A Brief History Development
In the late 1960s, high-range water reducing admixtures(superplasticizers) composed of salts of naphthalene sulfonate and melanine sulfonate were developed in Japan and Germany, respectively. The first applications in Japan were confined to high-strength precast products and cast-in-place girders and beams for bridges. In Germany, initially the objective was to develop underwater concrete mixtures possessing high fluidity without segregation. As it is possible to achieve both high strength and high workability simultaneously with the superplasticized concrete mixtures, they were found to be very suitable for use in the production of cast-in-place structural components for tall buildings. The drum mixers are common and small mixer that is used in civil building.
Definition
Concrete is defined as” high-strength” solely on the basis of compressive strength at a given age. In the 1970s, before the advent of superplasticizers, concrete mixtures that showed 40MPa or more compressive strength at 28 days were called high-strength concrete. Later, when 60 to 120MPa concrete mixtures because commercially available, in 2002 the ACI Committee on High Strength Concrete revised the definition to cover mixtures with a specified design strength of 55MPa or more. The pan mixer machine is the appropriate machine to mix concrete.
Although conventional practice is to specify concrete strength based on the 28-day test result, there is a growing movement to specify the 56- or 90-day strength because many structural elements are not fully loaded for periods as long as two to three months or even longer. When high strength is not needed at an early age, it is best not to specify it so as to achieve a number of benefits such as cement saving, ability to use relatively large proportions of mineral admixtures, and a more durable product. If you want to look for large cement mixer for sale, find more types from our factory.
Significance
Thirty years ago, tall buildings in Manhattan(New York City) were almost all steel-frame. Today, perhaps one-third of tall commercial buildings are concrete frame. It is believed that the choice of steel frame vs. reinforced concrete frame was decided in favor of the latter primarily on account of the high construction speed. Also, commercial availability of high-strength concrete provided an economical alternative to bulky columns of conventional concrete for the lower floors of high- rise buildings. According to one report, the load-carrying capacity of columns in multistory buildings increased 4.7 times for a threefold increase in price. For the construction of reinforced-concrete- frame buildings, 30 stories and higher, normal-size columns can be made in the upper third of the building with conventional 30 to 35MPa concrete; however, the use of high-strength concrete is justified for slender columns in the lower two-thirds of the building.