1.0 OBJECTIVE ο·
To determine the aggregate crushing value (ACV) by compressive testing machine.
2.0 INTRODUCTION The aggregate crushing value is the value which is mostly used in the design of the pavement of the road because it gives the crushing strength of the aggregate. Other than aggregate crushing value there are other parameter required in the design and these include; the elongation, flakiness index and the Californian bearing ratio (CBR) of the aggregate. Thus for this laboratory report these are not emphasized because their tests were not conducted. The aggregate crushing value is defined, as a ratio of the weight of fines passing the specified IS sieve to the total weight of the sample expressed as a percentage. The aggregate crushing value is a value which indicates the ability of an aggregate to resist crushing. The lower a figure the stronger the aggregates that is the greater its ability to resist crushing. 2.1 THEORY Granular base layers and surfacing are subjected to repeated loadings from truck tires and the stress at the contact points of aggregate particles can be quite high. Aggregate 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 aggregate is assessed by crushing test. The aggregate 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. These crushing tests can reveal aggregate properties subject to mechanical degradation and also indicate the magnitude of the problem for design purposes. The aggregate crushing value is found by the use of the following equation; Aggregate crushing value (ACV) =
π€πππβπ‘ ππ πππππ ππππππππ‘π πππ π πππ 2.5ππ πΌπ π πππ£π πππ‘ππ π€πππβπ‘ ππ π‘βπ π πππππ ππ ππππππππ‘π
Γ 100%
3.0 EQUIPMENT ο· An open steel cylinder of nominal 150mm internal diameter with plunger and base plate. (see Figure 1 below) ο·
A straight taping metal rod of circular cross-section 16mm diameter and 600mm long.
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A cylindrical metal measure for measuring the sample having an internal diameter of 115mm and an internal depth of 80mm.
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An electric scale balance with a maximum capacity of 60kg.
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A compression testing machine with a capacity of 72000kg force.
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BS test sieves of size of 12.7 mm, 9.52mm and 2.5mm. (see Figure 1 below)
Figure 1: Aggregate Crushing Machine (left). Metal rod and open steel cylinder with plunger and base plate (right).
4.0 PROCEDURE 1. The aggregate (see figure 2 above) passing the 12.7mm sieve and retained on the 9.25mm sieve were put in the cylindrical measuring cylinder and poured into the test cylinder as different layers. 2. The cylinder test apparatus was put on the base plate and the test sample (aggregates) added in two layers, each subjected to 25 strokes from the tamping rod, distributed evenly over the surface of layer and dropping from a height approximately 50mm above the surface of the aggregate. 3. The surface of the aggregate was then carefully leveled and the plunger inserted so that it rest horizontally on the surface.
4. The apparatus with the test sample and plunger was placed between the platens of the testing machine and loaded it at a uniform rate so that the required force of 72000kg force was reached. 5. After the required load was reached, the apparatus was released and the crushed materials were removed by holding the cylinder over a clean tray and hammering on the outside until the particles of the sample were disturbed to enable the mass of the sample to fall freely on to the tray. 6. The crushed sample on the tray was then sieved through a 2.5mm test sieve until no further significant amount passed, the mass that passed the 2.5mm was weighed and the aggregate crushing value determined. 7. Step 1 to step 7 was repeated for the second sample of the same aggregate and the average aggregate crushing value determined.
5.0 DATA COLLECTION AND ANALYSIS Table 1: results of sample 1 and sample 2
Total weight of dry sample
Sample 1
Sample 2
3172.8
3107.4
1167.8
1261.7
36.81
40.60
taken = W1 (g) Weight of portion passing 2.5mm sieve = W2 (g) Aggregate Crushing Value (%) Aggregate
Crushing
Mean
38.71
value (%)
5.1 Sample calculations 1167.8
Sample1. Aggregate Crushing Value (ACV) = 3172.8 Γ 100% = 36.81% 1261.7
Sample2. Aggregate Crushing Value (ACV) = 3107.4 Γ 100% = 40.60%
Aggregate Crushing Value (ACV) =
=
(ACV for Sample A + ACV for Sample B)
33.81+40.60 2
= 38.71%
2
6.0 DISCUSSION During the laboratory the dry test was conducted, that is, the aggregate was in surface dry condition. The procedure was followed up to giving results of the tests. These tests are a measure of the crushing properties of the aggregate. Two tests were carried out for the aggregate crushing value (ACV) and the mean obtained gave the crushing value. This was to cushion the errors which might have been realized during the exercise. The aggregate value that was obtained is used for assessing if the material is worth for the road construction (in this case, pavement construction). In road construction standard limits (BS EN 13043) are pegged which are used for these assessments, that is, the aggregate crushing value for cement concrete pavement shall not exceed 30% and, aggregate crushing value for wearing surfaces shall not exceed 45%. This is according to standards. From the results obtained above it is therefore important to mention that the crushing value (38.71%) is confirming that the aggregates are capable to be used in both cement concrete pavement and wearing surfaces. In other words low aggregate crushing value (ACV) indicates strong aggregates, meaning crushing fraction is low. And the opposite is equally true that high crushing value indicates weak aggregates implying crushing fraction is high. This is an indirect measure of crushing strength. All in all, the aggregate crushing value helps the highway engineers to ascertain the suitability of aggregates for various types of pavement components. The ACV is a basis for designing the pavement structure of the road way thereby helps to determine the quality, life span (durability), skid-resistance, performance and safety of the road way. Thus, the quality of the aggregate crushing value should not be compromised.
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 is affected therefore maintenance needs to be done to the machines 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 The experiment was a success because the objective was achieved. The ACV of the aggregate was found to be approximately 38.71% and it was concluded that it was not suitable to be used in the highway road construction as it was above the given ACV limit of 30%. It was also concluded that it is important to carry out the ACV test before choosing an aggregate for road construction because it helps in knowing the toughness and abrasion resistance of the aggregate.
9.0 REFERENCES ο·
Muniandy R., Radin Umar Radin Sohadi. HIGHWAY MATERIALS, A GUIDE BOOK FOR BEGINNERS. University Putra Malaysia: Penerbit Universiti Putra Malaysia; 2010.
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AGGREGATE CRUSHING VALUE TEST (IS: 2386-PART-4)
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Ms R.Mulanga (2015), CEE 4612 LECTURE NOTES, (PAVEMENTS), University of Zambia, Lusaka, Zambia.
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Bullas J.C. and West G. (1991), Specifying clean, Hard and Durable Aggregate for Bitumen Macadam Roadbase, Research Report 284, Transport and Road Research Laboratory, Department of transport (British).
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Millard, R.S. (1993). Road Building in the tropics. Transport Research Laboratory stateof-the-art Review 9, HMSO, London.
TABLE OF CONTENTS 1.0 OBJECTIVE ........................................................................................................................... 1 2.0 INTRODUCTION................................................................................................................... 1 2.1 THEORY ...................................................................................................................... 1 3.0 EQUIPMENT .......................................................................................................................... 2 4.0 PROCEDURE ......................................................................................................................... 2 5.0 DATA COLLECTION AND ANALYSIS ............................................................................ 4 5.1 Sample calculations ...................................................................................................... 4 6.0 DISCUSSION .......................................................................................................................... 5 7.0 RECOMMENDATION .......................................................................................................... 5 8.0 CONCLUSION ....................................................................................................................... 6 9.0 REFERENCES ........................................................................................................................ 6
