Management and Estimating
Management and Estimating covers construction planning, CPM and PERT, cost control, quantity take-off, rate analysis, contracts, and safety. The exam tests network calculations and material quantity estimates.
Core rules
- In CPM, the critical path has zero total float; total float = LS − ES = LF − EF.
- PERT expected time t_e = (o + 4m + p)/6, where o, m, and p are optimistic, most likely, and pessimistic times.
- Cost slope = (crash cost − normal cost)/(normal time − crash time); crash activities on the critical path with the lowest cost slope.
- For nominal concrete, dry volume = wet volume × 1.54; cement volume = dry volume × cement part/sum of mix parts.
- Rate analysis combines materials, labour, plant, overheads, and contractor profit.
Worked example
For 1 m³ of M20 nominal mix 1:1.5:3, dry volume = 1 × 1.54 = 1.54 m³. Sum of parts = 1 + 1.5 + 3 = 5.5. Cement volume = 1.54 × 1/5.5 = 0.28 m³. At 1440 kg/m³, cement = 0.28 × 1440 ≈ 403 kg. Add wastage separately if the specification requires it; do not mix dry-volume factor with wastage factor.
Traps that cost marks
- Using wet volume directly for cement content.
- Confusing total float with free float.
- Crashing a non-critical activity and expecting project duration to fall.
- Forgetting overheads and profit in rate analysis.
Exam focus
Practise network float calculations, PERT expected time, cost-slope crashing, and material take-off for concrete and masonry.