**3.1 Long term field tests**

Since 1940, a long-term study of "salt weathering" on concrete was carried out by the Portland Cement Association (PCA) [43-45]. Thousands of concrete beams (152×152×762mm) were laid horizontally to a depth of 75 mm in sulfate rich soils (about 5.6% sulfate ion by weight of soil) basins in Sacramento, California. About 10 to 12 wetting and drying cycles are carried out every year. As the experiment progressed, commercial salts were added into the soils to replenish losses through leakage, overflow, and possibly other undetermined causes. Water was added to the basins just before the soils began to show drying to maintain the soils saturated.

Three reports were published [43-45]: the first [43] provided the experimental results of initial set of beams resistance to sulfate attack between 1940 and 1949. The second [44] described the performance development of concrete beams for 5 years field exposure to soils containing sodium sulfate. The third [45] introduced the experimental results for 16 years exposure.

Some other five years field tests were carried out by Irassar and Di Maio [46]. Concrete cylinders with the size of Ø150 × 300mm were buried at half height in a soil containing approximately 1% sodium sulfate. There are several important common experimental observations of the above field experiences:


Concerning the deterioration mechanism, researchers attributed the failure of concrete to physical attack or salt crystallization. However, in effect the experimental results cannot be explained by salt weathering. Fig. 5 is the evolution of visual rating of the upper part of concrete in contact with air, obtained by Irassar and Di Maio [46].

In the test, the mix proportions of different mixes (the ratio of water : binder : sand : aggregate ) were almost the same with different dosages of fly ash, slag and natural pozzolan. From Fig.5, we can deduce some interesting observations:

1. Comparing concrete H1 and H2, the difference between them was the air content, namely 1.3% resp. 4.4%. Thus, if the damage mechanism of the upper part of concrete was caused due to salt weathering, there would be a big difference in visual rating of these two concretes due to the different pore structures. However, after 5 years exposure the visual ratings were almost the same.

Since 1940, a long-term study of "salt weathering" on concrete was carried out by the Portland Cement Association (PCA) [43-45]. Thousands of concrete beams (152×152×762mm) were laid horizontally to a depth of 75 mm in sulfate rich soils (about 5.6% sulfate ion by weight of soil) basins in Sacramento, California. About 10 to 12 wetting and drying cycles are carried out every year. As the experiment progressed, commercial salts were added into the soils to replenish losses through leakage, overflow, and possibly other undetermined causes. Water was added to the basins just before the soils began to show drying to maintain

Three reports were published [43-45]: the first [43] provided the experimental results of initial set of beams resistance to sulfate attack between 1940 and 1949. The second [44] described the performance development of concrete beams for 5 years field exposure to soils containing sodium sulfate. The third [45] introduced the experimental results for 16 years exposure.

Some other five years field tests were carried out by Irassar and Di Maio [46]. Concrete cylinders with the size of Ø150 × 300mm were buried at half height in a soil containing approximately 1% sodium sulfate. There are several important common experimental

1. The parts of the beams above ground, regardless of their cement content, cement composition, mineral additions, surface treatments and type of coarse aggregates, were deteriorated severely. The parts of the beams under ground, however, show little or no

2. Pozzolanic additions, such as fly ash, furnace slag or silica fume, play a negative role in

3. The water-to-cementitious material ratio (W/CM) is the primary factor affecting the durability and performance of concrete in contact with sulfate soils: applying a low

4. According to XRD, optical microscopy and SEM analysis, a large amount of chemical sulfate attack products, such as ettringite, gypsum and thaumasite, were identified in the upper part of concrete in contact with air. However, the samples for these tests were

Concerning the deterioration mechanism, researchers attributed the failure of concrete to physical attack or salt crystallization. However, in effect the experimental results cannot be explained by salt weathering. Fig. 5 is the evolution of visual rating of the upper part of

In the test, the mix proportions of different mixes (the ratio of water : binder : sand : aggregate ) were almost the same with different dosages of fly ash, slag and natural

1. Comparing concrete H1 and H2, the difference between them was the air content, namely 1.3% resp. 4.4%. Thus, if the damage mechanism of the upper part of concrete was caused due to salt weathering, there would be a big difference in visual rating of these two concretes due to the different pore structures. However, after 5 years

the performance of concrete exposed to these conditions;

W/CM ratio results in a higher resistance to sulfate attack;

concrete in contact with air, obtained by Irassar and Di Maio [46].

exposure the visual ratings were almost the same.

pozzolan. From Fig.5, we can deduce some interesting observations:

**3. Experimental studies of "salt weathering" on concrete** 

**3.1 Long term field tests** 

the soils saturated.

deterioration;

drilled with water [45, 46].

observations of the above field experiences:


Fig. 5. Evolution of visual rating at the atmosphere part of concrete [46]

Besides, there are also some field cases, in which a wide variety of efflorescence salts (sodium sulfate, sodium chloride and magnesium sulfate) were routinely observed on the evaporating surface of the foundation concrete in South California [48, 49] However, the damage was not caused by salt crystallization. Much of the cement paste had lost its integrity, mainly as a result of the removal of portlandite, de-calcification of the calcium silicate phases and the ultimate replacement of calcium with magnesium in many of the cementitious compounds. Many reaction products, in particular magnesium silicate hydrate, brucite, Friedel's salt (3CaO·Al2O3·CaCl2·10H2O), sodium carbonate and thaumasite were found at some depth within the concrete.

Another interesting case [50] concerns the slabs of Yongan Dam, which is in Keshi, Xinjiang, P.R. China, where the land is arid and rich in various kinds of salts, especially sulfate salts. The slabs were constructed in August – October 2003. The air temperature fluctuates significantly: the highest temperature is up to 37 oC and at night it is only 15-20 oC. Within

"Salt Weathering" Distress on Concrete by Sulfates? 441

Similar results were also observed in the tests performed by H. Haynes and his coworkers [2]. Narrower spalling zone was found in case of concrete specimens exposed to constant environment at 20 oC and 54% relative humidity from day 28 to day 530, and then at 20 oC and 32% RH from day 530 to day 1132. Extensive spalling zone was found under constant environment at 20 oC and 82% relative humidity from day 28 to day 1132. These tests will be

H. Haynes and his coworkers performed very important and systemical tests about the salt weathering distress on concrete. In the two papers [2, 9], different ambient conditions were created within storage cabinets whose temperature and relative humidity were controlled. The concrete cylinders (Ø76 × 145mm) were partially exposed to 5% Na2SO4, NaCO3 and NaCl solutions. A partial submergence condition was achieved by wetting the specimen to a height of 25 mm. At the height of 50mm, a plastic cover to the container functioned as a quasi-vapor retarder to minimize evaporation. The plastic cover did not touch the cylinder. Hence, within the region of 25 to 50mm the cylinder was exposed to a moist environment. Above 50mm (2 in.), the concrete was exposed to ambient environmental conditions. In the test program the author said that "the sulfate solution and tap water were replaced on a monthly basis; however, replacements for evaporation loss were provided at 2-week intervals. Much of the solution evaporated in the 40 °C and 31% relative humidity environment where, in general, at the end of 2 weeks, minor amounts of solution remained;

The tests were divided into two Phases for 3.1 years. The performance of concrete cylinders

Condition 1: steady at 20°C and 54% relative humidity from 28 to 530 days (Phase I), and

Condition 2: steady at 20°C and 82% relative humidity from 28 to 530 days (Phase I ), and

Condition 3: 40°C and 74% relative humidity from 28 to 406 days (Phase I), and then 40°C

Condition 4: 2-week cycles between 20°C and 54% relative humidity and 20°C and 82% relative humidity from 28 to 530 days (Phase I), and then 2-week cycles between 20°C and 31% relative humidity and 20°C and 82% relative humidity from 530 to 1132 days(Phase II), Condition 5: exposed to 2-week cycles between 20°C and 82% relative humidity and 40°C and 74% relative humidity from 28 to 406 days(Phase I), and then 2-week cycles between 20°C and 82% relative humidity and 40°C and 31% relative humidity from 406 to 560 (847)

The effects of Na2SO4, Na2CO3 and NaCl were compared. The visual observation was photographed, the average mass of scaling materials was collected, the species of concrete were identified by petrographic analysis, and chemical analysis was employed to study the ions distribution. According to the experimental results, they concluded that salt weathering

under five storage conditions was studied in detail, the exposures were:

then 20°C and 32% relative humidity from 530 to 1132 days (Phase II),

and 31% relative humidity from 406 to 1132 days (Phase II),

discussed in detail as follow.

and at times, no solution remained".

then from 530 to 1132 days (Phase II),

days (Phase II).

**3.2.1 H. Haynes tests [2, 9]**

this temperature range, the transformation between thenardite and mirabilite can occur. However, it was found that the slabs became gray and mushy throughout the thickness where they were in contact with groundwater due to thaumasite sulfate attack.

In summary, according to the above analysis the appearances of long term field tests did not show convincing evidences to support "salt weathering" causing the deterioration of concrete partially exposed to sodium sulfate environment.
