Effect of Fly Ash and Slag on the Interfacial Zone Between Cement and Aggregate


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Title: Effect of Fly Ash and Slag on the Interfacial Zone Between Cement and Aggregate

Author(s): Mitsuro Saito and Mitsunori Kawamura

Publication: Special Publication

Volume: 114


Appears on pages(s): 669-688

Keywords: aggregates; calcium carboaluminate; calcium hydroxides; slags; cement pastes; chemical analysis; ettringite; fly ash; x-ray diffraction; x-ray fluorescence; Materials Research

Date: 5/1/1989

Chemical characteristics of the cement paste-aggregate interfacial zone have been considered to influence the durability and mechanical properties of concrete. Particularly, effects of mineral admixtures such as fly ash and slag on the microstructure of the interfacial zone deserve attention. An x-ray diffraction technique was used to evaluate the amounts of Ca(OH)2, ettringite, and the orientation of Ca(OH)2 crystals in the interfacial zone. Composite specimens with several types of rocks were broken to produce a fracture surface on the cement paste prism to which the x-ray diffraction analysis was applied. The analyses showed that the addition of fly ash or slag considerably affected the peak height and orientation of Ca(OH)2 crystals in the interfacial zone, which normally extends up to 50 to 100 æm from the interface. The formation of ettringite in the vicinity of the aggregate surface was restricted by the addition of the admixtures. These results also suggest that the addition of the mineral admixtures favorably affects the resistance of the interfacial zone against aggressive agents from the surroundings. The x-ray fluorescence analysis was conducted to quantify calcium and silicon in the zone. The results obtained complemented the conclusions described previously. 137-389