Automated identification of the aggregate-paste interfacial transition zone in mortars of silica sand with Portland or alkali-activated slag cement paste

The interfacial transition zone (ITZ) between cement paste and aggregate strongly influences the mechanical and transport properties of mortar and concrete. Backscattered electron (BSE) imaging in the scanning electron allows anhydrous cement, hydration products, and porosity in this region to he quantified by compositional contrast. When the aggregate has a similar brightness to the hydrates, as in some alkali-activated cement mortars with silica sand, automated identification of the aggregate edge in the BSE image is difficult. Manual identification is laborious and prone to errors. Here we demonstrate use of energy dispersive X-ray (EDX) dot maps, acquired concurrently with the BSE to enable compositional identification of the aggregate edge automatically. The mortars studied were prepared with OPC or slag activated with either sodium silicate or potassium hydroxide. The edges of the silica sand aggregate particles were located to within 2.5 mu m, and the gradation of microstructure across the ITZ was quantified automatically. Hydrates were found most successfully to infill the ITZ in sodium silicate-activated slag cement mortars. (C) 2000 Elsevier Science Ltd. All rights reserved.