Papers by Keyword: Carbonation

Abstract: Green concrete is a recent sustainable practice in UAE that was enforced by Dubai Municipality in construction field within the emirate of Dubai to reduce the carbon foot print in construction industry and to increase the durability of the structures. This led the construction industry to reduce the usage of ordinary portland cement by replacing it with supplementary cementitious materials (SCMs) such as Grand Granulated Blast Furnace Slag (GGBS) and flyash (FA). Incorporating GGBS or FA in concrete mixtures can improve durability parameters of hardened concrete, such as resistance to water permeability, reduced water absorption and chloride penetration. This ultimately increases the structure’s service life by increasing the threshold of concrete mixture for chloride induced corrosion. On the other hand, carbonation induced corrosion to concrete is usually being ignored or forgotten generally, due its usual slow rate ingression in plain portland cement concrete mixtures. Several studies showed that incorporating some types of SCM – especially at high percentage - can reduce the concrete resistance to carbonation. Additionally and for concrete with recycled aggregate, carbonation investigation should be taken into consideration. This is since recycled aggregates are reused aggregates that are extracted from demolished structures and buildings which were already subjected to different environmental exposures and deteriorations. Unlike chloride penetration, there is no direct ASTM standard test to anticipate the concrete mixture resistance to carbonation at early ages. In this study, concrete mixtures with flyash and different recycled aggregate replacement percentages are investigated for carbonation resistance in accelerated proposed method, considering concrete mixtures’ key parameters like water-cement ratio, and total cement content. The results are analyzed to arrive to pertinent conclusions for the best utilization of sustainable concrete for carbonation resistance.

Abstract: The accelerated carbonation with different pressure steaming conditions was used to process the steel slag, so the slag could turn into a primary cementitious product with carbonation activity. XRD, FTIR, TG, N₂ absorption BET surface area analyzer and SEM were used to characterize the mineral and chemical compositions and microstructure of each sample before and after the carbonation. The results show that: the carbonation products with different morphologies are formed under different temperature conditions. The optimum temperature for the accelerated carbonation for processing the steel slag is selected to be 90 °C, which results in the compressive strength of 32.8 MPa. The BET specific surface area of the steel slag reduces after carbonation, the sample density increased after carbonation.

Abstract: There is an intensive construction of sewage collectors in the cities. The main structural material used in the construction of collector tunnels is reinforced concrete. Services engaged in the operation of sewage systems, increasingly began to face the destruction of concrete of non-pressure sewer collectors as a result of gas corrosion. Concrete corrosion takes place only in non-pressure manifolds, in the protruding part of the water pipeline or tunnel. The maximum intensity of corrosion is observed in the area, adjacent to the axis of the arch. Сorrosion damage can occur intensively on the walls and in the zone of variable water level. The article analyzes the causes leading to corrosion of reinforced concrete in tunnels.

Abstract: This paper studies the possibility of usage of chitosan derivatives (hydroxypropyl chitosan (HPCH) and carboxymethyl chitosan (CMCH)) as admixtures for aerial lime-based mortars. The physical-mechanical properties were studied on the specimens prepared with constant water/binder ratio and binder/aggregate ratio 1:3 by weight using siliceous sand with the grain size up to 4 mm and doses of admixture ranging between 0.5 and 10‰. The properties were studied on the specimens up to 365 days. The addition of admixtures improves workability of mortar, but in the early stages also decreases strengths of mortars, especially the compressive strength. The addition of HPCH significantly reduces the bulk densities of specimens, while CMCH decreases them just slightly. With the increasing amount of time, the difference in strengths between reference and tested mortars decreases, reaching the similar values after 90 days of curing time. The further ageing causes additional growth of strengths with a significantly higher increase in the case of CMCH.

Abstract: Carbonation governs the microstructure and the overall mechanical performance of mixes involving MgO cements as the main binder. Aggregate grading has a significant influence on the carbonation process due to the different particle arrangements that determine the porosity and permeability of the resulting formulations. This work investigates the effect of aggregate particle size distribution on the carbonation of blocks containing reactive MgO. Samples containing four different aggregate profiles were subjected to accelerated carbonation at 20% CO₂ concentration for up to 28 days. While the influence of gap grading on strength development was not very pronounced, mixes with the lowest initial porosity indicated the greatest increase in density at the end of 28 days. This also translated into the highest strength results obtained due to the formation of hydrated magnesium carbonates, reaching 10 MPa only after 1 day of carbonation. The porosity values measured before carbonation were inversely correlated with the corresponding densities and final strengths of each mix. An inverse correlation between porosity and permeability values before carbonation led to the conclusion that the connectivity of pores rather than the total pore volume controls the carbonation reaction. Mixes with higher initial permeabilities achieved the highest strengths, proving that the extent of CO₂ diffusivity is mainly dependent on pore connectivity.

Abstract: This paper is introducing results of diagnostic survey of bridge reg. No. 333-003 over the Elbe in Přelouč [1], which included an evaluation of the previous reconstruction carried out in the 1990s [2, 3] and the quality control of the concrete used in the construction after more than 90 years of operation. Visual inspection, comparison of depth of concrete carbonation and thickness of top layer of reinforcement concrete and concrete compression strength are presented in this paper. This paper come into existence with cooperation with the state-funded organization Road Administration and Maintenance of the Pardubice Region.

Abstract: This paper studies the possibility of usage of the guar gum and its derivatives (carboxymethylhydroxypropyl guar (CMHPG) and hydroxypropyl guar (HPG)) as admixtures for aerial lime-based mortars. The influence on the properties of mortars was studied on the aerial lime –based mortars prepared with quartz fine grained sand and doses of admixtures ranging between 0,5 and 10‰. The hardened bulk densities, flexural and compressive strength, porosity, water absorption coefficient due to capillarity action and carbonation rate were studied. The addition of the hydroxypropyl guar lowered the bulk density (due to an air intake), improved workability, slightly increased the strength, slowed carbonation rate, and nobbled the water transport in the mortar. The addition of carboxymethylhydroxypropyl guar does not impact the bulk density, the strengths were increased similarly to HPG: it does not impact carbonation rate significantly, so the long term strengths were comparative with the HPG. The water transport was slightly better in lower doses and slightly worse in larger doses in comparison with the reference mortar. The pure guaran was found not to be beneficial for the lime mortars for its only advantage is in the water transport, where in any dose the transport was better than any other mortar, but the benefit of this is questionable.

Abstract: This paper deals with determination of basic physical, mechanical, thermal and water transport properties of lime–based plasters whose composition was modified by the addition of diatomaceous earth. To eliminate possible deterioration of original lime plaster by natural weathering, the hydrophobic admixtures on the stearate and oleate basis were added into the plaster mixtures and boiled linseed oil as a painting was applied. All studied material parameters were tested after 28 days of wet curing and after exposition to accelerated carbonation. The results of examined properties of developed plasters gave promising outcomes for the use of hydrophobised materials in renewal of historical buildings. Based on the obtained data, plaster made of lime hydrate, diatomite, and combination of water repellent agents can be recommended for renovation purposes.

Abstract: In the current restoration practice, the mortars based on aerial or hydraulic lime with siliceous aggregate are used on repair / reconstruction of historical plasters. The resulting properties of lime mortars do not depend only on the type of aggregate, but also on its contamination, origin and a degree of hardening. For this reason, it is needed to know a detailed characteristic of the aggregate and the results obtained for the particular aggregate cannot be generally applied for the similar type of aggregate. This work presents the applicability of Czech local crushed limestone aggregate and limestone fines as a filler to natural hydraulic lime-based mortars. The role of aggregate and limestone fines on the properties of mortars is examined by comparing the mechanical strengths, porosity and frost resistance of the mortars with pure quartz sand and limestone aggregate and its quantity in the mortar. It was found that the limestone aggregate has produced lower strengths, higher total porosity of natural hydraulic lime-based mortars. It has resulted in low frost resistance of the mortars.

Abstract: The aggregate occupies most of the volume of the concrete; it significantly affects the diffusion of CO₂ in the concrete. In this study, we adopted the accelerated carbonation test to investigate the effect of the aggregate content and paste thickness on the carbonation resistance of cement-based materials. Results showed that for the mortar specimens, 44% was the critical percolation sand volume. Within the critical volume, the dilution and tortuosity effects were in the dominant position; while over the critical volume, the interfacial transition zone (ITZ) and percolation effects were in the dominant position. For the concrete specimens, the paste thickness had good correlation with the concrete carbonation depth: the paste thickness increased and the carbonation depth showed a decrease tend; otherwise, the paste thickness decrease and the carbonation depth showed an increase tend.