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Matthew A. Dettman, P.E. Western Kentucky University Getting the Best Bang for Your Buck in Materials Testing

Matthew A. Dettman, P.E. Western Kentucky University Getting the Best Bang for Your Buck in Materials Testing. Matthew A. Dettman, P.E. Western Kentucky University email matthew.dettman@wku.edu If you would like a copy of this presentation, send me an email and I will get it to you.

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Matthew A. Dettman, P.E. Western Kentucky University Getting the Best Bang for Your Buck in Materials Testing

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  1. Matthew A. Dettman, P.E. Western Kentucky University Getting the Best Bang for Your Buck in Materials Testing ABC National Conference February 20th, 2005 Orlando, Florida

  2. Matthew A. Dettman, P.E. Western Kentucky University email matthew.dettman@wku.edu If you would like a copy of this presentation, send me an email and I will get it to you ABC National Conference February 20th, 2005 Orlando, Florida

  3. What We’ll Talk About Today • 3 Very Common Material Testing Procedures • Concrete Testing and Inspection • Soil Testing and Inspection • Masonry Testing and Inspection • What are the Appropriate Tests and Methods • Passing vs Failing ABC National Conference February 20th, 2005 Orlando, Florida

  4. What We’ll Talk About Today Why do we do Materials Testing? Compliance with project specifications Owner wants it Contractor wants it ABC National Conference February 20th, 2005 Orlando, Florida

  5. Concrete Testing Common Tests Slump Air Content Compressive Strength ABC National Conference February 20th, 2005 Orlando, Florida

  6. Concrete Testing – Slump (ASTM C 143) • Slump – Roughly approximates the amount of water in the concrete mix • More Water = Less Strength ALWAYS • A 6 inch slump concrete typically has a higher water/cement ratio than a 3 inch slump concrete • What factors other than more water could increase slump? Water Reducer Super Plasticizer ABC National Conference February 20th, 2005 Orlando, Florida

  7. Concrete Testing – Slump • What factors other than less water could decrease slump? Time • Why Time? Over time all concrete will go to a slump of 0 as it sets • The solution of driving the truck around until the slump meets spec is not a good idea ABC National Conference February 20th, 2005 Orlando, Florida

  8. Slump – Cost Issues • Low Slump = Higher Labor Costs • Solution: If you need strength and high slump, order it from the batch plant that way • For example, they can deliver 4000 psi at a 9 inch slump if you need it • With experience, chemicals to increase slump and control set can help your bottom line by providing the strength, set, and workability you need ABC National Conference February 20th, 2005 Orlando, Florida

  9. Slump – Cost Issues • High Slump = Potentially Lower Strength • Other possible problems (assuming no slump increasing chemicals in the mix) • Slow set – delayed finishing and saw cutting • Increased shrinkage • Increased potential for scaling, spalling, etc • Lower durability • Why do we like High Slump? Lower Labor Cost ABC National Conference February 20th, 2005 Orlando, Florida

  10. Slump – Troubleshooting • High slump is typically the only “showstopper” related to this test with regard to specs • This can cause problems as people interpret higher slump as lower strength, which in general is true • However, the only spec that typically matters is the 28 day strength. • If the spec says 4 inch slump and 3000 psi and you get a 7 inch slump but it still breaks at 3000 psi, typically you will be ok ABC National Conference February 20th, 2005 Orlando, Florida

  11. Slump – Troubleshooting • But, it takes 28 days to determine the strength • So, if in the field you get a high reading, do or have done the following before you start sending trucks back or scheduling concrete to be removed: • Watch the technician periodically – make sure they are doing the test right and are certified or properly trained • Equipment and procedure is correct • Sample is taken off middle 80% of the truck ABC National Conference February 20th, 2005 Orlando, Florida

  12. Slump – Troubleshooting • Keep your break history handy. Often you have room for error in slump. A 7” slump on a 4” spec does not mean it will break below spec. Compare past slumps and breaks to see trends • Consider what you are pouring • A structural column where one truck is the entire pour poses a higher risk • A massive pour where lots of trucks are poured in one location and somewhat mixed through pour patterns and vibration are less risky. ABC National Conference February 20th, 2005 Orlando, Florida

  13. Slump – Troubleshooting • Slump in Summary: • Do some investigating before taking or allowing a knee jerk reaction to a high slump • In many cases, the problem can be solved with no additional cost or work if the big picture is considered • If all the info points to a risky pour – • Send it Back ABC National Conference February 20th, 2005 Orlando, Florida

  14. Concrete Testing – Air (ASTM C 231) • Air Entrained Concrete – Most often used to reduce the potential for damage in freeze/thaw situations • Specs typically call for 3% to 6% air content by volume in the mix. • You cannot see air bubbles in air entrained concrete • Visible bubbles are “entrapped” air ABC National Conference February 20th, 2005 Orlando, Florida

  15. Concrete Testing – Air • Problems with air entrained concrete are rare • If low air encountered, chemical dose can be increased • If it’s too high, strength and durability are reduced • Strength reduction is approximately 800 psi per 5% air, therefore there is some room for error with regard to strength and high air content ABC National Conference February 20th, 2005 Orlando, Florida

  16. Concrete Testing – Air • One issue to be aware of is air entrained concrete and low slump • With a slump less than 4, air entraining chemicals aren’t as effective at producing air in the field • If contractor adds water in the field to a low slump air mix, the air can shoot up rapidly • Therefore, to minimize potential problems, make sure mixes with air are 4” slump or higher ABC National Conference February 20th, 2005 Orlando, Florida

  17. Concrete Compression Testing (ASTM C 39) • Compression testing is simply placing a test sample into a compression machine and breaking ABC National Conference February 20th, 2005 Orlando, Florida

  18. Concrete Compression Testing • Along with slump and air, the test samples are made in the field ABC National Conference February 20th, 2005 Orlando, Florida

  19. Low Breaks – Cost Issues • What is a low break? • Let’s use an example to explain what a low break truly is • Assume a concrete mix is specified as 3000 psi at 28 days • Proper testing includes the collection of 4 test specimens 6” in diameter and 12” long ABC National Conference February 20th, 2005 Orlando, Florida

  20. Low Breaks – Cost Issues • 1 specimen is broken at 7 days • 2 specimens are broken at 28 days • The 2 specimens broken at 28 days are averaged and become ONE 28 day test • Typically, the 7 day break is about 2/3 of what the 28 day break will be ABC National Conference February 20th, 2005 Orlando, Florida

  21. Low Breaks – Cost Issues Sample data: 7 day break 2200 psi 28 day break 1 3200 psi 28 day break 2 3400 psi Average 28 day compressive strength = 3300 psi This is ONE 28 day strength test ABC National Conference February 20th, 2005 Orlando, Florida

  22. Low Breaks – Cost Issues • The true definition of 28 day concrete strength is a running average of 3 consecutive 28 day strength tests • So if you had a spec of 3000 psi and poured on Monday, Wednesday, and Thursday and took concrete samples each day, the average of those 3 days is the number you should be looking for • If you poured again on Friday, the average of Wednesday, Thursday, and Friday is needed ABC National Conference February 20th, 2005 Orlando, Florida

  23. Low Breaks – Cost Issues • Look at the following data: • Monday 28 day strength is 3200 • Wednesday 28 day strength is 2800 • Thursday 28 day strength is 3100 • Does this meet a spec of 3000 psi? • The average is 3033 psi so the concrete is OK • The exception is that NO individual concrete test specimen can break over 500 psi low ABC National Conference February 20th, 2005 Orlando, Florida

  24. Low Breaks – Cost Issues • If you do get a low break in accordance with these criteria, you must evaluate all of the data just like the slump • Was the test run right and is the technician certified? • What are you pouring? Do you really need full strength or is the concrete stressed below the design strength? • If so, is a few hundred psi low OK? ABC National Conference February 20th, 2005 Orlando, Florida

  25. Low Breaks – Cost Issues • Before you remove concrete, make sure and discuss the facts with the architect, structural engineer, and the testing agency to determine if the strength data is acceptable • If not, use the spare sample to break at a future date to see if you get more strength gain with time • You can also do in place testing through coring or use of a Windsor Probe • Rebound hammers are just not accurate enough ABC National Conference February 20th, 2005 Orlando, Florida

  26. Soil Compaction Testing • Compaction, or density testing can be a tricky thing • Compaction - Densification of soil by removing air voids using mechanical equipment • As compaction increases, the following occurs: • Strength increases • Potential for settlement decreases ABC National Conference February 20th, 2005 Orlando, Florida

  27. Soil Compaction Testing • In soils, compaction is a function of water content ABC National Conference February 20th, 2005 Orlando, Florida

  28. Soil Compaction Testing ABC National Conference February 20th, 2005 Orlando, Florida

  29. Soil Compaction Testing • The GE will provide compaction criteria • Other terms for compacted fill – engineered fill – controlled fill • Specs will refer to % Relative Compaction • Relative to what? • Proctor Test – standard or modified ABC National Conference February 20th, 2005 Orlando, Florida

  30. Soil Compaction Testing • Modified Proctor • 1/30 ft3 mold • 10 lb hammer • 18” drop • 5 layers of soil • 25 blows / layer • Standard Proctor • 1/30 ft3 mold • 5.5 lb hammer • 12” drop • 3 layers of soil • 25 blows / layer ABC National Conference February 20th, 2005 Orlando, Florida

  31. Soil Compaction Testing • As you can see, the modified proctor delivers more energy to the soil, compacting is more • Which test should you use? • It depends. Like concrete, is 10,000 psi concrete better than 3000 psi concrete? • It depends on what you need and what you are building • Compacting to a modified is much more expensive than compacting to a standard ABC National Conference February 20th, 2005 Orlando, Florida

  32. Soil Compaction Testing • Make sure your spec meets the need of the project • If in doubt, ask the GE • In many cases, the spec is “cut and paste” and the wrong test could be specified, potentially costing you money and time ABC National Conference February 20th, 2005 Orlando, Florida

  33. Soil Compaction Testing • The testing is determined in the field, typically using a nuclear density gauge ABC National Conference February 20th, 2005 Orlando, Florida

  34. Soil Compaction Testing • This test method is fairly reliable, however the operator must be experienced and know what they are doing • In addition, just because you pass a compaction test does not mean you have good material • Horse s____ can be compacted in the lab and you can test it in the field • If it passes compaction, it does not mean it is good • GE must determine 1st if the soil is acceptable as fill, then the compaction must pass ABC National Conference February 20th, 2005 Orlando, Florida

  35. Masonry Testing • Masonry testing is the least common of the 3 materials discussed today • If masonry testing is done, a common test is to perform compression testing of individual units • A specified amount of units per lot of units delivered to the site are collected and taken to the lab for strength and dimension testing • Since the units are typically fully cured, and the tests can proceed fairly quickly, the process of accepting or rejecting lots of units is fairly straightforward ABC National Conference February 20th, 2005 Orlando, Florida

  36. Masonry Testing • Another masonry test done in the field is grout testing • Sometimes, grout testing is mistakenly performed like concrete cylinder testing • The grout, which is basically high slump concrete with only fine aggregate, is sometimes tested using the same plastic cylinder molds as concrete • THIS IS A MISTAKE! • Grout by design is very high slump with an initial high water/cement ratio ABC National Conference February 20th, 2005 Orlando, Florida

  37. Masonry Testing • This is to allow the grout to be very “runny” and to be able to maneuver itself into the many cracks and crevices inside an assembled cmu wall • Once inside the wall, the excess water will be absorbed by the cmu units as they are absorptive • This will bring the grout quickly down to an acceptable water/cement ratio to allow it to gain sufficient strength • The testing method must account for this process ABC National Conference February 20th, 2005 Orlando, Florida

  38. Masonry Testing ABC National Conference February 20th, 2005 Orlando, Florida

  39. Masonry Testing ABC National Conference February 20th, 2005 Orlando, Florida

  40. Masonry Testing • The process allows the sample to simulate field conditions inside the wall • The most critical component of quality masonry construction is the observation of the process itself • To avoid costly repair and replacement of a grouted masonry wall, make sure the following at a minimum is done: • The grout is not poured in lifts higher than 4 feet • Adequate vibration or “puddling” is performed during the operation to maneuver grout into all the voids ABC National Conference February 20th, 2005 Orlando, Florida

  41. Masonry Testing • The last test that is sometimes required is the easiest one to remedy of them all • In my experience, I have been asked to perform mortar cube testing in the field to verify strength of the mortar, similar to concrete or grout testing • The reason this is easy to remedy is that • THERE IS NO FIELD TESTING PROCEDURE FOR MORTAR CUBE TESTING IN THE FIELD ABC National Conference February 20th, 2005 Orlando, Florida

  42. Masonry Testing • Often times architects and/or engineers read ASTM C 270, which is the standard for Mortar for Unit Masonry • This standard shows the mix proportion requirements for mortar and give strengths in psi • The standard is very clear where it states that these strengths are not to be tested for in the field, only in the lab • The lab mortar uses far less water that would be used in the field and the mortar would not be workable in the field ABC National Conference February 20th, 2005 Orlando, Florida

  43. Masonry Testing • This problem became so problematic for the construction industry, the ASTM designations for mortar were changed in an effort to reduce the notion that strength was critical, when in fact it is not • Mortar is designed as the “weak link” in the wall to provide some give • In addition, strong mortar is brittle, can bond less, and is less water resistant ABC National Conference February 20th, 2005 Orlando, Florida

  44. M A S O N W O R K A-1 A-2 B C D Old Mortar Designations New Mortar Designations ABC National Conference February 20th, 2005 Orlando, Florida

  45. One Final Item ABC National Conference February 20th, 2005 Orlando, Florida

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  47. ABC National Conference February 20th, 2005 Orlando, Florida

  48. ABC National Conference February 20th, 2005 Orlando, Florida

  49. ABC National Conference February 20th, 2005 Orlando, Florida

  50. Matthew A. Dettman, P.E. Western Kentucky University QUESTIONS? ABC National Conference February 20th, 2005 Orlando, Florida

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