Retardation behavior and mechanism of organic retarders on geopolymers at high temperatures and their effects on mortar properties

High temperature brings the negative effect of quick-setting, which hinders the application of geopolymers in low latitude regions. This study investigated the effects of three organic retarders (sucrose, glucose, and sodium gluconate) on setting behavior and mechanical properties of geopolymer mortar at different temperatures (30°C-50°C). Also, retardation mechanism of organic retarders was revealed by using microscopic tests, including SEM, EDS, FTIR, XRD and TGA/DSC. The results showed that all three retarders significantly extended the setting time, and 9 % sodium gluconate prolonged the setting time to 62.21 min. However, setting time declined by 70 % as temperature rose from 30 °C to 50 °C, indicating strong thermal sensitivity. Retarders had negligible influence on water retention and fluidity, but induced varying degrees of strength loss. Notably, a high dosage (9 %) of sodium gluconate slightly enhanced late compressive strength by optimizing product distribution, while low dosages (≤3 %) of sucrose or glucose improved early flexural strength due to increased viscosity. The mechanism of organic retarders can be summarized as “adsorption—complexation” process. Mechanistically, organic retarders function via an “adsorption–complexation” mechanism, reducing ion availability and slowing geopolymerization. This study provides a new understanding of the role of retarders on performance regulation, supporting the application of geopolymer mortar in low latitude regions. • In three retarders, Sodium gluconate exhibited the strongest retardation effect. • Setting behavior of geopolymers had remarkable temperature sensitivity. • Retarders had minimal impact on the water retention and fluidity of mortar. • Retarders resulted in varying degrees of mechanical strength loss. • Retardation mechanism can be summarized as “adsorption—complexation” process.