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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]

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."

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]

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]