Aggregate properties - voids ratio and bulk density, Other Engineering

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.

 

Posted Date: 3/1/2013 2:38:57 AM | Location : United States







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