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Concrete Temperature Calculator — ACI 305R / 207.2R Significance

Why cold mixing water pulls placement T down faster than cold aggregate — and what mass-concrete thermal cracking really costs.

Why this calc exists

Two temperature problems at a concrete pour: (a) fresh placement T too high — IS 7861-1 Cl 2.1 caps it at 40 °C because above this, water demand jumps, slump loss accelerates, and air entrainment collapses; (b) for mass concrete, the heat of hydration traps inside and creates a thermal gradient that cracks the section.

ACI 305R-10 Appendix A solves (a) with a mass-weighted placement-T formula using specific-heat ratios. ACI 207.2R §5.6 solves (b) with an adiabatic-rise exponential model and limits (peak T ≤ 70 °C, ΔT vs surface ≤ 20 °C). These are NOT IS-code provisions — they're international practice that ACI 207.2R / CIRIA C544 align with. The concrete temperature calculator handles both with both tab views.

Code references (with provenance)

  • ACI 305R-10 — Guide to Hot Weather Concreting. Appendix A: specific-heat-ratio placement T formula.
  • IS 7861-1 Cl 2.1 — When ambient exceeds 40 °C (or placement temperature will exceed 40 °C), hot-weather concreting per IS 456 Cl 14.1 applies; concrete shall reach the form at not more than 40 °C.
  • ACI 207.2R-95/2025 — Report on Thermal and Volume Change Effects on Cracking of Mass Concrete. Peak T ≤ 70 °C, ΔT ≤ 20 °C.
  • ACI 207.2R — Indian standard on mass concrete, concordant with ACI 207.2R.
  • CIRIA C544 — UK mass concrete practice (similar limits).

Worked: Pune summer pour + 2.5 m thick raft

Placement T (Tab A): ambient 38, aggregate 42, cement 75, mixing water 28, 1900/400/160 kg/m³; num = 0.22·(42·1900 + 75·400) + 28·160 = 0.22·121500 + 4480 = 26730 + 4480 = 31210; den = 0.22·2300 + 160 = 666; T = 31210/666 ≈ 46.8 °C — exceeds ACI 305R limit. With crushed ice replacing 30 L of water: ~38 °C, in ACI band.

Adiabatic rise (Tab B): 400 kg/m³ OPC, 2.5 m thick raft, placing T 30. T_ult = 90·400/(2400·0.96)·4.184 ≈ 65 °C theoretical; retention 0.90; peak rise ≈ 58 °C; peak T ≈ 88 °C — exceeds 70 °C limit. Switch to 30 % fly ash → T_ult 52, peak rise 47, peak T 77 — still over. Try 50 % fly ash + low-heat cement → peak T 65 °C.

Field notes (what trips people up)

  • Cooling the water is the most efficient lever. The 0.22 coefficient in the formula means cement+aggregate count for 1/5 of the heat capacity that water does. Cooling 1 kg of mixing water by 10 °C removes 5× more heat than cooling 1 kg of aggregate by 10 °C.
  • Mass concrete isn't just 'big pours'. ACI 207.2R defines mass concrete as any pour where the heat of hydration cannot dissipate fast enough to keep the thermal gradient below the cracking threshold. This can be a 600 mm thick slab in hot weather, not just dams.
  • ΔT vs surface is the cracking limit. Peak T can be 80 °C if the section cools uniformly over months. The 20 °C ΔT limit is about gradient-driven cracking within days of placement — this is the more practical concern.
  • Embedded cooling pipes. For very mass pours (> 2 m thick raft in hot climate), embedded HDPE pipes with chilled-water circulation can pull 30–50 °C out of the core. Required for some dam and nuclear projects; uncommon in commercial buildings.

Worked example

Site: IT park basement raft, 80 × 60 × 1.5 m, M30, August Pune pour.

Without intervention: T_ult 60 °C × retention 0.75 × (1 - e^(-0.5·28)) = ~45 °C rise → peak T 75 °C, exceeds 70 °C.

With 30 % fly ash + chilled water: T_ult 49 °C × retention 0.75 = 37 °C rise → peak T 67 °C, ΔT ~28 °C (still high — add surface insulation immediately after striking).

FAQ

What if my placement T is 42 °C?

Above IS 7861-1 Cl 2.1 limit. Either cool the mix (ice, chilled water, chilled aggregate) or schedule a cooler time of day. Concrete placed at 42 °C loses 5–10 % of 28-day strength vs same mix at 30 °C.

Is the adiabatic formula exact?

No — it's a single-exponential approximation. Real concrete has multi-stage hydration kinetics (silicate peak, aluminate peak). For final verification of critical mass pours, use FEM (MIDAS, LUSAS, ANSYS) or specialised software.

Does the calculator handle steel fibres or lightweight aggregate?

No — the heat of hydration and specific heat assumptions are for normal-weight OPC-based mixes. Lightweight aggregate has different thermal properties; steel fibres add negligible heat but reduce thermal conductivity.

Related reading & tools

  • ../calculators/concrete-temperature.html — Concrete Temperature calculator
  • hot-weather-concreting.html — Hot Weather Concreting (blog)
  • calc-evaporation-rate-significance.html — Evaporation Rate Significance
Indicative tool — not a substitute for engineering judgement. Results are computed from formulae and reference values cited to Indian Standards and other published codes as named on this page, using nominal default assumptions; clause and table references are given in good faith for study and preliminary checks. Always verify the current edition and amendments of any cited standard in the BIS catalogue before relying on it. Final mix proportions, structural checks and construction decisions must be confirmed by a qualified engineer against the project design brief, drawings and site conditions. ConcreteInfo accepts no liability for design, procurement or construction decisions taken on the basis of these tools. Code references & rights: Indian Standards are the property of the Bureau of Indian Standards (© BIS) — official PDFs at bis.gov.in. ACI references are copyrighted by the American Concrete Institute — official documents at concrete.org. CIRIA references are copyrighted by the Construction Industry Research and Information Association. Shared in good faith as technical reference for the civil engineering fraternity — always verify against the official publication.