Assessment of the Sustainability of Concrete by Ensuring Performance during Structure Service Life

The article presents an original method to assess the sustainability of concrete. The method uses three parameters, namely, performance, lifetime and environmental impact, to calculate a sustainability index. The originality and simplicity of the proposed method is shown when finding the sustainability index, where the first two factors (service life and performance) are kept constant. This approach is possible within the context of the new proposals that specify the durability of structural concrete in EN 1992 and EN 206. It allows the classification of concrete according to its performance, through environmental action resistance classes (ERC). For this purpose, specific experimental methods were used in order to determine the performance of concrete exposed to carbonation. The concretes were prepared with two cement types with additions (CEM II/A-S and CEM II/A-M (S-LL)). Based on the carbonation resistance classes (first parameter—performance) and exposure classes, the thickness of the concrete cover layer was determined to ensure a certain service lifetime (second parameter—service lifetime). Lastly, the global warming potential was calculated for each composition, allowing the users of the method to select the compositions with the lowest environmental impact.

Firing Parameters Effect on the Physical and Mechanical Properties of Scheelite Tailings-Containing Ceramic Masses

The firing parameters in ceramic masses incorporated with 0, 5, and 10 wt% of scheelite tailings were investigated. The ceramic masses were characterized by X-ray fluorescence, granulometric, mineralogical analysis, and Atterberg limits determination. The samples were obtained by uniaxial pressing (20 MPa), sintered at different temperatures (800, 900, and 1000 °C), and heating rates (5, 10, 15, and 20 °C∙min−1). Physical and mechanical tests (water absorption, apparent porosity, and flexural strength) and mineralogical tests were accomplished from the sintered samples. Natural aging tests were also carried out to assess carbonation resistance. For this, some samples were kept in an internal environment (inside the laboratory) for 3 months. The results showed a high content of calcium oxide in the scheelite tailings and a reduction in the plasticity index of the ceramic masses with the tailings addition. The best results were observed for the ceramic mass with 5% tailings. The best results were observed regarding the firing parameters for the temperature equal to 1000 °C, increasing the heating rate to 10 °C∙min−1 without compromising the material properties. The samples kept in an internal environment for 3 months showed a loss of physical and mechanical properties. Such behavior probably occurred due to the onset of the carbonation phenomenon.

Gum Arabic Nanoparticles as Green Corrosion Inhibitor for Reinforced Concrete Exposed to Carbon Dioxide Environment

The inhibiting effect of Gum Arabic-nanoparticles (GA-NPs) to control the corrosion of reinforced concrete that exposed to carbon dioxide environment for 180 days has been investigated. The steel reinforcement of concrete in presence and absence of GA-NPs were examined using various standard techniques. The physical/surface changes of steel reinforcement was screened using weight loss measurement, electrochemical impedance spectroscopy (EIS), atomic force microscopy and scanning electron microscopy (SEM). In addition, the carbonation resistance of concrete as well screened using visual inspection (carbonation depth), concrete alkalinity (pH), thermogravimetric analysis (TGA), SEM, energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The GA-NPs inhibitor size was also confirmed by transmission electron microscopy (TEM). The results obtained revealed that incorporation of 3% GA-NPs inhibitor into concrete inhibited the corrosion process via adsorption of inhibitor molecules over the steel reinforcement surface resulting of a protective layer formation. Thus, the inhibition efficiency was found to increase up-to 94.5% with decreasing corrosion rate up-to 0.57 × 10−3 mm/year. Besides, the results also make evident the presence of GA-NPs inhibitor, ascribed to the consumption of calcium hydroxide, and reduced the Ca/Si to 3.72% and 0.69% respectively. Hence, C-S-H gel was developed and pH was increased by 9.27% and 12.5, respectively. It can be concluded that green GA-NPs have significant corrosion inhibition potential and improve the carbonation resistance of the concrete matrix to acquire durable reinforced concrete structures.

A Study on the Carbonation Rate of Concrete Exposed in Different Climatic Conditions

Recently, the degradation of concrete has become a serious problem worldwide and one of the principle factors of degradation is the carbonation process. It is well established that environmental conditions affect the carbonation progress of concrete among the most important factors that can greatly affect the carbonation resistance of concrete are relative humidity (RH) and temperature. Carbonation has become a threat to concrete structures, especially in urban and industrial areas. Thus, it is necessary to have a proper design to maintain the structure's stability against degradation caused by carbonation. Therefore, this study was conducted to evaluate the effects of different environmental and climatic conditions on the carbonation rate of concrete. The specimens were prepared using OPC and fly ash (FA). After 28 days of air curing, specimens were exposed to different climate conditions under sheltered and un-sheltered conditions. The carbonation tests were conducted at the ages of 6 and 12 months. It was found that the carbonation rates were significantly influenced by the climate and environmental conditions; the specimens exposed to a relatively dry environment and low annual precipitations have shown higher carbonation during one-year exposure. Moreover, in unsheltered conditions, the annual precipitation significantly affects the carbonation rate of concrete. Furthermore, it was observed that a 20% replacement of FA does not enhance the carbonation resistance of concrete.

Assessment of the Sustainability of Concrete by Ensuring Performance During Structure Service Life

The article presents an original method to assess the sustainability of concrete. The method uses three parameters, namely: performance, lifetime and environmental impact, to calculate a sustainability index. The originality and the simplicity of the proposed method presented in the article consists in the fact that by applying the relation to determine the sustainability index, the first two factors service life and performance are constant. This approach is possible in the context of the new proposals to specify the durability of structural concrete in EN 1992 and EN 206. That allows classification of concrete according to its performance, through Environmental action Resistance Classes (ERC). For this purpose, specific experimental methods were used in order to determine the performance of concrete exposed to carbonation. The concretes were prepared with two cement types with additions (CEM II / A-S and CEM II / A-M (S-LL)). Based on the carbonation resistance classes (the first constant - the performance) and exposure classes, the thickness of the concrete cover layer was determined to ensure a certain service lifetime (second constant - the service lifetime). Finally, the global warming potential was calculated for each composition, consequently allowing the users of the method, to select the compositions with the lowest impact on the environment.

Evaluation of Eco-Efficient Concretes Produced with Fly Ash and Uncarbonated Recycled Aggregates

The fabrication of conventional concrete, as well as remains from demolition, has a high environmental impact. This paper assessed the eco-efficiency of concrete made with uncarbonated recycled concrete aggregates (RCA) and fly ash (FA). Two concrete series were produced with an effective water/cement ratio of 0.50 (Series 1) and 0.40 (Series 2). In both series, concretes were produced using 0% and 50% of RCA with 0%, 25% and 50% FA. After analysing the compressive strength, and carbonation and chloride resistance of those concretes, their eco-efficiency based on the binder intensity and CO2-eq intensity was assessed. We found that the use of 50% uncarbonated RCA improved the properties of concretes produced with FA with respect to using natural aggregates. The concrete made of 25% FA plus RCA was considered the most eco-efficient based on the tests of compressive, carbonation and chloride properties with the values of 4.1 kg CO2 m−3 MPa−1, 76.3 kg CO2 m−3 mm−1 year0.5 and 0.079 kg CO2 m−3 C−1, respectively. The uncarbonated RCA improved carbonation resistance, and FA improved chloride resistance. It can be concluded that the use of 50% un-carbonated RCA combined with FA considerably enhanced the properties of hardened concrete and their eco-efficiency with respect to concretes produced with natural aggregates.