Specific gravity and absorption of coarse aggregate

Introduction

The relative density (specific gravity) and absorption of aggregates are important properties, especially in mix design for concrete and asphalt mixtures. In mix design, it is necessary to measure accurately the volumes occupied by specified masses of aggregate. Therefore the voids in the aggregate must be considered.

Coarse aggregate

Purpose

To determine the saturated surface-dry (SSD) and bulk specific gravity (relative density)and water absorption of natural mineral aggregates used in Portland cement concrete, where ASTM-C-127 standard was used

Apparatus

Sample container.
Water tank.
Balance, with a minimum capacity of 4000g.
Suspended apparatus.
Drying oven.
Sieve (4.75mm), (No.4) standard sieve

Procedure

1. Secure a representative field sample and reduce to laboratory test size with a sample splitter or quartering method.
2. Reject all material passing from No.4 sieve.
3. Place the sample in a pan and cover it with water. 
4. Allow to soak for 15-19 hours.
5. Remove the test sample from the water and dry it by a piece of clothes, a Moving stream of air may be used.
6. Determine the mass of the test sample in the saturated surface dry condition B.
7. Place the saturated surface dry test sample in the sample container and determine its mass in water.
8. Record weight of submerged sample as C.
9. Dry the test sample in the drying oven and determine the mass and record as A.

 

Results

1	Weight of dry sample                                 (A)	1876.9gm
2	Weight of saturated surface of dry sample (B)	1891gm
3	Weight of saturated sample in water          (C)	719.7
4	Bulk specific gravity (dry sample)          = A/B-C	1.6
5	Saturated surface of dry specific gravity =B/B-C	1.614
6	Apparent specific gravity                        =A/A-C	1.622
7	Percentage water absorption        =(B-A/A)*100%	0.75%

 

Discussion and conclusion

Bulk specific gravity used for calculating in the concrete mix but apparent specific gravity used for calculating aggregate weight. Aggregate are porous materials and water can seep into the pores of the particles. Which effect the mix design for concrete.

The sources of errors in this experiment are personal errors in weighing the samples and determining the A, B and C.