The author details the reactions of various concretes on steel reinforcement. Although portland cements, slag cements and high alumina cements are all hydraulic binders, each possess special properties which are examined. The discussion of causes and methods of preventing the corrosion of steel reinforcement covers such aspects as galvanised steel reinforcement, effects of concrete composition, corrosion of steel reinforcments in concrete and prestressed reinforcement. It is concluded that the most significant influences on the corrosion of prestressing wire in concrete are: the presence of chloride; the presence of nitrates; the composition of the concrete; the degree of carbonation of the concrete; concrete compaction and, chlorides and sulphates should be used as far as possible when steel is embedded. (TRRL)

Corrosion of steel by concrete

Recycling of waste concrete has become an important issue worldwide due to the continued increase of construction wastes. Also, the growing global construction activities urge to find sustainable resources to replace natural materials for the production of concrete. In the past few decades, many researches have been carried out on the use of recycled aggregate (RA) derived from construction and demolition wastes to produce concrete products. This paper reviews the previous findings on the effects of use of RA on durability of concrete. In general, the amount of adhered mortar and the quality of the original concrete have a significant effect on the properties of resulting concrete. The increase of RA content and w/c ratio results in poorer durability of concrete. In comparison, the negative effect of recycled fine aggregate is more obvious than that of recycled coarse aggregate. The use of pozzolanic materials either for surface coating of RA or intermixed within the concrete are effective and feasible to improve the overall durability of concrete. Recent researches on CO2 treatment indicate that it can enhance the properties of RA and durability of concrete significantly.

Durability of recycled aggregate concrete – A review

A critical review and assessment for usage of recycled aggregate as sustainable construction material

Calcination of carbonate rocks during the manufacture of cement produced 5% of global CO_2 emissions from all industrial process and fossil-fuel combustion in 2013. Considerable attention has been paid to quantifying these industrial process emissions from cement production, but the natural reversal of the process—carbonation—has received little attention in carbon cycle studies. Here, we use new and existing data on cement materials during cement service life, demolition, and secondary use of concrete waste to estimate regional and global CO_2 uptake between 1930 and 2013 using an analytical model describing carbonation chemistry. We find that carbonation of cement materials over their life cycle represents a large and growing net sink of CO_2, increasing from 0.10 GtC yr^(−1) in 1998 to 0.25 GtC yr^(−1) in 2013. In total, we estimate that a cumulative amount of 4.5 GtC has been sequestered in carbonating cement materials from 1930 to 2013, offsetting 43% of the CO_2 emissions from production of cement over the same period, not including emissions associated with fossil use during cement production. We conclude that carbonation of cement products represents a substantial carbon sink that is not currently considered in emissions inventories.

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Substantial global carbon uptake by cement carbonation

Carbonation of cement-based materials: Challenges and opportunities

This paper reviews the effect of incorporating recycled aggregates, sourced from construction and demolition waste, on the carbonation behaviour of concrete. It identifies various influencing aspects related to the use of recycled aggregates, such as replacement level, size and origin, as well as the influence of curing conditions, use of chemical admixtures and additions, on carbonation over a long period of time. A statistical analysis on the effect of introducing increasing amounts of recycled aggregates on the carbonation depth and coefficient of accelerated carbonation is presented. This paper also presents the use of existing methodologies to estimate the required accelerated carbonation resistance of a reinforced recycled aggregate concrete exposed to natural carbonation conditions with the use of accelerated carbonation tests. Results show clear increasing carbonation depths with increasing replacement levels when recycled aggregate concrete mixes are made with a similar mix design to that of the control natural aggregate concrete. The relationship between the compressive strength and coefficients of accelerated carbonation is similar between the control concrete and the recycled aggregate concrete mixes.

/pdf/carbonation-behaviour-of-recycled-aggregate-concrete-2ga7i12jgz.pdf

Carbonation behaviour of recycled aggregate concrete

Corrosion Behavior of Stainless Steel Rebars Embedded in Concrete: an Electrochemical Impedance Spectroscopy Study

Statistical analysis of the carbonation coefficient in open air concrete structures

An experimental study to investigate the influence of matrix strength, fibre content and diameter on the compressive behaviour of steel fibre reinforced concrete is presented. Two types of matrix and fibres were tested. Concrete compressive strengths of 35 and 60 MPa, 0·38 and 0·55 mm fibre diameter, and 30 mm fibre length, were considered. The volume of fibre in the concrete was varied up to 1·5%. Test results indicated that the addition of fibres to concrete enhances its toughness and strain at peak stress, but can slightly reduce the Young's modulus. Simple expressions are proposed to estimate the Young's modulus and the strain at peak stress, from the compressive strength results, knowing fibre volume, length and diameter. An analytical model to predict the stress–strain relationship for steel fibre concrete in compression is also proposed. The model results are compared with experimental stress–strain curves.

Compressive behaviour of steel fibre reinforced concrete

The relationship between natural and accelerated concrete carbonation resistance has been investigated. Cores were taken from real structures and their non-carbonated inner part was subjected to accelerated carbonation resistance testing, allowing the assessment of natural and accelerated carbonation resistance on the same specimen. The carbonation resistance was characterised by means of a coefficient given by the ratio between carbonation depth and the square root of exposure time. According to the literature on the subject a linear relationship between accelerated and natural carbonation coefficients, not influenced by cement type, was assumed. A complementary experimental study was carried out to investigate how age influences accelerated carbonation resistance. Different factors, according to exposure classes, were determined by linear regression analysis to correlate accelerated and natural carbonation coefficients. The use of these factors together with Fick’s first law enables the long term prediction of carbonation depth in structures based on accelerated carbonation resistance testing.

R. Neves

Papers

Carbonation behaviour of recycled aggregate concrete

Corrosion Behavior of Stainless Steel Rebars Embedded in Concrete: an Electrochemical Impedance Spectroscopy Study

Statistical analysis of the carbonation coefficient in open air concrete structures

Compressive behaviour of steel fibre reinforced concrete

Field assessment of the relationship between natural and accelerated concrete carbonation resistance