Research On The Durability Of Natural Pumice Concrete In Saline Solution Environment Of Cold Regions

This research, abundant of pumice resources and industrial wastes in Inner Mongolia are fully used to study and develop the new light energy-saving material with a mixture of cement, pumice, sand and fly ash, i.e., natural pumice concrete. The study area is located in Hetao irrigation region of Inner Mongolia, where irrigation water is mainly sourced from Yellow River with pH range of 7.7-8.2 (mainly saline corrosion component:Na+、Mg2+、Ca2+、Cl-and SO42-). Flowing with water, salt was accumulated and carried into irrigation system, and the hydraulic structures would be eroded by salinity water from the irrigation region.According to the survey data of saline water, the natural environment and concrete engineering characteristics of Inner Mongolia in western China (There are a long cold season and large temperature differences between day and night, and etc.), There are five different proportion sets of natural pumice concrete(LC20, LC25, LC30 and two sets of air-entraining natural pumice concrete) and four types of working condition combinations: freezing-thawing cycling (fresh water and saline solution), dry-wet cycling (fresh waterand saline solution), freezin-thawing-dry-wet cycling (fresh water and saline solution) and test of soaking andleaching in fresh and salt water. Mainly in the following content test and simulation studies:1. Based on data analysis of mass loss rate and relative dynamic modulus, it is found that the loss of relative dynamic modulus is more sensitive to mass loss, so that it is more accurate to take the relative dynamic modulus as a durability evaluation index of natural pumice concrete. Meanwhile, the greater the strength is, the smaller the mass loss rate and the loss of relative dynamic modulus will be. Moreover, the microstructure and chemical compositions of spectrum diagram are used to analyze the failure mechanism of natural pumice concrete.2. In the study of natural pumice concrete, nuclear magnetic resonance (NMR) testing method is proposed for the first time, so as to obtain the internal pore damage and propagation characteristics prior and posterior to freezing and thawing from porosity, NMP T2 spectrum distribution, pore size distribution and NMR image results:Nuclear magnetic resonance T2 spectrum distribution of natural pumice concrete are generally four peak, freezing and thawing cycle makes natural pumice concrete small pore gradually expand to the big pore, cause porosity, T2 spectrum area increases, and the concrete damage is more serious in the saline solution, NMR signal is stronger, bright spots.3. In this paper, the new technology, such as electronic computer X-ray computed tomography (CT), environmental scanning electron microscope (ESEM) and optical microscope system experiments, are proved to comprehensively analyze the mesoscopic characteristic of natural pumice concretes. By combining analysis of nuclear magnetic resonance (NMR) imaging, It is concluded the internal pore damage and propagation characteritics from different perspectives during freezing-thawing. The conclusions are consistent, i.e., the internal damage of natural pumice concrete is more serious in saline solution.4. This article, by using nuclear magnetic resonance (NMR) during freezing-thawing testing, has evolved the amount of semaphore and frezing state of the concrete pore solution under various temperatures from the variation in the freezing and melting process. Those conclusion, about general features of pore solution icing:With the amount of ice in freezing process for evaluating the hydrostatic pressure caused by the freezing of pore solution compared with the actual phenomenon; The occurrence of natural pumice concrete freezing injury mainly more than-15℃.5. Finally, based on the hydrostatic pressure hypothesis, the damage mechanics theory and experimental conditions of pore structure, tensile resistance performance and freezing-thawing, the prediction model of frost resistance durability of lightweight aggregate concrete has been established, which would provide quantitative description for the process of freezing damage to natural pumice concrete.