EFFECTS OF PARTICLE INTERFERENCE IN MORTARS AND CONCRETES

DEVIATIONS OF CONCRETE STRENGTH BY THE WATER-CEMENT RATIO LAW DEPEND UPON THE GRADING OF ITS SOLID MATERIALS, CEMENT PLUS AGGREGATES. THIS STUDY SHOWS THAT VARIATIONS IN STRENGTH AND WORKABILITY ARE DUE TO A CHARACTERISTIC OF THE GRADING WHICH IS CALLED PARTICLE INTERFERENCE. THIS IS THE RESULT OF AN EXCESS OF ANY SIZE GROUP OF PARTICLES, WHETHER AMONG THE FINER OR THE COARSER SIZES. NON-UNIFORM VOID POCKETS AND SEGREGATION OF SIZES ARE ALWAYS THE EFFECT OF PARTICLE INTERFERENCE. THIS WAS CONCLUDED FROM SIEVE ANALYSIS TESTS AND VISUAL INSPECTION. WHERE INTERFERENCE IS PRESENT WHERE A CORRECTION COULD BE MADE FOR THE SAKE OF ECONOMY, THE MATERIAL REQUIRED IS FIGURED IN THE SIMPLE MATHEMATICAL ANALYSIS. EFFORTS TO SET UP THE IDEAL GRADING MUST TAKE INTO ACCOUNT WATER-CEMENT RATIO AND CONSISTENCY. THE LAYER MUST BE UNIFORM THROUGHOUT AND ALL THE VOID POCKETS WILL BE OF ABOUT THE SAME SIZE. PARTICLE INTERFERENCE RESULTS WHENEVER THE PARTICLES OF ANY SIZE GROUP ARE IN SUCH EXCESS THAT THE AVERAGE CLEAR DISTANCE BETWEEN ADJACENT PARTICLES OF THIS GROUP IS LESS THAN THE AVERAGE DIAMETER OF THE PARTICLES OF THE NEXT SMALLER GROUP SIZE, PLUS THE EFFECT OF A CEMENT FILM, IF THE PASTE IS STIFF. PARTICLE INTERFERENCE MAY OCCUR BETWEEN ANY TWO GROUPS OF SUCCESSIVE SIZES FROM THE FINEST TO THE COARSEST AGGREGATE WHEN THE LARGER DIAMETERS ARE IN EXCESS. IT MAY OCCUR IN THE CEMENT AND THE LOW STRENGTH IN CEMENT MAY RESULT FROM GRINDING CLINKERS SO BADLY THAT PARTICLE INTERFERENCE FOLLOWS. MEASUREMENT AND CALCULATION METHODS FOR PARTICLE INTERFERENCE ARE PRESENTED. ANY MIXTURE MAY BE EXAMINED FOR PARTICLE INTERFERENCE FROM RESULTS OF THE SIEVE ANALYSES OF THE AGGREGATES AND THE PROPORTION IN WHICH THEY ARE COMBINED. IT IS CONCLUDED THAT PARTICLE INTERFERENCE CAN BE ELIMINATED, WITHOUT UNDUE COST, BY THE REDUCTION OF THE AMOUNTS OF THOSE GROUPS THAT MAY BE PRESENT IN CRITICAL EXCESS, EITHER BY BLENDING, OR BY THE USE OF VARIOUS CLASSIFIERS IN THE PREPARATION.