THE STRENGTH CHARACTERISTICS OF SOIL-AGGREGATE MIXTURES & DISCUSSION

Abstract

THE EFFECTS WERE INVESTIGATID OF VARYING THE PROPORTIONS OF COARSE AND FINE-GRAINED SOILS ON THE STRENGTH OF SOIL- AGGREGATE MIXTURES. THE AGGREGATE-BINDER CONCEPT WAS EMPLOYED TO STUDY THE EFFECT OF SOIL PROPORTIONING ON STRENGTH. THE RELATIONSHIP BETWEEN MAXIMUM DENSITY AND THE PROPORTIONS OF AGGREGATE AND BINDER INDICATES THAT THE HIGHEST DENSITY IS PRODUCED BY 26% BINDER AND 74% AGGREGATE BY WEIGHT. THE MAXIMUM DENSITY IS GREATER THAN THAT OF EITHER THE AGGREGATE OR THE BINDER, AND IT IS ABOUT 12 LB PER CU FT HEAVIER THAN THEIR AVERAGE. IF THE VOLUME OF THE VOIDS IN THE COMPACTED AGGREGATE IS ASSUMED TO BE JUST FILLED WITH COMPACTED BINDER THE RESULTING PROPORTION WOULD BE 22% BINDER AND 78% AGGREGATE. THE MAXIMUM DENSITY OF THIS THEORETICAL MIX WOULD BE 148 LB PER CU FT WHICH IS FAR GREATER THAN THE GREATEST OBSERVED MAXIMUM DENSITY OF THE MIXTURES. THESE FACTS INDICATE THAT THE AGGREGATE-BINDER CONCEPT IS NOT STRICTLY CORRECT. PROBABLY THE AGGREGATE PARTICLES, BY CREATING HARD SPOTS THAT BRIDGE OVER THE LOOSER MATRIX OF BINDER, PREVENT 100% COMPACTION. THE INTERNAL FRICTION IN THE RANGE FROM 10% TO 26% BINDER DECREASES SLIGHTLY WITH INCREASING BINDER, SHOWING THAT THERE IS LITTLE ADDITIONAL SOIL TRAPPED BETWEEN THE AGGREGATE PARTICLES. WHEN THE AMOUNT OF BINDER EXCEEDS 26% THE BEARING FALLS OFF VERY SHARPLY TO A MINIMUM AT 33% BINDER. WITH MORE BINDER THE STRENGTH INCREASES SLIGHTLY BUT IT NEVER APPROACHES THE PEAK VALUE. COMPUTATIONS SHOW THAT THE CUSTOMARY ASSUMPTION THAT MAXIMUM DENSITY PRODUCES THE GREATEST STRENGTH IS JUSTIFIED. A SIMPLE METHOD OF DETERMINING THE BEST MIX FOR BEARING CAPACITY IS PROPOSED. THE AGGREGATE ALONE AND THE BINDER ALONE ARE COMPACTED. THE WEIGHT OF COMPACTED BINDER REQUIRED TO FILL THE AGGREGATE VOIDS IS COMPUTED. THE ACTUAL AMOUNT OF BINDER SPECIFIED COULD VARY FROM 50% OF THE COMPUTED VALUE TO 100% OF THE VALUE WITHOUT A SIGNIFICANT CHANGE IN SOIL BEARING.