Alkalinity and Its Consequences for the Performance of Steel-Reinforced Geopolymer Materials

This paper investigates the development of the alkalinity and its impact on carbon steel reinforcement embedded in alkali-activated fly ashes (AAFA) and alkali-activated fly ashes with ten percentage mass (wt%) of blast furnace slag (AAFAS)-based materials (geopolymer–GP). The pH analysis of eluates indicates a remarkable decrease of alkalinity in AAFA and AAFAS in the first hours of the geopolymerization process. Phenolphthalein solution and pore solution tests on concretes also show a sharp decrease of alkalinity with increased Ca content in the binder due to carbonation. Micro X-ray computer tomography (µXCT) and electrochemical techniques indicate that the changed pH in the GP systems was accompanied by a decrease in the corrosion rates of steel reinforcement when compared to ordinary Portland cement (OPC) systems. In contrast to calcite and vaterite, which were detected in OPC and AAFAS after a carbonation process, only sodium carbonate natron was determined at lower levels in AAFA by X-ray diffraction (XRD).

Optimization of Micro and Nano Palm Oil Fuel Ash to Determine the Carbonation Resistance of the Concrete in Accelerated Condition

The carbonation rate of reinforced concrete is influenced by three parameters, namely temperature, relative humidity, and concentration of carbon dioxide (CO2) in the surroundings. As knowledge of the service lifespan of reinforced concrete is crucial in terms of corrosion, the carbonation process is important to study, and high-performance durable reinforced concretes can be produced to prolong the effects of corrosion. To examine carbonation resistance, accelerated carbonation testing was conducted in accordance with the standards of BS 1881-210:2013. In this study, 10–30% of micro palm oil fuel ash (mPOFA) and 0.5–1.5% of nano-POFA (nPOFA) were incorporated into concrete mixtures to determine the optimum amount for achieving the highest carbonation resistance after 28 days water curing and accelerated CO2 conditions up to 70 days of exposure. The effect of carbonation on concrete specimens with the inclusion of mPOFA and nPOFA was investigated. The carbonation depth was identified by phenolphthalein solution. The highest carbonation resistance of concrete was found after the inclusion of 10% mPOFA and 0.5% nPOFA, while the lowest carbonation resistance was found after the inclusion of 30% mPOFA and 1.5% nPOFA.

Condition assessment of selected reinforced concrete structural elements of the bus station in Kielce

The paper presents the results of the research aimed at assessing the condition of reinforcement and concrete cover in selected elements of the structure of the most recognizable structure in Kielce, i.e. PKS station, located at Czarnowska Street. Currently, demolition works are underway resulting from the planned modernization. The assessment of the corrosion risk of the reinforcement in the construction elements was carried out with the use of a semi-non-destructive electrochemical method. The use of this method made it possible to determine the probability of reinforcement corrosion in the selected areas and to estimate its rate. The protective properties of concrete cover were checked by the carbonation test (test using a 1% phenolphthalein solution) and phase composition analysis (X-ray diffraction analysis). In order to determine the position of the reinforcing bars and to estimate the concrete cover thickness distribution in the areas corresponding to the aforementioned measurements, ferromagnetic detection system was used.

Determination of carbonation degree of existing reinforced concrete structures and their restoration

The research of carbonation of existing concrete structures presented in the article was executed in the process of conducting a technical survey of the building. According to the results of the study, places with varying degrees of carbonation were identified. A method for preparing the phenolphthalein solution used in the examination is described. A methodology for testing structures to determine the degree of carbonation is presented. The results of measuring the degree of carbonation of structures by the phenolphthalein method are presented. The data obtained show that the concentration of carbon dioxide has a significant effect on the corrosion process of reinforcing bars and the loss of the bearing capacity of structures during the operation of an existing building. A favorable range of pH values for concrete structures during operation is considered. The average actual depth of the neutralized concrete layer is determined. The method of restoration of building structures exposed to the carbonation reaction is described. The impact of carbonation on reinforced concrete structures during the operation of the building is assessed. The results of the restoration work are presented.

The Influence of Carbonization on the Performances of Fly Ash Geopolymeric Concrete

Two mixtures were designed to manufacture ordinary Portland cement concrete (PCC) and alkali-activated fly ash geopolymeric concrete (FGC). The depth of carbonation at 3rd,7th,14th and 28th day were measured according to the carbonization test method in “Ordinary Concrete Long-term Performance and Durability Test Method Standard”(GB/T 50082-2009) by spotting with phenolphthalein solution. The changes of compressive strength of the specimens carbonized with different days were tested and compared, as well as the pH value of specimens’ surfaces. Furthermore, the changes in microstructure and chemical composition were observed through the scanning electronic microscope (SEM) and energy dispersive X-ray spectrometer (EDX), respectively. The results show that although the compressive strength of FGC decreased significantly at first, but there is no obvious effect of carbonization on compressive strength, pH value and chemical composition of FGC as carbonation going on. Moreover, the microstructure of FGC is more homogeneous and denser. It can be concluded that compared with PCC, carbonization resistance of FGC is much better.

A New Fabrication Method for Paper-Based Microfluidic Device Used in Bio-Assay

Paper-based microfluidic devices have a significant potential for low-cost diagnostics in the developing world. This study reported a simple fabrication method based on the digitallization of microfluidic technology for paper based microfluidic devices. Melted wax was jetted steadily with PZT actuated microfluidic pulse inertia driving system and pulled-forged glass micronozzle in the form of droplets. The wax melted into filter paper to form hydrophobic wall and different patterns for paper microfluidic devices were made. The influence of system parameters such as driving force, frequency, the fabrication process and the tip diameter of glass micronozzle on the wax line width was experimentally studied. 75 μm500 μm wax lines were achieved with the wax printing system. The paper microfluidic devices fabricated could lead the capillary action of black ink and the color change reaction of NaOH and phenolphthalein solution. Result showed that the wax printing system is simple structured and this method suggests a novel path to develop simple, inexpensive, and portable diagnostic assays.

Carbonation Test Study on Low Calcium Fly Ash Concrete

Making full use of fly ash (FA) is an important part of sustainable materials development in the word. This paper discussed the carbonation resistance of concrete with 10%, 20% and 25% fly ash replacement ratios(FA%). The process was accelerated in artificial carbonation laboratory by controlling 20% concentration of CO2, 10°C~30°C temperature and 50%~70% relative humidity(RH). The depth of carbonation could be observed by spraying phenolphthalein solution on the fresh broken concrete surface. The test results show that adding fly ash into concrete results in the decrease of cement consumption and calcium hydroxide, so carbonation rate increases. But with the increase of FA% and carbonization time, the drop speed of carbonation rate slower, the differences in the microstructure are detailed. In addition, the carbonation rate increases when the ambient temperature varies from 10°C to 30°C and ambient RH falls from 70% to 50%. It concludes that the 10°C ambient temperature and 70% ambient RH are superior to other environmental conditions for enhanceing concrete carbonation resistance, and mixing 10%~25% FA into concrete have little influence on carbonation resistance of concrete if have adequate curing time.