---
title: "Effect of temperature on compressive strength"
subject: "Concrete Technology and Masonry Structure"
chapter: 4
key: "semester_5/concrete_technology_and_masonry_structure:temperature-effect-strength"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/temperature-effect-strength
site: BCT Engineering
---

# Effect of temperature on compressive strength

Concrete Technology and Masonry Structure · Chapter 4: Properties of hardened concrete

- Asked in: 2067 Ashadh (old course), 5 marks
- Video: [Concrete Maturity | Concept and Application](https://www.youtube.com/watch?v=XTtNN8Ikfe4) — Giatec Scientific Inc.
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/temperature-effect-strength
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-4

## Question

How does temperature affect the compressive strength of concrete? Explain.

## Short answer

Higher casting/curing temperatures accelerate early strength but produce coarser pores, lowering 28-day and long-term strength. Lower temperatures slow strength gain but yield denser gel and higher long-term strength; freezing stops hydration and damages fresh concrete. Moderate temperatures (15–25°C) with moist curing are optimal.

## Answer

Temperature affects both the rate of hydration and the structure of the hydrated cement paste, and so affects strength.

#### Effect of casting (initial) temperature
- Higher temperature gives faster hydration and higher **early strength** (1 to 7 days).
- But the hydration products form quickly and are non-uniform, with a coarser pore structure, so the **28-day and later strength is lower** (a concrete cast at 40 °C may have 10 to 20% less 28-day strength than the one cast at 20 °C).
- Low casting temperature (5 to 10 °C) slows the early strength but results in a higher long-term strength, since the gel is more dense and uniform.

#### Effect of curing temperature
- Curing at a higher temperature (for example steam curing) raises the early strength but lowers the long-term strength (the crossover effect).
- Low curing temperature slows the strength gain; hydration almost stops near 0 °C to -10 °C, and if concrete freezes before it has 3.5 MPa strength, it suffers permanent damage.
- Temperature fluctuations and rapid drying cause thermal and shrinkage cracks.

#### Maturity
Strength depends on both time and temperature, which is expressed by the maturity $M=\sum (T+10)\Delta t$ (T in °C, t in hours).

| Temperature | Early strength | 28-day strength |
|---|---|---|
| High (above 35 °C) | High | Lower |
| Normal (20 to 27 °C) | Normal | Normal |
| Low (5 to 10 °C) | Low | Equal or higher after longer curing |
| Freezing | Hydration stops, damage | Lost |

Hence a moderate temperature (15 to 25 °C) with continuous moist curing is best.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. A concrete cast at high temperature typically shows:
   A. Higher early strength but lower 28-day strength
   B. Lower early strength and higher 28-day strength
   C. Higher strength at all ages
   D. No change in strength
   Answer: A. Fast hydration forms non-uniform products with coarse pores, lowering later strength. (Key point: High casting temp)

2. Why can low casting temperature (5-10 C) give higher long-term strength?
   A. Hydration is faster and complete
   B. Less water is needed
   C. Slow hydration gives a denser, more uniform gel
   D. Unhydrated cement increases strength
   Answer: C. Slow formation of gel yields a denser uniform structure. (Key point: Low casting temp)

3. What is the key concern if concrete freezes?
   A. Strength increases at once
   B. Permanent damage if it freezes before reaching about 3.5 MPa
   C. Hydration speeds up
   D. Only surface colour changes
   Answer: B. Hydration nearly stops near 0 to -10 C, and early freezing causes permanent damage. (Key point: Freezing)

4. Maturity is expressed as:
   A. M = T x t only
   B. M = sum of (T - 10) x delta t
   C. M = w/c x T
   D. M = sum of (T + 10) x delta t
   Answer: D. Maturity combines temperature and time: M = sum (T+10) delta t. (Key point: Maturity)

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