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Understanding Concrete Workability

Putting cement on the road
Concrete is one of the best materials for installing features like sidewalks, driveways, and parking lots. Those who opt to pave with concrete often do so with its incredible durability and longevity in mind. Yet not all concrete surfaces will exhibit the same strength and resistance to damage. The nature and quantities of a concrete mix can have a lasting effect on its performance.

Workability is one of the key ways in which paving contractors evaluate a particular batch of concrete. To those outside the industry, this somewhat general term may seem shrouded in mystery. Yet understanding workability isn't as hard as you might think. This article will provide a useful overview of the subject, outlining some basic information about the relationship between workability and long-term strength.

Workability

Workability can be a frustrating and somewhat vague term to understand. Every definition of workability seems to differ in some slight way from the next. In general, however, the implications of workability are clear: workability reflects how easily a contractor can place a particular concrete mix and how well the concrete will resist what is known as segregation.

Segregation occurs when the principal ingredients in a concrete mix - in other words, gravel aggregate, cement, and water - separate prior to and during the curing process. Segregation causes excessive amounts of water to rise to the surface. This phenomenon is called bleeding.

Bleeding affects the strength of the resulting concrete by reducing internal hydration. As a result, cement particles will have a more difficult time binding to the aggregate. The resulting concrete will, therefore, be generally weaker and more prone to damage when exposed to shocks and negative environmental factors.

A concrete with good workability remains in a homogenous state from the time of its manufacture until it has fully hardened into a slab. Good workability also means that a contractor will have an easier time compacting, smoothing, and finishing the concrete after it has been poured.

Key Factors

A multitude of factors affect concrete's workability - a fact that increases the difficulty of replicating workability from one project to the next. Perhaps the most important factor involves the relationship between the amounts of water and cement used in the mix. Either too much or too little water can lead to poor workability.

Adding too much water to the mix will increase the rate of segregation and bleeding, leading to concrete that lacks the ideal strength and durability. Too little water, on the other hand, will make the concrete much harder to handle during installation. Insufficient water also means that, likely, not all of the cement will become hydrated.

The dimensions of the aggregate used also plays a key role in determining workability. Here, the shape and the size of the aggregate are the two most impactful qualities. Size and shape both affect the total aggregate surface area, which in turn dictates the amount of cement necessary to coat the aggregate completely.

As surface area increases, the ease of installation also changes. Larger or more angular aggregate makes it harder to ensure even mixing and smoothing. Too little surface area can also create workability issues by reducing the potential bond strength between aggregate and cement paste.

Experienced contractors possess a wealth of experience which allows them to accurately assess the workability of concrete. Contractors can also quantify workability by measuring the slump loss of a particular mix. Slump loss measures the tendency of a cone-shaped mass of wet concrete to collapse under its own weight.

For more information on what it takes to ensure ideal workability, contact the paving industry experts at P & L Concrete Products Inc.