Samir Surlaker, Director, Assess Build Chem Private Limited discusses some new joint treatments and injection systems in waterproofing.
It is a myth that waterproofing treatments can be carried out by application of single material on new concrete or existing treatments. There cannot be a single material that is right for every structure. Most of the failures in waterproofing are on account of this misconception. The only way to ensure reliable treatment is by considering the waterproofing treatment as a system. A System for Waterproofing can be defined as a combination of materials, preparation of specifications, application techniques designed by taking into considerations the requirement of the client or homeowner, which would provide efficient, reliable and long-term protection to concrete structures with minimum maintenance costs.
Waterproofing should never begin with a specific material in mind. The properties of material needed, are to be stated and then the material is to be selected as per the merit. To combat the different entry modes of water into concrete, a combined system of treatments is therefore necessary. To waterproof a structure completely, one has to address the 3 primary routes of entry into the structure, viz.
- Pores, Capillaries and Voids in the concrete
- Joints and Transitions
- Cracks in the concrete cover
- Admixtures and additives to reduce the porosity and capillarity in the concrete
- Treatment of joints, transitions and cracks using suitable coatings with reinforcement, flashing tapes and expansion joint tapes
- The cover concrete is to be protected by appropriate surface barrier coatings
Figure 1: Selection of Injection / Impregnation Materials based on Crack Width
Waterproofing using Injections Types and its Applications
Injection Technologies have long been used to treat waterproofing issues. In Brief, Table 1 below gives an idea of the type of Injection materials available and the conditions these materials can be used under. The areas of application of the suitable filling materials and filling methods depend mainly on the intended application goal, the crack width, crack movement, and dampness of the cracks/crack edges/crack flanks and voids. Usually three different injection systems/methodologies are specialized to solve critical waterproofing problems:
|Table 1: Materials and Crack / Void Property they can be used to Address|
|Crack Void Property / Materials||Cement Based||Epoxy||PU||Acrylic Gels||Coatings|
|Water Bearing / Damp||+||++||++|
|+: Suitable; ++: Most Suitable; Blank: Not Suitable|
- Grid Injection [Crack treatment or creation of a waterproof layer from the negative side]
- Water Bar Injection/Expansion Joint Treatments/Transitions
- Injection Hoses
Figure 2: Flow-Chart for Decision Making on Repair of Cracks [Ref.: Dr. V.K. Raina, Raina’s Concrete Bridge Practice: Construction, Maintenance and Rehabilitation (Second Edition)]Selection of materials based on crack width is shown in table 1 and figure 1. Figure 2 gives a brief flowchart for Injection Strategies.
Positive Waterproofing from Negative Side, Grid Injections Low Viscosity Pus or Low Viscosity Acrylic/Methacrylate Gels
Water penetration is often caused by bad concrete compaction, honey combing or defective seals. Sometimes an interconnected void system also allows water to pass through the element and causes leakages. Grid injection is an application technique, developed from the standard crack injection process. This method is more useful where a true source of leakage is not easily traceable and a complete water stopping solution is required.
Normally if the injection is to be performed into the element, (around a cracks) a combination of polyurethanes is generally used. For very low water ingress or dampness a low foaming polyurethane (PU) can be used in isolation. In case of heavy ingress or water under pressure, a high foaming PU is used as a primary injection to stop the heavy flow, followed by a non-foaming low viscosity structural PU.
Low viscosity Acrylic/Methacrylate gels are used specifically for curtain grouting beyond the structure into the soil, when a waterproofing injection into the element is not possible or successful, due to technical, or economic reasons. The gelling of the substrate adjacent to the structure or the injection of gels into gaps in the structure creates a sealing layer, which provides a secondary waterproofing for structural components. These materials can also be used to increase the bearing capacity of soils for foundations or abutment walls. The schematic for the injection is shown in figure 3 and the practical process is shown in figure 4. The advantages of using these materials include:
- Sealing without digging
- Long-term tested, Systems
- Waterproof up to 12 bars
- High chemical resistance
- Adjustable to soil conditions
Treating Failed Expansion Joints/Water-bar Injection
This is a special injection application used when joint treatments in an RCC Structure fail. Water-bars are used to seal joints in moving structures against pressurized water. However, the concrete often proves to be defective in the area of the water-bar because of inadequate compaction. Water-stop Injections effectively address this defect. The materials used here are flexible methacrylate/Acrylic Gel Injections. This schematic is shown in figure 5.
Other critical areas with regard to the water tightness of a building or structure are expansion joints that are not sealed with water bars. Inserting injection pipes provides the possibility of sealing expansion joints effectively at a later date. The material used for such cases must display excellent flow properties. Figure 6 shows the Injection Hose System.
Injection is a proven method of sealing against pressurized water in structural renovations. The grouting of injection hoses also provides the benefit of using the advantages of injection technology in new construction specifically for the sealing of construction joints. New generation injection hoses can be injected several times, have been used successfully for construction joint sealing for many years.
They can be injected with microfine cements, acrylate gels or urethane resins. In contrast to passive sealing systems such as conventional water stops, which only seal by so-called circumference extension, active systems such as injection hoses and injection grouts can be used to strengthen possible weak points in the concrete caused by cracks or badly compacted concrete.
The technologies highlighted in the article are a first step to stopping water leakages completely. The injection treatment is usually followed by treating the transition with flashing or expansion joint tapes. This is finally protected by a coating system to enhance the durability of the waterproofing system as a whole.
In conclusion, it is important to know and identify the water ingress avenues expected in the building structure. This will help us in identifying the system that can withstand these loads over time and provide a reliable seal against water ingress into living spaces. The consequences of water/dampness entering the living space is multifold and can impact health, safety, fire-worthiness, structural durability, aesthetics as well as can destroy property. These issues need to be addressed by the waterproofing system, to improve living conditions and safety. Of course, the combination of materials, detailing and application will finally determine the success of the waterproofing system.