lecture2a targoviste aguiar
Post on 03-Apr-2018
219 Views
Preview:
TRANSCRIPT
-
7/28/2019 Lecture2A Targoviste Aguiar
1/26
POLYMERS FOR CONSTRUCTION
Performance of Protected Concrete
Jos B. Aguiar, Pedro M. Moreira, Aires Cames
University of Minho
Portugal
-
7/28/2019 Lecture2A Targoviste Aguiar
2/26
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.
-
7/28/2019 Lecture2A Targoviste Aguiar
3/26
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.
-
7/28/2019 Lecture2A Targoviste Aguiar
4/26
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
-
7/28/2019 Lecture2A Targoviste Aguiar
5/26
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 -
-
7/28/2019 Lecture2A Targoviste Aguiar
6/26
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).
-
7/28/2019 Lecture2A Targoviste Aguiar
7/26
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
-
7/28/2019 Lecture2A Targoviste Aguiar
8/26
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.
-
7/28/2019 Lecture2A Targoviste Aguiar
9/26
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:
-
7/28/2019 Lecture2A Targoviste Aguiar
10/26
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)
-
7/28/2019 Lecture2A Targoviste Aguiar
11/26
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.
-
7/28/2019 Lecture2A Targoviste Aguiar
12/26
Figure 1. Test of penetration of chlorides.
-
7/28/2019 Lecture2A Targoviste Aguiar
13/26
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.
-
7/28/2019 Lecture2A Targoviste Aguiar
14/26
Figure 2. Colorimetric test of one specimen.
chlorides penetration
Xd
Xd
-
7/28/2019 Lecture2A Targoviste Aguiar
15/26
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
-
7/28/2019 Lecture2A Targoviste Aguiar
16/26
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.
-
7/28/2019 Lecture2A Targoviste Aguiar
17/26
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.
-
7/28/2019 Lecture2A Targoviste Aguiar
18/26
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.
-
7/28/2019 Lecture2A Targoviste Aguiar
19/26
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
-
7/28/2019 Lecture2A Targoviste Aguiar
20/26
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.
-
7/28/2019 Lecture2A Targoviste Aguiar
21/26
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.
-
7/28/2019 Lecture2A Targoviste Aguiar
22/26
Figure 6. Photos to assessment the degree of cracking, no preferentialdirection (ISO 4628-4).
(1) (5)(4)(3)(2)
-
7/28/2019 Lecture2A Targoviste Aguiar
23/26
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.
-
7/28/2019 Lecture2A Targoviste Aguiar
24/26
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
-
7/28/2019 Lecture2A Targoviste Aguiar
25/26
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.
-
7/28/2019 Lecture2A Targoviste Aguiar
26/26
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.
top related