Quantity Surveying

Homework question?

I'm sure you are as competant with a calculator as I am but consider that material content is variable (you need less for 10mm than you do for 15mm) labour is possibly variable (it will probably take less time) plant is unlikely to be variable and, knowing the bosses I've worked for profit is unlikely to reduce.

The variances are all down to the actual job of laying asphalt.

Sir actually, i am not sure myself also. I went for an interview for the post of quantity surveyor and i found this question in the written test. There may be a certain procedure to get the rates for various thicknesses.

Assuming all else but thickness being equal, it comes to 10.33/sq. m for 10mm thickness

Sir!

10.33 / S.M Can be calculated only from the given rate, what will be the role of other given data???

I also calculated like this but the reply was same as i am asking from u.

15mm thk asphalt

materials: 36% = 5.58 Dh

labour: 26% = 4.03 Dh

plant & equipment: 14% = 2.17 Dh

total direct cost = 11.78 Dh

profit: 24% = 3.72 Dh = 31.58% of direct unit cost

10mm thk asphalt

materials: 5.58(10)/15 = 3.72 Dh (materials cost is calculated by volume)

labour: 4.03 Dh (capability of labour is per square meter, same area, same cost)

plant & equipment: 2.17 Dh (capability of plant/equipment is per square meter, same area, same cost)

total direct cost = 9.92 Dh

profit: 31.58% of direct unit cost = 3.13 Dh

UNIT COST = 9.92 + 3.13 = 13.05 Dh

I hope the rest of your interview went well .

To be fair, I've known sharp inspectors with 25+ years experience that have had difficulty in this concept. Chances are good that your interviewers will have it wrong if they haven't been paving contractors.

The 'correct' answer as far as your owner goes is 10.33, always the cheapest.
As a former paving contractor, I would like 13.05 to be my 'correct' answer.

Target audience is always important with an estimate; Understanding the elements is how you defend it. But any answer that can be defended is correct, until the actual bid shows it to be wrong.

All that being said I present 12.10/m2 as my 'correct' answer.

Pro-rating only works when the production can be the same. It is important to understand that the paving and grading contractor will generally work and measure production in tonnes per hour.

Consider Asphalt ~ 2.4 tonne/m3, so the given cost of 15.5/m2 is actually 430 Dirhams/tonne of asphalt placed at 15mm thickness.

The given cost breakdown in Dirhams/tonne:
Material 155.00 (36%)
Labour 111.94 (26%)
P&E 60.28 (14%)
DIRECTS 327.22
Profit 103.33 (24% of total, 31.6% of directs)
TOTAL 430.56

Looking at paving at the same production, say 50 tph, the surface area to be covered is radically different.
50tph @ 15mm = .036 tonne /m2 yields 1389 m2/h (Same area on 10mm is 33 tph)
50tph @ 10mm = .024 tonne/m2 yields 2083 m2/h

This same rate of production does not hold at these thin depths, and you can see that 50% more area would have to be covered in the same time at 10mm.

The assumption that the labour production /m2 is fixed is not bad at these skinny thicknesses - but the cost impact is underestimated. This results in production being 66% of, or takes 1.5x longer than, the 15mm thickness for the same area. Or, if 500 tonnes take 10 hrs at 15mm, the same area at 10mm takes 10hrs, and uses only 333.33 tonnes - Same labour, less material, higher placed unit material cost.

Hold the costs for Materials & P&E fixed, Labour increases 1.5x and like any good contractor, the Profit margin will be held.

Material 155.00 (30.7%)
Labour 167.91 (33.3%)
P&E 60.28 (12.0%)
DIRECTS 383.19
Profit 121.01 (24% of total, 31.6% of directs)

TOTAL 504.20 /tonne

10mm @ 0.024 tonne/m2 = 12.10 Dirhams/m2

All this being said, this isn't taking into account the impact that reduced production has on the crew equipment that is roled into the P&E. And the biggest unmentioned variable in this is haul. Regardless, taking P&E as fixed is reasonable in this case.

I'm curious about the application. I have not seen asphalt mixes (other than chip seal topping on existing roads) that will stand up under regular vehicle loads at those thicknesses. Usual rule of thumb for minimum asphalt thickness for best compaction is 1.5x largest nominal aggregate size. We would only top-lift municipal pathways for foot and bicycle traffic with a mix so fine.

NOTE:
Again, pro-rating only works if the tonne per hour production is the same. At depths 40mm to 100mm+ the production will be all about tonnage placed, and the labour /m2 will have no impact, an experienced crew in a municipal environment can place and finish 1000-1600 tonnes per shift no matter what depth (over 40mm), highways and runways 2000+ per paver (Calgary Alberta Averages - Make sure you inquire locally to confirm, everywhere is different) With skim patch mixes at this depth, production is generally by hand @ 8 - 15 tph.

It is also interesting that Placed Cost / Unit Material is not linear when graphed. Take a fixed crew cost $/hour (Say $500/hr for a paving machine spread and 10man crew), and graph for $/tonne (Y) against productions(X) of 20 tph to 400 tph (25 $/tonne to 1.25 $/tonne). You'll find incremental changes at slower productions have a much greater impact to your cost than you may realize or be aware.

I know this is rather verbose - but it is a big part what I did for the last seven years. Though now Estimation Manager for an Oil and Gas EPCM, I still have a soft spot for asphalt (between my ears).

Hi, engrnoshad!

Since you already have percentages and the size of the roadway, you can calculate the cost of materials for the roadway by sending an enquiry to the providers of the roadway materials. It's set as a 36% figure. Use it to calculate the balance of the costs by multiplying that cost by 2.78 to discover 100% of the cost of the finished roadway.

Labour will be 26% of the finished cost you have just calculated. Plant & equipment will be 14%, and "profit" will be 24%.

That is, if you believe these figures. In my experience, however, your 'profit' will be nowhere near 24% based upon these bare-bones notes. You probably need to add a minimum additional 500% on top of your calculations to achieve any profit whatsoever, because your incidentals will eat up that 24% for breakfast. Have you considered the cost of liability insurance? Workers' compensation payments based upon a percentage of the expected salary schedule? Overtime runs? Inflation in leasing costs and materials provision? Equipment transportation? Grading? Bridges? Your own administration staff and consulting engineers? The cost of plans? Irrigation?

If you can afford it, I would suggest a certified quantity surveyor well-versed in the road-building business to give you the real cost breakdowns. Be certain to ask the QS what kind of padding you should apply to the bid to ensure a profit based upon over-cost running during the project.

Mark