Concrete – Strength in Knowledge. Concrete is used more than any other man-made material in the world. As of 2006, about 7.5 billion cubic meters of concrete are made each year-more than one cubic meter for every person on Earth.
In evaluating concrete problems, one of the important decisions home inspectors must make is determining whether a problem is the result of conditions that have stabilized with a low chance of continuing future problems, or whether the conditions that caused the problem are such that there is a high probability that problems will continue or worsen.
Concrete powers a US $35 billion industry, employing more than two million workers in the United States alone. More than 55,000 miles (89,000 km) of highways in the United States are paved with this material. Reinforced concrete, prestressed concrete and precast concrete are the most widely used types of concrete functional extensions in modern days.
Concrete, as the Romans knew it, was a new and revolutionary material. Laid in the shape of arches, vaults and domes, it quickly hardened into a rigid mass, free from many of the internal thrusts and strains that troubled the builders of similar structures in stone or brick. Modern structural concrete differs from Roman concrete in two important details. First, its mix consistency is fluid and homogeneous, allowing it to be poured into forms rather than requiring hand-layering together with the placement of aggregate, which, in Roman practice, often consisted of rubble. Second, integral reinforcing steel gives modern concrete assemblies great strength in tension, whereas Roman concrete could depend only upon the strength of the concrete bonding to resist tension.
Combining water with a cementitious material forms a cement paste by the process of hydration. The cement paste glues the aggregate together, fills voids within it and allows it to flow more freely. Less waterin the cement paste will yield a stronger, more durable concrete; more water will give a freer-flowing concrete with a higher slump. Impure water used to make concrete can cause problems when setting or in causing premature failure of the structure. Hydration involves many different reactions, often occurring at the same time. As the reactions proceed, the products of the cement hydration process gradually bond together the individual sand and gravel particles and other components of the concrete, to form a solid mass.
Plastic cracking occurs prior to concrete curing. Autogenous shrinkage is caused by internal drying. Since there is no loss of water to one exposed surface, autogenous shrinkage is more uniform than plastic shrinkage. However, tensile stresses still develop, and embedded steel can cause anomalies in an area of concrete with relatively uniform stress. These anomalies can cause variations in stress within the concrete that are relieved by cracking. Autogenous shrinkage cracking will be shallow and is not a structural issue. The cracks may look similar to those formed during plastic shrinkage and are often propagations of cracks created during plastic shrinkage.
The advantage to inspectors in being able to accurately determine the source of cracking is in understanding whether the condition that caused the cracking has stabilized so that it is no longer likely to cause additional cracking or encourage the propagation of existing cracks. Many cracks, like those caused by concrete shrinkage, are shallow cracks caused by forces that allow conditions to stabilize relatively quickly and do not lead to structural problems. Others, like those caused by soil subsidence or changes in soil volume, are caused by forces that can continue to affect concrete for a long time. This long-term instability can continue to cause serious structural problems over the long term.
When investing in a new property it is important to have the building inspected by a qualified residential or commercial inspector. Visit www.barrie-home-inspector.com to learn more about the Barrie Home Inspector, when purchasing Commercial or Residential Properties. With over 4,000 inspections, experience and knowledge can help protect your investment.
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