Part 5 of 6 | Why both quantity and quality of water matter
A concise technical series for homeowners, clients and construction enthusiasts
Water appears to be the simplest ingredient in concrete. On a construction site it may even seem too ordinary to deserve much attention.
In reality, water deserves careful consideration because both its quantity and quality can influence the performance and long-term durability of concrete.
For the homeowner, this is particularly important because water is often readily available at a construction site. Availability, however, does not automatically mean suitability.
Why is water needed?
Water performs two essential functions in concrete.
First, it participates in the chemical reactions that allow cementitious materials to hydrate and harden.
Second, it provides the required workability for handling fresh concrete.
These two functions need to be balanced carefully. Too little water can make concrete difficult to handle and can interfere with proper hydration. Too much water can leave additional pores in the hardened concrete and adversely affect strength and durability.
The water-cement relationship
At a basic level, the relationship between water and cementitious material is one of the most important considerations in concrete.
When excess water is present, some of that water eventually leaves the concrete, leaving behind capillary pores. Greater porosity can make concrete more vulnerable to the movement of water and aggressive substances.
This is why the common practice of adding “a little more water” to make concrete easier to work should not be treated as harmless.
Uncontrolled addition of water can change the intended properties of concrete and may adversely affect strength and durability. Any adjustment to a designed concrete should be made under appropriate technical control.
Water quality - a major durability consideration
The quantity of water is only one side of the story.
Water quality is one of the important criteria influencing the long-term durability of concrete.
Water used in concrete should be suitable and should not contain harmful substances in quantities that can adversely affect the concrete. This becomes especially important in coastal and saline environments.
What about saline water?
Saline water contains dissolved salts. It should not be treated as ordinary construction water simply because it is available.
Dissolved salts can adversely affect concrete and, particularly where steel reinforcement is present, can increase the risk of corrosion and other durability problems.
This is especially relevant in coastal areas where groundwater or other available sources may contain significant dissolved salts.
The important point is simple:
Clear-looking water is not automatically suitable water for concrete.
Water should be assessed against the applicable requirements for concrete use.
Why durability matters
A concrete structure is expected to perform for many years. Therefore, the objective is not simply to achieve strength shortly after construction.
Concrete must also resist the environment in which it is placed.
Moisture, salts, chemicals and other aggressive conditions can affect a structure over time. The quality and composition of the concrete are therefore important parts of long-term durability.
Water is one of those factors that can have a direct influence.
The homeowner's two simple questions
When concrete is being prepared for a house, two questions are worth asking:
1. Is the water suitable for concrete?
2. Is the quantity of water being controlled according to the specified concrete?
These questions are simple, but they go directly to concrete quality and durability.
A practical lesson from the construction site
Water is sometimes treated as a convenience material because it is easy to obtain and easy to add.
That approach can be misleading.
The source of water should be considered. If there is any doubt about its suitability, it should be evaluated against the applicable requirements rather than assumed to be acceptable. Similarly, adding water at the site merely to improve workability should not be done casually.
The right approach is controlled use of suitable water in accordance with the specified concrete.
Closing thought
Water may look like the simplest ingredient, but both its quantity and its quality can have a major influence on the strength, performance and long-term durability of concrete.
For a homeowner, understanding this one principle can prevent a surprisingly common misconception: that all water is the same when it comes to concrete.
Series note: Detailed limits for water quality and testing should be taken from the applicable concrete standards and project specifications.