Research Of Negative Effect Improvement Measuresof PHC Concrete With Accelerate Curing

Currently, with the rapid development of our country’s economy, infrastructure construction is much more common, and the concrete structure has been widely used in the various environments because of its superior comprehensive property. However, in some harsh environment, such as Marine, saline soil and large temperature difference environment, the mechanical properties and durability of the concrete are faced with the severe test. The ordinary concrete can’t satisfy the requirement of certain functional structures. Therefore, the demand of the high-strength and super-high strength concrete component which is the research focus is increasing. The factory prefabrication production of the high-strength concrete components is the inevitable trend in the machine age. The autoclave curing and steam curing technology are widely used in the high-strength concrete components production. According to the domestic and foreign engineering practice, many problems have been exposed in the service of the steam cured concrete prefabricated components, such as the easy crack and the insufficient durability. The long-term property of the autoclaved concrete components declines more seriously than the steam cured. Based on the above background, to systematically research the mechanical properties and the durability of the autoclaved prestressed high-strength pile concrete in the macroscopic and microscopic aspects and to explore the effective measures to relieve the degradation of the autoclaved concrete’s long-term properties, by improving the system of concrete material, the subsequent curing system and protective coating processing measures, the main conclusions have been obtained as follows:(1) To summarize the development of the strength and durability in the various curing conditions, the long-term and short-term strength and durability properties under the conditions of the standard curing, steam curing and autoclave curing have been systematically studied. It shows that the initial strength of the autoclave curing components is higher than the standard curing one. But the change of the later strength presents the negative phenomena and the long-term resistance to the carbonation and chloride ion erosion is weak. Autoclave curing measure makes the uneven distribution of the hydration products, the internal thermal damage effect and the large void ratio and the large proportion of the harmful void through the microstructure analysis.(2) Specimens with the mineral admixtures have the obvious advantages in the strength and the durability compared with blank specimen. The magnitude of strength improving is : single-slag > fly ash and slag> single fly ash. Improvement in terms of durability, it is the best to improve carbonation resistance with single-slag specimen; Whether single or double-doped specimens in improving chloride performance of the pile concrete specimens is very favorable, as follows: single-doped F> Double Mixture F + K> single doped K. In terms of microstructure, mineral admixtures make the number of hydration products in concrete multiply and distribute evenly and decrease the void ratio of concrete, so as to improve the compactness, the mechanics and durability of concrete.(3) The research of autoclave and steam cured concrete specimen in the normal temperature 20℃ shows that the follow-up maintenance specimen is superior to the same age period of blank specimen both in the initial or later strength development, and the resistances of the carbonation and chloride ion erosion increase much more. On the basis of the microscopic study, the subsequent curing can reduce the proportion of modal pore diameter and harmful pore diameter, and makes the distribution of hydration products more uniform. Thus, this technology can improve the comprehensive properties of the autoclaved concrete.(4) No matter silicone waterproof coating or epoxy resin paint has the advantage in the improvement of the resistance of the carbonation and chloride ion erosion based on the research of the anticorrosion coating of the autoclaved concrete. In practical terms, the performance of the epoxy is better than organosilicon waterproofing agent.(5) There is the linear relationship between the electric flux and chloride ion diffusion coefficient, and the equation describes as the y=-1.94073+0.0048 x, and the value of the correlation coefficient R2 is 0.90755. It is necessary to note that the parameter y means the diffusion coefficient of chloride ion and x stands for the value of the electric flux. In order to predict the service time of the autoclaved pipe pile concrete specimens in the coastal atmospheric zone, compared with the blank specimen, single mixing fly ash specimen increases the service time, the largest up to 4.2 times, reaching 71.6 years; which is followed by epoxy resin coating specimen, reaching 52.4 years, which increases 3.08 times service time according to the second Fick diffusion law.