## 1 Introduction  
High-strength precast concrete piles, with a design base strength of 80 MPa or greater, are widely used as foundations in civil engineering and construction projects across Japan. Figure 1 illustrates demand trends for different types of precast concrete piles [1]. The proportion of high-strength concrete piles has been increasing annually, with particularly strong demand for piles designed for base strengths of 105 and 123 MPa. This trend corresponds with advancements in high-bearing-capacity embedded pile construction technologies. Precast concrete piles are typically cured through steam curing or autoclaving, both of which are heat-assisted methods. These processes accelerate cement hydration reactions [2, 3, 4, 5], facilitating rapid strength development and enabling faster deployment. High-strength concrete is typically produced by minimizing the water-to-cement ratio and increasing the cement content to achieve the desired strength levels. However, this approach often reduces workability, making concrete more difficult to handle in practical applications. To mitigate this issue, silica fume (SF) is commonly added to high-strength concrete mixes used in piles. SF consists of ultra-fine particles compared to ordinary Portland cement (OPC) and enhances workability due to its ball-bearing effect [6]. Additionally, its high silica content and large specific surface area promote a pozzolanic reaction, further improving long-term strength. As a result, SF is a key additive in the production of precast high-strength concrete piles. Although SF is a byproduct of ferrosilicon and silicon metal production, Japan lacks manufacturing facilities for these materials. As a result, the country must import all required SF, leading to significant dependency issues related to supply, price, and quality. This reliance underscores the need for an alternative to SF. The research team has explored volcanic glass powder (VG) as a potential substitute. This high-purity volcanic glass material was recognized as a Japanese Industrial Standards (JIS) material in 2020. It is derived from natural pozzolanic volcanic deposits known as Shirasu in Japan [7; 8; 9], which are crushed, classified, and refined using a dry sorting air table to remove clay content that could hinder hydration [10; 11]. The estimated Shirasu reserve is 750 m\({}^{3}\)[11]. Additionally, VG has been identified as a precursor for alkali-activated materials (AAMs). Studies have shown that replacing 10-70% of fly ash with VG improves compressive strength [12]. Furthermore, in AAM formulations using ground blast furnace slag as a precursor, a 10% VG replacement enhanced both compressive strength and durability [13], while higher VG replacement rates effectively suppressed alkali-silica reaction expansion [14]. Carbon dioxide (CO\({}_{2}\)) emissions from cement production are a pressing global issue [15; 16; 17; 18]. One effective strategy to reduce these emissions is replacing cement with supplementary cementitious materials, such as industrial waste or natural pozzolans, which have lower CO\({}_{2}\) emissions during manufacturing [19; 20; 21]. VG, which does not require calcination in its production process, presents an environmentally advantageous alternative. The estimated CO\({}_{2}\) emissions from VG production are 0.0888 kg-CO\({}_{2}\)/kg-VG [22], significantly lower than the 0.756 kg-CO\({}_{2}\)/kg-OPC emitted during ordinary Portland cement production [23]. Therefore, substituting OPC with VG can reduce the overall CO\({}_{2}\) footprint of concrete production. VG has a specific surface area of 8 m\({}^{2}\)/g for Type I, 4 m\({}^{2}\)/g for Type II, and 1 m\({}^{2}\)/g for Type III. Although its SiO\({}_{2}\) content does not reach the 85% found in SF, it  
Figure 1: Demand trend based on the type of precast concrete piles [1]. remains above 70% and has a high glass content.