Eric Lozinguez
email: eric.lozinguez@cerema.fr

Jean-Franc ¸ois Barthélémy
email: jean-francois.barthelemy@cerema.fr

Véronique Bouteiller
email: veronique.bouteiller@ifsttar.fr

Tiffany Desbois
email: tiffany.desbois@cerema.fr

Contribution of Sacrificial Anode in reinforced concrete Patch Repair: results of numerical simulations

Keywords: Reinforded Concrete, Modelling studies, Patch repair, Sacrificial Anode for Cathodic Protection, Micro and Macro-cell corrosion

This paper deals with the numerical determination of potential and current distribution along the reinforcement when using patch repair applied to reinforced concrete elements. Numerical finite element models of the electrochemical phenomena demonstrate the useful contribution of Sacrificial Anode in improving the Cathodic Protection of the reinforcement by testing several configurations. The main result is that the Sacrificial Anode should be embedded in the substrate concrete area rather than in the patch area. Moreover, the influence of the resistivity of the repairing concrete is evaluated.

Introduction

Corrosion of the reinforcement is recognised as the main degradation of reinforced concrete structures [START_REF] Woodward | Bridge management in europe (brime)-deliverable d14-final report[END_REF]. From the point of view of service life, Tuutti, proposed a schematic sketch of steel corrosion sequence in concrete subdivided into an initiation stage and a propagation stage [START_REF] Tuutti | Corrosion of steel in concrete[END_REF]. In the initiation stage, the aggressive species penetrate the concrete cover (carbonation reaction or chloride ion ingress) and once the rebar level is affected corrosion occurs and the propagation stage begins. Due to the diffusion/precipitation of the corrosion products and because the volume of iron corrosion products are higher than the volume of iron metal [START_REF] Tuutti | Corrosion of steel in concrete[END_REF][START_REF] Gp | Concrete repairs: Performance in service and current practice[END_REF][START_REF] Bennett | Extending the life of concrete patch repair with chemically enhanced zinc anodes[END_REF][START_REF] Sergi | Sacrificial anodes for cathodic prevention of reinforcing steel around patch repairs applied to chloride-contaminated concrete[END_REF][START_REF] Dugarte | Modeling performance of galvanic point anodes for cathodic prevention of reinforcing steel in concrete repairs[END_REF], disorders such as rust stains, cracks or spallings can be encountered.

According to the analysis of the questionnaires of the European CONREPNET Project [START_REF] Gp | Concrete repairs: Performance in service and current practice[END_REF], from the 230 case histories (main types of structures were buildings, bridges, dams, power stations and car parks), corrosion was the most common process of deterioration, being responsible for 55% of the problems. Patching was the most applied repair type (60% of the case histories) and after removing the defective concrete, the material used for the patching was "cementitious" type for 60%. Concerning the performance of repair, cementitious patches were 45% successful due to insufficient defective concrete having been removed and incipient anodes becoming dominant.

Therefore, recurring corrosion after patch repair could initiate in one of the three following areas: the patch area, the substrate (adjacent unrepaired area) or the interface between them [START_REF] Bennett | Extending the life of concrete patch repair with chemically enhanced zinc anodes[END_REF][START_REF] Sergi | Sacrificial anodes for cathodic prevention of reinforcing steel around patch repairs applied to chloride-contaminated concrete[END_REF][START_REF] Dugarte | Modeling performance of galvanic point anodes for cathodic prevention of reinforcing steel in concrete repairs[END_REF][START_REF] Christodoulou | Diagnosing the cause of incipient anodes in repaired reinforced concrete structures[END_REF]. On the one hand, total or partial removal of contaminated concrete around the steel reinforcement will lead to two different situations: if the contaminated concrete is totally removed, corrosion damage will appear most likely within the substrate in the vicinity of the patch [START_REF] Dale | Corrosion of steel reinforcement in concrete adjacent to surface repairs[END_REF][START_REF] Soleimani | Modeling the kinetics of corrosion in concrete patch repairs and identification of governing parameters[END_REF] whereas if the contaminated concrete is only partially removed , the patch repair will more likely be deteriorated because of the creation of a macrocell between the top and the bottom of the steel and the subsequent development of rust below the rebar as schematized in Fig. 1 (3D view visible in the foreground of Fig. 22). On the other hand, incipient anode will consist in macrocell corrosion [START_REF] Qian | Theoretical and experimental study of microcell and macrocell corrosion in patch repairs of concrete structures[END_REF][START_REF] Raupach | Chloride-induced macrocell corrosion of steel in concrete-theoretical background and practical consequences[END_REF][START_REF] Elsener | Macrocell corrosion of steel in concrete-implications for corrosion monitoring[END_REF][START_REF] Hansson | Macrocell and microcell corrosion of steel in ordinary portland cement and high performance concretes[END_REF][START_REF] Cao | Modelling of interaction between corrosion-induced concrete cover crack and steel corrosion rate[END_REF][START_REF] Cao | Non-uniform rust expansion for chloride-induced pitting corrosion in reinforced concrete structures[END_REF][START_REF] Maruya | Simulation of steel corrosion in concrete based on the model of macro-cell corrosion circuit[END_REF][START_REF] Kim | Modeling steel corrosion in concrete structures-part 1: A new inverse relation between current density and potential for the cathodic reaction[END_REF][START_REF] Cao | 3d simulation of localized steel corrosion in chloride contaminated reinforced concrete[END_REF][START_REF] Lozinguez | Modelling of patch repair and efficiency of sacrificial anode for cathodic protection[END_REF] resulting from treated and not treated areas.

At the scale of the structure, it is worth recalling that the main difference between microcell and macrocell corrosion lies in the fact that the anodic and cathodic reactions take place at the same location for the former and at different locations for the latter, creating thus a ionic current within concrete.

Even if the removal of the contaminated concrete is complete and the alkalinity of the new concrete is supposed to protect the reinforcement from corrosion, experience shows that patch repair rarely exceeds the 10-year guarantee [START_REF] Matthews | Conrepnet: Performance-based approach to the remediation of reinforced concrete structures: Achieving durable repaired concrete structures[END_REF].

In order to reduce this recurring corrosion, the use of Sacrificial Anode for Cathodic Protection (SACP) embedded into the concrete seems an attractive solution. Indeed this technique takes advantage of the electrochemical properties of zinc which, as a less noble metal than iron, corrodes preferably and consequently protects the neighbouring rebars. This protection technique has been used for decades in civil engineering as well as in the maritime field and some feedbacks on protected structures can be found [START_REF] Costa | Controlling corrosion on the La Unidad bridge in Campeche[END_REF][START_REF] Daily | Using cathodic protection to control corrosion of reinforced concrete structures in marine environments[END_REF][START_REF] Lawson | Coasts & Ports Australasian Conference[END_REF][START_REF] Sharp | Survey of cathodic protection systems on Virginia bridges[END_REF][START_REF] Sohanghpurwala | Cathodic protection for life extension of existing reinforced concrete bridge elements. a synthesis of highway practice[END_REF]. In literature, few articles tackle the issue of the efficiency of SACP in patch repair and the feedbacks on structures do generally not give much details about the precise locations of the anodes. Christodoulou's study focused on the arrangement of galvanic anodes for the repair of reinforced concrete structures and highlighted that anodes had a dominant effect on potentials to a distance between 250 and 600 mm [START_REF] Christodoulou | A new arrangement of galvanic anodes for the repair of reinforced concrete structures[END_REF]. Soleimani modelled the kinetics of corrosion and found that resistivities of the patch repair and that of substrate concretes were the most significant factors affecting the corrosion that occurred mainly in the 2-5 cm portion of interface between them [START_REF] Soleimani | Modeling the kinetics of corrosion in concrete patch repairs and identification of governing parameters[END_REF]. Cheung modelled the electrochemical corrosion process with SACP by means of 2D numerical simulations and found that the location of the anode in the substrate rather than in the patch area lead to significant reduction of the macrocell corrosion [START_REF] Moe | Application of cathodic protection for controlling macrocell corrosion in chloride contaminated reinforced concrete structures[END_REF]. For patch repair of RC structures, Qian studied both components (microcell and macrocell) of corrosion from theoretical and experimental work [START_REF] Qian | Theoretical and experimental study of microcell and macrocell corrosion in patch repairs of concrete structures[END_REF]. Ribeiro proposed a criterion, based on experimentals results, to prevent the macrocell corrosion inside patch repairs based on the least electrochemical incompatibility between patch repair and substrate concretes in the case of corrosion induced by carbonation [START_REF] Jls Ribeiro | Proposed criterion to assess the electrochemical behavior of carbon steel reinforcements under corrosion in carbonated concrete structures after patch repairs[END_REF].

This paper presents the results of numerical simulations used to evaluate the efficiency of the SACP in patch repair. Eight cases are studied considering two repair situations (anodic area with total removal of contaminated concrete around the reinforcement on a limited longitudinal extension or cathodic area and partial removal of the contaminated concrete around the rebar) and four conditions: one before repair and three after repair without SACP, with SACP in the patch repair and with SACP in the substrate. Moreover the resistivity of the repairing concrete is also evaluated. These numerical results (mainly potential and current distributions) are very helpful as experimental work on this issue is scarce because rather difficult or impossible to be conducted. In addition, the use of 3D finite elements models and related softwares help illustrating and quantifying the reduction in corrosion that causes the sacrificial anode. When dealing with patch repair, several scenarii may occur. In this study, eight case studies are considered based on two situations that are subdivided into four conditions. The first situation refers to a repair where the contaminated concrete around the reinforcement is totally removed but the vicinity of the repaired area is still an anodic area (the concrete is still adhesive but is contaminated). For the second situation, the contaminated concrete around the reinforcement is only partially removed but the vicinity of the repaired area is not contaminated. The four conditions considered are:

• before repair;

• after repair, without SACP;

• after repair, with SACP embedded in the patch repair;

• after repair, with SACP embedded in the susbstrate (adjacent unrepaired area).

Corrosion associated to the first situation

For the first situation and before repair (Fig. 2), the entire length of the steel rebar is corroding (as the concrete is contaminated) and the resulting corrosion is of microcell type. This means that cathodic and anodic areas are merged: there is no macroscopic movement (at the scale of the studied reinforced concrete area) of electrons (along the steel) or ions (through the concrete pore solution). Corrosion of steel results from two simultaneous half-cell reactions: • the anodic reaction corresponding to the oxidation of iron creates a current density j a,micro considered positively outward from the steel rebar;

Fe → Fe 2+ + 2e - (1)
• the cathodic reaction corresponding to the reduction of oxygen in the presence of water creates a current density j c,micro considered positively inward to the steel rebar;

2H 2 O + O 2 + 4e -→ 4OH - (2)
In microcell corrosion, for any point distributed along the steel/concrete interface, j a,micro = j c,micro .

After patch repair, macrocell corrosion occurs as illustrated in Fig. 3. Electrical and ionic currents appear respectively in steel and concrete and j a becomes different from j c : • in active areas, the resulting anodic current corresponding to the iron oxydation, j a , is the sum of the micro and macro cell currents as illustrated in Fig. 4;

• in passive areas, only one current density corresponding to the reduction of oxygen dissolved in water, j c , is considered (the anodic current is so low that it can be neglected).

Corrosion associated to the second situation

The second case that is considered consists in a well-sized patch but with contaminated concrete not fully removed around the rebar as illustrated in Fig. 5 (cross section is given in Fig. 1). It is assumed that only half of the circumference of the steel is active after repair.

Before repair (at the top of Fig. 5), macrocell corrosion is already present between the contaminated concrete (concrete whose upper part will be replaced by the patch repair) and the sound concrete (substrate concrete). After repair (at the bottom of Fig. 6), the upper part of the steel becomes a passive region: the anodic/cathodic surfaces ratio decreases, which increases the macrocell corrosion under the rebar. For reasons of symmetry, half of the patch is considered in the model. As illustrated in Fig. 7, the geometry of the reinforced concrete to be repaired is considered as a rectangular parallelepiped with total dimensions of 100 cm width, 120 cm length and 24,3 cm thickness. Inside this box, the geometry of the patch area is rectangular (50 cm wide and 20 cm long): 4.3 cm thick in case 1 while in case 2 only 2.9 thick. The diameter of the steel reinforcement is equal to 8 mm. The concrete cover is chosen equal to 25 mm (for civil engineering bridges the concrete cover is generally around 30 mm but for buildings a concrete cover of 10 mm is often encountered).

The cylindrical SACP has a radius of 20 mm and a length of 15 mm. It is covered by 10 mm of concrete and its center is positioned at a distance of 50 mm from the rebar axis and 50 mm from the patch/substrate interface. Depending on the conditions, none or only one of the anodes (either in the patch or in the substrate) is active.

In reinforced concrete structures, steel rebars are arranged as a mat or cage with several layers connected [START_REF] Sc Kranc | Detailed modeling of corrosion macrocells on steel reinforcing in concrete[END_REF]. The proposed finite element model does not take into account the rebar mesh distribution even if technically it would not be a problem. Only one bar is considered in this 3D problem in order to simplify the interpretation of the results and to highlight the practice drawbacks observed on site (small patch repair area or contaminated concrete not completely removed around the steel). Finally taking into account a complete mesh would reduce the anodic/cathodic ratio and thus increase the corrosion current but the influence of the remote rebars on the macrocell current is expected to be lower than that of the cathodic zone in the immediate vicinity of the corroding area.

Detailed features of geometry depending on the repair situation are presented in Fig. 8.

For the first situation, the patch depth is extended by 10 mm (the patch depth is 43 mm and substrate concrete exceeds by 20 cm). For the second situation, the bottom of the patch is located at a depth of 29 mm (concrete cover in addition with a half diameter of the rebar) and substrate concrete exceeds by 21,4 cm.

Description of the numerical model

Numerical model of corrosion

This section aims at presenting the numerical procedure allowing to build the solution of a corrosion problem from the electrochemical point of view. A major hypothesis is that the active and passive steel zones, resulting from the incubation process, are known in the model although they can be very difficult to identify from measurements [START_REF] Cox | Corrosion and protection of metals in contact with concrete[END_REF][START_REF] Astm | standard test method for half-cell potentials of uncoated reinforcing steel in concrete[END_REF][START_REF] Tc | Recommendations of rilem tc-154emc:" electrochemical techniques for measuring metallic corrosion[END_REF]. The studied domain here is the space occupied by the concrete. The electrochemical reactions responsible for corrosion are written at the concrete/steel interface where the so-called electrode potential E, which controls the corrosion, is defined as [START_REF] Landolt | Corrosion and surface chemistry of metals[END_REF]:

E = Φ M -Φ S (3)
Where Φ M is the potential of the metal and Φ S that of the neighbouring electrolyte.

Hence E actually appears as a potential jump across the concrete/steel interface. Since the potential field is defined up to an arbitrary constant and can be considered as constant within steel due to the high conductivity of the latter with respect to concrete, it is proposed to choose Φ M = 0 in the following.

With the constant previously chosen, Eq. ( 3) simplifies:

E = -Φ S (4)
Thus the field E defined at the steel/concrete interface depends on the location along and around the rebar through Φ S

Equation in concrete

From the electrical point of view, concrete is considered here as an ohmic conductor owing its conductivity to its microstructure and the degree of saturation of the interstital solution as well as the conductive property of the latter. The macroscopic ohm's law and the local charge conservation leads to the following elliptic equation:

div(- 1 ρ gradΦ s ) = 0 (5)
with: Φ s : scalar field of potential in the solution (V/ES H); ρ: scalar field of electrical resistivity (Ω.m).

Boundary conditions

The anodic and cathodic current densities are related to the electrode potential by the classical polarization equations [START_REF] Cao | Modelling of interaction between corrosion-induced concrete cover crack and steel corrosion rate[END_REF]:

• For active steel:

j.n = -j 0 a,Fe exp ln(10)(-Φ S -E eq Fe ) β a,Fe + j 0 c,O 2 /Fe exp ln(10)(E eq O 2 + Φ S ) β c,O 2 /Fe (6)
• For passive steel: [START_REF] Christodoulou | Diagnosing the cause of incipient anodes in repaired reinforced concrete structures[END_REF] with: j: vector current density (A.m -2 ); n: outward unit normal to the concrete domain; j 0 a,Fe : anodic exchange current density (A.m -2 ); j 0 c,O 2 /Fe : cathodic exchange current density (A.m -2 ); E eq Fe : iron equilibrium potential (Vvs.S CE); E eq O 2 : oxygen equilibrium potential (Vvs.S CE); β a,Fe : anodic iron Tafel slope (V/dec); β c,O 2 /Fe : cathodic oxygen (/iron) Tafel slope (V/dec).

j.n = j 0 c,O 2 /Fe exp ln(10)(E eq O 2 + Φ s ) β c,O 2 /Fe
For all other boundaries of the model, there is no electrical transfer so Neumann conditions with zero flux apply:

j.n = - 1 ρ ∂Φ s ∂n = 0 (8)

Taking into account SACP

The principle of sacrificial anodes lies in the fact that zinc is less noble than iron: so if they are electrically connected in the presence of an electrolyte, zinc will tend to corrode instead of steel. This galvanic protection is a method based on the Mixed-Potential Theory [START_REF] Glass | Monitoring the passivation of steel in concrete induced by cathodic protection[END_REF].

At the interface of SACP two conditions are added: A mixed condition in the same way as for steel;

j.n = -j 0 a,Zn exp ln(10)(-Φ s -E eq Zn ) β a,Zn + j 0 c,O 2 /Zn exp ln(10)(E eq O 2 + Φ s ) β c,O 2 /Zn (9)
with: j 0 a,Zn : anodic exchange current density (A.m -2 ); j 0 c,O 2 /Zn : cathodic exchange current density (A.m -2 ); E eq Zn : zinc equilibrium potential (Vvs.S CE); E eq O 2 : oxygen equilibrium potential (Vvs.S CE); β a,Zn : anodic zinc Tafel slope (V/dec); β c,O 2 /Zn : cathodic oxygen (/zinc) Tafel slope (V/dec);

Model parameters

Electrochemical input data for this study (gathered in Tab. 1 ,polarization curves are plotted in Fig. 9 ) are chosen from literature [START_REF] Am Hassanein | Protection current distribution in reinforced concrete cathodic protection systems[END_REF][START_REF] Cao | 3d simulation of localized steel corrosion in chloride contaminated reinforced concrete[END_REF] although dispersions have already been highlighted [START_REF] Yu | Practical model for predicting corrosion rate of steel reinforcement in concrete structures[END_REF]. The equilibrium potential and the Tafel slopes are not so dispersed but the values of exchange current densities may be very different according to the authors. These dispersions can be explained by the state of the steel/concrete interface, the ionic content of the interstitial solution and finally the relative humidity and temperature conditions. Quantitative results of numerical simulations may of course depend on the chosen input data but preliminary results of parametric studies show that the qualitative conclusions drawn in this parer remain valid.

Influence of concrete resistivity

To determine the efficiency of patch repair, the resistivity of concretes (substrate as well as patch) is still an important issue. In this study, the electrical resistivity for substrate concrete is kept equal to 100 Ω.m. The electrical resistivity of the patch concrete is studied as a parameter and varied from 50 to 1400 Ω.m according to values from literature [START_REF] Cao | Modelling of interaction between corrosion-induced concrete cover crack and steel corrosion rate[END_REF][START_REF] Saleem | Effect of moisture, chloride and sulphate contamination on the electrical resistivity of portland cement concrete[END_REF][START_REF] Liu | Modeling the dynamic corrosion process in chloride contaminated concrete structures[END_REF][START_REF] Tc | Recommendations of rilem tc-154emc:" electrochemical techniques for measuring metallic corrosion[END_REF]. The 200 Ω.m value complies with the ISO EN 12696 standard [39] and is presented in detail. On-site, patch concrete (or repair mortar) can be reinforced and in this case, high values such as 1400 Ω.m can be found.

Results of numerical simulations

Numerical simulations of corrosion have been recently presented in the literature [START_REF] Yu | Practical model for predicting corrosion rate of steel reinforcement in concrete structures[END_REF][START_REF] Cao | Modelling of interaction between corrosion-induced concrete cover crack and steel corrosion rate[END_REF][START_REF] Cao | Non-uniform rust expansion for chloride-induced pitting corrosion in reinforced concrete structures[END_REF][START_REF] Laurens | Steady-state polarization response of chlorideinduced macrocell corrosion systems in steel reinforced concrete-numerical and experimental investigations[END_REF]. In this paper, Finite Element Method (FEM) is used with the free software GetFEM++ [START_REF]Getfem++[END_REF], GMSH for the mesh [START_REF] Geuzaine | Gmsh: A 3-d finite element mesh generator with built-in pre-and post-processing facilities[END_REF] and Paraview [START_REF] Henderson | The paraview guide[END_REF]. By means of very efficient generic elementary tools, GetFEM++ allows to build the solution to non-linear problems including those involving nonlinear boundary conditions (as Butler-Volmer equation). It also offers the possibility to consider coupled (e.g. electrochemical problem coupled with oxygen diffusion) as well as non-stationary problems (e.g. induced by the capacitive effect of the double layer at steel/concrete interface). Such features are also available in commercial softwares such as Comsol Multiphysics [START_REF] Polder | Numerical design for cathodic protection systems for concrete[END_REF] but GetFEM++ has the advantage to be free and open source, which makes it very accessible to the scientific community.

4.1. Situation 1: total removal of contaminated concrete around the steel reinforcement in the patch area but adjacent area is still contaminated Potential and current distributions along the steel reinforcement in the patch area (patch) and in the adjacent area (substrate) are presented in Fig. 10 and in Fig. 13 respectively. Before repair, the potential is uniform over the whole volume (i.e. microcell corrosion) and equal to -473.31 mV vs. SCE (Fig. 10) and the anodic current density (Fig. 13) is equal to 1.934 µA.cm -2 . Thus the calculated overall anodic current intensity along the steel reinforcement of one meter length is 486.06 µA.

After patch repair, 50 cm of the reinforcement is considered passive (in the patch area because the contaminated concrete has been totally removed) and 50 cm of the reinforcement is considered active (because the concrete adjacent to the repaired area remained contaminated). In this case macrocell corrosion occurs which results evolve depending on the conditions of SACP (without SACP, SACP in the patch or SACP in the substrate). In this study, the efficiency of the SACP is investigated.

Potential distributions

Potential distributions along the steel reinforcement in the adjacent area of the patch (substrate) presented in Fig. 10 shows different results:

• the potential after repair without SACP is less electronegative than before patch repair meaning that an increase of corrosion is achieved;

• the potential after repair with SACP is more electronegative than before patch repair as expected in a Cathodic Protection process. Results also highlight that a SACP embedded in the substrate concrete rather than in the patch concrete induces a better efficiency of the Cathodic Protection. In order to evaluate the efficiency of the CP obtained with SACP, the depolarisation values (difference of potentials without SACP and with SACP) are presented in Figure 11 together with the 100 mV protection criterion for Impressed Current Cathodic Protection (ICCP) as described in the ISO 12696 standard [39]. Results show that whatever the position of the sacrificial anode (in the patch or in the substrate), the criterion of 100 mV is achieved but over a rather small distance ( ≃ 15 cm) which does not even reach the active part of steel in the case of SACP in patch. This information is useful for field trials, first, to correctly design the protection and, second to determine the position of the embedded reference electrode on which is based the monitoring.

To go further in this optimization approach, numerical simulations of the potential distribution around the rebar depending on the angle with the anode are illustrated in Fig. 12. Depending on whether it is in front or opposite of SACP, this mask or screen effect can vary the potential from more than 30 mV. Moreover, it appeares that the potential distribution is strongly influenced by the angle, within a 20 cm area. This behaviour will also play an important role in the determination of the depolarisation value. As expected, when the distance increases this effect fades.

Current density distribution

Current density distributions along the steel reinforcement in the adjacent area of the patch (substrate) presented in Fig. 13 contribute to different observations:

• before repair, the current density along the steel is equal to 2 µA.cm -2 and is constant;

• after repair without SACP, a macrocell anodic current density occurred in substrate because the rebar remaines in a contaminated concrete;

• after repair with SACP, some of the corrosion of the rebar (still in a contaminated medium) is inhibited. The efficiency of the protection is improved when the SACP is embedded in the substrate rather than in the patch.

As shown on the top right of Fig. 13 current protection has a spatial effect: the current still present at 0.55m is double in backside as compared to the side in front of SACP. For a single layer of reinforcement in typical conditions, the surface of a steel bar facing the anode may receive 1.5 times the current received by the opposite surface.

Table 2 gathers the figures of the currents calculated as the integrals of current densities of the steel reinforcement located in the 50 cm of patch concrete and in the 50 cm of substrate concrete. It can be observed that:

• after patch repair without SACP, the corrosion of the steel in the substrate (adjacent to the repaired area) is increased by 33 %. This result is well known on-site where the degradations of the reinforced concrete appear at the vicinity of the repaired one after some years;

• after patch repair with SACP, the Ia-Ic values are negative, which likely means that only microcell current remaines (no macrocell). Moreover the contribution of the CP is quantified with a decrease of current by 48% and 69% respectively for SACP located in the patch or in the substrate. This latter case is more efficient because, first, the steel is corroding only in the contaminated substrate (steel in the patch area became passive) and, second, because the distance between the reinforcement and the substrate anode is smallest. Futhermore the relatively high electrical resistivity of patch concrete (i.e. 200 vs. 100 Ω.m ) prevents the sacrificial anode from properly disseminating its protective current.

Table 2 represents the global intensity: for example, current as 167.97 µA (resp. 99.81 µA) corresponds to an average density current at 1.34 µA.cm -2 (resp. 0.79 µA.cm -2 ) but macrocell corrosions create a non-uniformity of the current density. The finite element solution allows building the field of current density and more particulary the anodic one at the interface between active steel and concrete directly related to the oxidation of steel and material loss (area where corrosion peaks are observed).

With the SACP in substrate, self-corrosion of the zinc (i.e. microcell) is about 1836µA to which is added 576µA of macrocell totaling 2412µA of zinc consumption: this current reduces 224µA of steel corrosion in substrate concrete. The yield is close to 10% The previous findings can be visually observed on Fig. 14 which illustrates the 3D Finite Element Model results representing the potentials and the field lines (current) depending on the tested conditions:

• before repair, there is no current field line as the potential is uniform;

• after repair without SACP, current field lines appear between cathodic area (repaired area) and anodic area (substrate concrete which remain contaminated and therefore exhibit lower potentials);

• after repair with SACP, either in the patch or in the substrate, current field lines (from CP) were all over the steel reinforcement and no macrocell corrosion occurred between active and passive steel.

Effect of the electrical resistivity of the patch concrete

The resistivity of the patch concrete strongly impacts the current and therefore the efficiency of the treatment as represented in Fig. 15 which represents the global current on steel in the substrate. Before repair, the current is constant and equal to 240 µA. After Patch Repair without SACP, current increases (320 to 300 µA) with increasing resisitivity (50 to 1400 Ω.m): Thus the repair increases the corrosion where contaminated concrete is still present (decrease of anodic /cathodic surfaces ratio). The position of the SACP strongly influences the current. When embedded in the patch, the current increases from 100 to 250 µA and for resistivities exceeding 1000 Ω.m the current became equal to the one before repair meaning that the SACP brought no improvement. When the SACP is embedded in the substrate, the current almost reaches a step (100 µA) 2.5 times lower than the one before repair meaning that the efficiency is improved.

For SACP in substrate concrete, the efficiency slightly increases because the electrical field lines are less dispersed in the patch where the protective current is not necessary (steel becomes passive in an alkaline environment).

Potential distributions

Fig. 16 represents the potential along a line of the cylinder: this line is under the steel for this case. The corrosion is present only on the lower half of the cylinder (under the patch repair). As regards the steel below the patch, the potential without SACP is upper than before patch repair: the repair has therefore deteriorated the existing situation for the active steel. At about an abscissa of 0.45 m, the potential with SACP in the patch is lower than the one with SACP in substrate but this is not the case further away from the abscissa Fig. 17 shows that the depolarization criterion [39] is achieved only with SACP in patch and only on a very small range. With SACP in substrate concrete this criterion is only achieved in passive steel part but it is useless. Fig. 18 evinces the evolution of the potential around the rebar against the angle: in front of SACP in patch (at 0.45m X-axis linear), the potential varies from more than 30 mV (as in case 1). Once again, the spatial distribution of protection must be taken into account.

Current density distributions

Tab.3 shows that:

• for the steel still active, the overall intensity increases by 53 % after the repair without SACP; • with SACP in patch, the overall intensity drops by 67 % and with SACP in substrate by 69 %.

In both cases with SACP, the macrocell current (I a -I c ) values are negatives (only microcell current is still present). With 200 Ω.m of electrical resistivity for the concrete patch, the two situations look very similar. µA.cm -2 , while on the other side it is about 0.7 µA.cm -2 .

Effect of the electrical resistivity of the patch concrete

Conclusions

All along the studied cases, it has been established that: • patch repair always leads to corrosion increase of the active steel within the remaining substrate concrete: hence it is necessary to optimize the length of the repair as well as the position of the anodes;

• it is preferable to place the SACP in the substrate concrete: placing SACP within the patch appears as a more convenient solution but specific effort should be made to put it in the substrate in order to increase its efficiency when the repair mortar is significantly more resistive than the substrate concrete;

• the interest to remove all the contaminated concrete around the steel is also decisive for a sustainable repair.

Of course, the results provided in this study depend on the selected parameters but the conclusions are expected to remain qualitatively valid if the parameters vary within acceptable ranges.

Finally, and contrary to what is observed with the use of SACP in the maritime field, the relationship between macrocell current (i.e. which protects steel) and microcell current (i.e. zinc self-corrosion) is very different and far from the ratio 0.9: laboratory testing would be very relevant to approximate a coefficient of efficiency for the concrete sector. This coefficient will be useful to calculate the SACP lifetime because zinc consumption by microcell can only be estimated by autopsy and weighing. It is evident that the electrical resistivity of concrete (which varies according to the environmental conditions) will be the dominant factor.

Figure 1 : 2 .

 12 Figure 1: Illustration of macrocell corrosion around the steel

Figure 2 :

 2 Figure 2: Situation 1 -Microcell before patch repair

Figure 3 :

 3 Figure 3: Situation 1 -Macrocell after patch repair

Figure 4 :

 4 Figure 4: Microcell and macrocell current densities

Figure 5 :

 5 Figure 5: Situation 2 -Before patch repair

Figure 6 :

 6 Figure 6: Situation 2 -After patch repair

Figure 7 :

 7 Figure 7: Patch repair geometry (distances in meters)

Figure 8 :

 8 Figure 8: Geometry zoom in patch repair (XZ plan w.r.t Fig. 7)

Figure 9 :

 9 Figure 9: Polarization curves of iron and zinc with electrochemical parameters in Tab. 1

Figure 10 :

 10 Figure 10: Situation 1 -Potential distributions along the steel reinforcement in the patch area (patch) and in the adjacent area (substrate) (V vs.S CE)

Figure 11 :Figure 12 :

 1112 Figure 11: Situation 1 -Depolarisation values obtained with SACP embedded in the patch or in the substrate and criterion of efficiency for ICCP [39] (in dotted line)

Figure 13 :

 13 Figure 13: Situation 1 -Current distributions along the steel reinforcement in the patch area (patch) and in the adjacent area (substrate)

4. 2 .

 2 Situation 2: partial removal of contaminated concrete around the steel reinforcement in the patch area and adjacent area is not contaminated As in section 4.1, the electrical resistivity of patch repair is set to 200 Ω.m: It will only vary in subsection 4.2.3. Before the repair, macrocell corrosion is still present along the steel: the anode/cathode ratio decreases after the repair.

Figure 14 :Figure 15 :

 1415 Figure 14: Situation 1 -3D Finite Element Model simulating the potential and current distributions depending on the conditions (before repair and after repair considering no SACP, SACP in the patch and SACP in the substrate)

Figure 16 :

 16 Figure 16: Situation 2 -Potential distribution along the steel reinforcement (V vs. S CE)

Figure 17 :

 17 Figure 17: Situation 2 -Depolarisation values (V)

Figure 18 :

 18 Figure 18: Situation 2 -Potential distributions along the steel reinforcement and around the steel reinforcement depending on the angle (V vs. S CE)

Figure 19 :

 19 Figure 19: Situation 2 -Current densities along steel reinforcement (A.m -2 )

Figure 20 :

 20 Figure 20: Situation 2 -Current distribution around the steel reinforcement depending on the angle (A.m -2 )

  Fig 21 shows that 200 Ω.m approximately corresponds to the crossing of the two curves. The efficiency of the SACP in patch repair strongly decreases with the resistivity while it remains relatively independant of the resitivity of the patch when the SACP is located within the substrate. Fig 22 is etablished with a resistivity at 1000 Ω.m and with SACP in patch: only a small portion of the steel is protected by the SACP and macrocell currents are visible with the field lines of circular shape between active (below) and passive (up) steel rebar.

Figure 21 :

 21 Figure 21: Situation 2 -Effect of the patch concrete resistivity on current (µA)

Table 1 :

 1 Electrochemical parameters

		Parameter	Symbol Selected Value	Unit
	Fe Oxygen on Fe	Anodic equilibrium potential Anodic exchange current density Anodic Tafel slope Cathodic equilibrium potential Cathodic exchange current density Cathodic Tafel slope	E eq Fe j 0 a,Fe β a,Fe E eq O 2 j 0 c,O 2 /Fe β c,O 2 /Fe	-0.680 100.10 -6 90.10 -3 0.160 6.10 -6 180.10 -3	Vvs.S CE A.m -2 V/dec Vvs.S CE A.m -2 V/dec
	Zn	Anodic equilibrium potential Anodic exchange current density Anodic Tafel slope	E eq Zn j 0 a,Zn β a,Zn	-1.050 16.10 -6 60.10 -3	Vvs.S CE A.m -2 V/dec
	Oxygen on Zn	Cathodic exchange current density Cathodic Tafel slope	j 0 c,O 2 /Zn β c,O 2 /Zn	2.10 -6 180.10 -3	A.m -2 V/dec

Table 2 :

 2 Situation 1 -Current calculations in µA (patch concrete resistivity is equal to 200 Ω.m, substrate concrete resistivity is equal to 100 Ω.m)

				.0	-
		I a	243.03	243.03	-
		I c	109.70	214.23	-
	Without SACP	I a -I c	-	109.70	-
		I a	-	323.94	-
		I c	246.12	299.52	1874.32
	SACP in Patch	I a -I c	-	-131.54	377.67
		I a	-	167.97	2251.99
		I c	246.83	428.82	1835.93
	SACP in Substrate	I a -I c	-	-329.01	575.85
		I a	-	99.81	2411.78

  [START_REF] Gp | Concrete repairs: Performance in service and current practice[END_REF]

	Case	Current intensity	Patch (up)	Substrate (below the patch)	Substrate	SACP
		I c	106.18	105.64	117.22	-
	before repair	I a -I c	57.49	59.73	-	-
		I a	163.67	165.36	-	-
		I c	73.23	85.12	96.26	-
	Without SACP	I a -I c	-	169.48	-	-
		I a	-	254.60	-	-
		I c	144.39	158.71	227.54	1860.93
	SACP in Patch	I a -I c	-	-74.09	-	446.02
		I a	-	84.62	-	2306.95
		I c	139.84	156.24	372.44	1833.53
	SACP in Substrate	I a -I c	-	-76.62	-	588.90
		I a	-	79.62	-	2422.43

Table 3 :

 3 Situation 2 -Current calculations in µA (patch concrete resistivity is equal to 200 Ω.m, substrate concrete resistivity is equal to 100 Ω.m)

Acknowledgement

The authors warmly thank all the members of the building-construction commission of CEFRACOR (CEntre FRAnc ¸ais de l'AntiCORrosion) and especially the two working groups "Sustainable repairs for reinforced concrete structures" & "Modeling and electrochemical field measurements" for discussions coming from field case studies and feedbacks.


Muzungu Ngofuna

Alban Lemasson

Claude Monghiemo

Victor Narat

Florence Levréro

Clément Cornec
email: clement.cornec@hotmail.fr

A pilot study of calling patterns and vocal turn-taking in wild bonobos Pan paniscus

Keywords: wild bonobo, vocal communication, vocal behaviour, calling patterns, vocal turn-48 taking

de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Despite recent scientific interest, our knowledge of rule-governed call exchanges in our 77 closest living great ape relatives is still partial. All confirmatory evidence to date comes from 78 captive groups of Western lowland gorillas Gorilla g. gorilla, and bonobos Pan paniscus, and 79 is limited to one group per species (gorilla: [START_REF] Lemasson | Social basis of vocal interactions in Western lowland 573 gorillas (Gorilla g. gorilla)[END_REF]bonobo: Levréro et al. 2019).

80 The only study investigating rule-governed call exchanges in a wild great ape species (Arcadi 81 2000) has been conducted on wild chimpanzees Pan troglodytes schweinfurthii, which tended 82 not to respond to most of the calls of their group members (within 5 sec). Rather, wild 83 chimpanzees often called in chorus, with vocalisations greatly overlapping among individuals 84 [START_REF] Arcadi | Vocal responsiveness in male wild chimpanzees: implications for the 505 evolution of language[END_REF]. Thus, from existing scientific knowledge, wild chimpanzees do not appear to 85 display rule-governed call exchanges, while captive bonobos do.

86

However, due to differences in environmental conditions (wild versus captive) between 87 the studied chimpanzees and bonobos, we cannot readily attribute that such variation in their 88 vocal behaviour reflects species-specific factors rather than study conditions. For example, 89 [START_REF] Arcadi | Vocal responsiveness in male wild chimpanzees: implications for the 505 evolution of language[END_REF] focused only on male Eastern chimpanzees, focusing on a small sample of males 90 (N = 11) across a broad range of social contexts (communication between distant parties, 91 agonistic interactions, copulations and feeding). In contrast, [START_REF] Levréro | Social bonding drives 586 vocal exchanges in Bonobos[END_REF] studied both 92 sexes in bonobos but only in calm contexts (grooming, resting, foraging), that are more 93 amenable to organised vocal exchanges [START_REF] Henry | Social coordination in animal vocal 548 interactions. Is there any evidence of turn-taking? The starling as an animal model[END_REF][START_REF] Levinson | Turn-taking in human communication -origins and implications for 578 language processing[END_REF]Pougnault et al. 94 2020a). Interestingly, our primary prediction would have been that non-agonistic vocal 95 exchanges are more essential in the wild, wherein individuals more often lose visual contact 96 with one another in closed forest habitats, than in captive groups. The fact that captivity 97 deprives bonobos from their natural fission fussion social system may indeed reduce the 98 importance of vocal turn-taking and overlap avoidance, as these vocal behaviours appear to 99 function to reinforce social bonds and increase community cohesion. At the same time, call 100 overlap avoidance seems essential when animals must deal with a large number of potential 311 factors in all GLMMs to avoid pseudo-replication. We used likelihood ratio tests (LRTs) and 312 Akaike Information Criteria (AIC) to determine best fitting models. GLMMs were performed 313 using the function glmer of the 'lme4' package [START_REF] Bates | Fitting Linear Mixed-Effects Models Using 511 lme4[END_REF].

315 RESULTS

316 In total we analysed 259 call intervals from 63 independent vocal events during peaceful 317 activities (on average 5.72 vocal events per day, range 0 to 31 per day). Among these 259 call 318 intervals, there were 217 call intervals for which callers were identified. Among the remaining 319 intervals, there were two call intervals for which the sex and age category of the callers were 320 known, six call intervals for which only the age of the callers was determined, and 34 call 321 intervals for which we had no information about the age category, sex, or identity of the callers 322 but we were certain that they were distinct callers. We excluded 382 call intervals from analysis 323 due to poor acoustic quality that did not allow us to define the onset of the call or to reliably 324 identify the vocalisers (see Fig. 1). In conclusion, this pilot study supports the existence of coordinated vocal exchanges in 450 a wild great ape species. We acknowledge that our findings are based on a small sample size, 451 nevertheless these data corroborate the observations obtained from a captive bonobo group, and 452 pave the road for replication studies. Although preliminary, these new data will serve future 453 comparative studies investigating the temporal and social patterns of call exchanges in primates 454 along their natural range of social systems, and can potentially provide further insight into the 455 function of turn-taking in primates, and ultimately, the evolution and origins of language 456 [START_REF] Levinson | Cognition at the heart of human interaction[END_REF][START_REF] Levinson | Turn-taking in human communication -origins and implications for 578 language processing[END_REF].

F

457

Fig. 1 .Fig. 2 .

 12 Fig. 1. -Distinct calling patterns considered in the study. The baseline threshold of 2100 msec between two calls was determined by an analysis of the distribution of call intervals (see Results and Fig. 2) and was used to define the calling patterns. 396x418mm (59 x 59 DPI)

  101 vocal interlocutors, particularly because their identity is less predictable in the wild, and hence 102 it may be relatively important to extract vocal identity cues from the calls of conspecifics 103[START_REF] Keenan | 564 The reliability of individual vocal signature varies across the bonobo's graded 565 repertoire[END_REF]. Thus, even if we assume that studies of wild chimpanzees and captive 104 bonobos are comparable, the fact that captive bonobos show organised vocal exchanges and 105 wild chimpanzees do not is not in line with our predictions, and makes these opposing 106 observations even more puzzling. Critically, the avoidance of overlap and the reciprocal 107 exchange of alternating short turns remains to be confirmed in wild great ape species. Such 108 confirmation is of high interest to understand the evolutionary pressures that have shaped rule-151 habituation that lasted 6 months over 2010-2011(Narat et al. 2015b). The proper habituation 152 of the bonobos started in May 2012 (6 days per week; seeNarat et al. 2015b for details). The 153 community is now well habituated and tolerant to human presence(Narat et al. 2015b). An 154 approach of a minimum distance of 10 m was possible between the closest individual and the 155 observers. This minimum distance was maintained to decrease the risk of disease transmission.156 During our pilot study period (February to March 2019), the studied community was composed 157 of 20 weaned free-ranging individuals. Dependant infants (N = 2) were excluded from our 158 analyses as in similar studies investigating general patterns of vocal behaviour(Lemasson et al. All statistical analyses were performed using R version 3.6.1 (R Core Team 2019).302 We conducted a series of Generalised Linear Mixed Models (GLMMs) in R software. A first 303 GLMM tested whether the sex and/or age of bonobos were significant predictors of calling 304 patterns. Two additional GLMMs tested the contribution of the two behavioural contexts and 305 call type categories on calling patterns. The sex, age, behavioural context and call type 306 categories were respectively included as fixed factors. We coded a binary pattern where 1 was 307 attributed to a vocal exchange and 0 to a vocal non-exchange. The models were run using a 308 logit link function with a binomial distribution. Because one individual could be involved in 309 several vocal interactions and vocal interactions could come from the same or different vocal 310 events, the identity of the emitters and the code of the vocal event were included as random

	126 1999; Clay & Zuberbühler 2009; Clay et al. 2015). In other non-human primate species, there 300 Statistical analysis
	127 exists evidence that calling patterns are context-and call-type specific, and vary as a function 301
	128 of the biological (age, sex) or social characteristics of the caller (Digweed et al. 2007; Chen et
	129 al. 2009; Lemasson et al. 2013, 2018; Levréro et al. 2019). Such relationships, investigated in
	130 the present study, have not been previously demonstrated in wild bonobos.
	131
	F o r P e e r R e F o r P e e r R e MATERIAL AND METHODS 134 The study was carried out in the Manzano forest (2°38'S, 16°23'E) near Embirima village in 132 133 Study site 135 the Bolobo Territory of the Western Democratic Republic of the Congo. The study site is part 136 of the Forest Concession of Local Communities of the Mbali River, a community-based 137 conservation area led by the Non-Governmental Organisation Mbou-Mon-Tour, which has o r P e e r F o r P e e r F o r P e e r F o r P e e r F o r P e e r F o r P e e r F o r P e e r 138 worked in F R e R e R e R e R e R e R e
	v v v v v v v v v
	i i i i i i i i i
	e w 116 their importance in bonobo communication. To this end, we collected a unique dataset of e w e w e w e w e w e w e w e w
	O 117 individual vocal utterances within subgroups. We predicted to find three calling patterns: O O O O O O O O
	n l y 118 isolated calling (one call is emitted and no other consecutive calls can be heard), repeated n l n l n l n l n l n l n l n l 119 calling (the same caller calls several times in a row), and temporally-ruled vocal exchanges y y y y y y y y
	120 (with short call interval) between two or more callers. In addition, we examined the potential
	121 influence of the age-sex class of callers and their behavioural activities on calling patterns, with 171 Ngofuna and V. Narat). Individual identification relied on body size, face colour, hair growth
	122 a special focus on temporally-ruled vocal exchanges. We also investigated whether calling 172 on the head, anogenital area shape, and particular features such as mutilations caused by
	123 patterns were call type-dependent. Indeed, while several studies have attempted to link bonobo 173 poacher traps.
	124 call types or call sequences to specific behavioural contexts, these studies have not focused on 174
	125 calling patterns in which such calls are most often used (e.g., de Waal 1988; Bermejo & Omedes 175 Data collection
	5 6 7 13

109 governed communication

(Pougnault et al. 2020a)

.

110

In the present study, we describe the general calling patterns of a wild community of 111 bonobos in peaceful contexts and within subgroups. To date, the vocal behaviour of wild 112 bonobos has been mainly investigated in terms of group coordination (e.g.

Hohmann & Fruth 113 1994;[START_REF] White | Function of loud calls in wild 651 bonobos[END_REF][START_REF] Schamberg | Call combinations, vocal 625 exchanges and interparty movement in wild bonobos[END_REF][START_REF] Schamberg | Bonobos use call 628 combinations to facilitate inter-partytravel recruitment[END_REF]

, which is in the context of long-distance 114 communication (but see

[START_REF] Clay | Functional fexibility in wild bonobo vocal behaviour[END_REF]

. We thus first aimed to look at intimate vocal 115 interactions for evidence of conversational-like rules in wild bonobos, and second, to assess close connection with the local community since 2001

(Narat et al. 2015a

). The forest 139 is located in the Maï Ndombe Province, 300 km north of Kinshasa. The habitat is a forest-140 savanna mosaic with 58% forest and 42% savannah

[START_REF] Pennec | Floristic and structural vegetation typology of bonobo habitats in a forest-603 savanna mosaic (Bolobo Territory, D.R. Congo)[END_REF]

) but bonobos spend 141 more than 97% of their time in the forest

[START_REF] Pennec | Spatiotemporal variation in bonobo (Pan paniscus) habitat use in a forest-savanna mosaic[END_REF]

). The dry season extends from 142 June to September and the wet season from October to May

[START_REF] Pennec | Spatiotemporal variation in bonobo (Pan paniscus) habitat use in a forest-savanna mosaic[END_REF]

.

143 The home range of the bonobos in the Manzano forest covers approximately 20 km 2 with a 144 bonobo density of 1.2 individuals/km² (Pennec et al. 2020), thus comprised in the average 145 density of the broader Bolobo Territory, between 0.5 to 2.2 individuals/km 2 (Inogwabini et al. 146 2008; Serckx et al. 2014; Pennec et al. 2020). 147 148 Study group 149 Search of regular visual contact with the bonobo community started in 2007 with the presence 150 of local trackers in the forest twice a week during 3 years and was followed by a pilot study of 159 2018; Levréro et al. 2019). We used the age classes defined by Van Krunkelsven et al. (1999): 160 juveniles (3-9.9 years), subadults (10-14.9 years) and adults (15 + years). For individuals born 161 between 2012 and 2019, the exact month of birth was known while for individuals born between 162 2007 and 2012, the exact year of birth was known. Regarding individuals born before 2007, the 163 year of birth could be estimated for individuals who were still dependent infants in 2007 and 164 the other individuals were considered as adults at the time of our study (i.e., they were over 15 165 years old in 2019).

166 The group composition was thus three adult males, seven adult females, three subadult males, 167 two subadult females and five juvenile females. For the study of their vocal behaviours we 168 considered two age classes: the "immature class" which included juveniles and subadults, and 169 the adult class (see Table

1

) because of the limited sample size. Individual identification was 170 based on repetitive direct observations from 2012 and from photographs and film banks (M.

  8%, N = 43/56 for isolated calls and 60.5%, N = 75/124 for vocal turn-taking, Table5).[START_REF] Lemasson | Social basis of vocal interactions in Western lowland 573 gorillas (Gorilla g. gorilla)[END_REF]. We cannot rule out the possibility that the lack of differences 410 across ages was due to the small sample size and notably the low number of juveniles, who 411 consequently were included in the same category than subadults, as immature individuals.412 Similar to age, we found that calling patterns did not vary between males and females.

	401 that such temporal rule violation may be less crucial in captivity, it has been experimentally 375 (76.376 Repeated calls were equally composed of calls from the "peep" and "bark" categories (49%, N 400 size is limited in both studies. While the higher frequency of call overlap in captivity suggests 449
	377 = 24/49 and 44.9%, N = 22/49 respectively). Only overlapping calls more often included those 402 demonstrated that such rule violation remains relevant even to captive primates (Campbell's
	378 from the "bark" (4/6) than "peep" category. 403 monkeys Cercopithecus campbelli: Lemasson et al. 2011; gorillas: Pougnault et al. 2020b;
	379 404 bonobos: Levréro et al. 2017).
	380 405	DISCUSSION Second, we found no differences in calling patterns between adult and immature
	o r F o r F o r 381 This pilot study provides the first valuable data on the general calling patterns of a wild great 382 ape species, the bonobo. Focusing on peaceful contexts, we found that bonobos in our study 383 population exchanged calls that followed fundamental temporal rules of vocal turn-taking. F o r 406 bonobos, while other primate studies suggest that adults emit significantly more calls during F F 407 social interactions than do immature individuals (Common marmosets Callithrix jacchus, Chen 408 et al. 2009; wild spider monkeys Ateles geoffroyi, Briseño-Jaramillo et al. 2018; captive o r o r
	P e e r R e v P e e r R e v P e e r R e v First, this pilot study largely corroborates the findings of the only other studied bonobo P e e r R e v P e e r R e P e e r R e 409 gorillas: 413 Regarding vocal turn-taking specifically, adult males and females seemed to be equally 388 v v
		i i i i i i
	e w e w e w 389 group, which was in captivity (Levréro et al. 2019). Both studies followed a similar 390 methodology and analogous definitions, except for repeated calls that were not recorded in e w 414 involved, but interestingly no immature females were involved in exchanged calls. 415 Third, our results suggest that vocal exchanges are context-specific, at least during e w e w
	O O O 391 captivity. Excluding these repeated calls for comparison, the general vocal behaviour of wild O 416 sedentary or moving activities. The softest calls of the bonobo repertoire ("peep" category) O O
	n l y n l y n l y 392 and captive bonobos appears very similar, with 68.5% vs 73.6% of all coded calls respectively 393 produced within vocal exchanges (the remaining calls were isolated calls, see Levréro et al. n l y 417 were most often produced in vocal turn-taking without overlap as found in captive bonobos n l n l 418 (Levréro et al. 2019) and other primate species (reviewed in Pougnault et al. 2020a). Such soft y y
	394 2019 for values in captive bonobos). Within vocal exchanges, overlapping calls appear more 419 calls in bonobos convey information about caller identity (Keenan et al. 2020) and receivers
	395 frequent in captivity than in the wild (32.8% vs 5.8%, see Levréro et al. 2019 for captive values). 420 can extract such information (Keenan 2016). In the wild, because callers are not always in visual
	396 Call overlap may increase the risk of confusion during message transmission and so, makes 421 contact, overlap avoidance appears crucial for transmitting information that can enable
	397 individual recognition uncertain. However, this risk is limited in captivity where the group 422 individual recognition and ensure subgroup cohesion and affiliative bonding between
	423 conspecifics. The fact that vocal exchanges, as opposed to non-exchanged calls, are used
	424 preferentially during non-travelling contexts that typically favour socialising, may support the
		14 16 17 19

384 Vocal exchanges represented half of the calls produced and bonobos almost systematically 385 avoided overlapping the call of a previous caller, leaving a short delay of on average 2.1 sec 386 between callers. This call delay was consistent with that observed in other ape studies (2.5 sec 387 in captive bonobos:

[START_REF] Levréro | Social bonding drives 586 vocal exchanges in Bonobos[END_REF]

; 3 sec in captive gorillas:

[START_REF] Lemasson | Social basis of vocal interactions in Western lowland 573 gorillas (Gorilla g. gorilla)[END_REF]

.

398 composition is stable and individuals are more often in visual contact, and thus individual 399 recognition can be achieved through visual cues. Despite this, we acknowledge that the sample

Table 1 .

 1 458 ACKNOWLEDGMENTS459 We are very grateful to the NGO Mbou-Mon-Tour for logistical support and for providing 460 access to the Manzano forest, to field assistants who accompanied us in forest, as well as the 461 Embirima inhabitants and their Chief for a warm welcome. We thank two anonymous reviewers 462 who provided helpful comments on the previous version of this manuscript. Lastly, we thank 463 Katarzyna Pisanski for English corrections and scientific input.

	464
	465	DISCLOSURE STATEMENT
	466 The authors declare no competing interests.
	467
	468	FUNDING
	469 This study was financially supported by the program IDEXLYON ANR-16-IDEX-0005 (F.
	470 Levréro grant), the University of Lyon/Saint-Etienne, and the Labex CeLyA.
	471
	472	ETHICAL STANDARD

Table 2 .

 2 661Distribution of call intervals for different calling patterns. In italics we give the percentage of occurrence for each given

	662

Table 3 .

 3 667 Distributions of calling patterns per caller sex and age. Numbers in brackets refer to individual vocal rate production 668 obtained by dividing the total number of recorded calls by the number of individuals within each age and sex class.

	669
		Non-exchanged calls	Vocal exchanges	Total calls
		Isolated calls N = 51	Repeated calls N = 59	Vocal turn-taking N = 104	Overlapping calls N = 5	N = 219
	Adult males (N = 3)	14 (4.7)	5 (1.7)	22 (7.3)	2 (0.7)	43
	Adult females (N = 7)	16 (2.3)	26 (3.7)	45 (6.4)	0	87
	Subtotal adult inds (N = 10)	30 (3)	31 (3.1)	66 (6.6)	2 (0.2)	131
	Immature males (N = 3)	19 (6.3)	16 (5.3)	37 (12.3)	3 (1)	75
	Immature females (N = 7)	2 (0.3)	12 (1.7)	0	0	14
	Subtotal immature inds (N = 10)	21 (2.1)	28 (2.8)	37 (3.7)	3 (0.3)	89
	670
	671

Table 4 .

 4 674Distribution of calling patterns as a function of behavioural context. Percentages in italics correspond to the contribution of 675 each behavioural context to each calling pattern. The majority of the group was feeding or half of the group was feeding while the other half 677 was resting or grooming. 678 b About half of the group moved towards other group members or played or there was a 679 general movement of the group members.

		Non-exchanged calls	Vocal exchanges	Total calls
	Behaviour
		Isolated calls N = 57	Repeated calls N = 52	Vocal turn-taking N = 117	Overlapping calls N = 8	N = 234
	Sedentary behaviour a	39 68.4%	19 36.5%	108 92,3%	6 75%	172
	Movement b	18 31.6%	33 73.5%	9 7.7%	2 25%	62
	676 a 680
	681

Table 5 .

 5 684Contribution of the seven broad call type categories (defined fromBermejo & Omedes 1999 and de Waal 1988) to calling 685 patterns. Percentages in italics correspond to the contribution of each call type category to each calling pattern. Distinct calling patterns considered in the study. The baseline threshold of 2100 msec 690 between two calls was determined by an analysis of the distribution of call intervals (see Results 691 and Fig.2

		Non-exchanged calls	Vocal exchanges	Total calls
	Call type category	Isolated calls N = 56	Repeated calls N = 49	Vocal turn-N = 124 taking	Overlapping N = 6 calls	N = 235
	Peep category	43 76.8%	24 49%	75 60.5%	1 16.7%	143
	Bark category	9 16.1%	22 44.9%	34 27.4%	4 66.7%	69
	Whistle category	1 1.8%	3 6.1%	4 3.2%	0 0%	8
	Low hooting	1 1.8%	0 0%	4 3.2%	1 16.7%	6
	Hiccup	1 1.8%	0 0%	4 3.2%	0 0%	5
	Grunt category	0 0%	0 0%	3 2.4%	0 0%	3
	Pout moan	1 1.8%	0 0%	0 0%	0 0%	1
	686
	687

Ethology Ecology & Evolution

availability in a forest-savannah mosaic. PLoS ONE. 9(4):e93742.


Marcello De Michele

Stefano Corradini

Claudia Spinetti

Daniel Raucoules

The Use of Sentinel 2 to extract the Digital Elevation Model and the velocity of the volcanic ash cloud: comparison with multi sensors

scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

The Use of Sentinel 2 to extract the Digital Elevation Model and the velocity of the volcanic ash cloud: comparison with multi sensors analysis on Etna volcano.

Marcello de Michele 1 , Stefano Corradini 2 , Claudia Spinetti 2 and Daniel Raucoules 1 1 BRGM, Orleans, France

INGV, Rome, Italy

In this study, we demonstrate the use of Copernicus Sentinel 2 to extract the velocity and the Digital Elevation Model of a volcanic ash cloud. The elevation of the ash cloud is an important parameter in volcanology, for manifold reasons. Firstly, the injection height controls the ash dispersion in the atmosphere. Secondly, the injection height is controlled by the pressure in the magmatic chamber, thus this parameters gives indirect access to a solid Earth physical parameter. Thirdly, the roughness of the ash plume is an essential parameter to understand turbulences and plume cinematics/dynamics.

With the exception of dedicated spaceborne missions, such as Multi-angle Imaging Spectro Radiometer (MISR), most of the conventional stereo photogrammetric methods from satellite do not hold for the retrieval of the DEM of a volcanic ash cloud. This is because the volcanic cloud moves between the stereo images acquisitions (with time lag from tens to 60 seconds). This motion yields an offset that adds up to the offset due to stereoscopic parallax. Therefore, height estimation with these methods is biased. In a previous study, de Michele et al. (2016) showed that conventional multispectral push broom satellites, such as Landsat 8, present a small lag between the panchromatic and multispectral bands that can be used to extract both velocity and elevation of the ash plume at high spatial resolution. Here, we show that the methodology can be applied to Copernicus Sentinel 2, that present an improved repetition frequency of 5 days. In this study, we apply the method to two Mount Etna eruptive clouds on 29 December 2018 and 27 July 2019. Then, in a future work, we will compare the results with independent measurements from Sentinel 3, MODIS and SEVIRI.