Belgorod State Technological University named after V.G. Shukhov
United States of America
United States of America
Belgorod, Belgorod, Russian Federation
employee
Belgorod, Belgorod, Russian Federation
UDK 691 Строительные материалы и изделия
GRNTI 67.09 Строительные материалы и изделия
OKSO 22.06.01 Технологии материалов
TBK 62 Химические науки
BISAC TEC009020 Civil / General
The developed hydrophobic complex protective layer based on polymethylhydrosiloxane (PMHS) organosilicons on the top layer of the concrete surface along with hydrophobic characteristics and low ice adhesion strength enable to provide a developed surface roughness that is a direct measure of high traction forces between vehicle tires and road surface pavement, and its applicability in transport infrastructure as one of the inti-icing methods. Portland cement mortar samples treated with PMHS-based hydrophobic emulsion demonstrated very apparent hydrophobic and icephobic characteristics. The majority of the coated mortar samples reveal over- and superhydrophobicity. Ice adhesion of the mortars with hydrophobic coatings was 10 times lower in comparison with the reference non-treated hydrophilic samples.
anti-icing methods, hydrophobic and icephobic characteristics, ice adhesion, concrete surface roughness
Introduction. According to statistical reports, the level of road traffic injuries in Russia exceeds all acceptable limits, and the fatality risk as a result of road traffic accidents on the territory of the Russian Federation is one of the highest in the world. About one hundred people die in Russia every day due to road traffic accidents. This is a high rate of accidents giving a relatively low car dependency in the country where the average number of cars per thousand people in Russia is three times less than in Europe and almost four times less than in the United States [1].
At the same time, the annual average number of road accidents with fatality cases due to icy conditions of roads in Russia reaches ten thousand, while in the United States this number would not exceed 480 deaths [2]. Plus, the number of those accidents that resulted in people’s physical injuries and material damage is due to the car's loss of control on icy roads. Car accidents are caused due to multiple factors such as exceeding speed limits above 70 km/h on highways and two-lane roads in residential areas, a thin layer of invisible ice as well as intermittent areas of icing on the road pavements, winter precipitation such as snow, freezing rain, drizzle, fog, etc. Most of the road traffic fatalities and serious injuries occur in these conditions especially in the high-risk areas as depicted in Figure 1.
In search of the way to solve this problem on a global scale, many research studies have been conducted for more than a decade and resulted in various methods, materials, and technologies that are proposed to mitigate the issues related to icy slippery roads. The research studies focused on improving the anti-icing properties of a road surface have been conducted since the 70s of the XX century. Now, there established two fundamental methods for ice control, are physical and physical, and chemical methods. The physical method is based on the increase of anti-icing properties of a surface due to its treatment with various anti-icing compounds. The physical-and-chemical method considers the design of materials with anti-icing properties for building top protective layers of the road surface. Depending on the chosen approach to solve the problem, the research studies are being performed in the frame of one of the methods.
Among the most commonly applied solutions are the following:
Melting ice using heating devices. Despite the cost-effective benefits over mechanical deicing such as chopping off and breaking of ice crust, the method is very energy-intensive. This method of anti-ice control is actively used in factory areas, access roads, and residential areas [3, 4].
Introduction of chemical additives. Among the most common and effective methods of permanent action is the internal introduction of chemical additives which enable the increase of protective characteristics of portland cement concrete and other road surfaces, such as water repellence, frost resistance, and steel reinforcement corrosion control. These additives can be classified as follows:
- finely ground with hydraulic properties or properties of colloidal systems;
- salts of inorganic acids which accelerate the processes of hydration and structure formation of cement concrete;
- additives that increase the hydrophobicity of concrete road surfaces;
- polymer additives that polymerize in concrete [5].
Use of anti-icing coatings. A group of scientists led by Sture Persson and Lars-Orff Anderson [6] suggested the application of vulcanized non-polar rubbers as anti-icing coatings, where the vulcanization agent consists of sulfur and/or components derived from sulfur or metal oxides. In this case, the anti-icing effect is achieved due to the high deformability of rubbers which do not allow the formation of ice crust when vehicles are in motion.
The application of pervious asphalt concrete which intended to quickly remove moisture from the pavement and, so reduce the chance for ice formation was one of the proposed technologies [7]. However, the European practice of 1995–96 showed that the technology did not perform as well as was hoped. On the contrary, the field demonstrations with pervious asphalt concrete resulted in the increase of maintenance costs during the winter season by 10–20%, mainly due to the rapid removal of salts from the asphalt top layer and so, the increased demand for anti-icing agents.
Nowadays, physical-and-chemical method to prevent or remove ice formation has become more widely used. The method suggests making a hydrophobic coating on the surface of a material by introducing chemical additives which reveal water-repelling or hydrophobic properties.
In Switzerland, since 1974, field demonstrations have been carried out when in the composition of the top layer of fine-grained asphalt-concrete pavement was added 5% of a special multicomponent anti-icing additive "Verglimit". The additive was composed of 80% calcium chloride and 5 % sodium hydroxide as active agents [8, 9]. These pilot concrete pavements were placed in two areas, the carriageways and bridges in Switzerland, Austria, Germany, the USA, and France. The test results demonstrated significant benefits associated with maintenance labor and costs compared to conventional coatings. The pilot pavements had a reduced adhesion of snow and ice deposits to the applied anti-icing coating.
Earlier, the authors of this article proposed a complex coating based on PMHS compound applied over a specially engineered Portland cement concrete top layer that is enabled to provide superior hydrophobic properties to concrete surfaces [10-12]. Some wetting properties of the proposed complex hydrophobic coating such as contact angle and roll-off angle have been studied [12, 13].
The ice adhesion properties of the developed complex hydrophobic coatings were studied in this research work to evaluate icephobicity of the level of traction between vehicle tire and surface of concrete pavement as a factor of applicability of the proposed anti-icing method in concrete transportation infrastructure.
Materials and methods. Portland cement Type I supplied by LafargeHolcim (USA), as well as CEM I 42.5 N (Russia) were used to produce cement mortars as a top protective layer. Standard fractionated quartz sand with an average particle size of 425 microns and quartz sand from the Vyazemskoye deposit (Russia) was used as a fine aggregate to produce cement mortar samples. Polyvinyl alcohol (PVA) fibers with a diameter of 1 micron and length of 12 mm were used as a fibrous fine component to provide additional roughness on the surface of the cement mortars.
Polyvinyl alcohol in powder form (PVA) was used as an emulsifier for the production of hydrophobic oil in water emulsion. The procedure for emulsion preparation has been described in [10, 12].
Two analogous organosilicon compounds Polymethylhydrosiloxane produced by Dow Corning in the USA and by SIlan in Russia were used as active hydrophobic agents. Also, silica fume and metakaolin were used as fine mineral fillers in the hydrophobic emulsion. Wetting properties as well as icephobic (anti-icing) characteristics of the prepared mortar samples treated with the complex hydrophobic PMHS emulsion were evaluated by measuring contact angle and roll-off angle in the “water-solid-air” interface and the adhesion shear strength within the contact area of hydrophobic coating and ice using the goniometric system (Kruss DSA-100) and the force sensor PASCO CI-6746, respectively.
Experimental Results. In order to evaluate adhesion properties of a hydrophobic coating on the mortars surface to ice layer, the mortar samples treated with the developed complex hydrophobic PMHS emulsion were prepared, determined as optimal compositions based on the contact angle (CA) and the roll-off angle (ROA) test results [12-14]. To estimate the effectiveness of the complex hydrophobic PMHS coatings in assessing wetting properties, 30 mortar compositions were prepared with and without PVA fiber in the matrix as depicted in Table 1. The samples were divided into 3 series for further testing. Mortar samples from the first set were reference mortars (M1-M10). The second set of the samples was treated with the hydrophobic complex emulsion that contained 5% PMHS as an active hydrophobic component (M1/5-M10/5) and the third set of the samples were treated with the emulsion containing 25% of PMHS compound (M1/25-M10/25).
According to the previously obtained data [12, 13], the highest values of hydrophobicity were revealed by the mortars treated with a siloxane emulsion containing 5% of the active PMHS hydrophobic component.
Table 1
Mix design and wetting properties of the mortars
|
Mortars ID |
W/C ratio |
C/S ratio |
PVC fiber, % |
Contact angle, degree |
Roll-off angle, degree |
|
0.25 |
- |
1 |
9 |
- |
|
|
M2 |
1 |
1 |
12 |
- |
|
|
M3 |
0.5 |
1 |
0 |
- |
|
|
M4 |
0.4 |
1 |
0 |
- |
|
|
M5 |
0.33 |
1 |
25 |
- |
|
|
M6 |
- |
- |
13 |
- |
|
|
M7 |
1 |
- |
15 |
- |
|
|
M8 |
0.5 |
- |
1 |
- |
|
|
M9 |
0.4 |
- |
0 |
- |
|
|
M10 |
0.33 |
- |
0 |
- |
|
|
M1/5 |
- |
1 |
146 |
3 |
|
|
M2/5 |
1 |
1 |
148 |
2 |
|
|
M3/5 |
0.5 |
1 |
156 |
5 |
|
|
M4/5 |
0.4 |
1 |
131 |
8 |
|
|
M5/5 |
0.33 |
1 |
127 |
14 |
|
|
M6-5 |
- |
- |
146 |
8 |
|
|
M7/5 |
1 |
- |
144 |
15 |
|
|
M8/5 |
0.5 |
- |
146 |
21 |
|
|
M9/5 |
0.4 |
- |
141 |
27 |
|
|
M10/5 |
0.33 |
- |
139 |
35 |
|
|
M1/25 |
- |
1 |
123 |
- |
|
|
M2/25 |
1 |
1 |
119 |
- |
|
|
M3/25 |
0.5 |
1 |
122 |
74 |
|
|
M4/25 |
0.4 |
1 |
121 |
57 |
|
|
M5/25 |
0.33 |
1 |
120 |
66 |
|
|
M6/25 |
- |
- |
116 |
61 |
|
|
M7/25 |
1 |
- |
119 |
60 |
|
|
M8/25 |
0.5 |
- |
125 |
62 |
|
|
M9/25 |
0.4 |
- |
123 |
64 |
|
|
M10/25 |
0.33 |
- |
122 |
68 |
The contact angle values of water droplets on the surface of the mortar samples were in the range of 140 - 156° and that indicated over- and superhydrophobicity of the studied coatings.
Correlation between the wettability characteristics and the strength of ice adhesion on the surface of hydrophobic mortar samples.
To assess the icephobic characteristics of the developed hydrophobic protective layer of cement mortars, ten mixes of mortar compositions with and without PVA fibers were tested for ice adhesion strength to the surface of mortar samples by applying shear stress to an ice layer using the force sensor PASCO CI-67461 device, according to the method described in [15, 16]. The tests were performed for reference mortar samples, as well as those treated with 5% and 25% hydrophobic PMHS emulsion. The test results are graphically presented in Figure 3.
The shear stress data demonstrate a significant decrease in ice adhesion strength relative to the surface of mortar samples treated hydrophobic coating regardless of whether the samples contain PVA fibers or not. The ice strength adhesion for the mortar samples with coatings was 10 times lower than untreated reference mortar samples.
It should be noted that in the series of mortar samples treated with hydrophobic PMHS emulsion, the shear strength values were higher for the fiber-reinforced mortars in comparison with the non-reinforced samples and the difference between the values was 28% and 2% for the mortar samples treated with the emulsions containing 5% and 25% PMHS component, respectively. The higher values of ice adhesion observed for the fiber-reinforced mortars are justified by the greater roughness that PVA fibers have created on the surface of the mortar samples, with this creating topographical obstacle that requires greater stress to apply for ice to slide over the surface.
For the mortar samples treated with the emulsion containing 25% PMHS component, the ice adhesion values were lower by an average of 27% vs the mortar samples coated with an emulsion containing 5% PMHS.
Reduced ice adhesion to the coated top layer of the mortars, in this case, was the result of the thicker hydrophobic layer that the 25% PMHS emulsion was enabled to create on the surface of mortar samples, thus covering and reducing it's natural and impregnated with PVA fibers roughness of the top mortar layer. This is a similar adhesion effect under shear forces as was observed earlier in this study for the fiber-reinforced and non-reinforced mortar samples, when the roughness of surfaces is much lower, that enables ice to slide much easier over the smooth hydrophobic surface under shear loading due to the minimal surface roughness. The less the surface roughness, the lower the traction forces between surfaces that arise under horizontal shear loads. Taking into account the applicability of these protective hydrophobic coatings for concrete in road construction, the surface roughness is a fundamental factor as it has a direct correlation to the degree of traction forces of a vehicle tire to the road surface in motion [13, 14]. In this regard, the lower roughness characteristics and lower ice adhesion strength values of the mortar samples treated with 25% PMHS emulsion, having a smoother surface, will indicate lower traction forces of a vehicle tire against the road surface pavement.
At the same time, hydrophobic coatings produced by treatment of the mortar surface layer with 5% PMHS emulsion provides low adhesion of ice crust on the protective hydrophobic surface of mortar samples, which enables an anti-icing (ice-phobic) effect. The developed complex hydrophobic coatings also retain a highly developed surface roughness and, so the higher traction forces between vehicle tires and road surface pavement, which defined their applicability in concrete transport infrastructure as one of the inti-icing methods.
Conclusions. The developed protective complex hydrophobic coating based on PMHS compounds for concrete surface application demonstrated the effectiveness in mitigating ice adhesion, which is a critical factor when applied to the safety of roadways in the winter season.
Mortar samples treated with hydrophobic PMHS emulsion demonstrated very apparent hydrophobic and icephobic characteristics. The majority of the coated mortar samples reveal over- and superhydrophobicity.
Ice adhesion of the mortars with hydrophobic coatings was 10 times lower in comparison with the reference non-treated hydrophilic mortar samples.
Samples reinforced with PVA fibers and treated with 5% PMHS hydrophobic coatings demonstrated a good balance of high hydrophobicity and low ice adhesion to the mortar surface layer while retaining moderate traction forces when horizontal shear loads were applied.
Mortar samples, with and without PVA fiber-reinforcement treated with 25% PMHS hydrophobic emulsion showed minimal ice adhesion values and minimal traction effect, while the hydrophobic characteristics were 15-20% lower than those for the mortar samples treated with 5% PMHS emulsion.
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