Effect of cure temperature on the formation of metakaolinite-based geopolymer

A series of metakaolinite-based geopolymer was prepared at several curing temperatures and its relationship with porosity, infrared spectrometry (FT-IR) and mechanical properties was investigated. The samples were cured at the following temperatures: 55, 65 and 80 °C for 1 h. After a post cure of 28 days, the samples were investigated by using the following techniques: compressive strength, mercury intrusion porosimetry (MIP), helium pycnometry, X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectrometry (FT-IR). All samples were amorphous by XRD. The sample thermally treated at 65 °C (C65) presented the highest values of compressive strength and relative integrated area of peak at 792 cm−1. This peak was attributed to a higher concentration of tetra-coordinated aluminum, indicating a higher efficiency of the geopolymeric reaction. The C65 also presented the lowest volume of closed pores. The values of the skeletal and the true densities for C65 were very similar and consistent with the volume of the closed pores. On the other hand, this sample showed the highest bulk density obtained by MIP and the greatest difference between the open and closed porosity measured by MIP and helium pycnometry, respectively. All these results are coherent and clearly indicate that the amount of open pores is directly related to a better mechanical performance of the geopolymeric sample.