Air Date: 12-6-2019|Episode 566
This week on IAQ Radio+ we welcome Robert Higgins. Robert Higgins has been involved with moisture-related issues in concrete and waterproofing since 1976 and has been developing products for such use since 1980. He was a product development chemist for SINAK. Bob is equally involved in product and process development, having developed most of the products manufactured and marketed by his former company SINAK Corporation, as well as owning or co- owning patents for moisture testing. He has expertise in moisture-related concrete issues, having been involved with waterproofing, technical committees, professional groups, lecturing, teaching; and construction defect litigation.
Bob lives and works in Osmond Beach, FL. He has given lectures internationally and throughout the US on concrete and coatings related topics. He also continues to work on various committees and provides expert witness services on topics related to construction, concrete and coatings.
Bob Higgins has expertise in moisture-related concrete issues, having been involved with waterproofing, technical committees, professional groups, lecturing, teaching: and construction defect litigation. Bob is equally involved in product and process development, having developed most of the products manufactured and marketed by his former company SINAK Corporation, as well as owning or co-owing patents for moisture testing.
Nuggets mined from today’s episode:
Bob’s interest in inorganic chemistry began when he was a kid interested in moon rocks, crystals, etc. His father’s purchase of a cement sealer piqued his interest in waterproofing.
The history of concrete is an excellent example of “bait and switch”. The history of “modern concrete” essentially extends only to the mid-1950’s, NOT the thousands of years as we have been led to believe, nor even from the development of Portland Cement by Joseph Aspdin in 1824.
The Portland Cement Assn. dictates the specs of cement. From a chemistry standpoint, the commonly used Portland Cement has little resemblance to the geopolymers used in ancient structures.
In the Mediterranean Sea, there is a submerged concrete structure thousands of years old, saltwater deteriorates modern concrete.
Naturally developing stone tend to be crystalline. Geopolymers are amorphous, which means they have no clearly defined shape, unlike a crystal, which has a defined ordered structure. A mixture of materials that form amorphous cement. “An amorphous or non-crystalline solid is a solid that lacks the long-range order that is characteristic of a crystal.” Wikipedia
Grinding cement finer increases the strength of concrete. A clarification is needed, add: for concrete of identical cement content, a finer grind will yield greater strength, particularly for early strength development). Strength test 3000 psi at 30 days. Clarification: in a specification requiring 3,000 psi concrete, this requirement is based on a 30 day compressive value. New concrete has 75% greater permeability than old concrete. Clarification: based on the targeted 3,000 psi requirement. New concrete is much less durable than old concrete. The test has a 15% variance allowance.
Floor moisture claims constitute an estimated cost of several hundred million, to as much as a half billion per year. In some estimates for “soft dollars” and currently unquantifiable damages in the alteration of product development, reputation of person(s), companies, etc., it is estimated the damages may exceed a billion dollars annually.
The ONLY “progress” being experienced is basically a shuffling of responsibility, rather than a tangible reduction of actual damages.
The reasons for this continuation is a misunderstanding of why these damages are occurring and that the continuation of what are mostly unnecessary and completely avoidable costs. A dramatic change in our approach to these problems is needed/.
Moisture testing of concrete is unique and specific to concrete due to its internal chemical complexities and constant internal “re-arranging” it undergoes throughout its life cycle. Bob focuses on the seemingly mundane effort of determining the relative “dryness” of concrete and how a suitable condition can be obtained and even monitored to eliminate more than 90% of the problems we are currently facing in this industry.
The INTENT of moisture testing is to reduce or eliminate problems, the current methods have failed miserably in this regard; or to quote an article from several years back “If moisture testing was so accurate, why are we still having problems?”.
Concrete chemistry has changed in many areas of the country and has gone un-noted. In the early 2000’s, the EPA began to require recovery of cement flue gases, which eliminates much of the air pollution caused by the release of these gases. This recovery entails re-introducing alkaline material (usually sodium hydroxide) back into the cement mixture. Clarification: Cement chemistry has changed – in many areas of the country, quality aggregate has become scarce, which has led to an additional chemistry change of the concrete itself – which has not been clearly defined.
Because sodium hydroxide is highly buffered, the pH reading may not indicate a notable alkalinity increase, or only slightly elevated pH in this type of cement, buffering creates a disconnect between measurable pH and the alkalinity (concentration), the alkalinity in this type of cement is upwards of 400% higher. Coupled with a reduction of good quality aggregate, this combination has created a rise in incidents of what is termed ASR (Alkali-Aggregate Reaction). ASR is more of a problem in amorphous materials. “The alkali–silica reaction, more commonly known as “concrete cancer”, is a swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive non-crystalline silica found in many common aggregates, given sufficient moisture.” Wikipedia
One of the attempted methods of reducing ASR has been the use of lithium (in silicate, hydroxide and various other forms) in or on the concrete itself. Although somewhat effective, it appears that once the lithium concentration falls below a certain level (which is incompletely understood), the presence of lithium creates what is termed a “pessimum” effect (where an inadequate amount of lithium is present and the ASR activity INCREASES, rather than decreases).
ASR is generally a “time-dependent” activity, so in cases of polished concrete where a silicate is used, damage may not occur or be noticeable for several years and could easily be blamed on other “causes” of deterioration.
Due in large part to ASR, concrete bridges that were originally designed to last 100-150 years, are now “designed” to last 50-70 years, with many of these structures requiring significant repairs in less than 20 years.
Due to sodium hydroxide concrete can absorb moisture in conditions as low as 8.5% RH. Sand is hygroscopic, soldiers in the desert can obtain moisture from sand. “A solar still distills water with substances dissolved in it by using the heat of the Sun to evaporate water so that it may be cooled and collected, thereby purifying it.” Wikipedia
Concrete likes water. Curing cement takes time and moisture. The longer (minimum of 7 days) new concrete stays wet the stronger it will become. Specialty self- desiccating concrete uses all of the available moisture leaving no free water.
Concrete curing and drying is geographically driven, varying between 30 days and 6 months.
Water cement ratio is the amount of water per pound on concrete. “Water–cement ratios of 0.45 to 0.60 are more typically used. For higher-strength concrete, lower ratios are used, along with a plasticizer to increase flowability. Too much water will result in segregation of the sand and aggregate components from the cement paste.” Wikipedia
Gravimetric is the most accurate way to measure moisture in many materials. Most other moisture measurement methods don’t equate with gravimetric.
Slump test is the workability of concrete.
Opines that tensile strength test is more useful than compression strength test.
Standards and specifications. Was the concrete installed prior to the standard? What standard is applicable, concrete floors aren’t structural and conform to American Concrete Institute 302.1R-15 Guide to Concrete Floor and Slab Construction.
Use of calcium chloride when used as an admixture can cause latent problems.
Pouring temperature of concrete is important.
pH of efflorescence may be either alkaline or acidic.
Addition of water to lower the temperature of concrete during the pour weakens cohesive value. Use infrared thermometer to measure concrete temperature.
The concrete floor wasn’t causing the problem in 70% of Bob’s initial investigations. Less than 5% of floor problems are concrete related. When moisture levels concrete on upper floors can have higher moisture levels than the on-grade slab is due to stack effect. NOTE: This is what also helped him to understand the moisture was NOT originating from underneath the concrete. This was one of those “aha moments”.
Most Moisture isn’t originating from the concrete floor. Slab sweating syndrome and wet basketball courts are caused by condensation of warm humid air and cold surfaces. Greater differences result in greater accumulations.
Qualify concrete testing. Immediately before and at time of installation. Airborne humidity can change everything. Adhesives can add moisture and humidity to floor and air. Note: Bob actually has an example of where a moisture issue was created by one type of adhesive and then “corrected” by simply changing adhesives, even though the manufacturer of the adhesive that created the problem, blamed the higher moisture readings on the concrete…it makes me wonder how many times this actually happens!
Recommends impedance testing for floors. Tramex meter can measure 6% moisture in concrete. Water moves through concrete in liquid form. All salts within concrete create evaporation resistance.
Hysteresis in concrete, with regards to moisture absorption and evaporation is created by internal differences is structure and chemistry where the calculated evaporation rates given by diffusion models are delayed and/or disrupted. The internal contributors to this are varied and unpredictable and renders diffusion models as unreliable sources for moisture movement and evaporation. The explanation given above refers ONLY to structural issues. NOTE: This is an area where IAQ radio can contribute a potential blockbuster to the industry. Hysteresis effects might be able to explain many anomalies that would otherwise be blamed on incorrect data gathering, incorrect testing, operator error, etc. when in reality, it may be the concrete itself that creating and/or contributing to these issues that are relying on the often used, yet woefully incorrect (assumption) model of moisture diffusion in concrete.
Older vapor barriers disintegrate and fail to prevent the intrusion of hygroscopic elements into concrete.
Use of RH probe on old concrete is effective.
pH test on concrete. High pH and high alkalinity are different. A 5% solution of sodium hydroxide has a pH of 14, a 30% solution of sodium carbonate has a pH of 10 yet has higher alkalinity. Note: pH is the strength of the solution, whereas alkalinity is the concentration and/or buffering capacity of the solution – tip: pH cannot be measured in the absence of liquid water.
Incorrect information, relied upon, assumed to be correct. Note: Bob has a term for this: “Inherited misinformation”
ASR is a problem in 18% of new concrete.
Alkaline water from concrete will kill mold.
Moisture moves through concrete in BOTH liquid and vapor form. Fans REMOVE the evaporative cooling effect.
Floor fans cause an evaporative cooling effect and greater likelihood of evaporation.
Alkalinity causes flooring damage not water. Note: water can prevent the floor from being properly installed but is nearly NEVER the culprit after the floor has been successfully installed. Water CAN prevent and adhesive from setting and curing properly…humidity has essentially no effect other than potential delay of set and cure.
Z-Man signing off
How much concrete was used in China between 2011 and 2013?
Doug Kohnen and Adam Lesko