9.1 Concrete Work
Explain how the following factors may affect unit rates for concrete work ;
• Whether ready mixed or site mixed concrete is used
• Whether concrete is reinforced
• Surcharges for part loads
• Location of mixing plant on site
• Type and size of mixing plant
• Method of transporting, hoisting, placing and compacting mixed concrete
• Cost of protecting and curing unset concrete
Operatives working with concrete receive additional payments for skill and responsibility.
Items of plant should be priced separately.
Concrete is usually measured in m3 Site Mixed Concrete
TQ 7
Calculate the cost of mixing a m3 of Grade 15 concrete on site using the following information ;
To produce 1m3 of mixed Grade 15 concrete requires ; 250Kg of cement at £80 per tonne
600Kg of sand at £10 per tonne 1200Kg of aggregate at £9 per tonne Waste say 5%
Concrete mixer all-in rate £2-50 per hour, output 2m3 per hour Labour rate £7.20 per hour
Labour out put 0.5m3 per hour Ready-Mixed Concrete
TQ 8
Calculate the cost per m3 for laying plain concrete 20N/mm2 in foundations over 300mm thick laid against faces of excavation.
Ready mixed concrete costs £49.00/m3
Waste say 5%
Labour output 1.00 hours/m3 Labour rate £7.20 per hour
SAQ 4
What will happen to the labour output if the concrete is laid in foundations 150mm thick?
Reinforcement is measured separately in bills of quantities. Would you expect the unit rate for laying reinforced concrete (excluding the cost of reinforcement) to differ from the unit rate for plain (unreinforced) concrete for similar items of work and if so why?
9.2 Reinforcement
Reinforcement may be bar type or mesh/fabric Waste
Bars are usually delivered to site already cut and bent, if this is the case then allow 1% for loss and damage.
If straight bars are to be cut and bent on site allow 5% for waste.
On complex reinforced concrete work steel fixers are usually paid a craft operatives rate.
When laying straight bars or mesh an enhanced labourers rate is usually paid.
Mesh reinforcement is sheet material therefore allowances have to made for general waste say 2.5% plus an additional allowance for laps. The percentage to allow for laps will depend on the lap specified e.g. 150mm side and end laps.
TQs 9-10
Sheets of mesh are approximately 4.80m x 2.40m if they are to be laid with 150mm side and end laps what % must be allowed for loss in cover due to the laps ?
Mesh reinforcement Ref. A193 in beds laid with 200mm side and end laps.
Calculate the rate per m2.
Mesh costs £14-00 per sheet
Labour 0.05 hours / m2 at £7.20 / hour
Allow say 20p / m2 for spacers and tying wire
9.3 Guide to Using this Student Learning Pack
Throughout this and the series of learning packs you will find, extensive notes on the various aspects of work you will be measuring followed by a series of three tasks, These tasks are
49 designed to increasingly develop your skills in the aspect of measurement covered by the learning pack, and will include, one basic task, which requires you to copy down a worked example, using the correct measurement layouts. The second task and third tasks form the second section of the class, where the class develops into a tutorial based
9.4 Concrete Works
As with groundwork, before looking at the calculation of unit rates we must understand that our final unit rate will be influenced by several variables.
Task One
In the box below, describe how you think the following factors would impact on cost.
When considering concrete there are two main methods of producing concrete:
1. Site mixed concrete 2. Ready mixed concrete
In addition to the method of concrete production when costing concrete work we must also consider concrete accessories including:
1. Formwork 2. Reinforcement
3. Operatives working with concrete usually receive additional payments for skill and responsibility
4. Items of plant concerned with concrete mixing and placing are usually measured separately.
9.4.1 Site Mixed Concrete
1. Ready mixed or site mixed concrete
2. Whether the concrete is reinforced or un-reinforced 3. Surcharges for part-loads
4. Location of site in reference to mixing plant 5. Type and size of mixing plant
6. Method of transportation, hoisting, placing and compacting mixed concrete
7. Protection of un-set and curing concrete
Calculate the cost of mixing one m3 of grade 15 concrete on site using the following information:
The production of 1m3 of grade 15 concrete requires:
• 250kg of cement at £92.70 / tonne
• 600Kg of sand at £17.25 / tonne
• 1200kg of aggregate at £18.02 / Tonne
• Waste allowance say 7.5%
In addition allow for:
• concrete mixer @ all – in rate of £3.00 / hr
• Labour rate @ £8.68 / hr
9.4.2 Ready Mixed Concrete
Calculate the cost per m3 for laying plain concrete 20N/mm2 in foundations over 300mm thick laid on or against earth or unbinded hardcore.
• Ready mixed concrete say £80.59 / m3
• Waste say 5%
• Labour output = 1.00hrs / m3
• Labour rate £8.68 / hr Questions:
1. How would the labour output be affected if the concrete is laid in foundations 150mm thick?
2. What would be the financial impact? (If any)
9.5 Concrete Reinforcement
Reinforcement is measured separately in bill of quantities. Would you expect the unit rate for laying reinforced concrete (excluding the cost of reinforcement) to differ from the unit rate for plain (unreinforced) concrete for similar items of work, if so why
Reinforcement maybe either bar reinforcement or mesh / fabric reinforcement.
Waste
Bars are usually delivered to site already cut and bent, if this is the case then allow 1% for loss and damage.
If straight bars are to be cut and bent on site allow 5% waste
On complex reinforced concrete work steel fixers are usually paid a craft operatives rate.
When laying straight bars or mesh an enhanced rate is usually paid.
51 Mesh reinforcement is sheet material therefore allowances have to be made for general waste, say 2.5% plus an additional allowance for laps. The percentage to allow for laps will depend on the lap specified e.g. 150mm side and end laps.
Qu 1.
Sheets of mesh are approximately 4.80m x 2.40m if they are to be laid with 150mm side and end laps what percentage must be allowed for loss in cover due to the laps?
Qu 2
Calculate the rate per m2 for laying mesh reinforcement Ref A193 in beds, laid with 200mm side and end laps.
Additional information
• Mesh costs £15.08 per sheet
• Labour 0.05hrs / m2 @ £8.68 / hour
• Allow say 20p / m2 for spacers and tying wire
• Waste on mesh 5%