Concrete is a common part of buildings and structures everywhere. It would be a rarity to find a place where concrete is not used. This strong building material is used in the construction of public and private structures. It has extensive applications, from residential buildings to skyscrapers, roads, landmarks, and industrial structures. In many cities, concrete is even more common than trees. However, there are many interesting things that not everybody knows about it. This article aims to present these important facts along with some brief discussions.
The Nature of Concrete
Concrete does not equate to cement. Many still have the wrong idea about concrete being cement itself. This misconception can be attributed to the use of premixed bags of concrete especially in small projects. It is worth pointing out that concrete is a mixture of cement or binder and aggregates or fillers. Cement is only a component of it. It is the substance used to hold the aggregates together. Using cement alone in building structures does not result in the kind of material seen in today’s buildings or public works. Aggregates are coarse granular materials such as sand, crushed stones, slag, or recycled concrete obtained from demolished buildings.
Not All Concrete is The Same
This is something those who are bidding their construction projects should know. Cement is the most expensive component of concrete. Hence, using a less expensive alternative like fly ash can mean lower costs. If a bidder offers a substantially lower project cost, it would be wise to inquire about the concrete the bidder intends to use. Cheaper concrete can mean more “fly ash” and less cement—which also means less durability. Aggregates can be substituted with different kinds of materials but cement quality and amount should not be compromised.
Strong in Compression, Weak under Tension
Concrete is a very durable material. However, its ability to resist tensile stress is very weak. This is due to the nature of the materials used in making concrete. The cement that binds the aggregates in concrete is brittle and lacks elasticity and malleability. It has to maintain a well-supported structure that involves contact to a fixed base. This is the reason why bridges and massive horizontal structures that make use of concrete need to have a certain number of columns and supports shaped like triangles or arcs. The weight of a concrete structure has to be distributed evenly to prevent the concentration of tension on one point that can lead to collapse.
Curing Concrete under Different Weather Conditions
Temperature is an essential factor to consider in working with concrete. This may sound ridiculous for some but concrete can actually undergo some kind of freezing that it would require some form of anti-freeze in the mix. On the other hand, it is a misconception that concrete should be exposed to the sun to dry quickly or that it should be made to dry quickly. Concrete can benefit from slow drying. Water is even splashed onto the finished concrete to retard the drying process. Concrete gains strength through the process of hydration. To enable faster hydration in damp and cold weather, calcium is added to the mix. A retardant is used to do the opposite, when the weather condition speeds up the evaporation of moisture in the newly set concrete.
Concrete Never Dries
While everyone knows that concrete has to be dried for it to be in a useful state, the truth is concrete never completely dries up. Some amount of water will always stay in concrete. This water content is partly responsible for the continual expansion and contraction of concrete under different weather conditions. Concrete degrades or deteriorates when it loses almost all of its moisture as it is exposed to severely high temperatures. A building that has been through a fire is considered to have undergone concrete degradation. As such, its structural integrity is compromised so it should be taken down and replaced.
Control Joints Necessary for Good Concrete Placement
The cracking of concrete is inevitable. Control joints are hence needed to stop the indiscriminate cracking brought about by the natural contraction and expansion of concrete. They direct the development and direction of cracks. Positioned appropriately, control joints minimize the need for maintenance and prevent serious structural damage caused by cracks. Around 140 square feet is the recommended spacing but this also has to be adjusted based on the thickness and PSI of the concrete.
Using Wood with Concrete
Using wood to separate sections of concrete or as control joints is not advisable. This is due to the shorter useful life of wood and the tendency of concrete to induce damage in wood. As wood decomposes, it can leave a gap between the concrete sections it used to separate. This is not only unsightly; it also poses other risks and possible problems in structural integrity. Moreover, wood is not recommended because it also expands and contracts depending on temperature changes in the environment. As mentioned earlier, contraction and expansion leads to cracks on concrete.
The Older the Concrete Gets, the Harder it Becomes
It gets stronger as it becomes older. This is especially true for concrete that has been prepared and cured properly, which means concrete that has been made to dry at a slower rate and kept moist longer. Generally, concrete gains strength within the first month of its cycle life. It continues becoming stronger as it ages. However, some may ask: Why are old concrete buildings deemed weak or deteriorated? This is not really a conflict with concrete’s theoretical strength gaining. Concrete structures eventually weaken because of the corroded support rods and their exposure to tension, shocks, and environmental elements that cause bacterial corrosion, calcium leaching, and chemical damage.
Before using concrete or hiring someone to do a concrete-related project for you, it helps having some knowledge about how concrete works. The knowledge will provide guidance in ensuring building quality and the proper examination of construction costs. Understanding the different aspects of concrete is also helpful in doing regular maintenance and being able to spot defects or problems as they emerge.