Myths and Facts about Concrete Construction
There are myths and facts about concrete. The concrete is very useful in construction starting from buildings in homesteads and public constructions. The invaluable nature of this substance compels the need to put across the facts about it so that the mistakes that may arise from myths are eliminated.
Specification of concrete mix: concrete mix is specified in terms of number of bags or amount (myth). Giving only the amount of cement in number of bags is not considered a specification. Specification is grounded on the performance. The amount of water to cement ratio and the compressive strength values are the specification for the mix. From these values the amount of cement can be calculated but not the reverse way.
Slump increment: adding water to the mix is the only solution of increasing slump (myth). There are various ways of increasing slump apart from addition of water. Some of the methods are the use of super plasticizer or water reducer. The gradation of aggregates may also be modified to maintain the water to cement ratio. It should be noted that adding water to the mix may be costly and disadvantageous in some circumstances due to the fact that the compressive strength will be lowered by almost 200psi and a quarter bag of cement may be wasted in every gallon of water added.
Myth: the meaning of curing concrete is letting it dry. The fact is concrete requires water for continuity of hydration and further strengthening. By curing, the temperature and moisture content are maintained at satisfying levels which helps in achieving the properties desired. Curing for a long time is necessary since it provides durability to the concrete.
Myth: no bleed water and successful footprints mean thump up for concrete finishing. The fact is that this test is a general guideline in for finishing and relying fully upon on it may lead to slab surface defects. With the increase in technology, power finishing machines have been developed and this has considerable change the timing for finishing considerably. Therefore, for proper finishing knowledge and experience are necessary.
Calcium chloride is used as antifreeze. This is a myth, the fact is that calcium chloride is an accelerator but its purpose in the concrete is for attaining better strength. To protect concrete from freezing in cold condition the use of insulators, enclosures and curing blankets should be considered.
Concrete can be placed on the frozen without any consideration. The statement never holds since the difference between the concrete and the frozen ground may lead to super cooling of the concrete hence, leading to hardening. Precaution must thus be taken. The best way out is to reduce the temperature different. Spreading calcium chloride on the ground will only worsen the situation.
Cracking of concrete is prevented through reinforcement. This illusion does not hold any water. The fact is life of concrete depends on volume changes which are dictated by the moisture cycle and temperature. The reinforcement cannot prevent the cracking due to the tension weakness of the concrete. The rebar is what causes cracking and the reinforcement bind the crack faces together.
Fresh concrete never changes the shape after hardening. This is only a dream. The fresh concrete usually changes in shape during setting. The most common shaped formed after hardening is the curled. The curling arises due to the moisture and temperature differences between the top and bottom of the concrete.
Concrete is impermeable. Even the very dense concrete is never impermeable since vapor and liquid will pass through it. The permeability of the concrete is not an admirable property and a mix design should be applied to reduce the permeability. Some of the ways to achieve this are use of uniform aggregate gradation and lower water to cement ratio among others.
Concrete strength is the key factor to its durability. This is a myth, the fact is that it is not strength alone which dictates the durability of concrete but there are other factors which are even more important. Some of the factors that may lead to deterioration of concrete are alkali silica reaction, sulfate attack and corrosion of reinforcing still. All these factors are initiated with moisture exposure. The key factors in determining durability are adequate air system and system permeability.
To sum it up, the contractors and suppliers should be well informed about the products concrete so that the consumers are not misled. Imparting knowledge through education is the solution.
Reference
Portland Cement Association, (2001). Top 10 Myths in Concrete Construction. Retrieved from https://www.youtube.com/watch?v=ii2ZApfbe88
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Study Notes:
Myths and Facts about Concrete Construction:
Concrete construction takes a long time.
Fact: With advances in technology, concrete construction can now be completed in a relatively short amount of time, often in a matter of hours.
Concrete is a weak and brittle material.
Fact: Concrete is a strong and durable material that can withstand heavy loads and extreme weather conditions.
Concrete is expensive.
Fact: Concrete construction is often cost-effective in the long run due to its durability and low maintenance costs.
Concrete is not environmentally friendly.
Fact: Concrete production has become more environmentally friendly with the use of recycled materials and reduced carbon emissions.
Concrete requires a lot of water.
Fact: Concrete production has become more efficient, requiring less water and reducing waste.
Concrete cracks easily.
Fact: Concrete can crack, but with proper design, reinforcement, and maintenance, cracking can be prevented or controlled.
Concrete is not visually appealing.
Fact: Concrete can be colored, textured, and stamped to match any desired aesthetic, making it a versatile and visually appealing option for construction.
Concrete construction is a strong, durable, and cost-effective option for building structures. Advances in technology and sustainability have made concrete an environmentally friendly and visually appealing choice. It is important to separate myths from facts when considering concrete construction.
