A Study of Packing Effect on Strength Activity Index of Mortar as Specified by ASTM C 618 by Using Ground River Sand

Abstract

ASTM C 618 specifies that the strength activity index of mortar containing a pozzolanic materialused to replace Portland cement shall be higher than 75% of control cement mortar at 7 or 28 days. Additionally,it defines that the percentage of particle size of a pozzolanic material retained on a sieve No. 325should not be higher than 34%. The values of particle retained on a sieve No. 325 and the strength activityindex at 7 or 28 days may not sufficient to specify a good quality of pozzolan. The objective of this researchis to investigate the effect of fineness and replacement level of ground river sand, which having highcrystalline and non pozzolan, on compressive strength. Portland cement type I was replaced by groundriver sand at 10, 20, 30, and 40% by weight of cementitious materials. The ground river sand used in thisstudy was ground into 3 different sizes as retained on a sieve No. 325 of 5±2%, 13.5±2% (the retained on asieve No. 325 of Portland cement was 13.5%) and 34±2%.

The results showed that the compressive strength due to hydration reaction of ground river sandmortar having the same particle size as that of Portland cement was decreased when the replacement ofground river sand was increased. The percentages of compressive strength of ground river sand mortarswere 87, 81, 72, and 57%, respectively as compared to the control mortar when the replacements of groundriver sand of 10, 20, 30, and 40% were used. In addition, the compressive strength due to packing effect ofsmaller particle size of ground river sand was higher than the coaser one. The use of 20% of ground riversand with particles retained on a sieve No. 325 of 34% and 5.8% to replace Portland cement produced adifference in compressive strength due to packing effect of 6% of the control strength. The differencetended to be higher as the higher difference of fineness of ground river sand. The results suggested thatASTM C 618 specification is not practically suitable for the high fineness material since the strengthactivity index of mortar containing ground river sand (has high crystalline phase) with particle retained ona sieve No. 325 of 33.8% and used to replace Portland cement of 20% was higher than 75% at 7 and 28days.