22. Geopolymer Concrete Containing By-products from Shinkansen Rolling Stock as Raw Materials

Aluminum hydroxide, a by-product generated during the recycling and remanufacturing of aluminum used in Shinkansen rolling stock, is generally difficult to reuse and is therefore mostly disposed of.

To address this issue, we focused on the fact that some constituents of geopolymers contain aluminum and developed a concrete using aluminum hydroxide as a raw material for the geopolymer. Geopolymers are environmentally friendly materials that do not use cement, whose production emits large amounts of CO2. RTRI's geopolymer technology is characterized by a high degree of flexibility in material selection and mix proportion. For the base mortar strength, a mix incorporating blast furnace slag (a by-product of steelworks) in addition to aluminum hydroxide was found to achieve high strength. It was also confirmed that concrete containing coarse aggregate could attain sufficient strength exceeding the design requirement (Fig. 1).

Next, taking advantage of the high-strength properties of the developed geopolymer concrete, a prestressed concrete (PC) sleeper for use in severe impact environments was prototyped. The prototype was designed and fabricated in accordance with the specifications for the No. 3 PC sleeper (3PO) for general straight track sections on conventional railway lines, as specified in JIS E 1202 "Prestressed concrete sleepers - Post-tensioning type". Evaluation confirmed that it satisfied all specified requirements, including dimensions, workability, compressive strength, guaranteed bending load, bending breaking load, guaranteed pull-out load of embedded inserts, and pull-out breaking load (Fig. 2).

Future efforts will focus on verifying long-term durability and fatigue characteristics through field testing, with the aim of deploying the material in PC sleepers and contributing to a circular economy and the decarbonization of railways.