Aggregate properties
1.Aim: To compare the bulk density, voids ratio and angularity number of a nominal single sized aggregate when subjected to different levels of compaction.To compare the bulk density and percentage voids of a single sized aggregate and a continuously graded (all in) aggregate.
2. Procedure:
2.1 Standard empty cylinder container 150mm dia. x 300mm high is weighed (Volume 5.3 litres)
2.2 The container is filled with nominal single size (20.0 mm) aggregate in accordance with the three different methods outlined below, and the filled container is weighed.
Method 1
The container is filled with aggregate as follows:
a)In one continuous operation, the aggregate is slided gently down by tilting the scoop resting on the top edge of the cylinder.
b) The top surface of the last layer of the aggregate level is struck with the top of the container without forcing aggregate particles down.
Method 2
The container in four equal layers with aggregate are filled as follows:
Slide the aggregate by gently tilting the scoop resting on the top edge of the cylinder.Then each layer is compacted with 100 strokes of the standard tamping rod evenly applied over the area of the aggregate. The rod is held vertically 20-30 mm above the surface of the aggregate and then let it fall freely.
The top surface of the last layer of the aggregate level is struck with the top of the container without forcing aggregate particles down
Method 3
The container is filled with aggregate in three equal layers, as follows:
The aggregate is slided down by gently tilting the scoop resting on the top edge of the cylinder.One minute's compaction is applied on the vibrating table after each layer. The top surface of the last layer of the aggregate level is struck with the top of the container without forcing aggregate particles down.
exprimental Records
|
|
Aggregate type and maximum size
|
|
20 mm single sized
|
20 mm all in
|
|
Weight of empty container(kg)
|
14.1 Kg
|
14.1 Kg
|
14.1 Kg
|
14.1 Kg
|
|
Weight of container with aggregate (kg)
|
Method 1
|
21.6 Kg
|
21.5 Kg
|
21.6 Kg
|
21.5 Kg
|
|
Method 2
|
22.8 Kg
|
22.7 Kg
|
23Kg
|
22.8 Kg
|
|
Method 3
|
22.6 Kg
|
22.6 Kg
|
23.6 Kg
|
23.5Kg
|
|
|
|
|
|
|
4.Calculation:
For the 20mm single sized aggregate, for each method of compaction, calculate the bulk density, voids ratio and angularity number.
Bulk Density (kg/m3)=[Mass of aggregate (kg)/Volume of container (l)]*103
Void Ratio:[ (Volume of container(l)*PD)-Mass of aggregate(kg)]/Mass of aggregate(kg)
PD =Particle density of coarse aggregate may be taken as 2.57 kg/l and that of fine aggregate may be taken as 2.64 kg/l
Angularity Number:67-(Mass of aggregate(kg)/Volume of container*PD)*100
For the 20mm all in aggregate, for each method of compaction, calculate the bulk density and voids ratio. Angularity number is not required for the 20mm all in aggregate.
|
|
Weight of the aggregate only
|
|
20 mm single sized
|
20 mm in all aggregate
|
|
|
Method 1
|
7.5 Kg
|
7.4 Kg
|
7.5 Kg
|
7.4 Kg
|
|
Method 2
|
8.7 Kg
|
8.6 Kg
|
8.9 Kg
|
8.7 Kg
|
|
Method 3
|
8.5 Kg
|
8.5 Kg
|
9.5 Kg
|
9.4 Kg
|
|
|
Bulk Density
|
|
20 mm single sized
|
20 mm in all aggregate
|
|
|
Method 1
|
1.4*103 Kg
|
1.4*103 Kg
|
1.4*103 Kg
|
1.4*103 Kg
|
|
Method 2
|
1.6*103 Kg
|
1.6*103 Kg
|
1.67*103 Kg
|
1.64*103 Kg
|
|
Method 3
|
1.6*103 Kg
|
1.6*103 Kg
|
1.79*103 Kg
|
1.77*103 Kg
|
For coarse aggregate i.e Particle density of coarse aggregate may be taken as 2.57 kg/l
|
|
VOID RATIO
|
|
|
|
|
|
20 mm single sized
|
20 mm in all aggregate
|
|
Method 1
|
0.82
|
0.84
|
0.82
|
0.84
|
|
Method 2
|
0.57
|
0.58
|
0.53
|
0.57
|
|
Method 3
|
0.60
|
0.60
|
0.43
|
0.45
|
|
|
Angularity Number
|
|
|
|
20 mm single sized
|
|
Method 1
|
11.94
|
12.67
|
|
Method 2
|
3.13
|
3.86
|
|
Method 3
|
4.60
|
4.60
|
For fine aggregate PD taken as 2.64 kg/l
|
|
VOID RATIO
|
|
|
|
|
|
20 mm single sized
|
20 mm in all aggregate
|
|
Method 1
|
0.87
|
0.89
|
0.87
|
0.89
|
|
Method 2
|
0.61
|
0.63
|
0.57
|
0.61
|
|
Method 3
|
0.65
|
0.65
|
0.47
|
0.49
|
|
|
Angularity Number
|
|
|
|
20 mm single sized
|
|
Method 1
|
13.40
|
14.11
|
|
Method 2
|
4.82
|
5.54
|
|
Method 3
|
6.25
|
6.25
|
5.Discussion
a)Discuss the differences in aggregate characteristics due to the different compaction Methods
|
Differences due to different compaction
|
|
|
Weight of aggregate
|
Bulk Density
|
Void Ratio
|
Angularity Number
|
|
Method 1
|
Less as it is not compacted properly
|
Less as it is not compacted properly
|
More as it is not compacted properly
|
More angular and its rough aggregates
|
|
Method 2
|
More as it is compacted properly in four layers and with 100 strokes
|
More as it is compacted properly and with 100 strokes
|
Less as it is compacted properly and with 100 strokes
|
Less angular and its a smooth aggregates and with 100 strokes
|
|
Method 3
|
Medium in case of 20 mm single sized particle but more in 20 mm in all aggregate as compaction in three layers was perfect as vibrating table was used which allowed proper mix of all aggregates.
|
Medium in case of 20 mm single sized particle but more in 20 mm in all aggregate as compaction in three layers was perfect as vibrating table was used which allowed proper mix of all aggregates.
|
Medium in case of 20 mm single sized particle but more in 20 mm in all aggregate as compaction in three layers was perfect as vibrating table was used which allowed proper mix of all aggregates.
|
Medium in case of 20 mm single sized particle but more in 20 mm in all aggregate as compaction in three layers was perfect as vibrating table was used which allowed proper mix of all aggregates.
|
b)Discuss the differences in aggregate characteristics due to the different types of
Aggregates
Bulk Density:The bulk density of aggregate gives the valuable information regarding the shape and grading of the aggregate.Bulk density of aggregate is of interest when we deal with light weight aggregate and heavy weight aggregate.
Void Ratio:Porous aggregrate will affect the water/cement ratio of and the workability of concrete.
Angularity:Rounded aggregates are preffered over angular aggregate.Additional cement is required for angular aggregates.So an aggregate with higher angularity requires more cement but the interlocking of aggregate is more perfect in case of angular aggregate.The so called smooth surface aggregate is preffered because rounded aggregates are rough enough for developing a good bond.