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Journal ArticleDOI

Performance of a Fly Ash Geopolymeric Mortar for Coating of Ordinary Portland Cement Concrete Exposed to Harsh Chemical Environments

01 Sep 2015-Advanced Materials Research (Trans Tech Publications)-Vol. 1129, pp 573-580
TL;DR: In this paper, an experimental investigation on the resistance to chemical attack (by sulfuric and nitric acid) of several materials: OPC concrete, high performance concrete (HPC), epoxy resin, acrylic painting and a fly ash based geopolymeric mortar.
Abstract: Premature degradation of ordinary Portland cement (OPC) concrete infrastructures is a current and serious problem with overwhelming costs amounting to several trillion dollars. The use of concrete surface treatments with waterproofing materials to prevent the access of aggressive substances is an important way of enhancing concrete durability. The most common surface treatments use polymeric resins based on epoxy, silicone (siloxane), acrylics, polyurethanes or polymethacrylate. However, epoxy resins have low resistance to ultraviolet radiation while polyurethanes are sensitive to high alkalinity environments. Geopolymers constitute a group of materials with high resistance to chemical attack that could also be used for coating of concrete infrastructures exposed to harsh chemical environments.This article presents results of an experimental investigation on the resistance to chemical attack (by sulfuric and nitric acid) of several materials: OPC concrete, high performance concrete (HPC), epoxy resin, acrylic painting and a fly ash based geopolymeric mortar. Two types of acids, each with high concentrations of 10%, 20% and 30%, were used to simulate long term degradation by chemical attack. The results show that the epoxy resin had the best resistance to chemical attack, irrespective of the acid type and acid concentration.

Summary (2 min read)

Introduction

  • Premature degradation of OPC concrete infra-structures is a current and serious problem related to the fact that OPC concrete presents a higher permeability that allows water and other aggressive elements to enter, leading to carbonation and chloride ion attack resulting in corrosion problems [1].
  • They compared the waterproofing capacity of concrete with three polymeric resins (epoxy, silicone, acrylic) and mentioned that the silicone based is more effective (99.2%) in reducing water absorption by capillarity than the epoxy resin (93.6%), but in terms of chloride diffusion the epoxy resin is 100% effective, while the silicone varnish does not go beyond 67.5%.
  • Several scientist groups already suggest that chlorine industrial based products should be prohibited [12].
  • For the chemical designation of the geopolymer Davidovits suggested the name “polysialates”, in which Sialate is an abbreviation for aluminosilicate oxide.

Experimental work

  • Materials, mix design, mortar and concrete mixing and concrete coating.
  • A 10% percentage substitution of fly ash by calcium hydroxide in the mixture was also used.
  • Previous investigations showed that this ratio lead to the highest compressive strength results in geopolymeric mortars [19].
  • An expoxy resin often used as concrete coating protection against acid attack with a commercial reference Sikagard 62 PT was used for coating of the two concrete mixtures.

Experimental procedures

  • The compressive strength was performed under NP EN 206-1.
  • The compressive and flexural strength data of geopolimeric mortars was obtained using 160×40×40 mm3 cubic specimens according to EN 1015- 11.
  • This test his carried on according to Standard LNEC E393.
  • The resistance to acid attack followed a variation of the ASTM C267 (Standard test methods for chemical resistance of mortars, grouts, and monolithic surfacing’s and polymer concretes).
  • Three acid concentrations were used (10%, 20% and 30%) to simulate long time exposure at lower concentrations..

Results and discussion

  • Fig.1 shows the results of the compressive strength of the fly ash based geopolymeric mortars after 28 days curing as well as of the two concrete mixtures.
  • The fly ash geopolymeric mortar shows a good performance for both 10 and 20% sulphuric acid concentration..
  • Nitric acid attack at 10% concentrations is especially destructive for NC even after just 7 days immersion.
  • When the acid concentration is increased to 30% NC does not show an increase in the weight loss.

Conclusions

  • This article presents results of an experimental investigation on the resistance to chemical attack of several materials.
  • Normal concrete coated with epoxy resin shows the most stable performance for all three acid types and acid concentrations.
  • For a very high nitric acid concentration the geopolymeric mortar shows a disappointing performance that could be due to the ejection of tetrahedral aluminium from the aluminosilicate framework and in the formation of an imperfect highly siliceous framework.

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Performance of a Fly Ash Geopolymeric Mortar for Coating of Ordinary
Portland Cement Concrete Exposed to Harsh Chemical Environments
Walid Tahri
1, a
, Zahra Abdollahnejad
2,b
*, Jorge Mendes
3, c
,
Fernando Pacheco-Torgal
4, d
and José Barroso de Aguiar
5,e
1
University of Sfax, Tunisia
2,4,5
C-TAC Research Centre, University of Minho, Portugal
3
Civil Engineering Department, University of Minho, Portugal
a
walidtahri1980@yahoo.fr,
b
tolumahvash@gmail.com,
c
a50834@alunos.uminho.pt,
d
torgal@civil.uminho.pt,
d
aguiar@civil.uminho.pt
Keywords: Concrete infrastructures; Portland cement concrete; geopolymers; coatings; acid
attack
Abstract. Premature degradation of ordinary Portland cement (OPC) concrete infrastructures is a
current and serious problem with overwhelming costs amounting to several trillion dollars. The use
of concrete surface treatments with waterproofing materials to prevent the access of aggressive
substances is an important way of enhancing concrete durability. The most common surface
treatments use polymeric resins based on epoxy, silicone (siloxane), acrylics, polyurethanes or
polymethacrylate. However, epoxy resins have low resistance to ultraviolet radiation while
polyurethanes are sensitive to high alkalinity environments. Geopolymers constitute a group of
materials with high resistance to chemical attack that could also be used for coating of concrete
infrastructures exposed to harsh chemical environments.
This article presents results of an experimental investigation on the resistance to chemical attack (by
sulfuric and nitric acid) of several materials: OPC concrete, high performance concrete (HPC),
epoxy resin, acrylic painting and a fly ash based geopolymeric mortar. Three types of acids, each
with high concentrations of 10%, 20% and 30%, were used to simulate long term degradation by
chemical attack. The results show that the epoxy resin had the best resistance to chemical attack,
irrespective of the acid type and acid concentration.
Introduction
Premature degradation of OPC concrete infra-structures is a current and serious problem related
to the fact that OPC concrete presents a higher permeability that allows water and other aggressive
elements to enter, leading to carbonation and chloride ion attack resulting in corrosion problems [1].
Pacheco-Torgal et al. [2] mentioned the case of a tunnel in Dubai, which have been concluded in
1975 and needed to be completely repaired just after 11 years a case of pile foundations
disintegrated just after 12 years, and also a study on Norway OPC concrete bridges which indicate
that several presented corrosion problems 24 years after they were built. As a consequence
worldwide concrete infrastructure rehabilitation costs are staggering. In the European Union nearly
84,000 reinforced and prestressed concrete bridges require maintenance, repair and strengthening
with an annual budget of £215M, and that estimate does not include traffic management cost [3].
Many of the degraded concrete structures were built decades ago when little attention was given
to durability issues. Concrete durability means above all minimizing the possibility of aggressive
elements to enter the concrete, under certain environmental conditions for any of the following
transport mechanisms: permeability, diffusion or capillarity. The use of concrete surface treatments
with waterproofing materials (also known as sealers) to prevent the access of aggressive substances
is an important way of contributing to concrete durability.
Advanced Materials Research Vol. 1129 (2015) pp 573-580 Submitted: 2015-05-05
© (2015) Trans Tech Publications, Switzerland Revised: 2015-06-08
doi:10.4028/www.scientific.net/AMR.1129.573 Accepted: 2015-06-09
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans
Tech Publications, www.ttp.net. (ID: 89.180.88.126, Research Unit C-TAC, Sustainable Construction Group, University of Minho, Guimarães, Portugal-
17/09/15,18:48:42)

Almusallam et al [4] studied several concrete coatings concluding that epoxy and polyurethane
coatings performed better than acrylic, polymer and chlorinated rubber coatings.
Other authors [5, 6] showed that although some waterproof materials are effective for a particular
transport mechanism (diffusion, capillarity, permeability) cannot be for another. They compared the
waterproofing capacity of concrete with three polymeric resins (epoxy, silicone, acrylic) and
mentioned that the silicone based is more effective (99.2%) in reducing water absorption by
capillarity than the epoxy resin (93.6%), but in terms of chloride diffusion the epoxy resin is 100%
effective, while the silicone varnish does not go beyond 67.5%. Epoxy coatings exhibited excellent
durability under the laboratory and field test conditions and are recommended for protecting
concrete in cooling tower basins against sulphur oxidising or other acid producing bacteria [7].
Medeiros & Helene [8] used a water repellent material based on silane-siloxane noticing that
although it is effective to reduce the water absorption by capillarity of concrete (reduced from 2 to 7
times), it only managed to achieve a reduction of the chloride diffusion from 11% to 17% and also
failed to prevent the access of water by permeability.
Pacheco-Torgal and Jalali [9] confirm that the surface treatment of concrete with a water
repellent material is effective, but above all more cost-effective when compared with the alternative
of using a polymer additive in the composition of concrete.
Recently Brenna et al [10] study The efficiency of four commercial concrete coatings (a polymer
modified cementitious mortar and three elastomeric coatings) against chloride-induced corrosion
concluding that the polymer containing mortar shows the best effect on delay chlorides penetration
in concrete.In summary the most common surface treatments use polymeric resins based on epoxy,
silicone (siloxane), acrylics, chlorinated rubber, polyurethanes or polymethacrylate.
Bijen [11] mentioned that the epoxy resins have low resistance to ultraviolet radiation and
polyurethanes are sensitive to high alkalinity environments. Polyurethane is obtained from the
isocyanates, known worldwide for its tragic association with the Bhopal disaster. As for chlorinated
rubber it derives from reacting butyl rubber with chlorine and its important to remember that
chlorine is associated to the production of dioxins and furans that are extremely toxic and also bio-
cumulative. Several scientist groups already suggest that chlorine industrial based products should
be prohibited [12].
Besides recently the European Union recently approved the Regulation (EU) 305/2011 related to
the Construction Products Regulation (CPR) that will replace the current Directive 89/106/CEE,
already amended by Directive 1993/68/EEC, known as the Construction Products Directive (CPD).
A crucial aspect of the new regulation relates to the information regarding hazardous substances
[13].
Recent investigations on the geopolymer field [14] reveal a third category of mortars with high
potential to enhance the durability of concrete structures.Investigations in the field of geopolymers
had an exponential increase after the research results of Davidovits (1979) who developed and
patented binders obtained from the alkali-activation of metakaolin, having named it after the term
“geopolymer” in 1978. The technology of alkali-activation however predates this terminology by
several decades [15].
For the chemical designation of the geopolymer Davidovits suggested the name “polysialates”, in
which Sialate is an abbreviation for aluminosilicate oxide. The sialate network is composed of
tetrahedral anions [SiO
4
]
4-
and [AlO
4
]
5-
sharing the oxygen, which need positive ions such as (Na
+
,
K
+
,
Li
+
,
Ca
++
,
Na
+
,
Ba
++
,
NH
4
+
,
H
3
O
+
) to compensate the electric charge of Al
3+
in tetrahedral
coordination
(after dehydroxilation the aluminium changes from coordination 6 (octahedral) to
coordination 4 (tetrahedral). However Provis and Van Deventer [16] mentioned that the sialate
nomenclature “implies certain aspects of the geopolymer gel structure which do not correspond to
reality”.
Provis [17] as recently presented a rigorous and useful definition of these materials: “alkali-
activated materials are produced through the reaction of an aluminosilicatenormally supplied in
powder form as an industrial by-product or other inexpensive materialwith an alkaline activator,
574 ICPIC 2015

which is usually a concentrated aqueous solution of alkali hydroxide, silicate, carbonate or sulfate”.
Over the last years several authors have reported research in a large number of aspects related to
geopolymers.
However, very few studies have addressed the use of geopolymers for enhancement of concrete
structures durability. Since geopolymer performance concerning the resistance to acid attack, is far
better than that of Portland cement this means that this materials could be an alternative low
toxicity, coating material.
This paper presents results of an experimental investigation on the resistance to chemical attack
(with sulfuric and nitric acid) of several materials: OPC concrete, high performance concrete (HPC),
epoxy resin, acrylic painting and a fly ash based geopolymeric mortar.
Experimental work
Materials, mix design, mortar and concrete mixing and concrete coating. The fly ash used in
the geopolymeric mortars was supplied by Sines-EDP and according to the NP EN 450-1 it belongs
to B class and has an N class fineness modulus. Geopolymeric mortars were a mixture of
aggregates, fly ash, calcium hydroxide and alkaline silicate solution. The mass ratio for
aggregates/fly ash and activator was 2/1/0.6. A 10% percentage substitution of fly ash by calcium
hydroxide in the mixture was also used. This is because the use of minor calcium hydroxide
percentages is pivotal for the strength and durability of geopolymers [18].
The alkaline activator was prepared prior to use. An activator with sodium hydroxide and sodium
silicate solution (Na
2
O=13.5%, SiO
2
=58.7%, and water=45.2%) was used with a mass ratio of
1:2.5. Previous investigations showed that this ratio lead to the highest compressive strength results
in geopolymeric mortars [19].
Three different sodium hydroxide concentration (10M, 14M, 18M) were used. An ordinary
Portland cement (CEM I 42,5 N) where used to prepare the concrete mixtures. Two concrete mixes
(normal and HPC) were designed using the Faury concrete mix design method (Table 1).
Table 1 - Concrete mix proportions per cubic meter of concrete
Cement
(kg)
Sand
(kg)
Coarse aggregates
(kg)
Water
W/C
NC
270
1135
732
182
0.65
BED
442
876
782
205
0.45
An expoxy resin often used as concrete coating protection against acid attack with a commercial
reference Sikagard 62 PT was used for coating of the two concrete mixtures. The epoxy adhesive is
a two components system (resin and hardener) with a bulk density of 1,35 kg/dm
3
. An acrylic paint
often used as concrete coating protection to prevent the access of aggressive substances with a
commercial reference Sikagard 660 ES was also used for coating of the two concrete mixtures.
This material has a bulk density of 1,30 kg/dm
3
and is provided by the manufacturer as ready to be
used.
Experimental procedures
Compressive strength. The compressive strength was performed under NP EN 206-1. Tests were
performed on 100x100x100 mm
3
concrete specimens. The compressive and flexural strength data of
geopolimeric mortars was obtained using 160×40×40 mm3 cubic specimens according to EN 1015-
11.
Capillary water absorption. Capillary water absorption was carried out using 40x400x80 mm
3
specimens in the case of geopolymeric mortars and 100x100x100 mm
3
specimens for concrete.
After 28 days in a moist chamber the specimens were placed in an oven 105 ºC for 24 h. This test
his carried on according to Standard LNEC E393.
Advanced Materials Research Vol. 1129 575

Resistance to acid attack. The resistance to acid attack followed a variation of the ASTM C-
267 (Standard test methods for chemical resistance of mortars, grouts, and monolithic surfacing’s
and polymer concretes). Three different acids were used (sulphuric, hydrochloric and nitric). Three
acid concentrations were used (10%, 20% and 30%) to simulate long time exposure at lower
concentrations.. The resistance to acid attack was assessed by the differences in weight of dry
specimens before and after acid attack at 1, 7, 14, 28 and 56 days. The acid resistance was assessed
by the differences in weight of dry specimens before and after acid attack since compressive
strength of specimens immersed in acid media could not be evaluated. The fly ash based
geopolymeric mortar used in the resistance to acid attack was the one associated with the highest
compressive strength and low water absorption.
Results and discussion
Compressive strength. Fig.1 shows the results of the compressive strength of the fly ash based
geopolymeric mortars after 28 days curing as well as of the two concrete mixtures. The results show
that the compressive strength of geopolymeric mortars is very dependent on the molarity of the
sodium hydroxide. Increasing the molarity from 10M to 14M leads to a relevant compressive
strength loss. However, further increase from 14M to 18M shows no noticeable effects. Previous
investigations [20] have shown that although a high alkali content favours the dissolution of Al and
Si species of fly ash but can also negatively affect its strength. Normal concrete (NC) has a
compressive strength around 30MPa while HPC compressive strength slightly exceeds 45 MPa.
Fig. 1 Compressive strength
Capillary water absorption. Figure 2 shows the capillary water absorption coefficients. While
the fly ash geopolymeric mortars with a sodium hydroxide molarity of 14 and 18M show a capillary
water absorption around 0.45 kg/m
2
.h
0.5
the geopolymeric mortar with the lowest open porosity and
the highest compressive strength has a 0.1 kg/m
2
.h
0.5
capillary water absorption coefficient.The
capillary water absorption of the two concrete mixes used in this investigation is very low around
0.15 kg/m
2
.h
0.5
.As a comparison a plain C30/37 strength class concrete has a capillarity coefficient
of 0.251 kg/m
2
.h
0.5
for 28 days curing [21], while a plain C20/25 strength class concrete (the most
used strength class in Europe [22]) has capillarity coefficients between 0.85 and 2.6 kg/m
2
.h
0.5
[23].
Resistance to acid attack. Fig. 3 shows the weight loss after sulphuric acid attack for the
different acid concentrations. Normal concrete coated with epoxy resin shows the most stable
performance for all three acid concentrations conforming previous investigations.
576 ICPIC 2015

Fig. 2 Water absorption capillary coefficients
The fly ash geopolymeric mortar shows a good performance for both 10 and 20% sulphuric acid
concentration.. Even for a 30% sulphuric acid concentration this mortar shows a good acid
resistance for immersion until 14 days. HPC specimens shows the third best performance. It shows a
minor weigth loss after 56 days in a 10% sulphuric acid concentration. For a 20% sulphuric acid
concentration the weight loss is clear beyond 14 days reaching a maximum of 9%. When the
concentration increases to 30% the weigth loss starts after 7 days inmmersion and reaches a
maximum of 20% after 56 days. Specimens of normal concrete coated with acrylic paint show the
same performance of uncoated concrete specimens for both 10 and 20% sulphuric acid
concentration. Only for the 30% acid concentration and long-time immersion can this coat be of
some use. Since NC and HPC have almost similar capillary water absorption than the differences in
acid resistance lie in the leaching of calcium hydroxide (Ca(OH)
2
) from the pore solution and
decalcification of CSH that must be lower in the latter case due to a much higher Portland cement
content.
Weight loss after nitric acid attack is shown in fig.4. Again normal concrete coated with epoxy
resin shows the most stable performance for all three acid concentrations. Nitric acid attack at 10%
concentrations is especially destructive for NC even after just 7 days immersion. Nitric acid reacts
with calcium compounds forming calcium nitrate which has a solubility (56%). All the other
mixtures show a weight loss not exceeding 2% even after 56 immersion. The behaviour for a 20%
nitric acid concentration is almost the same. The difference being that NC shows a higher weight
loss. When the acid concentration is increased to 30% NC does not show an increase in the weight
loss. For this very high acid concentration the geopolymeric mortar shows a disappointing
performance. Allahverdi and Škvára [24, 25] suggested that the electrophilic attack of nitric acid
protons results in the ejection of tetrahedral aluminium from the aluminosilicate framework and in
the formation of an imperfect highly siliceous framework. Other authors [26] also suggested this
aluminosilicate depolymerisation.
a)
Advanced Materials Research Vol. 1129 577

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References
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TL;DR: Alkali-activated binders have emerged as an alternative to OPC binders, which seems to have superior durability and environmental impact as mentioned in this paper, and the proper terminology to designate these new binders will be discussed.

800 citations

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TL;DR: A review of alkali-activation technology, moving from the atomic scale and chemical reaction path modelling, towards macroscopic observables such as strength and durability of concretes is presented in this article.
Abstract: This paper presents a review of alkali-activation technology, moving from the atomic scale and chemical reaction path modelling, towards macroscopic observables such as strength and durability of alkali-activated concretes. These properties and length scales are intrinsically interlinked, and so the chemistry of both low-calcium (‘geopolymer’) and high-calcium (blast furnace slag-derived) alkali-activated binders can be used as a starting point from which certain engineering properties may be discussed and explained. These types of materials differ in chemistry, binder properties, chemical structure and microstructure, and this leads to the specific material properties of each type of binder. The secondary binder products formed during alkali-activation (zeolites in low-Ca systems, mostly layered double hydroxides in alkali-activated slags) are of significant importance in determining the final properties of the materials, particularly in the context of durability. The production of highly durable concretes must remain the fundamental aim of research and development in the area of alkali-activation. However, to enable the term ‘highly durable’ to be defined in a satisfactory way, the underlying mechanisms of degradation—which are not always the same for alkali-activated binders as for Portland cement-based binders, and cannot always be tested in precisely the same ways—need to be further analysed and understood. The process of reviewing a topic such as this will inevitably raise just as many questions as answers, and it is the intention of this paper to present both, in appropriate context.

621 citations


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Frequently Asked Questions (1)
Q1. What are the contributions mentioned in the paper "Performance of a fly ash geopolymeric mortar for coating of ordinary portland cement concrete exposed to harsh chemical environments" ?

This article presents results of an experimental investigation on the resistance to chemical attack ( by sulfuric and nitric acid ) of several materials: OPC concrete, high performance concrete ( HPC ), epoxy resin, acrylic painting and a fly ash based geopolymeric mortar.