6. Cementless geopolymer sleepers

A cementless, chemically stable fly ash geopolymer concrete sleeper was developed, cutting CO₂ emissions by 80% compared with traditional intensive manufacturing processes.
The newly developed geopolymer concrete sleeper satisfied all traditional sleeper requirements.

Based on the geopolymer hardening methods developed using alkali solution and waste fly ash from thermal power stations, a new environmentally friendly sleeper has been developed. The newly developed sleeper is manufactured with zero cement, reducing manufacturing process CO₂ emissions by 80%. Since geopolymers are more resistant to acid corrosion etc, they can be applied to places where ordinary concrete could not be used previously.

Up until now, the fact that the hardening of geopolymers was very rapid after mixing posed a problem from the point of view of workability. However, by adjusting the mixing temperature on samples, adding silica powder, inter alia, a method has been developed to extend the setting time and obtain a stable product.

As a result, geoploymer prestressed concrete sleepers were developed since this material can be applied in areas where previously traditional concrete could not, because of vulnerability to certain types of deterioration such as leakage of acid water (Fig.1).

In addition, given the problem of arranging steel rebars into blocks which are relatively short, a sleeper block without rebars was developed with steel fiber reinforced concrete instead (Fig.2).

Both types of sleeper were then tested and both met the operational requirements of traditional sleepers (table1). Future research aims to produce a geopolymer sleeper for practical use, reinforced with polymer fibers such as vinylon, inter alia.

Fig.1 Geopolymer PC sleeper
Fig.2 Steel fiber reinforced geopolymer sleeper block
(no rebars)
Table 1 Results of functional test on geopolymer sleeper (Units: kN)