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GRC mechanical properties for structural applications
J. G. Ferreira, F. A. Branco1
(1) Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
ABSTRACT
GRC - Glass Fiber Reinforced Concrete - is a material made of a cementitious matrix in
which short length glass fibers are dispersed. It has been widely used in the construction
industry for non-structural elements, especially in façade panels. This paper presents the
results of a research program aiming the implementation of GRC as a structural material. For
this, GRC was associated with continuum carbon and/or stainless steel reinforcement, leading
to an innovative material characterized by its lightness, impact strength and high durability
characteristics. The evaluation of the mechanical properties of the material are described in
this paper. This research work lead to the industrial production of different structural
elements, such as communication towers, pedestrian bridges and roof elements.
RÉSUMÉ
GRC (de l’anglais Glass Fiber Reinforced Concrete) est un matériau composé d’une
matrice de mortier à base de ciment avec des fibres de verre de petit longueur dispersées dans
son intérieur. Ce matériau a été utilisé dans des éléments non-structurelles, surtout dans des
éléments de façade. Cet article présent les résultats d’un programme de recherche ayant par
objectif l’utilisation structurelle de le GRC. Pour cela le GRC a été renforcé avec des
éléments continus de carbone et/ou d’acier inoxydable : on obtient un matériau caractérisé par
sa légèreté, résistance à l’impact et durabilité. Les propriétés mécaniques de ce matériau sont
décrives. Le travail effectué dans le cadre de ce programme de recherche a conduit à la
production industrielle de plusieurs éléments structurelles comme tours de
télécommunications, ponts piétonnier et éléments de couverture.
2
1. INTRODUCTION
Glass Fiber Reinforced Concrete (GRC) consists basically of a cementitious matrix
composed of cement, sand, water and admixtures, in which short length glass fibers are
dispersed. The effect of the fibers is reflected in the increase of the tension and impact
strength of the material. This composite material has been used for over thirty years in several
non-structural elements, namely façade panels (about 80 % of the GRC production) [1]. In the
early times of the GRC development one of the most concerning problems was the durability
of the glass fibers, which became fragile with time, especially because of the alkalinity of the
cement mortar. Since then, significant progresses have been made, with the development of
new types of alkali resistant glass fibers and of mortar additives to prevent the chemical and
physical processes that lead to the embrittlement of GRC [1,2].
Studies to use this material in structural elements were recently developed [3]. The
structural advantages of GRC arise from a reduced weight and a higher impact and tensile
strength as compared with concrete. To obtain a corrosion free material with high durability,
the structural elements studied were designed with reinforcement of carbon tendons and
stainless steel bars.
Two main production techniques of GRC were initially analyzed, namely the classical
projection and premixing. The later, however, proved to be much better for use in structural
elements due to the homogeneity of the material obtained, and the speed of production.
Although some of the mechanical and physical properties of GRC can be found in the
literature [4,5], there are important reasons that justify its experimental determination: For
structural applications, a much more complete and precise characterization is needed, when
compared with non-structural elements; It is necessary to know the specific values for the
material actually produced in each case, so the final quality of the structure can be assured;
Some properties, such as the cyclic loading behavior, were unknown.
3
Experimental tests were performed on GRC specimens to determine its mechanical
strength, Young modulus, creep and shrinkage behavior and stress-strain diagrams under
static and cyclic loading. The cementitious matrix was tested either plain or with glass fibers
and reinforced with carbon or glass tendons or with steel elements. The GRC compositions
were studied also in terms of length and percentage of fibers. The ageing effect was also
analyzed with accelerated ageing tests. These tests led to a characterization of the production
conditions to obtain optimized material properties.
2. TYPES OF GRC
There are two main production techniques of GRC, usually referred as spray-up (or
shotcreted) and premix [2].
In the process of producing GRC by shotcreting, the mortar is produced separately from
the fibers, which are mixed only at the jet of the spray gun, as shown in Fig. 1. The glass fiber
tendons are cut within the spray gun to the required size, typically between 25 mm and 40
mm, and constitute about 5 % of the GRC total weight. The subsequent compaction with a
cylindrical roll guarantees the mould of GRC in the form, the impregnation of the fibers
within the mortar, the removal of the air retained within the mix and the arising of an
adequate density.
Figure 1 – Production of element with spray-up GRC [6].
4
In the GRC production method by pre-mixture, mortar and pre-cut fibers are previously
mixed. The quantity of fibers added to the mortar is usually around 3.5 % in terms of weight.
The length of the fibers is generally around 12 mm. Longer fibers lead to an excessive
reduction of the mix’s workability. Production with premix GRC may involve several
techniques such as injection and vibration, pressing or shotcreting.
In Table 1 the values of some GRC current properties referred in literature [4,5] are
presented for effects of comparison with those experimentally obtained in this paper.
Property GRC spray-up GRC premix Dry density (kN/m3) 19-21 19-20
Compression strength (MPa) 50-80 40-60 Young modulus (compression) (GPa) 10-20 13-18
Impact strength (Nmm/mm2) 10-25 8-14 Poisson ratio 0.24 0.24
Bending: Limit of linearity (MPa) 7-11 5-8
Maximum strength (MPa) 21-31 10-14 Direct tension:
Maximum strength (MPa) 8-11 4-7 Maximum extension (%) 0.6-1.2 0.1-0.2
Table 1 – Typical values of some GRC properties.
3. COMPRESSION BEHAVIOR
3.1 Young modulus
Tests were performed to determine the Young modulus of GRC, following the national
standard LNEC E397 [7], for concrete. The cylindrical specimens had a diameter of 15 cm
and were 90 cm high (Fig. 2). The material was produced with spray-up technique, with the
following composition: White cement type BR I 42,5R: 100 kg; Sand: 100 kg; Polymer
Primal MC 76 S: 6,0 liters; Fluidizer type Sikament: 163: 10,0 liters; Water: 34 liters. Fiber:
4% to 5% Cem-FIL 53/76.
Values of Young modulus for spray-up GRC between 16,0 GPa and 17,0 GPa were
obtained, which are in the range of the technical data.
5
Figure 2 – Tests to determine Young modulus.
3.2 Compression strength
For assessment of the GRC compression strength different tests were carried out, either
on Spray-up and Premix specimens. The compositions of each production technique were
optimized based on former experience and on workability tests. The aim of these tests was to
assess the compression strength of GRC and to evaluate the role of the fibers.
Five series of specimens were tested, as follows: Series A – 9 specimens of premix GRC
(2,5% of 12 mm fibers); Series B – 8 specimens of spray-up GRC (4% to 5% of 31 mm or 63
mm fibers); Series C – 13 specimens of spray-up GRC (4% of 31 mm fibers); Series D – 10
specimens of premix mortar (without fibers); Series E – 6 specimens of spray-up mortar
(without fibers). All specimens were produced with standard dimensions.
Spray-up GRC mortar was composed as referred in 3.1, while premix GRC mortar was
produced with the following the composition: White cement type BR I 42,5R: 100 kg; Sand:
67 kg; Polymer Primal MC 76 S: 1,8 liters; Fluidizer type Sikament: 163: 1,0 liters; Water: 29
liters.
6
Fig. 3 shows the set-up of the tests, performed following the national standard LNEC
E226 [8], for the evaluation of concrete compression strength.
Figure 3 – Compression tests set-up.
The plain mortar specimens (without fiber reinforcement) practically exploded when the
maximum force was achieved, while the GRC ones, despite the crack pattern showed on their
surface, almost maintained their initial shape, denoting a much more ductile behavior (Fig. 4).
This distinct type of GRC behavior, when compared to plain mortar, is relevant for structural
use and is reflected in the stress-strain diagrams (Fig. 6).
Figure 4 – GRC and plain mortar ruptured specimens.
Based on the strength tests results, the average value, standard deviation and
characteristic value at 95% were determined for each series. A numerical treatment of the
cubic specimens values was carried out [9,10] to refer them to cylindrical specimens tests. In
Table 2 the results for all tested series are presented.
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Series fcm (MPa) σ (MPa) fck (MPa) A (9 premix GRC) 40.9 2.91 36.1
B (8 spray-up GRC) 37.4 2.93 32.6 C (13 spray-up GRC) 57.0 3.48 51.3 D (10 premix mortar) 51.8 0.70 50.6 E (6 spray-up mortar) 58.3 8.92 43.7
Table 2 – Statistics of compression tests results, referred to cylindrical specimens.
These results show that GRC strength is comparable to that obtained for good quality
concrete. The lower values of series A (premix GRC), when compared with series D (premix
GRC mortar), are probably related to a lesser compaction or excess of water. The average
strength of series E (spray-up GRC mortar) is higher than that of series B and C (spray-up
GRC), but its characteristic strength presents an intermediate value because of the low
number of specimens. The results show that the presence of fibers may imply a loss of
compression strength of the material.
3.3 Stress-strain diagrams
Five tests were performed to determine the stress-strain behavior in compression. Three
of these specimens were composed by premix GRC (series F), while the other two (series G)
were made of plain mortar.
All standard cylindrical specimens of series F and G were produced following,
respectively, the compositions of series A and E indicated in 3.2. The test set-up and the
general procedure adopted in these tests was identical to those indicated in 3.2.
The strain was measured by means of either electrical displacement transducers and
strain gauges, as showed in Fig. 5. In the initial phase of tests the strain gauges readings are
considered due to their higher accuracy. The displacement transducers may read deformation
far beyond the working limit of the strain gauges, allowing the evaluation of the post peak
behavior.
8
Figure 5 – Measurement of specimens deformation.
Fig. 6 shows the stress-strain diagrams obtained in these tests, that clearly reflect the
different type of collapse mode depending whether the fibers are present or not. It is
particularly evident the greater ductility of GRC when compared with plain mortar that, as
previously referred, disintegrates when maximum force is reached. Although the presence of
the fibers leads to a reduction of compression strength, it ensures a better behavior in the post-
peak zone, namely preventing its fragmentation.
0
10
20
30
40
50
0 2000 4000 6000 8000 10000
Strain (µm/m)
Stre
ss (M
Pa)
0
10
20
30
40
50
0 2000 4000 6000 8000 10000
Strain (µm/m)
Stre
ss (M
Pa)
Figure 6 – Stress strain diagrams of. premix GRC and of plain mortar.
4. TENSION BEHAVIOR
The tension behavior of GRC is one of the most important mechanical parameters when
considering its structural use. A large number of experimental tests was carried out to analyze
different aspects on tension behavior, such as production techniques, compositions,
continuous reinforcement or ageing.
The main set-up used to perform tension tests is showed in Fig. 7.
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Figure 7 – Tension tests set-up.
The test specimens were 30-35 cm long, with rectangular cross-section of 1 cm x 4-5 cm.
4.1 Spray-up GRC
The composition used in the spray-up GRC specimens was basically similar to that
referred in section 3.1. The different series are distinguished by the type (53/76 or 250/5),
quantity and length of dispersed fibers, the sand used (regular, sieved or siliceous), the type
(or absence) of continuous reinforcement and the previously accelerated ageing. Within each
series all the specimens have identical characteristics. The series were divided in four groups,
being the first made of plain GRC specimens, the second with carbon tendons reinforcement,
the third presenting glass-fiber tendons and, the last, made of specimens previously subjected
to accelerated ageing by immersion in hot water. Tables 3 to 6 present a description of each
series within each group.
Series Nº spec. Description 1 10 5.2% fiber 53/76, 63 mm long (non sieved sand) 2 10 4.0% fiber 53/76, 31 mm long (non sieved sand) 3 10 4.4% fiber 53/76, 31 mm long (non sieved sand) 4 10 4.6% fiber 53/76, 63 mm long (non sieved sand) 5 5 5.0% fiber 53/76, 31 mm long (non sieved sand) 6 5 5.0% fiber 53/76, 63 mm long (non sieved sand) 7 5 4.0% fiber 53/76, 63 mm long (non sieved sand) 8 5 4.0% fiber 53/76, 31 mm long (non sieved sand) 9 10 5.0% fiber 53/76, 31 mm long (sieve 0.6 mm)
10 10 5.0% fiber 53/76, 31 mm long (sieve 0.3 mm) 11 10 5.0% fiber 250/5, 31 mm long (sieve 0.6 mm) 12 10 5.0% fiber 250/5, 31 mm long (sieve 0.3 mm)
Table 3 – Series of plain spray-up GRC specimens.
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Series Nº spec. Description
13 15 5% fiber 250/5, 31 mm long, inox grid, 1 longitudinal carbon tendon (sieve 0.6 mm)
14 10 5% fiber 250/5, 31 mm long, inox grid, 1 longitudinal carbon tendon (sieve 0.3 mm)
15 9 5% fiber 250/5, 31mm long, wet carbon fiber at 45º (sieve 0.6 mm) 16 10 5% fiber 250/5, 31mm long, 4 wet sinusoidal carbon tendons (sieve 0.6mm) 17 9 5% fiber 250/5, 31mm long, 5 longitudinal wet twisted tendons (sieve 0.6mm)
18 11 5% fiber 250/5, 31mm, inox grid, 3 longitudinal wet twisted tendons (siliceous sand)
19 9 5% fiber 250/5, 31mm long, 3 wet sinusoidal carbon tendons (siliceous sand)
20 10 5% fiber 250/5, 31mm long, 3 longitudinal wet twisted carbon tendons with knots every 5 cm (siliceous sand)
Table 4 – Series of spray-up GRC specimens with carbon fiber tendons reinforcement.
Series Nº spec. Description 21 5 4% fiber 53/76, 31 mm long, 1 longitudinal fiber tendon (non sieved sand)
22 11 5% fiber 250/5, 31mm long, inox grid, 3 longitudinal wet twisted glass fiber tendons (siliceous sand)
23 10 5% fiber 250/5, 31mm long, 3 wet sinusoidal glass fiber tendons (siliceous sand)
24 10 5% fiber 250/5, 31mm long, 3 longitudinal wet twisted glass tendons with knots every 5 cm (siliceous sand)
Table 5 – Series of spray-up GRC specimens with glass-fiber tendons reinforcement.
Series Nº spec. Description
25 5 5% fiber 250/5, 31 mm long, inox grid, 1 longitudinal carbon tendon (sieve 0.6 mm)
26 5 5% fiber 250/5, 31 mm long, inox grid, 1 longitudinal carbon tendon (sieve 0.3 mm)
27 5 5% fiber 250/5, 31 mm long (sieve 0.6 mm) 28 5 5% fiber 250/5, 31 mm long (sieve 0.3 mm) 29 5 5% fiber 53/76, 31 mm long (sieve 0.6 mm) 30 5 5% fiber 53/76, 31 mm long (sieve 0.3 mm)
Table 6 – Series of spray-up GRC specimens subjected to accelerated ageing.
To analyze continuous reinforcing tendons, different patterns were considered, as
indicated in the previous tables, attempting to achieve optimized adherence to the matrix.
“Sinusoidal” layout indicates a longitudinal pattern where the same tendon passes different
times along the length of the specimen, without being cut at its ends. When “fiber at 45º” is
indicated, the tendons are positioned obliquely to the longitudinal axes. This patterns are
illustrated in Fig. 8.
“Sinusoidal” pattern
“Fiber at 45º” pattern
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Figure 8 – Patterns of continuous reinforcement.
The artificial ageing process consisted of submerging the specimens in 75 ºC water
during 17 days, what corresponds, in accordance with [11], to 22 years of natural ageing.
Fig.s 9 to 12 show the average and characteristic values of tension strength obtained for
each tested series.
0
2
4
6
8
10
12
Serie
s 1
Serie
s 2
Serie
s 3
Serie
s 4
Serie
s 5
Serie
s 6
Serie
s 7
Serie
s 8
Serie
s 9
Serie
s 10
Serie
s 11
Serie
s 12
Tens
ion
stre
ngth
(MPa
)
Average value Charact. value
Figure 9 – Tension test results. Plain spray-up GRC.
024
68
1012
14
1618
Serie
s 11
Serie
s 12
Serie
s 13
Serie
s 14
Serie
s 15
Serie
s 16
Serie
s 17
Serie
s 18
Serie
s 19
Serie
s 20
Tens
ion
stre
ngth
(MPa
)
Average value Charact. value
Figure 10 – Tension test results. Spray-up GRC with carbon fiber reinforcement.
0
2
4
6
8
10
12
14
Serie
s 2
Serie
s 11
Serie
s 12
Serie
s 18
Serie
s 20
Serie
s 21
Serie
s 22
Serie
s 23
Serie
s 24
Tens
ion
stre
ngth
(MPa
)
Average value Charact. value
Figure 11 – Tension test results. Spray-up GRC with glass fiber reinforcement.
12
0
2
4
6
8
10
12
Serie
s 9
Serie
s 10
Serie
s 11
Serie
s 12
Serie
s 13
Serie
s 14
Serie
s 25
Serie
s 26
Serie
s 27
Serie
s 28
Serie
s 29
Serie
s 30
Tens
ion
stre
ngth
(MPa
)
Average value Charact. value
Figure 12 – Tension test results. Accelerated aged spray-up GRC.
These figures show that the use of carbon tendons increases the tension strength of the
specimens, although its effectiveness depends on the anchor type. The sinusoidal pattern
proved to be the best anchoring system, followed in sequence by the simple longitudinal
layout, the knot arrangement and the 45º pattern. Twisting the tendons didn’t lead to
noticeable increase of the strength. The total strength of the carbon tendons was never
completely mobilized. The inox grid used in various series didn’t show practically any effect
because its intrinsic strength was not significant. Tension strength is not clearly affected by
the type of dispersed glass fibers. The use of glass-fiber tendons shows similar effects but is
less effective.
4.2 Premix GRC
The composition of premix specimens was similar to that referred in section 3.2, but with
a fiber incorporation of only 2,5%. This change proved to be necessary to increase the
workability and facilitate the fiber dispersion. The different series are distinguished by the
type (or absence) of continuous reinforcement.
In Table 7 the premix GRC series tested in tension are described.
13
Series Nº spec. Description 31 18 Plain GRC, cross-section 50mm x 15mm 32 14 Plain GRC, cross-section 40mm x 10mm 33 17 GRC with 1 carbon tendon, cross-section 50mm x 15mm 34 13 GRC with 1 carbon tendon, cross-section 40mm x 10mm 35 7 GRC with 1 carbon tendon and 1 φ3 mm steel bar, section 50mm x 15mm 36 16 GRC with 1 φ3 mm steel bar, cross-section 40mm x 10mm
Table 7 – Series of premix GRC specimens subjected to tension tests.
Fig. 13 show the average and characteristic values of tension strength obtained for the
various tested series.
0
2
4
6
8
Serie
s 31
Serie
s 32
Serie
s31
/32
Serie
s 33
Serie
s 34
Serie
s 35
Serie
s 36
Tens
ion
stre
ngth
(MPa
) Average value Charact. value
Figure 13 – Tension test results. Spray-up GRC with glass fiber reinforcement.
The analysis of the results shows that the continuous reinforcement increases the
specimens tension strength. Considering that the plain GRC tension strength value is not
changed by the presence of continuous reinforcement, the force exerted on these elements
was determined in each case. Based on such considerations it was concluded that the carbon
tendons are tensioned to 11%-13% of their capacity. In the case of steel bars this value is
worth 59%, in the series with carbon tendons, and of 29% without carbon. This phenomenon
is related to the reduced length of the specimens, that prevents the adequate anchoring of
continuous reinforcing elements. This fact is illustrated in Fig. 14, where the slip of this
elements is evident.
14
Figure 14 – Slipping of continuous reinforcing elements in GRC specimens.
5. CYCLIC BEHAVIOR
Different tests on GRC specimens were performed to characterize its cyclic behavior and
collect data to incorporate in numerical models to be developed for structural analysis. The
cyclic behavior is particularly important when considering the GRC structural use in seismic
zones or in windy areas.
The tested specimens were produced with premix GRC, being their composition equal to
tat referred in 4.2.
Fig.s 15 to 17 show the cyclic stress-strain diagrams obtained from rectangular specimens
tested under a cyclic increasing positive (“tension”) displacement history. In these figures,
together with the cyclic path, the curves respecting several monotonic tests under similar
specimens are presented.
-4.0
-2.0
0.0
2.0
4.0
6.0
0 1000 2000 3000 4000 5000 6000 7000 8000
Strain (µm/m)
Stre
ss (M
Pa)
Figure 15 – Cyclic test on plain GRC specimen.
15
-6.0
-4.0
-2.0
0.0
2.0
4.0
6.0
0 1000 2000 3000 4000 5000 6000 7000 8000
Strain (µm/m)
Stre
ss (M
Pa)
Figure 16 – Cyclic test on GRC specimen with 1 carbon tendon.
-12.0
-8.0
-4.0
0.0
4.0
8.0
12.0
0 5000 10000 15000 20000
Strain (µm/m)
Stre
ss (M
Pa)
Figure 17 – Cyclic test on GRC specimen with 1 carbon tendon and 1 φ3 mm steel bar.
The analysis of the results show that the stiffness gradually decreases along the test; the
cyclic diagrams of plain GRC and of GRC with 1 carbon tendon are approximately delimited
by the monotonic ones; the specimens with a steel bar show a more favorable behavior, with
higher stress values and an envelope diagram outside the monotonic lines.
Fig. 18 shows the cyclic stress-strain diagram obtained from a cylindrical specimen tested
under a cyclic increasing negative (“compression”) displacement history, together with curves
respecting monotonic tests under similar specimens.
16
05
1015
2025
3035
4045
0 2000 4000 6000 8000 10000
Strain (µm/m)
Stre
ss (M
Pa)
Figure 18 – Compressive cyclic test on GRC specimen.
The results obtained show the following aspects: the material stiffness in cyclic regimen,
because of damage accumulation, is greater than in monotonic tests; the monotonic diagrams
approximately envelope the cyclic path; the maximum cyclic strength was similar to the
monotonic one.
6. CREEP BEHAVIOR
Since some of the structural uses of GRC under development included pre-stressed
elements, an assessment of creep behavior was needed to evaluate long-term losses. Creep
tests were performed on 3 cylindrical specimens of spray-up GRC. To ensure the stability of
applied compressive stress, the specimens were subjected to a gravity load of 85 kN, as
shown in Fig. 19.
Figure 19 – Specimens subjected to creep test.
17
The specimens designated by S1 and S2 were loaded 8 days after casting. In the 28th day
the specimen S2 was substituted by specimen S3. The specimens deformations were
measured with strain gauges. Fig. 20 shows the tests results, where φ(t) represents the creep
coefficient (defined as the reason between creep and elastic strain). These results were
obtained considering the difference between the values measured on the tested specimens and
the average deformation of control unloaded specimens, kept under similar environment
conditions. This procedure aims to compensate the deformation components caused by
shrinkage and by atmosphere moisture.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0 20 40 60 80 100 120 140 160Age (days)
φ(t)
S1 S2 S3
Figure 20 – Creep tests results.
The creep coefficient values are comparable to those usually obtained in concrete.
7. CONCLUSIONS
The experimental test program carried out allowed the assessment of the main
mechanical parameters of GRC concerning its structural use. Though some indicative values
of the analyzed parameters are given in literature, the assessment of the GRC actually
produced was absolutely necessary, aiming an adequate control and knowledge of the
fabricated structural elements.
18
The GRC compositions of the tested specimens result from adjustments established in
fabrication tests, considering the actual production conditions and some specific structural
elements.
This study also provided important data respecting the effectiveness of continuous
elements reinforcement introduced in GRC.
Part of the experimental data obtained was later incorporated in numerical models to
analyze the structural behavior of the elements produced with GRC.
5. ACKNOWLEDGEMENTS
The authors wish to thank the financial support of the FCT (Fundação para a Ciência e
Tecnologia) and of the European Commission for the research developed within project
PRAXIS/P/ECM/14046/1998, “Betão Reforçado com Fibras de Vidro – Aplicações
Estruturais”.
6. REFERENCES
[1] Bentur, A., Mindess, S., “Fibre Reinforced Cementitious Composites”, (Elsevier
Applied Science, London 1990).
[2] “Cem-FIL GRC Technical Data”, Cem-FIL International Ltd, (Vetrotex, UK 1998).
[3] Ferreira, J., “Structural characterization of glass-fiber reinforced concrete (GRC).
Application to telecommunications towers”, available in Portuguese, PhD thesis,
(Instituto Superior Técnico, Lisbon 2002)
[4] Knowles, E., “Recommended Practice for Glass Fibre Reinforced Concrete Panels”,
PCI Committee on Glass Fibre Reinforced Concrete Panels, (PCI, USA 1987).
[5] Bijen, J., Jacobs, M., “Properties of Glass Fibre Reinforced Polymer-Modified
Cement”, Journal of Materials and Construction, Vol. 15, 1982.
19
[6] “Glass fiber reinforced cement”, Journal of Portuguese Producers of Precast Concrete
Products (anipc), (available in Portuguese),Year 2, nº 4, (anipc, Lisbon 1998) .
[7] Laboratório Nacional de Engenharia Civil (LNEC), “E397 standard - Assessment of
compressive Young modulus in concrete”, (available in Portuguese) (LNEC, Lisbon
1993).
[8] Laboratório Nacional de Engenharia Civil (LNEC), “E226 standard – Compression
tests in concrete”, (available in Portuguese) (LNEC, Lisbon 1993).
[9] “Concrete Core Testing for Strength”, Report of a Concrete Society Working Party,
Concrete Society Technical Report Nº 11, The Concrete Society, 1976.
[10] “Guide to Assessment of Concrete Strength in Existing Structures”, British Standards
Institution, BSI, BS 6089, (British Standards, UK1981).
[11] Litherland, K., Oakley, D., Proctor, B., “The Use of Accelerated Ageing Procedures to
Predict the Long Term Strength of GRC Composites”, Cement and Concrete
Research, Vol. 11, 1981.
[12] REBAP – Portuguese code for reinforced concrete structures, Decreto-Lei 349-C/83,
(available in Portuguese) (Imprensa Nacional Casa da Moeda, Lisbon 1986).
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BIOGRAPHIC NOTES
João Ferreira graduated in Civil Engineering and received his MASc and Ph.D. degrees at
IST - Technical University of Lisbon, Portugal, where he is an Assistant Professor. His
research work deals with new structural materials, steel structures, and experimental
assessment of structural behavior.
Fernando A. Branco is Full Professor of Civil Engineering at IST - Technical University of
Lisbon, Portugal. He is Vice-Chairman of the IABSE Technical Commission, Member of ACI
Committee Nº 342 on “Evaluation of Concrete Bridges” and member of the CSCE and
RILEM. His primary research interests deal with the behavior of bridges and other public
works.
