Investigation of the effect of hydratation development of blast furnace slag substituting cement mortars on mechanical properties

In cement and concrete technology, natural and artificial pozzolanic materials are intensively used. It is known that usage of artificial pozzolana have recently increased their use due to the fact that they reduce environmental pollution, protect energy sources, contribute to strength and durability. The blast furnace slag, which is in the artificial pozzolana class makes significant contributions to the cement and concrete sector. Blast furnace slag acquires a puzolanic property and improves the qualities of concrete when combined with cement as a result of grinding and having a very fine-grained structure. In the light of the experimental studies conducted; it is known that with the use of YFC, the setting time increase and therefore the workability of concrete increase, the heat of hydration, sweating and water permeability and chloride permeability decrease. Furthermore, it has been observed as a result of the studies conducted that the permeability of concrete decreases and the compressive strength increases with the use of blast furnace slag. This study has been carried out due to the fact that there are few studies on the hydration developments of blast furnace slag as a whole in our country. For this purpose, in the first stage of the study, water demands, setting times and volume expansion tests of reference and blast furnace slag-substituted (%0, %10, %15, %20 rates) cements with 2, 7, 28 and 90-day compressive strength tests were carried out. In order to examine the hydration developments in the second stage in more detail, analyses such as SEM, DTA/TGA, XRD, FT-IR were performed at the end of 28-day and the results were compared with each other. As a result of the data obtained, as the amount of blast furnace slag substitution increased, the setting time and the water demand increased, there was no difference in terms of expansion. The quantity of calcium hydroxide (CH) formed during hydration reduced in all BFS -substituted cement pastes, according to data obtained from TGA and XRD analyses done at the end of 28-day. In addition, it has been determined that the chemically bound water content is greater in 10% BFS-substituted cement paste than in the reference cement paste, so it has a denser microstructure by creating more hydration products. The results show that these pozzolanic materials have values very close to the reference cement in terms of strength even at an early age. In addition, at the 28-day, it was determined that the compressive strength values of all cement mortars with blast furnace slag substituted were reached above the minimum compressive strength value of PC 42.5 R type cement.