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Laboratory friction tests on cement mortar specimens, prepared with various fractions of limestone and emery sand, were carried out using the accelerated polishing machine and the British pendulum tester. Two types of investigations were performed. The first consisted of mixes with constant grading of sand, either limestone or emery, in which one fraction was replaced by the same fraction of the other type of sand. The second consisted of mixes of limestone sand in which a certain amount of emery sand, each one of four different fractions, was added each time. The exact amount of emery sand added was calculated for each fraction so that in each series of tests the total surface area of emery sand was constant, regardless of the fraction used.
It was found that the finer fractions are more effective in influencing the skid resistance value (SRV) of mortars. The max increase in SRV (29.7%) is achieved when the 0.297/0.149 fraction of limestone sand is replaced by the same fraction of emery sand; therefore, an SRV value of approximately 90% of the SRV of mortar, containing entirely emery sand, is obtained. The second investigation confirmed that the total surface area of hard particles determines the friction characteristics of the mortars. It seems, however, that an optimum total surface of hard particles exists, and further increase of which does not cause additional increase of the SRV.
Assistant professor, National Technical University of Athens, Athens,
Stock #: CCA10292J