EVALUATE CONCRETE MATURITY, WHY?

The common aproach to evaluate the concrete developed strength is usualy carried out trough test cilynders cured in the "same circumstances" of the real structure. This information is used to program the construction workflow. The Maturity Method makes use of the basic comcept that the concrete properties are developed with time at same time that the cement hydrates releasing heat during this chemical reaction.

The strength development rate in early ages is hevilly dependent on the hydration rate. By its turn the heat realeased by the hydration reaction also contributes to the temperature increase inside the concrete, fact that is also considered by the Maturity Method. In 1920 was published the ASTM C31 standard “Standard Practice for Making and Curing Concrete Test Specimens in the Field”. Later in 1927 ASTM published R.B. Young's work that questions the validity of the test cilynders method. E. Cohen, ACI president, wrote in 1972 that “these method [the test cilynders] (…) needs needs drastic improvement. The standard cylinder is useful for selecting mix proportions; it is a poor procedure for quality control." Identical conclusion is published in 1976 by Ramakrishnan: "the idea that cylinders represent the in-situ concrete is incorrect and it prevents the development of more realistic and economic concepts."  Isolated test colynders, in most cases, provide erroneous results about the actual stenght of the concrete in the real structure.

Preparing, handling and testing Test cilynders handling has impact in the test results.  Also the test cilynders can be prepared inadequatly which can lead to wrong test results, causing unnecessary delays to the construction workflow.
Diferences in the environmental conditions The diferences betwen the enviroment where the test cilynders are kept and the real structure have a significat impact in the stregnht development rate. The curing temperature of the test cilynders in the lab and in the construction site sheldon reproduce acuratly the temperature in the structure. The temperature history will be necessarilly diferent because of the environmental conditions, the geometry, the thermal characteristics and the mass volume. Consenquently the strenght development rate is diferent. Economic and safety reasons (striping forms, pos-tensioning, etc.) mandate that the strenght evaluation be as much acurate as possible (descofragem, pós-tensionamento, escoramento, etc.).
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