The Importance of Concrete Evaluation
Written by Dave Waldron
What Lies Beneath – The Importance of Concrete Evaluation & Testing When Applying Traffic Bearing Liquid Applied Membrane Waterproofing, Surfacing, & Protective Coatings on Concrete.
Often one of the last things considered with traffic bearing liquid applied membrane waterproofing, surfacing, and protective coating applications is concrete evaluation and testing. However, this is one of the most critical requirements for long-term performance with these applications. Evaluation and testing can involve both newly poured or existing concrete, and something best considered during the design phase of any project.
Inspecting & Evaluating Concrete Substrate Conditions
For most trafficable waterproofing and/or surfacing applications, concrete core testing should be performed to help determine the state and “health” of the in-place concrete. In simple terms of what to look for when evaluating concrete, one must be aware that concrete can contain contaminants that include residual curing compounds, penetrating hardeners, sealers, oil or other vehicular fluids, and chlorides; all which can cause bonding issues for primers. Contaminant free substrates with properly applied primer are important for all applications and vital for vehicular traffic bearing waterproofing and concrete protective surfacing applications.
Therefore, all concrete substrates, new or old, should be tested for contaminants, especially with unknown history or previously failed coating systems. If contaminants are found (i.e. hydrocarbons, other organic compounds, un-reacted water-soluble silicates, chlorides, Alkali-Silica Reaction or ASR, Sulfurous compounds, etc.), this information will help determine primer suitability and required substrate preparations. In some instances, capillary infiltration of oil or other chemicals from the ground, oil-contaminated slabs, or certain conditions may require use of an alternative primer, pre-treatment, or separation screed.
Identifying contaminants requires both visual inspection along with extraction of concrete core samples. The number and size of core samples required will vary by project area and surface conditions that are observed onsite. Regardless, all cores should be DRY extracted, 1 – 4 inches (25 – 100 mm) minimum in both diameter and depth, or as may be required by project conditions. Typically, one core is recommended for every 10,000 ft2 (929 m2) area and at any location with the appearance of differing concrete pours, excessive darkening, discoloration, or contamination (i.e. oil, grease, vehicular fluids).
Once the core samples are taken, depending on information gathered for the project and observed conditions, one or more of the following tests may be recommended or required:
- Ion Chromatography: To determine inorganic contaminants including Sodium (Na), Potassium (K), Sulfate (SO4) and Chloride (CI) concentrations in ppm at depths of 0-3 mm and 3-6 mm below the top of concrete.
- Infrared Spectroscopy Analysis: Determine any organic content, i.e., hydrocarbons including oil, grease, or other compounds with results in ppm and %.
- TSP (Thin Section Petrographic): Used to detect ASR (alkali silica aggregate reaction) in areas where ASR is prone or suspect.
Any qualified laboratory with the above testing capabilities may be used to evaluate concrete for a given project. However, the following is one company specializing in testing and evaluation of concrete in the U.S:
Mineralogy, Inc.
3321 E. 27th Street, Tulsa, OK 74114
Phone: (918) 744-8284 or 877-744-8284
Concrete Substrates - Basic Requirements
General industry practice for traffic systems requires a sound structural or lightweight structural concrete substrate, new or existing, with 3,500 psi (25 N/mm2) minimum compressive strength. Regardless of concrete type, all substrates must be mechanically prepared (shot blast or scarification) to ICRI Concrete Surface Profile CSP 3, CSP 4 or CSP 5; CSP 3 being the preferred profile.
Properly prepared, the substrate should provide the primer a minimum bond strength of 116 psi (0.8 N/mm2) for roofing and non-traffic bearing waterproofing or 220 psi (1.5 N/mm2) for traffic bearing waterproofing applications. Bond strength is tested in the U.S. in accordance with ASTM D4541 Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers.
Moisture mitigation epoxy primers typically can be applied to “green” concrete slabs that are properly mechanically prepared, clean, free of standing water, up to 100% RH, between 3 to 5 days old or have reached a minimum 2,500 psi (17 MPa) compressive strength.
Substrate Moisture Testing
If the project has known or assumed moisture issues, substrate moisture testing may not be necessary. However, when not known, moisture vapor emission rate (MVER) testing is recommended to help determine if the project will require use of a moisture mitigation primer. Using a moisture mitigation primer will mitigate MVER up to 25 pounds of moisture per 1,000 square feet over a 24-hour period (1.4 µg/s·m²) and 100% RH essentially eliminating most concerns over latent moisture and vapor drive.However, moisture testing can be of value to obtain additional project related data, identify possible unknowns, for record, and to determine if some form of venting should be employed to alleviate trapped moisture.
Two common tests for concrete substrates used to determine water vapor are the anhydrous calcium chloride moisture vapor emission rate test (ASTM F1869) and the in-situ relative humidity probe test (RH probe test, ASTM F2170). However, RH testing is preferred and recommended when required to determine primer requirements with moisture mitigation applications.
Excessive Contaminants & Concrete ASR
In some cases, slabs with high concentrations of hydrocarbons (at minimum requiring degreasing), other organic compounds, un-reacted water-soluble silicates, chlorides, ASR, sulfurous compounds, etc. may require concrete milling and removal to depth or new mortar separation screed typically 3/8 in (10 mm) or more to be applied. Bottom line is no primer can resolve all issues with heavily contaminated slabs.
In the case of alkali silica reaction (ASR) or excessive levels of potassium contamination which can lead to ASR, premature substrate failure is a known result. Alkali silica reaction is recognized as a construction defect and permanent condition that cannot be removed without complete demolition and removal of the effected concrete slab. ASR may not be active where moisture vapor can escape through open concrete but can be triggered when coating systems are applied. ASR is an expansive reaction of aggregate to high alkaline and moisture requiring reactive silica, sufficient alkali, and sufficient moisture be present in the concrete.
When ASR or excessive levels of potassium contamination are found, short of total concrete removal, the required mitigation steps would include milling and removing the top layer of contaminated concrete along with installation of a new mortar screed to isolate the concrete contaminants and help extend the service life of the primer system. By adding an appropriate calcium aluminate cement mortar screed overlay with lithium nitrate ASR inhibitor typically can provide up to 5 or more years of usage. However, contaminants remaining in the underlaying concrete slab will continue to degrade the concrete matrix and newly applied mortar screed at an unpredictable rate.
For projects involving these issues, owners should be made aware that the mortar screed will not eliminate presence of potassium contamination or ASR in the underlaying slab and only delay the potential ASR effects to the prepared substrate bond line and primer performance. In these situations, should the owner wish to proceed with the application, most manufacturers will require a warranty rider to be reviewed and accepted by the owner or owner’s representative prior to applying any the system in the affected areas of a project.
Righting Wrongs Before They Happen
Making assumptions regarding concrete conditions without evaluation and testing can lead to grave concequences. Low compressive strength, high moisture content and pH, moisture drive, contaminants, and ASR can all lead to early failure.
Substrate issues can present in many forms, but typically start as minor blistering or delamination, which tend to worsen and become more extensive over time. The best solution is preventative action before problems occur. Once problems present and occur, this often begins a continued process of patch and repair for the life of the traffic coating, waterproofing, or surfacing system.
On traffic surfacing systems, raised blisters become subject to mechanical damage, and delaminated areas subject to damage from shear. Even though these areas can be cut-out, patched, and repaired, often blistering or delamination are recurring and will return to the same or an adjacent area.
Aside from proper concrete evaluation and testing prior to installation, it is also good practice to design traffic surfacing systems for potential damage by compartmentalization. In order to maintain good aesthetics with any traffic waterproofing and surfacing system planning color breaks will allow for isolated repairs when problems or damage occurs.
Thinking Ahead: Color Breaks & Compartmentalization
Despite the best design or intentions, damage to any traffic waterproofing and surfacing system are always a posibility. Applying finishes and surfacing with color breaks provides several benefits to the appearance and repair-ability of any traffic surfacing system.
Color breaks help to:
- Provide enhanced aesthetics by simulating tile or other patterned layouts.
- Hide variations in surface gloss and texture.
- Hide minor variations in color.
- Allow for localized repairs if needed.
Before starting any project, color breaks should be planned and mapped out by the contractor and project designer working with the owner. Things to consider when planning color breaks are:
- What type of color break pattern is desired.
- Locations of doors, windows or other focal points that might be impacted.
- Locations of expansion or other moving joints.
Once a plan has been approved, the pattern can be masked off and made ready for application. Surfacing or finish may be applied in a variety of patterns, color combinations and textures depending upon the designers’ imagination and owner’s needs.
Generally, color breaks are applied in linear or non-linear patterns. Linear patterns are the easiest to work with and can be designed to simulate tile or pavers applied square or at angles.
Non-linear patterns can be designed in any shape or configuration. Complex patterns may also be applied with pre-cut templates prepared by third party vendors typically used for commercial paint applications.
Regardless of style or pattern, the color break must be applied in the appropriate layer of the installation depending upon the system and surfacing types used.
Summary
Concrete is formed at the jobsite using local materials, methods, additives, and varying environmental conditions, so no two concrete pours are alike. The above information is an outline of suggested “best practice” for evaluating and testing concrete where traffic bearing waterproofing and surfacing will be applied.
Although most concrete likely will be adequate to support these applications, in-depth evaluation and testing along with pre-planning will always help ensure integrity, success, and performance of any traffic bearing liquid applied membrane waterproofing, surfacing, and protective coatings system being considered or installed.
