EP2085518A1 - Method of manufacturing a bituminous coating with simultaneous insertion of the binder and a part of the solid mineral fractions in the mixer - Google Patents

Abstract

The method involves introducing a part of solid mineral fractions in a mixture containing a binding agent e.g. bitumen, and the solid mineral fractions, where the part of the mineral fractions is previously and partially heated for attaining a temperature higher than 80 degree Celsius at the moment of input to the mixture. Separate and simultaneous introduction of the binding agent and the remaining non-heated part of the mineral fractions is carried out in the mixture. The part of the solid mineral fractions is divided into two parts, where one of the parts includes binder aggregates.

Description

The invention relates to a process for producing a bituminous mix comprising inorganic solid fractions coated with a binder, the process comprising a step of heating a part of said mineral solid fractions and then a step of simultaneous introduction of the binder and of the part remaining of said mineral solid fractions.

"Mineral solid fractions" here means all solid fractions that can be used for the production of bituminous mixes, in particular for road construction, including in particular natural mineral aggregates (chippings, sand, fines), and asphalt aggregates resulting from recycling. materials recovered during road repairs and surplus asphalt plants. "Asphalt aggregates" means asphalt mixes (mixture of aggregates and bituminous binders) from milling asphalt layers, crushing plates extracted from asphalt pavements, pieces of asphalt mix coated or surplus production of asphalt (surplus production are coated or partially coated in the plant resulting from the transitional phases of manufacture

The mineral solid fractions may be chosen from elements less than 0.063 mm (filler or fines), sand whose elements are smaller than 2 mm, gravel, whose elements have dimensions greater than 2 mm, and aggregates originating from recycled materials, the elements of which can reach dimensions up to 31.5 mm.

The term "binder" any hydrocarbon binder of fossil or plant origin used for the production of asphalt, including bitumen pure or added fluxers and / or fluidizers and / or regenerants and / or pigments and / or modified by adding polymers. This binder can also be doped by adding tackifiers (fatty amine derivatives, such as Polyram L 200 supplied by the company CECA, or alkymamido-imidazo polyamines).

This binder can be introduced as is or be modified to be in the form of an emulsion, a dispersion or a bitumen foam. Bitumen foam means an injection process in the arrival of the binder of a quantity of water and possibly air, the water being pure or additive additives to modify the properties of adhesiveness or rheological of the binder.

In the conventional heat-embedding process, the mineral solid fractions are dried, before the coating step, so as to remove moisture from the mineral solid fractions, which requires a considerable energy expenditure because of the large amount of water initially contained in these fractions, especially sand and aggregates. In addition, drying and raising of temperature result in the release of fumes containing dust-laden water vapor. Given the environmental constraints, it is essential to take maximum precautions to reduce and / or treat these gaseous effluents, which leads to an implementation of the process both more complex and more expensive.

To resolve this problem, EP 1 469 038 A proposes to bring the drying step on a first portion of the mineral solid fractions, substantially free of fines, to coat hot bitumen this first part, and then adding to the mixture thus obtained a second portion of the mineral solid fractions, including sands and fines.

This process requires the provision of two mineral solid fractions, one free of fines and the other containing fines, which may involve difficulties. In addition, this process can not be effectively implemented in some existing coating plants, and may therefore require an expensive arrangement thereof.

FR 2 884 265 proposes an equivalent process in which the first part of the mineral solid fractions may contain fines.

FR 2 884 264 proposes a process in which all the mineral solid fractions (aggregates, sands and fines) are subjected to a drying process that leaves a fraction of the initial moisture and then remains coated.

However, such processes induce an increase in the mixing times taking into account the sequencing of the phases and consequently a reduction in the production rates of the batch type installations or the possible need for extension of the mixers in the context of continuous type installations.

The object of the invention is to eliminate all or part of these disadvantages.

1. a) introduction dans un mélangeur (dispositif dans lequel le liant et les fractions minérales solides sont mélangées) d'une première partie desdites fractions minérales solides, ladite première partie ayant été au moins partiellement préalablement chauffée pour atteindre une température au moment de l'entrée dans ledit mélangeur qui soit supérieure à 80°C, avantageusement supérieure à 100°C ; puis
2. b) Introduction séparée mais simultanée, dans ce même mélangeur, du liant et de la partie restante desdites fractions minérales solides non préalablement chauffée.

The subject of the invention is thus a process for manufacturing bituminous mixes comprising solid mineral fractions coated with a binder, comprising the following successive stages:

1. a) introducing into a mixer (device in which the binder and the solid mineral fractions are mixed) a first part of said solid mineral fractions, said first part having been at least partially previously heated to reach a temperature at the time of entry into said mixer which is greater than 80 ° C, preferably greater than 100 ° C; then
2. b) Separate but simultaneous introduction into the same mixer of the binder and the remaining portion of said solid mineral fractions not previously heated.

• a1) chauffage, à une température supérieure à 120°C, de la première subdivision de ladite première partie des dites fractions solides minérales exempte d'agrégats d'enrobés; puis
• a2) mélange de ladite première subdivision chauffée obtenue suite à l'étape a1), maintenue chaude, avec la seconde subdivision de ladite première partie des fractions solides minérales pouvant comprendre des agrégats d'enrobés.

Advantageously, said first portion of solid fractions is itself subdivided into two parts. In particular, step a) is subdivided into two successive steps:

• a1) heating, at a temperature above 120 ° C, the first subdivision of said first portion of said mineral solid fractions free of asphalt aggregates; then
• a2) mixing said first heated subdivision obtained following step a1), kept hot, with the second subdivision of said first portion of the mineral solid fractions may comprise asphalt aggregates.

The expression "kept hot" means that said first heated subdivision is, at the beginning of step a2), at a temperature such that the assembly resulting from mixing said first subdivision with said second subdivision is at a temperature greater than 80 ° C, preferably greater than 100 ° C.

Advantageously, said second subdivision does not need to be heated beforehand.

The solid mineral fractions introduced in steps a) and b) advantageously both comprise fines, sand and chippings (as defined above). They may further comprise asphalt aggregates (as defined above).

Thus, the solid mineral fractions introduced in step b) advantageously comprise sand whose elements are less than 2 mm, chippings, the elements of which have dimensions greater than 2 mm and possibly aggregates originating from recycled materials, whose elements can reach dimensions up to 31.5 mm.

It will be recalled that the solid mineral fractions introduced in step b) are advantageously used in cold (that is to say at room temperature), in particular they have not been previously heated. Aggregates from recycled materials that can be introduced in this step b) are advantageously used cold, they have not been previously heated.

The term "separate but simultaneous introduction" means that said remaining portion of the solid mineral fractions is not already mixed with the binder at the time of introduction and that the beginning of the introduction of the binder and said remaining part into the binder. the mixer is carried out substantially simultaneously.

The term "not previously heated" means that the solid mineral fraction is introduced cold (ie at room temperature) and that it was not, at any time during the process, dried by heating.

In step b), the binder and said remaining portion of the solid fractions are introduced separately but simultaneously into said first portion of the solid mineral fractions. The binder and said remaining portion of the solid fractions have not been previously mixed.

The end times for introducing the binder and said remaining portion of the solid fractions may coincide or diverge. According to a variant of the invention, during step b) all of said remaining portion of the solid mineral fractions is introduced simultaneously to the binder so that all of said remaining portion of the solid mineral fractions is introduced while only a portion of the binder has been introduced ( or the entire binder and then the insertion end times coincide). According to another variant of the invention, during step b) the entire binder is introduced simultaneously with the introduction of said remaining portion of said solid mineral fractions so that all the binder is introduced at the same time as only a part of said remaining portion of the solid fractions is introduced (or all and then the insertion end times coincide).

According to a preferred variant of the invention, the process allows the recovery of asphalt aggregates resulting from the recycling of materials recovered during the repair of roads (and others).

• a1) chauffage, à une température supérieure à 120°C, avantageusement supérieure à 130°C, de la première subdivision de ladite première partie des fractions solides minérales exempte d'agrégats d'enrobés ; puis
• a2) mélange de ladite première subdivision obtenue suite à l'étape a1), maintenue à cette même température, avec la seconde subdivision de ladite première partie des fractions solides minérales comprenant des agrégats d'enrobés.

The process according to the invention is therefore characterized in that in step a) said first part of the solid mineral fractions comprises asphalt aggregates. In this case, said first portion of solid fractions is itself subdivided into two parts, a subdivision comprises asphalt aggregates. Step a) is then advantageously subdivided into two successive steps:

• a1) heating, at a temperature above 120 ° C, preferably above 130 ° C, the first subdivision of said first portion of the mineral solid fractions free of asphalt aggregates; then
• a2) mixing said first subdivision obtained following step a1), maintained at this same temperature, with the second subdivision of said first part of mineral solid fractions comprising asphalt aggregates.

The inventors have found that even better results are obtained when using regenerated asphalt aggregates; that is to say aggregates of mixes having been brought into contact with a regenerating agent. The aim is to regenerate the old binder, whose hardening comes from the physico-chemical transformation of some of its constituents, by corrections of its consistency and its chemical constitution by means of a suitable agent, which must be a solvent of binder. This regenerating agent has a fluidifying and repeptising power (dispersion of asphaltenes) on the old binder sufficient to reconstitute, with said old binder, a binder having the desired properties (mechanical and rheological properties). The use of such a regenerating agent makes it possible to improve the migration of the old binder (present in the asphalt aggregates) towards the new mineral solid fractions, so as to be equally distributed over all the mineral solid fractions.

The regenerating agent can be of petroleum, coal, vegetable, mineral or combined origin of the different products. These include vegetable oils, mineral oils (paraffin), aromatic oils and recycling binders having an aromatic character with low levels of asphaltenes. These last two families are notably marketed by TOTAL in the Regenis ^® product range. The amount of regenerating agent will be between 1 and 50% relative to the binder content in the aggregate asphalt and preferably between 10 and 30%.

In an advantageous variant of the invention, the asphalt aggregates represent between 5% and 70% and preferably 20 to 40% of the mass of the weight of the mineral solid fractions constituting said first part.

The grade of the bitumen and its quantity will be defined according to the percentage of regenerating agent, the bitumen present in the asphalt aggregates and the expected specifications for the asphalt mix.

In the process according to the invention, the remaining part, introduced in step b), advantageously represents from 5 to 50%, more advantageously 10 to 50%, still more advantageously 20 to 40%, of the mass of the weight of said fractions. solid minerals.

According to an advantageous variant of the invention, a controlled quantity of water is added. This water may be added during step b) of simultaneous introduction of the binder and of said remaining part. It can also be added after step b). It can finally be added to said remaining portion of solid mineral fractions prior to step b). Water can be added to only one or more of these stages. By the use of solid mineral fractions not previously heated (and therefore wet because not dried) and the possible addition of water, it is possible to control the water content in the mixer during this step b).

The binder is advantageously used at a temperature between 100 and 200 ° C, preferably about 160 ° C. The binder emulsion is advantageously used at a temperature of between 10 and 95 ° C.

Thus, the addition of an undried solid mineral fraction (step b) at room temperature has the effect of reducing the outlet temperature of the mixes.

Compared to the method of the prior art, given that the mixture of said remaining portion of the fractions mineral solids and binder is carried out in the same phase, this method makes it possible to reduce the cycle times and thus to increase the production capacities of the batch type production facilities and to reduce the lengths of the mixers of the continuous type installations. , with equivalent coating quality.

• Dans les brevets FR 2 884 265 et EP 1 469 038 A , l'interface liant/fractions solides est déjà constituée avant l'apport d'eau réalisée soit directement soit indirectement par l'apport des fragments solides humides et ne peut donc plus être modifiée.
• Dans le brevet FR 2 884 264 , l'apport d'eau sous forme directe ou indirecte est effectué:
  • oSoit dans une phase précédent celle de l'introduction du liant, la majeur partie de cette eau s'est évaporée et ne permet donc plus une expansion suffisante permettant de prétendre réduire les temps de cycles et/ou de malaxage pour une qualité d'enrobage équivalente.
  • oSoit dans une phase postérieure à l'enrobage, avec les mêmes inconvénients que pour les brevets FR 2 884 265 et EP 1 469 038 A (cf ci-dessus)

This method also makes it possible to improve the coating by substantial expansion of the binder and therefore of its specific surface, in contact with the water introduced directly or indirectly via the introduction of said remaining portion of the unheated solid fractions while.

• In patents FR 2 884 265 and EP 1 469 038 A the binding interface / solid fractions is already constituted before the supply of water carried out either directly or indirectly by the contribution of wet solid fragments and can therefore no longer be modified.
• In the patent FR 2 884 264 , direct or indirect water supply is carried out:
  • oIt is in a phase preceding that of the introduction of the binder, most of this water has evaporated and therefore no longer allows sufficient expansion to claim to reduce cycle times and / or kneading for a coating quality equivalent.
  • oIt is in a phase subsequent to the coating, with the same disadvantages as for patents FR 2 884 265 and EP 1 469 038 A (see above)

In one embodiment, the method according to the invention is implemented in discontinuous power plants. In another embodiment, it is implemented in continuous power plants, advantageously those with a parallel-current coater-drying drum, with a single-envelope countercurrent-coating drum dryer. and drum dryer with separate parallel shaft type mixer or drum mixer type.

The invention is illustrated hereinafter by examples. In these examples, the binder is a 35/50 or 20/30 penetrability bitumen according to the NF EN 1426 standard. The percentages are given in mass relative to the total mass of the bituminous mixes.

Examples 1 to 3 are made in laboratories. Examples 4 to 6 were made on a construction site.

Example 1 : BBSG 0/10 Diorite

6/10

35%

2/6

19%

0/2

40,6%

The solid fragments consist of aggregates with a particle size of 0/10 mm, consisting of diorite having the following particle size distribution in the final mix:

6/10

35%

2/6

19%

0/2

40.6%

The binder is a 35/50 penetration bitumen: 5.4%.
65% of the aggregates (11% 0/2, 19% 2/6 and 35% 6/10) are heated to 140 ° C and then mixed using a kneader. Then, the addition of the fraction 0/2 having a moisture of 3% and the bitumen (heated to 160 ° C) simultaneously are introduced into the kneader (containing the heated fraction).

The mix is mixed and the final temperature is 98 ° C.

The characteristics of the mix obtained are given in Table 1 below: Table 1 results Specifications NF EN 13108-1 THIS C II C III DURIEZ test NFP 98-251-1 % empty average
R18 (MPa)
r18 (MPa)
r / R 7
12.4
10
0.81 > 0.75 rutting NF EN 12697-22 empty% rut to 30000% cycles 7.2

4.5 <10 5-8

<7.5 <5 PCG NF EN 12697-32 % empty 60 girations 7.8 5-10 Module according to NF EN 12697-26 Average direct tensile modulus (15 ° C-0.02s in MPa)% average voids 11640
6.8 > 5500 > 7000
5-8 > 7000 Fatigue resistance according to NF EN 12697-24 ε6 at 10 ° C -25Hz (μdef)% empty medium fatigue 104
7.5 > 100
5-8

Example 2 : BBSG 0/10 Diorite + asphalt aggregates

6/10

32,6%

2/6

15,3%

0/2

24%

The solid fragments consist of 24% aggregates of mixes and aggregates with a particle size of 0/10 mm, consisting of diorite having the following particle size distribution in the final mix:

6/10

32.6%

2/6

15.3%

0/2

24%

The binder is a 35/50 penetrability bitumen: 4.1% (ie total bitumen: 5.4%)

Asphalt aggregates and 2/6 and 6/10 aggregates are heated to 140 ° C. Then, the 0/2 fraction having a humidity of 4% and the bitumen (heated to 160 ° C.) are introduced simultaneously into the mixer (containing the heated fraction).

The mix is mixed and the final temperature is 100 ° C.

The characteristics of the mix obtained are given in Table 2 below: Table 2 results Specifications NF EN 13108-1 THIS C II C III DURIEZ test NFP 98-251-1 % empty average
R18 (MPa)
r18 (MPa)
r / R 8
13.2
10.5
0.80 > 0.75 rutting NF EN 12697-22 empty% rut to 30000% cycles 7.9
4.1
<10 5-8
<7.5
<5 PCG NF EN 12697-32 % empty 60 girations 8.7 5-10 Module according to NF EN 12697-26 Average modulus in direct traction (15 ° C-0.02s in MPa)
% empty average 12930
7.2 > 5500 > 7000 > 7000
5-8 Fatigue resistance according to NF EN 12697-24 ε6 at 10 ° C -25Hz (μdef)
% empty medium fatigue 102
7.9 > 100
5-8

Example 3 : BBSG 0/10 Diorite + asphalt aggregates, 20/30 bitumen + regenerant

6/10

32,7%

2/6

15%

0/2

24,1%

et d'agrégats d'enrobés : 24,1%The solid fragments consist of aggregates with a particle size of 0/10 mm, consisting of diorite having the following particle size distribution in the final mix:

6/10

32.7%

2/6

15%

0/2

24.1%

and asphalt aggregates: 24.1%

The binder is a 20/30 penetrability bitumen: 3.8% and a regenerant is introduced (0.3%) (ie total bitumen: 5.3%)

The asphalt aggregates and 2/6 and 6/10 aggregates are heated to 150 ° C. The aggregates heated with the regenerant at 150 ° are mixed using a mixer with two parallel shafts. Then, introduced into the mixer (containing the heated fraction) fraction 0/2 comprising 4% humidity and bitumen (heated to 170 ° C) simultaneously.

The mix is mixed and the final temperature is 105 ° C.

The characteristics of the mix obtained are given in Table 3 below: Table 3 results Specifications NF EN 13108-1 THIS C II C III DURIEZ test NFP 98-251-1 % empty average
R18 (MPa)
r18 (MPa)
r / R 7.6
13.6
11
0.81 > 0.75 rutting NF EN 12697-22 % empty
rut to 30000
% cycles 7.1
4
<10 5-8
<7.5
<5 PCG NF EN 12697-32 % empty 60 girations 8.2 5-10 Module according to NF EN 12697-26 Average modulus in direct traction (15 ° C-0.02s in MPa)
% empty average 14156
6.8 > 5500
5-8 > 7000 > 7000 Fatigue resistance according to NF EN 12697-24 ε6 at 10 ° C -25Hz (μdef)
% empty medium fatigue 106
7 > 100
5-8

Example 4 : BBSG 0/10

6/10

35%

4/6

15%

0/4

44,4%

The solid fragments consist of aggregates of particle size 0/10 mm, having the following particle size distribution in the final mix:

6/10

35%

4/6

15%

0/4

44.4%

5.6% of 35/50 bitumen is introduced.

70% of aggregates (20% of 0/4, 15% of 4/6, 35% of 6/10), of which the initial humidity is 3%, are heated in a counter-current drying drum at a temperature of 140 ° C.

• 24,4 % de granulats 0/4, comportant une humidité initiale moyenne de 4% (temps d'introduction : 8 secondes).
• 5,6 % de bitume à une température initiale de 160°C (temps d'introduction : 8 secondes)

On obtient un enrobé bitumineux économique en énergie, à une température de 98°C, avec un temps de cycle de fabrication de 45 secondes (identique à celui d'un enrobés à chaud équivalent). La teneur en vides et le module sur des carottes prélevées sur chantier après 7 jours sont conformes à la norme NF EN 13108-1.These heated aggregates are mixed in a mixer with two parallel shafts and at the same time:

• 24.4% aggregates 0/4, with an initial average humidity of 4% (introduction time: 8 seconds).
• 5.6% bitumen at an initial temperature of 160 ° C (introduction time: 8 seconds)

An energy-efficient bituminous mix is obtained at a temperature of 98 ° C., with a manufacturing cycle time of 45 seconds (identical to that of an equivalent hot mix). The voids content and the modulus on cores taken from the building site after 7 days comply with standard NF EN 13108-1.

Example 5 : BBSG 0/10

6/10

25%

4/6

15%

0/4

30,8%

The solid fragments consist of 25% aggregates of mixes and aggregates with particle size 0/10 mm, whose particle size distribution is as follows:

6/10

25%

4/6

15%

0/4

30.8%

• Etape a1: Séchage direct dans un tambour sécheur de 10% de granulats 0/4 + 15% de granulats 4/6 + 25% de granulats 6/10 à une température d'environ 245°C.
• Etape a2: Séchage indirect de 25% d'agrégats d'enrobés introduit dans un anneau de recyclage, d'humidité moyenne initiale 4%, par échange thermique avec les granulats chauffés précédemment pour obtenir un mélange final à une température de 140°C.

4.2% 35/50 bitumen is introduced.

• Step a1: Direct drying in a drying drum of 10% of 0/4 aggregates + 15% of 4/6 aggregates + 25% of 6/10 aggregates at a temperature of about 245 ° C.
• Step a2: Indirect drying of 25% of asphalt aggregates introduced into a recycling ring, of 4% initial average moisture, by heat exchange with the previously heated aggregates to obtain a final mixture at a temperature of 140 ° C.

• 20,8 % de granulats 0/4, comportant une humidité initiale moyenne de 6% (temps d'introduction : 7 secondes)
• 4,2 % de bitume pur à une température initiale de 160°C (temps d'introduction : 6 secondes)

The previously obtained mixture is then mixed in a twin-shaft kneader and, at the same time:

• 20.8% aggregates 0/4, with an initial average humidity of 6% (introduction time: 7 seconds)
• 4.2% pure bitumen at an initial temperature of 160 ° C (introduction time: 6 seconds)

An energy-efficient bituminous mix is obtained at a temperature of 98 ° C., with a manufacturing cycle time of 45 seconds (identical to that of an equivalent hot mix).

The voids content and the modulus on cores taken from the building site after 7 days comply with standard NF EN 13108-1.

Example 6 : BBSG 0/10

The formula of the mix is the same as that described in Example 4.

70% of aggregates (20% of 0/4, 15% of 4/6, 35% of 6/10), the initial moisture content of which is 2%, are heated in a counter-current drying drum at a temperature of 115 ° C.

• 24,4 % de granulats 0/4, comportant une humidité initiale moyenne de 2,5% (temps d'introduction : 8 secondes).
• 5,6 % de bitume additivé (0,3 ppc Polyram® L 200) à une température initiale de 160°C (temps d'introduction : 8 secondes)

These heated aggregates are mixed in a mixer with two parallel shafts and at the same time introduced:

• 24.4% aggregates 0/4, with an average initial humidity of 2.5% (introduction time: 8 seconds).
• 5.6% additive bitumen (0.3 pph Polyram® L 200) at an initial temperature of 160 ° C (introduction time: 8 seconds)

An energy-efficient bituminous mix is obtained at a temperature of 95 ° C., with a manufacturing cycle time of 45 seconds (identical to that of an equivalent hot mix). The voids content and the modulus on cores taken from the building site after 7 days comply with standard NF EN 13108-1.

Claims (12)

A process for producing bituminous mixes comprising solid mineral fractions coated with a binder, comprising the following successive steps: a) introducing into a mixer a first portion of said solid mineral fractions, said first portion having been at least partially preheated to reach a temperature at the time of entry into said mixer that is greater than 80 ° C; then b) Separate but simultaneous introduction in the same mixer, of the binder and the remaining part of said solid mineral fractions, not previously heated. Process according to Claim 1, characterized in that the said first part of solid fractions is itself subdivided into two parts and in that step a) is subdivided into two successive stages. a1) heating, at a temperature above 120 ° C, the first subdivision of said first portion of said mineral solid fractions free of asphalt aggregates; then a2) mixing said first heated subdivision obtained following step a1), kept hot, with the second subdivision of said first portion of the mineral solid fractions may comprise asphalt aggregates. Method according to claim 2, characterized in that in step a2) said second subdivision of the first part of the solid mineral fractions includes asphalt aggregates. Process according to any one of claims 1 and 3, characterized in that during step b) all of said remaining portion of the solid mineral fractions is introduced during the introduction of the binder. Process according to any one of claims 1 and 3, characterized in that during step b) the entire binder is introduced during the introduction of said remaining portion of the solid mineral fractions. Process according to any one of the preceding claims, characterized in that the said remaining portion of the said solid mineral fractions, introduced during step b), represent between 10 and 70% by weight, advantageously between 20 and 40% by weight, of the total weight of solid mineral fractions. Process according to any one of claims 3 to 6, characterized in that the asphalt aggregates are aggregates of regenerated mixes. Process according to any one of claims 3 to 7, characterized in that the asphalt aggregates represent between 5 and 70% by weight of the weight of the mineral solid fractions constituting said first part. Process according to one of the preceding claims, characterized in that a controlled quantity of water is added in the separate introduction step b) but simultaneous binder and said remaining portion and / or after step b). Process according to any one of the preceding claims, characterized in that prior to step b) a controlled amount of water is added to said remaining portion of solid mineral fractions. Method according to one of the preceding claims, wherein the binder is used at a temperature of between 100 and 200 ° C, preferably about 160 ° C. Process according to one of the preceding claims, wherein the binder emulsion is carried out at a temperature of between 10 and 95 ° C.