Chemistry of Composite Cements; Interaction between BlastFurnace Slag and Natural Pozzolan in Portland CementMixtures

Composite cement has several technical, environmental, and economicadvantages. thus, we investigated the properties of a new composite cementcomposed of four components, including ground granulated blast-furnace slag(ggbfs) from isfahan steel co., pozzolan from rafsanjan pozzolan mine, portlandcement type ii from sepahan cement co., and limestone filler. at first, the chemicaland physical properties and activity of the above components were determined. eightcomposite cements were prepared and their physical and chemical properties werecharacterized. after compressive strength test (1 to 90 days), measurement offlowability and setting time, a composite cement made of 20% slag, 10% pozzolan,and 2.5% limestone was selected for additional investigations. after 120 days ofcuring, sem, xrd, and tga testing on cement pastes made of the proposed blend,the control cement, portland-blast-furnace slag cement (30% slag), and portland-pozzolan cement (30% pozzolan) were investigated. the blast-furnace slag improvedthe long-term compressive strength of the composite cement, provided a greater flow to the mortar, and displayed less permeability. incontrast, the pozzolan offered essential benefits, including proper initial strength, suitable setting time, and good grind-ability. thestandard quality tests do not evaluate the durability of concrete containing a composite cement, while our study is based on the hydrationreactions that occurred in the composite cement for four months. the microscopic investigation and tga tests further revealed that thepozzolan additive reduces the portlandite content of the composite cement paste. the xrd results indicated that the slag had fewcrystals, whereas numerous crystals were observed in the pozzolan sample, potentially reducing the compressive strength in thecomposite cement. the sem images displayed that the pozzolan crystals have not reacted with water after 120 days in the compositecement. the experimental results revealed that the slag and pozzolan positively affect the properties of composite cement and improve itscapabilities.