Last edited 08 Jul 2021




[edit] Introduction

Curing is a term applied to the chemical process that describes a change in the state of materials, usually as they turn from liquid (or semi-liquid) to solid. It can apply to cement, concrete, adhesives, plasters, thermosetting plastics and other materials. It usually has important implications for strength development and so its effects must be considered carefully in the construction industry.

[edit] Concrete

The curing time for cast-in-place concrete can be anything from three days to two weeks. The process involves an exothermic reaction, i.e heat is given off. Ensuring the correct conditions for curing requires protecting the concrete from both high and low temperatures.

If freshly-poured concrete is not cured properly, it may:

Both consequences could be catastrophic as cracks can allow the ingress of humidity and water which can cause corrosion of steel reinforcement or frost damage; while failing to reach its design strength will mean a weaker concrete than designed with potentially serious consequences.

[edit] Hydration

The strength of concrete depends on the reactions in its matrix and in particular on the growth of crystals. These are the result of the hydration process – the reaction between water and Portland cement. This process will continue almost indefinitely as long as there is water in the matrix. But a deficiency in water content will mean the crystals will not develop as they should and the concrete will:

[edit] Temperature

Maintaining the correct temperature of the concrete is critical. It is currently thought that below 10°C sees a slow-down in hydration, while 4°C signals a virtual stop. In contrast, a temperature that is too high speeds up the exothermic reaction causing temperature differentials within the concrete that can lead to cracking. This causes weaker strength development as the matrix crystals have not developed as they should have.

[edit] Methods of curing concrete

Curing aims to control the rapid loss of moisture from the setting concrete, so the aim is to provide a seal to prevent or slow down the rate of water evaporation. However, methods differ according to the type of structure or curing requirement. Some of the more common curing methods include:

[edit] Curing time

The length of time for proper curing to take place will depend on specific conditions, national codes, etc. Flat concrete (e.g pavements, driveways, car parks etc) and structural concrete (e.g beams, columns, slabs, walls, retaining walls etc) typically require a seven-day curing time when temperatures are above 4°C. This usually allows the concrete to attain 70% of the specified compressive strength.

Curing time will depend on:

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