Self Healing Concrete

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Self Healing Agent

For Concrete Mixtures

 

Since Roman times men build constructions using concrete as an all-round building material. While ordinary concrete can handle substantial compressive loads, tensile and flexural load carrying capacity is however limited. Even when reinforced with steel rebars, concrete is sensitive to crack formation. Cracking can result in a number of problems such as water leakage, frost damage and reinforcement corrosion. These detrimental phenomena shorten the functional service lifetime of concrete constructions substantially and require therefore costly maintenance and repair actions. For difficult to reach constructions manual inspection and repair is however often not possible or otherwise even more expensive. A solution to avoid costly maintenance and repair actions is provided by self-healing concrete.

 

From now on concrete is able to self-repair cracks, making constructions more durable thereby increasing its service lifetime while reducing maintenance and repair costs. Self Healing Concrete will make constructions last longer, while at the same time reducing costly maintenance and repair. The choice for owners who consider construction life cycle costs.

 

Characteristics

Self Healing Agent is applied in special repair mortars and concrete mixtures. It is composed of a biodegradable granular additive (healing agent) what autonomously seals and waterproofs up to 1-mm wide occurring cracks. Permanent sealing occurs due to concrete compatible limestone formation. Compatible with commercial concrete mixtures. Contains a biodegradable polymeric mineral precursor compound and a bio-based enzymatic catalyst.

 

Typical applications

  • Tunnel elements
  • Liquid-containing reservoirs
  • Basement walls
  • Subsurface constructions
  • Marine constructions
  • Bridge- and parking decks
  • Flooring systems

 

Tailor made solutions

One of our technical specialist will support your company to design your concrete self-healing mix. It is tailor made special for your project. In general between 5 and 15 kg healing agent per m3 concrete mix is required, depending on environmental conditions of application. Healing Agent can be applied in ready mixes, prefab applications, or added directly to the truck mixer on site.

 

Health and environmental aspects Safety

Non-flammable / nonexplosive

 

Self Healing Repair Mortar

For Existing Concrete Structures

 

Cracks in concrete, specifically below ground water level, can be detrimental to water tightness of constructions and can therefore result in leakage problems. For structural and durable repair of such cracks Self Healing Repair Mortar has been developed.

 

It is a 1-component repair mortar modified with Healing Agent. It contains natural enzymes and is specially developed for waterproofing leakage spots in concrete. After applying the mortar the Healing Agent will start to react within 24 hours resulting in permanent waterproofing of the construction. This mortar is particularly suitable for permanent and durable repair of larger than 1 mm wide cracks and porous leaky parts of concrete constructions.

 

Repair Mortar can be typically applied to:

  • Stop water leakage in basement walls
  • Permanently repair water-leaking cracks
  • Provide ductile dilatations under dynamic loading conditions
  • Repair of structural defects

 

Benefits

  • Increase durability of the concrete structure
  • Non-flammable and nonexplosive
  • Enhance water and freeze-thaw resistance
  • Reduce maintenance costs
  • Reduce discomfort due to maintenance

 

Characteristics

Based on biodegradable granular additive (Healing Agent) Contains strain hardening PVA fibers providing:

  • Low shrinkage
  • Strong bonding
  • Ductile behaviour
  • Self-healing

 

Composition

  • Portland cement
  • Limestone powder
  • Fly ash
  • PVA fibres
  • Plasticizer
  • Biodegradable polymeric mineral precursor compound
  • Bio-based enzymatic catalyst

 

Storage conditions

Dry, between 10 and 40°C

 

Packaging

Self Healing Repair Mortar is available as ready mix in 20 kg bags

 

Health and environmental aspects

R 38 – Irritating for bare skin

S 24 – Avoid direct skin contact

 

Safety

Non-flammable / nonexplosive

 

 

Method Statement

 

1. Removal of any loose, incoherent and contaminated concrete parts
Note: If corrosion has occurred due to carbonation or there are hazardous substances the concrete surrounding the corroded rebar should also be removed.

 

2. Preparation of concrete surface
(a) Creating sufficient bonding surface
(b) Removal of dust, oil paint and algae etc.

 

3. Preparation of steel rebar
(a) Remove corrosion residue from rebar

 

4. Preparation of bonding surface
(a) Pre-wet surface with water
Note: 1. Surface must be moist when applying it; but not soakingly wet)
(b) For good bonding, apply it as a scratch coat.

 

5. Application of mortar

(a) Proportion

Water dosage: 15 kg bag : 3.8 ~ 4.2 litre

Note:

– Never mix less than a full bag

– Tap water to be used

(b) Mixing

i) Mix Repair Mortar mechanically until a homogenous mix is obtained.

ii) Mixing time depends on the type of mixer. Recommended: approximately: 3 min.

iii) Use of a contra twin mixer is advised

(c) Application by spraying / shotcrete

(d) Application by hand

Note: 1. Apply in layers of approximately 30mm thickness.

 

6. Curing

(a) Prevent mortar from drying out within the 1st 24 to 48 hours.

(b) Use of a curing compound might affect the bonding if future coating or additional repair layers

(c) Continously wet surface with water or cover damp burlap and plastic sheets.

 

Information Sheet

 

Technical specification tested conform NEN-EN 1504:

Performance Characteristic Standard Test Values
Compressive strength test NEN-EN 12190 > 38 N/mm2
Chloride Ion content NEN-EN 1015-17 < 0,05%
Adhesive bond NEN-EN 1542 > 1,9 N/mm2
Restrained shrinkage / expansion NEN-EN 12617-4 > 1,5 MPa
Carbonation resistance NEN-EN 13296 dx < control concrete (MC(0,45))
Elastic modulus NEN-EN 13412 > 14000 MPA
Thermal Compatibility
1. frost thaw
2. Thermal shock
3. Temperature Fluctuation
NEN-EN 13687
Part 1
Part 2
Part 4

Bond strength after 50 cycles > 1,5 N/mm2
Bond strength after 30 cycles > 1,5 N/mm2
Bond strength after 30 cycles > 1,5 N/mm2
Capillary absorption NEN-EN 13057 0,5 kg/m2/h0,5

 

Self-healing Repair Mortar is suitable for repair methods conform NEN-EN 1504-3 Label 1:

  • Hand applied mortar
  • Spraying concrete or mortar
  • Adding mortar or concrete
  • Increasing cover with additional mortar concrete
  • Replacing contaminated or carbonated concrete

 

Composition

  • Cement
  • Limestone powder
  • Fly ash
  • PVA fibres
  • Plasticizer
  • Biodegradable polymeric mineral precursor compound
  • Bio-based enzymatic catalyst

Self-healing Repair Mortar is a concrete repair mortar suitable for existing as well as new concrete structures. The mortar is developed as structural repair mortar conform class R3 (NEN-EN1504). The mortar has additional characteristics, it is very ductile and has a good bond together.

The magic self-healing agent for concrete mixtures

Self Healing Agent is applied in special repair mortars and concrete mixtures. It is composed of a biodegradable granular additive (healing agent) what autonomously seals and waterproofs up to 1 mm wide occurring cracks. Permanent sealing occurs due to concrete compatible limestone formation. Compatible with commercial concrete mixtures. Contains a biodegradable polymeric mineral precursor compound and a bio-based enzymatic catalyst.

 

Advantages

  • Seals and waterproofs autonomously
  • Permanent sealing
  • Compatible with commercial concrete mixtures
  • Project specific tailor-made solutions

 

Typical application field

  • Tunnel elements
  • Liquid-containing reservoirs
  • Basement walls
  • Subsurface constructions
  • Marine constructions
  • Bridge- and parking decks
  • Flooring systems

 

Tailor made solutions

One of our technical specialist will support your company to design your concrete self-healing mix. It is tailor made special for your project. In general, between 5 and 15 kg healing agent per m3 concrete mix is required, depending on environmental conditions of application. Healing Agent can be applied in ready mixes, prefab applications or added directly to the truck mixer on site.

 

Application

Healing Agent can be added as a precautionary measure in the original mix design or as a tool for crack management. Always add the Healing Agent to the wet concrete mixture. Once added the HA, apply mixing until a homogeneous mixture is obtained, typically a mixing time of approximately 3 minutes is sufficient depending on the type of mixture is used.

When adding HA to the concrete mixture at the ready-mix plant, always add the HA when the concrete is poured into the truck. Apply 3 minutes of high intensity mixing in the truck at the plant. During transport, keep the truck mixer running as usual. When at the site, apply additional 3 minutes high intensity mixing before pouring concrete.

 

Application dosage

The dosage of HA may vary between 1 – 4% of the amount of Portland cement clinker in the concrete mixture. For use of HA in mixtures with a composite cement type (e.g. blast-furnace slag cement) the percentage of Portland cement clinker should be at least 50%. For clinker-percentages lower than 50%, a lower maximum dosage is advised depending on the effect on strength development and workability. Additional testing with the specific mixture is recommended.

Typically, the dosage for precautionary purposes is between 5-7, 5kg/m3 of concrete. Addition of HA to the concrete mixture may affect the workability and strength development slightly depending on the mixture. However, when using a dosage of 5-7, 5kg/m3, the influence can be considered negligible. For addition to new mixtures (with no experience with HA) or higher dosages, it is advised to test the effect on workability (slump) and strength development (3, 7 and 28 days).

 

Mechanism:

 

 

How it works:

 

 

 

 

Choosing the Healing Agent additive

 

Healing Agent

Healing agent is an additive consisting of solid particles of size 0-2 mm to add to the dry constituents or wet mixture of new mortar or concrete up to a dosage of 10 kg per m3. Healing agent in its current form is typically applicable to mortar and concrete with conventional cements containing more than 30% clinker. The healing agent disperses in the mortar or concrete matrix, where the particles wait upon occurrence of a crack or surface porosity and water entering. Upon contact with water, the bacteria inside the healing agent activate and convert the healing agent components into carbonate-based minerals that seal the crack or porosity automatically up to a crack width of 0.8 mm. This limits the amount of required repair and extends the service life of the structure.

 

Crack sealing

Places where the healing agent can come in very useful are structures that either need to keep surface water outside or inside, for example in water reservoirs, basements or irrigation systems. Watertight sealing of concrete structures is quite a challenge. Current methods to obtain water tightness of concrete are for instance by applying a water tight membrane or by increasing the amount of steel reinforcement, which limits the crack widths in the concrete in such a way that the concrete can restore its own water tightness. For the latter case, the added steel can be up to double the amount of steel required for the structural function. Aside from that the added steel does not have an additional function and increases the environmental and economic burden of the structure, it can also complicate the casting of the concrete and therefore hamper the quality, due to the complex and dense steel cage.

 

Surface densification

The quality of the concrete surface is very important to guarantee the service life and durability of the concrete structure. Additionally, as concrete structures typically make use of steel reinforcement to take over tensile stresses, the surface of the concrete should be in good condition to protect the embedded steel. One of the ways to indicate a good quality surface is a limited surface water absorption, indicating reduced susceptibility to ingress of deleterious materials.

 

Comparison

Upon addition of the healing agent cracks can be made watertight that have a width more than double of that of concrete without healing agent [1]. Given that the healing product is carbonate based, effectiveness of the sealing function decreases with increasing acidity of the solution that needs to be retained. For the typical blocking of water leakage no limitations are expected. Something quite special when compared to alternative additives such as expanding minerals, is that in case of addition of healing agent the same crack was able to restore its water tightness multiple times. After healing, the same crack was fully healed again upon re-opening the same crack three times. Additionally research was undertaken to demonstrate the automatic sealing of the cracks when water was actively leaking through the crack. A maximum crack width of 0.8 mm was found to seal, without the presence of water pressure. With increasing water pressure it is recommended to allow a crack width based on a comparable rate of water leaking through the crack.

An additional function upon addition of the healing agent to the concrete mixture is the ability for the surface to densify [2]. The surface absorption was up to half of that of the concrete without healing agent. This property allows to delay the ingress of deleterious materials and therefore extend the surface life of the concrete.

 

Pricing

Given that more than double the crack width can be automatically sealed upon addition of healing agent, part of the crack width controlling steel reinforcement can be reduced, slightly increasing the crack width. This already compensates the economic and environmental impact of the addition of the healing agent to the mixture. Additional cost benefits occur because there is no need to close the access to the structure for repair and the actions for repair.

Considering the densified concrete surface upon addition of the Healing Agent, less ingress of deleterious materials can be expected. This approximately doubles the time until maintenance is required.

 

Conclusion

In case of constructing a concrete structure or element that requires to be watertight, addition of the healing agent can be considered. Especially in case limited crack widths (< 0.2 mm) are difficult or expensive to obtain, for instance due to added steel reinforcement, the healing agent can be of service and cost effective.

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