Introduction

Concrete roads are subjected to harsh environmental conditions, resulting in a high level of deterioration and the need for regular maintenance. Concrete is a porous material that allows water and waterborne chemicals to penetrate into the concrete matrix, causing concrete to crack and spall – eventually leading to possible structural failures. Concrete used to construct roads is most commonly subjected to carbonation, freeze-thaw cycle damage, corrosion due to road salts and sulfate attack.

Carbonation takes place when the carbon dioxide (CO₂) in the environment - exaggerated by vehicle emissions – dissolves in water, penetrates into the porous concrete and reacts with the calcium hydroxide in the cement paste to form calcium carbonate (CaCO₃). This reaction lowers the pH of the concrete to around 9, causing embedded reinforcing to corrode. It is as a result of the reinforcement corrosion that the concrete cracks and spalls.

The freeze-thaw cycles that occur within porous concrete causes deterioration by creating internal pressures within the voids, resulting in cracks and eventual spalling. When the entrapped water inside the cracks, pores and capillaries within the concrete matrix freeze, it expands, forcing the voids open and enlarging them. As the freeze-thaw cycles repeat, the voids become bigger and bigger, causing concrete to break apart, little by little. Another problem encountered during winter months is that road salts are used to melt or prevent ice from building on the roads, to ensure safer driving conditions. These salts dissolve in the water and penetrate into the porous concrete, causing the embedded reinforcing to corrode, which results in concrete deterioration.

Concrete roads are subjected to sulfate rich soils, used to construct the bases of the roads and pavement structures. Sulfates dissolved in water penetrate into the concrete matrix causing damage to the concrete.

Concrete roads will be more durable and require minimal maintenance if we could stop water and waterborne chemicals from entering the concrete. Impermeable concrete is durable concrete.
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Penetron Admix Makes Concrete Impermeable

Penetron Admix is a permeability reducing admixture that lowers the permeability of concrete by self-healing all cracks, pores and capillaries up to 0.5mm (1/51”) in size. Penetron Admix treated concrete is impermeable, stopping all water and waterborne chemicals from entering the concrete, even under high hydrostatic pressures.

The main objective of the tests conducted, as shown below, is to prove that Penetron Admix treated concrete is resistant against carbonation, freeze-thaw cycle damage, corrosion and sulfate attack, which in turn increases the durability of concrete roads.
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Carbonation Testing

Penetron (P) and Penetron Admix (A) treated samples were tested to determine the CO₂ diffusion coefficient as per GOST 31383-2008: Protection of Concrete and Reinforced Concrete Structures against Corrosion compared to the untreated, control samples (K).

After the samples were prepared and cured for 28 days, they were exposed to capillary suction for 19 days, removed and left in controlled drying conditions before the testing commenced. The samples were kept in a controlled CO₂ chamber for 14 days, with permanent fluid parameters: CO₂ concentration of (10?5)% by volume, relative air humidity of (75?3)% and temperature of (20?5)?C. Intermediate determinations were carried out within 7 days. Samples were then removed from the chamber, split and treated with 0.1% alcohol solution of phenolphthalein. Figure 1-3 below provides visual representation of the samples after phenolphthalein was applied.
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Figure 1: 14 days - Samples with Penetron (P)

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Figure 2: 14 days - Samples with Penetron Admix (A)

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Figure 3: 14 days – Control Samples (K)

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Table 1 below contains a summary of the carbonation depth and effective diffusion coefficient of CO₂ results collected during the carbonation testing described above.
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Table 1: Carbonation Test Results

Sample Set	Effective diffusion coefficient of CO2 (Д'cm2/s)	Carbonation Depth Average (mm)
		7 Days	14 Days
Control (K)	1.10 x 10-4	7.2	10.1
Penetron Treated (P)	0.30 x 10-4	1.22	3.72
Penetron Admix Treated (A)	0.19 x 10-4	1.15	3.0

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Freeze-Thaw Cycle & Sulfate Resistance Testing

Penetron Admix treated samples were tested on the basis of accelerated methods according to the recommendations in the Methods of Concrete Protection under the Conditions of Sulfate Exposure and compared to the untreated, control samples.

After the samples were prepared and cured for 2 days, they were exposed to capillary suction for 19 days, removed and left in controlled drying conditions for 7 days before the testing commenced.

Freeze-Thaw Cycle Testing: After the number of variable freeze-thaw cycles established for the given grade of concrete (37 freeze-thaw cycles), according to GOST 10060, for roads and airfield coatings, the mass loss of the samples should not exceed 3% and maintain a set strength ratio. Table 2 below contains a summary of the results.
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Table 2: Freeze-Thaw Cycle Test Results

Sample Number	Control Samples: Concrete Strength (MPa)		Penetron Admix Treated Samples: Concrete Strength (MPa)
	Test Samples	Main Samples	Test Samples	Main Samples
1	47.03	58.32	60.56	59.84
2	50.86	56.81	59.03	59.49
3	50.11	57.47	60.87	61.84
4	49.73	55.51	61.33	61.70

Sulfate Test: Samples were submerged in aggressive water for a total of 12 weeks. The relative amount of aggressive SO₃ ions, in g/g, absorbed by the concrete (QSO₃^b) was measured after 3, 6, 9 and 12 weeks and plotted on a graph as sulfate ion absorption by concrete over time compared to the accepted sulfate resistance reference curve. If the curve is below the reference curve, the concrete is considered sulfate-resistant and may be used in concrete exposed to a concentration of S0₄^2- ions not more than 2,000 mg/l. Table 3 below contains a summary of the results.
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Table 3: Sulfate Test Results

Sample Set	Absorption of Sulfate Ions (QSO3b)				Total Sulfate Ion Absorption (%)
	3 Weeks	6 Weeks	9 Weeks	12 Weeks
Control	0.0048	0.0048	0.0049	0.0051	6%
Penetron Admix Treated	0.0048	0.0048	0.0048	0.0048	Constant (0%)

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Conclusion

Penetron Admix treated concrete roads will last longer and require minimal maintenance due to the impermeable nature of the Penetron Admix treated concrete. Impermeable concrete is proven resistant against carbonation, freeze-thaw cycles, corrosion and sulfate attack, making it a durable and permanent solution.

Carbonation Testing: The test results and calculations have shown that the concrete samples, with a concrete cover of 20mm, ensures the integrity of reinforcement in concrete structures for a certain amount of years.

• Penetron Treated Sample (P) = 80 years

• Penetron Admix Treated Sample (A) = 105 years

• Untreated, Control Sample (K) = 35 years

This concludes that Penetron treated concrete will last up to 70 years longer compared to untreated concrete exposed to the same carbonation prone environment.

Freeze-Thaw Cycle Testing: The test results and calculations have shown that Penetron Admix treated concrete has increased the frost resistance from F200 to F300 when compared to the control sample. This means the Penetron Admix treated sample can withstand at least a hundred freeze-thaw cycles more than the control sample. F300 is the highest level of frost resistance classification.

Sulfate Resistance Testing: The test results and calculations have shown that Penetron Admix treated concrete is more sulfate resistant compared to the control sample and may be used in aggressive (sulfate) environments to improve the durability and extend the service life of concrete.

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References

1. Stepanova, V. (2017). Testing of Penetron waterproofing materials to determine CO2 diffusion permeability rate according to GOST 31383-2008 in comparison with unprotected concrete and issue of research appraisal. NITs Stroitel’Stvo Research and Development Center.
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2. Teltayev, B. (2016). Certificate on the use of Penetron Admix additive for the improvement of the quality of cement-and-concrete mixture and cement concrete. Republic of Kazakhstan: Ministry for Investments and Development, Committee on Motor Roads, Scientific and Research Institute for Motor Roads Kazdornii.