TechCrete 2500 Waterproofing Agent offers a unique solution to the dilemma of how to protect concrete structures from premature deterioration (by providing excellent waterproofing protection, while also increasing the durability and sustainability of the concrete). This paper provides an overview of the proprietary chemical reaction that effectively waterproofs the concrete itself for the design life of the structure.

NOTE: This one-of-a-kind product was recently voted by the concrete industry as the ‘Most Innovative Product for 2020’ at the World of Concrete Convention held in Las Vegas (category: Materials for Concrete Construction).

Using the spray applied TechCrete 2500 Waterproofing Agent as part of the TechCrete 2500 Waterproofing System, provides complete long-term protection for concrete structures (15-year and 30-year labor and materials warranties are available). This involves performing any necessary cleaning, preparation and repair work, followed by the completion of a 3-step waterproofing application process:

• Step 1: Spray apply TC 2500 over the entire surface (and allow it to dry to the touch). Then saturate the entire area with water (and let it dry to the touch).

• Step 2: Spray apply TechCrete Crack & Void Treatment on any visible cracks, and then spray apply TechCrete Accelerating Agent over the entire surface (and allow it to dry to the touch).

• Step 3: Saturate the entire surface area with water once more.

Once the TC 2500 has been applied and watered in (Step 1), a chemical reaction will begin to occur, that creates a protective waterproofing gel. The chemical reaction that forms this gel occurs ½” – ¾” below the surface of the concrete, and prevents any water, chemicals, chloride ions, etc. from reaching the steel reinforcement bars that were placed in the concrete during construction of the structure. This gel does not form on the surface of the concrete, and does not change the appearance or the slipperiness coefficient of the concrete surface. The concrete surface looks the same after the waterproofing application as it did before the application.

NOTE: Paint, coatings, paving asphalt, etc. can be applied to the surface of the concrete following the completion of the waterproofing system (if desired).

THE CHEMICAL REACTION

The following components are necessary for this biochemically modified silicate gel to form just below the surface of the concrete, and those components are:

• TechCrete 2500 Waterproofing Agent
• Calcium (readily available in the concrete)
• Water
• Carbon Dioxide

TC 2500 penetrates below the surface of the concrete during the initial application, and remains reactive inside the matrix of the concrete indefinitely. As future cracks occur, rainwater will reactivate the chemicals, forming new gel and sealing the cracks as they occur. Stable cracks up to 2.0 mm in width will be sealed during the application of the waterproofing, and future cracks up to 0.4 mm in width will be sealed for the remaining life of the structure. Any stable cracks that are wider than these dimensions, and any structural or moving cracks must be properly repaired as outlined in the Alchemco repair procedures.

TC 2500 has a unique and proprietary, biochemically modified catalyst that separates it from all other spray applied concrete sealers and waterproofing products. A catalyst is a material that enables, speeds up or slows down a chemical reaction, without changing the chemical reaction itself. When TC 2500 is used to waterproof a concrete structure, there are two distinct catalytic reactions that occur, creating a ‘virtuous cycle’ that continually repeats itself over and over for the remaining life of the structure.

TC2500 is primarily made up of silicates, combined with this proprietary biochemical catalyst. During the three application steps, the silicates within TC 2500 react with metallic ions in the concrete (primarily the calcium hydroxide that is a by-product of cement hydration). During this stage, TC 2500 is highly reactive, and creates a complex Calcium Silicate Hydrate (CSH) gel. This gel swells when it comes in contact with water (blocking cracks, pores, capillaries, voids, etc.) reducing the permeability of the concrete and preventing the penetration of water.

Over time, Carbon Dioxide from the atmosphere extracts some of the Calcium from the CSH gel to form Calcium Carbonate. This creates an inert mass that further reduces the permeability and porosity of the concrete, by permanently blocking the cracks, voids, micro-fractures, etc. However, the ‘carbonation of concrete’ problem that is usually associated with Carbon Dioxide, is not a problem for TechCrete 2500.

THE LIFETIME CYCLE: In order for TC 2500 to seal all future cracks that form after the application, it must produce more mass than was originally applied … in other words it must ‘grow’. When Carbon Dioxide in the atmosphere extracts some of the Calcium from the waterproofing gel, it leaves a ‘low ratio’ CSH gel. As a result of this interaction, the waterproofing gel is now ‘ready to react’ again, and actively looks to attract Calcium ions to bring it back into equilibrium. So, when water enters the concrete, the cement continues to hydrate, and through the process of diffusion within the concrete, the Calcium moves from areas of high concentration to areas of low concentration. The ‘low ratio’ CSH gel then reacts with the newly available Calcium and once again becomes a ‘high ratio’ CSH gel. At this point, the cycle begins all over again with the ‘high ratio’ CSH gel reacting with Carbon Dioxide in the atmosphere, once again forming Calcium Carbonate, which permanently plugs the cracks, pores, microfractures, voids, etc. (once again leaving a ‘low ratio’ CSH gel).

This ongoing chemical reaction creates a dynamic and reliable self-healing process within the concrete. The process of ‘carbonation’ is normally considered detrimental to concrete, because it lowers the pH level of the concrete (which deteriorates the protective ‘passive layer’ surrounding the steel reinforcement bars, and allows corrosion to occur). TechCrete 2500 Waterproofing Agent does not have this problem. It creates a ‘virtuous’ carbonation cycle which does not lower the alkalinity level of the concrete, but in fact increases the alkalinity level, thereby enhancing the protection of the steel reinforcement. In addition, the Calcium Carbonate that is formed during this carbonation cycle increases the long-term durability of the concrete.

The difference between TechCrete 2500 and normal silicate products is that the biochemical catalyst allows this carbonation cycle to repeat itself indefinitely. Plain silicates get stuck when they go thru the carbonation process, and are not available later to react again. As a result, normal silicate products are not even able to seal ‘existing cracks’, much less any ‘future cracks’ that will occur.

Also, the fact that there are two reaction components that occur when using TC 2500 is important. The Calcium Carbonate that is formed acts as a consolidating glue or space filler, in the cracks, pores, capillaries, etc. The CSH gel also plays a vital role, because not only does it allow the virtuous cycle to occur over and over (a Calcium Carbonate factory), but this colloidal gel is not rigid like crystalline technology products are; so it allows for small dynamic movement such as shrinkage or thermal movements in the concrete.

In summary, when TC 2500 comes in contact with water it forms a waterproofing gel that swells; filling and blocking off the spaces (cracks) that allowed the water to enter.Then the ‘factory’ gets to work depositing Calcium Carbonate to permanently seal it.The waterproofing gel will then remain ‘dormant’ until water comes in contact with it again.