How long does reinforced concrete last

Many times, a concrete shell of a building or home can be reused when the other materials such as wood begin to deteriorate. The structural material of concrete is used as it will withstand the elements of nature, including regular weather and natural disasters. When considering the durability of concrete, it can be determined that the meaning involves the ability of the material to resist weathering from natural elements, chemical attack and abrasion.

Consider a smaller scale project. A sidewalk or pathway will be installed with a certain type of concrete. The mixing and pouring process should be considered along with grading of the property for a quality installation.

The right process should be completed so the sidewalk will not be damaged. If the installation is not done properly , perhaps with no sealing or with improper leveling, the concrete will eventually buckle or crack , possibly deteriorating due to coming in to contact with salt or other chemicals. Concrete also makes up the largest proportion of construction and demolition waste, and represents about a third of all landfill waste.

Recycling concrete is difficult and expensive , reduces its strength and may catalyse chemical reactions that speed up decay. The world needs to reduce its concrete production, but this will not be possible without building longer-lasting structures.

Rebar reclamation: an expensive job. In a recent paper , I suggest that the widespread acceptance of reinforced concrete may be the expression of a traditional, dominant and ultimately destructive view of matter as inert. But reinforced concrete is not really inert. Concrete is commonly perceived as a stone-like, monolithic and homogeneous material.

In fact, it is a complex mix of cooked limestone, clay-like materials and a wide variety of rock or sandy aggregates. Limestone itself is a sedimentary rock composed of shells and coral, whose formation is influenced by many biological, geological and climatological factors. This means that concrete structures, for all their stone-like superficial qualities, are actually made of the skeletons of sea creatures ground up with rock. It takes millions upon millions of years for these sea creatures to live, die and form into limestone.

This timescale contrasts starkly with the life spans of contemporary buildings. Steel is often perceived to be inert and resilient too. If construction steel is visible, it can be maintained — for instance, when the Sydney Harbour Bridge is repeatedly painted and repainted. Several years later, the jacket was opened for inspection. Because the concrete was saturated with seawater, the iron had dissolved in places on the steel reinforcement rather than form expansive corrosion products that put stress on the concrete.

Typically, Broomfield notes, the carbonation and chloride diffusion processes take many years to reach the reinforcing steel in concrete, which is known as time to corrosion initiation. The time period from corrosion initiation, when the passive layer is damaged, to the first signs of corrosion damage is known as the active corrosion time. This time frame also can be modelled with equations that calculate the time until cracking.

This can be calculated from the corrosion rate, concrete strength, cover depth, and rebar diameter. This is a much shorter time period than time to corrosion initiation—typically one to five years—and is dependent on the corrosion rate. Once corrosion damage does strike, performing durable repairs on corrosion-damaged reinforced concrete can be challenging. When corrosion initiates on the steel, the area that is actually corroding is anodic, while the non-corroding areas surrounding the corroding site are cathodic.

Essentially the corroding area is cathodically protecting the non-corroding areas around it, Broomfield explains. When the corroding area is repaired with a patch, typically the damaged concrete is removed and new, good-quality concrete is used to replace it. This ruins the durability of concrete structures in ways that are difficult to detect and costly to repair. While repair may be justified to preserve the architectural legacy of iconic 20th-century buildings, such as those designed by reinforced concrete users like Frank Lloyd Wright , it is questionable whether this will be affordable or desirable for the vast majority of structures.

The writer Robert Courland, in his book Concrete Planet , estimates that repair and rebuilding costs of concrete infrastructure, just in the United States, will be in the trillions of dollars — to be paid by future generations. Steel reinforcement was a dramatic innovation of the 19th century. The steel bars add strength, allowing the creation of long, cantilevered structures and thinner, less-supported slabs. It speeds up construction times, because less concrete is required to pour such slabs.

These qualities, pushed by assertive and sometimes duplicitous promotion by the concrete industry in the early 20th century, led to its massive popularity. Reinforced concrete competes against more durable building technologies, like steel frame or traditional bricks and mortar. Around the world, it has replaced environmentally sensitive, low-carbon options like mud brick and rammed earth — historical practices that may also be more durable.

Early 20th-century engineers thought reinforced concrete structures would last a very long time — perhaps 1, years. In reality, their life span is more like years, and sometimes less. Building codes and policies generally require buildings to survive for several decades, but deterioration can begin in as little as 10 years. But there is still a lack of knowledge about their composite qualities — for example, in regard to sun-exposure-related changes in temperature.