About PVC Waterstop Tapes
09-02-2023
16:43
The purpose of using water-retaining tapes or water-stopping materials is to prevent water from passing from one side to the other along the concrete joint (construction joint and/or expansion joint) where water pressure is present. They achieve this, in principle, by lengthening the water path.
This effect is achieved in water-retaining tapes by extending the path of water along the joint and creating areas of resistance, while in tapes that can only be used in construction joints and swell upon reaction with water, it is achieved through a sealing effect created by the counter-pressure they generate on the surfaces where they contact the concrete. Therefore, water-retaining tapes play a critical role in preventing water from entering the structure through joints or leaking from a water-filled structure in water structures and reinforced concrete buildings.
Waterstop strips are generally used in the following parts of all types of reinforced concrete structures built below the groundwater level:
- Raft foundation - raft foundation joints
- Raft - curtain wall junctions
- Curtain - Curtain joints
- Partial contraction joints (construction joints) are used in expansion joint areas or in any areas with discontinuities such as weir constructions.
- Subways and Tunnels
- Water canals, water reservoirs
- Drinking water and wastewater treatment plants
- In reinforced concrete dam structures and all types of water retention structures.
PVC-Based Waterstop Tapes
PVC-based waterproof tapes are the most common type of waterproof tape used in buildings. They are easy and economical to apply on-site by expert teams. They are preferred because their elastic structure prevents loss of function during horizontal and vertical movements that may occur in buildings.
Advantages
- High elasticity (275% elongation at break in products conforming to TSE standards)
- High tensile strength, high tear resistance.
- Low water absorption
- 200% elasticity even at -20°C.
- Its corrosion-resistant structure
- High resistance to hydrostatic pressure and shocks.
- Resistance to outdoor weather conditions
- Long service life
While the performance of water retention belts varies from country to country, there are certain tests and standards for measuring their performance. In Turkey, the TS 3078-1 and TS 3078-2 standards, which came into effect in 2018, are valid. The shape and dimension requirements for water retention belts, the raw material requirements, and the related tests are controlled by these standards. With the gradual completion of market surveillance and regulation according to these standards, the aim is for both the materials produced and the manufacturing processes in our country to reach world standards.
The new standard groups water retention tape types into two main categories based on their intended use.
- Externally Applied Waterstop Tapes (DA Type, AA Type, FA Type / TS3078-1)
- Internally applied Waterstop Tapes (Type D, Type A / TS 3078-1)
The dimension definitions shown in the images below are found in TS 3078-1.
Externally Applied Waterstop Tapes
AA TYPE
AA type waterstop tapes are external waterstop tapes without an expansion gap in the middle. They are applied externally in construction joints (foundation and retaining wall constructions) where concrete pouring needs to be interrupted or as a structural measure.
DA TYPE
DA type waterstop strips are strips placed outside the concrete and have an expansion gap in the middle. They are placed in expansion gaps, under the raft foundation, and on the outside of the walls. The same type of waterstop strip is welded to the wall joints by turning it upwards from the raft foundation edges, using a hot heat gun or a waterstop welding machine.
The most important aspect of sealing a structural joint is the continuity of the waterproofing. That is, the waterproofing applied to the raft foundation must continue into the shear walls and extend to at least 30 cm above the calculated water level. In applications using both types of water-retaining tape, it is necessary to install the tapes at short intervals to the ground and the shear wall formwork during concrete pouring so that they maintain their initial shape. Particular care should be taken to avoid damaging the water-retaining tape when removing the shear wall formwork.
INTERNALLY APPLIED WATERPROOF TAPES
TYPE A
Type A waterstop tapes are the most common type of waterstop tape used in construction joints. In raft-to-raft joints, concrete is poured in the first section first. The waterstop tape, applied by constructing a special two-part formwork in the exact center of the raft, must be securely fixed before concrete pouring.
Type D
These are water-retaining bands embedded in concrete, containing an expansion gap in the middle. They are used in raft-raft and shear wall connections where expansion joints (settlement joints, movement joints, expansion joints) are present. Thanks to the middle section, they do not lose their compressive strength and function in both horizontal and vertical displacements within certain limits.
JOINT FINISH WATERPROOFING TAPES - FA TYPE
This type of waterstop tape is primarily used in expansion joints of walls and floors, where the reinforcing steel placed towards the outside of the structural element is not suitable for other types of installation. Its hydrostatic pressure resistance is slightly lower compared to other types.
APPLICATION PRINCIPLES
The sealing function of waterstop tapes depends on the correct formation of the joint, the selection of the waterstop tape material, and the quality of application. To ensure the watertightness of the structural joint, a closed system must be created, and the waterstop tapes must be extended at least 300 mm beyond this system.
The concrete thickness of the water-retaining bands to be placed inside the reinforced concrete structural element must provide the minimum water-retaining band width. The embedment depth (G) of the water-retaining bands into the concrete must be at least equal to the concrete cover thickness (T), and the distance between the outer edges of the water-retaining band and the nearest reinforcement around it must be at least 20 mm (Figure 5.1).
The distance between the joints of the water retention bands must be at least 0.50 m and they must be carefully welded. If a portion of the water retention bands is to remain exposed during concrete pouring, the length of the exposed portion must be at least 1 meter. In horizontal and slightly inclined structural elements (base or ceiling, etc.), the bands embedded in the concrete should be placed in a slight "V" shape during concrete pouring.
Water retention bands placed outside the concrete are positioned on the side where the water is present. These bands must be adequately and continuously protected against mechanical damage in retaining walls. When water retention bands placed outside the concrete are subjected to loads up to 0.2 bar against non-pressurized water or infrequent and short-term water accumulation, these bands must have at least two notched anchor threads on both sides. For infrequent and short-term water accumulation or continuous water pressure exceeding 0.2 bar, these bands must have at least three notched anchor threads on both sides.
CRITERIA FOR SELECTING WATERPROOFING BANDS
SIZING OF EXPANSION JOINT WATERPROOFING BANDS
INITIAL CHOICE
The following table should be used to assist the designer in selecting water retention tapes. For expansion joint water retention tapes embedded in concrete, the concrete cover layer thickness rule (G≤T) as shown in Figure 5.1 should be observed.
APPLICATION
The joining of waterstop tapes at corners, T-shaped joints, cross joints, and transitions should be done using custom-shaped parts or special-shaped connection pieces made on-site. Due to their thermoplastic structure, PVC-based waterstop tapes replasticize when heated to a certain degree. During this plasticization process, welding occurs when they are pressed together with a certain force. Using welding equipment and a heat gun (to be requested from the manufacturer), the entire surface at the joint should be heated as evenly as possible, and when the welding temperature is reached, the two parts should be pressed together with equal force. Adhesives, solutions, or adhesive tapes should not be used for joining. Any accumulated and excess PVC mixture at the joint should be carefully pressed towards the joint with a small spatula. The force should be removed when the temperature drops to 50°C. The joint should not be moved immediately; it should be allowed to cool to room temperature.
FIELD OPERATIONS
Until the construction phase, water retention belts should be stored in a protected facility, away from prolonged exposure to sunlight. Any physical defects in the water retention belts (folds, slippage, etc.) resulting from storage or transportation should be eliminated by heat treatment. Water retention belts should be secured to prevent movement during concrete pouring. Water retention belts outside the concrete should be protected; exposed belts should not be walked on or driven over by vehicles. The belts should not be covered with formwork materials or similar products. If work is interrupted for an extended period, exposed water retention belts should be protected against adverse weather conditions and mechanical damage.