Nano SiO2 Katkılı Çimento Harçlarının Mekanik Özelliklerine Yüksek Sıcaklığın Etkisi

Abstract

tudies for the use of nano materials in cementitious composites are increasing day by day. Especially nano SiO2 is one of the most used materials due to its superior pozzolanic feature and space filling ability. Researchs continue to examine how nano SiO2 affects not only the strength properties of mortar or concrete, but also its durability properties. High temperature is one of the effects that structures are exposed to directly or indirectly. Knowing the behavior of building materials under high temperature is an important issue in terms of durability. The aim of this study is to determine the effects of nano SiO2 on the high temperature resistance of cement mortars. For this purpose, four different mortar mixes were prepared by 0, 1, 2 and 3% nano SiO2 substituting cement. On the 7th, 28th and 90th days, flexural and compressive strength tests were carried out on the mortar mixtures. In order to determine the effects of nano SiO2 on the high temperature resistance of mortars, the samples produced in the dimensions of 50x50x50 mm3 were exposed to 300 and 600 ° C for 3 hours after 90 days of curing. The samples were then self-cooled in the oven. 20 ⁰C was used as reference temperature. After high temperature application, weight loss, loss of ultrasonic pulce velocity and compressive strenght of hardened mortar samples were examined. In addition, SEM images of the samples were taken for microstructure analysis after 600 ⁰C temperature. As a result, it was determined that on the 7th day, 2% nano SiO2 substitution increased the flexural strength by 20.0% and compressive strength by 24.25% compared to the reference mixture and had a positive effect especially on early age strength. It was determined that as the temperature increases, the weight loss increases and the ultrasonic pulce velocity decreases, the optimum nano SiO2 ratio for high temperature resistance is 2%, but the residual compressive strenght results of all mixtures with and without nano material substitution at 600 ⁰C are very close to each other. In SEM images, cracks occurred in all samples.