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Frequent Causes of Concrete Slump Loss

Slipform Paving new Curb at a Construction Site

Concrete has few rivals when it comes to strength, durability, and resistance to damage and stress. Yet not all concrete will display such positive traits. In order to ensure optimal results, concrete must be installed by a professional with a consummate knowledge of the techniques that lead to sure and lasting results.

One frequently overlooked source of concrete problems is slump loss. Unfortunately, even many people in the construction industry fail to understand the principles of slump loss, let alone how to successfully prevent it. If you would like to improve your knowledge of concrete installation, read on. This article will discuss three frequent causes of slump loss and how to prevent them.

Slump Loss

Three main ingredients make up concrete: cement, water, and aggregate. Water and cement combine to form a chemical reaction known as crystallization that results in the hardening of the cement. The aggregate acts to provide a filler material, making up as much as 80 percent of the concrete's physical volume.

Once a batch of concrete has been mixed, the process known as slump loss will soon set in. Slump loss is a natural phenomenon, one that has to happen for the concrete to cure and harden correctly. Yet slump loss that occurs before the concrete has been poured can make it incredibly difficult to work with. Moreover, it may lead to less than stellar results in terms of durability and appearance.

Time

Time is the most important factor when it comes to predicting slump loss. The normal slump loss discussed above operates chiefly as a function of time. In other words, the more time that elapses between mixing and pouring the concrete, the more of an effect slump loss will have on its performance. 

For this reason, concrete installers should do their best to minimize the amount of time between mixing and pouring the concrete. If possible, the concrete should be mixed at the job site. Where on-site mixing is not possible, a savvy installer may compensate for slump loss by adding additional amounts of water and cement to the original mix.

Temperature

Slump loss proceeds by means of evaporation. The gradual decrease of the concrete's water content causes it to behave more and more stiffly — in other words, with a slump value that grows gradually lower. The term slump value designates the propensity of a fixed amount of concrete to collapse under its own weight.

While evaporation will occur to a certain degree in any environment, higher temperatures will accelerate the process. During hot times of the year, you might struggle with slump loss when installing concrete.

To counteract evaporative forces and minimize slump loss, installers may choose to cool the materials before mixing a batch of concrete. For instance, you might add a portion of ice to the water.

So-called retarders can also be added to keep the concrete from setting too quickly. The amount of retarder must be carefully calculated, as other problems may ensue if the concrete hardens too slowly.

Aggregate

In some cases, aggregate itself may be the cause of slump loss. Aggregate on the smaller end of the size spectrum poses a particular threat, as it demonstrates a much greater ability to absorb moisture. Simply put, aggregate can be too dry for its own good. Dryness limits the amount of water available to bond with cement molecules while resulting in a stiffer than expected mix.

To avoid this problem, it may be necessary to pre-hydrate the aggregate slightly to reduce its thirst for water. Installers must take care to not overly saturate the aggregate, however, as this can alter the overall hydration of the mix. Wise contractors will also avoid the use of aggregate types that demonstrate a higher natural absorption rate.

Expert Installation

As you can now appreciate, installing a concrete surface correctly takes a lot of experience and specialized knowledge. For more information about what an expert can do to ensure perfect results, please don't hesitate to contact the professionals at Accu-Krete.