AGGREGATE PROPERTIES

INTRODUCTION

There are two basic two types of aggregate coarse aggregate and fine aggregates.

Coarse Aggregate :- The material of coarse aggregate is typically greater than 5 mm. Ex- Crushed Rocks and gravel.

Fine Aggregate :- The material of fine aggregate is generally categorized as a rock less than 5mm. Ex- Sand and Crusher fine.

Rough-textured, angular, and elongated particles require more water to produce a workable concrete than smooth, rounded compact aggregate

The main purpose of this experiment is to determine the value of bulk density, voids ratio and angularity number of 20mm single sized aggregates and compare it with 20mm all in aggregates when subjected to different methods of compaction.

METHOD

In this experiment, a cylinder container is used to compact the aggregate. The diameter and height of a cylinder container are 150mm and 300mm. This experiment is done by following three methods.

METHOD 1 – The aggregate is filled into the container by sliding down and tilting the scoop which resting on the top edge of the cylinder. After that, the top surface of the last layer is strike down with the top of the container without forcing the aggregate particles down.

METHOD 2 – The aggregate is filled into four equal layers. The first step is gently sliding and tilting the scoop resting on the top edge of the cylinder. Next, each layer of the container is compacted with 100 strokes of the standard tamping rod evenly over the area of the aggregate. The rod must be hold vertically between 20 to 30mm above the surface of the aggregate and let it fell freely. The final step is striking the top surface of the last layer of the aggregate level with the top of the container without forcing aggregate particles down.

METHOD 3 – The aggregate is filled into three equal layers. The aggregate is being sliding by gently tilting the scoop which resting on the top edge of the cylinder. Then, one minute of compaction is applied on the vibrating table after each layer. Finally, the top surface of the last layer is strike down with the top of the container without forcing the aggregate down.

Figure- Method 2 in which 20mm single sized aggregates are compacted using rod.

Figure- Method 2 in which 20mm all in aggregates are compacted using rod.

Figure- Method 3 in which 20mm single sized and 20mm all in aggregates are compacted using compaction vibrator machine.

RESULTS

The weight of an aggregate can be determined by using equation 1, whereas the bulk density, voids ratio and angularity number of an aggregate can be calculated by using equation 2, 3 and 4 respectively.

Weight of aggregate (kg) = Weight of container with aggregate – Weight of empty container

(1)

Bulk density (kg/m^3 )=(Mass of aggregate (kg))/(Volume of container (l))×?10?^3

(2)

Voids ratio=((Volume of container (l)×P.D.)-Mass of aggregate (kg))/(Mass of aggregate (kg))

(3)

Angularity number=67-((Mass of aggregate (kg))/(Volume of container (l)×P.D.)×100)

(4)

Particle density (P.D.) of coarse aggregate may be taken as 2.57 kg/l, while particle density of fine aggregate may be taken as 2.64 kg/l.

Table 1: Weight of aggregate with container

Aggregate type

20mm single sized 20mm all in

Weight of empty container (kg): 12.85 kg 12.90 kg 12.90 kg 13.00 kg

Weight of container with aggregate (kg): Method 1 21.00 kg 21.05 kg 21.50 kg 21.46 kg

Method 2 21.35 kg 21.30 kg 21.90 kg 22.20 kg

Method 3 21.50 kg 21.75 kg 22.45 kg 22.56 kg

Table 2: Weight of aggregate only

Weight of aggregate only (kg):

20mm single size aggregate 20mm all in aggregate

Method 1 8.15 kg 8.15 kg 8.60 kg 8.46 kg

Method 2 8.50 kg 8.40 kg 9.00 kg 9.20 kg

Method 3 8.65 kg 8.85 kg 9.55 kg 9.56 kg

Table 3: Bulk density of an aggregate

Bulk Density (kg/m3)

20mm single size aggregate 20mm all in aggregate

Method 1 1537.7 kg/m3 1537.7 kg/m3 1622.6 kg/m3 1596.2 kg/m3

Method 2 1603.7 kg/m3 1584.9 kg/m3 1698.1 kg/m3 1735.8 kg/m3

Method 3 1632.1 kg/m3 1669.8 kg/m3 1801.9 kg/m3 1803.7 kg/m3

Table 4: Voids ratio of an aggregate

Voids Ratio

20mm single size aggregate 20mm all in aggregate

Method 1 0.67 0.67 0.63 0.65

Method 2 0.60 0.62 0.55 0.52

Method 3 0.57 0.54 0.47 0.46

Table 5: Angularity number for 20mm single size aggregate

Angularity Number

20mm single size aggregate

Method 1 7 7

Method 2 5 5

Method 3 3 2

DISCUSSION

1. To compare the bulk density, voids ratio and angularity number when subjected to different levels of compaction – This experiment shows how aggregate characteristics difference due to the different compaction methods

The characteristics of an aggregate include unit weight, bulk density, voids ratio and angularity number. The calculation results shows that

From (table 2), it illustrates that the weight of aggregate in method 3 compaction is the highest as compared to the other method 1 and method 2 compaction. This shows that the Method 1 compaction has attained the lowest value of weight of aggregate.

The value of bulk density (table 3) differs due to the difference in the weight of aggregate, as the formula for the bulk density (eq. 2) is the mass of an aggregate divided by the volume of a container, which means that the large amount of aggregate weight will obtain a greater value of bulk density.

Moreover, the voids ratio (table 4) and angularity number (table 5) in method 1 had the highest values than method 2 and method 3 because of its total mass. This not only depends upon the shape and size of an aggregate, but also due to compaction processes that make the unit weight of an aggregate slightly different in each method.

This experiment concludes that Method 3 made the aggregate more compacted as compared to Method 1 and Method 2.

2. To compare the bulk density and voids ratio of a 20mm single sized and a 20mm all in aggregate – This experiment shows the characteristics difference due to the different types of aggregates

The calculation result from table 2 shows that

From (table 2), it shows that the total unit weight of 20mm all in aggregates is high as compared to the 20mm single sized aggregates which is due to the mixed shape and texture of 20mm all in aggregates.

As a result, the higher weight of aggregates for 20mm all in aggregates describes that the Bulk density value of 20mm all in aggregate is higher than 20mm single sized as shown in (table 3).

However, the value of voids ratio for 20mm all in aggregates is lower as compared to the voids ratio for 20mm single sized aggregates as shown in (table 4). This illustrates that the lowest value of voids ratio will have less porosity and will increase the workability or strength of concrete.