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The article announces that T. A. Harrison and his colleagues have received the MCR Award from the "Magazine of Concrete Research" for their paper "Experience of using the prTS 12390-12 accelerated carbonation test to assess the relative performance of concrete."

From first principles, criteria for the EN 12390-10 outside protected test have been developed and compared with existing practice. These criteria align well with the UK recommendations but are more conservative than the current French and Spanish requirements. The EN 12390-10 outside protected test is unsuitable for classification as this would require anybody using the procedure with identical concrete to get the same result. Unfortunately, current tests that are suitable for classification, whilst safe, do not reflect the real performance of slowly reacting cements. Improving the test for classification purposes will take time and meantime the use of the EN 12390-10 outside protected test and the criteria given in this paper provides a procedure by which both sustainability and durability may be achieved. The downside of this test is its slowness and, therefore, it is only suitable for type testing or the determination of limiting values and other criteria to be used in specifications or production. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of magnesium oxide (MgO) on the carbonation resistance of alkali-activated slag-fly ash blend containing 75% ground granulated blast furnace slag (GGBS) and 25% low-calcium fly ash. Two types of GGBS were used with different magnesium oxide content. Phenolphthalein indicator and pH profiles showed that the GGBS with higher levels of magnesium oxide offered no significant improvement in resistance against natural and 1% accelerated carbonation. X-ray diffraction confirmed no hydrotalcite formation, although the magnesium oxide content was 9·1%. A very small amount of free magnesium ions (Mg2+) was available in the pore solution, which was deemed insufficient to form hydrotalcite. Lack of its formation was the major reason for the lower carbonation resistance. Excessive silicate in the system reduces the calcium oxide/silicon dioxide ratio, which leads to the incorporation of magnesium ions in the calcium silicate hydrate structure. Hydrotalcite was observed when the activator concentration was reduced. The results suggest that in addition to magnesium and aluminium ion (Al3+) availability, silicate concentration also plays a strong role in deciding the hydrotalcite formation in alkali-activated GGBS concrete. [ABSTRACT FROM AUTHOR]

As the low content of calcium-bearing components in demolished recycled fine aggregates (RFA) significantly limits the carbon dioxide (CO2) curing efficiency, the effects of pre-soaking demolished RFA with calcium source solutions before the curing process are presented in this paper. Effects of varied types of calcium source solutions, including calcium hydroxide (CH), calcium chloride (CL) and calcium nitrate (CN) on the curing process are investigated. In addition, the influence of the other two parameters pertaining to curing conditions, namely, the carbon dioxide pressure and curing temperature, on the curing process are also studied. The experimental results show that, after the pre-soaking and curing process, the values of powder content, water absorption and crush value are all decreased for RFA. Furthermore, the compressive strength of mortars at 28 d are increased by as much as 56%. In addition, CN pre-soaking allows the RFA to achieve the lowest water absorption, and CL pre-soaking enables the mortars to obtain the highest compressive strength at 28 d; increasing gas pressure brings about a minor improvement in the properties of RFA and mortars, and curing temperature has complex effects on the carbonation reactions. [ABSTRACT FROM AUTHOR]

In this paper an experimental study is presented on the interaction between concrete carbonation and chloride attack. The experiments are carried out on chloride-contaminated cement pastes that have been exposed to a carbon dioxide environment. Free and total chloride contents at different carbonation times are measured in the tested specimens using traditional leaching and acid-soluble methods. Bound chloride contents are calculated from the measured total and free chlorides. The experimental data show that the carbonation of cement paste results in a release of bound chlorides, which is related to not only the decomposition of Friedel's salt, but also the decomposition of calcium-silicate-hydrate (C-S-H) gel. Based on the obtained experimental results, a numerical model is also developed for simulating the carbonation process of the chloride-contaminated cement paste. The model can be used to explain how the bound chlorides are released in a chloride-contaminated cement paste under the influence of carbonation reactions. [ABSTRACT FROM AUTHOR]

Based on systematic analysis, evaluation and synthesis of a 30 000 strong data matrix generated from 213 studies from 33 countries published since 1968, this paper details the extent of research that has been undertaken and discusses the effect of fly ash (FA) on the carbonation and carbonation-induced corrosion of concrete. It is shown that FA as a cement component, such as those adopted in BS EN 197-1:2011, increases the carbonation rate of concrete, both when concrete is designed in terms of equal water/cement ratio or strength, though with the latter to a lesser extent. This increase in carbonation has also been confirmed for in-service concrete. The net effect of FA content on the carbonation of concrete is dependent upon the combination of mix design, curing and exposure related parameters. FA in concrete is also shown to increase the corrosion of reinforcement, which can only be overcome by increasing the cover to reinforcement, concrete strength, or a combination of the two, beyond those specified in standards such Eurocode 2, BS EN 206-1:2013 and BS 8500. Contrary to the commonly held view, this study shows that the relative rate of carbonation of FA concrete with reference to corresponding Portland cement concrete remains similar under accelerated and natural carbon dioxide exposures. [ABSTRACT FROM AUTHOR]

The environment around concrete structures may be influenced by a changing climate, especially in the long run, leading to an acceleration of deterioration. Therefore, the safety, serviceability and durability of concrete infrastructure may decline at a faster rate than expected. Carbonation-induced deterioration to concrete structures constructed in Sydney, Australia and Kunming, China under a changing climate is investigated in this paper. Two emissions scenarios are considered - RCP 8.5 and RCP 4.5, representing high and medium greenhouse gas emissions scenarios respectively. The spatial time-dependent reliability analysis includes time-dependent climate scenarios and deterioration processes, as well as a large number of random variables and spatial random fields of material properties and dimensions. The surface of concrete structures is discretised into a large number of elements and the likelihood and extent of corrosion damage is calculated by tracking the evolution of the corrosion process of each element using Monte Carlo simulations. The results show that a changing climate could cause the extent of damage to increase by up to 6% for reinforced concrete infrastructure in Kunming. The findings may be used to assess climate adaptation measures in the design stage, as well as a cost-benefit analysis of climate adaptation measures. [ABSTRACT FROM AUTHOR]

In this paper, the influence of six different mineral admixtures on the long-term properties of concrete within 1080 d is investigated; these admixtures include steel slag, ground granulated blast furnace slag (GGBS) and composite mineral admixtures with four different GGBS-to-steel slag ratios. The results show that steel slag and composite mineral admixtures with a high content of steel slag have many negative effects on the long-term properties of concrete, such as decreasing strength, increasing porosity and chloride penetrability, and decreasing carbonation and sulfate resistance. GGBS tends to improve the long-term properties of concrete. Concrete containing composite mineral admixture with a high content of GGBS can achieve similar long-term strength, porosity, chloride penetrability, and carbonation and sulfate resistance to Portland cement concrete. The influence of the composite mineral admixture composed of 80% GGBS and 20% steel slag on the long-term properties of concrete might be very close to that of GGBS. All the mineral admixtures tend to decrease the long-term drying shrinkage of concrete. The effect of composite mineral admixtures with higher GGBS content on the long-term drying shrinkage of concrete is more significant. [ABSTRACT FROM AUTHOR]

After water, concrete is the most widely used substance on the planet. Carbonation of cementitious materials is an inevitable process through which concrete compositions react with carbon dioxide. Carbonation leads to rebar corrosion in reinforced concrete (RC) structures, reducing structures' longevity. This process increases cement production, for repair and replacement, which brings about more carbon dioxide emission. Conversely, plain concrete could be one of the materials with the most potential in terms of carbon dioxide storage. Therefore, an understanding of concrete carbonation and the influential parameters on its carbonation is significant. Identifying the effective parameters helps engineers increase RC structures' carbonation resistance and increase plain concrete capacity as a carbon dioxide capture source, which could be both cost-effective and environmentally friendly. In this review, an attempt has been made to summarise present-day knowledge considering cementitious materials' carbonation and point out the areas that need more research to be conducted. Influential factors have been categorised comprehensively. Affecting factors have been explained. Environmental conditions, concrete characteristics and construction operation effects have been reviewed. Furthermore, mathematical models for concrete carbonation proposed by different researchers have been examined to investigate influential parameters in the models and their precision in prediction. [ABSTRACT FROM AUTHOR]

This paper describes the effect of an inorganic coating of concrete (ICC) on the residual compressive strength and carbonation depth of fire-damaged concrete. The concrete specimens were cooled by water-spraying, which is usually used for fire extinguishing in a real fire. The ICC was applied to enhance the residual compressive strength and to reduce the carbonation depth of fire-damaged concrete at different recuring periods. The results showed that the performance of concrete with ICC was better than that of uncoated concrete. After being exposed to 150, 300, 450, 600 and 750°C, compared to uncoated concrete, the compressive strength of concrete with ICC was enhanced by 3·8%, 3·7%, 11·0%, 17·3% and 6·1%, respectively. For concrete exposed to temperatures below 750°C, the carbonation depth of concrete with ICC was reduced significantly compared to the uncoated concrete. In the case of 750°C, the concrete was neutralised completely for both uncoated and coated concrete. The most obvious enhancement of the compressive strength and the most significant reduction of carbonation depth of concrete with ICC can be found after the concrete was exposed to 600°C. Similar results were confirmed with the other two types of concrete with different compressive strength. [ABSTRACT FROM AUTHOR]

This study presents an analysis of a 30 000 strong data matrix derived from 227 studies originating from 35 countries since 1968. Similar to the fly ash effect, the carbonation of concrete increases with the incorporation of ground granulated blast-furnace slag (GGBS), but the rate increases as GGBS content is increased. This effect is greater for concrete designed on an equal water/cement (w/c) basis to the corresponding Portland cement (PC) concrete than on an equal strength basis. The Eurocode 2 specification for XC3 carbonation exposure in terms of the characteristic cube strength of concrete (or its w/c ratio) may need to be increased (or decreased) with the addition of GGBS. Other influencing factors, including GGBS fineness, total cement content and curing, were also investigated. In some cases, the carbonation of in-service GGBS concrete has been estimated to exceed the specified cover before 50 years of service life. Measures to minimise the carbonation of GGBS concrete are proposed. Fully carbonated reinforced GGBS concrete is assessed to show a higher corrosion rate. In relation to PC concrete, the carbonation of GGBS concrete is essentially similar when exposed to 3-5% carbon dioxide accelerated or indoor natural exposure, and the conversion factor of 1 week accelerated carbonation equal to 0·6 year is established. [ABSTRACT FROM AUTHOR]

The combined use of coal bottom ash (CBA) and ground CBA (GCBA) as partial replacement of fine natural aggregate (FNA) and Portland cement, respectively, was investigated for the production of concrete mixtures. Five concrete mixtures incorporating GCBA at 20 wt% replacement of binder and CBA at 0, 25, 50, 75 and 100 wt% replacement of FNA were produced and tested for strength, microstructural characteristics and carbonation resistance. A base concrete mixture made of conventional concrete was also produced as a reference concrete mixture. Test results showed that the combined use of GCBA and CBA in concrete mixtures results in enhancement of the microstructure, carbonation resistance and compressive strength of the resulting concrete mixtures. Scanning electron microscopy and X-ray diffraction analyses pointed at the occurrence of pozzolanic reaction and pore-filling effect of GCBA and CBA in the resulting concrete mixtures. It was observed that 25 wt% replacement of FNA with CBA is an optimum dosage considering its effects on the later age strength and durability characteristics of the resulting concrete mixtures. [ABSTRACT FROM AUTHOR]

The potential of utilising alkaline industrial waste with weak or no cementitious properties for carbon dioxide (CO2) capture and for new binders by accelerated carbonation was studied; steel slag (SS), calcium carbide residue (CCR) and waste hydrated cement (WHC) were compared. The carbon dioxide uptake and strength development of SS, CCR and WHC were studied and the relationship of strength development with carbon dioxide uptake and characteristics of carbonation products was analysed. The results indicate that carbon dioxide uptake of SS, CCR and WHC strongly depends on the mineral composition: calcium hydroxide (Ca(OH)2) and calcium silicate hydrate (C–S–H) show relatively higher carbonation activity; dicalcium silicate (Ca2SiO4) absorbs less carbon dioxide than calcium hydroxide and C–S–H. The carbon dioxide uptake of SS, CCR and WHC are 6.1, 23.2 and 17.9%, respectively, after 2 h carbonation curing. Compacted SS, CCR and WHC specimens displayed a compressive strength of 74.9, 20.5 and 28.6 MPa after carbonation for 2 h. Compressive strength development depends on carbon dioxide uptake and mechanical properties of raw materials and carbonation products. Calcium carbonate (CaCO3) and amorphous products fill the pore structure, making the matrix denser; improvement of pore structure relates positively to carbon dioxide uptake. The highest compressive strength of compacted SS is mainly caused by the high elastic modulus of SS and formation of C–S–H gel in the carbonation process. [ABSTRACT FROM AUTHOR]

Numerous studies have been performed on the carbonation model based on the boundary (carbonation front line) between the partially carbonated and non-carbonated zones. However, a significant difference exists between the traditional phenolphthalein spray test results and the prediction model results on carbonation depth. The difference is mainly caused by the partially carbonated zone. In this study, the changes in the microstructure of cement paste during the carbonation process at different carbon dioxide (CO2) concentrations (0·03, 3 and 20%) were determined through the phenolphthalein spray test, thermogravimetric analysis and mercury intrusion porosimetry (MIP). The results showed that carbonation depth and the square root of carbonation time have a linear relationship. Compared with that in the natural carbonation condition, the effect of 20% carbon dioxide concentration on the size of the partially carbonated zone was significant. However, no effect was seen for 3% carbon dioxide concentration. MIP showed that, in the same carbonation zone, low carbon dioxide concentration led to low total porosity; there was a clear refinement in the pore size and there was a high degree of carbonation. [ABSTRACT FROM AUTHOR]

The service life of reinforced concrete structures is assessed for carbonation environments using mathematical models based on different tests: carbonation test-based modelling and air permeability test-based modelling. The study includes experimental testing of five concrete mixes with respect to compressive strength, accelerated carbonation and air permeability with different types of cement, in order to assess the models using probabilistic calculus. Both mathematical models are part of the Portuguese National Annex to the European standard EN 206 for the estimation of design service life. Engineers have the option of choosing which of the two models to use, which means that using either model should produce similar results. The design service life results show that the two models do not converge. The different principle of each test - accelerated carbonation and air permeability - and their different characteristics regarding the various parameters of the modelling equations are some of the aspects discussed. [ABSTRACT FROM AUTHOR]

Systematic analysis and evaluation of experimental results on carbonation and carbonation-induced corrosion resistance of concrete made with Portland limestone cement (PLC) are presented; these results have been extracted from 143 globally published studies in the literature since 1986, by 274 researchers from 131 institutions and 34 countries, and yielding a 19 000 data matrix are presented. It is shown that the carbonation of concrete increases with increasing limestone content, within the range permitted by standard BS EN 197-1:2011. This effect, however, is less marked for concrete designed on an equal strength basis to the corresponding Portland cement (PC) concrete than concrete designed on an equal water/cement ( w/c) basis. Eurocode 2 standard specifications for XC3 carbonation exposure for characteristic cube strength of concrete (or its w/c ratio) may need to be reviewed for the addition of limestone. Other influencing factors: curing, limestone fineness, total cement content, were also studied. A comparison has been conducted for the carbonation performance of concrete made with PLC and cement containing fly ash and ground granulated blast-furnace slag. Procedures to reduce the carbonation of PLC concrete are proposed. Response to accelerated carbonation, at 3-5% carbon dioxide concentration, of PLC concrete is similar to natural indoor exposure. A conversion factor of 1 week accelerated carbonation equal to 0·75 year natural indoor exposure was determined. [ABSTRACT FROM AUTHOR]

The carbonation resistance of a blended slag and low-calcium fly ash (FA) geopolymer concrete was investigated. The geopolymer binder studied was composed of 90% low-calcium FA and 10% ground granulated blast-furnace slag. The alkalinity of the pore solution plays a pivotal role in carbonation progression and subsequent corrosion initiation. pH profiles were measured to assess the pore solution alkalinity. Phenolphthalein indicator was used to measure the carbonation depth. X-ray diffraction (XRD) and quantification were carried out to identify and quantify the carbonation products. The obtained pH profiles illustrated a wider semi-carbonation zone in the geopolymer specimens, although the pH drop was insignificant in most cases. XRD analysis revealed that nahcolite mainly formed at 3% carbon dioxide concentration and led to a significant drop in pH values. The results further demonstrated that 1% accelerated carbonation replicated the natural carbonation process well, with only natron identified as a carbonation product. This work contributes to the assessment of the risk of carbonation-induced reinforcement corrosion in low-calcium FA geopolymer concrete. [ABSTRACT FROM AUTHOR]

The corrosion behaviour of mortar samples reinforced with three different types of ribbed stainless steel (SS) was tested after 9 years. The reinforcements had been both similar welded (SS-SS) and dissimilar welded to carbon steel (SS-CS). After welding, the bars were cleaned by pickling, although this treatment was unable to remove the welding oxides completely. The prepared reinforcements were then embedded in carbonated mortar with chlorides and exposed to high relative humidity. Corrosion potential and electrochemical impedance spectroscopy measurements were used to monitor the spontaneous corrosion behaviour of the samples over 8 years. The welded bars were then anodically polarised in order to force attack. Exposure was continued for a further year to allow progression of the pits. For the SS-SS welded samples, S20430-S20430 showed poor corrosion resistance under these conditions, whereas S32205-S32205 reinforcements demonstrated excellent corrosion behaviour. [ABSTRACT FROM AUTHOR]

This study investigates how the porosity and compressive strength of ordinary Portland cement (OPC) blended with different ratios of synthetic gamma dicalcium silicate (γ-C2S) change in the first 28 d of curing. The composites are cured either under normal atmospheric conditions (standard curing) or in a carbon dioxide chamber (accelerated carbonation curing). The carbon dioxide capture experiments are performed under constant conditions (10% carbon dioxide, 20°C and 60% relative humidity) and results are evaluated on days 3, 7 and 28, representative of the early curing days for the blends. The results show that the samples cured under carbonation exhibit higher compressive strengths after 28 d of curing than their corresponding samples cured under standard conditions. The results also show that the porosity of the 20 wt% γ-C2S/OPC blend cured under carbonation conditions is reduced from 29·0% to 19·4%, indicating the densification of the final product. This decrease in porosity is attributed to the formation of calcite and vaterite (µ-CaCO3) phases, by the free calcium oxide inside the pore structure reacting with carbon dioxide. These findings confirm that a 20 wt% γ-C2S/OPC blend cured under carbon dioxide undergoes densification, and this contributes to the enhanced durability and strength of carbon dioxide-cured cement products. [ABSTRACT FROM AUTHOR]

Thermogravimetric analysis and mercury intrusion porosimetry were used to determine the relationship between cement paste porosity and calcium silicate hydrate (CSH) carbonation during the carbonation process. A method that is not based on the chemical formula of CSH was developed to calculate porosity variation during CSH carbonation. This method is based on the variation of calcium hydrate volume and total volume to obtain the CSH volume variation during carbonation, as well as the porosity variation caused by CSH carbonation. The CSH carbonation results showed that the main factor in the variation of paste porosity was CSH carbonation, which accounted for more than 70% of the total porosity variation. A transition point was observed on the CSH volume variation curve. CSH generated calcium carbonate during the early carbonation process, at which a volume expansion also occurred. The volume shrinkage and calcium carbonate content reached maximum when the carbonation process was completed. [ABSTRACT FROM AUTHOR]

This study investigated the effects of elevated temperature and cooling method on the compressive strength and carbonation depth of concrete specimens which were re-cured for different durations. The concrete specimens were heated to different temperatures up to 750°C and were then cooled in air or by spraying with water. After cooling to room temperature, the specimens were post-fire cured in a controlled environment for a total duration of 90 d. Compressive strength and accelerated carbonation tests were conducted to measure the changes in the compressive strength and carbonation depth of the concrete specimens. The experimental results indicate that the compressive strength of air-cooled concrete exposed to temperatures of 150, 300 and 450°C reached respectively 101·6%, 97·2% and 81·9% of the original values. However, after exposure to temperatures of 600°C and 750°C, the compressive strength of the air-cooled concrete decreased to 40·4% and 26·2% of the original values respectively. The compressive strength values of water-cooled concrete heated to 150, 300, 450, 600 and 750°C gradually changed to respectively 102·7%, 96·7%, 80·2%, 46·9% and 28·7% of the original values. The carbonation resistance of concrete was not recovered for concretes exposed to temperatures above 450°C and the carbonation resistance of the water-cooled concrete was lower than that of air-cooled concrete. After exposure to a temperature of 600°C, similar variations were observed in concretes with water-to-cement ratios of 0·55 and 0·35. [ABSTRACT FROM AUTHOR]

The reaction of fresh lightweight concrete with carbon dioxide during early-age carbonation curing is hindered by surface saturation due to vibration consolidation. To promote a high degree of carbonation of fresh lightweight concretes, a dynamic carbonation system was developed to remove surface free water and inject carbon dioxide simultaneously. Based on cement mass, the resulting carbon uptake reached 13% in 4 h carbonation and 20% in 18 h carbonation. The early strength by fresh carbonation is comparable to that of steam curing, while the late strength is higher in a much reduced process time. The dynamic system can effectively control the relative humidity of the chamber to prevent water accumulation and create a route of capillaries for carbon dioxide diffusion and precipitation of carbonates. Dynamic carbonation creates a carbonate-bond matrix. The process provides an excellent means to recycle carbon dioxide, with economic and environmental benefits. [ABSTRACT FROM AUTHOR]

The purpose of this research was to compare self-compacting concrete (SCC) and conventional concrete (CC), which are used in beams with dense reinforcement, in terms of their carbonation resistance. It was observed that, in both air and moist curing environments, SCC had less carbonation depth than CC and the carbonation depths of both SCC and CC samples stored under moist curing were less than those of samples undergoing air curing. The experiments also showed that, regardless of the type of concrete, carbonation depth decreased with increasing concrete strength class. Furthermore, the study showed that beams produced from SCC were more uniform than CC beams. Consequently, instead of CC, SCC can be used to produce any reinforced concrete components in order to provide increased carbonation resistance and uniformity. The findings of this study may thus lead to increased usage of SCC in construction sites. [ABSTRACT FROM AUTHOR]