The effect of high temperature on the neutron attenuation propertiesof alkali-activated mortars produced by usingcolemanite

In recent years, concrete has started to be produced with the use of chemical and mineral additives resistant to high temperatures in buildings.For this purpose, in the thesis study, it was aimed to examine the effect of colemanite on the physical and mechanical properties of mortars prepared by using two different binders, alkali-activated material and cement, on their neutron attenuationperformance after high temperature. Forthis purpose, the mortar samples produced by substitution of colemanite powder at 5 and 10% into the binder at suitable curing conditions were exposed tothetemperatures of 300and 500°C.In addition, within the scope of the study, the effect of high temperature on thermal neutron (25.4 MeV) attenuation performance was investigated theoretically with the NGCal program and the linear attenuation coefficients.The use of 5 and 10%colemanite in binding materials increased the initial setting times by 11,8 and 88,2%, and thefinalsetting times by 90,8and182,9%for cement series. In the alkaline activated paste series, it was observed that the initial setting times reduced by 66,7 and 22,0%,and the final setting times by 6,7and 9,1%. Although the use of colemanite increased the water absorption values by up to 30%,decreased the compressive strength values by up to 21,8% in cement mortar samples. In the alkali-activated mortar samples, the water absorption values increasedbyup to 8%, and the compressive strength valuesreducedby up to 41,1%. It is seen that thecolemanite substitutionpresents more satisfactory compressive strength results in cement mortar series. The 5 and 10%colemanite increased the thermal neutron attenuation factors by %10,81and %18,91 in cement mortar mixtures,and by 6,15and 10,3%in alkali-activated mortar mixtures, respectively. At %10 colemanite substitution, while the compressive strength values of mortars exposed to 500-°C high temperature decreased by %20,2for cement series, reduced by 33,3for alkali-activated mortar series. In parallelwith these results, similar losses were observed in neutron attenuation performances. At the high temperature, while the linear attenuation factors of cement mortars which have lower thermal neutron attenuation performance decreasedfrom 1,76cm-1to 1,55 cm-1with a loss of 11,9%, reduced from 2,87 cm-1to 2,38 cm-1with a loss of 17,1%in alkali-activated mortars. It decreased from. As a result of thethesisstudy, it has been seen that thecolemanite which has been and importantboron ore in our country can be used as an substitution material in cement and alkali-activated bindersin terms of neutron attenuation performance, anditsexistingusage areacan be expandedin this respect.