Concrete work in NYC is one of the most intricate building jobs, for it requires striking accuracy, expert workmanship and the right combination of raw materials and tools. Different types of work require different forms of concrete, for not all tasks have the same requirements.
Now the key to different concrete mixtures is changing the amount of cement in them, obtaining different properties as desired. Some of the common types of concrete mixture used in concrete work in NYC are:
Normal concrete has a setting time of 30 to 90 minutes. It takes about 7 days for the cement to start hardening, and requires about 28 days to attain 80% of the total strength. It has high compressive power and low tensile strength. It is used in areas of normal weather, cannot stand harsh weather like freezing without being treated externally. Most of the concrete work in NYC is of normal concrete.
High Performance Concrete:
It is prepared by careful selection and preparation of the cement mixtures, with plasticizers being added to enhance its workability. It has high strength, easy to work on, gains strength early, better permeability, high density and extremely durable. They can be made to resist freezing by using air entraining agents in the concrete mix.
High Strength Concrete:
High strength is attained by lowering the cement to water ratio in the concrete mixture with silica being added to prevent strength reduction during the hardening process. HSC is slightly difficult to work with due to lower cement to water ratio, but has extremely high strength, making it suitable for construction skyscrapers and sidewalks. Careful selection of aggregates is necessary for maintaining its strength for long periods of time.
Air Entrained Concrete:
When air entraining admixtures (chemicals which enhance the properties of concrete) are added to concrete, they form air entrained concrete. It is extremely beneficial in areas where it is prone to freezing and thawing. It is one of the latest advancement in concrete technology. The only drawback of this concrete mixture is that it has lower strength than regular concrete.
It is significantly lightweight and has lower mass per unit volume of all concrete mixtures. They also have low strength and density. They are protected from freezing by addition of air entraining admixtures. They are used in places where less load is applied on them, i.e. sidewalk linings, road linings, decorative structures, parapet wall etc.