ACI Certification Section 4 ASTM C 138 Introduction

ACI Certification –Section 4 [ASTM C 138] Introduction: • Standard Test Method for Density (unit weight), Yield, and Air Content (Gravimetric) of Concrete –Apparatus –Sample –Procedure

ACI Certification –Section 4 [ASTM C 138] Apparatus –Balance 0. 1 lbs accuracy or within 0. 3% of the test load [Whichever is greater] at any point within the range of use. Range of use shall be from mass of the measure empty to [measure plus contents @160#/cft] i. e. air meter bowl - 10#s concrete@160#/cft for. 25 cft. - 40#s (Range of use) - 50#s

ACI Certification –Section 4 [ASTM C 138] Apparatus Tamping Rod – A round , Straight Steel Rod, 5/8 inch dia. – 24 in. in length –Tamping end rounded to a hemispherical tip – 5/8 in.

ACI Certification –Section 4 [ASTM C 138] Apparatus Internal Vibrator – 7000 vibrations per min. or more –Outside dimension 0. 75 in and less than 1. 50 in. –The length of the shaft shall be at least 24 in.

ACI Certification –Section 4 [ASTM C 138] Apparatus Strike-off Plate – A flat rectangular metal plate at least ¼ in. thick or a glass or acrylic plate at least ½ in. thick with a length and width at least 2 in. Greater than the diameter of the measure with which it is to be used.

ACI Certification –Section 4 [ASTM C 138] Apparatus Mallet – A mallet (with a rubber or rawhide head) having a mass of 1. 25± 0. 50 lb for use with measures of 0. 5 cft or smaller –Mass of 2. 25± 0. 50 lb for greater than 0. 5 cft.

ACI Certification –Section 4 [ASTM C 138] Sample ASTM C 172 – 1” nominal max size aggregate – 0. 2 cft capacity measure

ACI Certification –Section 4 [ASTM C 138] Procedure Rod for slumps > 3” Rod or vibrate bet. 1”-3” Vibrate < 1”

ACI Certification –Section 4 [ASTM C 138] Procedure Rod 25 times <= 0. 5 cft Rod 50 times = 1 cft Rod 1 per 3 sqin. > 1 cft Rod bottom layer not touching the bottom of pale For two top layers penetrate 1 in. into layer below

ACI Certification –Section 4 [ASTM C 138] Procedure –After each layer is rodded, tap the sides 10 -15 times –The force should close voids and release air bubble from mix –Add the final layer so as to avoid overfilling

ACI Certification –Section 4 [ASTM C 138] Procedure –Fill and vibrate the measure in two approximately equal layers –Do not allow vibrator to touch or rest on bottom or sides during bottom layer vibrating –When vibrating final layer, penetrate only 1 inch into layer below. –No air pockets should be left in mix when withdrawing vibrator –Continue vibration until proper consolidation is achieved

ACI Certification –Section 4 [ASTM C 138] Procedure –Concrete must not contain a substantial excess or deficiency of concrete –An excess of concrete protruding approx 1/8 in. above the top of the mold –A small quantity of conc. May be added to correct the dificiency –If there is an excess, remove with a scoop or trowel immediately after consolidation but before struck -off

ACI Certification –Section 4 [ASTM C 138] Procedure –Strike-off should be pressed on top of surface about 2/3 of the surface and withdrawing the plate in a sawing motion to finish area originally covered –The place the plate on the top of the measure to cover the original 2/3 of the surface and advance it with a vertical pressure and sawing motion until it slides of the edge –Several final strokes with the inclined edge of the plate will produce a smooth finished surface –After the strike-off, clean all excess concrete from exterior measure and determine mass