Ultrasonic testing and microscopic analysis on concrete under sulfate attack and cyclic environment

The damage process of concrete exposed to sodium sulfate attack and drying-wetting cycles was investigated. The water to binder(W/B) ratio and the concentration of sulfate solution were taken as variable parameters. Through the experiment, visual change, relative dynamic modulus of elasticity(RDME) and the surface damage layer thickness of concrete were measured.Furthermore, SEM and thermal analysis were used to investigate the changing of microstructure and corrosion products of concrete.The test results show that the ultrasonic velocity is related to the damage layer of concrete. It approves that an increase in damage layer thickness reduces the compactness and the ultrasonic velocity. The deterioration degree of concrete could be estimated effectively by measuring the surface damage layer and the RDME of concrete. It is also found that the content of gypsum in concrete is less than that of ettringite in test, and some gypsum is checked only after a certain corrosion extent. When the concrete is with high W/B ratio or exposed to high concentration of sulfate solution, the content of ettringite first increases and then decreases with corrosion time. However, the content of gypsum increases at a steady rate. The content of corrosion products does not correspond well with the observations of RDME change, and extensive amount of corrosion products can be formed before obvious damage occurs.

Characteristics of dry deposited mineral particles associated with weather conditions in the adjacent sea areas of East China during a cruise in spring 2011

Dry deposited particles, larger than 1.3 μm, were collected under clear, cloudy, and foggy conditions during a cruise, traversing the Yellow Sea and the East China Sea from 23 March to 8 April 2011. In these areas, air masses are influenced by pollution outflows from the Asian continent. The size and elemental composition of dry deposited particles were investigated using a scanning electron microscope. Number-size distributions of these particles were approximately lognormal. Under clear conditions, the mode size was about 5.0 μm, with a mean diameter of 6.9 μm. Under cloudy and foggy conditions, the mean diameters were 5.7 and 6.0 μm, respectively, but the mode sizes were vague. Non-mixed mineral particles, sea salt, and mixed mineral-sea salt particles were the major particle types. Correspondingly, Al and Si were the most frequently detected elements. Frequencies of K-, Ca-, and S-containing particles were highest under foggy conditions, while the frequency of Na-containing particles was lowest. These results indicate that fog favored sulfate production on the particles and led to the deposited mineral particles more abundant in secondary salt, suggesting the importance to consider the dependence of the comoosition of deoosited mineral narticles on weather as well as narticle size.