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Assessment of the residual expansion potential of concrete from structures damaged by AAR
Cement and Concrete Research 52 (2013) 182–189
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Assessment of the residual expansion potential of concrete from structures damaged by AAR Christine Merz a, Andreas Leemann b,⁎ a b
Holcim (Schweiz) AG, Würenlingen, Switzerland Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland
a r t i c l e
i n f o
Article history: Received 29 August 2012 Accepted 2 July 2013 Keywords: Alkali aggregate reaction (C) Residual expansion (C) Validation (E)
a b s t r a c t The determination of the residual expansion potential can provide important information on the prognosis of AAR in concrete structures. However, there are still uncertainties about the test protocol and data analysis. In this study, residual expansion of cores from several concrete structures damaged by AAR was measured. The expansion during the test can be divided into different phases with different expansion rates. The results indicate that the expansion in the first phase, that takes place after sample conditioning but before a linear expansion rate is reached, is specific for each concrete and proportional to the further expansion of the cores during the test. Therefore, it can be used to distinguish concrete with different residual expansion potentials. The residual expansion correlates both with the expansion rates on the investigated structures and the expansion of lab concrete, having a similar composition as the on-site concrete, determined with a concrete performance test. © 2013 Elsevier Ltd. All rights reserved.
1. Introduction In the assessment of structures damaged by alkali-aggregate reaction, the determination of the residual expansion potential of the concrete plays an important role. Compared to the on-site monitoring of damaged structures, the measurements permit a relatively fast assessment of the concrete's expansion potential in the future. In combination with data about temperature and moisture conditions of the structure, it may be used for modelling [1]. As such, it is an important tool to plan maintenance and costs involved. However, there are only few studies that deal with the subject up to date (eg. [2–4]). Consequently, several uncertainties still exist regarding both the methodical approach for such measurements and the data analysis. In most cases, residual expansions are measured under storage conditions of 38 °C and saturated air. But other tests, e.g. in water or NaOH solutions, are taken into consideration as well [5–8]. There is a consensus that the reaction should be accelerated by an increase in relative humidity and temperature. But the opinions diverge about which point in time during conditioning and later testing should be used as point zero and which phase of expansion is suitable to assess the residual expansion potential. Most of the published data of the residual expansion measured in saturated air and different temperatures show a similar pattern of the expansion with time. The pronounced expansion at the start of the test is interpreted as a result of moisture uptake. The initial expansion depends thus on the degree of water saturation of the cores, the swelling of already existing and newly formed reaction ⁎ Corresponding author. E-mail address: [email protected] (A. Leemann). 0008-8846/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.cemconres.2013.07.001
products. The asymptotic decrease of the expansion reached after several months is regarded as the end of the reaction phase [9,10]. Usually the leaching of alkalis from the specimens is mentioned as an explanation for this levelling off of the expansion curves. However, the analysis of literature data [10] shows that the expansion of cores from some structures does not cease but stays constant at a certain level even over years. Since the absolute expansion values can be very high, depending on the concrete measured and the duration of the test, the question arises if these late stage expansions should be taken into account for analysis. Another problem of the data analysis is the anisotropy between longitudinal and diametral expansions which has often been observed and analysed in detail [7,9,11]. In summary, there are several uncertainties in regard to the assessment of the residual expansion potential: • How do the different parameters like core size and temperature affect the measured expansions? • How should the different phases of expansion be taken into account? • Should an expansion gradient or an absolute expansion value at the end of the test be used as decisive parameter? • Has the test to be performed for a given time or until the expansion ceases? • What is the influence of alkali leaching? This study is part of a larger project aiming to validate different test methods used to assess AAR-risk. The starting point of the study was the selection of structures damaged by AAR. The selection is representative for the range of aggregates used in Switzerland. After determining the crack-index in different parts of the structures, cores were taken to
C. Merz, A. Leemann / Cement and Concrete Research 52 (2013) 182–189
determine the concrete properties and composition. Sources of the cement and aggregates used in the different structures were identified. Based on these results, the aggregates were tested with the ultraaccelerated microbar test according to AFNOR XP 18-594 [12] and expansions of concrete mixtures with a similar composition as the on-site concrete were determined using the concrete performance test according to AFNOR P18-454 [13]. Results about the validation of these two methods are published in [14,15]. The goals for the residual expansion potential measurements are an assessment of the influence of sample conditioning, sample size and storage temperature on the expansion. The results should allow identifying the decisive parameter permitting a prognosis of the future development of AAR in structures. Cores with a diameter of 50 and 100 mm were exposed to saturated air (N 95% RH) at 20 and 38 °C for a year. Expansion and mass change were monitored during this period. The results obtained in the residual expansion test were compared with the degree of damage observed on the structures and the expansion obtained with the concrete performance test (CPT) on concrete with a similar composition as the one present in the damaged structures. 2. Materials and methods 2.1. General Seven between 25 and 40 years old structures were selected from different parts of Switzerland [15], covering different geological settings and exhibiting damages due to AAR with the exception of structure GU which was selected as a reference for an undamaged on-site concrete (Table 1). The structures include four bridges, two supporting walls and one dam. Cores taken both in strongly and weakly damaged areas were prepared for the residual expansion measurements. The samples chosen for the residual expansion measurements contained no major cracks and originated from a depth N 10 cm, because the alkali level in the surface area of the concrete might be reduced due to leaching and therefore not be representative for the structure. The orientation of the cores in relation to the casting direction can significantly influence the expansion [8,11]. Therefore, all cores were taken in the horizontal direction, perpendicular to the casting direction. The stress state of the concrete at the coring site can have an effect on the following expansion and has to be taken into account when the determined values are used for modelling [1,16,17]. The cores were taken from the abutment in case of the bridges, from the medium height of one supporting wall and from the upper part of the other supporting wall and the dam. Crack width measurements on the on-site concrete were conducted according to the method presented in [18].
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After cutting them to a length of 200 mm, the samples were equipped with pins glued into predrilled holes with a depth of about 4 mm. The attached pins permit diametral and longitudinal measurements on the cores (Fig. 1). 2.2.2. Residual expansion potential The residual expansion potential was measured on two series of three cores with a diameter of 50 (20 and 38 °C) and one series of three cores with a diameter of 100 mm (38 °C). The cores stored in the reactor at 38 °C were wrapped in a plastic film because experience shows that it is difficult to avoid mass loss even in a reactor with N95% RH. This measure possibly offers some protection against leaching of alkalis. The series of three samples with a diameter of 50 mm and a length of 200 mm were stored at a temperature of 20 °C and N95% RH according to the method described by Wood [4]. Mass changes, diametral and longitudinal expansions of the all cores were monitored for at least one year (measurements every 4 weeks at 20 °C). The ratio between core diameter and maximum aggregate size can have an impact on the measured expansion [19]. However, the amount of reinforcement present in the structures and restrictions from the owner of the structures led to the choice of the 50 and 100 mm core diameters. In principle, the expansion of the cores tested at 38 °C (similar to protocol in [20]) can be divided into three different phases (Fig. 2): • Phase 1: The initial measurements of dimension and mass were done before the samples were conditioned at 20 °C in containers with a thin layer of water at the bottom of the container, permitting capillary suction until reaching constant mass (usually after one or two weeks). The water saturation is accompanied with a first swelling of the samples. • Phase 2: The cores were stored in the reactor at 38 °C, respectively at 20 °C with N95% RH. During 30–60 days at the beginning of phase 2 a strong but quickly levelling off expansion could be observed. In the following, it will be designated as “non-linear expansion at the beginning of phase 2”. Afterwards, the expansion rate is constant, in certain cases also levels off. This part of the expansion is designated as “linear expansion during phase 2”. • Phase 3: After removing the cores from their containers, they were dried at 60–70% RH to their initial weight (at the start of conditioning) and the final “irreversible” expansion is measured. This step takes 2–8 weeks. 2.2.3. Alkali content The water-soluble and the acid-soluble alkali content of the concretes GU and MB were measured before and after the residual expansion test according to the method described in [8].
2.2. Methods for assessment and analysis 2.2.1. Sample preparation Immediately after coring, the samples were welded into plastic bags to prevent moisture loss during the transport to the laboratory.
2.2.4. Crack-index The width of the cracks present on the surface of the concrete structures was determined according to [18]. A square with a side length of 1 m was drawn on the concrete surface. The crack width
Table 1 Location, type and abbreviated name of the investigated structures with a simplified petrography of the aggregates (n.a. = not analysed, aggregate Ømax = maximum grain size used in structure). Location, type of structure, year of construction
Cement content [kg/m3]
w/c
Aggr. Ømax [mm]
Label of aggr. and structure
Present rock types (in order of decreasing amount)
Wangen, viaduct, 1977 Mattsand, dam, 1963 Ganter, bridge, 1980 Bornisses, supporting wall, 1967–68 Rorbach, bridge, 1982–83
325–350 400 400 400
0.45–0.50 0.45–0.50 0.40–0.45 0.45–0.50
32 60 16 32
GU MS MB VI
350–400
0.45–0.50
20
UR
Mels, viaduct, 1969 Mur 10, supporting wall, 1980
300–350 400
0.45 0.43–0.45
20 32
MF ME
Sandstone, quartzite, gneiss, siliceous limestone, limestone Gneiss Gneiss, schists, amphibolites, quartzites Limestone with detritic quartz, siliceous limestone, gneiss, quartz, limestone, schist Gneiss, siliceous limestone, sandstone, schist, limestone with detritic quartz, quartzite Limestone with detritic quartz, sandstone, gneiss, quartzite, schist, granophyr Limestone with detritic quartz, siliceous limestone, limestone, sandstone, gneiss, quartzite, silex
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cores Ø100 mm, 38°C, longitudinal MF GU ME UR MB
expansion [mm/m]
0.8
0.6
0.4
0.2
phase 2
0 0
50
100
150
200
250
300
350
time [day] Fig. 3. Total expansion (average longitudinal measurements, storage at 38 °C) of field concrete from five structures, without phase 3 (drying).
was measured along two sides of the square and the two diagonals using a magnifier with scale (resolution: 0.05 mm). The crack-index was calculated as width of cracks per measured length. The crack width does not take into account the expansion taking place before the cracking occurred. Moreover, there are additional factors like curing conditions, shrinkage and temperature at the time when the measurements are conducted that can affect the crack index. Even with these restrictions, the crack widths measured in strongly-damaged parts of AAR-affected structures are regarded as meaningful values to characterise concrete expansion [3,21]. 3. Results 3.1. Phase 1: conditioning of the samples — water saturation The mass increase during conditioning is between 0.2 and 2.8 mass-%. The samples swell with increasing water saturation. The expansions of the different cores during phase 1 are not proportional to the following expansions during the storage in the reactor, as i.e. shown by the non-linear expansion at the beginning of phase 2 (Figs. 3 and 4). 3.2. Phase 2: non-linear and linear expansions Fig. 1. The longitudinal expansion has been measured on the length axis between two metallic pins fixed with glue in boreholes. The diametral expansion has been measured at two positions perpendicular to the length axis of the cores.
The extent and the duration of the non-linear expansion at the beginning of phase 2 vary between the different concretes (Fig. 3). This
non linear expansion [mm/m]
1.00
0.2
expansion [mm/m]
diametral expansion longitudinal expansion
0.15
0.1
0.05
0 0
100
nonlinear conditioning expansion phase 1
phase2
time[d] 200 linear expansion phase2
300 irreversible expansion phase 3
Fig. 2. Different phases of expansion during the residual expansion measurements in longitudinal and diametral directions of cores.
0.90
diametral at 38°C diametral at 20°C
longitudinal at 38°C longitudinal at 20°C
0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
expansion due to water absorption [mm/m] Fig. 4. Non-linear expansion at the beginning of phase 2 versus the expansion due to water adsorption during conditioning of the samples (phase 1).
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2.0
diametral, D= 100mm at 38°C
0.80
longitudinal , D=100mm at 38°C
0.60
diametral, D = 50mm at 38°C
0.40
0.20
0.00 0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
longitudinal ,D= 50mm at 38°C
1.6 1.4
1.0
0.6 0.4
3.3. Phase 3: irreversible expansion
non linear expansion rate [mm/m/year]
The irreversible expansion (Fig. 2) is measured after drying the cores to their initial mass (mass before the start of conditioning). It varies depending on the measurement direction (longitudinal or diametral) and the diameter of the samples (Fig. 6). The highest values are obtained diametrically on the cores with a diameter of 50 mm stored at 38 °C (1.5 mm/m). The irreversible expansion also depends on the duration of the storage, especially if the linear expansion
diametral, D = 100mm at 38°C lengthwise, D = 100mm at 38°C diametral, D = 50mm at 38°C lengthwise, D = 50mm at 38°C
6.0
diametral, D = 100mm at 20°C
4.0
lengthwise, D = 100mm at 20°C
2.0
0.0
diametral, D = 50mm at 20°C 0.0
0.4
0.8
1.2
1.6
2.0
total, longitudinal at 38°C
0.2 0.0 0.0
0.5
1.0
1.5
2.0
lengthwise, D = 50mm at 20°C
irreversible expansion [mm/m]
Fig. 7. Expansion during phase 2 (linear and non linear) and total expansion versus irreversible expansion at the end of phase 3 of 100 mm cores.
rates are high and not levelling off during phase 2 (i.e. structure MB, Fig. 3). Total expansion (phase 1 and phase 2) is higher than the irreversible expansion while the expansion during phase 2 is lower than the irreversible expansion (Fig. 7). Obviously, a part of the expansion during conditioning (phase 1) is irreversible since otherwise the irreversible expansion would be identical with the expansion obtained during phase 2. 3.4. Comparison of the samples with diameters 50 mm and 100 mm The non-linear diametral expansions at a core diameter of 50 mm at the beginning of phase 2 are clearly higher than those of the cores with a diameter of 100 mm (Figs. 5 and 8). Only the longitudinal non-linear expansion rates are comparable. As shown in Fig. 5, the linear expansion rates of the 50 mm cores level off in comparison to those of the 100 mm cores. Therefore, as shown in Fig. 8, the diametral expansions of the 50 mm cores increase clearly less than those of the 100 mm cores. The longitudinal expansions even stay constant at 0.4 mm/m. 3.5. Comparison of the storage temperatures 20 °C and 38 °C The irreversible longitudinal expansion of the cores with a diameter of 50 mm is 1.2 to 4 times larger and the diametral expansions 1.6 to 2.5 times larger at 38 °C than at 20 °C (Fig. 9). The linear expansion rates
expansion of cores with D=50mm [mm/m]
non-linear expansion is proportional to the following linear expansion (Fig. 5) and the irreversible expansion (Fig. 6). This also applies to the samples stored at 20 °C (data not shown). The expansion of the cores is relatively small with the exception of the cores from structure MB. But even taking into account the standard deviation, the expansion obtained from the cores of the different structures can be clearly distinguished. The diametral non-linear expansion rates of the cores with a diameter of 50 mm are clearly higher than those of the cores with a diameter of 100 mm, while the diametral linear expansion rates are similar for both core diameters (Fig. 5). The longer the phase 2 is, the larger the resulting expansions during this period are. During this phase, the samples show no significant mass changes (b0.2 mass-%). None of the 100 mm cores shows a levelling off of the expansion until the end of the test after one year.
8.0
total, diametral at 38°C
0.8
irreversible expansion [mm/m]
Fig. 5. Linear expansion rates versus non-linear expansion rates at the beginning of phase 2 (storage at 38 °C). Correlation coefficients R2 of linear regression following the order of the legend are 0.72, 0.79, 0.23 and 0.90.
10.0
phase 2, longitudinal at 38°C
1.2
non linear expansion rate [mm/m/year]
12.0
phase 2, diametral at 38°C
1.8
expansion [mm/m]
linear expansion rate [mm/m/year]
1.00
185
irreversible expansion diametral total expansion diametral
2.0 1.8 1.6 1.4
phase 2, diametral
1.2 1.0
irreversible expansion longitudinal total expansion longitudinal
0.8 0.6 0.4 0.2 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
phase 2, longitudinal
expansion of cores with D = 100mm [mm/m] Fig. 6. Non-linear expansion rates versus irreversible expansion of cores with diameters of 50 and 100 mm stored at 20 °C and 38 °C. Circle: samples of structure MB.
Fig. 8. Expansion of 50 mm cores versus expansion of 100 mm cores at 38 °C.
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irreversible expansion[mm/m]
186
0.4
0.3 structure MS
0.2
structure MF structure GU structure VI
0.1
structure ME structure UR
0.0 0.0
0.2
0.4
0.6
0.8
1.0
expansion CPT[mm/m] Fig. 11. Irreversible expansion (longitudinal, samples with D = 100 mm stored at 38 °C) versus the expansion reached at the end of the concrete performance test of the field concrete reproduced in the laboratory. Fig. 9. Expansion rates at 20 °C and versus expansion rates at 38 °C of 50 mm cores.
are comparable as well diametrically and longitudinally at both storage temperatures. However, the non-linear expansion rates are clearly higher at 38 °C (diametral 2.1–3.5 times; longitudinal 2.3–3.8 times). 3.6. Anisotropy of the expansions There is a systematic difference between the diametral and longitudinal expansions (Figs. 4–6). The ratios of diametral/longitudinal expansions (calculated over the full duration of phase 2) are always higher than 1 and vary at 38 °C from 0.9 to 2.5 for the 100 mm cores and from 1.7 to 3.7 for the 50 mm cores. The ratio is even higher for the 50 mm cores at 20 °C with values of 2.3 to 4.5. For the non-linear expansion rates at 38 °C, the diametral/longitudinal ratios range from 1.3 to 2.7 for the 100 mm cores and from 2.9 to 4.4 for the 50 mm cores. The highest ratios were measured again on the 50 mm cores at 20 °C, namely from 2.8 to 6.1 (Fig. 10). The anisotropy is observed during the entire duration of the storage. The diametral/longitudinal ratios of the non-linear expansion rates are comparable with the ratio of the irreversible expansions at the end of the test with a few exceptions. The anisotropy is higher in the 50 mm cores and at 20 °C compared to 38 °C (Fig. 10). 3.7. Comparison with the field concrete The irreversible expansions of the reactive concretes correlate well with the expansion of the prisms of the reproduced field concretes D=100mm at 38°C
D=50mm at 38°C
D= 50mm at 20°C
D=100mm at 20°C
7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0
3.8. Alkali leaching As the water-soluble alkalis represent the amount of alkalis present in the pore solution, differences before and after the test should be caused by leaching and chemical binding in reaction products. As the acid dissolves the hydrates thereby releasing the bound alkalis, differences before and after the test can be attributed to leaching. Usually, the acid-soluble alkali contents of most Swiss field concretes are between 0.1 and 0.2 mass-% Na2Oeq. However, concrete with aggregates containing micas and feldspar can reach up to 0.4 mass-% Na2Oeq. There are differences in the alkali contents of the selected two structures before and after the test. The analysis of the alkali contents at the end of the test (335 days) showed no changes of the water-soluble alkali (0.05 mass-% Na2Oeq) and acidsoluble alkali contents (0.12 mass-% Na2Oeq) for 100 mm cores from the structure GU (the non-reactive reference concrete). On the other hand, the analysis of samples from structure MB after 492 days of storage showed a decrease of 0.09 mass-% acid-soluble Na2Oeq (initial value: 0.41 mass-% Na2Oeq) and of 0.03 mass-% water-soluble Na2Oeq
irreversible expansion[mm/m]
ratio diametral/longitudinal of irreversible expansion
8.0
after 5 months of the concrete performance test (Fig. 11). The longitudinal expansions of the 100 mm cores were used for the comparison as only longitudinal expansions are measured in the concrete performance test. The higher storage temperature of 60 °C instead of 38 °C leads to up to 2.5 times greater expansions. The expansions measured so far on the 30 to 40 year old buildings (crack indices) are clearly larger than the irreversible expansion that could be measured in the laboratory (Fig. 12). Only structure MB differs clearly from the other structures.
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
ratio diametral/longitudinal of non linear expansion rate
0.7 0.6 0.5 0.4 0.3 structure MS structure GU structure ME structure MB
0.2 0.1
structure MF structure VI structure UR
0.0 0.0
1.0
2.0
3.0
4.0
5.0
crack index structure [mm/m] Fig. 10. Diametral/longitudinal-ratios of the irreversible expansion versus diametral/ longitudinal-ratios of the non-linear expansion rates at the beginning of phase 2 of 50 and 100 mm cores stored at 20 °C and 38°.
Fig. 12. Irreversible expansion (longitudinal, samples with D = 100 mm at 38 °C storage temperature) versus the crack index measured on the structures.
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(initial value: 0.13 mass-% Na2Oeq) for the 100 mm cores. The decrease of the 50 mm cores was greater with 0.17 mass-% acid-soluble Na2Oeq and 0.07 water-soluble mass-% Na2Oeq. 4. Discussion 4.1. Expansion during phase 1 The comparison between the expansion in phases 1 and 2 with the irreversible expansion shows that the expansion in phase 1 attributed to the increasing water saturation is not completely reversible. This indicates that reversible hygroscopic swelling in this phase is overlapping with an AAR induced expansion. Drying to the initial mass of the concrete allows determining this irreversible part of the swelling. However, expansion not caused by the swelling of newly formed reaction products within existing cracks but by the formation of new cracks is not or only partly reversible by drying. The good correlation between the expansion during phase 2 and the irreversible expansion indicates that this effect is minor in the analysed cores but it may have to be taken into account when assessing cores from other structures. 4.2. Expansion during phase 2 The following phase 2 is divided in a phase of non-linear expansion followed by a stable state of linear expansion with lower gradient. In contrast to the s-shaped expansion curve observed in structures, the cores lack an induction period as ASR is already progressing. The expansion of the cores from structure ME during phase 2 is in the same range as the one of the cores from structure GU, which shows no AAR related damage. Obviously, there is very little expansion potential left in structure MF. The expansion of the cores from the structures UR and MF indicates a higher residual expansion potential and the one obtained with the cores from structure MB indicates a considerably higher compared to the non-reactive reference structure GU. The non-linear expansion rate at the beginning of phase 2 is larger than the following linear expansion and additionally depends on the temperature. This could be an effect on the importance of dissolution and diffusion at different temperatures. The fact that AAR proceeds relatively fast with easily dissolvable aggregates as chert and relatively slow with quartz indicates that dissolution is the limiting factor of the reaction at ambient temperature. However, the dissolution rate of silica is increased by a factor of about 7 by a temperature increase from 20 to 38 °C [22] and silica solubility by a factor of about 1.4 [23]. If the dissolution rate of quartz is the limiting factor of reaction at 20 °C, this situation is possibly changed by the temperature increase to 38 °C. At a given pH and availability of alkalis and calcium within reactive aggregates, AAR is accelerated first during the temperature change from 20 to 38 °C. After this initial acceleration, the reaction might be slowed down as the consumed hydroxides, alkali and calcium ions have to diffuse into the aggregate again to sustain the reaction. The increase of the diffusion rate of ions in cement paste increases by a factor of about 1.8 going from 20 to 38 °C [24] which is significantly less than the dissolution rate of silica. Even if the data about dissolution rates and solubility of silica were not determined in a high pH environment, this still may indicate that the transition from the non-linear to the linear expansion is caused by the change from a solubility-limited system to a system governed by diffusion. Anyway, the characteristic expansion starts immediately after exposing the cores to elevated temperature [9] and reaches a concretespecific extent. Comparing cores of different structures, the extent of this expansion is not proportional to the swelling during phase 1. Both, the non-linear expansion and the linear expansion characterise the behaviour of the concrete of a specific structure as they correlate
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linearly for a given core size, storage temperature and test duration (Figs. 5–7). The 100 mm cores of the investigated concrete structures still expand at the end of the test after one year. Therefore, the question arises if the measured expansion in such cases mirrors the residual expansion or only shows the expansion rate under the test conditions. The comparison between the expansion determined in the test and expansion in the structures can give indications on the answer. 4.3. Irreversible expansion The irreversible expansion after one year shows a correlation to the crack-index determined in strongly damaged areas of the investigated structures (Fig. 12). This shows that the expansion rate in the structures is mirrored in the expansion rate in the residual expansion test. This correlation is made possible, because the investigated structures have a similar age. Even if the final expansion is not reached in the residual expansion test, it gives information about the expansion rate relative to other tested cores from other structures. However, long time experience with the CPT shows that in this particular test the expansion rate during the first four weeks and as such the kinetics of the reaction are related to the final expansion at the end of the test when the expansion rates have decreased significantly compared to the first four weeks. If a similar relation exists in the residual expansion potential test, then the irreversible expansion and with it the non-linear and linear expansions could be used as relative value for the final expansion of the concrete. The only exception showing no correlation between irreversible expansion and crack-index is structure MB that shows little cracking on-site but the highest expansions in the residual expansion tests. In fact, the areas of the bridge that were accessible for taking the cores showed considerable less cracking than other parts of the structures that were not accessible either due to logistic reasons or because of the presence of pre-stressed cables. As such, the crack-index used may not be representative for a strongly damaged part of the structure as it is the case in all other investigated structures. 4.4. Anisotropy of the expansion The anisotropy of the expansion, diametral versus longitudinal, stays constant during the different phases of the test. This has been observed and discussed in various studies [7,9,11]. The anisotropy seems to depend not only on sample shape (diameter, diameter/ length-ratio) but also on the testing conditions. Within a given test arrangement, the ratios of the diametral and longitudinal expansions are constant. Accordingly, constant ratios of 1.3–2.8 with high correlation coefficients are found by [8] at test temperatures of 23 and 38 °C. The phase of the linear expansions is reached simultaneously diametrically and longitudinally. Multon [7] observed ratios of 1.4, 1.9 and 2.2 depending on the storage (saturated air, water storage, sealing with aluminium). This anisotropy could be partly an effect of the moisture profile in the test specimens. In the CPT conducted with concrete having w/c-ratios of 0.30, 0.45 and 0.60, the relative humidity in the outer 25 mm of the specimens is between 1 and 6% higher than in their interior [25]. If this applies as well for the cores in the residual expansion potential test, the outer parts of the cores would have more favourable conditions for AAR and expand more. When the outer areas of a core expand more than the interior areas, anisotropic expansion results. In the present study the longitudinal expansion (meaning perpendicular to the filling direction) is only little influenced by the diameter of the sample while the diametral expansion (parallel to the filling direction) is clearly influenced by the core diameter. For 100 mm cores, the anisotropy seems to decrease with increasing expansion rates. It has been suggested that anisotropy in the microstructure due to segregation and a preferred orientation of flaky aggregates
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could be the reason for the anisotropy of the expansion of cores taken perpendicular to the filling direction [9,11,26]. In the on-site concrete studied, there were flaky and non-flaky aggregates present depending on the specific structure, but the anisotropy was always in the same range independent of aggregate shape (Fig. 10). Consequently, the effect of flaky grains and filling direction on the anisotropy cannot be confirmed. As the longitudinal expansion shows no or little effect of core diameter, it is reasonable to take it as the decisive parameter for assessing the residual expansion. 4.5. Assessing the residual expansion potential In order to assess the expansion rate of a particular concrete, both the non-linear expansion and the linear expansion can be used. Such an assessment is possible within a few month of running the residual expansion test. However, if the expansion rate during the linear expansion in phase 2 is not decreasing, the test duration should be at least a year. However, at a very long test duration alkali leaching may become a problem as discussed below. There are examples of strongly damaged structures that show only minor length changes in the residual expansion test because they indeed have reached the end of the reaction [8/unpublished data, C. Merz]. It has to be pointed out that even concrete with non-reactive aggregates expands in the test although at a much lower rate than concrete with reactive aggregates [10]. Consequently, some of the recorded expansion is not attributable to AAR. The reactive concrete mixtures differ from the non-reactive concretes by a higher non-linear and linear expansion rate. This is confirmed by the present observations. The correlation between the crack index, the irreversible expansion and the expansion in the CPT performed on concrete with a similar composition as the on-site concrete shows the close relation between the structures and the two laboratory tests (Figs. 11 and 12). The expansion of the 50 mm cores levels off more during phase 2 than the one of the 100 mm cores. The likely reason for the slowing down of the reaction is the leaching of alkalis leading to a decrease of the alkalinity of the pore solution, as observed as well in [5]. The leaching of alkalis has two consequences. Firstly, the duration of the residual expansion measurements cannot be extended for years as the decrease of the expansion will not be caused by an exhaustion of the expansion potential per se but by leaching. As the 100 mm cores show no decrease of the expansion gradient, it seems safe to use this diameter for test durations of one year. The diameter of the cores has to be as large as possible, as large cores have a smaller surface/volume-ratio compared to smaller ones, decreasing the effect of leaching. The effect of core size on leaching is confirmed in the case of structure MB. The cores of structure GU showed no such effect but at considerably lower alkali levels in the concrete possibly limiting the effect of leaching. The degree of reinforcement present in the investigated structures did not permit to take cores of a diameter larger than 100 mm. However, in structures with no or little reinforcement it would be beneficial to increase the diameter to 150 mm. However, not the entire differences in expansion of the differently sized cores may be attributable to leaching. The size of the specimens can directly affect the measured expansion as well, where increasing expansion is measured with increasing specimen size. This scale effect has been demonstrated by Gao et al. [19] using mortar prisms of various sizes immersed in alkaline solutions. Consequently, it does not seem reasonable to directly transfer expansion measured on cores to structures. In the case of concrete showing an unusually high linear expansion rate in relation to their non-linear expansion rate, it cannot be excluded that the reaction might be enhanced by an internal alkali source [27] as it could be the case for structure MB. The aggregates in structure MB consist of gneiss that contains heavily altered feldspars as possible source for alkalis.
If the cores do not expand or stop expanding during the test, it clearly shows that the concrete has reached its expansion potential or is close to reaching it. If the cores are still expanding at the end of the test, further expansion and damages of the structure have to be expected. The expansions reached in the residual expansion test likely represent maximum values as the temperature and RH during the test are more favourable for AAR than the conditions generally present in structures. Because various factors influence the measured expansions, like location and orientation of the cores in the structure, the stress and moisture state of the concrete at these locations and the uncertainties in testing as discussed above, care is advisable when expansion values are transferred to a structure or used for modelling. At the current state of knowledge, the residual expansion potential can be used to qualitatively compare different structures or different components of the same structure. An expansion rate derived from the crack index and the age of the structure can further help to assess the results of the residual expansion test. However, if more accurate data are needed, longtime monitoring is recommended [21,28]. It is moreover clear that more data are needed from a variety of structures to improve the data base and with it the interpretation of the measured expansion values. 5. Conclusions The residual expansion potential of cores with diameters of 50 and 100 mm taken from structures damaged by AAR was determined. The determined expansions during the different phases were compared and discussed to improve and confirm the methodical approach. Additionally, the results were compared with the crack-index of strongly damaged parts of the investigated structures and with the expansion of concrete, having a similar composition as the on-site concrete, determined with the CPT to further assess the significance of the residual expansion test. The following conclusions can be drawn in regard to the different expansion phases: • The expansion during the water saturation of the samples (phase 1) is partially irreversible indicating AAR-induced expansion in addition to expansion caused by moisture uptake. • The non-linear expansion (rate and duration) after the water saturation and at the beginning of the storage is specific for each concrete and depends on the temperature condition. It influences the following linear expansion rates, respectively the irreversible expansion reached at the end of the test. Additionally, it correlates with the expansion obtained in the concrete performance tests. • The following linear expansion rate of the samples is independent of temperature and sample diameter, but it levels off rapidly for small samples likely due to alkali leaching. High linear expansion rates indicate the presence of an internal source of alkalis in the concrete. • The irreversible expansion is determined by drying the cores back to their initial mass at the start of phase 1. It includes the part of the expansion reached during phase 1 which is not caused by the increase of water saturation but likely by AAR and the expansion during phase 2. The following recommendations for conducting the residual expansion potential test can be given: • During the non-linear expansion phase, the longitudinal expansions are independent of the core diameter in contrast to the diametral expansion. Therefore, it is recommended to use the longitudinal expansion for assessing the residual expansion potential. • Cores with a large diameter are less prone to alkali leaching. Therefore, 100 mm cores are better suited for the residual expansion test than 50 mm cores. A core length of 200 mm has proven to provide the needed accuracy in the length measurements and to be easy enough to handle in the laboratory.
C. Merz, A. Leemann / Cement and Concrete Research 52 (2013) 182–189
• Expansion rates are faster at a temperature of 38 °C compared to 20 °C. As results are obtainable within a shorter time period, a temperature of 38 °C is recommended. Different parameters permit to assess expansion rates and the residual expansion potential: • Both the non-linear and the linear expansion during phase 2 permit an assessment of expansion rate of a specific concrete if the latter shows no levelling off. • It is preferable to use the expansion during phase 2 for assessing the residual expansion potential. • If the expansion of the 100 mm cores levels off before the end of the test after one year, the expansion potential is exhausted and the measured expansion represents the residual expansion potential of a specific concrete. If this happens with 50 mm cores it can either be caused by leaching or by the exhaustion of the expansion potential. The residual expansion potential is a valuable tool to assess the further development of AAR in a structure. However, more data are needed to support the conclusions of this study. Acknowledgement The Federal Road Authorities of Switzerland (ASTRA) are acknowledged for the financial support of the project and P. Lura for the critical review of the manuscript. References [1] S. Multon, J.F. Seignol, F. Toutlemonde, Chemomechanical assessment of beams damaged by alkali–silica reaction, J. Mater. Civ. Eng. 18 (2006) 500–509. [2] M.A. Bérubé, J. Frenette, A. Pedneault, M. Rivest, Laboratory assessment of the potential rate of ASR expansion of field concrete, in: M.A. Bérubé, B. Fournier, B. Durand (Eds.), Proceedings of the 11th ICAAR, Québec, Canada, 2000, pp. 821–830. [3] B. Godart, B. Mahut, P. Fasseu, M. Michel, The guide for aiding to the management of structures damaged by concrete expansion in France, in: M. Tang, M. Deng (Eds.), Proceedings of the 12th ICAAR, Beijing, China, 2004, pp. 1219–1228. [4] J.G.M. Wood, When does AAR stop: in the laboratory and in the field? in: M. Tang, M. Deng (Eds.), Proceedings of the 12th ICAAR, Beijing, China, 2004, pp. 1016–1024. [5] M.A. Bérubé, N. Smaoui, T. Côté, Expansion tests on cores from ASR-Affected structures, in: M. Tang, M. Deng (Eds.), Proceedings of the 12th ICAAR, Beijing, China, 2004, pp. 821–832. [6] N. Smaoui, M.A. Bérubé, B. Fournier, B. Bissonnette, B. Durand, Evaluation of expansion attained to date by ASR-Affected concrete, in: M. Tang, M. Deng (Eds.), Proceedings of the 12th ICAAR, Beijing, China, 2004, pp. 1005–1015. [7] S. Multon, Evaluation expérimentale et théorique des effets mécaniques de l'alcali-réaction sur structures modèles, (PhD Thesis) 46LCPC, Paris, OA, 2004.
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[8] S. Multon, J.-X. Barin, B. Godart, F. Toutlemonde, Estimation of the residual expansion of concrete affected by alkali silica reaction, ASCE, J. Mater. Civ. Eng. 20 (2008) 54–62. [9] C. Larive, Apports combinés de l'expérimentation et de la modélisation à la comprehension de l'alcali-réaction et de ses effets mécaniques, (PhD Thesis) ENPC, 28, LCPC, Paris, OA, 1998. [10] A. Carles-Giberges, M. Cyr, Interpretation of expansion curves of concrete subjected to accelerated alkali-aggregate reaction (AAR) tests, Cem. Concr. Res. 32 (2002) 691–700. [11] N. Smaoui, M.A. Bérubé, B. Fournier, B. Bissonnette, Influence of specimen geometry, orientation of casting plane and mode of concrete consolidation on expansion due to ASR, Cem. Concr. Aggre. 26 (2004) 58–70. [12] AFNOR XP 18-594, Méthodes d'essai de reactivité aux alcalis, Association Française de Normalisation, Paris, 2004. [13] AFNOR P18-454, Réactivité d'une formule de béton vis-à-vis de l'alcali-réaction (essaie de performance), Association Française de Normalisation, Paris, 2004. [14] A. Leemann, C. Merz, Comparison between AAR-induced Expansion Determined with an Ultra-Accelerated Microbar Test and a Concrete Performance Test, Proceedings of the 14th ICAAR, Austin, Texas, 2012. [15] A. Leemann, C. Merz, An attempt to validate the ultra-accelerated microbar and the concrete performance test with the degree of AAR-induced damage observed in concrete structures, Cem. Concr. Res. 49 (2013) 29–37. [16] S. Multon, F. Toutlemonde, Effect of applied stresses on alkali–silica reactioninduced expansions, Cem. Concr. Res. 36 (2006) 912–920. [17] E. Grimal, A. Sellier, S. Multon, Y. Le Pape, E. Bourdarot, Concrete modelling for expertise of structures affected by alkali aggregate reaction, Cem. Concr. Res. 40 (2010) 502–507. [18] LCPC, Détermination de l'indice de fissuration d'un parement de béton, Méthode d'essai LPC 47, 1997. [19] X.X. Gao, S. Multon, M. Cyr, A. Sellier, Optimising an expansion test for the assessment of alkali–silica reaction in concrete structures, Mater. Struct. 44 (2011) 1641–1653. [20] LCPC, Alcali-réaction du béton: Essais d'expansion résiduelle sur béton durci, Méthode d'essai 44, 1997. [21] D. Vézina, D. Bouchard, Concrete highway structures showing signs of ASR distress: monitoring program at the Ministère des Transports du Québec, in: B. Fournier (Ed.), Marc-André Bérubé Symposium on Alkali-Aggregate Reactivity in Concrete, Montréal, Canada, 2006, pp. 413–422. [22] J.P. Icenhower, P.M. Dove, The dissolution kinetics of amorphous silica into sodium chloride solutions: effects of temperature and ionic strength, Geochim. Cosmochim. Acta 64 (2000) 4193–4203. [23] G.B. Alexander, W.M. Heston, R.K. Iler, The solubility of amorphous silica in water, J. Phys. Chem. 58 (1954) 453–455. [24] A. Atkinson, A.K. Nickerson, The diffusion of ions through water-saturated cement, J. Mater. Sci. 19 (1984) 3068–3078. [25] J. Lindgård, E.J. Sellevold, M.D.A. Thomas, B. Pedersen, H. Justnes, T.F. Rønning, Alkali-silica reactions (ASR) — Performance testing: Influence of specimen pre-treatment, exposure conditions and prism size on concrete porosity, moisture state and transport properties, Cem. Concr. Res. 53 (2013) 145–167. [26] C. Larive, M. Joly, O. Coussy, Heterogeneity and anisotropy in ASR affected concrete, consequences for structural assessment, in: M.A. Bérubé, B. Fournier, B. Durand (Eds.), Proceedings of the 11th ICAAR, Québec, Canada, 2000, pp. 969–978. [27] M.A. Bérubé, J. Duchsene, J.F. Dorion, M. Rivest, Laboratory assessment of alkali contribution by aggregates to concrete and application to concrete structures affected by alkali–silica reactivity, Cem. Concr. Res. 32 (2002) 1215–1227. [28] A. Sellier, E. Bourdarot, S. Multon, M. Cyr, E. Grimal, Combination of structural monitoring and laboratory tests for assessment of alkali-aggregate reaction swelling: application to gate structure dam, ACI Mater. J. 106 (2009) 281–290.
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Assessment of the residual expansion potential of concrete from structures damaged by AAR Christine Merz a, Andreas Leemann b,⁎ a b
Holcim (Schweiz) AG, Würenlingen, Switzerland Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland
a r t i c l e
i n f o
Article history: Received 29 August 2012 Accepted 2 July 2013 Keywords: Alkali aggregate reaction (C) Residual expansion (C) Validation (E)
a b s t r a c t The determination of the residual expansion potential can provide important information on the prognosis of AAR in concrete structures. However, there are still uncertainties about the test protocol and data analysis. In this study, residual expansion of cores from several concrete structures damaged by AAR was measured. The expansion during the test can be divided into different phases with different expansion rates. The results indicate that the expansion in the first phase, that takes place after sample conditioning but before a linear expansion rate is reached, is specific for each concrete and proportional to the further expansion of the cores during the test. Therefore, it can be used to distinguish concrete with different residual expansion potentials. The residual expansion correlates both with the expansion rates on the investigated structures and the expansion of lab concrete, having a similar composition as the on-site concrete, determined with a concrete performance test. © 2013 Elsevier Ltd. All rights reserved.
1. Introduction In the assessment of structures damaged by alkali-aggregate reaction, the determination of the residual expansion potential of the concrete plays an important role. Compared to the on-site monitoring of damaged structures, the measurements permit a relatively fast assessment of the concrete's expansion potential in the future. In combination with data about temperature and moisture conditions of the structure, it may be used for modelling [1]. As such, it is an important tool to plan maintenance and costs involved. However, there are only few studies that deal with the subject up to date (eg. [2–4]). Consequently, several uncertainties still exist regarding both the methodical approach for such measurements and the data analysis. In most cases, residual expansions are measured under storage conditions of 38 °C and saturated air. But other tests, e.g. in water or NaOH solutions, are taken into consideration as well [5–8]. There is a consensus that the reaction should be accelerated by an increase in relative humidity and temperature. But the opinions diverge about which point in time during conditioning and later testing should be used as point zero and which phase of expansion is suitable to assess the residual expansion potential. Most of the published data of the residual expansion measured in saturated air and different temperatures show a similar pattern of the expansion with time. The pronounced expansion at the start of the test is interpreted as a result of moisture uptake. The initial expansion depends thus on the degree of water saturation of the cores, the swelling of already existing and newly formed reaction ⁎ Corresponding author. E-mail address: [email protected] (A. Leemann). 0008-8846/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.cemconres.2013.07.001
products. The asymptotic decrease of the expansion reached after several months is regarded as the end of the reaction phase [9,10]. Usually the leaching of alkalis from the specimens is mentioned as an explanation for this levelling off of the expansion curves. However, the analysis of literature data [10] shows that the expansion of cores from some structures does not cease but stays constant at a certain level even over years. Since the absolute expansion values can be very high, depending on the concrete measured and the duration of the test, the question arises if these late stage expansions should be taken into account for analysis. Another problem of the data analysis is the anisotropy between longitudinal and diametral expansions which has often been observed and analysed in detail [7,9,11]. In summary, there are several uncertainties in regard to the assessment of the residual expansion potential: • How do the different parameters like core size and temperature affect the measured expansions? • How should the different phases of expansion be taken into account? • Should an expansion gradient or an absolute expansion value at the end of the test be used as decisive parameter? • Has the test to be performed for a given time or until the expansion ceases? • What is the influence of alkali leaching? This study is part of a larger project aiming to validate different test methods used to assess AAR-risk. The starting point of the study was the selection of structures damaged by AAR. The selection is representative for the range of aggregates used in Switzerland. After determining the crack-index in different parts of the structures, cores were taken to
C. Merz, A. Leemann / Cement and Concrete Research 52 (2013) 182–189
determine the concrete properties and composition. Sources of the cement and aggregates used in the different structures were identified. Based on these results, the aggregates were tested with the ultraaccelerated microbar test according to AFNOR XP 18-594 [12] and expansions of concrete mixtures with a similar composition as the on-site concrete were determined using the concrete performance test according to AFNOR P18-454 [13]. Results about the validation of these two methods are published in [14,15]. The goals for the residual expansion potential measurements are an assessment of the influence of sample conditioning, sample size and storage temperature on the expansion. The results should allow identifying the decisive parameter permitting a prognosis of the future development of AAR in structures. Cores with a diameter of 50 and 100 mm were exposed to saturated air (N 95% RH) at 20 and 38 °C for a year. Expansion and mass change were monitored during this period. The results obtained in the residual expansion test were compared with the degree of damage observed on the structures and the expansion obtained with the concrete performance test (CPT) on concrete with a similar composition as the one present in the damaged structures. 2. Materials and methods 2.1. General Seven between 25 and 40 years old structures were selected from different parts of Switzerland [15], covering different geological settings and exhibiting damages due to AAR with the exception of structure GU which was selected as a reference for an undamaged on-site concrete (Table 1). The structures include four bridges, two supporting walls and one dam. Cores taken both in strongly and weakly damaged areas were prepared for the residual expansion measurements. The samples chosen for the residual expansion measurements contained no major cracks and originated from a depth N 10 cm, because the alkali level in the surface area of the concrete might be reduced due to leaching and therefore not be representative for the structure. The orientation of the cores in relation to the casting direction can significantly influence the expansion [8,11]. Therefore, all cores were taken in the horizontal direction, perpendicular to the casting direction. The stress state of the concrete at the coring site can have an effect on the following expansion and has to be taken into account when the determined values are used for modelling [1,16,17]. The cores were taken from the abutment in case of the bridges, from the medium height of one supporting wall and from the upper part of the other supporting wall and the dam. Crack width measurements on the on-site concrete were conducted according to the method presented in [18].
183
After cutting them to a length of 200 mm, the samples were equipped with pins glued into predrilled holes with a depth of about 4 mm. The attached pins permit diametral and longitudinal measurements on the cores (Fig. 1). 2.2.2. Residual expansion potential The residual expansion potential was measured on two series of three cores with a diameter of 50 (20 and 38 °C) and one series of three cores with a diameter of 100 mm (38 °C). The cores stored in the reactor at 38 °C were wrapped in a plastic film because experience shows that it is difficult to avoid mass loss even in a reactor with N95% RH. This measure possibly offers some protection against leaching of alkalis. The series of three samples with a diameter of 50 mm and a length of 200 mm were stored at a temperature of 20 °C and N95% RH according to the method described by Wood [4]. Mass changes, diametral and longitudinal expansions of the all cores were monitored for at least one year (measurements every 4 weeks at 20 °C). The ratio between core diameter and maximum aggregate size can have an impact on the measured expansion [19]. However, the amount of reinforcement present in the structures and restrictions from the owner of the structures led to the choice of the 50 and 100 mm core diameters. In principle, the expansion of the cores tested at 38 °C (similar to protocol in [20]) can be divided into three different phases (Fig. 2): • Phase 1: The initial measurements of dimension and mass were done before the samples were conditioned at 20 °C in containers with a thin layer of water at the bottom of the container, permitting capillary suction until reaching constant mass (usually after one or two weeks). The water saturation is accompanied with a first swelling of the samples. • Phase 2: The cores were stored in the reactor at 38 °C, respectively at 20 °C with N95% RH. During 30–60 days at the beginning of phase 2 a strong but quickly levelling off expansion could be observed. In the following, it will be designated as “non-linear expansion at the beginning of phase 2”. Afterwards, the expansion rate is constant, in certain cases also levels off. This part of the expansion is designated as “linear expansion during phase 2”. • Phase 3: After removing the cores from their containers, they were dried at 60–70% RH to their initial weight (at the start of conditioning) and the final “irreversible” expansion is measured. This step takes 2–8 weeks. 2.2.3. Alkali content The water-soluble and the acid-soluble alkali content of the concretes GU and MB were measured before and after the residual expansion test according to the method described in [8].
2.2. Methods for assessment and analysis 2.2.1. Sample preparation Immediately after coring, the samples were welded into plastic bags to prevent moisture loss during the transport to the laboratory.
2.2.4. Crack-index The width of the cracks present on the surface of the concrete structures was determined according to [18]. A square with a side length of 1 m was drawn on the concrete surface. The crack width
Table 1 Location, type and abbreviated name of the investigated structures with a simplified petrography of the aggregates (n.a. = not analysed, aggregate Ømax = maximum grain size used in structure). Location, type of structure, year of construction
Cement content [kg/m3]
w/c
Aggr. Ømax [mm]
Label of aggr. and structure
Present rock types (in order of decreasing amount)
Wangen, viaduct, 1977 Mattsand, dam, 1963 Ganter, bridge, 1980 Bornisses, supporting wall, 1967–68 Rorbach, bridge, 1982–83
325–350 400 400 400
0.45–0.50 0.45–0.50 0.40–0.45 0.45–0.50
32 60 16 32
GU MS MB VI
350–400
0.45–0.50
20
UR
Mels, viaduct, 1969 Mur 10, supporting wall, 1980
300–350 400
0.45 0.43–0.45
20 32
MF ME
Sandstone, quartzite, gneiss, siliceous limestone, limestone Gneiss Gneiss, schists, amphibolites, quartzites Limestone with detritic quartz, siliceous limestone, gneiss, quartz, limestone, schist Gneiss, siliceous limestone, sandstone, schist, limestone with detritic quartz, quartzite Limestone with detritic quartz, sandstone, gneiss, quartzite, schist, granophyr Limestone with detritic quartz, siliceous limestone, limestone, sandstone, gneiss, quartzite, silex
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cores Ø100 mm, 38°C, longitudinal MF GU ME UR MB
expansion [mm/m]
0.8
0.6
0.4
0.2
phase 2
0 0
50
100
150
200
250
300
350
time [day] Fig. 3. Total expansion (average longitudinal measurements, storage at 38 °C) of field concrete from five structures, without phase 3 (drying).
was measured along two sides of the square and the two diagonals using a magnifier with scale (resolution: 0.05 mm). The crack-index was calculated as width of cracks per measured length. The crack width does not take into account the expansion taking place before the cracking occurred. Moreover, there are additional factors like curing conditions, shrinkage and temperature at the time when the measurements are conducted that can affect the crack index. Even with these restrictions, the crack widths measured in strongly-damaged parts of AAR-affected structures are regarded as meaningful values to characterise concrete expansion [3,21]. 3. Results 3.1. Phase 1: conditioning of the samples — water saturation The mass increase during conditioning is between 0.2 and 2.8 mass-%. The samples swell with increasing water saturation. The expansions of the different cores during phase 1 are not proportional to the following expansions during the storage in the reactor, as i.e. shown by the non-linear expansion at the beginning of phase 2 (Figs. 3 and 4). 3.2. Phase 2: non-linear and linear expansions Fig. 1. The longitudinal expansion has been measured on the length axis between two metallic pins fixed with glue in boreholes. The diametral expansion has been measured at two positions perpendicular to the length axis of the cores.
The extent and the duration of the non-linear expansion at the beginning of phase 2 vary between the different concretes (Fig. 3). This
non linear expansion [mm/m]
1.00
0.2
expansion [mm/m]
diametral expansion longitudinal expansion
0.15
0.1
0.05
0 0
100
nonlinear conditioning expansion phase 1
phase2
time[d] 200 linear expansion phase2
300 irreversible expansion phase 3
Fig. 2. Different phases of expansion during the residual expansion measurements in longitudinal and diametral directions of cores.
0.90
diametral at 38°C diametral at 20°C
longitudinal at 38°C longitudinal at 20°C
0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
expansion due to water absorption [mm/m] Fig. 4. Non-linear expansion at the beginning of phase 2 versus the expansion due to water adsorption during conditioning of the samples (phase 1).
C. Merz, A. Leemann / Cement and Concrete Research 52 (2013) 182–189
2.0
diametral, D= 100mm at 38°C
0.80
longitudinal , D=100mm at 38°C
0.60
diametral, D = 50mm at 38°C
0.40
0.20
0.00 0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
longitudinal ,D= 50mm at 38°C
1.6 1.4
1.0
0.6 0.4
3.3. Phase 3: irreversible expansion
non linear expansion rate [mm/m/year]
The irreversible expansion (Fig. 2) is measured after drying the cores to their initial mass (mass before the start of conditioning). It varies depending on the measurement direction (longitudinal or diametral) and the diameter of the samples (Fig. 6). The highest values are obtained diametrically on the cores with a diameter of 50 mm stored at 38 °C (1.5 mm/m). The irreversible expansion also depends on the duration of the storage, especially if the linear expansion
diametral, D = 100mm at 38°C lengthwise, D = 100mm at 38°C diametral, D = 50mm at 38°C lengthwise, D = 50mm at 38°C
6.0
diametral, D = 100mm at 20°C
4.0
lengthwise, D = 100mm at 20°C
2.0
0.0
diametral, D = 50mm at 20°C 0.0
0.4
0.8
1.2
1.6
2.0
total, longitudinal at 38°C
0.2 0.0 0.0
0.5
1.0
1.5
2.0
lengthwise, D = 50mm at 20°C
irreversible expansion [mm/m]
Fig. 7. Expansion during phase 2 (linear and non linear) and total expansion versus irreversible expansion at the end of phase 3 of 100 mm cores.
rates are high and not levelling off during phase 2 (i.e. structure MB, Fig. 3). Total expansion (phase 1 and phase 2) is higher than the irreversible expansion while the expansion during phase 2 is lower than the irreversible expansion (Fig. 7). Obviously, a part of the expansion during conditioning (phase 1) is irreversible since otherwise the irreversible expansion would be identical with the expansion obtained during phase 2. 3.4. Comparison of the samples with diameters 50 mm and 100 mm The non-linear diametral expansions at a core diameter of 50 mm at the beginning of phase 2 are clearly higher than those of the cores with a diameter of 100 mm (Figs. 5 and 8). Only the longitudinal non-linear expansion rates are comparable. As shown in Fig. 5, the linear expansion rates of the 50 mm cores level off in comparison to those of the 100 mm cores. Therefore, as shown in Fig. 8, the diametral expansions of the 50 mm cores increase clearly less than those of the 100 mm cores. The longitudinal expansions even stay constant at 0.4 mm/m. 3.5. Comparison of the storage temperatures 20 °C and 38 °C The irreversible longitudinal expansion of the cores with a diameter of 50 mm is 1.2 to 4 times larger and the diametral expansions 1.6 to 2.5 times larger at 38 °C than at 20 °C (Fig. 9). The linear expansion rates
expansion of cores with D=50mm [mm/m]
non-linear expansion is proportional to the following linear expansion (Fig. 5) and the irreversible expansion (Fig. 6). This also applies to the samples stored at 20 °C (data not shown). The expansion of the cores is relatively small with the exception of the cores from structure MB. But even taking into account the standard deviation, the expansion obtained from the cores of the different structures can be clearly distinguished. The diametral non-linear expansion rates of the cores with a diameter of 50 mm are clearly higher than those of the cores with a diameter of 100 mm, while the diametral linear expansion rates are similar for both core diameters (Fig. 5). The longer the phase 2 is, the larger the resulting expansions during this period are. During this phase, the samples show no significant mass changes (b0.2 mass-%). None of the 100 mm cores shows a levelling off of the expansion until the end of the test after one year.
8.0
total, diametral at 38°C
0.8
irreversible expansion [mm/m]
Fig. 5. Linear expansion rates versus non-linear expansion rates at the beginning of phase 2 (storage at 38 °C). Correlation coefficients R2 of linear regression following the order of the legend are 0.72, 0.79, 0.23 and 0.90.
10.0
phase 2, longitudinal at 38°C
1.2
non linear expansion rate [mm/m/year]
12.0
phase 2, diametral at 38°C
1.8
expansion [mm/m]
linear expansion rate [mm/m/year]
1.00
185
irreversible expansion diametral total expansion diametral
2.0 1.8 1.6 1.4
phase 2, diametral
1.2 1.0
irreversible expansion longitudinal total expansion longitudinal
0.8 0.6 0.4 0.2 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
phase 2, longitudinal
expansion of cores with D = 100mm [mm/m] Fig. 6. Non-linear expansion rates versus irreversible expansion of cores with diameters of 50 and 100 mm stored at 20 °C and 38 °C. Circle: samples of structure MB.
Fig. 8. Expansion of 50 mm cores versus expansion of 100 mm cores at 38 °C.
C. Merz, A. Leemann / Cement and Concrete Research 52 (2013) 182–189
irreversible expansion[mm/m]
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0.4
0.3 structure MS
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structure MF structure GU structure VI
0.1
structure ME structure UR
0.0 0.0
0.2
0.4
0.6
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1.0
expansion CPT[mm/m] Fig. 11. Irreversible expansion (longitudinal, samples with D = 100 mm stored at 38 °C) versus the expansion reached at the end of the concrete performance test of the field concrete reproduced in the laboratory. Fig. 9. Expansion rates at 20 °C and versus expansion rates at 38 °C of 50 mm cores.
are comparable as well diametrically and longitudinally at both storage temperatures. However, the non-linear expansion rates are clearly higher at 38 °C (diametral 2.1–3.5 times; longitudinal 2.3–3.8 times). 3.6. Anisotropy of the expansions There is a systematic difference between the diametral and longitudinal expansions (Figs. 4–6). The ratios of diametral/longitudinal expansions (calculated over the full duration of phase 2) are always higher than 1 and vary at 38 °C from 0.9 to 2.5 for the 100 mm cores and from 1.7 to 3.7 for the 50 mm cores. The ratio is even higher for the 50 mm cores at 20 °C with values of 2.3 to 4.5. For the non-linear expansion rates at 38 °C, the diametral/longitudinal ratios range from 1.3 to 2.7 for the 100 mm cores and from 2.9 to 4.4 for the 50 mm cores. The highest ratios were measured again on the 50 mm cores at 20 °C, namely from 2.8 to 6.1 (Fig. 10). The anisotropy is observed during the entire duration of the storage. The diametral/longitudinal ratios of the non-linear expansion rates are comparable with the ratio of the irreversible expansions at the end of the test with a few exceptions. The anisotropy is higher in the 50 mm cores and at 20 °C compared to 38 °C (Fig. 10). 3.7. Comparison with the field concrete The irreversible expansions of the reactive concretes correlate well with the expansion of the prisms of the reproduced field concretes D=100mm at 38°C
D=50mm at 38°C
D= 50mm at 20°C
D=100mm at 20°C
7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0
3.8. Alkali leaching As the water-soluble alkalis represent the amount of alkalis present in the pore solution, differences before and after the test should be caused by leaching and chemical binding in reaction products. As the acid dissolves the hydrates thereby releasing the bound alkalis, differences before and after the test can be attributed to leaching. Usually, the acid-soluble alkali contents of most Swiss field concretes are between 0.1 and 0.2 mass-% Na2Oeq. However, concrete with aggregates containing micas and feldspar can reach up to 0.4 mass-% Na2Oeq. There are differences in the alkali contents of the selected two structures before and after the test. The analysis of the alkali contents at the end of the test (335 days) showed no changes of the water-soluble alkali (0.05 mass-% Na2Oeq) and acidsoluble alkali contents (0.12 mass-% Na2Oeq) for 100 mm cores from the structure GU (the non-reactive reference concrete). On the other hand, the analysis of samples from structure MB after 492 days of storage showed a decrease of 0.09 mass-% acid-soluble Na2Oeq (initial value: 0.41 mass-% Na2Oeq) and of 0.03 mass-% water-soluble Na2Oeq
irreversible expansion[mm/m]
ratio diametral/longitudinal of irreversible expansion
8.0
after 5 months of the concrete performance test (Fig. 11). The longitudinal expansions of the 100 mm cores were used for the comparison as only longitudinal expansions are measured in the concrete performance test. The higher storage temperature of 60 °C instead of 38 °C leads to up to 2.5 times greater expansions. The expansions measured so far on the 30 to 40 year old buildings (crack indices) are clearly larger than the irreversible expansion that could be measured in the laboratory (Fig. 12). Only structure MB differs clearly from the other structures.
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
ratio diametral/longitudinal of non linear expansion rate
0.7 0.6 0.5 0.4 0.3 structure MS structure GU structure ME structure MB
0.2 0.1
structure MF structure VI structure UR
0.0 0.0
1.0
2.0
3.0
4.0
5.0
crack index structure [mm/m] Fig. 10. Diametral/longitudinal-ratios of the irreversible expansion versus diametral/ longitudinal-ratios of the non-linear expansion rates at the beginning of phase 2 of 50 and 100 mm cores stored at 20 °C and 38°.
Fig. 12. Irreversible expansion (longitudinal, samples with D = 100 mm at 38 °C storage temperature) versus the crack index measured on the structures.
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(initial value: 0.13 mass-% Na2Oeq) for the 100 mm cores. The decrease of the 50 mm cores was greater with 0.17 mass-% acid-soluble Na2Oeq and 0.07 water-soluble mass-% Na2Oeq. 4. Discussion 4.1. Expansion during phase 1 The comparison between the expansion in phases 1 and 2 with the irreversible expansion shows that the expansion in phase 1 attributed to the increasing water saturation is not completely reversible. This indicates that reversible hygroscopic swelling in this phase is overlapping with an AAR induced expansion. Drying to the initial mass of the concrete allows determining this irreversible part of the swelling. However, expansion not caused by the swelling of newly formed reaction products within existing cracks but by the formation of new cracks is not or only partly reversible by drying. The good correlation between the expansion during phase 2 and the irreversible expansion indicates that this effect is minor in the analysed cores but it may have to be taken into account when assessing cores from other structures. 4.2. Expansion during phase 2 The following phase 2 is divided in a phase of non-linear expansion followed by a stable state of linear expansion with lower gradient. In contrast to the s-shaped expansion curve observed in structures, the cores lack an induction period as ASR is already progressing. The expansion of the cores from structure ME during phase 2 is in the same range as the one of the cores from structure GU, which shows no AAR related damage. Obviously, there is very little expansion potential left in structure MF. The expansion of the cores from the structures UR and MF indicates a higher residual expansion potential and the one obtained with the cores from structure MB indicates a considerably higher compared to the non-reactive reference structure GU. The non-linear expansion rate at the beginning of phase 2 is larger than the following linear expansion and additionally depends on the temperature. This could be an effect on the importance of dissolution and diffusion at different temperatures. The fact that AAR proceeds relatively fast with easily dissolvable aggregates as chert and relatively slow with quartz indicates that dissolution is the limiting factor of the reaction at ambient temperature. However, the dissolution rate of silica is increased by a factor of about 7 by a temperature increase from 20 to 38 °C [22] and silica solubility by a factor of about 1.4 [23]. If the dissolution rate of quartz is the limiting factor of reaction at 20 °C, this situation is possibly changed by the temperature increase to 38 °C. At a given pH and availability of alkalis and calcium within reactive aggregates, AAR is accelerated first during the temperature change from 20 to 38 °C. After this initial acceleration, the reaction might be slowed down as the consumed hydroxides, alkali and calcium ions have to diffuse into the aggregate again to sustain the reaction. The increase of the diffusion rate of ions in cement paste increases by a factor of about 1.8 going from 20 to 38 °C [24] which is significantly less than the dissolution rate of silica. Even if the data about dissolution rates and solubility of silica were not determined in a high pH environment, this still may indicate that the transition from the non-linear to the linear expansion is caused by the change from a solubility-limited system to a system governed by diffusion. Anyway, the characteristic expansion starts immediately after exposing the cores to elevated temperature [9] and reaches a concretespecific extent. Comparing cores of different structures, the extent of this expansion is not proportional to the swelling during phase 1. Both, the non-linear expansion and the linear expansion characterise the behaviour of the concrete of a specific structure as they correlate
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linearly for a given core size, storage temperature and test duration (Figs. 5–7). The 100 mm cores of the investigated concrete structures still expand at the end of the test after one year. Therefore, the question arises if the measured expansion in such cases mirrors the residual expansion or only shows the expansion rate under the test conditions. The comparison between the expansion determined in the test and expansion in the structures can give indications on the answer. 4.3. Irreversible expansion The irreversible expansion after one year shows a correlation to the crack-index determined in strongly damaged areas of the investigated structures (Fig. 12). This shows that the expansion rate in the structures is mirrored in the expansion rate in the residual expansion test. This correlation is made possible, because the investigated structures have a similar age. Even if the final expansion is not reached in the residual expansion test, it gives information about the expansion rate relative to other tested cores from other structures. However, long time experience with the CPT shows that in this particular test the expansion rate during the first four weeks and as such the kinetics of the reaction are related to the final expansion at the end of the test when the expansion rates have decreased significantly compared to the first four weeks. If a similar relation exists in the residual expansion potential test, then the irreversible expansion and with it the non-linear and linear expansions could be used as relative value for the final expansion of the concrete. The only exception showing no correlation between irreversible expansion and crack-index is structure MB that shows little cracking on-site but the highest expansions in the residual expansion tests. In fact, the areas of the bridge that were accessible for taking the cores showed considerable less cracking than other parts of the structures that were not accessible either due to logistic reasons or because of the presence of pre-stressed cables. As such, the crack-index used may not be representative for a strongly damaged part of the structure as it is the case in all other investigated structures. 4.4. Anisotropy of the expansion The anisotropy of the expansion, diametral versus longitudinal, stays constant during the different phases of the test. This has been observed and discussed in various studies [7,9,11]. The anisotropy seems to depend not only on sample shape (diameter, diameter/ length-ratio) but also on the testing conditions. Within a given test arrangement, the ratios of the diametral and longitudinal expansions are constant. Accordingly, constant ratios of 1.3–2.8 with high correlation coefficients are found by [8] at test temperatures of 23 and 38 °C. The phase of the linear expansions is reached simultaneously diametrically and longitudinally. Multon [7] observed ratios of 1.4, 1.9 and 2.2 depending on the storage (saturated air, water storage, sealing with aluminium). This anisotropy could be partly an effect of the moisture profile in the test specimens. In the CPT conducted with concrete having w/c-ratios of 0.30, 0.45 and 0.60, the relative humidity in the outer 25 mm of the specimens is between 1 and 6% higher than in their interior [25]. If this applies as well for the cores in the residual expansion potential test, the outer parts of the cores would have more favourable conditions for AAR and expand more. When the outer areas of a core expand more than the interior areas, anisotropic expansion results. In the present study the longitudinal expansion (meaning perpendicular to the filling direction) is only little influenced by the diameter of the sample while the diametral expansion (parallel to the filling direction) is clearly influenced by the core diameter. For 100 mm cores, the anisotropy seems to decrease with increasing expansion rates. It has been suggested that anisotropy in the microstructure due to segregation and a preferred orientation of flaky aggregates
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could be the reason for the anisotropy of the expansion of cores taken perpendicular to the filling direction [9,11,26]. In the on-site concrete studied, there were flaky and non-flaky aggregates present depending on the specific structure, but the anisotropy was always in the same range independent of aggregate shape (Fig. 10). Consequently, the effect of flaky grains and filling direction on the anisotropy cannot be confirmed. As the longitudinal expansion shows no or little effect of core diameter, it is reasonable to take it as the decisive parameter for assessing the residual expansion. 4.5. Assessing the residual expansion potential In order to assess the expansion rate of a particular concrete, both the non-linear expansion and the linear expansion can be used. Such an assessment is possible within a few month of running the residual expansion test. However, if the expansion rate during the linear expansion in phase 2 is not decreasing, the test duration should be at least a year. However, at a very long test duration alkali leaching may become a problem as discussed below. There are examples of strongly damaged structures that show only minor length changes in the residual expansion test because they indeed have reached the end of the reaction [8/unpublished data, C. Merz]. It has to be pointed out that even concrete with non-reactive aggregates expands in the test although at a much lower rate than concrete with reactive aggregates [10]. Consequently, some of the recorded expansion is not attributable to AAR. The reactive concrete mixtures differ from the non-reactive concretes by a higher non-linear and linear expansion rate. This is confirmed by the present observations. The correlation between the crack index, the irreversible expansion and the expansion in the CPT performed on concrete with a similar composition as the on-site concrete shows the close relation between the structures and the two laboratory tests (Figs. 11 and 12). The expansion of the 50 mm cores levels off more during phase 2 than the one of the 100 mm cores. The likely reason for the slowing down of the reaction is the leaching of alkalis leading to a decrease of the alkalinity of the pore solution, as observed as well in [5]. The leaching of alkalis has two consequences. Firstly, the duration of the residual expansion measurements cannot be extended for years as the decrease of the expansion will not be caused by an exhaustion of the expansion potential per se but by leaching. As the 100 mm cores show no decrease of the expansion gradient, it seems safe to use this diameter for test durations of one year. The diameter of the cores has to be as large as possible, as large cores have a smaller surface/volume-ratio compared to smaller ones, decreasing the effect of leaching. The effect of core size on leaching is confirmed in the case of structure MB. The cores of structure GU showed no such effect but at considerably lower alkali levels in the concrete possibly limiting the effect of leaching. The degree of reinforcement present in the investigated structures did not permit to take cores of a diameter larger than 100 mm. However, in structures with no or little reinforcement it would be beneficial to increase the diameter to 150 mm. However, not the entire differences in expansion of the differently sized cores may be attributable to leaching. The size of the specimens can directly affect the measured expansion as well, where increasing expansion is measured with increasing specimen size. This scale effect has been demonstrated by Gao et al. [19] using mortar prisms of various sizes immersed in alkaline solutions. Consequently, it does not seem reasonable to directly transfer expansion measured on cores to structures. In the case of concrete showing an unusually high linear expansion rate in relation to their non-linear expansion rate, it cannot be excluded that the reaction might be enhanced by an internal alkali source [27] as it could be the case for structure MB. The aggregates in structure MB consist of gneiss that contains heavily altered feldspars as possible source for alkalis.
If the cores do not expand or stop expanding during the test, it clearly shows that the concrete has reached its expansion potential or is close to reaching it. If the cores are still expanding at the end of the test, further expansion and damages of the structure have to be expected. The expansions reached in the residual expansion test likely represent maximum values as the temperature and RH during the test are more favourable for AAR than the conditions generally present in structures. Because various factors influence the measured expansions, like location and orientation of the cores in the structure, the stress and moisture state of the concrete at these locations and the uncertainties in testing as discussed above, care is advisable when expansion values are transferred to a structure or used for modelling. At the current state of knowledge, the residual expansion potential can be used to qualitatively compare different structures or different components of the same structure. An expansion rate derived from the crack index and the age of the structure can further help to assess the results of the residual expansion test. However, if more accurate data are needed, longtime monitoring is recommended [21,28]. It is moreover clear that more data are needed from a variety of structures to improve the data base and with it the interpretation of the measured expansion values. 5. Conclusions The residual expansion potential of cores with diameters of 50 and 100 mm taken from structures damaged by AAR was determined. The determined expansions during the different phases were compared and discussed to improve and confirm the methodical approach. Additionally, the results were compared with the crack-index of strongly damaged parts of the investigated structures and with the expansion of concrete, having a similar composition as the on-site concrete, determined with the CPT to further assess the significance of the residual expansion test. The following conclusions can be drawn in regard to the different expansion phases: • The expansion during the water saturation of the samples (phase 1) is partially irreversible indicating AAR-induced expansion in addition to expansion caused by moisture uptake. • The non-linear expansion (rate and duration) after the water saturation and at the beginning of the storage is specific for each concrete and depends on the temperature condition. It influences the following linear expansion rates, respectively the irreversible expansion reached at the end of the test. Additionally, it correlates with the expansion obtained in the concrete performance tests. • The following linear expansion rate of the samples is independent of temperature and sample diameter, but it levels off rapidly for small samples likely due to alkali leaching. High linear expansion rates indicate the presence of an internal source of alkalis in the concrete. • The irreversible expansion is determined by drying the cores back to their initial mass at the start of phase 1. It includes the part of the expansion reached during phase 1 which is not caused by the increase of water saturation but likely by AAR and the expansion during phase 2. The following recommendations for conducting the residual expansion potential test can be given: • During the non-linear expansion phase, the longitudinal expansions are independent of the core diameter in contrast to the diametral expansion. Therefore, it is recommended to use the longitudinal expansion for assessing the residual expansion potential. • Cores with a large diameter are less prone to alkali leaching. Therefore, 100 mm cores are better suited for the residual expansion test than 50 mm cores. A core length of 200 mm has proven to provide the needed accuracy in the length measurements and to be easy enough to handle in the laboratory.
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• Expansion rates are faster at a temperature of 38 °C compared to 20 °C. As results are obtainable within a shorter time period, a temperature of 38 °C is recommended. Different parameters permit to assess expansion rates and the residual expansion potential: • Both the non-linear and the linear expansion during phase 2 permit an assessment of expansion rate of a specific concrete if the latter shows no levelling off. • It is preferable to use the expansion during phase 2 for assessing the residual expansion potential. • If the expansion of the 100 mm cores levels off before the end of the test after one year, the expansion potential is exhausted and the measured expansion represents the residual expansion potential of a specific concrete. If this happens with 50 mm cores it can either be caused by leaching or by the exhaustion of the expansion potential. The residual expansion potential is a valuable tool to assess the further development of AAR in a structure. However, more data are needed to support the conclusions of this study. Acknowledgement The Federal Road Authorities of Switzerland (ASTRA) are acknowledged for the financial support of the project and P. Lura for the critical review of the manuscript. References [1] S. Multon, J.F. Seignol, F. Toutlemonde, Chemomechanical assessment of beams damaged by alkali–silica reaction, J. Mater. Civ. Eng. 18 (2006) 500–509. [2] M.A. Bérubé, J. Frenette, A. Pedneault, M. Rivest, Laboratory assessment of the potential rate of ASR expansion of field concrete, in: M.A. Bérubé, B. Fournier, B. Durand (Eds.), Proceedings of the 11th ICAAR, Québec, Canada, 2000, pp. 821–830. [3] B. Godart, B. Mahut, P. Fasseu, M. Michel, The guide for aiding to the management of structures damaged by concrete expansion in France, in: M. Tang, M. Deng (Eds.), Proceedings of the 12th ICAAR, Beijing, China, 2004, pp. 1219–1228. [4] J.G.M. Wood, When does AAR stop: in the laboratory and in the field? in: M. Tang, M. Deng (Eds.), Proceedings of the 12th ICAAR, Beijing, China, 2004, pp. 1016–1024. [5] M.A. Bérubé, N. Smaoui, T. Côté, Expansion tests on cores from ASR-Affected structures, in: M. Tang, M. Deng (Eds.), Proceedings of the 12th ICAAR, Beijing, China, 2004, pp. 821–832. [6] N. Smaoui, M.A. Bérubé, B. Fournier, B. Bissonnette, B. Durand, Evaluation of expansion attained to date by ASR-Affected concrete, in: M. Tang, M. Deng (Eds.), Proceedings of the 12th ICAAR, Beijing, China, 2004, pp. 1005–1015. [7] S. Multon, Evaluation expérimentale et théorique des effets mécaniques de l'alcali-réaction sur structures modèles, (PhD Thesis) 46LCPC, Paris, OA, 2004.
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