone, 2.82 million tons of this ﬁne powder, or 25% of the amount of non-ferrous metal mineral waste including glass waste, was not recycled, but discarded in ﬁnal disposal sites, such as landﬁlls, in 2017 [4–6]. In a series of studies [7–10], the authors developed a solidifying material for ground improvement that contributes to a reduction in the amount of waste treatment by utilizing inorganic waste as a starting material. This solidifying material is composed of the ﬁne powder of blast furnace slag and an additive developed independently. About 40% of the additive is the ﬁne powder of waste glass containing a large amount of silica as the starting material, which is mixed with a powdery alkaline aid, heat-treated, and pulverized by pulverization (hereinafter, the “heat-treated type of ES additive” in which ES means Earth-Silica). The ﬁne powder of blast furnace slag is pulverized blast furnace granulated Materials 2021, 14, 5169. https://doi.org/10.3390/ma14185169 https://www.mdpi.com/journal/materials