The potential for further expansion due to ASR is an important parameter in the process of assessing the current condition of ASR-affected concrete and selecting appropriate remedial actions. The in-situ monitoring of the current deformations is the only accurate method of estimating this potential. The current rates of deformation are measured periodically or continuously, and can be then extrapolated to forecast future behaviors. Moreover, "in-situ" measurements on existing structures often lead to more optimistic results than expansion tests on concrete cores taken from these structures, which are not tested under the same environmental (temperature, humidity, wetting-drying, freezing-thawing, etc.) and stress conditions. However, in-situ monitoring usually requires several years to generate relevant data, i.e., data where the permanent and cumulative deformation due to ASR can be clearly distinguished from the reversible and cyclic movements related to mechanical (loading, traffic, operation condition etc.) and thermal/climatic (daily and seasonal) variations. On the other hand, expansion tests on cores can yield results in a relatively short period of time, e.g., one year. This accounts for their common use in assessing the potential for further expansion of ASR-affected concrete (prognosis), and for diagnosis as well (e.g., confirmation of the expansive character of the concrete under study).
The procedures used for testing cores from ASR-affected structures vary greatly from one study to another (Bérubé et al. 2004). Two test procedures are recommended hereafter, where the cores are: (1), tested in air at > 95 percent R.H. and 38°C (100°F), and (2), tested in 1N NaOH solution at 38°C (100°F). The first test is considered the most realistic for evaluating the "residual concrete expansivity" and the potential for further expansion of ASR-affected concrete (Bérubé et al. 2002). The concrete is tested with its own alkali content and the test conditions used (temperature and humidity) are similar to those used in the Concrete Prism Test ASTM C 1293. The second test in alkaline solution is recommended for determining the "residual aggregate reactivity" in the concrete under study (Bérubé et al. 2002). The results from expansion tests on cores can be used in combination with a number of other parameters for estimating the current rate of expansion of ASR-affected concrete in the field (see Appendix I).
The diameter of the cores should be at least three times the maximum size of aggregates, and their length should be two to three times their diameter. For concrete with aggregates of nominal size smaller than 35 mm (1.4 in), a core diameter of 100 mm (4 in) is the most practical. However, as discussed hereafter, a core diameter of 150 mm (6 in) is always recommended when testing in humid air (> 95 percent R.H. and 38°C (100°F)), which reduces alkali leaching during the test and postpones the consequent leveling off of the expansion curve.
The skin of concrete (from the exposed surface down to about 25 to 75 mm (1 to 3 in) in the concrete) is usually more macro-cracked and may have suffered from significant alkali leaching or, conversely, alkali concentration through evaporation or supply of de-icing chemicals. Therefore, this concrete may be not representative of the ASR-affected member under study regarding the evaluation of potential for further expansion. In particular, wetting/drying and freezing/thawing cycles may have greatly contributed to the development of cracking in the surface concrete. It is recommended that, at least, the first 50 mm (2 in) of concrete be avoided.
Large variations in mixture proportioning, exposure conditions (humidity, temperature, etc.), stress conditions, and internal deterioration (expansion and microcracking), may occur within a single structure or a single member of a structure, leading to variations in the test results. It is therefore important to take cores from various members of the concrete structure under investigation in order to have a good coverage of such variations. For a given type of concrete member, it is recommended to test a minimum of three specimens in humid air at >95 percent R.H. and 38°C (Section F.7), and a minimum of two specimens when testing in 1N NaOH at 38°C (Section F.8). More than one test specimen can be taken from cores of sufficient length, provided that the above considerations about concrete variability are taken in account.
At the time of coring, it is important to note the orientation of the cores in the concrete member(s) under study and, if possible, to monitor the deformations of the cores during the expansion tests along three directions: the longitudinal direction and two diametrical directions at right angles, with one perpendicular to the casting plane.10
After coring, the volume of the core samples may change to reach a relative equilibrium with respect to the new stress and environmental (temperature and moisture) conditions to which the concrete is now exposed. These short-term variations can be related to:
In order to minimize the effects of drying (shrinkage, microcracking) and expansion due to rewetting at the beginning of the tests, the core samples should be sealed immediately after coring by wrapping them in heavy duty shrink wrap and storing them in sealed polyethylene bags.11
It is recommended to wait at least one week before the cores are subjected to expansion tests in order to reach a relative mechanical equilibrium (stress release). However, the volumetric changes taking place during the storage period (which could be related to stress release when the cores are kept moist after coring), could also be monitored by installing gauge reference studs and taking initial length measurements shortly after coring (Section F.4.2).
The core samples are sawn perpendicular to their axis using a diamond saw. As already mentioned, their length should be two to three times their diameter (see Table F1). This step is not absolutely required when only lateral and diametrical measurements are made, but the presence of flat ends facilitates the handling and the storage of the cores.
|Core diameter (mm)||Recommended length1 (mm)||Minimum length1 (mm)|
|50 (2 in)||150 (6 in)||100 (4 in)|
|75 (3 in)||225 (11 in)||150 (6 in)|
|100 (4 in)||300 (12 in)||200 (8 in)|
|150 (6 in)||300 (12 in)||300 (12 in)|
1Approximately (max ± 5mm)
Stainless steel bolts or gage studs, 13 mm in length by 3 mm in diameter (approximately 0.5 by approximately 0.12 in) with a machined "demec point" at the end are commonly for that purpose. They are installed in small holes drilled dry and cemented with a shrinkage-free cement paste. The drill holes are about 8 mm (approximately 0.3 in) in diameter by 20 mm (0.8 in) deep.
For the reasons mentioned before (i.e., influence of directions of principal stresses and casting plane), the gage studs should be installed in order to monitor the (longitudinal and diametrical) expansion of the cores along the three directions, including one direction perpendicular to the casting plane.
Axial (longitudinal) measurements - They are more recommended than lateral (longitudinal) measurements because they generally result in lower experimental variability (Bérubé et al. 1994, Smaoui et al. 2004b). Gage studs are centrally installed at both ends of the core, and the measurements can be performed using an arch-type device (Figure F1-A). Axial measurements can also be performed with the measuring device used for the Concrete Prism Test ASTM C 1293, provided that appropriate gage studs are fixed at both ends of the cores.
Lateral (longitudinal) measurements - They are also possible, however less recommended than axial measurements because of the larger variability often observed between the individual measurements performed on the same core (Bérubé et al. 1994).
For such measurements, at least two diametrically opposite lines of two gage studs are installed on the cores tested, with 50 to 250 mm (2 to 10 in) between the studs, depending upon the length of the core specimens and the measuring device available (Figure F1-C).12
The studs should be placed not less than 20 mm (0.8 in) from the ends of the cores (50 mm (2 in) from the end corresponding to the exposed concrete surface) (see Table F2).
Diametrical measurements - They are performed by installing, at mid-length of the cores, two diametrically opposed studs. Measurements can also be made near (≥ 20 mm) (0.8 in) both ends of the cores (Smaoui et al. 2004b). They are performed using the same arch-type measurement device as for axial measurements (Figure F1-B).
Figure F1. Expansion measurements. A) Axial reading using an arch-type measuring device. B) Diametrical measurement using the same measuring device. C) Lateral reading using standard conventional length-change measuring device used for freeze-thaw / creep testing.
|Length of cores (mm)||Distance between studs (mm)||Distance between studs and end portions of cores (mm)|
|90 - 140 (0.36 - 5.6 in)||50 (2 in)||20 - 45 (0.8 - 1.8 in)|
|140 - 190 (5.6 - 7.6 in)||100 (4 in)||20 - 45 (0.8 - 1.8 in)|
|190 - 240 (7.6 - 9.6 in)||150 (6 in)||20 - 45 (0.8 - 1.8 in)|
|240 - 290 (9.6 - 11.6 in)||200 (8 in)||20 - 45 (0.8 - 1.8 in)|
|≥290 (≥ 11.6 in)||250 (10 in)||≥ 20 (≥ 0.8 in)|
When testing length changes of cores, a preliminary expansion phase is observed due to various mechanisms unrelated to the residual/further ASR expansion (see Section F.3.1):
The only way to properly account for these short term variations consists in conditioning the samples under the same conditions as for the tests, until a relative equilibrium in mass and expansion is reached. Then, the time and expansion scales are reset to zero (see Figure F2). The time at which this equilibrium is reached is recognized by the presence of points of inflexion on corresponding mass and expansion curves. The points of inflexion are sometimes difficult to locate precisely, particularly on the expansion curve, but it is better to take the zero reading later rather than too early; the most critical point is to ensure that all initial adjustments are completed; otherwise the expansion due to residual/further ASR would be overestimated. On the other hand, exceeding the equilibrium point just delays the completion of the tests.
Figure F2. Results from expansion tests in air at > 95 percent R.H. and 38°C (100°F) on core samples taken in the abutment of a bridge located in the Québec City area and incorporating a siliceous limestone coarse reactive aggregate. A) Mass variation. B) Measured bulk axial expansion. C) "Reset" (after removing the portion related to the preconditioning) axial expansion after a preconditioning of 60 days.
In order to recognize more easily the above short term volumetric changes unrelated to the residual/further ASR, the mass of the core samples is measured in addition to their volumetric changes (diameter, length). Moreover, the temperature of the immersion solution (test in 1N NaOH) or the storage room (test in humid air) at the time of measurement is also recorded in order to normalize all length values with respect to the nominal test temperature of 38°C (100°F). The correction factor used is 0.001 percent/°C which is an estimate of the thermal expansion coefficient of conventional concretes. The temperature correction is particularly critical when testing cores in humid air at > 95 percent R.H., because small expansions are generally obtained (Bérubé et al. 1994).
Because the alkali content of field concrete is normally lower than for laboratory concrete made in accordance with the Concrete Prism Test ASTM C 1293, relatively low expansions are usually obtained. However, an expansion as low as 0.003 percent per year, which is the lower limit considered in the methodology proposed in the Appendix I, may be of great importance for the existing structure under study. In fact, expansion rates in the range of 0.002 to 0.005 percent per year are common in the case of AAR-affected concrete structures (CSA 2000).13
On the other hand, very low expansions, e.g., ≤ 0.005 percent per year, are not statistically significant considering the experimental variation despite the reading precision of the expansion measurements is about ± 0.0005. In order to improve the statistical significance of the results, (1), the tests are often extended over the usual one-year period; (2), the measurements are more frequent than in the standard Concrete Prism Test ASTM C 1293, and (3), linear regression analysis is recommended in order to better assess the annual rate of expansion.
The expansions measured in the tests may have been underestimated if the concrete specimens tested were abnormally fractured or porous compared to the overall concrete member under investigation. In such a case, some ASR gel produced during the test may have expanded freely in voids without causing additional expansion. The interpretation of the test results is thus not always easy. Table F3 may be useful in this regard. 14
|1-yr exp.1( percent)||Case||Conclusion about the concrete||Preexisting ASR gel (before test)||Secondary ASR gel (after test)||Result for companion cores tested at 38°C (100°F) in 1N NaOH||Further expansion expected in the field|
|<0.003||1||Non-expansive since construction||No/small amounts||No/small amounts||Non-expansive (nonreactive aggregates) or expansive (low alkali concrete content)||Non-expansive (non-reactive aggregates or low-alkali content)|
|2||Non-expansive anymore||Yes||No/small amounts||Non-expansive (aggregates nonreactive anymore) or expansive (alkali content not sufficiently high anymore)||Non-expansive (aggregates non-reactive anymore or alkali content not sufficiently high anymore)|
|3||Reactive but non-expansive (cracked/porous concrete)||Yes or no depending on age and humidity||Yes||Non-expansive (porous/ cracked concrete) or expansive (concrete not as cracked)||Expansive or non-expansive depending on porosity/ cracking, humidity, and confinement|
|>0.003||4||Expansive||Yes or no depending on age and humidity||Yes||Expansive||Expansive or non-expansive depending on humidity and confinement|
1 Excluding the preconditioning period. The expansion results obtained could be underestimated if the concrete tested is significantly more porous/cracked (open spaces for free expansion of the ASR gel) than the overall concrete of the field member under study.
Nevertheless, significant expansion in this test does not necessarily mean that it will be the case in the corresponding structure, as the humidity conditions may not be sufficiently high in nature or the concrete may be subjected to "beneficial" compressive stresses.
Alkali leaching and influence of core diameter - Considering the relatively low expansion rates obtained for most field concretes tested and the necessity to often perform the test up to 2 years, it is highly recommended to test cores of 150 mm (6 in) in diameter, in order to minimize alkali leaching and to prevent the expansion to level off and to be underestimated15(see Figure F3).
Figure F3. Expansion of concrete specimens of various sizes, made with a rhyolitic tuff and stored in air at 38°C (100°F) and > 95 percent R.H. (After Landry 1994).
Determination of the ultimate expansion in the field - According to the ISE (1992), the maximum AAR expansion that a concrete member may attain in the field corresponds to the maximal expansion obtained for concrete cores tested in humid air (> 95 percent R.H.) at 38°C (100°F). However, the maximum expansion is likely to be underestimated this way since cores suffer significant alkali leaching under the above test conditions; consequently, the expansion tends to level off after a certain time, which is not really due to consumption of reactive mineral phases or alkalies (Rogers and Hooton 1993).16
In this respect, the greater the core diameter, the lesser the alkali leaching during the expansion test in humid air and the higher the expansions in the long term (Bérubé et al. 2004, Landry 1994). The alkali leaching during expansion tests in humid air is also influenced by the concrete permeability (i.e., water-to-cement ratio), which varies from one concrete to another.
The proposed expansion limit criterion for distinguishing between innocuous and deleteriously expansive concrete when testing in 1N NaOH solution at 38°C (100°F) is 0.04 percent at one year after the preconditioning period (Bérubé et al. 1994).
Expansions in alkaline solution are affected by numerous parameters, such as the core diameter, the concrete alkali content, the water-to-cement ratio, the concrete permeability, and the extent in preexisting cracking (Bérubé et al. 1994). In particular, (1) the larger the core diameter (longer delay before the test solution impregnates the core samples), (2) the lower the alkali content (slower equilibrium between the initial concrete pore solution and the immersion solution), and (3) the lower the water-to-cement ratio (lower permeability and slower penetration of the alkaline solution), the lower is the expansion in the short term. However, in the long term, e.g., after one year, the influence of these three parameters is in general not as important, provided the water-tocement is not too low. 17
The interpretation of the test results is not always easy. Table F4 may be useful in this regard. One can note that the petrographic examination of the concrete before the tests (cracking, primary reaction products, etc.), the measurement of the water-soluble alkali content (Appendix H), the verification of the presence of secondary reaction products after the tests, the chemical analysis (dissolved silica) of the immersion solution after the tests18, and the expansion results obtained for companion cores stored at > 95 percent R.H. and 38°C (100°F) (Section F.7) may greatly help in the interpretation of the test results. It must be noted that the K/Na ratio of the secondary reaction products formed during the immersion test in NaOH is generally significantly lower than in the primary products, due to the presence of NaOH, since most cements contain a larger proportion of potassium than sodium.
|1-yr exp.1( percent)||Case||Conclusion of the test about aggregates||Preexisting ASR gel (before test)||Secondary ASR gel (more Na) (after test)||Results for companion cores tested at 38°C and >95 percent RH||Further expansion expected in the field|
|<0.04||1||Non-reactive since construction||No/small amounts||No/small amounts||Non-expansive||Non-expansive (nonreactive aggregates)|
|2||Non-reactive anymore||Yes||No/small amounts||Non-expansive||Non-expansive (aggregates non-reactive anymore)|
|3||Reactive but cracked/porous concrete||Yes or no depending on age, concrete alkali content, and humidity||Yes||Non-expansive (porous/ cracked concrete or low-alkali content) or expansive (concrete not as cracked)||Expansive or non-expansive depending on porosity/cracking, alkali content, humidity, and confinement|
|4||Reactive but silica dissolved in the test solution||Yes or no depending on age, alkali content, and humidity||No/small amounts||Non-expansive (low-alkali concrete content) or expansive||Expansive or non-expansive depending on alkali content, humidity, and confinement|
|5||Reactive but very-low permeability concrete||Yes or no depending on age, alkali content, and humidity||No/small amounts||Non-expansive (low-alkali concrete content) or expansive2||Expansive or non-expansive depending on alkali content, humidity, and confinement|
|>0.04||6||Reactive||Yes or no depending on age, alkali content, and humidity||Yes (higher K/Na ratio)||Non-expansive (low-alkali content) or expansive||Expansive or non-expansive depending on alkali content, humidity, and confinement|
1 Excluding the preconditioning period. The expansion results obtained could be underestimated if the concrete tested is significantly more porous/cracked (open spaces for the ASR gel expand freely) than the overall concrete of the field member under study.
2 Considering the low concrete permeability, the expansion results should be similar in 1N NaOH and in humid air.
Figure F4. Expansion results in humid air at 38°C (100°F) and > 95 percent R.H. for three non-reinforced concrete blocks, 230 by 230 by 810 mm (9 by 9 by 32 in) in size, made with an extremely-reactive gravel from New Mexico, and for cores, 100 mm (4 in) in diameter, taken in two of these blocks at different times. (Axial measurements on cores and transverse measurements on blocks along the same direction as the core axis).
Immersion tests in 1N NaOH solution can be useful to assess the residual reactivity of the aggregates present in the concrete under study. However, significant expansion in the tests cannot be directly used to estimate the potential for further expansion in the existing structure. The immersion solution used is highly basic and alkaline and the humidity conditions are extreme. Despite the presence of highly-reactive aggregates, the concrete might not expand in the existing structure if the two other essential conditions for ASR, i.e. high humidity and high concentration of alkali hydroxides (or pH) in the concrete pore solution, were never or are no longer satisfied in the field. Also, compressive stresses in the field tend to reduce the expansion due to ASR.
American Standards for Testing and Materials (ASTM), "Standard Test Method for Determination of Length Change of Concrete Due to Alkali-Silica Reaction," ASTM International, ASTM C1293.
British Cement Association (BCA), "The Diagnosis of Alkali-Silica Reaction - Report of a Working Party," Wexham Springs, Slough (UK), SL3 6PL, 44 p., 1992.
. Bérubé, M.A., Smaoui, N. and Côté, T., "Expansion Tests on Cores from ASR-Affected Structures," 12th International Conference on AAR, Beijing (China), pp. 821-832, 2004.
Bérubé, M.A., Frenette, J. and Rivest, M., "Laboratory Assessment of the Potential Rate of ASR Expansion of Field Concrete," Cement, Concrete, and Aggregates, 24 (1), 28-36, 2002a.
Bérubé, M.A., Chouinard, D., Pigeon, M., Frenette, J., Rivest, M. and Vézina, D., "Effectiveness of Sealers in Counteracting Alkali-Silica Reaction in Highway Median Barriers Exposed to Wetting and Drying, Freezing and Thawing, and Deicing Salts," Canadian Journal of Civil Engineering, Vol. 29, No. 2, pp. 329-337, 2002b.
Bérubé, M.A., Chouinard, D., Pigeon, M., Frenette, J., Rivest, M. and Vézina, D., "Effectiveness of Sealers in Counteracting Alkali-Silica Reaction in Plain and Air-Entrained Laboratory Concretes Exposed to Wetting and Drying, Freezing and Thawing, and Salt Water". Canadian Journal of Civil Engineering, Vol. 29, No. 2, pp. 289-300, 2002b.
Bérubé, M.A., Pedneault, A., Chouinard, D., Duchesne, J., and Frenette, J., "Évaluation, gérance, protection et réparation des ouvrages de béton affectés de réactivité alcalis-silice - Projets 1, 2 et 3," Final report, Submitted to Hydro Québec, 68 p., 1996.
Bérubé, M.A., Frenette, J., Landry, M., McPhedran, D., Pedneault, A., and Ouellet, S., "Évaluation du potentiel résiduel de réaction et d'expansion du béton en service atteint de réactivité alcalis-silice," Final report, Report No.CO-93-04, Submitted to Hydro Québec, 151 p., 1994.
Canadian Standards Association (CSA), "Guide to the Evaluation and Management of Concrete Structures Affected by Alkali-Aggregate Reaction," CSA A864-00, Canadian Standards Association, Mississauga, Ontario, Canada, 2000.
Institution of Structural Engineers (ISE), "Structural Effects of Alkali-Silica Reaction - Technical Guidance Appraisal of Existing Structures," Institution of Structural Engineers, 11 Upper Belgrave Street, London SW1X 8BH, 45 p., 1992.
Landry, M., "Influence de l'air occlus, du rapport eau/ciment, de la granulométrie des granulats et de la dimension des éprouvettes testées sur la réaction alcalis-granulats dans le béton," M.Sc. Memoir, Laval University, Québec City (Québec, Canada), 105 p., 1994.
Pedneault, J., "Development of Testing and Analytical Procedures for the Evaluation of the Residual Potential of Reaction, Expansion, and Deterioration of Concrete Affected by ASR," M.Sc. Memoir, Laval University, Québec City, Canada, 1996.
Rivard, P., Bérubé, M.A., Ollivier, J.P., and Ballivy, G., "Alkali Mass Balance During the Accelerated Concrete Prism Test for Alkali-aggregate Reactivity," Cement and Concrete Research, 33 (8) : 1147-1153, 2003.
Rogers, C.A., and Hooton, R.D., "Reduction in Mortar and Concrete Expansion with Reactive Aggregates Due to Alkali Leaching," Cement, Concrete and Aggregates, 13 : 42-49, 1993.
Smaoui, N. Bérubé, M.A., Bissonnette. F., and Fournier, F., "Stresses Induced by ASR in Reinforced Concrete Incorporating Various Aggregates," Proceedings of the 12th International Conference on AAR, Beijing (China), pp. 1191-1201, 2004a.
Smaoui, N., Fournier, F., Bérubé, M.A., and Bissonnette, F., "Influence of Specimen Geometry, Orientation of Casting Plane, and Mode of Concrete Consolidation on Expansion Due to ASR," Cement, Concrete and Aggregates, 26 (2): 58-70, 2004b.
Smaoui, N. B. Bissonnette, Bérubé, M.A., Fournier, B., and Durand, B., "Stresses Induced by ASR in Prototypes of Reinforced Concrete Columns Incorporating Various Types of Reactive Aggregates," Canadian Journal of Civil Engineering (submitted for publication), 2007.
10Smaoui et al. (2004a, 2007) reported that ASR expansion is greatly reduced in the direction of the main restraints (reinforcements, prestressing, postensioning, loading…), while restraining concrete samples in one or two directions can actually contribute at increasing expansion in the unrestrained (or less restrained) direction(s). Moreover, a number of studies also indicated that the ASR expansion of non-reinforced concrete is greater in the direction perpendicular to the casting plane, which phenomenon is amplified in the presence of flat and elongated reactive aggregate particles (Smaoui et al. 2004b).
11This also prevents carbonation. It was observed that cores tested in 1N NaOH at 80°C (176°F), which were allowed to dry for one month in the laboratory before being tested, presented higher expansions and mass increases at the beginning of the tests, i.e. during the so-called "preconditioning" period discussed hereafter (Section F.5), than companion cores kept sealed since coring (Bérubé et al. 1994). However, after correction for these short-term effects which are not related to further ASR expansion in the new storage conditions, the expansion results were similar for both series of cores. Nevertheless, it is always recommended that all cores be wrapped immediately after coring in order to prevent drying. This could actually contribute at significantly reducing the duration of the preconditioning period, which can be particularly long (up to 2-3 months) when cores that were allowed to dry have to be tested in humid air.
12BCA (1992) recommends that nine gage studs be fixed to each core along three equally spaced lines with two 50 mm (2 in) gage lengths each (6 readings per core).
13For instance, in the study by Bérubé et al. (2002b) on the effectiveness of sealers against the ASR developed in median barriers located in Québec City (Québec, Canada), an expansion rate of 0.005 percent per year has been measured for the unsealed control sections of barriers.
14One can note in Table F3 that the petrographic examination of the concrete cores before the tests (cracking, primary reaction products, etc.) the measurement of the water-soluble alkali content of the concrete, the verification of the presence of secondary reaction products after the tests, and the expansion results obtained for companion cores immersed in 1N NaOH at 38°C (100°F) (section F.8) may greatly help in the interpretation of the results of tests in humid air.
15Concrete prisms made in accordance with ASTM C 1293 (i.e. 75 by 75 by 275 to 405 mm in size) (3 by 3 by 11 to 16 in) suffer significant alkali leaching when tested in humid air at 38°C (100°F) (Rogers and Hooton 1993, Rivard et al. 2003). In a particular study (Bérubé et al. 1994, Landry 1994), prisms of 56 by 56 by 300 mm (2 by 2 by 12 in) and of 75 by 75 by 300 mm (3 by 3 by 12 in), and cylinders of 150 by 300 mm (6 by 12 in) and of 255 by 300 mm (10 by 12 in), were tested in air at 38°C (100°F) and > 95 percent R.H. The smaller the specimens tested, the higher was the expansion in the short term; this was explained by the easier access of humidity inside the concrete. However, the smaller the specimens tested, the lower was the expansion in the long term (Figure F3); this was explained by more alkali leaching from the smaller specimens, as confirmed by measurements of the water-soluble alkali content of the specimens tested at the end of the tests, using the hot-water extraction method described in Appendix H.
16This is clear from Figure F4 where the expansion results obtained for concrete cores taken in concrete blocks (230 by 230 by 810 mm in size) (9 by 9 by 32 in) having reached different expansion levels, are compared with the expansion of a companion block. Whatever the expansion level at which the blocks were cored, the expansion of the core samples leveled off after a relatively short period of time while the companion block continued to expand at a regular rate.
17 When the water-to-cement ratio is in the range of 0.30 or less, the concrete almost behaves as a closed system such as the expansion is mostly controlled by the initial concrete alkali content, exactly like if the test was performed in humid air (Bérubé et al. 1994).18 It might be that residual/further ASR develops during the test without significant additional expansion if the concrete was already presenting a lot of cracks where the ASR products might have expanded freely or if the reactive silica was just dissolved in the immersion test solution. The latter phenomenon has been often observed for concretes incorporating the Potsdam siliceous sandstone (Bérubé et al. 1994, 1996; Pedneault 1996).