CEMENTITIOUS COMPOSITION FOR PROTECTING SURFACES AGAINST (BIO)CORROSION

Abstract

Disclosed is a novel cement and aggregate compositions, to uses thereof for protecting surfaces, in particular surfaces likely to be affected by biocorrosion.

Claims

1. A mortar composition for protecting surfaces against corrosion, said composition comprising: a hydraulic binder of calcium aluminate type; a calcium aluminate aggregate; wherein the binder/aggregate ratio is lower than 0.13 (by weight).

2. The mortar composition according to claim 1, also comprising a source of alumina soluble at pH 3 in water.

3. The mortar composition according to claim 1 having a total alumina content of between 35 and 70 % by dry weight of the mortar composition.

4. The mortar composition according to claim 1 , wherein the mortar composition comprises fines.

5. The mortar composition according to claim 1 , wherein the mortar composition comprises one or more additives.

6. The mortar composition according to claim 1 , such that the composition is in the form of a dry preparation having a particle size distribution of less than 800 .Math.m.

7. The composition according to claim 1 also comprising 10 to 20 % water (by weight).

8. A protective layer for a corroded surface or a surface likely to be corroded, said layer comprising the mortar composition according to claim 1 applied to all or part of said surface.

9. The layer according to claim 8, such that the thickness of said layer is between 2 and 10 mm.

10. The layer according to claim 8, such that the surface is a smooth surface or a rough surface.

11. The layer according to claim 8, such that the layer adheres to any concrete surface condition.

12. The layer according to claim 8, such that the surface is corroded or likely to be corroded by H.sub.2S.

13. A method for preparing a protective layer for a surface likely to be corroded according to claim 8, comprising: applying said mortar composition to all or part of said surface, and hardening said layer thus obtained.

14. The method according to claim 13, such that application is performed by spraying.

15. A sewage plant comprising a protective layer according to claim 8 on all or part of one or more corroded surfaces or likely to be corroded.

16. The mortar composition according to claim 2 having a total alumina content of between 35 and 70 % by dry weight of the mortar composition.

17. The mortar composition according to claim 2, wherein the mortar composition comprises fines.

18. The mortar composition according to claim 3, wherein the mortar composition comprises fines.

19. The mortar composition according to claim 2, wherein the mortar composition comprises one or more additives.

20. The mortar composition according to claim 3, wherein the mortar composition comprises one or more additives.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0070] FIG. 1 illustrates the abrasion resistance of the composition of the invention.

[0071] FIG. 2 illustrates adhesion results at 8 days and 28 days for composition 41B-F of the invention on CSP1 roughness test surfaces.

[0072] FIG. 3 illustrates visual observation of Block A (Concrete A protected by Cement CEM 1) after 3 and 9 months.

[0073] FIG. 4 illustrates visual observation of Block B (Concrete A protected by composition 41B-S).

[0074] FIG. 5 illustrates visual observation of Block C (Concrete A protected by composition 41B-F).

[0075] FIG. 6 illustrates visual observation of Block E (Concrete E protected by cement 65 % GGBFS + 15 % fumed silica).

[0076] FIG. 7 illustrates changes in surface pH of the tested compositions as a function of time.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Examples

[0077] Raw materials used: [0078] SecarⓇ 71: Hydraulic binder marketed by Imerys aluminates. [0079] G1: synthetic aggregate obtained by grinding calcium aluminate clinker derived from a fusion process. It has a particle size of between 250 and 800 .Math.m. [0080] G2: synthetic aggregate obtained by grinding calcium aluminate clinker derived from a sintering process. It has a particle size of between 250 and 800 .Math.m. [0081] Limestone filler: allows acid neutralization and an increase in the particle load of fines, and hence control over reactivity of the binder. Preferably, the limestone filler/CAC ratio is about 1. [0082] Aluminas soluble at pH 3 in water, derived from bauxite, bayerite, boehmite, diaspore, hydrargillite, nordstrandite, alumina gels, transition aluminas, or alumina hydrates. Fumed silicas: such as Cofermin and MasterRoc MS 610, RW-Fuller (marketed by AMG Silicon), Elkem Microsilica 920 (marketed by Elkem), Elkem Microsilica 940 (marketed by Elkem) to limit bleeding, generally used in an amount up to 2-3 %. [0083] REFPAC 500 (marketed by Imerys aluminate): Fumed silica dispersing agent also providing a water-reducing effect. [0084] Citric acid: allows workability of longer than 30 minutes to be maintained when temperature increases to 20 / 25° C. If needed, an additive can be added to maintain workability. [0085] Setting accelerator such as Li.sub.2CO.sub.3: allows initiation of kinetics between 5 and 20° C. [0086] Texturizing agent such as starch, cellulose ether, guar ether (Escal HS 16F marketed by Lamberti, or Esacol HS 20): used to improve texture and tackiness of the solution on application. [0087] Resin such as afore-defined to improve adhesion of the composition.

[0088] Aggregates G1 and G2 have the following chemical composition:

TABLE-US-00001 G1 G2 Al.sub.2O.sub.3 (wt. %) 33.5 - 43.5 58.0 - 66.0 CaO (wt. %) 35.0 - 40.0 23.0 - 28.0 Fe.sub.2O.sub.3 (wt. %) 14.0 - 18.0 2.0 - 3.0 SiO.sub.2 (wt. %) 3.0 - 5,0 5.0 - 6.0 MqO (wt. %) - 0.5 - 1.0 TiO.sub.2 (wt. %) - 3.0 - 4.0 Percentages are weight % relative to total aggregate weight

Operating Modes

Particle Size Distribution

[0089] Measurements of particle size distribution were carried out in particular for particle sizes of less than 100 microns via laser diffraction on Malvern Mastersizer 3000 optical system equipped with Aero S a dry power disperser with measuring range of between 0.1 and 1500 .Math.m.

[0090] For larger particle sizes (larger than 100 microns), and in particular for the aggregates, particle size was measured by screening, for example using a square-mesh sieve in stainless steel cloth meeting standard ISO 3310. Typically, the sieve apertures can be selected from among the following ranges: 125, 160, 250, 400, 800, 1000. Said sieves are commercially available and marketed for example by Prolabo, Tripette & Renaud, Retsch.

[0091] Accuracy is to within 5 % and results are expressed in volume percentage relative to equivalent spherical diameter.

RAJA Measuring Equipment

[0092] RAJA measuring equipment was used to measure variations in size during the setting phase (plastic phase). The test specimens were prisms 50 cm in length for thickness of 2.5 cm and width of 9.5 cm. Measurements were conducted on the basis of lasers pointed onto specific mobile Teflon wedges affixed to each end of the specimen. The specimens were measured for 24 hours at 23° C., 50 % relative humidity. The anchor points of the tested product on these wedges were released while continuing measurement of the specimen after the setting time with conventional size variation measurements.

Cracking Test Under Restrained Shrinkage

[0093] ASTM C 1581 standard (Standard test method to determine age at cracking and induced tensile stress characteristics of mortar and concrete under restrained shrinkage) describes how to measure restrained or controlled shrinkage.

I-Shaped Mould

[0094] Cracking potential can be observed with an I-shaped mould such that the two parallel bars are rough while the median bar is smooth. Therefore, the cementitious material is retained by the two rough portions and, if cracks occur, they will occur in the median portion due to tensile stress at the two ends. Daily monitoring of the specimens was carried out for 28 days and up until the onset of cracks.

Mechanical Properties

[0095] The mechanical properties of the different mixtures were measured by compression using a press made by 3R of RP 300-10 ELC type, and three-point bending using a 3R press of RP 50-SYNTRIS type. The load increase for the 3R press of RP 300-10 ELC type was 2400 N/s ± 200 N/s and for the 3R press of RP 50-SYNTRIS type it was 50 N/s ± 10 N/s. Accuracy was ± 15 %. Prisms of 2 × 2 ×16 cm.sup.3 were released from the moulds after 6 hours. Measurements were taken after 1, 2, 3, 7 and 28 days on the specimens stored either at 23° C. and 50 % relative humidity or under water (container stored at 23° C.).

Adhesion Test via Tensile Pull-Off

[0096] The mortar was applied to concrete slabs (marketed by Antoniazzi) using a Sablon roughcast applicator until a thickness of 10 mm was obtained. Once the material had set, the surface was lightly sanded to facilitate adhesion of square test studs of size 50 × 50 mm bonded using an epoxy resin (Uratep, PAREX LANKO). These were pulled off after 24 hours, 7 and 28 days using an extractor (23° C., 50 % RH). For determination of underwater adhesion, the concrete slabs coated with the tested coatings were kept 7 days at 23° C. and 50 % RH and then immersed until the time of measurements in water at 23° C. The pull-off tests were performed at 7 days and 21 days.

Abrasion Resistance

[0097] Abrasion resistance was defined using a Taber circular abrasion tester equipped with H22 grinding wheels (500 g additional weight) with the following procedure: 2 kg of mortar of each specimen were first mixed in a Perrier mixer and then moulded in two lubricated Taber Teflon moulds to a thickness of 3 mm. After 24 hours, the specimens were released from the moulds and stored at 23° C. ± 2° C. and 50 ± 5 % relative humidity for the defined measurement times (1, 2, 3, 7 and 28 days). Weights were measured after 50, 100, 150, 200 and 500 rotations. Before each measurement, dust was removed from the surfaces of the specimens and grinding stones. The measurement range was between 0 and 20 g. Accuracy of about 10 %.

Results

[0098] The impact of modification of type of aggregate on shrinkage measured with RAJA equipment and mixtures having low cement content were tested:

TABLE-US-00002 Aggregate G1 G2 Secar.sup.Ⓡ 71 (%) 5 10 5 10 Shrinkage (in .Math.m/m) 850 1250 350 550

Percentages are weight % relative total weight of the mixture.

[0099] A synergy exists between type of aggregate and the cement used.

[0100] Two types of additive mixtures were investigated. The basic mixture was:

TABLE-US-00003 REFPAC 500 1% Citric acid 0.005% Lithium carbonate 0.0012%

Percentages are weight % relative total weight of the mixture.

[0101] The first mixture was developed from a mixture based on kinetics: T.sub.off and T.sub.max of less than 2 hours 30 and workability of between 30 and 60 minutes. This mixture contained citric acid, lithium carbonate, cellulose and a resin:

TABLE-US-00004 REFPAC 500 1% Citric acid 0.005% Lithium carbonate 0.0012% Redispersible polymer powder 2% Guar ether 0.015%

Percentages are weight % relative total weight of the mixture.

[0102] The second mixture led to workability of about 60 minutes and T.sub.off less than 2 hours 30 and T.sub.max of about 3 hours. This second mixture contained REFPAC 500, citric acid, lithium carbonate and cellulose. It was chosen for subsequent developments based on low water demand.

Mortar Spraying Test

[0103] Four mixtures were chosen to be sprayed using a Sablon roughcast applicator. The tested mixtures are given below:

TABLE-US-00005 41B-S 43B-S 41B-F 43B-F G1 65 75 G2 65 75 Soluble alumina 20 5 20 5 Secar.sup.Ⓡ 71 5 9 5 9 Limestone filler (d50=2.Math.m) 5 5 5 5 Fumed silica 1 1 1 1 Metakaolin (d50=6.Math.m) 5 5 5 5 Total 101 100 101 100 Water 16 16 14 15 Total A1.sub.2O.sub.3 content (weight % relative to total weight of mixture) 54.5 55.8 42.5 40.4

[0104] In this Table, the heading in each column refers to type of aggregate: S for G2 and F for G1.

[0105] Spraying of the four mixtures with the Sablon roughcast applicator to a thickness of about 3 to 5 mm was easy to carry out. In a thin layer, these products showed scarce slipping. Guar ether provided tackiness. The appearance of the coatings was particularly smooth and less grainy for those mixtures containing the most fines (mixtures 41B-S and 41B-F). No cracking was observed after one week.

[0106] The properties were characterized for these four mixtures at 23° C. and 50 % relative humidity: [0107] rheology; [0108] mechanical properties; [0109] RAJA; [0110] cracking after spraying; [0111] cracking as per standard C 1581; [0112] cracking in I-shaped moulds.

[0113] The results are summarized below:

TABLE-US-00006 41B-S 43B-S 41B-F 43B-F Water (weight % relative to total weight of the formula) 16 16 15 14 14 Slump 25 tamps T.sub.0 (mm) 220 210 230 185 235 T.sub.30 (mm) 170 225 T.sub.60 (mm) 165 197 T.sub.off (h) 2 3 2.5 T.sub.max (h) 3 5 6 6 Raja (.Math.m/m) 300-350 450 1650 (?) 900 Sablon applicator Yes Yes Yes Yes Cracking after spraying No No No No Cracking in I-shaped mould No No No No Cracking as per standard C1581 No n.d. n.d. No Mechanical compression at 7 days (MPa) 3 10 45 42

Abrasion Resiance

[0114] Abrasion resistance of the 4 mixtures tested on a Taber abrasion tester is illustrated in FIG. 1.

[0115] Compositions 41B-F and 43B-F are particularly resistant to abrasion

Impact of Surface Preparation

[0116] Full-scale (worksite type) wet process spraying tests were conducted with composition 41 B-F of the invention on L-shaped walls in tamped concrete i.e. very smooth. The surfaces were prepared in different manners to obtain surface conditions of different roughness: [0117] Surface 1: « as struck », e.g. smooth; [0118] Surface 2: « as struck », and coated with an adhesion primer; [0119] Surface 3: « as struck », scoured and dried; [0120] Surface 4: « as struck », scoured and left wet; [0121] Surface 5: « as struck », and cleaned with water; [0122] Surface 6: « as struck », and sanded to reach roughness 1 (CSP 1), [0123] Surface 7: « as struck », and sanded to reach roughness 2 (CSP 2), [0124] Surface 8: « as struck », and sanded to reach roughness 3 (CSP 3).

[0125] By CSP 1, CSP 2, CSP 3 it is meant surfaces such as described in the ICRI Technical Guidelines (International Concrete Research Institute « Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, and Polymer Overlays », Guideline 0310.2 (corresponding to Guideline 03732 of 1997, re-approved in 2002)).

[0126] Adhesion was measured in accordance with standard NF EN 1542.

[0127] The adhesion values obtained after 28 days and 8 months are grouped together in FIG. 2.

[0128] These results show that: [0129] the compositions of the invention are capable of adhering both to rough surfaces (surfaces 6 to 8) and to smooth substates (surfaces 1 to 5). The compositions exhibit adhesion of at least 0.5 MPa. [0130] An increase in level of adhesion is observed as a function of time.

Resistance to Biogenic Acid Corrosion

[0131] Two mixtures (41B-S and 41B-F) of the invention were applied to 15×15×15 cm blocks of concrete containing binder OPC CEM-1 and siliceous aggregate to a thickness of 3 mm (respectively block B and block C).

[0132] A third identical block (block A) was not coated with a layer of the invention.

[0133] A fourth 15×15×15 cm block of concrete was prepared containing binder with 65 % blast furnace slag (GGBFS) plus 15 % fumed silica and siliceous aggregate (block E). This type of binder containing blast furnace slag is reputed to be more resistant than CEM-1 to biogenic corrosion.

[0134] These four blocks were placed in a Fraunhofer chamber for accelerated testing of biogenic corrosion by H.sub.2S on these blocks.

[0135] Before the start of corrosion, these blocks were specifically prepared to lower the surface pH thereof via carbonatation, for the purpose of allowing the development of bacteria that are the source of biogenic corrosion.

[0136] The details of this process and the operating of the Fraunhofer corrosion chamber are described in detail in the publication by Wack, H. et al., Accelerated testing of materials under the influence of biogenic sulphuric acid corrosion (BSA), Microorganisms-Cementitious Materials Interactions, 25-26 Jun. 2018, Toulouse, 23-32.

[0137] These tests were conducted with a concentration of 100 ppm H.sub.2S in the chamber and 100 % relative humidity.

[0138] The surface pH values were regularly measured on the four blocks. Visual observation of these blocks was carried out over a period of 9 months. The visual observations of these blocks at the end of time periods of 3 months (104 days) and 9 months (301 days) are given in FIGS. 3 to FIGS. 6. It follows from FIGS. 4 and 5 that the blocks still remain in good condition after 9 months.

[0139] The changes in surface pH values over more than 9 months in the corrosion chamber are given in FIG. 7.

[0140] As shown in Table 7 and FIG. 7, it is ascertained that the condition of blocks A and E after 9 months is highly deteriorated.

[0141] Conversely, blocks B and C coated with mixtures 41B-S and 41B-F remain in very good condition even after 9 months in the Fraunhofer chamber.

[0142] The pH of blocks B and C remains stable at pH values higher than 3, whilst the pH of blocks A and E has dropped to as low as pH=2, even pH=1.2.

TABLE-US-00007 Surface pH after t=XX days in the chamber t=0 t=104 days t=203 days t=301 days Block A 9.1 3.8 2.2 2.2 Block B =Concrete A protected with compo 41BS 8.6 6.4 3.9 3.3 Block C =Concrete A protected with compo 41BF 8.5 6.8 3.8 3.1 Block E 8.3 3.4 1.8 1.2