Proceedings of the International rilem conference Materials, Systems and Structures in Civil Engineering 2016
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- Bu səhifədəki naviqasiya:
- 2. Materials and methods
- Mixture notation w/b SCM content, % Cement Water GGBFS FA Sand
- 2.2 Methods
107 International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Service Life of Cement-Based Materials and Structures 22-24 August 2016, Technical University of Denmark, Lyngby, Denmark
reduced, e.g. from 30° C to 5° C, all thenardite absorbed inside the sample will convert to mirabilite. The expansion caused by the crystallization and phase change during such thermal cycles is significant (more than 3 times volume increase [13]) resulting in rapid deterioration. Since the sample is submerged, the whole sample surface is exposed to the deterioration process, so extent of damage is higher and easier to quantify. Folliard and Sandberg achieved complete disintegration of 25 mm concrete cubes with w/cm ratio of 0.5 after only 30 thermal cycles when submerged in 30% sodium sulfate solution. This exposure condition was compared with other different exposures involving drying cycles, partial drying, with and without thermal cycles. While particular damage was seen in all exposures, other exposures didn’t cause such fast and extensive damage. Since the thermal cycling between 5 and 30 °C in 30% sodium sulfate solution is reported as the one of the most severe exposures (due to rapid crystallization of mirabilite [13]), this exposure condition was selected for the current research.
In the field studies of sulfate attack, the extent of damage was often assessed using visual rating [8], [9]. However, rating damage based on visual appearance is subjective, semi- quantitative method, which is not suitable for PSA considering the surface scaling nature of degradation. Considering the similarity of degradation mechanism and character of the damage, methods used for assessment of concrete resistance to freezing and thawing, such as mass loss, ultrasonic pulse velocity or fundamental resonance frequency appear to be particularly promising for quantification of extent of damage and rate of deterioration in PSA.
The objective of this research is to identify exposure conditions and deterioration evaluation methods suitable for standard testing that can be used for rapid comparison of mixture compositions, durability design, and analysis of life cycle cost. For this purpose, mortars with various w/cm ratio and different types and contents of supplementary cementitious materials were subjected to the selected exposure conditions. Mortars were preferred over concrete because of higher permeability, which shortens the testing time, and over cement paste because of the presence of interfacial transition zones. High-sulfate resistant cement (ASTM Type V) was used in all mixtures to reduce the possibility of chemical interaction between cement and sodium sulfate. Various methods for assessment of deterioration were applied using selected exposure. It was found that 100 thermal cycles between 5 and 30 °C immersed in 30% sodium sulfate solution were sufficient to assess the resistance of a range of mortar mixtures. The most suitable techniques for evaluation of deterioration rate was mass loss, while fundamental resonance frequency and ultrasonic pulse velocity were found to be unsuitable.
2. Materials and methods
High sulfate-resistant cement produced by Lafarge was used in all mixtures in order to reduce the possibility of chemical sulfate attack. SCMs used in this research were Holcim GGBFS, from Ontario, and FA type F from Avon Lake, Ohio, USA. Natural glacial sand of mixed mineralogy from Sunderland Pit, Ontario, Ontario Canada was used in all mortars at a constant rate of 45% by volume.
108 International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Service Life of Cement-Based Materials and Structures 22-24 August 2016, Technical University of Denmark, Lyngby, Denmark
cement mortars to PSA were investigated. Sulfate resistant portland cement (ASTM Type V) mortars with w/cm ratio of 0.35, 0.40, 0.45 and 0.50 were tested. Sulfate resistant cement was used in order to minimize chemical sulfate attack. The effect of SCM on PSA was studied using mortars with w/b ratio of 0.40. The replacement levels of cement by SCM were: 45 and 65% for GGBFS, and 20 and 40% for FA. The mix designs are shown in Table 2. The mass of sand is given in oven dry condition, and additional water was added to compensate for water absorption of 0.6% by mass.
Table 1: Mixture proportions [kg/m 3 ].
Mixture notation w/b SCM content, % Cement Water GGBFS FA Sand Slag FA M50
0.50 0 0 663 332 0 0 1182 M45
0.45 0 0 706 318 0 0 1182 M35
0.35 0 0 811 284 0 0 1182 M40
0.40 0 0 755 302 0 0 1182 SG45
0.40 45 0 406 295 332
0 1182
SG65 0.40
65 0 256 292 475 0 1182 FA20 0.40
0 20 594 297 0 148
1182 FA40
0.40 0 40 438 292 0 292 1182
For each mixture, three mortar prisms of 51 mm × 51 mm × 266 mm were cast for PSA exposure. The specimens were demolded at the age of 1 day and kept in saturated lime solution until 3 days. After 3 days of age the specimens were removed from the solution and kept in sealed conditions at 23 °C until the start of sulfate exposure at 28 days. This curing regime was selected considering common practice and standard requirements in North America. For sulfate exposures CSA A23.1-14 [6] requires “additional” curing for the highest level of sulfates that corresponds to 7 days of curing, though no wet curing is required. Sealed curing would meet the CSA definition of additional curing. According to this Canadian standard [6] “extended” wet curing of 7 days is only required for extremely severe chloride exposure. Thus the curing conditions used here,
wet curing until the age of 3 days and sealed curing until the age of 28days, exceed the “additional” curing requirements of [6] but would likely be inferior to “extended” curing.
Sulfate exposure involved thermally cycling mortar prisms submerged in sodium sulfate solution. Thermal cycles were between 4 ±1 and 32 ±2 °C with maximum cooling and heating rates of 2.5 and 4 °C/h, respectively. The duration of one full thermal cycle was 24 hours. The concentration of sodium sulfate solution was 30% by mass and the solution was replaced Yüklə 8,6 Mb. Dostları ilə paylaş:
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