lecture2a targoviste aguiar

7/28/2019 Lecture2A Targoviste Aguiar

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POLYMERS FOR CONSTRUCTION

Performance of Protected Concrete

Jos B. Aguiar, Pedro M. Moreira, Aires Cames

University of Minho

Portugal


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INTRODUCTION

The durability of the reinforced concrete depends mainly on the composition

and properties of the concrete surface layer.

This layer is most of the times the only responsible for the corrosion protectionof the reinforcement.

Surface treatments act as a barrier between the

environment and the concrete.


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INTRODUCTION

With a wide range of products available in the market, it becomes extremely

difficult to choose the right type of hydrophobic agent or coating.

The performance of the available generic types under different service

conditions needs to be studied.

There is also a need to develop performance criteria and guidelines for the

evaluation and the selection of hydrophobic agents and coatings appropriatefor various exposure conditions.


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EXPERIMENTAL PROGRAM

Materials

Two types of cements were used:

- Portland cement (CEM I 42.5R);

- Pozzolanic cement (CEM IV/A (V) 32.5R), made with

35% of fly ash.

According to EN 197-1

Three types of concretes were used


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Concretes I-A and IV

w/c = 0.60; slump = 60 mm;

Concrete I-Bw/c = 0.40; slump = 180 mm.

Table 3. Composition of the concretes

Quantities (kg/m3)

MaterialsConcrete I-A Concrete I-B Concrete IV

Cement CEM I 320 500 -

Cement CEM IV - - 320

Gravel 510 796 888 814

Sand 05 940 690 898

Water 181 184 180

Superplasticizer - 5 -


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The average compressive strength at 28 days was:

Concrete I-A - 27.5 MPa;

Concrete I-B - 55.6 MPa;Concrete IV - 20.8 MPa.

The experimental campaign was designed in order to test concrete specimens

without any type of hydrophobic agent or coating and treated concrete specimens.

Concrete hydrophobic agents and coatings were selected to represent

the following three generic types:

Silicone agents (S);

Acrylic coatings (A);

Epoxy coatings (E).


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Table 4. Description of the selected hydrophobic agent and coatings

Silicone

Acrylic Epoxy

Generic type siloxane resin insolvent base

acrylic resinaqueous based

two componentepoxy resin

Consistency liquid dense liquid dense liquid

Coverage rate(m

2/dm

3)

2.8 3.5 4.0

Density at 20 C(kg/dm3) 0.83 1.40 1.30

Brookfield viscosity at 20 C(mPa.s)

11 6000 1500

Surface drying time(min)

60 40 300

Interval between coats

(h)

2 24 24


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The hydrophobic agent and the coatings were applied when the concrete had 28days.

The application was made by brush following the recommendations of the

supplier and after drying of the specimens under laboratory conditions for at least7 days.

Immediately before application of hydrophobic agent and coatings the concretesurfaces were spurted with compressed air.

The tests started 7 days after hydrophobic agent and coatings were applied onconcrete specimens.


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Penetration of chlorides

Tests based on a non-steady state.

The depth of penetration determined by a colorimetric method using

silver nitrate.

The average penetration was considered the depth of penetration.

The diffusion coefficient is obtained using the equation:


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where D: diffusion coefficient, m2

/s; z: absolute value for ion valence, for chlorides, z =1; F: Faraday constant, F = 9.648 x 104 J/(V.mol); U: absolute value of potential

difference, V; R: gas constant, R = 8.314 J/(K.mol); T: solution temperature, K; L:

specimen thickness, m; x: penetration depth, m; t: test duration, s, t = t CTH x 3600; erf-1:

inverse of error function; cd: chloride concentration at which the colour changes, cd

0.07 N; c0: chloride concentration in the upstream cell, N.

t

xx

UFz

LTRD

dd

with:

0

1 2

12 c

c

erfUFz

LTR d

,

(1)

(2)


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Cylinders with 110x230 mm were moulded.

These cylinders were cut in cylinders with 110x50 mm, in order

to obtain the specimens used in the tests.

The products were only applied in one face of the cylinders.

The tests occurred 7 days after hydrophobic agent or coatings were

applied on concrete specimens.


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Figure 1. Test of penetration of chlorides.


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After the conclusion of the test, the specimens were broken in twohalves by the mean of splitting tensile test.

The solution of silver nitrate was then applied on the concrete surfaceand the colorimetric test was made in order to measure the depth of

chlorides penetration.

Five specimens of each product and composition were tested.


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Figure 2. Colorimetric test of one specimen.

chlorides penetration

Xd

Xd


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Figure 3. Coefficients of diffusion in a non-steady regime for different concretes,hydrophobic agent and coatings.

0

2

4

6

10

12

14

16

I-A I-B IV ACR I-A ACR I-B EP I-A EP I-B

D(10-12

m2/s)

8


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Sulphate attack

The tests were made following ASTM C 88 standard with some adaptations.

The procedure of the tests consists on cycles of immersion in the prepared solution of

sodium sulphate for not less than 16 h nor more than 18 h.

After the specimens were removed from the solution, permitted to drain for 155 min,

and placed in the drying oven.

According to the standard ASTM C88 the temperature of the oven shall have been

brought previously to 1105C.


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The test of specimens with hydrophobic agents and coatings did not

recommend the use of a temperature such high.

So, the temperature of the oven in our tests was changed to the maximum

of 505C.

After the production of the concretes, cubes with 100x100x100 mm were

moulded.


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A total of eight cycles was made.

Analyze of sulphates attack was made by the weight variation along the

cycles.

Each value presented is the average of the weight variation of five

specimens.


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Figure 4. Mass losses for different concretes, hydrophobic

agent and coatings.

0

1

2

3

4

Massloss(%)

I-A I-B IV SIL I-A SIL I-B ACR I-A ACR I-B EP I-A EP I-B


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Acids and bases attack

The resistance of paintings to severe chemical attack was measured by exposition of

one face to the test liquid following the European standard EN 13529.

The specimens used on the test had the dimensions of 750x400x50 mm.


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The results of blistering, cracking, flaking and chalking will be presented

following ISO standards that give methods for evaluation of the degreesof degradation of paintings.

At the end of the exposition to the test liquids, adhesion tests were made

following the ASTMD 4541by pull-off method.


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Figure 6. Photos to assessment the degree of cracking, no preferentialdirection (ISO 4628-4).

(1) (5)(4)(3)(2)


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Table 6. Results of acid and base attack

References Blistering Cracking Flaking Chalking

Test liquid ConcreteDimension(Degree)

Surface(Degree)

Dimension(Degree)

Surface(Degree)

Degree Degree

H2SO4 ACR I-A 5 5 0 0 0 1

H2SO4 ACR I-B 5 5 0 0 0 *H2SO4 EP I-A 3 3 4 2 0 2

H2SO4 EP I-B 5 2 5 4 0 4

NH4OH ACR I-A 1 1 0 0 0 2

NH4OH ACR I-B 0 0 0 0 0 0

NH4OH EP I-A 0 0 2 1 0 1NH4OH EP I-B 0 0 2 1 0 2

[Note] *: The test was not possible due to 100 % of blistering.


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Table 7. Results of loss in adhesion strength after acid and base attack

References

Test liquid Concrete

Loss in adhesion strength(%)

H2SO4 ACR I-A 100

H2SO4 ACR I-B 100

H2SO4 EP I-A 8H2SO4 EP I-B 10

NH4OH ACR I-A 0

NH4OH ACR I-B 5

NH4OH EP I-A 0

NH4OH EP I-B 1


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CONCLUSIONS

The performance of the used coated concretes against chemically aggressive

environments was generally better than the performance of the unprotected concretes.

The used epoxy coated concrete achieved the best results against penetration of

chlorides.

The composition of the concretes is an important factor affecting performance againstchemically aggressive environments.


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CONCLUSIONS

Related to sulphates attack, uncoated and coated concretes that performed best were

made with the lower cement content and the higher water-cement ratio.

The high porosity is good to accommodate expansions caused by reactions that occurduring this attack.

The ammonium hydroxide caused an insignificant degradation on the coated concretes.

On the contrary, the degradation caused by the sulphuric acid was important.

lecture2a targoviste aguiar

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