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This paper focuses on the evaluation of sulfate resistance in carbonated pastes prepared from low-lime calcium silicates (CCS). The chemical interaction between the sulfate solution and paste powders was assessed by monitoring the leaching of the Ca and Si species, reduction in the content of carbonates and formation of gypsum. The analytical techniques used in the study included TGA, ICP-OES and IC. The results of the study revealed that the level of the resistance to the chemical effect of the sulfates depends on the type of the calcium silicate, degree of crystallinity of calcium carbonate, and the type of cation present in the sulfate solution. [ABSTRACT FROM AUTHOR]

In order to follow the progress of cement hydration by analytical methods, the ongoing hydration reaction needs to be stopped by removing free water from the samples. There are several water removal techniques, affecting in varying degrees the chemical composition of cement-based materials. Oven drying is one of the most widely used drying techniques because of its high effectiveness and easy availability. Nevertheless, elevated temperatures may speed up hydration processes and support carbonation. This paper aims to investigate the impact of oven drying and sample dimensions on the amount of calcite generated in the cement pastes. The cement pastes are prepared with a water-to-cement ratio of 0.4 and are stored in water for 28 days. The hydration stoppage methods applied thereafter include oven drying at 50 °C, 80 °C, and 110 °C. Their impact on the chemical composition and microstructure development, with emphasis on the calcite content in the studied cement pastes, is analyzed by means of thermal analysis (DSC/TG), X-ray diffraction analysis, and these results were complemented by mercury intrusion porosimetry. [ABSTRACT FROM AUTHOR]

Limestone collected from Gunung Kidul Regency (Special Region of Yogyakarta, Indonesia) has been used to synthesize precipitated calcium carbonate (PCC) without calcination step. This paper evaluates the effect of calcination of limestone, HNO3 concentration of dissolution, and reaction time of carbonation on the PCC properties. The PCC was synthesized by dissolving the limestone powder in HNO3 solution in various concentrations (0.5 M, 0.7 M, and 1.0 M with) for different times, and followed with carbonation with CO2 flow at various times (30, 45, and 60 minutes) to produce precipitate (CaCO3). The residue was then washed and heated at 105 °C for 8 h to result in PCC and then characterized with FTIR, XRD, and SEM-EDX. Analog work was performed with a limestone calcination step at 900 °C for 5 h before being dissolved in HNO3 solution. The result showed that the highest PCC yield (more than 90%) containing calcite and vaterite was found when the dissolution was used 1.0 M HNO3 and a carbonation time was 30 minutes. Due to low energy consumption, comparable yield and properties, preparation of PCC without limestone calcination step revealed a green and prospective process for the large scale production. [ABSTRACT FROM AUTHOR]

In the paper it is presented first of all the investigations and the carried out studies for founding the rehabilitation solutions of the decantation pond made from washing out, transport and carbonation of the sugar beet which has the code 02 04 01 in the European Catalogue of wastes. There are presented, shortly, the results towards the possibility of flooding the terrain, the hydrogeological conditions, the pedological conditions and the most important issue the dates towards the pollution with heavy metals, organohalogen compounds, polycyclic aromatic hydrocarbons and polychlorinated biphenyls. In order to evaluate the pollution it were taking soil assays from three points of the location and they were chemical and physical analyzed. The carried out determinations showed that the Romanian limit values are not gone beyond the limit towards the pollution containing substances for the agriculture. On the other hand, it were made investigation towards the fertility level of the soil from the location. On these lines, it is also presented the reliability study made for the evaluation of the fertility and of the favorable conditions for using the surface of the lake as an agricultural terrain. The studies shows that there are some limitations towards using it as an agricultural terrain most of all towards pedological and fertility reasons. Having all these studies as a starting point in the paper it is presented the set of measures in order to use the terrain in agriculture. The proposed measures are enduring measures (it is estimated the period of rehabilitation 3... 4 years) which include: the degrease of the soil humidity throughout temporally works: leveling and modeling of the surface, making a ploughing for turning the soil, discing of the ploughed surface, the amelioration of the soil fertility and of the soil structure throughout the cultivation of fertility plants which are covered during the autumn by the ploughing. [ABSTRACT FROM AUTHOR]

This work desires to impart awareness about the carbonation effect in concrete. Carbonation favors the deterioration of steel due to the action between carbon dioxide and calcium hydroxide in cement paste. The work aids in finding the highly carbonated concrete by reviewing the correlation between the distinct types of concrete and enhancing the life of the concrete. The types of concrete under study are Fly ash and Silica fume concrete. Besides, the factors influencing the carbonation are noticed. The furnished details are a part of many research works waiting to prevent the existing old and new structures from failure due to corrosion by carbonation. [ABSTRACT FROM AUTHOR]

Corrosion of steel is a damaging agent that reduces the functional and structural responsibilities of reinforced concrete structures. Accordingly, reinforced concrete members in the environments that are prone to concrete carbonation or chloride attack coupled with high temperature and relative humidity suffer from accelerated corrosion of reinforcing material. Also, literature proves that climate influences corrosion of concrete, and suggests investigation of impact of corrosion on concrete based on climate zone. Therefore, this paper presents the effects of climate and corrosion on concrete behavior, using bond strength of concrete as a case study. Concrete specimens were prepared form concrete mix that was infested with 3.5 kgm-3 of sodium chloride to accelerate corrosion. The specimens were cured sodium chloride solution 3.5% by weight of water for 28 days before placing them in the exposure conditions. Pull-out tests were conducted at time intervals for one year to measure the impact of exposure condition and corrosion on bond strength of concrete. The results show reduction of bond strength of concrete by 32%, 28% and 8% after one year of subjection of the specimens to the unsheltered natural climate, sheltered natural climate, and laboratory ambient environment respectively. The findings indicate that the climate influences corrosion, which reduces the interlocking bond between the reinforcing bar and the adjacent concrete. [ABSTRACT FROM AUTHOR]

The purpose of this paper is research on curing behavior of cold-weather concrete with anti-frost admixtures. During the study derivative thermal and X-ray phase analyses were performed and tests were carried out according to the standard GOST technique. The research results obtained reveal the peculiarities of cement hydration and concrete curing at subzero temperatures. The influence of subzero temperatures and anti-frost admixtures on hydrated phases of hardened cement paste and concrete strength formation was studied. It is found that cold-weather concrete does not cure at subzero temperatures, but when defrosting it attains 80 to 85% of its grade strength by the 28th day. Concrete achieves its grade strength when curing in normal conditions in 60 days only. Freezing concrete with anti-frost admixtures results in increase of calcium hydroxide content in hardened cement paste immediately when produced and has increased tendency of concrete to carbonation. [ABSTRACT FROM AUTHOR]

The paper summarizes sorption properties of limestones with variable content of calcium carbonate. Changes of sorption capacities during cyclic calcinations and carbonations were investigated using laboratory apparatus with vertical quartz reactor. Application of suitably chosen limestones and process conditions offered sustainable capacity up to 11 kg CO2 / 100 kg of initial limestone. Method of reactivation of the spent limestone using a gas saturated by water vapor was proposed to eliminate decreasing of the capacity in the carbonate looping process. [ABSTRACT FROM AUTHOR]

This paper deals with effects of pre-cracks on both initiation and propagation of reinforcement steel corrosion due to carbonation. The ring shaped mortar samples with 8 mm steel bar inside were cracked with different crack widths ranging from 12 micrometers to 600 micrometers and then subjected to carbon dioxide environment for different terms to assess the carbonation profile in cracks and along the interface between steel and concrete, damaged by the internal pressure applied to the ring samples. After carbonation of interface, ring samples were submitted to wetting-drying cycles to study the propagation of corrosion and the effect of corrosion products on healing and then repassivation of steel bar or corrosion cracks development. Results show that irrespective of width of cracks, the carbon dioxide reaches the interface between steel and mortar and propagates along this interface. The samples then subjected to wetting-drying cycles exhibit corrosion development all along the interface, the appearance of oxides does not lead to create corrosion cracks for the duration of the experiments. [ABSTRACT FROM AUTHOR]

CaCO3 powder in the form of PCC is needed in various industrial fields. The formation of the CaCO3 phase is influenced by the reaction medium. Ethanol is used as a reaction medium because it has a lower surface tension coefficient than water. The surface tension coefficient is related to the energy of crystal formation. In this study, Ca(OH)2 solution was mixed with ethanol with a volume ratio of 30% and 50% with a stirring rate of 200 rpm at room temperature. The carbonation method is carried out with a CO2 gas flow rate of 2.35 lt/min. The results of observations with XRD and SEM showed the formation of calcite, vaterite and aragonite phases. The addition of 30% ethanol into the reaction medium for 5 hours and immersion for 3 days increased the vaterite phase by 53.57% and the aragonite phase by 4%. Meanwhile, the addition of 50% ethanol decreased the vaterite phase by 69.77% and increased the aragonite phase by 375%. [ABSTRACT FROM AUTHOR]

The current study evaluates the influence of the static compaction pressure applied during the casting process on Carbonated Reactive Magnesia Cement-based mortars. For this purpose, mortars, embodying biomass fly ash as filler, were designed and moulded through static compaction pressures of 10, 30, 50, and 70 MPa. The moulded specimens were submitted to an accelerated carbonation curing period of 24 h under controlled conditions. The devised mortars were evaluated through compressive strength tests, and their microstructure was assessed through Mercury Intrusion Porosimetry (MIP), Thermogravimetry and Derivative Thermogravimetry (TG-DTG), and Fourier-transform Infrared Spectroscopy (FTIR) analyses. The results showed that the increment in the static compaction pressure during the specimens' casting process not only led the mortars to reduce their porosity by up to ~30% and increase their compressive strength by up to ~58% (from 19.8 MPa to 31.2 MPa) but also that such a change seems to hinder the CO2 diffusion into the specimens' core, thus resulting in a lower content of carbonated products. In addition, the MIP analyses demonstrated that the static compaction pressure applied in the mortar casting process changes the pores' characteristics, while TG-DTG and FTIR analyses provided evidence that the devised mortars were carbonated to a certain degree. Therefore, this work demonstrated that Carbonated Reactive Magnesia Cement-based mortars are highly influenced by the static compaction pressure applied during the casting process, at least up to a certain value. [ABSTRACT FROM AUTHOR]

Synthesis of precipitated CaCO3 from limestone Blumbungan, Madura island (East Java, Indonesia) using carbonation process have been done. The carbonation process is carried out with variations of the CO2 gas flow rate of 1.175, 2.35, 3.525 and 4.7 l/min at room temperature. The crystalline phase formed was characterized by X-ray diffraction (XRD) X-Pert MPD with Cu-Kα radiation (λ = 1,5406 Ǻ) and scanned from 10° to 60°. The morphological investigation was analyzed by Scanning Electron microscope (SEM) FEI Inspect S50 X'pertPRO PANalytical. Crystal size was analyzed using the Scherrer equation. The XRD test results show that the phases formed at CO2 gas flow rates 1.175, 2.35, and 3.525 l/min are vaterite and calcite, while at 4.7l/min only calcite phase is formed. Variations in CO2 gas flow rate affect the percentage of calcite and vaterite formed. The crystal size of precipitated CaCO3 the Scherrer equation ranged from 55,572 - 81,290 nm. The morphology of precipitated CaCO3 is mix rhombohedral cubic and needle-like. [ABSTRACT FROM AUTHOR]

The carbonation process of prepared lime plaster and lime based plaster with pozzolana active metakaolin is performed in an accelerated test arrangement. The depth of carbonation head is determined using colorimetric method and FTIR spectroscopy. Based on experimental data of carbonation head, time dependent k factor function is calculated that points to the decelerated and retarded propagation of the carbonation process due to metakaolin used in plaster composition. [ABSTRACT FROM AUTHOR]

Recent years, CaO-based synthetic materials have been attracted attention as potential adsorbents for CO2 capture mainly due to their high CO2 adsorption capacity. In this study, micro/nanostructured aragonite CaCO3 was synthesized by a simple hydrothermal method with using polyacrylamide (PAM). The structural, morphological and thermal properties of the synthesized sample were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and thermogravimetry analysis (TG-DTA). The XRD and FESEM results showed that the obtained sample was aragonite CaCO3 with aggregated nanorods and microspheres composed of nanorods. A TG-DTA apparatus with Thermoplus 2 software was used to investigate the effect of carbonation temperature on the CO2 adsorption capacity of CaO derived from aragonite CaCO3 sample. At 300 °C, the sample reached the CO2 adsorption capacity of 0.098 g-CO2/g-adsorbent, whereas the sample achieved the highest capacity of 0.682 g-CO2/g-adsorbent at 700 °C. The results showed that the carbonation temperature significantly influenced on the CO2 adsorption capacity of the CaO derived from aragonite CaCO3. [ABSTRACT FROM AUTHOR]

The Cementitious Barriers Partnership (CBP) is focused on reducing uncertainties in current methodologies for assessing cementitious barrier performance and increasing the consistency and transparency in the assessment process. One important set of US Department of Energy challenges is assessing the integrity and closure of the high-level waste (HLW) tanks that currently store millions of gallons of highly radioactive wastes. Many of these tanks are decades past their design lives, have leaked or been overfilled, and must be emptied and closed to satisfy regulatory agreements. Carbonation-induced corrosion has been identified as a primary degradation and possible failure mechanism for the HLW tanks prior to closure. After closure the impact of carbonation (and concurrent oxidation) may be to increase the release and short-range transport of contaminants of concern. HLW tanks may be significantly empty for many years (and possibly decades) prior to closure; the performance of the closed tank over centuries, if not millennia, must be assessed to evaluate the potential release of residual radionuclides to the environment. CBP is developing models to evaluate a representative HLW tank closure scenario including the potential impacts of carbonation on waste tanks prior to and post closure. CBP modeling tools, including LeachXS™/ORCHESTRA, are being used to simulate waste tank carbonation, major constituent leaching, and contaminant releases to evaluate the source term and near-field conditions. Simulations presented here include sensitivity analysis for uncracked concrete to varying input parameters including composition, effective diffusivities, and thermodynamic parameters. [ABSTRACT FROM AUTHOR]

The embodied carbon dioxide content of concrete is already among the lowest of the main construction materials. Tom De Saulles of MPA The Concrete Centre reports on a new study into carbonation, which is set to provide a further boost to concrete's environmental credentials. [ABSTRACT FROM AUTHOR]