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Concrete is the most used construction material worldwide, but if often faces durability issues due to rebar corrosion, and cement production can be energy consuming. Attempts to improve its resilience versus corrosion while reducing its carbon footprint are ongoing at an international level. In this objective, in France within the framework of the national project PERFDUB, a series of reinforced concrete walls were cast with innovative concrete designs, two shapes of rebars and two concrete covers. The standard performances of the different concrete mix designs were evaluated at a laboratory scale. Then the walls were exposed in the French La Rochelle harbor, in the tidal zone in order to monitor the evolution of the corrosion of the bars for a period of twenty years. The first results of the electrochemical follow-up of these reinforced walls are presented in this paper.

The aim of this study is to investigate the cause of the self-cementing properties of recycled aggregates used for pavement base. Clay bricks were added to the recycled aggregates to study the pozzolanic reactions. The evolution of the mechanical performances of the materials was investigated in the laboratory (California Bearing Ratio) and in the field (plate test). Both tests showed that initially, the mechanical performances of recycled aggregates are equivalent or even lower than those of natural aggregates. However, recycled aggregates become much better than natural aggregates with time. Therefore, setting tests, microcalorimetric analysis, and two pozzolanicity tests (pH evolution and consumption of Ca2+ ions) were carried out in a laboratory in order to explain the observations made on the test beds. The microcalorimetric analysis showed that there is only a slight hydraulicity due to residual anhydrous cement content in recycled aggregates. However, the other tests highlight that the presence of clay bricks particles in recycled aggregates results in pozzolanic reactions that can explain the time-evolution of mechanical performances. This study suggests that recycled aggregates have a high added value when they are used as pavement base. [ABSTRACT FROM AUTHOR]

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The article offers a study which evaluates the plastic shrinkage cracking of the mixture of self-consolidating concrete (SCC) and ordinary concrete (OC). The study compares the mixtures of SCC with comprehensive strengths ranging from 30 to 50 MPa with the five mixtures of ordinary concrete (OC). The result of the study revealed that, plastic shrinkage of both mixtures have almost the same plastic shrinkage except for the controlled mixtures in which cracks on SCC are less compared to OC.

This paper presents a study on cracking risk due to shrinkage of self-compacting concrete (SCC). Cracking of SCC was investigated through a comparison of material properties, such as shrinkage, modulus of elasticity, creep, and fracture parameters, between SCC mixtures and ordinary concrete (OC) mixtures. Restrained shrinkage tests (ring tests) were also performed on the same mixtures. Numerical simulations were then used to assess the correlation between material properties and results of restrained shrinkage tests. SCC and OC were found to have equivalent shrinkage cracking tendency, provided that compressive strength is kept the same and that SCC has adequate segregation resistance. [ABSTRACT FROM AUTHOR]

Marine bacterial biomineralisation by CaCO3 precipitation provides natural limestone structures, like beachrocks and stromatolites. Calcareous deposits can also be abiotically formed in seawater at the surface of steel grids under cathodic polarisation. In this work, we showed that this mineral-rich alkaline environment harbours bacteria belonging to different genera able to induce CaCO3 precipitation. We previously isolated 14 biocalcifying marine bacteria from electrochemically formed calcareous deposits and their immediate environment. By microscopy and µ-Raman spectroscopy, these bacterial strains were shown to produce calcite-type CaCO3. Identification by 16S rDNA sequencing provided between 98.5 and 100% identity with genera Pseudoalteromonas, Pseudidiomarina, Epibacterium, Virgibacillus, Planococcus, and Bhargavaea. All 14 strains produced carbonic anhydrase, and six were urease positive. Both proteins are major enzymes involved in the biocalcification process. However, this does not preclude that one or more other metabolisms could also be involved in the process. In the presence of urea, Virgibacillus halodenitrificans CD6 exhibited the most efficient precipitation of CaCO3. However, the urease pathway has the disadvantage of producing ammonia, a toxic molecule. We showed herein that different marine bacteria could induce CaCO3 precipitation without urea. These bacteria could then be used for eco-friendly applications, e.g., the formation of bio-cements to strengthen dikes and delay coastal erosion. [ABSTRACT FROM AUTHOR]