Papers by Keyword: Carbonation

Abstract: The effects of corrosion on the reinforced concrete structure due to carbonation affect its operation life. The research work considers a major critical component causing global warming as it studies the links between reinforced concrete deterioration mechanisms and anthropogenic carbon aerosol (black carbon soot) emissions in the atmosphere. Experimental tests were carried out to study the effect of carbonation caused by the emission of black carbon soot on mechanical properties and durability of reinforced concrete. Mass concrete and reinforced concrete prepared with Ordinary Portland cement (OPC) in water/cement ratios ranging from 0.45 to 0.65 were used to produce concrete samples. Compressive strength tests, tensile strength test, and carbonation depth tests were carried out on concrete to determine its level of deterioration following the carbonation effect. The carbonation chamber was prepared with carbon soot of different concentrations to simulate different levels of black carbon soot in the atmosphere. Results showed that concrete compressive strength was not totally affected by carbonation, but there was reduction in the tensile strength of reinforcing steel. The carbonation depth was observed to progress deeper into the concrete with a longer duration of exposure to carbonation agents in the chamber. The result of this study will serve as a guide during concrete installations.

Abstract: Mortar finishing is frequently used to improve the carbonation service life of structural concrete. Moreover, carbonation is aggravated due to global warmings, such as the increase of CO₂ concentration and temperature. This study shows a probability-based approach for evaluating the carbonation service life of coated concrete considering global warming. First, a carbonation model is proposed for assessing the carbonation depth of concrete with mortar finishing. The effect of global warming on carbonation is considered in the carbonation model. Second, a probability-based method is employed to determine the carbonation service life considering the thickness and mixtures of mortar finishing and substrate concrete. Based on the statistical analysis of calculation results, we find that for a concrete structural with 50 years’ service life, 15% service life will be reduced due to global warming.

Abstract: This paper concerns the degradation of fire protection boards in the ceiling structure of the 4^th tube of Elbtunnel in Hamburg, Germany. During the routine inspection an irregularity in the ceiling material was observed. Based on this inspection five cores were drilled out of the fire protection boards. These samples were examined and analyzed using visual, X-Ray Diffraction analysis (XRD), Differential Thermal Analysis (DTA) and Scanning Electron Microscopy (SEM) images. From the inspection and the analysis of data it was possible to conclude the cause of the material corrosion of the autoclaved calcium silicate fire protection boards.

Abstract: The carbonation process in alkali-activated slag cement concrete is more complicated. This paper reviews the research progress of carbonation resistance of alkali-activated slag cement concrete at home and abroad and summarizes the existing research on carbonation. The focus is on the carbonation mechanism, test methods, influencing factors and the effect of carbonation on the performance of alkali-activated slag cement concrete. The problems existing in the current research on the anti-carbonation property of alkali-activated slag cement concrete and the issues for further research are proposed.

Abstract: Influence of exometabolites of Bacillus cereus strain microorganism on cement mortar properties was studied. According to the strength criterion, the optimal dosages of the bioadditives and the order of its introduction into the solution are established. The description of the mechanism of formation of the effect of bio-cementation is given.

Abstract: The aim of this paper is the evaluation of concrete carbonation depth from a probabilistic analysis, focusing specifically on the study of the marble powder diameters randomness effect on the reinforced concrete carbonation. Monte Carlo simulations are realized under the assumption that the marble powder diameter (Dmp) is random variable with a log-normal probability distribution.

Abstract: The construction industry is now facing expanding and extensive activities in the area of assessing and retrofitting buildings and bridges that aligns with the sustainable construction strategy. These activities recognise the importance of extending the life of existing construction works thereby delivering environmental, economic and socio-political benefits. Reinforced concrete structures and their reliability are currently receiving considerable attention as a significant part of these structures reaches the design service life. Degradation processes such as carbonation- and chloride-induced corrosion have a major influence on the reliability and serviceability of concrete structures. The submitted study is primarily focused on reinforced concrete structures whose main degradation factor is carbonation of the concrete cover. Examples of such structures are cooling towers or industrial chimneys. Structures in the power industry are usually designed for service life of 40 years. Carbonation-induced corrosion results in visible cracks and unacceptable spalling of concrete cover. The aim of the study is to improve predictions of carbonation-induced corrosion propagation and to critically compare the criteria for degradation level assessment used in practice. The probabilistic analysis is based on measurements of concrete cover and carbonation depths and continuous observations of signs of corrosion on structural surfaces. The example of an industrial chimney shows that the limit of a severe failure, which requires (possibly repeated) minor repairs, is exceeded after about 17 years. The critical failure limit (30% of structural surface with visible signs of corrosion) is reached after 50 years, which seems to be sufficient as it is after 10 years than the usual design service life.

Abstract: This paper presents an experimental study to investigate the effects of compressive stress during the CO₂ attack on wellbore cement under carbon capture and storage (CCS) conditions. Oil well cement samples were designed to be exposed to humid supercritical CO₂ gas and CO₂-saturated brine and simultaneously subjected to external compressive stresses with load levels of 0, 25%, 50%, and 75% of the ultimate compressive strength. Morphology changes were determined using phenolphthalein dye testing and scanning electron microscopy. Mineral changes were detected by X-ray diffraction. Relative compressive strength and gas permeability of exposed cement were analyzed. It is shown that the 25% stress level has little effect on degradation of cement while the applied compression load up to 50% increased the compactness of cement and finally slowed down the degradation rate. In contrast, a much higher compressive stress level up to 75% facilitated the generation and propagation of micro-cracks. The stress induced micro-crack finally caused a surge in CO₂-rich fluids and then significantly accelerated the degradation rate of oil well cement. Findings from this study expanded the understanding of the integrity of oil well cement for CCS wells.

Abstract: Nowadays, in order to design durable construction materials all collected knowledge on material science as well as modern technologies allow solving the problems by applying mimicry or nature-like are technologies based on interdisciplinary study of geonics. Considering the principles of geology, it is important to study the influence of genetic characteristics of raw materials on structural performance and durability of final construction materials. The following paper focuses on assessment of effect of genetic characteristics of industrial by-products such as materials derived from iron-ore production at the Kursk Magnetic Anomaly on carbonation resistance in autoclave cellular concrete was studied. The secondary products of ore rigging process, the screening fraction of sandstone, shale rocks as well as tailings of wet magnetic separation were used as a quartz-bearing mineral components. The evaluaton parameters in this study were compressive strength, density and carbonation resistance of autoclave cellular concrete (ACC) specimens. The carbonation process was reproduced in laboratory prepared concrete. In order to eccelerate carbonation reaction all specimens were stored in a sealed chamber saturated with CO₂. The density and compressive strength characteristics of ACC with regular quartz sand were 630 kg/m³ and 3.6 МPа, respectively. The same parameters were slightly higher in case of full replacement of quartz sand by sand stone and demonstrated 655 kg/m³ and 3.9 МPа, respectively, and carbonation resistance was increased by 20 %. The results support the view, that screening fraction of sandstone that had been formed under natural metamorphosis is more preferable for use in ACC production. Full replacement of regular quartz sand by sand stone in ACC specimens showed improved compressive strength and carbonation resistance.

Abstract: Alkali activated slag (AAS) offers opportunities to the construction industry as an alternative to ordinary Portland cement (OPC). The production of OPC and its use contributes significantly to release of CO₂ into the atmosphere while AAS is an industrial by-product that contributes much less to the environmental footprint that needs to be recycled if not landfilled. This paper outlines some of the key properties, merits and demerits of AAS when used as alternative to OPC. Competitive compressive strength of AAS concrete is amongst of the advantages of replacing cement with AAS while high shrinkage and carbonation levels are potential disadvantages.