When a blemish appears on the surface of a concrete slab it will likely be one of these: blisters, cracking, crazing, curling, delamination, discol- oration, dusting, efflorescence, low spots, popouts, scaling, or spalling.
One of the most common causes of poor concrete installation is incorrect mixing. If the wrong proportions of sand, gravel, water, and cement are used, the resulting concrete will be too weak or too brittle. In some cases, adding too much water can also cause problems.
Different types of defects in concrete structures can be cracking, crazing, blistering, delamination, dusting, curling, efflorescence, scaling and spalling. These defects can be due to various reasons or causes.
These defects in concrete structures can be due to poor construction practices, poor quality control or due to poor structural design and detailing. Common types of defects in concrete structures are honeycombing, form failure or misalignment of formwork, dimensional errors, rock pockets and finishing errors.
Problems with concrete include construction errors, disintegration, scaling, cracking, efflorescence, erosion, spalling, and popouts.
Scaling is one of the most common problems of concrete. In scaling, the surface layer of concrete gets deteriorated by getting peeled or by breaking off.
Poor concrete mix design or vibration techniques can result in honeycombing—when coarse aggregate is exposed without sufficient surrounding morta—or bugholes, in which a lean mix displays small holes on the surface.
Corrosion of reinforcing steel and other embedded metals is the leading cause of deterioration in concrete. When steel corrodes, the resulting rust occupies a greater volume than the steel. This expan- sion creates tensile stresses in the concrete, which can eventually cause cracking, delamination, and spalling (Figs.
Structural distress in a concrete structure
Structural distress can be caused by a variety of factors, the most common being the corrosion of the embedded reinforcing steel.
Never overwork or over finish the surface of any exposed concrete slab. This brings too much fine material to the surface, works out the designed air entrainment*, and will weaken the surface of the slab leaving the top of slab more vulnerable to freeze/thaw damage and sheet scaling*.
Concrete spalling describes the state when the concrete begins to degrade or break away. Common signs include cracking, crumbling or flaking concrete, rust stains or bubbling on the concrete or cement render – plus leaks in the roof and walls.
What is the maximum life of modern concrete? Generally, for large infrastructures, the lifespan of modern concrete is about 100 years if properly maintained.
As the water leaves the concrete, it creates a volume change, known as drying shrinkage. If the concrete is not strong enough during the curing process to withstand the tensile forces of this volume change, the concrete will crack.
Compared to other binding materials, the tensile strength of concrete is relatively low. Concrete is less ductile. The weight of concrete is high compared to its strength.
Too much water added to the mix means that excess water is retained inside the concrete after the curing process has finished. This will often result in the formation of small cracks as the water eventually evaporates over time, which reduces the compressive strength of the concrete.
The type of material, their moisture content, suitability for construction, and their chemical and physical properties affects the mix design of concrete.
Failure modes in reinforced concrete beams are classified into two major types: flexural failure and shear failure. The former occurs when the imposed load exceeds the flexural capacity of the materials of the beam, while the latter occurs due to deficiency in shear resistance between different materials of the beam.
Modern concrete is porous and degrades in contact with seawater. Seawater can seep into its pores, and when dried out the salts crystalize. The crystallization pressure of the salts produces stresses that can result in cracks and spalls.
Deeply spalled concrete can be repaired with a concrete overlay. Think of this as just applying stucco to the concrete. You just mix up some sand, a little hydrated lime and Portland cement and trowel this onto the concrete.
Hairline cracks or cracks under 1/4-inch wide may not indicate serious underlying damage, but if water gets into them and repeatedly freezes and expands, and vehicles continue to drive over them, the cracks can get bigger and the problem can worsen. These cracks can usually be repaired.