Formwork Striking, Loading & Full Cure Estimator 2026
Concrete curing maintains moisture and temperature conditions enabling cement hydration achieving design strength and durability. Initial set occurs 2-6 hours post-placement with formwork striking at 5-15MPa depending on element type and conditions. Full 28-day strength represents 99% design capacity though hydration continues years producing marginal gains beyond specification testing period.
Temperature accelerates hydration doubling rate every 10°C with 30°C achieving 80% strength in 3 days versus 14 days at 5°C. Moisture retention through wet curing, membranes, or polythene sheeting prevents plastic shrinkage cracking and surface carbonation. Relative humidity below 85% accelerates drying increasing autogenous shrinkage risk requiring extended curing periods in arid conditions.
Slabs strike formwork 7MPa (5-7 days 20°C) enabling backfilling while beams/columns require 10MPa (7-10 days) preventing buckling. Walls conservative 5MPa due restraint cracking risk with precast elements 15MPa ensuring lifting safety. Minimum 7-day wet curing prevents surface weakness regardless element type maintaining durability gradient from exterior to core.
Optimal 10-25°C curing produces uniform hydration with below 5°C requiring heated enclosures or accelerators extending striking 2-3x. Above 30°C risks thermal cracking mitigated through low-heat cement, cooling pipes, or night pouring maintaining temperature differentials below 20°C throughout mass concrete elements.
Wet curing utilises hessian, polythene sheeting, or ponding maintaining 95%+ surface moisture for 7 days achieving optimal strength gradient. Curing compounds form 0.5mm membrane reducing evaporation 85% suitable exposed vertical surfaces. Insulating blankets prevent frost damage in winter maintaining 5°C minimum through initial 48 hours critical setting period.
OPC concrete achieves 40% strength day 1, 70% day 7, 90% day 28 with rapid-hardening reaching equivalent milestones 2 days earlier. GGBS/PFA blends slow early gain requiring extended striking despite superior 56-day performance. Maturity methods quantify cumulative hydration predicting strength independent temperature variations ensuring programming reliability.
Curing verification utilises temperature-matched cubes confirming strength development matches site conditions. Surface hardness testing rebound hammer assesses readiness for loading preventing premature failures. Moisture meters verify internal RH below 75% prior decoration preventing adhesion failures and efflorescence.
| Element | Striking (MPa) | 20°C OPC | 10°C OPC |
|---|---|---|---|
| Slab | 7MPa | 5-7 days | 10-14 days |
| Beam/Column | 10MPa | 7-10 days | 14-21 days |
| Wall | 5MPa | 4-6 days | 8-12 days |
| Precast | 15MPa | 3-5 days | 7-10 days |
| Strength | OPC 20°C | Rapid 20°C | GGBS 20°C |
|---|---|---|---|
| Day 1 | 40% | 60% | 25% |
| Day 7 | 70% | 85% | 55% |
| Day 28 | 99% | 100% | 95% |
BS 8110/CP 110 requires 7 days moisture retention preventing surface carbonation and strength gradient.
Hydration rate halves below 20°C doubling required curing period for target strengths.
5-7 days 20°C enables backfilling without deflection or cracking risk.
7-10 days prevents buckling during formwork removal and propping.
Wet curing essential first 7 days achieving optimal durability gradient.
Specification testing though hydration continues producing marginal gains.
Slabs 7MPa (5-7 days 20°C), beams/columns 10MPa (7-10 days), walls 5MPa (4-6 days). Maturity methods predict strength independent temperature ensuring safe striking preventing construction delays and structural failures.
Minimum 7 days wet curing using hessian, polythene, or compounds preventing plastic shrinkage and carbonation. Exposed vertical surfaces utilise membrane curing reducing labour while achieving equivalent performance.
10°C below 20°C doubles curing time, 10°C above halves time risking thermal cracking. Winter concreting utilises heated enclosures maintaining 10°C minimum optimising programming and strength development.
70% strength day 7 enables normal construction loading with full design capacity day 28. Prestressed transfer 50-60% fck typically day 5-10 preventing tendon slip during jacking operations.
Insulating blankets or heated enclosures maintain 5°C minimum preventing frost damage. Accelerators enable cold weather concreting reducing striking times despite low ambient temperatures.
Surface dry 14-28 days depending thickness/humidity with internal RH <75% preventing adhesion failure. Moisture meters verify readiness avoiding blistering and paint peeling issues.
Rapid-hardening reaches milestones 2 days faster, GGBS/PFA slower early gain requiring extended striking. Site trials establish mix-specific strength development curves guiding construction sequence.
Temperature-matched cubes confirm strength development with rebound hammer assessing surface hardness. Moisture meters verify internal conditions prior decoration ensuring long-term performance.
For curing compounds, visit BASF Construction | Sika UK | For standards, check Concrete Society