Waterproofing Additives

The waterproofing of concrete used in buildings is directly affected, aside from water-reducing, plasticising and waterproofing admixtures added to the mix, by project conditions, concrete design, production, transportation, placement and, subsequently, concrete maintenance and cold joint measures appropriate to the structural element. For these reasons, concrete waterproofing should be considered as a whole, and necessary applications and measures should be applied carefully and in compliance with procedures at every stage of production. Consequently, the primary objective in this type of application should be: "to ensure the building's waterproofing."

1. Definition

TS EN 13515 standard, clause 5.5.3, defines resistance to water ingress (penetration) as follows: Concrete with low water permeability characteristics must meet the following conditions: • For elements thicker than 40 cm, water/cement ratio must be ≤ 0.70. • For elements 40 cm and thinner, water/cement ratio must be ≤ 0.60 and minimum cement dosage must be 280 kg/m³ (minimum 270 kg/m³ cement when Type II mineral admixtures are used). Concrete class must be at least C25/30. • When tested according to TS EN 12390-8, water penetration depth must not exceed 50 mm. For concrete structures exposed to water with harmful chemical effects, this value shall be applied as maximum 30 mm.

Waterproofing admixtures (WA), in TS EN 934-2 Chemical Admixtures Standard;

defined as "chemical admixture that reduces capillary water absorption of hardened concrete." Generally, they are defined as admixtures that reduce permeability to increase concrete's resistance to water. WA admixtures provide waterproofing by reducing water passage from the concrete surface inward and/or by reducing or blocking capillary voids within hardened concrete.

Operating mechanism of WA admixtures;

• By reducing the amount, volume and continuity of capillary voids (interconnection of voids), • By blocking capillary voids within hardened concrete, • By reducing water passage as a result of expansion of hydrophobic materials contained in the admixture when reacting with water. WA admixtures exert their effect on capillary voids present in the cement paste, reducing absorption and permeability. However, they cannot prevent water passage resulting from large cracks formed on the concrete surface or structural damage caused by segregation. WA admixtures can also be used to prevent the chemical reaction known as efflorescence that forms on the concrete surface.

2. Standard

The standard relating to WA admixtures is "TS EN 934-2: Chemical admixtures – Concrete, mortar and grout – Part 2: Concrete admixtures – Definitions, requirements, conformity, marking and labelling," found in Table 9. (Figure-1 TS EN 934-2 Table 9)

3. Material

Concrete permeability varies depending on the volume, number of capillary voids within the concrete and whether these voids are interconnected [1-2-3]. Water and other substances can progress through concrete thanks to these connected capillary voids that are not filled by hydration products. Variables such as the permeability of aggregates used in concrete mixes, mixture proportions, fine material content, aggregate-paste interface, placement, compaction and curing conditions affect concrete permeability. At the same time, micro-cracks resulting from ambient temperature and moisture cycles can significantly increase concrete's permeability characteristics [4-5]. The first measure that can be taken to reduce capillary voids is to reduce the water/cement ratio in the concrete. Additionally, mineral and chemical admixtures are used to reduce concrete permeability. To reduce water/cement ratio and reduce capillary voids, concrete generally contains: • "Water-reducing / plasticising admixtures" found in Table 2 of TS EN 934-2 standard, and/or • "High-range water-reducing / superplasticising" admixtures found in Tables 3.1 and 3.2 of TS EN 934-2 standard. These admixtures reduce the amount of free water, thereby lowering the capillary void ratio and improving concrete's waterproofing. Mineral admixtures (fly ash, blast furnace slag, etc.) when used as cement replacement or filler in concrete improve permeability characteristics of concrete by reducing capillary voids and improving the aggregate-paste interface, as they are finer and exhibit pozzolanic reaction [16-17]. Blocking of voids through WA admixture use can be accomplished through: • Active and reactive filler materials that are water-soluble or water-insoluble (limestone, silica fume, etc.), • Water-soluble organic polymers. Hydrophobic (water-repellent) chemical admixtures are generally chemicals that are long-chain fatty acid ester derivatives. WA admixtures are produced through combinations of water-reducing or high-range water-reducing admixtures, hydrophobic chemicals and void-blocking filler materials.

4. Mechanism

Concrete's water absorption rate depends on the amount of voids it contains. Void volume varies with the ratio of free water that does not hydrate with cement. This excess water in concrete is necessary for concrete production, transportation, workability, proper placement and compaction. For example, in high-strength concrete containing 350-400 kg/m³ cement and 175-200 kg/m³ water, 98-112 kg/m³ of the water in the recipe is used for hydration. The remaining excess water of 77-88 kg/m³ (7.7%-8.8% of concrete volume) exits the concrete through surface efflorescence and natural evaporation, creating capillary voids in the concrete. These voids formed allow water, air and harmful chemicals to gradually enter the hardened concrete. By reducing the amount of water in the concrete recipe (for w/c ratio of 0.45, the water amount in the example above decreases to 157-180 kg/m³), the amount of capillary voids can be reduced. The best method for this is to use water-reducing and/or high-range water-reducing admixtures in concrete. This increases both concrete's workability and facilitates placement, while also reducing shrinkage. Void-blocking admixtures consist of active and reactive filler materials not exceeding 0.1 micrometers in size, or water-insoluble polymers. These materials physically block voids created as a result of hydration, assisting in waterproofing. Hydrophobic chemicals dissolve in water and react with calcium components of cement, creating insoluble crystals on the surfaces of capillary voids. Once this crystalline structure dries, it prevents water from entering the concrete. Provision of waterproofing depends on the effectiveness of the admixture used, water pressure and concrete quality.

5. Usage 5.1 Dosage

Usage dosage for WA admixtures varies depending on admixture type and variety. Water-reducing admixtures can be used at ratios between 0.2% and 2% of cement weight. For hydrophobic admixtures this ratio is 1-2%, and for void-blocking admixtures it can range between 5-10%. Consequently, usage ratio for WA admixtures should be determined in accordance with manufacturer's declaration.

5.2 Admixture Selection

To reduce concrete's water/cement ratio below 0.45, use of a water-reducing chemical admixture complying with TS EN 934-2 is recommended. Hydrophobic admixtures, subject to wetting-drying cycles and low water pressure effects, assist waterproofing by reducing surface water absorption of concrete. With this type of admixture selection, chloride ion passage is prevented in early and advanced ages, increasing concrete's durability (service life). For structures continuously immersed in water and exposed to high water pressure, WA admixtures containing void-blocking chemicals or both void-blocking and hydrophobic chemicals should be preferred.

5.3 Cement Type

WA admixtures can be used with all cement types listed in TS EN 197-1 and with Sulphate-Resistant Cements.

5.4 Overdose Usage

In case of overdose usage of WA admixtures, the manufacturer's technical data sheet should be reviewed. Excessive use of admixtures containing inorganic fillers reduces workability. Overdose use of admixtures containing organic materials may entrain excessive air into concrete and/or hydration may be slowed/stopped due to materials coating the cement surface. In both cases exceeding manufacturer's declaration, a decrease in concrete compressive strength is expected.

6. Effect on Concrete Properties 6.1 Effect on Compressive Strength

Since WA admixtures with water-reducing properties enable production of concrete with lower water/cement ratio, an increase in compressive strength is expected. For hydrophobic admixtures and organic and inorganic void-blocking admixtures, no change in strength is expected. Some organic WA admixtures entrain air into concrete. An increase in air content of 1-2% causes a 10-20% reduction in compressive strength. This situation can be balanced by reducing water/cement ratio.

6.2 Workability

WA admixtures generally contain water-reducing properties, so an increase in workability is expected. For equal water/cement ratio, similar slump loss characteristics are expected between reference concrete without admixture and concrete using WA admixture.

6.3 Setting Time

For equal water/cement ratio, similar setting time characteristics (90 minutes) at 15-25°C are expected between reference concrete without admixture and concrete using WA admixture. Setting time may be prolonged at lower temperatures. In cases where hydrophobic admixtures are used at high dosages under normal temperatures, setting time may be prolonged.

6.4 Air Content

Hydrophobic chemicals or chemicals containing organic materials may entrain air into concrete. WA admixtures by their nature do not entrain more than 2% air compared to reference concrete. An increase in air content is expected in case of overdose use.

6.5 Durability

WA admixtures increase concrete's durability (service life) by preventing the ingress of water, air, chloride and sulphate and other harmful chemicals into concrete. Hydrophobic chemicals reduce concrete's water absorption under repeated wetting-drying cycles, reducing salt concentration that causes structural deterioration in concrete. This extends concrete's service life. Reinforced concrete structures are expected to safely perform their functions over a long period; however, due to various durability problems, many structures fail to achieve the desired service life and various repairs become necessary. Structures are subjected to various environmental effects throughout their service lives [6]. These may be physical, chemical, physico-chemical or mechanical effects. Under these effects, the structure must continue to perform its function, the durability of materials used in the structure must be adequate and their performance must not fall below a certain level. Otherwise, various environmental effects can cause various cracks in concrete, reduce its performance over time and cause it to lose functionality before the desired service life is reached [7]. With the development of concrete technology today, liquid or powder-form WA admixtures with different mechanisms are being produced. These admixtures are chemical additives that improve concrete's waterproofing characteristics and extend service life [8]. Consequently, key points that should be considered in concrete design to increase waterproofing of hardened concrete can be summarized as follows: • Reduction of capillary voids, by reducing Water/Cement ratio, by using materials with pozzolanic activity or mineral admixtures (fly ash, slag, microsilica, etc.). • With properly adjusted grading curve in cases of low fine material content, • By calculating binder quantities and ensuring adequate fine material content, • Plastic or fluid consistency concrete should be preferred due to ease of compaction, better placement and achieving a more void-free structure (S-3, S-4, S-5 consistency class or self-compacting concrete). • Waterproofing can be provided with appropriate WA admixture* use.

*The concrete producer must be consulted in the use of this type of admixture. 7. Areas of Use

• In all projects where waterproofing is required, • In densely reinforced sections, • In water structures, water reservoirs and water treatment facilities, • In all structures exposed to chemical effects, • In basement foundation and diaphragm walls. Gökhan Yılmaz / Sales Manager / Polisan Yapı Kimyasalları A.Ş.

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