Mechanical and durability properties of alkali activated slag concrete

In this study, to obtain sustainable concrete alkali activated slag concrete was researched. Portland cement has a significant role about CO2 emission. To reduce this emission, Portland cement was replaced with granulated blast furnace slag. On the other hand, due to the slow reaction of pozzolans, alkali actviators are used to accelerate strength gaining. In this research, to activate slag, sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) were used. NaOH which is in bead form, was prepared solution with water. The other Na2SiO3 was used in a solution form. Four different concrete mix series were prepared. Each series had three different water/binder ratios and these are 0.36, 0.50 and 0.65. The first series was reference concrete and they were produced to compare the results of alkali activated slag concrete. In alkali activated slag concrete, NaOH solution molarity was constant, and 8 M. The Na2SiO3/NaOH ratio of second series is 2.5, third series is 1 and fourth series is 4. 12 cylindrical specimens were obtained for each production. In addition, all specimens were cured at 20+2ºC in the saturated lime water during 28 days. For fresh concrete state, slump test and unit weight test were applied. Also, the real air content was calculated from the real unit weight. To identify the workability, alkali activated slag concretes show S4 and S5 classes, the reference concretes show S4 class. However, while molding process of alkali activated slag concretes, setting was observed quickly and loss of concrete consistency was occurred. 28th day compressive strength and modulus of elasticity were obtained to analyze mechanical properties of specimens. Compressive strength results show that water/binder ratio is a determinative property. The highest compressive strength results were obtained from AASC specimens. Also, 0.36 water/binder ratio shows linear trend with the increment of Na2SiO3/NaOH ratios. 0.50 and 0.65 water/binder ratio specimens show the lowest compressive strength when Na2SiO3/NaOH ratio is 2.5. Beside that, modulus of elasticity shows reverse results of compressive strength results. To identify durability properties, water absorption, capillary water absorption, rapid chloride penetration and electrical resistivity tests were applied. For water and capillary water absorption test results show that reference concretes show the lowest permeability properties. Results of rapid chloride test show similar results like water absorption results, in an other saying 0.36 water/binder ratio specimens show lower chloride penetration potential. In addition, two point electrical resistivity test was applied and results show similarity with chloride penetration results. After the durability tests, it has been understood that water/binder ratio is the determinative factor for the results. The reason of this is air voids in the inner structure of geopolymer mixes. Also, durability properties depend on both source and chemical composition of alkali activators, mixing and cure properties. The cost analyses of mixes were investigated. The reference concrete mixes are more economical than alkali activated slag concrete mixes. The reason of this is, used alkali activators made the cost increased.