Concrete shrinkage is a complication many civil engineers come across, yet few fully understand. It can pose a serious problem in the foundations of buildings, whether it is the grounds or walls constructed from this material. Cracking, warping, or joint spalling can occur due to shrinkage, thus making the foundation unstable.
The first step to be taken in preventing concrete shrinkage is choosing the right material. That is to say, the concrete mixture that best fits a building’s needs. Certain blends can be considered low shrinkage, typical, or high shrinkage, all of which ranging in slab thickness. Low shrinkage mixtures are thicker with a further distance between joints, whereas high shrinkage mixtures are the opposite. Choosing between the two depends entirely on the building’s requirements. Factors to consider are a concrete’s workability and finishability to best gauge just how long it will last.
Cracks formed in concrete are often recognizable and can form from the friction between the lower-most slab and the base of the foundation. The mixture and environmental conditions can also play significant roles in the material’s durability. All of these complications can have a profound effect on how well a facility operates, as well as an increase in maintenance fees. Cracking can even develop within a slab, making it that much harder to fix.
Warping is typically caused by the surface layer of a slab drying faster than the concrete deeper within, causing the top to shrink and curl upward. Much like cracking, environmental conditions like extreme temperatures can worsen these effects. However, depending on the severity of the warping, the potential consequences can be much worse. As the edges of a slab begin to curl, the support weakens. This curling can drastically increase stress upon the concrete slabs, leading to further cracking and breaking.
Joint spalling is defined breaking of a joint’s edges from excessive stretching, weight from heavy traffic, or misalignment. Though it may cure within 30 days, concrete continues to dry for roughly 12 to 18 months, during which it is prone to separation from the joints. Once it does become separated, support weakens very quickly, causing the cracking and chipping of the concrete.
Work closely with a material designer to properly evaluate potential shrinkage and avoid it if possible. Accommodations can be made should the mixture be more susceptible than expected, like adding aggregates with a higher stability for example. Joint spacing can be reduced as well if necessary. However, having a solid understanding of the dangers of shrinking concrete beforehand is crucial in order to choose the right mixture for your project.