The Setting Process
At a fundamental level, concrete is made by combining water, cement and aggregate. The water and cement first bind together in a chemical process known as hydration, eventually creating a tough mass. This mass then adheres to the aggregate contained in the mixture, and concrete is formed. Over a period of time – usually a month – the concrete hardens as the setting process progresses and its workability diminishes.
Initially, concrete is able to be poured and moulded in place, which makes this type of building material incredibly useful for many applications. However, concrete is a time-sensitive material and any attempt to rework setting concrete will weaken the concrete’s structure and, therefore, its strength. It is only when a cement mixture has fully set that its durability and robustness will be fully realised.
The Constituents of Concrete
The ingredients used in concrete will be determined by the type of concrete to be created, with various properties, such as density and strength, being associated with certain ingredients. Concrete is mostly made up of cement, which can contain different constituents, such as slag, fly ash and asphalt, the latter of which is the most commonly used.
Water and aggregate are the other main ingredients. Aggregate has a coarse consistency, combining materials such as chunks of limestone or gravel and fine sand. Water is introduced to react with the cement and create a semi-liquid mixture that can be poured and shaped. There are also other ingredients that are often included to reinforce or achieve a certain property, such as water resistance.
Time Periods for Concrete Hardening
Generally, concrete will harden over the first two hours to a point where any re-work done will damage the concrete’s structure. Over three days, concrete will have strengthened to be of some use, although certain ingredients will affect this strengthening time period. After a month, most of a concrete’s structure (90%) will have reached final strength.
While a month is sufficient time to fully strengthen the majority of a concrete’s structure, the hardening process will continue for many years after. This is because concrete contains calcium hydroxide, which converts to calcium carbonate through the absorption of CO2, and it is this process that continues to harden concrete for years after the laying date.
Factors that Affect Concrete Setting
There are many factors that can affect the way concrete sets, including the weather. Hot conditions can speed up the chemical reactions taking place inside concrete, reducing the time it takes to set. Moisture also affects the setting process. Without the required levels of moisture during setting, concrete can have reduced durability and strength.
Moisture is also a concern when wind levels increase the evaporation of water during the placing and setting of concrete, with complications such as tensile stresses becoming a potential problem. As has already been stated, certain ingredients will affect the setting process as well, with some promoting high-strength early on through faster hydration.
All Mix Concrete are the leading concrete suppliers of readymix and volumetric concrete in the North West, providing high quality materials to customers throughout the region, including Manchester, Warrington & Liverpool. Get in touch today to find out more.