Is concrete better today than it was a century ago? There are several concrete structures all around us, even the most recent ones, and none of them is totally intact. When concrete cracks, it reveals the inherent vulnerability of this material. Because of its compatibility with steel and its capacity to meet the needs of an advanced building material, reinforced concrete has become a preferred choice. What’s more, are cracks the same everywhere? The answer is a resounding nay! A number of various processes, such as deformation, hydraulic shrinkage, thermal shrinkage, or swelling, can lead to cracks in a material. Here are the primary distinctions between the two.
Deformation-caused cracks
Concrete is subjected to tensile, compressive, or shear forces. Deformation can occur as a result of these stresses, leading to cracking. For example, a crack’s location and shape can be used to identify its cause by studying the cracks.
- Compression cracks are parallel to the force imparted.
- Tensile cracks appear perpendicular to the force applied.
- Perpendicular to the tensile stress are shear cracks.
For this reason, concrete is practically never utilized in its unreinforced form because of its low tensile strength. Steel reinforcement bars are the most common method of reinforcing structures that are subjected to tensile stress. Reinforced concrete is the usual name given to this form of concrete. Synthetic fibers may also be used as a form of reinforcement. The most common causes of deformation cracks are soil settling and excessive loads.
Hydraulic shrinkage cracks
During curing, concrete in the open air tends to shrink. The concrete has shrunk as some of the water in the mix has evaporated. When shrinkage pressures exceed the concrete’s tensile strength, cracks form. The evaporation of water and the strengthening of concrete might be perceived as a race against time. This is also valid for non-deformable concrete components. Deformation cannot occur in the case of shrinkage. When the stress surpasses the concrete’s strength, cracks will form in the structure. Dimensional variation in concrete structures is extremely low when they are submerged or located in a damp environment. Before the concrete has hardened, cracks can occur. Because of the evaporation of some water or absorption by the support, the shrinkage is not solely attributable to hydraulic shrinkage. Affected pavements are those that were cast in hot and dry conditions, or those that were laid in warm rooms or on porous supports in cold weather. Concrete joints and the proximity of reinforcements are two places where cracks are most likely to occur.
Thermal shrinking is the cause of these cracks.
Large constructions are the focus of this investigation. An exothermic reaction, cement hydration generates heat that eventually dissipates. Differential deformation, which may lead to cracking, is caused by temperature change, which is not uniform across the structure.
Swelling-induced cracks
Concrete can swell for a variety of reasons. The following are the most important. It’s possible that salts like sulfates, which can be found in the ground directly in touch with a concrete slab, can cause it to expand. As a result, an expanding substance is formed by this chemical reaction with aluminate. Swelling can also be caused by the freezing of the free water in the concrete, which expands when it freezes. Swelling can also be produced by the oxidation of the concrete’s internal reinforcement, which is exacerbated when cracks are present. For all of these events, the end consequence is the same: creating internal tensile pressures that, when they exceed the concrete’s strength, lead to fractures appearing.
Cracks in the steel reinforcing as a result of corrosion
Reinforced concrete is extremely durable because concrete is highly alkaline, protecting the steel reinforcement. However, the rebars may corrode and develop rust if specific conditions are met. This leads to tensile stress in the concrete because of an increase in the volume of corrosion products (rust) generated. The concrete may delaminate and crack if the corrosion is advanced enough. When steel is exposed to concrete, it corrodes for the following reasons:
- In the presence of moisture, concrete carbonation may trigger a corrosion reaction.
- marine salts or deicing salts in the concrete and in the rebars’ surrounding areas Moisture initiates the rusting reaction once more.
As a follow-up to the first part of this essay, “Why concrete cracks?” we’ll examine the consequences of cracking and the most effective preventative strategies. Call us at: (202) 559-8998.
