Study On Effective-curing-age Of Concrete Under The Same Curing Condition To Structures

It is a creative work that the strength of the sample cured under the same condition to structures used as the representation to the strength of the structural concrete. And now, more and more engineers pay much attention to the relation between fcu,t (the strength of the sample cured under the same condition to the structure) and fcu,o (the strength of the sample cured under the standard condition). The relationship between them is very complicated for different factors, such as the weather, material and construction management level in different area. The most important thing is effective-curing-age of the same curing condition to structures. At present, the research has been carried through in Zhengzhou University. But conclusions they get is still limited in guiding checking and acceptance quality of concrete construction for factors as resources and environment etc. So banding together the factors such as the material of concrete, construction management level and curing conditions and carrying through the engineering survey and systematic research, it is significant to make clear the factors which could influence the effective-curing-age and how much it will be. It is very important to ensure the quality of construction. The testing and survey have been used in this thesis. Combined with the local climate and material of concrete, factors that influence the early strength and effective-curing-age of concrete cured under the same curing condition to structures, such as mineral admixture, setting-time, cement type, temperature and humidity of curing conditions have been studied in this thesis. In addition, the thesis also analyses data from 15 concrete-manufacture-plants and 18 constructions-in-site's testing. The result of testing and survey shows: 1) Relative-strength of concrete added with mineral admixture increase slower than that of ordinary concrete, and the relative-strength-increasing-curve of fly-ash concrete is nearly equal to that of blast-furnace-slag concrete. Before the simplify-maturity reached 450℃·d, the silica concrete's relative-strength is greater than that of fly-ash concrete and blast-furnace-slag concrete, when the simplify-maturity over 450℃·d, the result is opposite exactly. 2) The effective-curing-age of ordinary concrete should be 600℃·d, but that of concrete added with mineral admixture is greater than or equal to 800 ℃·d. Engineers of construction should attach importance to the effective-curing-age of concrete added with mineral admixture, especially construction in winter. 3) There are many factors influence the effective-curing-age of concrete. The result of this study shows: the higher temperature and humidity of curing condition, the shorter effective-curing-age can be coming; when the setting-time of concrete is delayed, the effective-curing-age can increase; uprating the strength-grade cement, the effective-curing-age can be reduced, and the effective-curing-age of concrete used rapid-hardening cement is obvious less than that of concrete used the corresponding non-rapid-hardening cement; furthermore, the sample's making process and it's water losing are also important influencing factors. 4) The engineering-survey shows that there have good relativity between fcu,t and fcu,o, but the relative-strength has a little divergence. 5) when maturity just reached 600℃·d in Chongqing area, the average value of relative strength can be 0.94; if the guarantee rate is 95%, the adaptive relative strength should be 0.82; if the guarantee rate is 85%, the adaptive relative strength should be 0.86.