Limits for the freeze-thaw resistance of road concrete in the presence of de-icing salts: results

of the GELAVIA projectAuthor 1: Sylvie Smets, MSc, Researcher & Technological Advisor, Belgian Road Research Centre (BRRC), Sterrebeek, Belgium

Author 2: Elia Boonen, PhD, C.E., Researcher, Belgian Road Research Centre (BRRC), Sterrebeek, Belgium

Corresponding author: s.smets@brrc.be

KEYWORDS: CONCRETE PAVEMENTS / DE-ICING SALTS / FREEZE-THAW RESISTANCE / STANDARDIZATION

Conflict of Interest: None

1. ABSTRACT

The durability of a concrete road strongly depends on the resistance of the concrete to freezing and thawing cycles in the presence of de-icing salts. The test procedure used until now in Belgium to evaluate the resistance of concrete to de-icing salts is based on the international draft standard ISO/DIS 4846-2. Experience with this test method dates back a long time, and limits to scaling as a function of traffic loads are well established. However, since the publication of CEN/TS 12390-9 the so-called “Slab Test” is becoming the reference method in various standard specifications.

In the recently completed Belgian pre-normative research project GELAVIA, the aim was to define relevant performance classes for freeze-thaw resistance with de-icing salts as measured by this Slab Test, including scaling limits for representative road concrete compositions.

Additionally, in some specific cases such as manual placement, colored and pattern-imprinted concrete pavements, hydrophobic impregnation is applied in Belgium to increase resistance to scaling. The products used for this treatment are specified according to the guidelines of NBN EN 1504-2, but the reference concretes used for testing differ substantially from typical road concrete compositions in Belgium. Furthermore, there is some question about the durability in time of the protective action of the impregnation. Hence, a second objective of the aforementioned research was to investigate and develop testing methods to evaluate the effectiveness and durability of hydrophobic impregnation products applied on representative pavement concretes.

In this contribution, we will present and discuss the results and outcomes of the GELAVIA-project.

2. INTRODUCTION

The durability of a concrete road is to a large extent dependent on the resistance of the concrete composition against freezing and thawing cycles in the presence of de-icing salts.

The Belgian standard tender specifications impose some quite severe requirements regarding the concrete composition in terms of minimum cement content, maximum water to cement ratio and air content. Furthermore, for concrete applied in road construction, some more specific guidelines are given in EN 13877-1, in which it is stated that freeze-thaw resistance should be tested according to the CEN/TS 12390-9:2016 (CEN, 2016).

The test procedure used until now in Belgium for the evaluation of freeze-thaw resistance with de-icing salts is based on the draft international standard ISO/DIS 4846-2 (ISO, 1984). For this test method, long-term experience and well established scaling limits as a function of traffic load exist. In the recently completed national Belgian pre-normative research project GELAVIA, the aim is to define relevant performance classes for freeze-thaw resistance with de-icing salts following the “Slab test” (using a method derived from CEN/TS 12390-9) and to incorporate scaling limits for representative road concrete compositions. This was done by a comparative study between the new reference method (“Slab test”) and the old one (“ISO/DIS 4846.2”).

It is known from practice that manually placed road concrete and some special applications, such as colored bicycle lanes or pattern-imprinted concrete pavements, are more sensitive to de-icer effects and can show rapid signs of deterioration. In those specific cases, a hydrophobic impregnation is applied in Belgium to increase the resistance against scaling. These products are specified according to the guidelines of NBN EN 1504-2 (NBN, 2005), but the reference concretes for testing used here, differ substantially from typical road concrete compositions in Belgium. Furthermore, there is also some question about the durability in time of the protective action of the impregnation. Hence, a second objective of the aforementioned research was to study and elaborate testing methods to evaluate the effectiveness and durability of hydrophobic impregnation products applied on representative pavement concretes.

3. RESEARCH SIGNIFICANCE (required)

This research forms a logical follow-up in a series of Belgian research projects (Smets et al., 2018) which have studied the freeze-thaw resistance in detail in the presence of de-icing salts of concrete in general, and elaborating on test methods to determine the resistance against scaling. The GELAVIA-project is a further advancement of the current state-of-the-practice focusing on typical road concrete compositions in Belgium, establishing a more clear relationship between the traditional and more recently applied scaling tests and demonstrating the effect of the type of exposed surface (e.g. sawn, cast or finished surface) on the test results.

Furthermore, testing the effectiveness and especially the durability of hydrophobic impregnation products applied on pavement quality concrete is quite novel and has so far only been studied very limited in the available literature, e.g. (Raupach & Büttner, 2009; Kolisko et al., 2013).

4. METHODOLOGY4.1 TESTING FOR RESISTANCE OF CONCRETE AGAINST DE-ICING SALTS

Many different methods exist in order to assess the freeze-thaw resistance in the presence of de-icing salts. Most of them consist in applying freeze-thaw cycles on samples whose surface is covered with a layer of de-icing salt solution. The freeze-thaw resistance is evaluated by weighing the scaled material after a specified number of cycles.

In this study, the focus is on the method which was applied until now in the regional tender specifications, the so-called “ISO/DIS 4846.2” method, and on a test method derived from the reference method of CEN/TS 12390-9, also called “Slab test”.

Based on previous research at BRRC (Vandewalle et al., 2009), the “Slab test” (as one of the 3 reference methods in CEN/TS 12390-9) was selected as the most suitable and robust test method to assess the freeze-thaw resistance of road concrete, in replacement of the old test procedure used before in Belgium (based on ISO/DIS 4846-2).

The Slab test has very recently been incorporated as reference method in a technical note which is applied in the certification process of road concrete in Belgium, the RNR 06 (COPRO, 2017). In this document, requirements and testing methods for the initial testing of concrete compositions are given. For the evaluation of the freeze-thaw resistance with de-icing salts, the reference method is the “Slab test” as described in paragraph 5 of the technical specification CEN/TS 12390-9. However, some modifications to this testing method have been applied, regarding the number of cycles, the size, form and storage conditions of the samples, the tested surface and the collecting of the scaled material. Those differences are reported in table 1.

Table 1: Differences between CEN/TS 12390-9 and RNR 06 Slab-test methods

CEN/TS 12390-9 RNR06

Samples 4 cubes (150 mm sided) 4 cores (diam. 113 mm) extracted from 2 cubes

Test surface sawn side of a cube Side cast (against formwork) of a cube

Conditioning 7d under water at (20±2)°C, then 21d in climate room at (20±2)°C and (60±5)%RH

28d under water at (20±2)°C, then 14d in climate room at (20±2)°C and (60±5)%RH

Number of cycles 56 28

Collecting scaled material spray bottle and brush (annex B) spray bottle

Since the Slab test following the RNR06 is becoming the reference method in Belgium, this method was selected in the current research to be compared with the former ISO/DIS 4846.2 method which was applied until now in the regional standard tender specifications. The most significant differences between the Slab test “RNR 06” method and the ISO/DIS 4846.2 method are shown in table 2 (below).

Table 2 - Differences between test methods “Slab test RNR06” and “ISO/DIS 4846.2”

Slab test RNR06 (based on CEN/TS 12390-9) ISO/DIS 4846.2

Samples 4 cores (diameter 113 mm, height 50 mm)

3 cores (diameter 113 mm, height 45 mm)

Test surface cast side of a cube (but can also be applied on extracted cores)

Upper side of core extracted from the road

Number of cycles 28 (24h each) 30 (24h each)De-icing salt 3% NaCl 3% CaCl2

Conditioning 28d under water at (20±2)°C, then 14d in climate room at (20±2)°C and (60±5)%RH

After extracting, minimum 14d in climate room at (20±2)°C and (60±5)%RH

Isolation of sample

Yes no

Result unit kg/m2 g/dm2

Difference in temperature cycle

0 2 4 6 8 10 12 14 16 18 20 22 24-30

-20

-10

0

10

20

30slab upper on sample surface

slab lower on sample surfaceISO/DIS 4846.2 upper in climate roomISO/DIS 4846.2 lower in climate room

t(h)

Tem

pera

ture

(°C)

Note: For the Slab test, the temperature is measured on the surface of one sample which is isolated. This makes the cycles more aggressive than those applied for the testing method ISO/DIS 4846.2

In the past, it has been observed that results (if expressed in kg/m2) obtained following the ISO/DIS 4846.2 method after 30 cycles generally show a trend to be 2 to 4 times lower than those obtained following the Slab-test method after 28 cycles (Beeldens et al., 2014). This observation was based only on a limited amount of test data and the relationship between both methods needs to be verified and/or confirmed by results obtained on the most frequently applied and representative road concrete compositions.

The aim of the research project GELAVIA is thus to define more precisely and verify the relationship between the results obtained following both test methods, and this for the commonly used mix compositions for road concrete in Belgium.

As many questions still remain about the relevance of performing the Slab test on the sawn or on the cast surface, a comparison between results obtained on finished surfaces (exposed aggregates or transverse brooming), on sawn surfaces as well as on cast surfaces was also performed.

Finally, a round robin test with the three partner laboratories has also been executed in order to make an evaluation of the repeatability of the Slab-test method following RNR06.

4.2 WATER REPELLENT OR HYDROPHOBIC IMPREGNATION PRODUCTS

Water repellent impregnation products are used to improve the durability of concrete by preventing the penetration of water and salt solution into the surface. The exposed surface of the concrete is impregnated with a water repellent agent, which is usually based on silane or siloxane compounds. After polymerization of those products, silicon resin is fixed in the pores, which become water repellent, but water vapor can still diffuse outside through this surface.

In the standard NBN EN 1504-2 (NBN, 2005), a clear distinction is made between “hydrophobic impregnation”, “impregnation” (or “sealing”) and “coating”. When hydrophobic impregnation is applied, the pores and capillaries are internally coated, but not filled and there is no film and no change of appearance on the surface of the concrete.

In Belgium, the use of a hydrophobic impregnation product is required in some specific cases such as manual placement, colored and/or imprinted concrete pavements. The aim of this hydrophobic impregnation is to increase the resistance against scaling.

The performance characteristics for hydrophobic impregnation products are summarized in standard NBN EN 1504-2. The test methods defined in this standard for all intended uses are the determination of the penetration depth (as described in NBN EN 1504-2), the water absorption and resistance to alkali test (NBN EN 13580) and the drying rate coefficient (NBN EN 13579).

The resistance against freeze-thaw salt stress is to be determined for certain intended uses, but the reference test method described in NBN EN 13581 (NBN, 2002a), is not comparable with the ISO/DIS 4846.2 nor with the Slab-test methods; freeze-thaw cycles are applied on totally immersed test cubes - not only on the exposed sample surface - and temperature cycles are also slightly different with temperature measurements located at the center of the samples.

In addition, all these test methods have to be performed on reference concretes (NBN EN 1766) that are quite different from traditionally applied road concrete compositions. Hence, in current research penetration depth, drying rate coefficient, and water absorption and resistance to alkali testing was performed on one typical concrete road composition with a moderate to low scaling resistance according to the Slab test.

The penetration depth of hydrophobic impregnation products depends on many different factors such as the age of the concrete, the water-cement ratio, the relative humidity, the surface preparation, the amount and the type of impregnation product. Penetration depth is considered to be an essential characteristic to measure the effectiveness of hydrophobic impregnation (Johansson, 2007). However, no direct relationship between penetration depth and resistance against freeze-thaw with de-icing salts has been established on road concrete compositions.

Finally, to study the durability of the hydrophobic impregnation, the resistance to scaling was tested before and after ageing of the concrete samples, using different methods (Figure 1):

PEI-test following EN ISO 10545-7 (CEN, 1999) using abrasion by steel balls, aluminium oxide and water;

Wearing resistance following NBN EN 12274-5 (NBN, 2018) for slurry surfacing: abrasion by rubber pads;

UV radiation: Q-SUN Chamber (with 5x12h at 0,63 W/m2, λ= 340 nm, Black Panel Temperature (BPT) = 45°C, T = 25°C), reproducing the full spectrum of sun light;

Natural ageing: keeping samples for 9 months on rooftop of BRRC building in Sterrebeek, Belgium.

Figure 1: Different ageing methods used to study durability of hydrophobic impregnation (from left to right: PEI-test, wearing following EN 12274-5, Q-SUN chamber)

4.3 SELECTION OF MIX COMPOSITIONS

During the research project GELAVIA, combinations which are representative for compositions and surface finishing of heavy trafficked roads (traffic classes I in Wallonia and B1-B5 in Flanders and Brussels) and medium trafficked roads (traffic classes II in Wallonia and B6-B10 in Flanders and Brussels) were tested. Two different types of surface finishing (“exposed aggregates” or transverse brooming = “brushed”) can be applied, depending on the requirements of the regional standard tender specifications (see table 3).

One special composition concerns external floors (360 kg/m3 cement) with a surface finishing by troweling. This composition meets the requirements related to exposure class XF4 according to the concrete standards NBN B 15-001 and NBN EN 206.

The selected materials are those traditionally used in Belgium for road concrete. All combinations are made with cement CEM III/A 42.5 N LA, and with two rounded sand fractions (0/2 and 0/4). Four fractions of Belgian porphyry aggregates were used (4/6.3, 6.3/10, 10/14, 14/20) in all mixes excepted for mixes RIII-360-S4(W)-T which were made with limestone aggregates. Excepted for this last specific concrete mix, all other mixes were designed with the same aggregate proportions in order to follow as closely as possible an ideal grading curve for road concrete.

Six compositions were selected to meet all standard specifications regarding the minimum cement content, the maximum water to cement ratio and the air content for a given traffic class and maximum aggregate size. A plasticizer was used when necessary to obtain the expected workability. For the mix compositions designed for a manual application, an S3 slump class was obtained either by the use of a plasticizing agent, or either by adding water in the mix until the desired workability was reached (code with “S3W”). These latter compositions consequently have a higher water to cement ratio than the maximum recommended value and do not meet the requirements of the tender specifications. These compositions are thus expected to show a lower resistance against scaling.

Regarding the traffic class, as well as the maximum aggregate size (20mm), all compositions should have an air content between 3 and 6%. Some of the compositions were intentionally made without using an air-entraining agent. Consequently, these compositions are not in conformity with the standards specifications and are again expected to be less resistant against freeze-thaw cycles with de-icing salts.Table 3 - Concrete combinations tested in the GELAVIA research program. The “out of specification” compositions are labelled in italic.

Combination Code

Traffic classSB 250/

Qualiroutes

Cementcontent (kg/m3)

W/C ratio (-)

Limiting air content

values (%)

Slump class

Surface finishing

RI-400-S1-air-L B1-B5/I 400 0.45 3-6 S1-S2Exposed

aggregates

RII-375-S1 -air-L B6-B10/ II 375 0.50 3-6 S1-S2Exposed

aggregates

RII-375-S1-air-B B6-B10/ II 375 0.50 3-6 S1-S2 Brushed

RI-400-S3- air-L B1-B5/ I 400 0.45 3-6 S2-S3Exposed

aggregates

RII-375-S3- air-L B6-B10/ II 375 0.50 3-6 S2-S3Exposed

aggregates

RII-375-S3-air-B B6-B10/ II 375 0.50 3-6 S2-S3 Brushed

RI-400-S3-L B1-B5/ I 400 0.45 - (1) S2-S3Exposed

aggregates

RI-400-S3W-L B1-B5/ I 400(0.45)(2)

0.51- (1) S2-S3

Exposed aggregates

RII-375-S3-L B6-B10/ II 375 0.50 - (1) S2-S3Exposed

aggregates

RII-375-S3W-L B6-B10/ II 375(0.50)(2)

0.56- (1) S2-S3

Exposed aggregates

RII-375-S3-B B6-B10/ II 375 0.50 - (1) S2-S3 Brushed

RII-375-S3W-B B6-B10/ II 375(0.50)(2)

0.56- (1) S2-S3 Brushed

RIII-360-S4-T External floor 360 0.45 - S4 Troweling

RIII-360-S4W-T - External floor 360 0.55 - S4 Troweling

(1) No air-entraining agent was used for these compositions although the standard specifications require an air content between 3 and 6%

(2) For this mix composition, a slump value S1-S2 is initially reached using a plasticizer, respecting the maximum water cement ratio between brackets, and subsequently an excess of water is added in order to reach a slump value corresponding to an S3 class. The water to cement ratio obtained after water adding is also noted.

5. RESULTS5.1 Scaling resistance of road concrete compositions

The ISO/DIS 4846.2 and the Slab test were performed on each combination. The ISO/DIS 4846.2 was performed on the finished surface. The Slab test was performed on the exposed aggregates or brushed surface finish, as well as on sawn and on cast surfaces extracted from cubes (150 mm sided) by drilling.

From the beginning of the research project, it was decided to extend the duration of all freeze-thaw tests until 63 cycles. In a preceding research project (CRIC-OCCN, 2013) it was observed that the evolution of scaling as a function of the number of cycles could give useful information about the intrinsic resistance of a given concrete composition against scaling.

The evolution of the mass losses on finished surfaces as a function of the number of cycles is reported in figure 2, where results for the Slab test as well as for the ISO-DIS method are shown. The mass losses measured after 30 (ISO/DIS) or 28 (Slab) cycles are reported in table 4.

Figure 2: Mass losses as a function of the number of cycles on finished surfaces (L = exposed aggregates, B = brushed)

As expected, the concrete compositions with high cement contents (400 kg/m3), water to cement ratios of 0.45, and with air content between 3% and 6% (RI-400-S1-air-L and RI-400-S3-air-L) show the lowest mass losses of the series after 28 cycles. The losses measured by the Slab method are 0.47 kg/m2 and 0.34 kg/m2 on average respectively. Those compositions are conforming to the most severe building class for heavy trafficked roads, the upper limiting value being 1.500 kg/m2 in Flanders for the moment.

Subsequently, the compositions (RII-375-S1-air-L, RII-375-S3-air-L, RII-375-S1-B-air, RII-375-S3-B-air) with a cement content of 375 kg/m3, a water to cement ratio of 0.50 and with air entraining agent, show higher scaling losses, 1.57 kg/m2, 1.78 kg/m2, 2.58 kg/m2 and 2.40 kg/m2

respectively (measured by the Slab-test method after 28 cycles). Nonetheless, these values are still conforming to the requirements for medium trafficked roads in Flanders (upper limit of 3.000 kg/m2).

The other compositions for which no air-entraining agent was used, show much higher scaling values. When looking at the results for the finished surface (table 3), all scaling values are above the maximum acceptable losses after 28 cycles (Slab test) or after 30 cycles (ISO-DIS method) that are required in the different standard tender specifications.

The highest mass losses regardless of the testing method (ISO/DIS 4846-2 or Slab test), can be observed for the compositions RII-375-S3W-L and RII-375-S3W-B where no air entraining agent was used, and where water was added afterwards to enhance the workability without using a plasticizing agent. For these compositions, the water to cement ratio was 0.06 above the maximum authorized value (0.50).

As shown in table 4, the mass losses following the Slab-test method obtained on sawn surfaces are significantly lower than those obtained on the finished surface. The mass losses measured on sawn surfaces probably reflect the intrinsic resistance of the concrete composition against scaling directly and do not take into account the surface finishing and the excess of cement paste (concrete skin) at the exposed surface.

The influence of the type of surface finishing on the scaling resistance is more clearly visible in Figure 3. Here, it is obvious that sawn surfaces are less sensitive to scaling while a cast surface seems to resemble more closely the finished (exposed) surfaces in terms of scaling resistance. Note that the brushed surface finish shows the largest scaling values although reproducing the brooming process in the lab is quite difficult; a study of the influence of the intensity of brushing in the lab revealed that the texture depth of the brushed surface could also influence significantly the scaling results (Figure 4).

Table 4 - Mass losses after 28 or 30 cycles – The non-conforming compositions/values are reported in bold italic.

Method ISO/DIS Slab Slab SlabMass loss after 30 cycles 28 cycles 28 cycles 28 cyclesTested surface Finished Finished Sawn Cast

Unit g/dm2 kg/m2 kg/m2 kg/m2

RI-400-S1-L-air 1.74 0.47 0.23 0.71RII-375-S1-L-air 2.76 1.57 0.24 1.40RII-375-S1-B-air 7.64 2.58 0.24* 1.40*RI-400-S3-L-air 2.08 0.34 0.24 0.93RII-375-S3-L-air 2.82 1.78 0.26 1.89RII-375-S3-B-air 8.37 2.40 0.26* 1.89*

RI-400-S3-L 10.62 3.51 0.95 3.96RI-400-S3W-L 15.11 4.33 1.19 4.07RII-375-S3-L 18.38 4.03 1.92 4.33

RII-375-S3W-L 20.79 5.64 2.58 5.02RII-375-S3-B 28.91 5.67 1.92* 4.33*

RII-375-S3W-B 32.18 6.31 2.58* 5.02*RIII-360-S4-T 1.74 0.47 0.23 0.71

RIII-360-S4W-T 2.76 1.57 0.24 1.40*Idem value for exposed aggregates surface

RI-400-S1-air

RI-400-S3-air

RII-375-S1-air

RII-375-S3-air

RI-400-S3 RI-400-S3W RII-375-S3 RII-375-S3W

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

sawncastexposed aggregatesbrushed

Mas

s los

ses a

fter 2

8 cy

cles (

kg/m

2)

Figure 3: Influence of the tested surface on the mass losses at 28 cycles of the Slab test.

0 5 10 15 20 25 30 350.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

0

5

10

15

20

25

30

35

40

Slab Light brooming Slab Moderate BroomingSlab Strong Brooming ISO/DIS Light BroomingISO/DIS Moderate Brooming ISO/DIS Strong Brooming

Number of cycles

Scal

ing

Slab

(kg/

m2)

Scal

ing

ISO

/DIS

(g/d

m2)

Figure 4: Influence of intensity of brushing on mass losses on finished surface measured during 28 cycles of the Slab test and 30 cycles of the ISO/DIS method.

In figure 5, the mass losses on the finished surface (exposed aggregates and brushed) measured after 28 cycles by the Slab-test method versus the mass losses measured after 30 cycles by the ISO/DIS method are plotted. Applying a polynomial regression, it is possible to correlate the upper and lower scaling limits following the ISO/DIS method into limits following the Slab-test method. The limits of 10 g/dm2 (low trafficked roads) and of 5 g/dm2 (heavy trafficked roads) would then become 2.98 kg/m2 and 1.63 kg/m2. This interesting finding lies in the range of a preceding study (Beeldens et al., 2014) and also confirms the current threshold values used in the Flemish specifications, taking into account the possible variation on the scaling test results (see bottom of Figure 5).

5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.000.001.002.003.004.005.006.007.008.009.00

ISO/DIS-Slab finished surface

exposed aggregatesbrushed

Scaling ISODIS 30 cycles (g/dm2)

Scal

ing

SLAB

28

cycle

s (kg

/m2)

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.000.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

f(x) = − 0.00574998685075847 x² + 0.358233637477845 xR² = 0.980434011457694

ISO/DIS-Slab finished surface

Scaling ISODIS 30 cycles (g/dm2)

Scal

ing

SLAB

28

cycle

s (kg

/m2)

5 g/dm2 → 1,63 kg/m2

10g/dm2 → 2,98 kg/m2

Figure 5: Mass losses on finished surface (exposed aggregates + brushed) measured after 28 cycles by the Slab test versus mass losses measured after 30 cycles by the ISO/DIS method.

Intrinsic variation of the scaling test results following the Slab-test method was also investigated in a round robin study among the three partner institutes (Figure 6) using a typical concrete composition for industrial pavements, similar to roads of category RII, but with a different slump value:

Concrete of slump class S4 with 360 kg/m³ of cement, water-cement ratio of 0.45 and tests performed on sawn surface of samples

For laboratories A and C the tested surfaces came from the same saw cut, 4 cores were tested per lab

The results of the round robin scaling tests for the three participating laboratories (A, B and C) are depicted in Figure 6, and table 5 shows the calculated repeatability and reproducibility; overall, very comparable results were obtained between all labs with a reproducibility value of 24% for an average scaling value of 2 kg/m². This is also in line with previous round robin tests where a value of 31% was obtained for a nominal value of 1 kg/m² of scaling (CEN, 2016).

This means we could indeed expect an absolute value of variation of around 0,5 kg/m² for a nominal scaling value of 1,5 kg/m².

0 7 14 21 28 35 42 49 56 630

1

2

3

4

5

Lab ALab BLab C

Number of cycles

Scal

ing

[kg/

m²]

Figure 6: Scaling results for round robin test among three partner institutes (A, B and C) following Slab-test method (average of 4 samples per lab).

Table 4 - Calculated repeatability (sr) and reproducibility (sR) for the round robin test of Figure 6

Number of cycles 7 14 28 42 56 63

Average (kg/m2) 0,43 1,04 1,99 2,77 3,55 3,90

sL2 (kg/m2) (∆ 4

samples)

0,07 0,13 0,20 0,30 0,35 0,37

sr2 (kg/m2) (∆ result) 0,10 0,15 0,29 0,41 0,54 0,61

sR2(kg/m2) (sL

2+sr2) 0,17 0,28 0,49 0,71 0,89 0,98

sR2 (%) -

Reproducibility

39,30 27,22 24,52 25,74 25,06 25,11

Finally, in figure 7, the mass losses measured after 28 cycles by the Slab-test method on cast surfaces versus the mass losses at 28 days on finished surfaces (exposed aggregates or brushed) are plotted. This relationship can be useful if an initial type testing is to be done in the laboratory on concrete cubes, as for instance is obliged in the recent certification process for road concrete in Flanders (SB 250). As can be seen on figure 7, the results obtained on a cast surface and on a finished surface correlate quite well in the lab. However, more results of samples taken on site are needed to confirm this hypothesis and the correspondence between the certification study in the lab (RNR 06) and the control on the construction site (exposed surface).

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.000.00

1.00

2.00

3.00

4.00

5.00

6.00

f(x) = 0.864316224381982 xR² = 0.96594025621756

Slab test cast surface vs. finished surface

Scaling 28 cycles finished surface (kg/m2)

Scal

ing

28 cy

cles c

ast s

ide

(kg/

m2)

Figure 7 - Mass losses measured at 28 days by the Slab test on cast side face versus mass losses at 28 days by the Slab test on finished surface (exposed aggregates or brushed).

5.2 Properties and effect of hydrophobic impregnation products

First of all, some measurements of the characteristics of hydrophobic impregnation products following NBN EN 1504-2 were performed in the lab, using the road concrete composition RII-375-S3 (see Table 3) conforming to low trafficked roads but without the use of an air-entraining agent. This composition has a moderate to low resistance against scaling (cf. figure 2 and table 4) to be able to better distinguish the effect of the hydrophobic impregnation on the scaling of road concrete.

The cast surface of samples was impregnated with different products (8 different products IP1-IP8) at a concrete age of 35 days and the freeze-thaw tests (according to the Slabtest method) started at 49 days. Following the test methods of the European standards NBN EN 13579-13580-13581, the impregnation was performed on cubes with side 10 cm by immersion of all sides in the product during two minutes, use two impregnations (2 x 2 minutes) in this case.

For the samples undergoing freeze-thaw testing on the other hand, concrete slabs with a thickness of 5 cm were produced, from which cores with diameter of 113 mm were taken and where impregnation was performed by spreading the manufacturer’s recommended quantity of product on the tested surface.

Figure 8 – Application of impregnation on test cubes or concrete slabs for testing the properties and effect of hydrophobic impregnation products

Penetration depth was measured following the instructions of table 3 of European standard EN 1504-2 (NBN, 2005):

Figure 9 – Abstract from Table 3 of NBN EN 1504-2 (NBN EN 1502) concerning measurements of penetration depth

The measurement is thus done on a fractured surface by spraying the surface with water and measuring the depth of de dry zone. However, it was sometimes very difficult to measure this zone because the depth was only a few millimeters. Moreover, the interface between the dry and the wet zone was not always straight. Consequently, a quite high variability on measurements of one sample was observed, putting also some doubt to the accuracy of the measured penetration depth (Figure 10); the average results for measurements of the penetration depth are reported on the left of Figure 10.

First measurements of penetration depth were done on cubes which were impregnated by immersion as described in the standards (blue bars in Figure 10, left). Subsequently, measurements were performed on cores impregnated following the manufacturer’s recommendation (yellow bars in Figure 10, left) for which the repeatability was better.

Nonetheless, all results for the penetration depth are below 10 mm, which is the limiting value between class I and class II following NBN EN 1504-2. However, we must keep in mind that in current research, measurements are done on a different concrete composition compared to the reference concretes of the European standard.

Figure 10 – Results for measurements of penetration depth and correlation with scaling test results for impregnated concrete

The scaling curves obtained on samples with the different impregnation products are depicted on the right of Figure 10. They all show a depletion of the curve after 7 cycles, compared to the untreated reference concrete (blue curve). The scaling is more or less delayed as a function of the efficiency of the product and we can observe that hydrophobic impregnation really has a measurable effect on the resistance against scaling. In figure 10 on the right, near the scaling curves, the average measured penetration depth is also reported.

As can be seen, we did not observe any logical relationship between the measured penetration depth and the scaling values. Furthermore, measurements for determination of water absorption and resistance to alkali according to NBN EN 13580 (NBN, 2002b) were also performed, the results of which are shown in Figure 11.

The principle of the latter test method is to compare the rate of water uptake of impregnated versus non-impregnated test cubes. The ratio of these rates is defined as the absorption ratio, where a lower value thus corresponds to a more effective reduction of the water uptake. In addition, the long term durability of the hydrophobic impregnation product is assessed by measuring the water absorption ratio after immersion of the test cubes in a saturated potassium hydroxide (KOH) solution.

Figure 11 – Results for measurements of water absorption and resistance to alkali and correlation with scaling test results for impregnated concrete

As is evident from Figure 11 (on the left), all of the measurements are above the limits set by NBN EN 1504-2; however, as discussed before, the road concrete composition tested here, is fairly different than the reference concretes normally used for EN 1504-2.

Likewise as for the penetration depth, on the right of Figure 11 the scaling curves obtained with different impregnation products are plotted together with the results obtained for the absorption ratios with regular water and after immersion in potassium hydroxide (AR_alkali). Again, no obvious relationship was found between both characteristics.

Hence, determination of the characteristics of hydrophobic impregnation products according to NBN EN 1504-2 solely, seems to be insufficient in order to evaluate the effect of the product on the freeze-thaw resistance with de-icing salts of road concrete.

Next, during the follow-up of the construction site of CRCP in Couvin (see section 6.3), fresh samples of concrete were taken to be able to test the influence of the curing compound (generally applied to protect the fresh concrete against desiccation) on the efficiency of hydrophobic impregnation.

One prism and some cubes were prepared on site and then treated in the laboratory to produce four series of samples (Figure 12, top):

two series were stored under water (20°C), one of which was impregnated with a hydrophobic product at 28 days, one remained unimpregnated;

two series were treated with a curing compound and stored at 20°C and 60% RH, one of which was impregnated with the same hydrophobic product at 28 days, and one remained once again with no impregnation.

Afterwards, the Slab test was performed on the cast surface of cores taken from the four different slabs at an age of 49 days, the results of which are shown in the bottom of Figure 12.

Figure 12 – Testing for effect of curing compound on effectiveness of hydrophobic impregnation; Top: preparation of samples taken of construction site in Couvin; bottom: Average scaling test results for four series of samples

The scaling curves of Figure 12 show that the curing product probably interacts with the impregnation product, even after 28 days of age (in a lab environment); by applying the curing product, the reduction of scaling by impregnation seems to be effective during a more limited period.

If hydrophobic impregnation has to be done after curing, we would recommend certainly not to impregnate before an age of 28 days and eventually to clean the surface before the impregnation.

Finally, results were also obtained on a laboratory impregnated concrete composition after ageing of the samples by different methods (see section 4.2 and Figure 1) on the same composition as before: RII-375-S3 (w/c = 0,50, 375 kg/m3 CEM III/A 42,5, no AEA) with moderate resistance to scaling (4,5 kg/m2 on average after 28 cycles, cast surface; see table 4).

0 10 20 30 40 50 600

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4

No impregnation

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Figure 13 – Scaling curves of composition RII-375-S3 (w/c = 0,50, 375 kg/m3 CEM III/A 42,5, no AEA) for effect of ageing of impregnated surfaces.

Slab testing was performed on the samples before and after the ageing process. The scaling curves are reported in figure 13.

One can observe that Q-SUN ageing and rubber wearing have a weak effect on the efficiency of impregnation. The scaling curves after ageing of the impregnated specimens are quite similar to the reference.

PEI abrasion strongly reduces the efficiency of impregnation. On the scaling curves, it is observed that the protective action against scaling diminishes after 7 cycles, then the scaling process starts again.

The results from natural ageing by keeping samples for 9 months on the rooftop of the BRRC building will be presented in a next communication.

5.3 Validation on road construction sites

The most important campaign was lead on the airport of Brussels (Zaventem) where the concrete slab pavement of the parking zones (Aprons) is systematically impregnated after casting. Forty-eight cores were extracted from treated and untreated zones. The applied hydrophobic impregnation product is IP3 which was tested in § 5.2.

The average scaling curves of the untreated samples are represented on figure 14 in solid line; the treated samples are represented in dashed lines. The scaling values of all samples are quiet low, even on the untreated samples, but as for the laboratory results, the impregnated samples show a depletion of the scaling material during the 28 first freeze-thaw cycles.

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Apron 40 West (2017) not impregnatedApron 40 West (2017) impregnatedZone “Satelliet” = Apron 3 south (2010) impregnatedZone “SNECMA” (september 2017) not impregnated

n° cycle

Scal

ing

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m2)

Figure 14 – Scaling curves of cores from Zaventem airport; samples with hydrophobic impregnation (IP3) are represented in dashed lines.

In figure 15, the scaling values at 28 cycles are reported. The measurements were executed with Sodium Chloride and with Potassium acetate, the latter being the de-icing product that is used on the airport nowadays.

As one can observe, there is a clear difference in the scaling values between impregnated and not impregnated samples, the scaling values being significantly lower for the impregnated surfaces. The efficiency of impregnation in reducing the scaling material is even measured on surfaces which were impregnated since 8 years.

The scaling values for the samples were Potassium Acetate was used as de-icing agent are far lower than those for the samples were Sodium Chloride was used.

not i

mpr

egna

ted

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egna

ted

impr

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Apron 40 West (2017)

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(september 2017)

Zone “Satel-liet” = Apron 3 south (2010)

Apron 40 East (2013)

Apron 40 West (2017)

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Slab-NaCl Slab-Kacetate

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at 2

8 cy

cli [

kg/m

²]

Figure 15 – Cumulated scaled material after 28 cycles of cores from Zaventem airport following the Slab-test method; test performed with Sodium Chloride (standard method) and Potassium Acetate (airport tender specification).

6. CONCLUSIONS

Concrete mix compositions that are representative for application on heavy and medium trafficked roads in Belgium were submitted to two different freeze-thaw test methods, the ISO/DIS 4846.2 method and the Slab-test method according to RNR 06, based on CEN/TS 12390-9. New limiting values can be found by correlating results between each other.

Great care has to be taken in the interpretation of results obtained on different surface types: finished surface (exposed aggregates or brushed), sawn surface or cast surface of a cube. The results show that the mass losses by scaling of cast surfaces are quite similar to the losses of exposed aggregates finished surfaces. In a next step, these results are to be confirmed by further on site measurements.

It was demonstrated that hydrophobic impregnation can enhance the durability of road concrete with respect to freeze-thaw cycles in presence of de-icing salts. This effect was observed even on surfaces which were treated since 8 years.

No obvious relationship was observed between the penetration depth or the absorption ratio on the one hand and the resistance against scaling of impregnated concrete surfaces on the other hand. The determination of the characteristics of hydrophobic impregnation products according to NBN EN 1504-2 should be complemented by Slab test measurements on impregnated samples if a better freeze-thaw durability with de-icing salts is aimed at.

Furthermore, application of a curing compound can have an influence on the efficiency of impregnation. For this reason, impregnation should be applied at least 28 days after concrete placing and/or eventually, the surface should be cleaned before impregnation in order to remove the curing compound.

It was observed that Q-SUN ageing and rubber wearing have a weak effect on the efficiency of impregnation. PEI abrasion though reduces more strongly the efficiency of impregnation and results for natural ageing are still expected.

Finally, it is clear that the execution and surface finishing on the construction site itself also remains crucial for the resistance against scaling of road concrete.

7. ACKNOWLEDGEMENTS

The authors wish to thank FPS Economy (Federal Public Service), for the (financial) support of the project, and Brussels Airport Company for their collaboration in the research.

8. REFERENCES

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CEN (2016), CEN/TS 12390-9:2016 « Testing hardened concrete – Part 9: Freeze-thaw resistance Scaling »; Brussels, 2016.

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NBN (2002a), NBN EN 13581:2002 « Products and systems for the protection and repair of concrete structures - Test method - Determination of loss of mass of hydrophobic impregnated concrete after freeze-thaw salt stress”, Brussels, 2002.

NBN (2002b), NBN EN 13580:2002 « Products and systems for the protection and repair of concrete structures - Test Methods - Water absorption and resistance to alkali for hydrophobic impregnations”, Brussels, 2002.

NBN (2005), NBN EN 1504-2:2005 “Products and systems for the protection and repair of concrete structures - Definitions, requirements, quality control and evaluation of conformity - Part 2: Surface protection systems for concrete”, Brussels, 2005.

NBN (2018), NBN EN 12274-5:2018 “Slurry surfacing - Test method - Part 5: Determination of the minimum binder content and wearing resistance”, Brussels, 2018.

Qualiroutes (version 2016 consolidée) Ministère de la Région Wallonne, Service Public de Wallonie, online : http://qc.spw.wallonie.be/fr/qualiroutes/doc/Qualiroutes/Chapitre%20G.pdf

Raupach M., Büttner T. (2009), “Hydrophobic treatments on concrete—Evaluation of the durability and non-destructive testing”, in Concrete Repair, Rehabilitation and Retrofitting II – Alexander et al (eds), © 2009 Taylor & Francis Group, London, ISBN 978-0-415-46850-3, p. 907-913.

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Smets S,. Boonen E., Pierre C., Vanhamme G., Piérard J. (2018), “Limits for the freeze-thaw resistance of road concrete in the presence of de-icing salts: first results of the GELAVIA project”, Proceedings of 13th International Symposium on Concrete Roads, June 19-22 2018, Berlin, Germany, 13 pp.

Vandewalle Lucie, Figeys W. , Pierre Christian, Germain Olivier, De Myttenaere Olivier, Beeldens Anne “Comparative study of concrete resistance against freeze-thaw cycles as described in CEN/TS 12390-9, ISO-DIS 4846-2 and NTN-018”; ConMat Conference, Japan; August 2009.