Effect of stone color, dosage and alkali type on Ahlat Stone (volcanic origin) based geopolymer concretes

In this study, the usability of volcanic based Ahlat Stone for the production of geopolymer con-crete was investigated using two different physical colors (beige and black) of Ahlat Stone, two different alkali activators, NaOH + Na2SiO3 and KOH + Na2SiO3, and three different dosages (400, 500 and 600 kg/m3). The pozzolanic activity index, fresh unit weight, compressive and flexural strength, capillary absorption, length change, radiation absorption properties and microstructure analyze with scanning electron microscope with energy dispersive X-ray analysis (SEM/EDS) and Fourier Transform Infrared (FT-IR) of the mixtures were examined. The photon interaction parameters such as effective atomic number (Zeff) and half value layer (HVL) were obtained experimentally and theoretically. According to the results, the pozzolanic activity index was determined as beige-colored Ahlat Stone was higher than the black-colored due to the high of Si content. The sample included KOH has the lowest capillary absorption ration with increasing value depending on dosage. Black Ahlat Stone has the higher length changes at early ages and compressive strengths comparing with the beige one. Microstructure analyzes revealed that black Ahlat Stone including KOH, has more reticulated and compact structure than the other sample. Optimum results were obtained in the production of Ahlat Stone based geopolymer concrete by using KOH + Na2SiO3, 500 kg/m3 and black Ahlat Stone. Moreover, the samples with KOH were more effective in absorbing radiation.