There are various types of joints in water retaining structures during construction. Sealing materials for joints in these structures are discussed.
There are three types of joints in concrete construction, viz. construction joint, expansion joint and contraction joints. Learn more about Joints in Concrete Structures.
Materials for Sealing Joints in Water Retaining Structures(1) Materials for joints in water retaining structures and water tight structures for sewage and effluent treatment shall be resistant to aerobic and anaerobic microbiological attack and resistant to attack by petrol, diesel oil, dilute acids and alkalis. (2) Materials for joints in water retaining structures for potable and fresh water shall comply with the requirements of BS 6920.
Joint fillerJoint filler shall be firm, compressible, single-thickness, non-rotting filler. Joint filler for joints in water retaining structures and watertight structures shall be non-absorbent.
Bitumen emulsionBitumen emulsion for joints in water retaining structures and watertight structures shall comply with BS 3416. Bitumen emulsion for surfaces against which potable or fresh water will be stored or conveyed shall comply with BS 3416, type II.
Fig: Joints in concrete structures
Joint sealant(1) Joint sealant shall be a grade suited to the climatic conditions of Hong Kong and shall perform effectively over a temperature range of 0°C to 60°C. Joint sealant for exposed joints shall be grey. (2) Joint sealant other than cold-applied bitumen rubber sealant shall be: (a) A gun grade for horizontal joints 15 mm wide or less and for vertical and inclined joints, (b) A pouring grade for horizontal joints wider than 15 mm. (3) Polysulphide-based sealant shall be a cold-applied two-part sealant complying with BS 4254. Polysulphide-based sealant for expansion joints in water retaining structures and watertight structures shall have a transverse butt-joint movement range of at least 20%. (4) Polyurethane-based sealant shall be a cold-applied two-part sealant complying with the performance requirements of BS 4254. (5) Hot-applied bitumen rubber sealant shall comply with BS 2499, type N1. (6) Cold-applied bitumen rubber sealant shall be of a proprietary type. (7) Joint sealant for joints in water retaining structures and water tight structures shall be as stated in Table-1. (8) Primers and caulking material for use with joint sealant shall be of a proprietary type recommended by the joint sealant manufacturer. (9) Different types of joint sealant and primers that will be in contact shall be compatible.
Table-1: Joint sealant for water retaining structures and water tight structures
|Structure for retaining / excluding||Type of joint||Type of joint sealant|
|Sewage||All joints||Polyurethane based|
|Other than sewage||Expansion joint||Polyurethane based or Polysulphide based|
|Horizontal joints other than expansion joints||Hot applied bitumen rubber, Polysulphide based or polyurethane based|
|Vertical and inclined joints other than expansion joints||Polysulphide based, polyurethane based or cold-applied bitumen rubber|
Bond breaker tapeBond breaker tape shall be of a proprietary type recommended by the joint sealant manufacturer and approved by the Engineer. The tape shall be a polyethylene film with adhesive applied on one side and shall be the full width of the groove.
Bearing strip for sliding jointsBearing strip for sliding joints shall consist of two plastic strips of a proprietary type approved by the Engineer. The strips shall be resistant to all weather conditions and to chemicals to which the structure will be subjected without impairing the reaction, durability or function of the strips. The strips shall be of a type that will not require maintenance after installation. The strips shall be capable of withstanding a vertical load of at least 300 kN/m2 and shall have a maximum coefficient of friction of 0.3 under a constant shearing force.
Waterstops or water stoppersWaterstops, including intersections, reducers and junctions, shall be of a proprietary type approved by the Engineer. Waterstops shall be natural or synthetic rubber or extruded polyvinyl chloride and shall have the properties stated in Table-2.
Table-2: Properties of waterstops or water stoppers
|Property of water stops||Rubber waterstops||PVC waterstops|
|Density||1100 kg/m3 (+/-5%)||1300 kg/m3 (+/-5%)|
|Hardness||60 – 70 IRHD||70 – 90 IRHD|
|Tensile strength||>/= 20 N/mm2||>/= 13 N/mm2|
|Elongation at break point||>450%||>285%|
|Water absorption||<5% by mass after 48 hours immersion||<0.15% after 24 hours immersion|
|Softness number||-||42 – 52|