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Alkali-activated slag concretes stored for 7 years under atmospheric conditions are assessed, and the structural characteristics of naturally carbonated regions are determined. Concretes formulated with a 400 kg/m 3 and water/binder (w/b) ratio between 0.42 and 0.48 present similar natural carbonation depths, although these concretes report different permeabilities after 28 days of curing. The inclusion of increased contents of binder leads to a substantial reduction of the CO 2 penetration in these concretes, so that negligible carbonation depth values (2 mm) are identified in concretes formulated with 500 kg/m 3 of binder. Calcite, vaterite, and natron are identified as the main carbonation products formed in these concretes. These observations differ from the trends which would be expected in comparable ordinary Portland cement-based concretes, which is attributable to the physical (permeability) and chemical properties of alkali-activated slag concretes promoting high long-term stability and acceptably slow carbonation progress under natural atmospheric conditions.

The environmental impact from the production of cement has prompted research into the development of concretes using 100% replacement materials activated by alkali solutions. This paper reports research into the durability of AAS concrete. The durability properties of AAS have been studied for a range of sodium oxide dosages and activator modulus. Properties investigated have included measurements of workability, compressive strength, water sorptivity, depth of carbonation and rapid chloride permeability. Microstructure studies have been conducted using scanning electron microscopy and energy dispersive X-ray spectroscopy. It was concluded that an activator modulus of between 1.0 and 1.25 was identified as providing the optimum performance for a sodium oxide dosage of 5% and that AAS concretes can exhibit comparable strength to concrete currently produced using Portland cement (PC) and blended cements. However, with regards to the durability properties such as water sorptivity, chloride and carbonation resistance; the AAS concretes exhibited lower durability properties than PC and blended concretes. This, in part, can be attributed to surface microcracking in the AAS concretes.

Strain-hardening cement-based composites were named after their ability to resist increased tensile force after crack formation, over a significant tensile deformation range. The increased resistance is achieved through effective crack bridging by fibres, across multiple cracks of widths in the micro-range. Whether these small crack widths are maintained under sustained, cyclic or other load paths, and whether the crack width limitation translates into durability through retardation of moisture, gas and other deleterious matter ingress, are scrutinised in this paper by evaluation of test results from several laboratories internationally. This contribution is a short version of the State-of-the-Art report by RILEM TC 208-HFC, Subcommittee 2: Durability, developed during the committee life 2005–2009.

This paper presents the results of recent experimentation performed to study time-dependent changes in the mechanical performance of textile reinforced concrete (TRC) made with AR glass fibre and to specify the decisive mechanisms influencing the durability of this composite material. The effect of the matrix composition was investigated by varying hydration kinetics and alkalinity of the binder mix. At first, tensile tests on (accelerated) aged specimens made of TRC were performed. The results showed a pronounced decrease in the tensile strength and strain capacity for TRC whose matrix was most alkaline (Portland cement was used exclusively as binder in this composition). The performance of TRC made with modified, alkali reduced matrix composition was to a great extent unaffected by exposure to accelerated ageing. In order to investigate the mechanisms leading to such different behaviours, changes in the mechanical performance of the fibre–matrix bond were studied using double-sided pullout test specimens with under-critical fibre reinforcement after they had undergone accelerated ageing. Furthermore, the appearance of the microstructure in the interface between fibre and matrix was described by images obtained from SEM-investigations. Measured reductions in the toughness of the composite materials could be attributed mainly to the visual observed disadvantageous new formation of solid phases in the fibre–matrix interface, while the deterioration of the AR glass fibre seemed to play only a secondary role. It could be shown that the morphology of the formed solid hydration phases depends to a large extent on the matrix composition.

Generally, concrete with high resistance to the marine environment should have high compressive strength, a low chloride diffusion coefficient ( D C ), and a high acceptable chloride level (Ac). Considering all parameters simultaneously, this study evaluated the degree of fly ash concrete durability based on 10-year results in a marine site. Based on the concrete durability (Ac/ D C , as compared to cement concrete with a W/B ratio of 0.45) and compressive strength, the degree of concrete durability proposed in this study indicates that fly ash concretes with a W/B ratio of 0.45 and 15–35 wt % fly ash replacement exhibit high-quality performance in a marine site.

The main aim of this work was to determine creep and shrinkage variations experienced in recycled concrete, made by replacing the main fraction of the natural aggregate with a recycled aggregate coming from waste concrete and comparing it to a control concrete. It was possible to state that the evolution of deformation by shrinkage and creep was similar to a conventional concrete, although the results after a period of 180 days showed the influence of the substitution percentage in the recycled aggregates present in the mixture. In the case when 100% coarse natural aggregate was replaced by recycled aggregate there was an increase in the deformations by creep of 51% and by shrinkage of 70% as compared to those experienced by the control concrete. The substitution percentages of coarse natural aggregate by coarse recycled aggregate were 20, 50 and 100%. Fine natural aggregate was used in all cases and the amount of cement and water–cement ratio remained constant in the mixture.

Durability of reinforced concrete remains a pervasive concern. At present, as-built concrete quality and hence durability is inadequate in many cases. This relates partly to use of prescriptive specifications that do not appropriately address actual quality concerns. Performance-based specifications may offer greater advantages in improving concrete durability, but to be viable require suitable quality parameters to be defined and measured. In South Africa, a ‘Durability Index’ (DI) approach has been developed to address these concerns. ‘Durability indexes’ are quantifiable parameters which characterise concrete quality and are sensitive to material, processing, and environmental factors. The approach is based on measurement of transport-related properties of the cover layer of laboratory and in-situ concrete, thus reflecting the dual aspects of material potential and construction quality. Rational durability design and performance-based durability specifications are being developed and in some cases applied in actual construction. The paper presents a framework within which the DI approach is used to craft performance-based specifications, based on service life models that utilise the relevant DI values. Steps to establish appropriate DI test values for a given structure are described, and a procedure for implementing their use as a quality control measure is recommended. The approach is integrated, allowing for continual improvement and modification as additional data become available.

Durability of reinforced concrete is primarily influenced by the penetration of aggressive substances into concrete, which are degrading concrete and reinforcement. For structures in marine environment chlorides are the most critical environmental load, which are causing serious corrosion damages. Data collected during the survey of the Krk Bridge, a large reinforced concrete arch bridge structure located on the Adriatic coast, is used as documented reference in this research. The structure has been exposed to the marine environment for over 25 years. Based on collected materials data and the exposure conditions, the service life of this structure is estimated using three currently available prediction models, two deterministic models, the North American Life - 365 model and the Croatian CHLODIF model, and the DuraCrete probabilistic method. All these models are based on the chloride diffusion process, but with different detailing of the model parameters. The conclusion is an evaluation of the service life predictive ability of each of these three service life models.

This paper presents an experimental study of combined effects of curing method and high replacement levels of blast furnace slag on the mechanical and durability properties of high performance concrete. Two different curing methods were simulated as follows: wet cured (in water) and air cured (at 20°C and 65% RH). The concretes with slag were produced by partial substitution of cement with slag at varying amounts of 50–80%. The water to cementitious material ratio was maintained at 0.40 for all mixes. Properties that include compressive and splitting tensile strengths, water absorption by total immersion and by capillary rise, chloride penetration, and resistance of concrete against damage due to corrosion of the embedded reinforcement were measured at different ages up to 90 days. It was found that the incorporation of slag at 50% and above-replacement levels caused a reduction in strength, especially for the early age of air cured specimens. However, the strength increases with the presence of slag up to 60% replacement for the 90 day wet cured specimens. Test results also indicated that curing condition and replacement level had significant effects on the durability characteristics; in particular the most prominent effects were observed on slag blended cement concrete, which performed extremely well when the amount of slag used in the mixture increased up to 80%.

The use of waste materials and by products from different industries for building construction has been gaining increased attention due to the rapid depletion of natural resources. It has been found that oil palm shell (OPS), which is a waste from the agricultural sector, can be used as coarse aggregate for the manufacture of structural lightweight concrete. However, for OPS concrete to be used in practical applications, its durability needs to be investigated. Therefore, this paper presents the durability performance of OPS concrete under four curing regimes. The durability properties investigated include the volume of permeable voids (VPVs), sorptivity, water permeability, chloride diffusion coefficient and time to corrosion initiation from the 90-day salt ponding test, and Rapid Chloride Penetrability Test (RCPT). Results showed that the durability properties of OPS concrete were comparable to that of other conventional lightweight concretes and proper curing is essential for OPS concrete to achieve better durability especially at the later ages.