Tuesday, June 28th, 2022
CECR

Crack Treatment In Waterproofing: Methods & Materials

 

Samir Surlaker
Director
Assess Build Chem Private Limited

 

Sunny Surlaker
Head Technical Services
Assess Build Chem Private Limited

 

The fundamental certainty of concrete is that it will crack.

Concrete is known to have the ability to sustain high compressive loads. The ability of concrete to sustain tensile and flexural loads on the other hand is very limited due to its brittle nature. The concrete is therefore prone to cracking when the tensile stresses in the concrete exceed its tensile strength. When compared, the tensile strength of concrete is barely 1/10th the compressive strength of concrete. That is the reason, why concrete is reinforced with steel.

Concrete may crack due to many reasons, viz., improper mix design, insufficient curing, improper joint design, overloading, shrinkage and many other factors. These may occur due to errors in the construction stage (improper design, improper mix design, improper workmanship) or due to loading after construction (mechanical overloading, accident, fire, thermal changes, chemical attack or biological attack). Some of the types of cracks and/or their causes are shown in Figure 1.

In practice, we cannot eliminate cracks completely, but with proper mix design, production, placing, compaction and curing practices, we can limit the extent of cracking to a degree where it will not adversely affect the structure. For durability purposes international codes recommend limiting the crack widths in concrete to:

  • ≤ 4 mm crack widths for interior structural elements
  • ≤ 3 mm crack widths for external structural elements exposed to weather
  • ≤ 2 mm crack widths for special structural elements exposed to weather or special loads
  • ≤ 1 mm crack widths for structural components where waterproof concrete is being used, e.g. in basements, tunnel sections, etc.

The problem with cracks is that they are both a symptom and a cause. General perception of cracks is that they are unsightly, and observers feel that the element that has cracked has failed. In the case of walls, if a crack is not structural, is not too wide and is not leaking water, it may be considered acceptable.

Cracks may affect RCC elements in three fundamental ways:

  1. It may affect/reduce load carrying capacity as loads around the crack are redistributed
  2. It surely affects the durability of the structural element by allowing water, chlorides and other aggressive elements easy access to the reinforcement

Fig. 1: Types of Cracks

  1. It’s a precursor to loss of serviceability of the structure as corrosion begins from cracks, propagates and leads to further cracking Cracks are also a fundamental problem in waterproofing as these are the primary avenues for water to enter the living space. Therefore, for both new structures as well as remedial waterproofing, repair of cracks becomes very important to seal water ingress pathways. 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.
Understanding Cracks

Before we can start to treat cracks, we need to understand them. Solutions to treat cracks are not universal. They are based on the characteristics of the cracks themselves. Cracks (shown in Figure 2) can be characterized based on:

  • Crack Depth: Near Surface or Deep Cracks
  • Crack Width: Crack Tip Width, Crack Width at Surface
  • Crack Movement: Moving or Static
  • Crack Wetness: Dry, Damp, Wet or Pressurized Flow through
Fig. 2: Characteristics of Cracks to be Evaluated

 

Prior to selection of a material and method to remediate a crack or void, the characteristics of the defect need to be clearly assessed. Assessing these properties will help us in selecting the correct material and in turn determine the success of the crack repair. Injection is the first step of rehabilitation both when structural distress is encountered as well as when leakages are detected, and durability of the RCC Element/Structure is compromised. The injection technique is often the only viable solution in order to repair/waterproof damaged structures and thus avoid any further ensuing consequential damage. Table 1 shows various reasons for Injection.

Table 1: Reasons for Crack Injections

CRACK INJECTIONS IN CONCRETE STRUCTURES

Structural injection for dry cracks

Structural injection for damp cracks

Sealing of cracks and cavities for waterproofing

Sealing against pressurized water

Injections for imparting stability in Masonry structures

Frictional Sealing of loose masonry

External sealing using curtain injection technology

Grid injection for dampness

 
Summary Of Remedial Measures

Some of the remedial measures based on the characteristics seen above can be summarized in the schematics and sections below.

1.      Solutions Based On Crack Depth

A summary of these methods is shown in Figure 3. Near Surface Cracks (up to 5 mm) can be repaired by simply coating them with a crack bridging coating, by impregnating the crack with a low viscosity resin grout or by cutting a groove along the crack, filling it with a fine polymer modified mortar and overcoating it with a crack bridging coating.

Fig. 3: Summary of Crack Treatment Methods Based on Crack Depth

2.      Solutions Based On Crack Width

The injection grout material and methods also need to be selected on the basis of crack width. The width of the crack will dictate the viscosity and particle size of the injection grout. The types of materials that can be used for different crack widths are shown in Figure 4.

Fig. 4: Material Selection for Grouting Based on Crack Width

 

Generally, as a rule of thumb, mineral slurries (cementitious injection grouts) are most suitable for crack widths or voids > 1.5 mm. Hence in many of the cases of waterproofing where cement grouting is used, it is unable to fill the finer cracks in the concrete and the leakage continues. Hence, for Crack Widths < 1.5 mm it is recommended to inject / grout them using a resin [Epoxy or Polyurethane].

3.      Solutions Based On Crack Movement
The movement characteristics of a crack needs to be carefully evaluated before it is treated. In more cases than not including for structures such as terraces, podiums, which are slightly dynamic due to thermal or traffic variations. In these cases, when cracks are treated with a rigid material such as Cement, Epoxy, Methacrylate or even PU Foam, the rigid nature of these systems are unable to cope with the minute movements in the concrete elements and the system gives way, starting the leakage problem again. The selection of material systems based on crack movement are shown in Figure 5.
Fig. 5: Material Selection Based on Crack EP
 
4.      Solutions Based On Crack Wetness

Wetness of the crack has quite an impact on material chosen. For e.g. the materials used for repairs or strengthening such as cementitious grouts and epoxies can be applied in dry or damp conditions, but not when a crack is leaking water. In those cases, the only system that can work is an elastic methacrylate gel or polyurethanes. The table based a German Standard for Repair, 2017 is shown in Figure 6. This table guides the selection of various crack filling materials based on the wetness of the crack.

Going by these four considerations, the material and method selection becomes very important in treatment of cracks. Most often than not, these guidelines are not followed in practice and the crack treatment remains ineffective, being referred to as “failed waterproofing”.

The Materials

Assessing cracks for the properties discussed previously will help us in selecting the correct material and in turn determine the success of the crack repair. Internationally and in India at the moment, the following types of filler materials are being used for crack/void filling:

  • Epoxy resin (EP)
  • Polyurethane (PU)
  • Cement slurry (FC)
  • Micro fine/fine cement suspension (MFC)
  • Injection Hydrogels Based on Methacrylate/ Polyurethane Resins [AG]

There are two different ways to fill the filling materials into the cracks and voids of a structural component:

  • Injection: Filling of cracks and voids under pressure through packers (filler plugs)
  • Impregnation: Filling of cracks without pressure (by penetration, gravity and atmospheric pressure)

Fig. 6: Guidelines on Selection of Materials Based on Crack Wetness

Table 1: Injection Materials Available and Their Usage Guidelines

CRACK VOID PROPERTY / MATERIALS

CEM

EPOXY

PU RESIN

GELS

COATINGS

Surface Crack

+

++

 

 

++

Deep Crack

++

++

++

 

 

Load Transfer / Strengthening

++

++

+

 

 

Water Stopping / Durability Enhancement

 

 

++

++

 

Moving Crack

 

 

++

++

 

Non Moving Crack

++

++

 

 

 

Water Bearing / Wet Crack

+

 

++

+

 

Dry Crack

++

++

++

 

 

Fast Flowing Water

 

 

++ FOAM

 

 

+: Suitable; ++: Most Suitable; Blank: Not Suitable

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 Process Of Injection

After completion of diagnosis and selection of materials for injection the work of injection passes through following stages:

  1. Preparation of the crack
  2. Location of points for injection
  3. Surface sealing of cracks
  4. Injection of resin proper
  5. Removal of packers and plugging
  6. Removal of sealing material
  7. Final surface treatment after injection resin/grout hardens
Injection Machinery And Appurtenances
1.      Machinery

The Injection process comprises of the mixing device, the injection device, packers (filler plugs), possibly an injection hose and insulation, if necessary. The manufacturer generally provides the methodology for the work with the approved system components. The equipment required for crack injection can range from a simple bucket with an outlet to most sophisticated pneumatically compressed machines capable of producing about 500 bar pressure. Other variants are available with hand-controlled nozzles with a mixing assembly to mix the two components at the point of injection. Modern sophisticated machineries are designed to provide better working pressures, better nozzle / packer combinations and to take care of pot life considerations.

Modern Injection Machinery for injection of cementitious materials, a one component injection pump and a two- component injection pump are shown in Figure 7.

The injection method should be clearly specified prior to the commencement of the work and should be supervised to conform to the specifications. After the injection resin or grout has hardened and after the removal of the nipples, the surface sealing material, which is normally quick setting cementitious system or resin should be scrapped off completely and the surface should be prepared for further cosmetic or strengthening treatment.

2.      Selection Of Packers For Injection

Packers or Nipple Systems are the link between the structure and face of the crack and the injection nozzle. Packers must be of adequate size to guarantee the flow of injection resin to the desired place with or without being displaced or de-bonded due to injection pressure or rebounds. The critical selection depends upon the access to crack, quality of surface, surface condition as well as pressures used in injection process. Figure 8 shows different type of commonly used packers for Injection Grouting.

 

Fig. 7: Modern Injection Machinery

Fig. 8: Commonly Used Packers for Injection Grouting

There are normally three types of Packers used under general conditions:

  1. Adhesion Packers: For the injection of dry cracks, cavities and substrates with Epoxy and Polyurethane resins where surface conditions are suitable and
  2. Drill or Bore Injection Packers: for the injection of dry, moist and water bearing (pressurized and non-pressurized) cracks, cavities and substrates with Epoxy, Acrylic and Polyurethane resins
  3. Hammer Packers: for the injection of cement injections and acrylic The main differences are valve openings, dimensions and pressures.
Conclusions

In conclusion, modern injection technology coupled with proper equipment can solve almost all types of waterproofing problems thereby providing economical solution in comparison to removal and replacement of older waterproofing systems. The specifications should be very clear and unambiguous. The specifications should at least cover points like material, viscosity, techniques to be adopted, the equipment to be employed, type of nozzles and spacing, pressure to be applied etc. The repair of cracks is a part of waterproofing and repairs of damaged and distressed structures and cannot replace other remedial measures adopted for successful waterproofing.

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