1、 1 ACI 364.17T-18TechNoteHow to Measure pH of a ConCrete surfaCe prior to installation of a floor CoveringKeywords: adhesive compatibility; alkalinity; material properties; pH measurement; pH testing; resilient flooring adhesive; surface pH.IntroductionA review of published literature indicates that
2、 there is plenty of information regarding the pH of concrete as it relates to carbonation, embedded steel corrosion, alkali-silica reaction, and effects of mineral admixtures such as fly ash and silica fume. There are, however, only a few research papers published that are related to test methods to
3、 measure the pH of a concrete surface.Portland cement and many other hydraulic-cement-based concretes are highly alkaline materials. Depending on the actual chemistry of the portland cement and amount of alkalis present, the pH of freshly placed concrete can vary from approximately 12 to over 13. Th
4、e carbonation of concrete is known to lower the surface pH to a value in the vicinity of 9.The pH of a concrete surface plays an important role in the selection of flooring adhesive and placement of flooring materials, especially with resilient flooring such as sheet vinyl. A concrete pH below 7.0 a
5、nd above 10.0 is known to negatively affect resilient flooring, its adhesive, or both. The flooring installer is typically required to clean and prepare concrete slab surfaces prior to flooring installation. Pressure washing is not used to clean the concrete surface, as the process will saturate the
6、 concrete surface with water and cause flooring failure due to excess slab moisture. Flooring installers often clean and scarify the concrete surface with sandpaper, or shot-blast the surface. The process of sanding or shot blasting can remove the carbonated surface layer of concrete and expose a co
7、ncrete surface that has higher pH.When using the ASTM F710 test procedure (Appendix A), testing laboratories have reported concrete surface pH values as low as 6 or 7 because the test method is incorrect. In fact, it essentially measures the pH of water and readily-soluble materials on the concrete
8、surface versus the true pH of the concrete. Incorrect pH test results could lead to the selection and use of an incompatible adhesive for the flooring, resulting in the risks of flooring failure. The concrete and flooring industries require a test method that measures the pH of concrete surface more
9、 accurately.QuestionHow does one measure the pH of a concrete surface prior to the installation of a floor covering?AnswerThe following method, using either pH paper or a pH meter, is recommended to determine the pH of a newly placed or an existing concrete surface.Proposed methoda) Calibrate the pH
10、 meter or pH paper with three pH calibration solutions supplied by the pH meter manufac-turer or an independent chemical supplier. The three calibration solutions should be of pH 7, 10, and 12. The measuring tip of the pH meter should be cleaned by dipping it in a clean container of fresh distilled
11、water and wiping it dry with a clean paper towel prior to the pH reading. Repeat the same cleaning procedure immediately after each reading and make a note of the pH measurement results.American Concrete Institute Copyrighted Material www.concrete.org2 HOW TO MEASURE pH OF A CONCRETE SURFACE PRIOR T
12、O INSTALLATION OF A FLOOR COVERING (ACI 364.17T-18)b) Use an infrared thermometer to measure concrete surface temperature. Note the temperature to the nearest degree in Fahrenheit (Celsius). The concrete temperature should be within 10F (5.6C) of the temperature expected during the flooring installa
13、tion.c) If the concrete surface is unclean, mechanically remove surface contaminants such as dirt, concrete sealer, and old adhesive residue. Do not use chemicals to clean the concrete surface.d) Lightly abrade approximately a 12 in. (300 mm) diameter area of the clean concrete surface for 60 10 sec
14、onds with 50-grit sandpaper. Collect and measure 0.0011 lb (0.5 g) of concrete powder.e) Add 0.0011 lb (0.5 g) of concrete powder to a bottle containing 0.338 oz. (10 mL) of fresh distilled water. Close the bottle lid and shake the bottle for 30 5 seconds.f) Allow the concrete powder solution in the
15、 bottle to rest for approximately 2 minutes.g) Insert the pH meter or pH paper into the concrete powder solution and note the stable pH reading to the first decimal.h) Note and report calibration pH readings, pH of concrete surface as measured from the liquid portion of the concrete powder/water sol
16、ution in the previous steps, and concrete surface temperature.Three pH tests are recommended for the first 1000 ft2(92 m2) area of the concrete slab and an additional pH test is recommended for each additional 1000 ft2(92 m2) or fraction thereof. The pH tests can be conducted in different areas of t
17、he building, on different concrete placements, and different concrete mixtures used in a project.DiscussionThe pH, which is an approximate measure of acidity or alkalinity of a solution, is defined as the negative loga-rithm of hydrogen ion concentration. In fact, the pH is a measured property of a
18、solution. Because concrete is a solid substance, it is challenging to accurately measure the pH of hardened concrete. To test the pH of solid concrete, the following questions need to be answered:a) How should the samples be collected? Is there a procedure?b) How does one prepare the concrete powder
19、 to prepare a test solution?c) What concentration of the solution is required to get a consistent and repeatable pH measurement?d) What factors affect the pH measurement?The following is a summary of a few ASTM and industry publications related to measuring pH of concrete and solid substances such a
20、s limestone. The dilution ratio used for preparing a solution for pH measurement varies among the standards in the range of 1:4 and 1:20 by weight.a) ASTM C25Using a dilution ratio of 1:20, mix 0.022 lb (10 g) of sample with 200 g (6.76 oz or 200 mL) of deionized water; stir for 30 minutes and let t
21、he solution stand for 30 minutes; measure with a pH probe and meter; report pH value to four significant figures. Although ASTM C25 is not directly related to concrete, but instead to limestone and hydrated lime, testing laboratories in the industry often use dilution ratio of 1:20 when preparing so
22、lutions to measure the pH of concrete.b) ACI 364.3RUsing a dilution ratio of 1:9, mix 0.022 lb (10 g) of sample passed through the No. 170 mesh with 0.198 lb (90 g) of distilled or deionized water for 1 minute; after settling, measure pH using pH paper or pH probe and meter.c) STN 73 1341Using a dil
23、ution ratio of 1:4, mix 0.11 lb (50 g) of powdered concrete sample with 200 g (6.76 oz or 200 mL) of distilled water; agitate the solution for 6 hours and then filter the solution; use the chemical indicator to determine the pH.Fundamental research on pH measurement of concrete surfaces has been pub
24、lished by Grubb et al. (2007) and Kakade (2014), who studied the influence of various test parameters. The research works addressed the following variables and their effects:American Concrete Institute Copyrighted Material www.concrete.orgHOW TO MEASURE pH OF A CONCRETE SURFACE PRIOR TO INSTALLATION
25、 OF A FLOOR COVERING (ACI 364.17T-18) 3a) Particle sizeb) Scarification depthc) Type of concreted) Sample sizee) Dilution ratiof) Soaking or waiting timeg) Sample gradationh) TemperatureTable 1 provides test data on the relationship between particle size of concrete powder and pH of concrete. The da
26、ta show that a finer concrete sample has a higher pH measurement as compared to a coarser sample. A satis-factory sample for this test was obtained by sanding the concrete surface using 50-grit sandpaper. Table 2 shows the test data on different sanding durations using 50-grit sandpaper and the corr
27、esponding scarified depths. The sanding duration of 60 seconds generated enough concrete powder sample for testing and limited the scarifica-tion depth to approximately 0.036 in. (less than 1 mm).Figures 1 through 4 show the effects of several variables, such as type of concrete, sample size, diluti
28、on ratios, soaking time, and temperature of the pH values. The test results show that the dilution ratio and the tempera-ture have the most pronounced effects on the measured pH of concrete as compared to the sample size and soaking time.The dilution ratio of 1:1 resulted in a higher pH measurement
29、than a dilution ratio of 1:20. However, a dilution ratio of 1:1 creates a mixture that is too stiff and can cause damage to the pH meter probe. A dilution ratio of 1:20 creates a fluid mixture that can be used to safely insert a pH meter probe. For example, in Fig. 2, the pH readings for the diluton
30、 ratio of 1:1 was approximately 12.6 and for a dilution ratio of 1:20 was 12.45. For flooring purposes, a pH reading of 12.45 measured using a dilution ratio of 1:20 is accurate enough for selecting an appro-priate adhesive for the flooring. Therefore, the proposed method uses a dilution ratio of 1:
31、20.It is essential to note that once the concrete surface is covered with an impervious flooring such as sheet vinyl, the moisture will redistribute within the concrete. If this redistributed moisture condenses under the imperme-able flooring, the pH of concrete surface will likely increase, which m
32、ay have a detrimental effect in altering the bonding capability of the adhesive. It should also be remembered that the moisture in the substrate below the concrete slab can vary with time and environmental conditions. The increase in pH can have detrimental effect on the flooring adhesive. The adhes
33、ive could lose its bonding characteristics.SummaryThe pH determination method described in this TechNote will provide a more accurate pH measurement of a concrete surface than the present ASTM F710 test method. This will assist design professionals in selecting an appropriate flooring adhesive for a
34、 concrete surface.Table 1Effect of particle size on pH of concrete (Grubb et al. 2007)Particle size of concrete powder Distribution, % Measured pHSmall, passing 850 m (No. 20) sieve 59.6 12.48Intermediate, passing 2.00 mm (No. 10) sieve and retained on 850 m (No. 20) sieve 19.2 11.87Large, retained
35、on 2.0 mm (No. 10) sieve 21.2 11.55Combined 100 12.37Note: sample size = 5 g; dilution ratio = 1:2Table 2Results of scarification of concrete surface using 50 grit sand paper (Kakade 2014)Duration of scarificationAverage depth of scarification, in.Maximum depth of scarification, in.Quantity of concr
36、ete powder collected, gpH of concrete using pH meter30 seconds 0.0099 0.036 1.1 12.660 seconds 0.0130 0.036 1.6 12.5120 seconds 0.0174 0.047 2.5 12.6Notes: The depth of scarification measurement is an average of 21 measurements. A pH measurement of the concrete surface by ASTM F710 resulted in a pH
37、measurement of 9.5. 1 in. = 25.4 mm.American Concrete Institute Copyrighted Material www.concrete.org4 HOW TO MEASURE pH OF A CONCRETE SURFACE PRIOR TO INSTALLATION OF A FLOOR COVERING (ACI 364.17T-18)ReferencesCommittee documents are listed first by document number and year of publication followed
38、by authored documents listed alphabetically.American Concrete InstituteACI 364.3R-09Guide for Cementitious Repair Material Data SheetASTM InternationalASTM C25-11Standard Test Methods for Chemical Analysis of Limestone, Quicklime and Hydrated LimeASTM F710-11Standard Practice for Preparing Concrete
39、Floors to Receive Resilient FlooringSlovak Standards InstituteSTN 73 1341:1987Corrosion Protection of Reinforcement Provided by the Properties of Concrete, Methods of TestAuthored documentsGrubb, J. A.; Limaye, H. S.; and Kakade, A. M., 2007, “Testing pH of Concrete,” Concrete International, V. 29,
40、No. 4, Apr., pp. 78-83.Kakade, A. M., 2014, “Measuring Concrete Surface pH A Proposed Test Method,” Concrete Repair Bulletin, Mar.-Apr., pp. 16-20.Fig. 1Influence of temperature on measured pH of concrete surface (Grubb et al. 2007).Fig. 2Influence of the dilution ratio upon the measured pH over tim
41、e for concrete with w/cm of 0.40 (Grubb et al. 2007).Fig. 3Influence of the sample size upon the measured pH as a function of the dilution ratio for concrete with a w/cm of 0.40 (Grubb et al. 2007).Fig. 4Influence of the sample size on the measured concrete pH as a function of the dilution ratio for
42、 a concrete with 50 percent cement replacement by weight with fly ash. (Grubb et al. 2007).American Concrete Institute Copyrighted Material www.concrete.orgHOW TO MEASURE pH OF A CONCRETE SURFACE PRIOR TO INSTALLATION OF A FLOOR COVERING (ACI 364.17T-18) 5Reported by ACI Committee 364Ashok M. Kakade
43、, Chair Paul E. Gaudette, SecretaryRandal M. Beard Liying Jiang Consulting MembersBenoit Bissonnette Keith E. Kesner Robert V. GeveckerRyan Alexander Carris John S. Lund Stephen A. JohansonLarry D. Church Marjorie M. Lynch Emory L. KempBruce A. Collins Surendra K. Manjrekar Howard H. Newlon Jr.Timot
44、hy R. W. Gillespie James E. McDonald Weilan SongFred R. Goodwin Jay H. Paul Dela TharmabalaPawan R. Gupta Murat B. Seyidoglu Robert TracyAnn Harrer K. Nam Shiu Alexander M. VaysburdJohn L. Hausfeld Kyle D. Stanish William F. WescottRobert L. Henry David A. VanOckerCharles J. Hookham David W. Whitmor
45、eAppendix AASTM F710 pH Test Procedure(1) Place several drops of distilled or deionized water on a clean surface of concrete, forming a puddle approx-imately 1 in. (25 mm) diameter.(2) Wait for 60 5 seconds(3) Dip pH test paper into the water puddle. Remove the paper immediately to compare with color chart to determine pH of the concrete surface.
