Papers by Keyword: Carbonation

Abstract: Reinforcing steel deterioration is complicated by corrosion. Reinforcing steel corrosion can weaken a structure. Corrosion cannot be eliminated; however, it can be reduced to increase building service life. The objective of the research it to demonstrate the effect of coating method as corrosion prevention and the cover depth to the corrosion performance of steel bar embedded in seawater mixed mortar. This study examines the corrosion rate of steel reinforcement in a 15 x 15 x 15 cm mortar cube made by using seawater as mixing water and containing Portland Pozzolan Cement (PPC) as a binder material. This study also experiences numerous corrosion mitigation methods using wet, dry, and dry-wet cycle exposure methods. The reinforcement and mortar surface were protected with anti-corrosive paint. Additionally, specimens without protective measures were also fabricated for comparison. Two reinforcing steels were attached in the two different cover depths, 3 cm and 5 cm. This study used sand and batching plant byproducts as fine aggregate. Study found a hierarchy of corrosion-causing exposures. The dry-wet cycle was the most corrosive, followed by wet and dry. Steel coating prevents corrosion better than surface coating. However, both methods outperformed the uncoated method in corrosion resistance. The mortar cover was 5 cm thick, compared to 3 cm expected. A combination of mortar with fine sand aggregate outperformed dry mortar made from batching plant leftovers. The investigation of corrosion potential through the utilization of the half-cell potential technique reveals that the outcomes obtained from test specimens using the steel coating prevention approach exhibit a higher degree of positivity in comparison to the prevention method including surface coating. The unprotected approach exhibits outcomes that lean towards being more unfavorable compared to the steel coating prevention method and the surface coating prevention method. The findings indicate that the performance of reinforcing steel embedded within a 3 cm mortar cover depth is often worse when compared to reinforcing steel situated inside a 5 cm mortar cover depth.

Abstract: Mineral sequestration technology is one of the most effective carbon capture and storage techniques. Basic oxygen furnace slag (BOFS), one of the by-products generated during the steelmaking process, has a particularly high potential for mineral sequestration compared to other similar wastes such as blast furnace slag and ladle slag. In the case of BOFS, mineral sequestration not only contributes to carbon uptake but also stabilizes its internal structure. So far, most of the investigations on BOFS mineral sequestration rely on accelerated carbonation involving high pressures and supplying concentrated CO₂ in a short period. Although these studies are useful for investigating the overall potential for carbon capture of BOFS, they are less useful for practical applications on a large scale. Moreover, it is hard to draw any conclusions regarding the carbonation reactions lasting for years in stockpiles of BOFS. This research identified the consequences of long-term carbonation on BOFS samples and determined the best conditions for natural mineral sequestration.

Abstract: CO₂ levels in the world are constantly increasing and have generated a great impact on reinforced concrete structures causing increased carbonation. The phenomenon of carbonation causes corrosion of the reinforcing steel, therefore, reinforced concrete structures present a high risk of corrosion of its reinforcing steel causing the reduction of the useful life of the structure, or in extreme cases, a demolition must be carried out. The objective of the present study is to propose a prediction model for carbonation depth in pure concretes which are not designed for durability (w/c<0.50), but when they are designed for resistance (w/c>0.55). CEB-FIP model presents the limit of serving only for concrete with w/c<0.50, due to this, the present study proposes a model that will help as a reference to estimate the useful life of structures that are built and designed in cities where they do not are exposed to these durability conditions. The modified model for predicting the carbonation depth based on CEB-FIP in pure concrete with high w/c (0.60 and 0.72) uses the parameters of temperature, relative humidity, CO₂ concentration, and water/cement ratio. The objective is to obtain the accuracy of the modified model for predicting the carbonation depth in concrete over the years. For the results, the theoretical data obtained from the modified model was used and a comparison was made with the experimental results obtained from concrete specimens tested inside an accelerated carbonation chamber to find the model's accuracy.

Abstract: Concrete carbonation serves as one common durability issues in reinforced concrete structures at present. In order to understand the carbonation mechanism, many methods were developed by previous researchers for the characterization of concrete carbonation. For example, Phenolphthalein spraying method, Thermo-gravimetric analysis (TGA), X-ray diffraction, Fourier Transform Infrared Spectroscopy (FTIR), Mercury intrusion porosimetry (MIP), etc.. In this paper, all existed carbonation methods were summarized, and, based on the parameter (pH value inside pores, microstructure, chemical composition, etc. ) each method focuses, the function behind method was elaborated. Finally, this paper discussed the pros and cons of current methods, and further developing directions were proposed.

Abstract: In order to reveal the carbonation mechanism of alkali-activated concrete, the accelerated carbonation tests based on alkali-activated slag pastes were carried out. The evolution of microstructure and chemical composition for alkali-activated slag pastes subjected to carbonation was analyzed combining thermogravimetric analysis (TGA), mercury intrusion porosimetry (MIP) and a recently developed extended X-ray attenuation method (XRAM). The results showed that, the microstructure of alkali-activated slag pastes deteriorated gradually. Based on MIP and XRAM, the porosity of S4 (sample with a water-binder ratio of 0.4) increased by 8.24% and 11% after carbonation, and that of S6 (sample with a water-binder ratio of 0.6) increased by 7.45% and 10%, respectively. Besides, thermal analysis showed that, after carbonation, 11.45 mol / L and 19.57 mol /L CaCO₃ were produced separately by S4 and S6. The main carbonation product for S6 was calcite, but for S4 vaterite and disorderly stacked calcite were also presented.

Abstract: Lime is used in a variety of industrial sectors (e.g. construction materials, iron and steel industry, flue gas cleaning, etc.) By the thermal decomposition of limestone (CaCO₃), known as calcination, two products are obtained: CO₂ and quicklime, i.e. calcium oxide (CaO). There is a growing interest in quantifying and improving the potential of CO₂ absorption of lime containing products during their operational life. The carbonation occurs during the lifetime of the lime application and it consists in the absorption of atmospheric CO₂ that closes the loop by forming calcium carbonate back. Thus, a portion of the CO₂ emitted during calcination is reabsorbed and stored in a permanent stable form. A literature review was carried out on the Carbonation Rate (CR) of lime used in three different construction materials: air-lime mortars, mixed air-lime mortars and hemplime. Out of 205 scientific publications reviewed, only 57 provide information about CR, specifically 21 for air-lime mortars, 27 for mixed air-lime mortars and 9 for hemplime. CR is 80-92% for pure air-lime mortars, 20-23% for mixed ones and 55% for hemplime. For all the materials, the CR trend over time was also assessed, according to the Fick’s law.

Abstract: Carbonation of concrete causes corrosion of the steel reinforcement and reduces the service life of the structure. Based on the reality that fly ash discharge is increasing year by year and construction sand is becoming increasingly limited, it is of practical importance to study the effect of fly ash dosage and desert sand replacement rate on the carbonation resistance of concrete. Orthogonal test L₉(3⁴) with four factors and three levels was designed to study the influence of water-binder ratio, fly ash dosage, sand ratio and DSRR on carbonation resistance of desert sand concrete (DSC). The results of the orthogonal tests were analysed by range analysis and ANOVA and a comparatively better concrete mix ratio was given. Next, single-factor tests were designed to investigate the effects of fly ash and desert sand replacement rates on the carbonation resistance of DSC respectively. The regression model among carbonation depth, fly ash dosage and DSRR was established. The experimental results show that the carbonation depth of concrete with fly ash as a single variable increases with the amount of fly ash, increasing more rapidly in the early stages than in the later stages. As the DSRR increases, the carbonation depth of concrete with desert sand as a single variable first decreases and then increases and reaches its lowest value when DSRR equals 20%. When fly ash and desert sand are mixed into concrete simultaneously, the carbonation depth reaches minimum value on the condition that fly ash dosage is 10% and DSRR is 20%.

Abstract: Concrete bridges are widely widespread as a main roadway infrastructure. The maintenance and the restoration or renewal of such artefacts are a major concern for the public administration. The reinforced concrete objects are exposed to detrimental atmospheric condition. The deterioration is different for the sixteen highway bridge elements. Some parts are sheltered or directly exposed to the atmospheric events, such as sun, rain, snow, salt spreading, splashing and washing. South-west sides or partially sheltered zones are more susceptible to cyclic temperature and humidity variation. This results in increased carbonation. The North-east sides, especially the curbs, are less carbonated because of enhanced presence of high humidity and are more prone to organic growth. The limit of 0.025 % of chloride content by concrete weight is exceeded in some bridge elements down to 40 mm, apart from the piles. Shoulders and curbs exhibit the highest Chloride content. Lower contents are observed for beams, struts and piles partially sheltered from the direct salt spreading action. A slight correlation exists between high Chloride content and low mean carbonation and depends on the humidity presence. This is observed for the shoulders, the shelves and the curbs, but less for the beams, the piles, the struts and the heads.

Abstract: Hempcrete is a natural building material obtained mixing hemp shives (i.e., the woody core of the hemp plant) with a lime-based binder and water. Hempcrete as construction material is gaining increasing interest as the EU aims to achieve net zero emissions by 2050. This material has, in fact, the ability to uptake carbon dioxide from air (i.e., via carbonation) and to store carbon for long time. The goal of the present work is to deeper analyze the environmental profile of hempcrete, in order to assess its potentials in reducing emissions of construction sector. Specifically, Life Cycle Assessment (LCA) of a non-load-bearing wall made of hempcrete blocks is carried on. The analysis encompasses the whole life cycle from the extraction of raw materials to the end of the service life. The analyzed blocks are produced by an Italian company. Only aerial lime is used as binder, microorganisms are added to the blocks to accelerate carbonation. The impact on climate change is assessed through the GWP 100 method proposed by IPCC. Preliminary results reveal a nearly neutral carbon budget.

Abstract: Sustainable building materials have been developed to reduce the polluting emissions and the exploitation of natural resources of the building sector. Among these materials, an outstanding category is that of nature-based solutions which are produced recovering waste or by-products of agricultural cultivations and using them as vegetal aggregates to replace the traditional ones. This paper focusses on hempcrete which is produced mixing the by-product of industrial hemp cultivation (i.e., shives) and lime to obtain a sustainable, breathable and insulating material. The strength of hempcrete develops through carbonation of the binder that, leading to the formation of calcium or magnesium carbonates and mineralization of shives, determines the microstructure and hence most of the characteristic properties of the material. The aim of this research is to investigate how carbonation influences the microstructure of hempcrete when different recipes are used for blocks production. This study consists in the characterization of the material through techniques such as XRD (X-ray Diffractometry), SEM (Scanning Electron Microscopy) and TG-DTG (thermogravimetric analyses). Moreover, the evolution of carbonation is studied analyzing samples at different maturation times. The investigation of the carbonation reaction degree is also crucial to evaluate the environmental performances of the material because it allows the quantification of the carbon dioxide uptake. Also, periodic characterization allows to assess the durability of hempcrete and to select the best formulation according to the designed application and the corresponding service conditions.