Saturday, February 25, 2012

Aggregate Crushing Value

1.0 Introduction

The principal mechanical properties required in stones are satisfactory resistance to crushing under the roller during construction and adequate resistance to surface abrasion under traffic.

Aggregates used in road construction, should be strong enough to resist crushing under traffic wheel loads. If the aggregates are weak, the stability of the pavement structure is likely to be adversely affected. The strength of coarse aggregates is assessed by aggregates crushing test. The crushing value provides a relative measure of resistance to crushing under a gradually applied compressive load. To achieve a high quality of pavement, aggregate possessing low aggregate crushing value should be preferred.

2.0 Objective

To ascertain the hardness of the aggregate.

3.0 Apparatus

  1. Open ended steel cylinder of nominal 150mm internal diameter with plunger and base plate (plate 7)


Figure 3.1: Open ended steel cylinder


  1. A tamping rod with a 16mm diameter and 600mm long.


Figure 3.2: Tamping rod



  1. British standard sieves of sizes 14.0mm, 10.0mm and 2.36mm.


Figure 3.3: Sieve size 2.36mm

  1. Compression testing machine which capable of applying force of 400kN.


Figure 3.4 Crushing machine

  1. Cylindrical metal measures for measuring the sample.

Figure 3.5: Cylindrical metal measure







4.0 Methodology

a)    The cylinder of the apparatus is filled in 3 layers, each layer tamped with 25 blows of a tamping rod.
b)    The weight of aggregates is measured.
c)    The surface of the aggregates is then leveled and the plunger inserted.
d)     The apparatus is then placed in the compression testing machine and loaded at a uniform rate so as to achieve 40kN load in 10 minutes.
e)    After this, the load is released and crushed materials are removed.
f)     The sample is then sieved through a 2.36mm IS Sieve and the fraction passing through the sieve is weighed.
  
5.0 Result
AGGREGATE CRUSHING VALUE (BS 812 PART: 3)

Sample
Weight of size
(mm)
Weight if sample before crush (g)
Weight of sample after crushed (g)
Weight passing 2.36mm sieve (g)
A
14 – 10
2870
2207
663
B
14 – 10
2854
2238
616

Percent Wear (Ave)
22.34 %


Calculation

Sample A
 = Weight of sample before crush (g) - Weight of sample after crushed (g)
             =  2870 g – 2207 g
             = 663 g

Sample B
 = Weight of sample before crush (g) - Weight of sample after crushed (g)
             =  2854 g – 2238 g
             = 616 g


Average weight passing 2.36mm = 663 + 616
                                                                   2
                                                          = 639.5 g

Average weight before crush = 2870 + 2854
                                                                 2
                                                    = 2862 g

Percent wear (ave)

x 100 %
 
            = Average weight passing 2.36mm
x 100 %
 
               Average weight before crush
            = 639.5
               2862
            = 22.34 %
              





6.0 Discussion

a)    Sample can expel from the mould because the mould not closed mould can affected the error measuring reading.


b)    Heavy crushing mould and machine may not relevance to do the work outside the laboratory.

c)    The crushing machine is damage and can’t do the experiment.

d)    Balance of 3kg minimum capacity are not achieving at this experiment.



7.0 Recommendation

a)    Upgrading the crushing mould to high collar mould to avoid the aggregate to expel from the mould and affected the reading.

b)    These experiments are done at the laboratory after taking the aggregate sample from sites.

c)    Consistence maintenance needs to do to the machine to avoid this kind of problem.

d)    Sample need to be taken double from the balance of 3kg minimum capacity to achieve the 3kg balance.


8.0 Conclusion

From the experiment, we get average percent wear are 22.34% still not exceeding JKR’s standard, <30%. So we can conclude that the aggregate crushing value provides a relative measure of the resistance of an aggregate to crushing under a gradually applied compressive load. The aggregate are mild tough to have the resistance pressure under traffic wheel loads such as car, lorry, motorcycle and etc. These aggregate have the stability of the pavement structure. It’s because the strength of coarse aggregates can effect the capability of the pavement to sustain.






9.0 Reference:


a)    Civil Engineering Portal. Aggregate Crushing Value Test. 1(1): [7 screen]. Available from: URL: http://www.engineeringcivil.com/aggregate-crushing-value.html


b)    Aggregate Crushing Value Apparatus. 1(1): [7 screen]. Available from: URL: http://www.thetestequipment.com/aggregate-crushing-value-apparatus.html


c)    LYS. Aggregate Crushing Value Test (BS 812: Part 3). Editted October 28, 2010.  1(1): [8 screen]. Available from: URL: http://scienceray.com/technology/aggregate-crushing-value-test-bs-812-part-iii/

d)    Aggregate Crushing Value. 1(1): [8 screen]. Available from: URL: http://civil-online2010.blogspot.com/2010/02/aggregate-crushing-value_10.html

e)    Muniandy R., Radin Umar Radin Sohadi. Highway Materials, A Guide Book For Beginners. University Putra Malaysia: Penerbit Universiti Putra Malaysia; 2010.

f)     Paul H.W., Karen K.D. Highway Engineering [Seventh Edition]. USA: John Wiley & Son; 2003.









2 comments:

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