RESUMEN
The pH values of pore solutions are of great significance for the durability of concrete, but the influencing factors and mechanisms of geopolymer pore solutions are still unclear and the composition of raw material elements has a great influence on the geological polymerization behavior of geopolymers. Therefore, we prepared geopolymers with different Al/Na and Si/Na molar ratios using metakaolin, and the pH and compressive strength values of the pore solutions were determined using solid-liquid extraction. Finally, the influencing mechanisms of sodium silica on the alkalinity and geological polymerization behavior of geopolymer pore solutions were also analyzed. The results showed that the pH values of the pore solutions decreased with an increase in the Al/Na ratio and increased with an increase in the Si/Na ratio. The compressive strength of the geopolymers first increased and then decreased with an increase in the Al/Na ratio and decreased with an increase in the Si/Na ratio. The exothermic rates of the geopolymers first increased and then slowed down with an increase in the Al/Na ratio, indicating that the reaction levels first increased and then decreased with an increase in the Al/Na ratio. The exothermic rates of the geopolymers gradually slowed down with an increase in the Si/Na ratio, indicating that an increase in the Si/Na ratio reduced the reaction levels. In addition, the results obtained from SEM, MIP, XRD and other test methods were consistent with the pH change laws of geopolymer pore solutions, i.e., the higher the reaction level, the denser the microstructure and the smaller the porosity, whereas the larger the pore size, the smaller the pH value of the pore solution.
RESUMEN
In order to accurately calculate the long-term prestress losses of prestressed tendons, a time-varying model of long-term prestress loss considering the interaction between concrete shrinkage, creep, and the stress relaxation of prestressed tendons was constructed. Then, a method for calculating the long-term prestress losses of concrete structures was developed. A long-term prestress loss test of a prestressed concrete T-beam in a long-term field test environment was carried out. The measured values of long-term prestress losses are compared with the calculated results of JTG 3362-2018, AASHTO LRFD-2007, and the time-varying law model. The results show that the long-term effective tension of the T-beam decreases gradually with the increase in the load holding time. At the beginning of loading, the tensile force changes rapidly and then gradually slows down. The later the tensile age or the higher the initial loading stress level, the smaller the long-term prestress losses of the prestressed tendons. The long-term prestress loss values calculated by JTG 3362-2018, AASHTO LRFD-2007, and the time-varying law model increase with the increase in the load holding time. In the early stage of loading, the rate of change slows down and tends to be stable. The calculated results of JTG 3362-2018 and AASHTO LRFD-2007 are significantly different from the measured values. However, the calculated results of the time-varying law model are in good agreement with the measured values. The average coefficients of variation of the long-term prestress loss calculated by JTG 3362-2018, AASHTO LRFD-2007, and the time-varying law model are 17%, 10%, and 5%, respectively. The time-varying law model of the long-term prestress losses of prestressed tendons is accurate, and the long-term prestress loss of prestressed reinforcement can be predicted effectively.
