Processing of electron microprobe data from the analysis of altered cementitious materials (original) (raw)
Related papers
Journal of Nuclear Science and Technology, 2006
Application tests for advanced TEM analysis techniques were carried out to study the cement alteration processes associated with water penetration at high spatial resolution. Prior to TEM analysis, we measured the changes in the penetration coefficient and determined the characteristics of the penetrating water in order to gain a fuller understanding of the overall process. These experiments revealed that the process begins with the preferential dissolution of Ca(OH) 2. After most of the Ca(OH) 2 is dissolved out, the penetration coefficient increases, while the pH value of the water decreases. It has been demonstrated that scanning transmission electron microscope (STEM) techniques are quite useful for determining local structures and compositions in the cement at sub-micron meter spatial resolution. The preferential dissolution of Ca ions results in refinement of cement grains. When the Ca/Si ratio decreases to 1.05, most grains have a round shape in the sub-micron range. X-ray mapping suggests the formation of 3CaOÁAl 2 O 3 Á xSiO 2 Á(6À2x)H 2 O (x¼0{3). Ettringite has been mostly dissolved out. But Mg ions remain still in form of brucite. When Ca/Si reaches 0.91, the morphology has changed to a mixture of fibers and granules. The fibers have been identified as a mixture of Calcium Silicate Hydrate Gel and silica gel. Quantitative EDX composition analyses have demonstrated that the granules are altered products of hydrogrossular, 3CaOÁAl 2 O 3 Á2SiO 2 Á2H 2 O, which have been predicted by previous theoretical studies. It is also been shown that hydrotalcite with Mg and Al has been also formed. The results thus obtained are in principle in accordance with the process predicted by previously proposed thermodynamic models.
Cement and Concrete Research, 2007
When concrete is exposed to the elements, its underlying microstructure can be attacked by a variety of aggressive agents; for example, rainwater and groundwater. The knowledge of concrete resistance to long term water aggression is necessary for predictions of their performance in different environments. This study aims to analyse the effects of leaching on the microstructure of Portland cement binders. Leaching of cement pastes was performed by an accelerated extraction leaching test that produces significant degradation and helps to achieve equilibrium or near-equilibrium conditions between the leachant medium and cement paste. FTIR spectroscopy, TG-DTA thermal analysis, low temperature nitrogen gas sorption, and geochemical modelling were used to characterize the microstructural changes produced in cement pastes at different equilibrium pHs reached during the leaching process.
The degree of cement hydration determined by backscattered electron microscopy
The degree of hydration of Portuguese composite cement pastes mixed with 0.25, 0.35, 0.45, 0.55 and 0.65 w/c ratios and cured at 5ºC, 20ºC and 38ºC was determined by electron backscattered imaging. Specimens for microscopic study were prepared at the ages of 4, 12 and 24 hours, 2, 3, 7 and 28 days and 11 months hydration time. From each specimen, two random image files of two random 'fields' were obtained at 120 times magnification. Image files were enhanced and the percentage of unhydrated cement, in relation to the total amount of pixels of the image file, was clearly distinguished and estimated by histogram thresholding. The degree of hydration was calculated for each different age from the percentage of unhydrated cement measured by a proposed method that does not require measurements from fully hydrated samples; i.e. it only uses the percentage of unhydrated cement at each age and the w/c ratio of the mix. The degree of hydration obtained by electron backscattered imaging was compared with the degree of hydration obtained from thermogravimetric analysis and from specific gravity measurements. The comparison indicate that a good relation exist.
International Journal of Structural Engineering, 2013
SEM-BSE image analysis technique is one of promising approaches to determine water/cement ratios in hardened cementitious materials. In this study, a method using under-pixel information in the BSE images is proposed. It is hypothesized that a gray level of each pixel reflects the under-pixel porosity. It is also assumed that the porosity smaller than the resolution results in the shifts in position of the gray levels of specific phases. The amounts of shifting are combined with the Powers and Brownyard model so that the degree of hydration is directly estimated from the BSE images. The method was applied to hardened cement pastes with different water/cement ratios. There was a good agreement between estimated and real water/cement ratios. An estimate within an error of ±0.02 was attained except an extremely low water/cement ratio. The shift in the gray level histogram is useful information on microstructure in cement pastes.
Degradation of cement pastes by organic acids
Agriculture produces effluents, like liquid manure and ensilage effluents, that cause serious environmental problems. In order to limit this pollution, manure needs to be stored in water-tight silos often made of concrete. Manure contains organic acids which constitute a severe chemical threat for concrete.
Materials
Concrete tanks, in coke wastewater treatment plants, are exposed to aggressive wastewater with high ammonium and chloride content, deteriorating the concrete binder. Due to this, toxic compounds may migrate to the environment. The results of the experimental work presented confirmed the changes in the phase, microstructure and concentration of chlorides caused by the penetration of NH4Cl into the hardened cement paste in dry conditions. Geochemical modeling of the interactions between the aggressive solution, the cement stone matrix and the pore water was performed in order to track the destruction process effects. The results are useful for condition assessment of the structures operating under occasional immersion.
Iranian endodontic journal, 2017
The present study evaluated the element distribution in completely set calcium-enriched mixture (CEM) cement after application of 35% carbamide peroxide, 40% hydrogen peroxide and sodium perborate as commercial bleaching agents using an energy-dispersive x-ray microanalysis (EDX) system. The surface structure was also observed using the scanning electron microscope (SEM). Twenty completely set CEM cement samples, measuring 4×4 mm2, were prepared in the present in vitro study and randomly divided into 4 groups based on the preparation technique as follows: the control group; 35% carbamide peroxide group in contact for 30-60 min for 4 times; 40% hydrogen peroxide group with contact time of 15-20 min for 3 times; and sodium perborate group, where the powder and liquid were mixed and placed on CEM cement surface 4 times. Data were analyzed at a significance level of 0.05 through the one Way ANOVA and Tukey's post hoc tests. EDX showed similar element distribution of oxygen, sodium, ...
Cement and Concrete Research, 2014
According to recent developments in cement clinker engineering, the optimization of chemical substitutions in the main clinker phases offers a promising approach to improve both reactivity and grindability of clinkers. Thus, monitoring the chemistry of the phases may become part of the quality control at the cement plants, along with the usual measurements of the abundance of the mineralogical phases (quantitative X-ray diffraction) and the bulk chemistry (X-ray fluorescence). This paper presents a new method to assess these three complementary quantities with a single experiment. The method is based on electron microprobe spot analyses, performed over a grid located on a representative surface of the sample and interpreted with advanced statistical tools. This paper describes the method and the experimental program performed on industrial clinkers to establish the accuracy in comparison to conventional methods.