In situ monitoring of corrosion processes by coupled micro-XRF/micro-XRD mapping to understand the degradation mechanisms of reinforcing bars in hydraulic binders from historic monuments

International audienceHistoric monuments have been partly built since antiquity with iron or steel reinforcements sealed in mortars or hydraulic binders. But the presence of chloride in the environment can weaken the structures due to the corrosion of these metallic parts, leading to the cracking of the binder. In this context, in order to better understand the first steps of these corrosion mechanisms a chemical cell was designed to operate in situ analyses of the phases precipitated when a chlorinated solution is introduced in the vicinity of the bar. The chemical and structural characterization (micro-XRF and micro-XRD respectively) was performed under synchrotron radiation at the SOLEIL-DiffAbs beamline. Moreover, complementary SEM-EDS analyses were carried out before and after the in situ cell experiment in order to determine the final localisation of the corrosion products inside the crack network. The results show that iron can spread up to 1 mm away from the metallic bar inside the pores of the binder after 44 h of corrosion. Moreover, in accordance with laboratory experiments conducted in solution in the presence of Fe2+ and Cl- ions the reaction pathways conduct to the successive formation of an intermediate Fe(ii)-Fe(iii) chlorinated green rust which transforms into ferric oxyhydroxides such as akaganeite or goethite depending on the local concentration of iron

Variations of Sorptivity with Rheological Properties of Concrete Cover in Self-Consolidating Concrete

Transport properties of the concrete cover can influence the durability of concrete. Concrete cover of conventional vibrated concrete has greater porosity because of the looser packing density of coarse aggregate against the surface of the formwork, which is referred to as the wall effect . In the case of self-consolidating concrete (SCC), the volume of coarse aggregate is lower, and the packing density of the aggregate can depend on the flow properties of the SCC under its own weight. The extent of the wall effect on the quality of the concrete cover can vary with the rheological properties of the concrete. The work presented in this paper seeks to evaluate the effect of changes in rheological properties of SCC on the sorptivity of the concrete cover that can be affected by the degree of consolidation of the SCC near formed surfaces as well as changes that can result from water migration and changes in the packing of solid particles in the vicinity of formed surfaces. The sorptivity of the concrete cover is also compared to that of the bulk concrete. In total, 17 SCC mixtures covering a wide range of rheological properties were investigated. Good correlation between initial plastic viscosity of SCC determined by the modified Bingham model and the sorptivity measured during the first 6 h of testing is established. It is likely that the initial plastic viscosity has a marked influence on the volume of the largest capillary pores of concrete, which can significantly affect transport properties and durability. Test results indicate that the sorptivity of the concrete cover in SCC is similar to that obtained in the interior bulk concrete

Influence of Formwork Material on Transport Properties of Self-Consolidating Concrete near Formed Surfaces

This study aims at determining the influence of the formwork material on transport properties of concrete cover when using self-consolidating concrete (SCC). Two types of formwork were used. The plywood (PW) formwork material which is relatively rough and absorbent compared to the PVC material that has a very smooth and non-absorbent surface. A total of 17 SCC and highly flowable concrete mixtures with wide range of slump flow and T50 values were investigated. The concrete was used to fill 400 x 500 x 200 mm3 moulds made with either PVC or PW. Sorptivity tests were performed on core samples (100 mm in diameter and 50 mm in length) taken from the sides and center of the prepared moulds after 28 days of moist curing. This paper presents new experimental method using image analysis to quantify the relative surface area of coarse aggregate along different sections near formed surfaces. Sorptivity of concrete near the surface cast against the PW formwork was found to be significantly lower than that of PVC one due to the decrease of local w/c and wall effect. The examination of packing density of coarse aggregate near PVC and PW surfaces showed limited wall effect near the PVC formwork and significant wall effect within a thickness comparable to the maximum size of coarse aggregate near the PW formwork

Assessment of concrete slab quality and layering by guided and surface wave testing

This paper presents an experimental study on the investigation of concrete properties by guided and surface wave nondestructive testing. Applications were made on two large slabs simulating homogeneity and layering in concrete, respectively. An efficient non-intrusive method was used to evaluate the concrete quality by solving the modal propagation problem of Lamb guided waves and Rayleigh surface waves. Lamb waves were used to determine the Poisson's ratio and the Young's modulus of the concrete slabs. Rayleigh waves were identified using Lamb wave fundamental-modes; thereafter, the inverse problem of Rayleigh waves was solved to evaluate the variation of shear wave velocity with depth and thus characterize the layered slab. The obtained results demonstrate the high potential of this tool that can easily be used for insitu assessment of concrete structures.Ce document pr\ue9sente une \ue9tude exp\ue9rimentale investigant les propri\ue9t\ue9s du b\ue9ton par des essais non destructifs par onde guid\ue9e et par onde de surface. Des applications ont \ue9t\ue9 faites sur deux (2) dalles de grandes dimensions simulant respectivement l'homog\ue9n\ue9it\ue9 et la formation de couches dans le b\ue9ton. On a employ\ue9 une m\ue9thode non intrusive efficace dans le but d'\ue9valuer la qualit\ue9 du b\ue9ton en r\ue9solvant le probl\ue8me de la propagation modale des ondes guid\ue9es de Lamb et des ondes de surface de Rayleigh. Les ondes de Lamb ont \ue9t\ue9 utilis\ue9es aux fins de la d\ue9termination du nombre de Poisson et du module d'\ue9lasticit\ue9 des dalles de b\ue9ton. Les ondes de Rayleigh ont \ue9t\ue9 identifi\ue9es au moyen des modes principaux de vibration de l'onde Lamb; par la suite, on a r\ue9solu le probl\ue8me inverse des ondes de Rayleigh afin d'\ue9valuer la variation de la vitesse de propagation de l'onde \ue9quivolumique en fonction de la profondeur et, ainsi, de caract\ue9riser la dalle \ue0 couches multiples. Les r\ue9sultats que l'on a obtenus mettent au jour tout le potentiel de cet outil, qui peut \ueatre facilement utilis\ue9 pour l'\ue9valuation in situ des structures de b\ue9ton.Peer reviewed: YesNRC publication: Ye