Uniformity assessment of carbon fibres dispersion in cement paste by impedance measurements

An alternating current was applied to measure the impedance of a hardened cement paste with various contents of carbon fibres, When the free water content in the hardened cement paste is 90%-98%, and the measuring-frequency 500 Hz, an approximate linear relationship was found between fibre content and impedance of the composite, Based on this relationship, a new attempt was made to evaluate the dispersion uniformity of carbon fibres in cement paste by impedance measurement. The standard deviation S and the coefficient of variation S/(X) over bar(i) of impedance of the fibre-cement specimens randomly taken locating in different points were used as main parameters for the uniformity assessment. As a case, four different mixing processes were designed for dispersing carbon fibres into the cement paste. The results demonstrate that the relative longer mixing time increases the dispersion uniformity;ty of carbon fibres in cement paste, and the addition of the water reducer dramatically improves the uniformity due to the change of the fluidity of the paste, The ground fly ash can increase the uniformity to a certain extent.