Concrete Compacting Factor Test

Compacting Factor TestLEE CHUN YEE 0321748YEE ALGEL 0315890YONG BOON XIONG 0321754GAN JET FOONG 0315998KHOO XIN YEE 0316180HII PAI LING 0320598

Aim: To study the workability of concrete.

Apparatus Required: (a) Compacting Factor apparatus

(b) Trowels

(c) Graduated cylinder

(d) Balance

(e) Tamping rod and iron buckets

Procedure: Step 1:- Apply Grease on inner surface of the apparatus Step 2:- Measure the mass as w1 kg by weighing the cylinder accurately and fix the cylinder on the base in such a way that the central points of hoppers and cylinder lie on one vertical line and cover the cylinder with a plate.

Procedure: Step 3:- For each 5 kg of aggregate mixes are to be prepared with water-cement ratio by weight with 2.5 kg sand and 1.25 kg of cement and then add required amount of water thoroughly until and unless concrete appears to be homogeneous.

Step 4:- fill the freshly mixed concrete in upper hopper part. Two minutes then release the trap door so that the concrete may fall into the lower hopper such that it bring the concrete into standard compaction.

Procedure: Step 5:- Fall the concrete to into the cylinder causes the concrete in standard Compaction immediately after the concrete has come to rest and open the trap door of lower hopper and then remove the excess concrete above the top of the cylinder.

Procedure: Step 6:- Clean the cylinder from all sides properly. Weight the partially compacted concrete thus filled in the cylinder and say it W2 kg. After this refill the cylinder with the same sample of concrete in approximately 50 mm layers, by vibrating each layer heavily so as to expel all the air and obtain full compaction of the Concrete.

Procedure: Step 7:- Struck off level the concrete and weigh and cylinder filled with fully compacted concrete. Let the mass be W3 kg.

Step 8:- Calculate compaction factor by using the formula:-

CALCULATION The compaction factor is defined as the ratio of the weight of partially compacted concrete to the weight of fully compacted concrete. It shall normally to be stated to the nearest second decimal place.

Compaction Factor= (W2-W1/ W3-W1)

Precaution 1. Accurate amount of water, cement and sand are to be taken to avoid collapsing of sample.

2. Maintain the consistency throughout the experiment to avoid the failure.

3. Convenient time for releasing the concrete from the upper hopper has been found to be two minutes after the completion of mixing

Factors that Affect Concrete strength

Age of concrete

•In theory, provided the concrete is not allowed to dry out, then it will always be increasing slowly at an ever reducing rate.

•For convenience and for most practical applications, It is generally accepted that the majority of the strength has been achieved by 28 days.

Effect of age of concrete on concrete strength

The table below shows the compressive strength gained by concrete after 1, 3, 7, 14 and 28 days

Age Strength per cent

1 day 16%

3 days 40%

7 days 65%

14 days 90%

28 days 99%

Water / Cement Ratio:• The higher the water/cement ratio, the greater the initial spacing between the cement grains and the greater the volume of residual voids not filled by hydration products.

•There is one thing missing on the graph. For a given cement content, the workability of the concrete is reduced if the water/cement ratio is reduced. A lower water cement ratio means less water, or more cement and lower workability.

•However if the workability becomes too low the concrete becomes difficult to compact and the strength reduces.

The relation between water cement ratio and strength of concrete is shown in the plot as shown below:

Temperature • The rate of hydration reaction is temperature dependent.

• Temperature increases, the reaction also increases.

• The concrete kept at higher temperature will gain strength more quickly than a similar concrete kept at a lower temperature.

• The final strength of the concrete kept at the higher temperature will be lower.

Compressive strength against temperature