Injection Techniques And New Materials For RCC Waterproofing

feature-top Fig. 1: Leakages in Underground Structures
Introduction
With increase in the number of infrastructure and high-rise residential projects, use of Concrete has tremendously increased. Major RCC Structures such as bridges, dams and buildings are seeing deterioration much before their service life is completed [1]. Due to construction and material problems, concrete structures both over and below ground are especially susceptible to waterproofing problems [2]. Waterproofing plays a very important role in protecting the structure and ensuring that the structure is usable over its service life, above or even below ground levels. Water can enter a structure through many different routes. Some typical problems are shown in Figure 1. A reliable waterproofing system installed by professionals is essential to achieve lasting protection from water. Much is demanded in a waterproofing system, from both the material and its applicators. While designing the waterproofing system, actual service conditions are to be borne in mind. It should be decided at this stage whether damp proofing or waterproofing is desired.
Generic placeholder image Mr. Sunny Surlaker
The most important factor for waterproofing treatments is performance requirements. Materials and systems should be tested for capillary absorption as well as penetration under hydrostatic pressure. Such tests are available internationally and materials can be tested anywhere in the world to adhere to ASTM/EN standards. To give an example of the nature of the detrimental forces water can exert on a surface, Table 1 below shows the impact pressure of the average raindrop at different wind speeds. We can, thus see, that even at nominal wind speeds of around 40 km/h a drop of water can exert a pressure of over five and a half metre head of water[3]. To encounter this nature of water, waterproofing systems are a must in our structures.
Mechanisms of Entry of Water through Concrete / Structure
Before we consider waterproofing systems, we need to understand the concepts of how water enters the concrete / structure. The basic routes of entry of water into the concrete structure are shown in Figure 2. Once we understand the concept of entry of water into the concrete / structure, we can then design systems for diverting, draining or keeping water out of it. The basic routes of entry are:
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- Permeability - Porosity - Capillarity and - Diffusion
feature-top Fig. 2: Mechanisms of Entry of Water into Concrete Structures
Water enters the concrete structure through interconnected voids and pores, cracks, structural defects or through faulty joints.The aim of waterproofing is to keep unwanted water out of the system, i.e. the inside water in the structure (e.g. water tanks) and outside water of the structure (e.g. roofs, basements, etc.).
Injection Systems
Cracks and voids occur in concrete despite adequate quality control. Cracks are one of the signs indicating damage or distress in a structure. However, it is fortunate that all cracks are not a sign of structural failure. Cracks must be repaired for two reasons viz. for structural or for durability. The selection of material for injection requires thorough understanding of the properties of the material and functions that such a process must perform. In all the cases, it is imperative that the cause of crack is properly determined otherwise the selection of material can be faulty. Basically, the injections can be of three categories:
1. Injections undertaken to restore the structural stability / load transfer capability of structural elements
2. Injections undertaken to protect the reinforcement to avoid the moisture and air entering the concrete and to lower the rate of corrosion
3. Injections that are undertaken to stop the water entering the structure
The repair of cracks alone cannot guarantee the structural stability or durability of concrete and therefore, if necessary should be complimented with other treatments as per the established practices of civil engineering. Under all circumstances it is advisable to trust these types of jobs to experienced contractors having the knowledge of materials as well as experience in the use of specialized equipment.
Reasons for Crack Injection
Injection is the first step of rehabilitation when structural distress is encountered [4], or when leakages are detected and durability of the RCC structure is compromised. This system is necessary to bring the concrete back to its original condition, prior to application of a waterproofing system. Table2 shows various reasons for Injection.
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After completion of diagnosis and selection of materials for injection the work of injection passes through following stages:
a. Preparation of the crack
b. Location of points for injection
c. Surface sealing of cracks
d. Injection of resin proper
e. Removal of packers and plugging
f. Removal of sealing material
g. Final surface treatment after injection resin/grout hardens
Injection Material Properties
All cracks are different. They vary depending on the construction material, cause, location and environment. One single system is not able to achieve durable and reliable results. Various solutions based on different materials, which are tailored to specific application needs, are now available to users. A range of solutions is essential depending upon job and site conditions. Table 3 shows selection of materials with respect to job and site conditions.
Assessing these properties will help us in selecting the correct material. Internationally and in India now, the following types of filler materials are being used for crack / void filling:
- Epoxy resin (EP)
- Polyurethane (PUR) [Elastomeric]
- Cement slurry (CG)
- Microfine cement suspension (CS)
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In addition to the above substances injection gels are also used for the injection of structural components. Injection gels [Waterproof Structural-gels] are aqueous systems based on special acrylate or polyurethane resins [4]. A Description of these materials is given below:
Epoxy Resins
Epoxy resins harden into a solid plastic. They are suitable for the strengthening and waterproofing filling of cracks (without changes in crack width). The essential properties of epoxy resins are:
- Good injectability (Ultra low viscosity)
- Constant-volume curing (without solvent)
- Good bonding with concrete
- Fast strength development
- Durability
- Even Load Transfer
Limitations of Epoxy Resins
- Cannot be used for moving cracks (These are Non-Elastic)
- Cannot be used in active water bearing or very damp cracks
For application at the construction site the following information must be available to determine crack treatment strategy (Injection or Impregnation):
- Application temperature (temperature of the structural component)
- Working life of the material (application time)
- Period of additional injection (maximum injection time)
- Strength development
Elastic Polyurethane Resins
The polyurethane resins (PUR) usually used for the filling of cracks and voids are mainly elastic, pore-forming reaction resins. They are used for the waterproofing of structures. The essential product characteristics of polyurethane resins are:
- Good injectability (low viscosity)
- Constant-volume curing (without solvent)
- Good bonding with concrete
- High reactivity
- High elasticity
- No adverse reaction with water / dampness
Limitations of PU Resins
- Cannot be used for transfer of high loads (These are Elastomeric and have lower compressive strength as compared to epoxies) Polyurethane resins may also be used against pressurized water. This may be achieved using a 1 or 2-step injection process. In the 2-step process, to temporarily decrease the ingress of pressurized water, polyurethane foam is injected first followed by an injection of a permanently waterproofing structural polyurethane resin (main injection).
For application at the construction site the following technical data must be available:
- Application temperature (temperature of the structural element)
- Working life of the container (application time)
- Period of re-injection (maximum injection time)
- Flexibility of the filling material hardened in the crack
Cement Suspensions and Cement Pastes
Cement suspensions and cement pastes are mineral substance systems made from cement, micro-fine cement, additives and water. In Europe the distinction by maximum grain size has led to the subdivision into micro-fine cement suspensions (d95% ~ 16 µm) and fine cement pastes (d99% ~ 200 µm). Both injection systems are mixtures of insoluble particles extremely finely distributed in a liquid. This mixture may only be made at the construction site using suitable mixing and processing equipment.
The essential product characteristics of cement suspensions / cement pastes are:
- Good injectability (low viscosity/flow time)
- Stable mixture (little sedimentation)
- Constant-volume curing
- Sufficient bonding with concrete
- Sufficient strength development
Limiting Factors for use of Cementitious Systems: Due to the limited tensile strength of mineral filling materials [< 3 MPa], cracks filled with these materials can withstand only limited tensile and compressive stress. Its main area of application is the filling of voids, where only compressive forces apply. These materials are also very suitable and extremely economical for ground stabilization applications for the wing walls or foundations. For processing at the construction site, the following technical data must be available
- Application temperature (temperature of the structural element)
- Working life of the container (application time)
- Period of re-injection (maximum injection time)
- Strength development
Injection Gels
Injection gels are used structure specifically for curtain grouting beyond the structure into the soil, when a waterproofing injection into the element is not possible or successful. 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.
In Brief, Table 4 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 about the dampness of the cracks/crack edges/crack flanks and voids. The filling of crack and voids requires minimal crack widths at the concrete surface and minimal dimensions and permeability of the voids, depending on the method of filling and the chosen filling material. Selection of materials based on crack width is shown in Table 5 and Figure 3 below. Figure 4 gives a brief flowchart for Injection Strategies.
Injection Waterproofing
Usually three different injection systems are specialized applications to solve critical waterproofing problems:
Grid Injection: Water penetration is often caused by bad concrete compaction, honey combing ordefective seals. Using grid injection systems, a special method developed from the standard injection process rectifies this defect [5]. Figure 5 shows a Grid Injection Principle.
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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 defectivein the water-bar because of inadequate compaction. Water-stop Injections effectively address this defect. This schematic is shown in Figure 6.
Re-injectable hoses: Other critical areas about the watertightness of a building or structure are expansion joints that are not sealed with
feature-top Fig. 4: Flow-Chart for Decision Making on Repair of Cracks [10] Crack Width (Courtesy: MC-Bauchemie, Germany)
water-bars. Inserting injection pipes provides the possibility of sealing expansion joints effectively later. The material used for such cases must display excellent flow properties. Figure 7 shows the Injection Hose System.
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Surface Barrier Waterproofing Materials
One of the major parts of waterproofing is the selection and application of surface waterproofing barriers. The main function of these barriers is to arrest the passage of water through the body of concrete either by capillary action or hydrostatic pressures. The surface applied barrier materials are not a substitute to joint sealants, which are to be applied in the third dimension. Only a few of these materials can be applied both for Positive side and Negative side waterproofing. The performance of barrier materials for Waterproofing and Damp proofing should also be checked for exposure to aggressive soil contaminants.
Though several materials are available as surface protective systems, the concept of waterproofing has remained the same, which is the tanking system. Built up bituminous membranes were very popular a few years ago and they were bonded to the surface either by self-adhesion cold application or heat welding. Major difficulty in the application of bituminous or polymeric bituminous membranes was covering the geometry of the structure, overlapping joints and use of moisture sensitive adhesives to bond the membrane to the substrate [6].
Liquid Applied Membranes became more popular in the last decade because of their ease of application and mould ability to form seamless membranes over any curvature. Some Liquid Applied Membranes are of the non-breathable type and this would give rise to blisters and craters, which would eventually affect the barrier performance [7].
Waterproofing by polymer modified mineral slurries is becoming more popular because of ease of application, compatibility with substrate as well as competitive pricing. Mineral slurries are manufactured by incorporating acrylic polymers either in powder or liquid form depending upon flexibility required. Figure 8 shows this type of coating.
Crack bridging characteristics is one of the most important criterions for the flexible slurries as well as chloride diffusion is an added feature for underground structures. These slurries are of breathable type, which contribute to better waterproofing because of no blistering and bubbles.
Applications for these kinds of membranes are multi-fold, in basements, wet areas, swimming pools, tanks, dead walls, terraces, terrace-gardens, structural elements and so on. The main point to remember while using a slurry-applied membrane is the correct detailing of joints, water stops and interfaces (covings) between horizontal and vertical surfaces.
feature-top Fig. 8: Flexibility of Polymer Modified 2 Component Mineral Slurry Waterproofing System
The latest generation material systems for Waterproofing Include:
1. Special Coatings, resistant to permanent water loading
2. Polymer Modified Coatings with properties like asphaltic coatings
3. Thermal Barrier Coatings that also behave as waterproofing in addition to insulation
The Thermal Barrier Coating is described below.
Thermal Barrier Coating
To supplement a Green Building Concept, aluminium formwork wall system buildings or fair finished surfaces and roofs can be coated with a Thermal Barrier Coating System. This coating, in addition to providing insulation (energy reduction of over 25%), would provide a waterproof barrier and aesthetic finish to the green building. This Thermal Barrier Coating is a specially formulated solar radiation and heat resisting; one component acrylic co-polymer-based surface coating incorporating selected white microscopic hollow ceramic spheres. The coating works as a thermal barrier, by reflecting, refracting and dissipating radiant heat.
Incident Heat is Composed of UV Heat [about 3%], Visible Heat [about 44%] and Infrared Heat [about 53%]. This heat on a substrate is transferred through the substrate into the living / occupied spaces by means of conduction [through the substrate], convection [heating of air below substrate] and by radiation [back to the atmosphere].
Working Mechanism
The coating is composed of advanced hollow ceramic microspheres, heat resisting fillers and special pigments, bound in a special acrylic co-polymer matrix enhanced to minimize heat transmission through the coating. Applied as a thin layer [0.7 to 1 mm thick], the coating behaves like insulation on any substrate it is applied to. Due to the Ceramic Microspheres, the heat is partly reflected, partly dissipated and a very small amount is lost by convection through the coating. This mechanism is shown in Figure 9.
feature-top Fig. 9: Working Mechanism of Thermal Barrier Coating
This is the guiding principle in the design of the coating and allows minimal amount of heat to transfer to the substrate, keeping it cool and the environment in the living / occupied spaces also cool. Since it can keep the substrate and air around it cooler, lesser energy is required to heat or cool the area, leading to tremendous energy savings [Heating or AC].
The material can be used as an intermediate primer, protective topcoat or replacement for a complete insulating system. The coating exhibits excellent test values for R Value, Emittance, and Solar reflectance and is an effective means of lowering solar heat gains in a structure. It adds to sustainability of a structure, by reducing heat gains, increasing cooling efficiency and reducing energy consumption and cooling costs.
The unique feature of this thermal barrier coating, versus others available in the present market has a low specific gravity (~ 0.65), but a very high solid content [> 80% by volume]. This lends unique thermal properties to the coating. The product is water based and thus sustainable with low VOC content and gives off no fumes when applied externally or internally. The presences of ceramic and special fillers ensure the coating is strong, resistance to foot traffic after application and is totally waterproof. The special acrylic binder ensures
feature-top Fig. 10: Features of Thermal Barrier Coating
the coating is resistant to carbonation, chlorides and salts as well, so that the coating and the protected substrate is ensured of long term durability. Some of the other features of this type of thermal barrier coating are shown in Figure 10.
Advantages of Using a Thermal Barrier Coating
- Replacement for Bulky Insulation Systems in Buildings and Industrial Structures
- Prevents Corrosion of Pipes and Metal Substrates
- Waterproof and Insulating External Coatings for Buildings
- Does not lose efficiency over time like other insulation systems [can be easily cleaned and restored]
- Applied like paint, no special mechanical fastenings, screwing or multi-layer systems needed
- The cost of the coating can be offset by lower capacity AC Systems
- Saves Energy and Increases Efficiency by over 25%
- Prevents Cracking of Concrete / Masonry / Other Substrates due to thermal variation
- Ensures Long Life of Protected Substrates
- Can be walked on, thus apt for flat terraces / roofs
- Can be applied to any substrate and any geometry – seamless insulation and protection
- Will not rot due to dampness [like wool / foam insulation systems] as it is breathable
Conclusion
The success of waterproofing system depends not only on the materials, but also on application and understanding limitations of the materials in question. Rather than asking for Guarantees from applicators, which has not stopped failures, the adherence to Quality Assurance systems should be reverted to. Guarantees can only be asked from bonafide, qualified and authorized applicators. Such qualifications should form a part of specifications. Even for, materials test certificates conforming to international codes and tested by bonafide agencies must be procured.
References:
1. Chapter 1 and 2, Handbook of Repair and Rehabilitation of RCC Structures, Director General Works, Central Public Works Department, Govt. of India, New Delhi
2. Surlaker, Sunny, “Waterproofing – Best Practices”, NBM&CW Magazine, April 2012
3. M.R. Rixom, Noel P. Mailvaganam, Chemical Admixtures for Concrete, Third Edition, Section 4.4
4. EN 1504
5. MC-Bauchemie Documentation on Injection Systems
6. https://en.wikipedia.org/wiki/Membrane_roofing
7. Liquid Applied Membrane Market Analysis expected to reach USD 6.92 billion by 2022, http://www.prnewswire.com/news-releases/liquid-applied-membrane-marketanalysis- expected-to-reach-usd-692-billion-by-2022-300366916.html
8. MC-APC Product Application Guide, MC-Bauchemie Mueller GmbH and Co. KG
9. Dr. V.K. Raina, Raina’s Concrete Bridge Practice: Construction, Maintenance and Rehabilitation (Second Edition)