Tender Build-Up and Cube Nonconformity for a Concrete Frame
An estimator is pricing a small reinforced-concrete frame. The measured quantities are 180 m³ of C30/37 concrete, 18 t of reinforcement and 1,350 m² of formwork. Supply rates are €96/m³ for concrete, €880/t for reinforcement and €23/m² for formwork. Separate labour and plant allowances are €35/m³ for placing concrete, €320/t for fixing reinforcement and €14/m² for formwork. Preliminaries are 8% of direct cost, overheads and profit are 12% of direct cost plus preliminaries, and contingency is 5% of the resulting subtotal. The client's budget is €125,000. On a previous similar project the concrete cubes gave a mean of 31.5 MPa and an individual result of 26.0 MPa against C30/37. The tender clarification requires the concrete to conform to the specification.
1. Build up the direct cost and tender sum, showing each stage of the calculation.
Read the worked answer
Concrete supply: 180 × 96 = €17,280. Concrete placing: 180 × 35 = €6,300. Reinforcement supply: 18 × 880 = €15,840. Reinforcement fixing: 18 × 320 = €5,760. Formwork supply: 1,350 × 23 = €31,050. Formwork labour: 1,350 × 14 = €18,900. Direct cost = 17,280 + 6,300 + 15,840 + 5,760 + 31,050 + 18,900 = €95,130. Preliminaries = 8% × 95,130 = €7,610. Subtotal = €102,740. Overheads and profit = 12% × 102,740 = €12,329. Subtotal = €115,069. Contingency = 5% × 115,069 = €5,753. Tender sum = €120,823.
2. Compare the tender with the budget and identify the largest cost risk.
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The tender sum of about €120,823 is below the €125,000 budget by about €4,177, or 3.3%. That is a thin margin, not a comfortable one. Formwork is the largest element: supply plus labour is €49,950, or 52.5% of direct cost. A 10% increase in formwork cost would add about €5,000 and eliminate the margin. Concrete is €23,580 and reinforcement is €21,600 in total. The main commercial risk is therefore formwork productivity and repetition, followed by reinforcement fixing. The estimator should check the formwork cycle assumed, the number of reuses and the labour output before treating the 3.3% margin as adequate.
3. Assess the cube results and state how they should affect the tender or clarification.
Read the worked answer
C30/37 requires a characteristic cube strength of 37 MPa. A mean of 31.5 MPa and an individual result of 26.0 MPa cannot demonstrate conformity; the individual value is below the usual lower limit of 37 - 4 = 33 MPa. These results are from a previous project, so they are not proof that this project will fail, but they are a clear warning. The tender should not absorb the risk silently. Clarify the conformity criteria, require the supplier's recent control data, and allow for identity testing or a stronger mix if necessary. If the client insists on full conformity, price the testing and possible remediation; do not rely on the 5% contingency to cover a systemic concrete problem.