Reducing Reinforcing Steel Corrosion with SCP

Since the late-1800’s, the use of reinforced concrete has been the most widely used construction practice globally because reinforcement helps concrete in tension. However, one concern of using this practice is the durability and longevity of the concrete due to the corrosion potential of the reinforcement. Corrosion of reinforcing steel is the number one cause of failure in reinforced concrete structures.

Corrosion as defined by American Concrete Institute (ACI) is the deterioration of a material, usually a metal, that results from a chemical reaction with its environment.1 The corrosion of reinforcing steel is an electrochemical reaction consisting of the flow of electrons and ions that produces a deterioration of the steel and its properties. One significant way to reduce the corrosion potential is to completely encapsulate reinforcing steel in concrete with a high pH value, as the high alkaline environment acts as a protective oxide film. If no other outside forces are applied to the reinforced concrete, the steel should not rust. Unfortunately, almost all reinforced concrete is exposed to environmental conditions that shorten its lifespan, increasing the potential for the corrosion.

The corrosion potential of reinforcing steel is influenced by several factors: moisture intrusion, lowered pH values over time, quality of the concrete and construction materials, proper concrete coverage of reinforcing steel, initial curing conditions and the formation of cracks in the concrete. These factors can speed up chloride movement into the concrete, disrupting the protective oxide film around the reinforcing steel and leading to rusting. This corrosion can lead to spalling and delamination of the concrete structure and reduced tensile capacity.

Spray-Lock Concrete Protection (SCP) provides treatments that penetrate the pores and bleed-water capillaries in concrete. SCP products bring the pH of older concrete to a higher value and stabilize the pH of new concrete to maintain a high value, lowering the potential of reinforcing steel corrosion. Additionally, the colloidal silica in SCP Technology reacts with the available alkalis in the capillary and pore space to form calcium silicate hydrate (C-S-H). By filling these spaces, SCP products waterproof concrete within the interaction zone. If the concrete structure does not have any structural cracks, SCP products also waterproof the structure in the application area. With SCP Treatments stabilizing pH levels and preventing moisture migration from carrying chlorides within the concrete matrix, the corrosion potential is greatly reduced.

1 ACI CT-16 ACI Concrete Terminology ERRATA January 6, 2017

 

Is Spray-Lock Concrete Protection a Bond Breaker?

“Are Spray-Lock Concrete Protection (SCP) products bond breakers?” To answer this question, we need to define a bond breaker and examine how SCP reacts in the concrete matrix. A bond breaker is a product that forms varying layers of separation between contact surfaces. SCP is a penetrating concrete treatment that does not change the surface of the concrete matrix. An SCP application is not a coating and has no negative effect on bond integrity.

Testing of SCP’s application on concrete was performed to show that the product is not a bond breaker. Test methods included (1) ASTM C1583 Standard Test Method for Tensile Strength of Concrete Surfaces and the Bond Strength or Tensile Strength of Concrete Repair and Overlay Materials by Direct Tension (Pull-off Method) and (2) ASTM E303 Standard Test Method for Measuring Surface Frictional Properties Using the British Pendulum Tester.

In the ASTM C1583 test method, the concrete sample is cleaned of surface contaminants and loose or deteriorated concrete. The sample is then prepared to the typical surface conditions of the in-place concrete structure. The test material is applied and cured in accordance with the manufacturer’s specifications. After cure, a core drill is used to make a circular cut perpendicular to the surface. The test material is left intact on the concrete substrate, while a steel disk is attached to the top of the material using an epoxy adhesive. A tensile loading device is then attached to the steel disk to apply a tensile load to the test sample with force parallel to the vertical axis of the specimen. The load is applied until failure, and results are recorded.

In the ASTM E303, the concrete surface is cleaned and freed of loose particles. The instrument is placed and leveled. The pendulum is lowered so that the edge of the slider just touches the concrete surface. Water is applied to thoroughly cover the test area. One swing is performed, and the reading is not recorded. Four more swings are made, and the surface is rewet before each swing. The results are recorded.

Testing shows that SCP Treatments increased the pull-off strength of concrete up to 73% compared to untreated concrete and had no statistical effect on surface friction. Since SCP Treatments become an integral part of the concrete matrix and are not surface coatings, there is no need for a mechanical key, additional treatments or removal prior to using a covering or coating. SCP can be used in conjunction with all types of coverings and adhesives without a negative impact on a covering material or adhesion of material to the concrete.

Calcium Hydroxide Consumption by SCP’s Colloidal Silica

Concrete in service can sometimes be exposed to attack from chemical agents. Two principal factors affect concrete’s durability in chemical attack situations: 1) the concrete’s permeability and 2) readily available reactants in the concrete. When Portland cement reacts chemically with water, it produces several reaction products.  Calcium Silicate Hydrate (C-S-H) is the primary reaction product of hydration, contributing the most to strength and other desired properties of concrete.  An additional reaction product is Calcium Hydroxide (CH), which has little or no cementitious properties and contributes very little to the strength of hardened concrete.  CH is often described as a weak link in concrete as it is easily attacked by chemical agents and easily leached by water.  Pozzolans containing silica, however, can potentially react with CH to form secondary C-S-H, increasing concrete’s strength and reducing permeability1.

 

Colloidal silica treatments from Spray-Lock Concrete Protection (SCP) enter concrete through capillary voids, reacting with CH to form more C-S-H. Because of the colloidal silica’s extremely small particle size, it has a tremendous amount of pozzolanic potential, greater even than silica fume2.  During the reaction, SCP Treatments consume the readily-available CH, denying CH the opportunity to react with chemical agents that commonly attack concrete such as nitrates and sulfates.

 

Research has demonstrated that CH is consumed by colloidal silica, illustrated in Figures 1-2 below3.

Figure 1: Calcium Hydroxide Consumption by Colloidal Silica (CS), 1st 24-hours.

 

Figure 2: Calcium Hydroxide Consumption by Colloidal Silica (CS), 1st 56 Days

A logical concern among concrete technologists may be that the colloidal silica could exhaust the supply of CH for reaction with other pozzolans present in the concrete.  Research has shown that this is not the case, with pozzolan contents as high as 80% by weight of cementitious properties, demonstrating improved performance with colloidal silica additions.  As with most concrete technologies, SCP recommends testing of its products with project-specified concrete mixtures and constituent blends to establish the product’s performance with local raw materials.

References:

[1] Kosmatka, S.H. & Wilson, M.L. Design and Control of Concrete Mixtures, EB001, 15th edition, Portland Cement Association, Skokie, Illinois, USA, 2011, pp. 72-73.

[2] Singh, L.P., Karade, S.R., Bhattacharyya, S.K., Yousuf, M.M., & Ahalawat, S. “Beneficial role of nanosilica in cement based materials – a review,” Construction and Building Materials 47 (2013), 1069-1077.

[3] Hou, P., Kawashima, S., Kong, D., Corr, D., Qian, J., & Shah, S. “Modification effects of colloidal SiO2 on cement hydration and its gel property,” Composites Part B 45 (2013) 440-448.

Polished Concrete with Spray-Lock Concrete Protection Products

The Concrete Polishing Council defines polished concrete as the result of “changing a concrete floor surface, with or without aggregate exposure, to achieve a specified level of gloss.”1 Concrete polishing is a process where the upper paste portion of the concrete surface is removed. Based on the desired appearance, polishing can expose fine and/or coarse aggregates in the concrete. During the process, a densifying liquid is used to harden the concrete by filling capillaries and pores at the surface.

How does Spray-Lock Concrete Protection (SCP) work with concrete that will have a polished finish? SCP Treatments penetrate concrete through the concrete capillary system and react with free alkali to fill the capillaries and connected pore structure. The reaction creates more Calcium Silicate Hydrate (C-S-H) that fills the pores and capillaries with more concrete and densifies the slab. Polishing on SCP-treated concrete may lead to a lighter appearance and may be harder to grind. Typically, the time frame for grinding SCP-treated concrete is comparable to high performance concrete. There have been many SCP-treated slabs that have been ground and polished without the use of an additional densifier with excellent results. However, the contractor can still use a densifier if the project specifications call for one to be used during the polishing process. Using a densifier will not interfere with performance of SCP products. SCP recommends performing a test area for polishing to see the final result prior to polishing an entire floor section. A topical sealer may also be used to help reduce staining of concrete.

At time of placement, spray-applied SCP Treatments can benefit polished concrete in the following ways:

  • Reduce the plastic shrinkage of the concrete slab
  • Densify concrete within the interaction zone
  • Provide a superior cure
  • Increase durability
  • Reduce concrete maintenance
  • Allow floors to be polished within 14 days of concrete placement.

1 https://www.ascconline.org/concrete-polishing-council/concrete-polishing-council-overview

Freeze/Thaw Mitigation of Exterior Concrete with SCP

Spray-Lock Concrete Protection (SCP) Technology closes concrete capillary void space within the interaction zone, significantly reducing permeability to liquids. Because of this action, SCP mitigates liquid water’s ability to enter the concrete, subsequently freeze and cause freezing/thawing damage. For concrete in freeze/thaw exposure conditions, SCP can extend the service life when used as a remediation measure when existing concrete air entrainment values are lower than specified, when the concrete’s air void system is not conducive to freeze/thaw resistance or when both conditions are present.

When specifying SCP products as freeze/thaw remediation measures, consideration should be given to the potential routes of water ingress.  SCP should be applied to any surface of the concrete where water may potentially enter and cause subsequent freeze/thaw damage. To evaluate whether SCP products are the correct product to specify for freeze/thaw mitigation, the following results from water permeability and freeze/thaw testing are provided for evaluation by the engineer of record.

 

Water Permeability Testing under Hydrostatic Pressure (EN 12390-8)

SCP Technology, when applied to new or existing concrete correctly, greatly reduces the ability of liquid water to penetrate the matrix.  The following results represent testing in accordance with EN 12390-8, a European norm that introduces water under 5 bar (72 psi) hydrostatic pressure to concrete for 72 hours and is used to indicate permeability reduction of concrete.

Table 1:SCP Products Reduction of Water Penetration Under Hydrostatic Pressure

 

Freeze/Thaw Durability Testing (ASTM C666-15, EVS 814:2003)

SCP Technology, when applied correctly, mitigates freeze/thaw damage. The following results show freeze/thaw durability testing under ASTM C666-15 and EVS 814:2003. Note: these laboratory samples were treated with SCP products within the first 24 hours of casting.

Table 2: SCP Products Mitigation of Freeze/Thaw Damage

 

Conclusion/Discussion

Damage from freezing and thawing is mitigated by reducing concrete’s permeability or by using an appropriate air void system. When used to reduce water permeability, SCP products may sufficiently mitigate the potential for freeze/thaw damage of existing concrete. When specifying SCP as a freeze/thaw mitigation measure for existing concrete, SCP recommends that pre-treatment and post-treatment cores should be extracted and subjected to water permeability testing to verify that the treatment meets the design professional’s requirements for low permeability concrete for freeze/thaw mitigation.

Cover Image Source: University of Illinois

Is SCP a Bond Breaker?

“Are Spray-Lock Concrete Protection (SCP) products bond breakers?” To answer this question, we need to define a bond breaker and examine how SCP reacts in the concrete matrix. A bond breaker is a product that forms varying layers of separation between contact surfaces. SCP is a penetrating concrete treatment that does not change the surface of the concrete matrix. An SCP application is not a coating and has no negative effect on bond integrity.

Testing of SCP’s application on concrete was performed to show that the product is not a bond breaker. Test methods included (1) ASTM C1583 Standard Test Method for Tensile Strength of Concrete Surfaces and the Bond Strength or Tensile Strength of Concrete Repair and Overlay Materials by Direct Tension (Pull-off Method) and (2) ASTM E303 Standard Test Method for Measuring Surface Frictional Properties Using the British Pendulum Tester.

In the ASTM C1583 test method, the concrete sample is cleaned of surface contaminants and loose or deteriorated concrete. The sample is then prepared to the typical surface conditions of the in-place concrete structure. The test material is applied and cured in accordance with the manufacturer’s specifications. After cure, a core drill is used to make a circular cut perpendicular to the surface. The test material is left intact on the concrete substrate, while a steel disk is attached to the top of the material using an epoxy adhesive. A tensile loading device is then attached to the steel disk to apply a tensile load to the test sample with force parallel to the vertical axis of the specimen. The load is applied until failure, and results are recorded.

In the ASTM E303, the concrete surface is cleaned and freed of loose particles. The instrument is placed and leveled. The pendulum is lowered so that the edge of the slider just touches the concrete surface. Water is applied to thoroughly cover the test area. One swing is performed, and the reading is not recorded. Four more swings are made, and the surface is rewet before each swing. The results are recorded.

Testing shows that SCP Treatments increased the pull-off strength of concrete up to 73% compared to untreated concrete and had no statistical effect on surface friction. Since SCP Treatments become an integral part of the concrete matrix and are not surface coatings, there is no need for a mechanical key, additional treatments or removal prior to using a covering or coating. SCP can be used in conjunction with all types of coverings and adhesives without a negative impact on a covering material or adhesion of material to the concrete.

Commentary on ASTM E96 Testing of SCP Products

ASTM E96-10 Standard Test Methods for Water Vapor Transmission of Materials is an umbrella standard that allows the user to choose the most appropriate method to test a material for water vapor transmission.  ASTM E96 is written to allow for multiple products to be covered by a single standard, and it is appropriate for materials up to 1 ¼ inches (32mm) in thickness.  The thickness limit has been set primarily because the time to reach equilibrium of water permeance increases as a square of the thickness.  Therefore, thicker materials would potentially take much longer to test.  When testing concrete specimens, a laboratory should select test conditions that most closely approach the conditions of use, as set forth in section 5 of the standard, “Significance and Use.”

ASTM E96 details two primary methods of testing.  The first is the Desiccant Method.  The Desiccant Method utilizes a test specimen sealed to the open mouth of a test dish containing a desiccant with the assembly placed in a controlled atmosphere.  Periodic weighing of the sample determines the rate of water movement through the specimen into the desiccant.  Spray-Lock Concrete Protection (SCP) does not consider this method as most appropriate for use with concrete because concrete almost always contains water that is nonevaporable, held in reserve for later hydration (chemical reaction).  This nonevaporable water may be extracted artificially with a desiccant and provide false moisture transmission readings.

The second method of testing involves the use of a dish that contains distilled water that is affixed to the specimen.  The specimen and dish are exposed to a controlled environment where the water moves through the specimen in vapor form, allowing calculation of water movement.  SCP selected this method as the nearest to actual conditions in the field where water vapor movement from below a concrete slab to the top of the slab is most critical for flooring manufacturers and installers.  A 1 inch concrete slab thickness was chosen to enable calculations within the normal time frame of the testing regime.  Although greater thicknesses could be tested, the time for the test to run would have been increased considerably.  The specified relative humidity in the test chamber is 50 +/- 2%.  The specified temperature is 100 +/- 1° F (38 +/- 1° C).  An air velocity of 0.066 and 1 ft./sec (0.02 and 0.30 m/s) is specified in the test chamber.  E96 allows for extreme humidity, if desired, and temperatures between 73.4° F (23° C) and 80° F (26.7° C).  The specified, rather than alternate, test values for temperature and humidity were utilized for the testing under consideration.

SCP decided to use the second test method utilizing a dish and distilled water.  After the test method to use, a secondary decision then had to be made whether to test with one side of the specimen being wet or not. An additional consideration was that of isolating the effects of the SCP concrete treatment on the water vapor transmission of the concrete. To remove the possible effects of capillary action with liquid water, and to isolate the water vapor transmission only, the decision was made to test specimens that were dry on both sides at the beginning of the test.

The test results presented by SCP for water vapor transmission values are compared to a control specimen that was tested following the same procedure and at the same time as the experimental samples.  The calculations used to determine water vapor transmission are also the same, and are detailed in section 13 of the standard.  When interpreting results, consideration should be given to the statement contained in section 1 of the standard: “Agreement should not be expected between results obtained by different methods.”  Of additional importance is that the laboratory conditions described above were chosen to best test the efficacy of the treatment to reduce water vapor transmission, and they likely will not mirror exact performance in the field where environmental conditions, the concrete mix used, and the concrete thickness will all vary considerably from laboratory conditions.

 

Waterproofing Concrete: One-time Treatment vs Topical Treatments

Most waterproofing sealers can be grouped into two categories: topical and penetrating. Before examining treatment options, however, the difference between waterproofing and dampproofing should be established. The American Concrete Institute (ACI) Terminology Committee (TAC 90-02) has changed the definitions of these terms:

Waterproof: an idealized property of a material indicating imperviousness to water in either liquid or vapor state. 1

Dampproof: a treatment of concrete or mortar to retard the passage or absorption of water or water vapor either by application of a suitable coating to exposed surfaces, or by use of a suitable admixture or treated cement, or by use of a preformed film such as polyethylene sheets placed on ground before placing a slab. 2

ACI has limited the use of waterproofing so that products now fall under the dampproofing descriptor, but most product manufacturers are still using “waterproofing” to describe their products. Spray-Lock Concrete Protection (SCP) utilizes the terms “waterproofing” and “dampproofing” interchangeably to facilitate fair comparison of product performance.

Topical sealers, which include acrylics, epoxies and polyurethanes, form protective barriers on top of the concrete surface. Some of the common issues when applying protective film sealers are surface traffic and proper application. Acrylic and epoxy sealers require regular maintenance because both have a high wear potential. Polyurethane sealers are thicker, with a durable abrasion-resistant finish, but they cannot have any water on the surface during application. Additionally, with all topical sealers, reapplication is required when removing flooring placed over a sealed surface.

Then there are the penetrating sealers, which include silanes, silicates, siliconates and siloxanes. These sealers penetrate the top surface of the concrete and react within the bleed water capillaries of the concrete to stop the migration of moisture and deicing chemicals. These products also create problems when installing floor covering systems, as ASTM F710 requires them to be removed from the surface prior to installation.

SCP products also penetrate the surface, but work differently than other sealers. Colloidal silica chemically reacts with the available alkali in concrete to create calcium silicate hydrate (C-S-H), blocking capillaries and pores and chemically stabilizing the pH within. SCP is a one-time treatment that penetrates the concrete matrix, reducing water migration levels to an acceptable range for most coatings, adhesives and floor coverings. Within the interaction zone of SCP, the concrete becomes permanently dampproofed for the life of the concrete. Unlike topical treatments, SCP does not wear away or need to be reapplied. SCP Treatment also provides many additional benefits, including reducing drying shrinkage up to 91% and vapor transmission up to 88%.

 

1 ACI Concrete Terminology – ERRATA as of January 6, 2017
2 ACI Concrete Terminology – ERRATA as of January 6, 2017

The SCP Solution to Fast Tracking without Sacrificing Performance

 

Some may wonder how the concrete is affected when SCP allows contractors to install coatings and coverings on concrete in only 14 days? Is SCP technology good or bad for concrete?

The answers will surprise many. Spray-Lock Concrete Protection (SCP) Technology achieves the results of curing by working differently than a membrane system. Unlike membrane systems and other sealers, SCP doesn’t simply create a barrier against moisture. Instead, our treatments penetrate inches into concrete capillaries and pores where colloidal silica chemically reacts with calcium hydroxide and forms calcium silicate hydrate (C-S-H). This C-S-H formation becomes part of the concrete structure itself, greatly reducing the diameter of capillary pores. With this reduction, the C-S-H is able to shut down liquid water movement, trapping the remaining water needed for proper hydration in the concrete.

To really see if SCP’s “curing system” is effective, we tested concrete treated with SCP for improvements in performance that are related to better curing. We also measured how well SCP-treated concrete performed in areas that are not achieved by curing alone. SCP-treated concrete outperformed in the following areas:

  • Compressive Strength – ATSM C39: up to a 20% Increase
  • Drying Shrinkage – ASTM C157: up to a 92% Reduction
  • Abrasion Loss – EN 5470-1: up to a 58% Reduction
  • Water Permeability – ASTM D5092 @ 328ft Head Pressure: up to an 89% Reduction
  • Water Permeability – DIN 1048 @ 72.5-psi Pressure: up to a 99.8% Reduction
  • Water Vapor Transmission – ASTM E96: up to a 88% Reduction
  • Pull-Off Strength – ASTM C1583/C1583M: up to a 73% Increase
  • Carbonation (Dusting) – BS EN 13295: up to a 31% Reduction
  • Freeze-Thaw Damage – ASTM C666: up to a 78% Reduction
  • Chloride Content – ASTM C1543: up to a 64% Reduction

As the results show, properly cured concrete performs better! Contractors everywhere are asking for a way to build buildings faster and better.  SCP helps fill this demand by curing concrete, waterproofing concrete at time of placement and allowing fast-track installation of any coating or covering.

SCP Accelerates Schedule with a Superior Cure for Tukwila’s First High-Rise

The city of Tukwila, WA, just outside of Seattle, has experienced significant growth over the past decade. Washington Place, slated to be complete in 2017, will be the city’s first high-rise. Construction began on the 19-story, 418,000 ft2 building in 2014, and to accelerate the schedule of this large project, Absher Construction chose SCP Treatments to cure and waterproof several decks, creating “dry-slabs.” By doing so, they were able to avoid weather delays during construction, in addition to providing insurance against future problems caused by leaks throughout the service life of the mixed-use structure.

With a tight schedule, curing the multi-slab structure quickly was crucial for Absher. They used SCP 327 on multiple levels for an excellent cure that allowed slabs to be accessed in only 1 hour. The treatment increased the concrete’s compressive strength and reduced shrinkage cracking, while allowing other trades to access lower levels without the need or cost of installing a temporary roofing system.

Absher also chose SCP 578 to treat a preexisting outdoor concrete patio deck. With proper sealing on cracks and penetration joints, the deck is now waterproofed throughout and will last for years to come. The deck now has better chemical stabilization, as SCP 578 reconditions the pH of existing concrete to improve its resistance to environmental and chemical attacks. Additionally, SCP-treated concrete allows for all coatings and decorative applications, improving performance and reducing maintenance costs.

Once complete, Washington Place will be a major part of Tukwila’s city center. By using SCP Treatments, the contractors ensure that the concrete will be protected throughout its service life and require significantly less maintenance, all while keeping the project on schedule.