| |
University of New Mexico Civil Engineering Department Civil Engineering Materials Laboratory, CE 305L UNIT WEIGHT & VOIDS IN AGGREGATE ASTM C29 Scope Test method ASTM C29 covers the determination of unit weight in a compacted or loose condition and calculated voids in fine, coarse, or mixed aggregates based on the same determination. This test method is often used to determine unit weight values that are necessary for use for many methods of selecting proportions for concrete mixtures. References ASTM C127 Specific Gravity and Absorption of Coarse Aggregate ASTM C128 Specific Gravity and Absorption of Fine Aggregate ASTM C125 Terminology Relating to Concrete and Concrete Aggregates AASHTO T19 Unit Weight and Voids in Aggregates Terminology Mass - the quantity of matter in a body. Weight - the force exerted on a body by gravity. Unit weight - the weight per unit volume. Voids in unit volume of aggregate - the space between particles in an aggregate mass not occupied by solid mineral matter. |
Apparatus Scale (or balance, 0.1 lb (0.05 kg)) Tamping Rod - a round, straight steel rod, 5/8 in. in diameter and approximately 24 in. in length, having one end rounded to a hemispherical tip of the same diameter as the rod. Measure - a cylindrical metal watertight measure (nominal 1/3 ft3 for coarse aggregate and 1/10 ft 3 for fine aggregate) Scoop Materials Coarse Aggregate - Oven dried at 110°C, then cooled to room temperature. Fine Aggregate - Oven dried at 110°C, then cooled to room temperature. Note: Sample size should be 125 to 200% of the quantity required to fill the measure. |
Procedure Download Procedures for Unit Weight and Voids in Aggregate Download Excel form for Unit Weight and Voids in Aggregate Measure Calibration 1) Determine weight of dry measure. 2) Fill the measure completely full with water and determine the weight of measure plus water. 3) Calculate the weight of water by taking the difference between the measurements obtained in (1) and (2) above. 4) Calculate the volume of the container V = Ww / γw where Ww is the weight of water used to fill the container and γw is the unit weight of water (62.3 lb/ft3 or 998 kg/m3). The computed volume should be close to the nominal value state in the apparatus section. The following loose and compact unit weight procedures are to be performed on both the coarse and fine aggregates. Loose Unit Weight (shoveling procedure) 1) Fill the measure to overflowing by means of a scoop, discharging the aggregate from a height not to exceed 2 in. (50 mm) above the top of the measure. 2) Level the surface of the aggregate with a straightedge. 3) Determine the weight of the measure plus content, and the weight of the measure alone, recording values to the nearest 0.1 lb (0.05 kg). Compact Unit Weight (rodding procedure) 1) Fill the measure one-third full and level the surface with the fingers. 2) Rod the layer of aggregate with 25 strokes of the tamping rod evenly distributed over the surface. 3) Add additional aggregate to the measure to the two-thirds full level, level with the fingers, and rod again with 25 strokes of the tamping rod. 4) Finally, add additional aggregate to overflowing and rod again using 25 strokes of the tamping rod. 5) Level the surface of the aggregate with a straightedge. 6) Determine the weight of the measure plus content, and the weight of the measure alone, recording values to the nearest 0.1 lb (0.05 kg). Note: When rodding the first layer, do not allow the rod to strike the bottom of the measure. When rodding the subsequent layers, do not force the rod into the previous layer of aggregate. Compact Unit Weights (rodding procedure) of sand and gravel mixtures (coarse & fine aggregate mixtures) 1) Each group will determine the compact (dry rodded) unit weight of an assigned sand-gravel mixture. 2) Mix the fine and coarse aggregate in a large mixing pan. 3) Determine the unit weight using the Compact Unit Weight procedure (steps 1-6) above.
1) Calculate the unit weight in both the loose and compact (dense) conditions for both the fine and coarse aggregates. γbulk = (G - T) / V where: γbulk = unit weight of the aggregate, lb/ft3 G = mass of the aggregate plus the measure, lb T = mass of the measure, lb V = volume of the measure, ft3 2) Calculate the void content, n (%), in the aggregate (for fine and coarse compact unit weights only) n (%) = [(Gs γw - γbulk)/ Gs γw ](100) where: γbulk = unit weight of the aggregate, lb/ft3 Gs = bulk specific gravity, dry basis (from ASTM C127 or C128, as applicable) γw = unit weight of water (62.3 lb/ft3 or 998 kg/m3 ) 3) Calculate the void content, n (%), for the compact fine-coarse aggregate combinations as follows a) n (%) = [(Gcom* γw - γbulk)/ Gcom* γw](100) where: b) Gcom = 100/[(C/Gc) + (F/Gf)] Gcom = the specific gravity of the combined sand-gravel mixture Gc = the bulk specific gravity of the coarse aggregate Gf = the bulk specific gravity of the fine aggregate, and C and F are the fractions (%) of the Coarse and Fine aggregates comprising the sand-gravel mixture, respectively (the sum of C and F must equal 100%). Report 1) Report the loose and dense unit weights for both the fine and coarse aggregates to the nearest 1 lb/ft3 . 2) Report the results of the void content to the nearest 1% for both the loose and dense unit weights. 3) Plot class curve of the unit weight vs. % sand. 4) Plot class curve of the void content vs. % sand. Questions 1) What is the sand-gravel combination which yields maximum density? Does this also yield lowest void content? 2) Would you recommend measuring quantities of material by weight or volume? Why?
|