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Over 350 mixtures of quartzite aggregate with locally available pit sands have been made in the laboratory, and the proportions of fine aggregate for 34 least-void content mixtures have been obtained experimentally. Plots have been made between the proportion of aggregate fraction finer than largest size fraction and the fineness modulus of such a fraction. The proportions required for least-void content followed a linear trend fairly similar to what one would obtain from the theoretical gradings of Fuller, Weymouth, or Ehrenberg, but the actual proportions of fine fractions were somewhat lower than those obtained from such hypotheses. Reasons for the difference are discussed.
An empirical equation has been fitted for this linear trend so that it can be used to determine the proportions of coarse and fine aggregates of least-void contents. Based upon Powers' modification of Butcher's and Hopkins' equation, the nature of particle interference in aggregate mixtures has been discussed. The experiments have also shown that use of gap-graded or sands of restricted sieve sizes results in reduced particle interference when compared with using fine aggregates of continuous grading, even though aggregate mixtures having gap-graded fine aggregates may have slightly higher values of void ratio.
The experiments were extended to study the optimum microfilier content needed to fill some of the remaining voids of the system. The amount of microfilier that can be used before further particle interference takes place is obtained by one of the three methods suggested, including the use of Powers' equation as modified in this work.
Mixtures of coarse and fine aggregates and microfilier with least possible void ratios are preferred for making polymer (resin) concretes.
Professor, Indian Institute of Technology, Hauz Khas, New Delhi,
Kantha Rao, VVL
Research scholar, Centre for Materials Science and Technology, Indian Institute of Technology, Hauz Khas, New Delhi,
Stock #: CCA10595J