Roughness of Steel Fibre and Composition of Cement Paste Close to Fibre Surface

The SEM and EDX methods were used to study both the profile along the perimeter of steel fibres and the composition of the cement paste close to the fibre surface. The paste was made of cement clinker blended with slag and limestone. The results indicate that a wavelength of 31.5 mu m and an amplitude of 0.925 mu m represent the changes of fibre radius on average, which can be used to estimate the size of empty spaces that particles touching the fibre surface may create and the particles that are able to fill these empty spaces. EDX line analyses in four orthogonal directions from the fibre surface were performed with a step of 0.5 mu m along the lines of 60 mu m. The distributions of elements indicated that the steel fibre mostly affected the relative amounts of Ca and Si. The comparison between the Si/Ca and Al/Ca ratios pointed out the absence of the AFm type phase close to the fibre surface and that the CSH gel was mostly intermixed with CH, as only a small amount of the AFt type phase was observed. Generally, the counts describing the existence of the CSH gel were larger than those of the CH within a distance of 60 mu m from the fibre surface. The counts were closest to each other at about 20 mu m from the fibre surface, where the CSH gel had its minimum and CH its maximum value.