Concrete, Formwork and Reinforcement Measurement
These three are separate work sections and must never be merged: concrete is cubic, formwork is superficial, reinforcement is by mass. Most exam marks in this domain turn on keeping the three apart and applying the deduction rules of each independently.
Concrete
- Measured net as fixed in m³. No deduction is made for reinforcement or for voids below the method's threshold; larger voids are deducted.
- Classify by grade, by element (foundations, beds, walls, suspended slabs, columns) and by placement method such as pumped or placed by crane.
- Joints, curing and surface finish are described; fair-faced work is an 'extra over' the ordinary finish.
Formwork
- Measured to the area of concrete in contact, in m², classified by surface: soffit, sides, sloping, curved; and by finish: ordinary, fair faced, struck or left in.
- Wrought formwork to edges and reveals is linear; small openings are ignored under the threshold, larger ones deducted.
- Formwork is never deducted for reinforcement, only for openings above the threshold.
Reinforcement
- Measured in tonnes (sometimes kg) by bar diameter, with cutting, bending, laps, tying wire, spacers and rolling margin included in the rate.
- Fabric is measured in m² with the mesh designation or mass per m² stated.
Worked example
A suspended slab 6.000 × 4.000 m, 200 mm thick, with one 1.000 × 1.000 m opening. Concrete = 6.000 × 4.000 × 0.200 = 4.800 m³, less the opening 1.000 × 1.000 × 0.200 = 0.200 m³, giving 4.600 m³. Soffit formwork = 24.000 − 1.000 = 23.000 m², because the opening exceeds the threshold. Edge formwork = perimeter 20.000 m × 0.200 m = 4.000 m². Reinforcement at 100 kg/m³ of concrete = 4.600 × 100 = 460 kg = 0.460 t. The opening is deducted from both concrete and soffit; edges are perimeter × depth, not area of slab.
Traps that cost marks
- Deducting the volume of reinforcement from the concrete.
- Measuring formwork to the top surface of a slab instead of the soffit and edges.
- Counting laps separately after they have been included in the rate.
- Mixing kg and t in the same reinforcement item.
- Forgetting that fair-faced concrete needs both the base item and the extra over.