As a common issue for cold weather regions, premature deterioration of concrete at joints has been reported in many states. In this paper, the mechanisms of joint deterioration were investigated, and then, experimental investigations were conducted to further verify some of the mechanisms. It was found that freeze-thaw (F-T) damage and salt crystallization are not enough to cause the observed deterioration, but the deterioration near the interfacial transition zone (ITZ) may be the cause of some of the observed phenomena. In the experimental work, samples were tested at 40°F in salt solutions to observe the deterioration in the ITZ using the scanning electron microscope (SEM). Concrete tested in MgCl2 solution indicated distress in ITZ under SEM. It was found that ITZ may act as a shortcut for ion transfer to surrounding concrete near the joints and may also be the weak point for cracking due to expansion of the paste.
Sawn joints in concrete pavements are used to control both transverse and longitudinal cracking, which are induced by shrinkage or contraction of the pavement. According to the American Concrete Pavement Association [
Performance and service life of concrete pavements are heavily dependent on the performance of the joints. Hence, premature joint deterioration is a great concern, particularly in cold weather regions. Figure
Photos of joint deterioration from multiple states. (a) Arizona, 2011. (b) Colorado, 2010. (c) Illinois, 2014. (d) Kansas, 2012. (e) Missouri, 2005. (f) Nebraska, 2010.
The objective of this research was to review the current state of knowledge of possible causes of joint deterioration and further investigate the mechanism behind this form of deterioration.
Damage is typically observed in two different forms. The first is the formation of small flakes in the paste near the joint (Figure
Typical F-T deterioration: (a) F-T damage and (b) joint deterioration.
The current knowledge of joint deterioration indicates that there are four major mechanisms by which concrete joints may deteriorate: Freezing-thawing (F-T) damage Salt crystallization Oxychloride expansion Interfacial transition zone damage
It is widely accepted that the freeze-thaw mechanism is typically associated with concrete that contains marginal air-void systems that are exposed to abundant moisture. Moisture in a joint may be higher than that at the surface because water is trapped due to insufficient drainage of the base layer or the cracks not opening up. Li et al. [
Deicing salts are applied to roadways in areas that experience snow and ice in order to ensure the safety of traffic on roadways. Salts in pore solutions may crystallize out and form crystals due to changes in external humidity or temperature. A state of supersaturation is required for crystallization to occur. Under supersaturation, the cumulative crystals generate stress on the confining pore walls and cause damage in the solid matrix of a concrete mixture [
Certain deicers contain chemicals that may deteriorate concrete pavement. Chloride deicers will increase the concentration of calcium and magnesium in pore water of concrete. At the same time, the chloride is able to react with cement paste and forming a new expansive phase that may be expansive, calcium chloride [
Formation of calcium oxychloride occurs at temperature just above freezing [
When MgCl2 is used as a deicer on concrete pavements, a reaction between Ca(OH)2 from cement hydration and magnesium chloride will produce brucite (Mg(OH)2 (Equation (
As the secondary reaction, brucite produced from Equation (
CaCl2 produced from Equation (
Formation of magnesium oxychloride is dependent on the concentration of magnesium chloride [
The interfacial transition zone (ITZ) in concrete is a 10–50
In a previously reported project, Taylor et al. [
Weight change of beams for 600 freezing and thawing cycles (W/C ratio 0.4/0.5; silica fume content 0%, 3%, and 5%; 0.5–0% SF (S) sample with W/C = 0.5, 0% silica fume, soaked in NaCl).
SEM map analysis on distressed samples under cyclic freeze thaw in CaCl2 (calcium and sodium).
It is well known that the solubility of calcium solutions increases with decreasing temperature. It was hypothesized that, as temperatures are reduced in a freezing system, then an ITZ containing high amounts of Ca(OH)2 might tend to dissolve more readily than the bulk C-S-H system nearby. Such dissolution would encourage separation of the coarse aggregate particles from the paste. In addition, chloride ions can penetrate into hydrated cement pastes [
The F-T damage and salt crystallization stresses discussed above can be quantified. Based on an equation proposed by Correns [
Figure
Sample exposed to 3% NaCl solution showing washed aggregate on the corner.
Therefore, the purpose of the work discussed below was to study whether the formation and expansion of oxychloride was a part of mechanism causing the deterioration observed in Figures
Materials used in this study include the following: Coarse aggregate: one inch nominal maximum size of round gravel (specific gravity (SpG) = 2.66, absorption = 0.3%, and dry-rodded unit weight = 1541 kg/m3) Fine aggregate: No. 4 sieve size nominal maximum size river sand (SpG = 2.68, absorption = 0.6%, and fineness modulus = 3.08) Portland cement: ASTM C150 Type I Supplementary cementitious materials (SCMs): ASTM C618 Class C fly ash and silica fume
Mixtures used in this study had a constant water-to-cementitious material ratio (w/cm) of 0.45 and a cementitious material content of 335 kg/m3. Mixture parameters are shown in Table
Mixture proportions.
Material | Quantity |
---|---|
Cementitious materials (kg/m3) | 335 |
Type I cement | 80% |
C fly ash | 20% |
Water (kg/m3) | 151 |
Water-to-cementitious material ratio | 0.45 |
Course aggregate (kg/m3) | 1125 |
Fine aggregate (kg/m3) | 666 |
Concrete mixing and curing were conducted in accordance with ASTM C 192. Air content, slump, and unit weight were measured after mixing. Two 7.6 × 10.2 × 40.6 cm beams were cast from each mix. Sample preparation comprised 3 days wet curing followed by exposure to air until 28 days of age. Beams were cut into 7.6 × 10.2 × 6.35 cm prisms using a diamond saw at 28 days (Figure
Saw cut slice sample from concrete beam.
All samples were vacuum saturated in accordance with ASTM C1202 for 24 hours using the following solutions: 3% sodium chloride (NaCl), 3% magnesium chloride (MgCl2), and water.
Six slices were placed in a pan, partially submerged in assigned solutions (Figure
Samples partially immersed in deicers.
SEM images of sample soaked in water, NaCl, and MgCl2 for 56 days.
It is observed that the samples soaked in water did not exhibit any distress, as was expected, since no F-T cycles were applied. Likewise, neither osmotic pressure nor critical saturation should occur.
For samples soaked in NaCl, there was some microcracking in the paste matrix, and the zone between paste and aggregate was undamaged. A possible explanation for this damage is the reactions between aluminate phases of the matrix and deicer solutions [
SEM images of samples soaked in MgCl2 showed cracking in the boundary between aggregate and paste (Figure
Photo of sample after 56 days in MgCl2: paste was pushed above aggregate.
Zhang et al. [
For samples soaked in 3% MgCl2, whole aggregate particles were observed to be removed in several samples (Figure
Samples exposed to MgCl2 solution during F-T. Left to right: 10%, 5%, and 0% silica fumes [
To explain the phenomenon in Figure Salt solution is trapped in the kerf of a sawn joint, either because it has not cracked out or the base material below the crack is impermeable. Salt solution is preferentially transported around coarse aggregate particles through the ITZ. Oxychloride compounds are formed in the paste around and near the aggregate particles. The paste expands, setting up tensile stresses and so cracking in the ITZ. Any dissolution of the ITZ will accelerate this damage. Cracks are propagated under traffic through the paste to the top surface, typically parallel to and about 1.9 to 2.5 cm from the sawn face. Aggregates are either removed and left, paste free, loose in the joint, or remained in the concrete, projecting into the joint.
Joint deterioration in sawn pavements has been found in many cold regions of the United States. The major mechanisms by which concrete joints may deteriorate include (1) freezing-thawing (F-T) damage, (2) salt crystallization, and (3) oxychloride expansion. The interfacial transition zone (ITZ) between cement paste and aggregate permits more salt solution to penetrate around aggregate particles and potentially accelerates the joint deterioration.
By reviewing the previous work and testing samples subjected to soaking and F-T cycles, a mechanism has been described that explains the observed formation of so-called incremental cracks at joints. Solutions containing magnesium and calcium chloride appear to be penetrating the exposed ITZ around coarse aggregate particles in nondraining joints (Figure
Crack developing out of a saturated ITZ. (a) Schematic sketch of the theory. (b) Laboratory observation supporting the theory.
The data generated from this research are available upon request to the corresponding author.
The authors declare that they have no conflicts of interest.
The present study is an extension of Dr. Jiake Zhang’s PhD work “Investigation of deterioration of joints in concrete pavements” (2013). This work was funded by the National Concrete Pavement Center, Ames, Iowa. This study was also partially supported by the National Natural Science Foundation Project (NSFC 51868066) and the Qinghai Science & Technology Department Natural Science Foundation Project (2018-ZJ-931Q).