Water permeability of concrete and its effect on the durability of structures

Because of its strength and versatility, concrete is one of the materials used in construction the most frequently. However, not all concrete is made equal, and water permeability is one of the main elements that affects how long it lasts. The ease with which water permeates concrete is referred to as its water permeability. This seemingly uncomplicated feature can significantly affect how long-lasting buildings and bridges are.

Concrete can absorb moisture from the air when it is wet, which can cause a variety of problems. Water deterioration of the concrete over time can result in cracks and possibly structural failures. This is particularly true if the concrete is exposed to harsh environmental conditions or is not mixed properly. Buildings that are better able to withstand these difficulties can be designed with an understanding of how concrete’s water permeability affects it.

This article will discuss how water permeability affects concrete structure durability and provide solutions for these effects. We’ll offer advice on maintaining the durability and strength of your concrete structures, covering everything from the function of the composition of the concrete to preventive measures.

Aspect	Details
Water Permeability	Water permeability refers to how easily water can pass through concrete. Low permeability means water has a harder time penetrating the surface.
Impact on Durability	Concrete with low water permeability is generally more durable because it resists damage from water-related issues, like rusting of reinforcement bars and freeze-thaw cycles.
Factors Affecting Permeability	Factors such as mix design, curing methods, and the quality of materials used affect how permeable concrete is. Properly mixed and cured concrete typically has lower permeability.
Testing Methods	Common tests to measure water permeability include the water absorption test and the rapid chloride penetration test. These help determine how well the concrete will perform over time.
Preventive Measures	To reduce water permeability, use additives that improve the concrete mix, ensure proper curing, and apply sealants to the surface. Regular maintenance also helps keep concrete structures in good shape.

The durability of structures is largely dependent on the water permeability of the concrete. Water absorption by concrete can cause cracking, deterioration, and rusting of steel reinforcements over time. The concrete is weakened by this increased water permeability, increasing the structure’s susceptibility to environmental harm and lowering its overall durability. Designing concrete structures that are more durable and resilient can be aided by an understanding of and management of water permeability.

General information

The ability of a material to resist the effects of liquid-aggressive environments on the composition and functionality of products is the ultimate definition of concrete permeability.

The material has the ability to absorb moisture from the surrounding air as well as from direct contact with water because of its capillary-porous structure.

Concrete that is heavy and dense has the lowest permeability rate. This parameter is relatively important for cellular (porous) concrete, but it falls between 7 and 8% for options with light fillers. For instance, aerated concrete has a 20–25% water absorption capacity.

Factors Affecting Concrete Permeability

Structures’ permeability is dependent on the following conditions:

• the overall porosity of the product;
• the pore structure;
• the properties of the binder and fillers.

Concrete is a multiphase, intricate system made of cement stone, a large number of tiny pores saturated with air and aqueous solutions, and regularly distributed inclusions of sand and coarse-grained filler.

Characteristics of the porous structure of the material

Permeability, or the ability to absorb water, is not primarily caused by the existence of a sizable amount of free cells within the material’s structure. The form and distribution of porous formations have a significant impact on the moisture resistance of concrete.

Three categories can be used to categorize pores based on how they form:

• voids that appear during the laying of the mixture;
• of sedimentation origin;
• contraction caverns formed due to a decrease in the volume of hardening stone;
• capillary formations;
• gel pores.

The following are the primary causes of the appearance of laying pores in the mixture’s structure:

• incorrect selection of binders and fillers (porosity of components);
• incorrect calculation of the composition of the required grade of concrete taking into account the porosity of the materials;
• excessive water content in the solution;
• insufficient compaction of the mixture when pouring into the formwork
• concrete shrinkage.

Water in the concrete’s pores evaporates during the product’s hardening process, leaving behind spaces that may eventually become the primary source of water filtration.

• Sedimentation air cells also appear during the pouring period, as a result of internal water separation (stratification) of the mixture.
• Fillers, as a rule, have a greater weight in comparison with other components, therefore, in combination with cement particles, they, under the action of their own weight, slowly settle downwards, and free water, at the same time, is squeezed out and accumulates at the surface.
• After the gradual evaporation of excess moisture, voids connected by small capillaries (capillary pores) are formed in this structure, which during the operation of the structures will facilitate the penetration of water into the concrete body.
• Gel pores appear during the hydration period of the cement stone and evenly fill the gaps formed between the capillary pores. By their structure, they belong to the category of closed waterproof cells.

The size of open pores and capillaries poses the greatest threat to water resistance indicators because they become completely permeable at a diameter of more than 0.3 microns under conditions of adequate liquid pressure.

Influence of binders on the water resistance of products

The following elements have an impact on how much moisture concrete absorbs:

• brand and type of cement;
• water-cement ratio of the mixture.

The water permeability of products is significantly influenced by the type and brand of cement used. Use of the finest ground cement compositions is required to prepare concrete that is resistant to moisture. In this instance, the cement stone’s structure becomes more uniform and dense, which aids in lowering the material’s water permeability.

Conversely, a high water content in the solution causes the water-cement ratio to be disrupted, which greatly increases the number of pores and capillaries in the product’s structure and, as a result, adversely impacts the water permeability parameters of structures. The ideal proportion of water in conventional components to the total volume of cement in the concrete mix is known as the water-cement ratio.

For instance, the water-to-cement ratio for moisture-resistant concrete (see table) should be between 0.40 and 0.50.

Hints: – The use of special plasticizers that decrease the total number of pores and raise the water resistance of concrete results in a decrease in the water-cement ratio with optimal mobility of concrete mortar.

The role of fillers in calculating optimal water resistance

The makeup and structure of the fillers used in concrete have a significant impact on its ability to withstand moisture.

• For the production of mixtures with high requirements for water resistance, dense coarse-grained rocks of crushed stone and gravel are usually used. Such solutions require less water for their preparation, and have positive workability indicators.
• At the same time, a correctly selected fraction of sand and its amount in the concrete mixture also help to reduce the water permeability of concrete. The volume and quality of sand is calculated for each mixture individually.

• Thus, for thin-walled moisture-resistant structures, the use of fine-grained sand is recommended. In this case, the homogeneity of the solution increases, little stratification and high rheological properties of mixtures are observed.
• Based on the studies and the results obtained, it was determined that in order to obtain high values ​​of water resistance, the optimal content of sand in the total volume of aggregates should be 45–55%.

Water resistance: characteristics of materials, requirements

Concrete’s ability to absorb GOST water is controlled by permeability requirements for structures.

• A value that guarantees the optimal moisture resistance of concrete for a given brand is indicated by the symbol W.
• Widespace of concrete W can change within the following brands W2-W20 (GOST 26633-2015).
• The value of the material of the material in water resistance is determined by the maximum pressure of the water, which withstands a sample of a cylindrical or square form in standard tests until the moisture is filtered through the structure of the studied copy.
• For example, W6 brand concrete with water pressure is 0.6 MPa.

Materials needed to produce hydraulic and moisture-resistant concrete, depending on the kind of structure and the environment in which it is used:

1. For the manufacture of structures with low water permeability, it is recommended to use Portland cement, pozzolanic Portland cement and slag Portland cement.
2. Sulfate-resistant cements are used to resist sulphate liquid aggressive environments.
3. Sand of artificial or natural origin with a grain size of 1.5–3.5 μm is used as fine aggregates. Fractions less than 2.0 μm should be used only with the use of plasticizing additives.
4. For large aggregate, it is customary to use crushed stone of volcanic and sedimentary rocks with a fraction of 5–150 mm. Moreover, the grade of crushed stone from volcanic rocks should be 2.5 times higher than the concrete grade, and the grade of sedimentary rocks should be at least 2 times higher.

Methods for monitoring the water resistance of products

In compliance with GOST 12730.5-84, which specifies the following testing procedures, the water absorption of concrete is measured in laboratories using specialized equipment.

• water permeability study by "wet spot";
• by filtration coefficient;
• accelerated method for establishing the filtration coefficient;
• accelerated technique based on air permeability.

Determination of permeability by the first method

Samples are tested using the "wet spot" method using a unique UVB-MG4 unit (see photo).

The device’s design enables automated determination of concrete’s water impermeability using the "wet spot" method.

• Samples are sealed in cylindrical metal test tanks, to which water is supplied from below under pressure.
• The water pressure increases automatically (by 0.20 MPa) at equal intervals.
• The formation of a test program, the pressure value at each stage, recording the degree of wetting of materials, and at what force, is provided by a microcontroller.
• Water is supplied until a wet spot begins to appear on the surface of the sample.

The product’s water resistance (W) is determined by measuring the highest water pressure at which no filtration symptoms were noticed.

Study of samples by filtration coefficient

The only way that the methodology of the filtration coefficient study varies from the prior one is in how the water resistance values are determined. In this instance, in addition to recording the water pressure, there is also a planned period of time for the periodic collection of filtered liquid, unlike the previous one.

For the duration of the testing phase, the filtrate from each study sample is taken every half an hour and weighed. The average value of all liquid weight measurements is then computed, and the filtration coefficient is computed using a specific formula based on this indicator.

The concrete water resistance parameter W is found by comparing the obtained coefficient with the findings of measurements made using the "wet spot" method.

Accelerated technology for obtaining the filtration coefficient

A filtratometer is the tool used in the accelerated method of obtaining filtration data (see photo).

Guidelines for using a hydraulic pump to quickly determine the filtration coefficient:

1. A cylindrical sample (b), drilled from the structure under study, is connected to the working cylinder of the filtratometer using a special fastening device.
2. By rotating the pump handle (2), the pressure in the tank is increased to 10 MPa.
3. At the end of the tests, the filtratometer is removed from the sample, and the surface of the cylinder under study is wiped with a rag.
4. At scheduled intervals, six measurements of the diameter of the wet spot on the surface of the sample are taken, and the arithmetic mean of the measurement results is calculated.
5. Then, these results are substituted into the formula, and the filtration coefficient is calculated.
6. The obtained filtration coefficient is compared with the values ​​in the table, and the grade of water permeability is determined.

Method for determining the water absorption of concrete by its air permeability

When compared to the previously mentioned methods, this approach allows for a significant reduction in the testing time required to investigate the water impermeability of concrete. For such investigations, a unique apparatus called "Agama" (GOST 12730.5-84) is employed.

By passing air through the sample’s body and into a vacuum chamber that is hermetically fixed to the product’s surface, the air filtration rate is determined.

The following is the test protocol:

1. A vacuum chamber is installed on the cleaned surface of the sample.
2. The joint of the chamber flange and the concrete surface is sealed with a special mastic.
3. Connect a hand vacuum pump and start pumping out air until the vacuum in the chamber of the device reaches 0.8–0.9 kg/cm 2 .
4. When the set pressure is reached, close the air valve, disconnect the pump and wait until the pressure in the chamber reaches 0.7 kg/cm 2 .
5. Then turn on the stopwatch and watch: how long does it take for the pressure in the tank to drop to 0.65 kg/cm 2 .
6. At the end of the experiment, release the pressure in the chamber using the valve and replace the sample. In this way, six control concrete samples are tested.
7. The obtained indicators of the rate of decrease in vacuum (t_i) are recorded in the log in ascending order.
8. Then determine the arithmetic mean time (t_c) between the values ​​of the third and fourth samples, and based on this coefficient, determine the water resistance according to the table (see. photo).

In order to guarantee the long-term durability of structures, it is essential to comprehend the water permeability of concrete. Concrete’s ability to withstand environmental elements like moisture, which over time can cause reinforcing material corrosion and deterioration, is directly impacted by its water permeability. Controlling this permeability can help us prolong the life and increase the security of concrete buildings.

Selecting the appropriate combination and adding additives that strengthen the material’s water resistance are frequently necessary to reduce water permeability. This lessens maintenance costs and increases the structure’s service life in addition to helping to prevent problems like erosion and cracking. These efforts are further supported by appropriate curing methods and quality control throughout the building process.

In conclusion, keeping an eye on concrete’s water permeability is critical to preserving the structural integrity and longevity of infrastructure and buildings. We can construct structures that endure the test of time and guarantee safety and dependability for many years to come with the correct materials and methods.

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