The Effect of High Temperatures on the Mechanical and Microstructural Properties of Geopolymer Concrete

The concrete structures used in various applications including iron and aluminum foundries and hazardous waste disposal lose performance when subjected to heat. As aluminum silicate materials however, geopolymers behave in a much more stable manner than normal concrete when exposed to high temperatures. Calcium silicate hydrate (C-S-H) and calcium-aluminum-silicate-hydrate nanostructures, which are products of the geopolymerization process that strengthens geopolymer concrete, undergo many changes when exposed to heat. The study therefore investigates the effect of high temperatures on geopolymer concrete’s strength parameters from a microstructural perspective and according to nanostructural changes of C-S-H and C-A-S-H.

In this regard, about 300 samples were cured in the humidity bath for 1, 3, 7, 14, and 28 days. All samples were then put in of 25, and 900°C temperatures for 2 hours. Length and weight change percentages, compressive strength, and ultrasonic and cracking behavior tests were performed on all samples. Images from the (SEM) and the energy-dispersive X-ray (EDX) analysis were also used to evaluate the microstructural behavior of samples in various temperatures.

According to the results, sample weight and length changes and compressive strength depended on the behavioral nature of C-S-H and C-A-S-H nanostructures. Nanostructural analysis of C-A-S-H points to high temperatures reducing compressive strength and weight as well as causing more cracks. The compressive strength of the 28 samples in 900°C temperature also decreased from 604 kg/cm2 to 75 kg/cm2. The complete disintegration of the C-S-H and C-A-S-H nanostructures.