FAQ

— Special Inspector in Sacramento, California

Mortar testing is normally required for schools and hospitals, hence your reference to table 2103A.8(2) in 2007 CBC. In the title block of the reference table under Average Compressive Strength there is a small b notation, referring to the note at the bottom, which reads “b. Average of three 2-inch cubes of laboratory-prepared mortar, in accordance with ASTM C270.:” So, the specified strength is based on 2-inch cubes prepared in the laboratory.

Section 2105A.5 specifies “Test specimens for mortar shall be made as set forth in ASTM C1586”. As we were informed in FAQ 10.043, C1586 refers us to C780 Annexes A.7, which describes specimens made as cylinders or cubes.

A further clarification is found in “Reinforced Concrete Masonry Construction Inspector’s Handbook” Fourth Edition, which indicates “The 2-inch cube is typically used for laboratory prepared mortar while the 2-inch x 4-nch cylindrical specimen is used for field cast mortar.” To obtain an equivalence of a 2″x4″ cylinder field test specimen to a 2″ cube specimen, divide the compression test result of the cylinder specimen by 0.85. The factor of 0.85 is the normal correction h/d found in ASTM C780 5.2.6 Note 3.

When testing for compressive strength of mortar in the field you could use either 2-inch cube molds or 2-inch x 4-inch cylindrical molds. The typical standard of practice that most testing laboratories follow is to test field mortar by preparing specimens in a 2-inch x 4-inch cylindrical mold and if required showing a correction factor when the specimens are tested depending on which specimen, cubes or cylinders, was specified for the project.

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— Technician in San Leandro, California

In general, there exists a fundamental inverse relationship between porosity and strength of solids. This strength-porosity relationship is applicable to a wide range of materials, such as iron, stainless steel and granite. Think of examining a concrete core, which exhibits voids created by a lack of consolidation. You can imagine, why with a lack of internal structure, the compressive strength would be lower than expected. On a much smaller scale, there is a theoretical volume of water (based on curing conditions) required to hydrate a given volume of cement. Once you have added more than that amount, it creates capillary porosity (i.e. microscopic cavities or voids). The higher the water-cement ratio, the more porous and the weaker the strength. Generally, to maximize strength and durability, the water-cement ratio should be the lowest possible to hydrate the cement while maintaining its workability.

— Terry Egland, P.E., San Leandro, California

Test specimens (cylinders) are made, cured and tested under certain standard conditions that are usually appreciably different from the conditions existing in the structure. The value of field-cast test specimens is that they give a measure of the strength potential (they evaluate the materials and mix as supplied by the producer, to ascertain the concrete meets project specifications). Test specimens are not intended to yield an exact strength of the concrete in the structure, and the actual strength of the concrete in the structure can be appreciably different. Besides

variable environmental site conditions and curing, other variables between test specimens and the concrete in the structure include variations of mix components, water content, size and shape of the structure, workmanship, degree of consolidation, possible presence of defects such as rock pockets, restraint, and combinations of loading in the structure. It is because of these unknowns that the Structural Engineer must consider a factor of safety when the structure is designed.

Variations in cylinder strengths are not always reflective of a problem in the structure. For instance, if three sets of specimens are made from one day’s concrete placement and maintained under identical conditions throughout the test duration, there is no assurance they will all fail at the same strength when they are tested at the same age. In fact, each one will almost always break at a different strength. These are normal variations, and should be expected.

Cored specimens are usually obtained days or weeks, even months, after the laboratory testing of cylinders. This additional time must be taken into account when comparing cylinder and core test results. In addition, cored specimens are tested in a dry or moist condition, but rarely in the saturated condition similar to test cylinders. It is well documented that dry specimens have a higher compressive strength than saturated specimens.

We do know that there are variations in the strength of the structure that are not caused by basic variations in the concrete itself. For example when cores are taken from a column, the cores from the upper portion of the column invariably indicate lower strength than the cores from the bottom portion of the column. The reason is that the concrete near the bottom was compacted by static hydraulic head of the concrete being worked above, yet there was no change in mix or materials.

— Structural Engineer in Oakland, California

The head of a bolt is formed by heating the end of a piece of steel round bar and then forging (reshaping) the heated end into a head. The head is not welded on or otherwise attached to the end of the round bar.

For example, the production of a 1″ diameter x 12″ long A325 bolt begins by cutting a 20 ft. length of 1045 steel round bar into 13-11/6 pieces. Since the finished bolt length of 12″ is measured from the end of the bolt to the underside of the head, we must add 1-11/16 to the cut length of the bolt. After cutting the bolt to length, this added material (1-11/16) is heated to approximately 2000 degrees Fahrenheit and forged into whatever head style the specific bolt requires. In the case of an A325 bolt, the head style is a heavy hex structural bolt. After the head is forged, an A325 bolt undergoes a heat-treating process in which the bolts are quenched and tempered to develop the high strength mechanical properties required by the specification. The next step in the the process is to test the bolts to ensure that they meet the strength requirements. After verification, they are threaded with 1-3/4 of 8 pitch Unified National Coarse thread,

Information provided by Portland Bolt & Manufacturing Company
www.portlandbolt.com

7-day strength = 2780 psi
28-day strength = 3890 psi (average of 2 cylinders)
56-day strength = 4150 psi (1 cylinder)

Do you report the results as meeting the requirements of the DSA approved documents?

— Testing Lab Manager in Northern California

California Building Code, Title 24, Part 2, Chapter 1905.A.6.3 Strength Test Specimens states:  Strength test acceptance criteria shall comply with the provisions of ACI 318, Section 5.6.3.  Section 5.6.3.3 notes:  Concrete shall be considered satisfactory if both of the following requirements are met:

     A) Every arithmetic average of any three consecutive strength tests equals or exceeds f’c.
B) No strength test falls below f’c by more than 500 psi when f’c is 5000 psi or less.

Using this guideline, the results above would be acceptable if the 28-day cylinders, when averaged with three consecutive strength test results on the project are equal to or greater than 4000 psi. This assumes than no individual test was less than 3500 psi.

The Division of the State Architect holds a different position regarding low strength concrete test results. DSA believes that the LEA approved laboratory should report all failing test results immediately as a non-conformance. It is then up to the design professional and DSA to determine a corrective action plan. If an approved stamped change order is not received from DSA, the failing results should be reported on your laboratory verified report, DSA Form 291. In the 2007 California Administrative Code, Title 24, Park 1, Section 4-335b, Performance of Tests, states:  Where a sample has failed to pass the required tests the architect of engineer, subject to the approval of DSA, may permit retest of the sampled material. Section 4-335d, Test Reports, also notes:  Reports of test results of materials not found to be in compliance with the requirements of the plans and specifications shall be forwarded immediately to DSA, the architect, the structural engineer, ad the project inspector.

So, although the 56-day strength test met the 28-day f’c requirements, DSA does not consider the results to be valid. The test report must be distributed noting “the results do not meet the requirements of the DSA approved documents“. there are no provisions in the California Building/Administrative Code, Title 24 that allow the use of a 56-day test result in lieu of the required 28-day test result. However, a 56-day test result may be useful to the design professional and DSA in arriving at a corrective action plan.

Reference Documents

2007 California Administrative Code, California Code of Regulations, Title 24, Part I

2007 California Building Code, California Code of Regulations, Title 24, Part 2, Volume 2

Building Code Requirements for Structural Concrete (ACI 318-08) and Commentary

— Project Manager in Southern California

Care must be taken in how we sample, test, and report mortar tests. Mortar, by its nature, retains water for an extended period of time. The water in the mix is necessary to maintain the workability of the mortar and to create the bond between the masonry unit and mortar. There have been significant problems lately with field-testing pre-blended mortars that are proportioned to meet the property requirements of ASTM C270. Many of these pre-blended products have constituents that retain a greater amount of water requiring less retempering of the mortar. Due to the high water/cement ratio of these mortars when sampled soon after mixing, and the molding of samples in watertight containers, sampled strength may be much lower than the strength of the mortar used in construction. ASTM C1586 5.5.3.1 states: Measuring mortar compressive strength of field-sampled mortar has no relevance unless preconstruction testing is performed in the laboratory using similar mixing equipment, mortar materials, and the same specimen geometry. Even when this is done, the field compressive strength data can only be compared to the preconstruction mortar strength data in general, due to other factors, such as weather, temperature of mortar, and the absorption properties of the specific masonry units being used.

Reference Documents

ASTM C270 Standard Specification for Mortar for Unit Masonry

ASTM C1586 Standard Guide for Quality Assurance of Mortars

— Steve Marcki, Construction Inspection Manager at Youngdahl Consulting Group, Inc.

For pre-construction prisms we refer to Section 2105A.2.2.2.2 of the 2007 California Building Code which states that “Prior to start of construction, a prism test shall consist of five prisms constructed and tested in accordance with ASTM C 1314.”

We find the age that prisms should be tested in ASTM C1314 Section 7.1, which states “Test prisms at an age of 28 days or at the designated test ages. Test a set of prisms at each age.”

A set of prisms is defined in ASTM C1314 Section 3.1.1 as “a set consists of at least three prisms constructed of the same material and tested at the same age.”

If the project specification indicates a different number of prisms to be tested than indicated in the building code or ASTM, a different age for testing the prisms other than that found in the ASTM, or anything less than three prisms per set, a request for clarification should be forwarded to the design professional.

It is critical that the prisms be transported and handled with care in accordance with ASTM C1314 Section 6.1.

ASTM C1552 should be followed closely to properly cap each prism. Care should be taken to avoid voids between the capping material and prism. Only caps using gypsum cement or sulfur materials are authorized for capping prisms.

Reference Documents

ASTM C1314-07 Standard Test Method for Compressive Strength of Masonry Prisms

ASTM C1552-07 Standard Practice for Capping Concrete Masonry Units, Related Units and Masonry Prisms for Compression Testing

— Unknown

The standardization record for the recorder is a record that details the comparison made between the recorder and a reference thermometer as described in ASTM C511, and adjusting the recorder if it is outside the allowable tolerance. There are six items of information you’ll want to include on the record:

1. Unique identification of the recorder.
2. Unique identification of the reference thermometer.
3. Name of the person who performed the standardization.
4. Reference to the procedure used, for example “Procedure Used: ASTM C511”.
5. Date the standardization was performed.
6. Detailed results including the temperatures indicated by both thermometers, and indication of adjustments made and new temperature readings if necessary.

According to Section 5.2.1.3 of ASTM C511-06, the laboratory is to verify the accuracy of the temperature recorder with that of the reference temperature-measuring device and adjust the temperature recorder if the difference is greater than 1 degree C. This process is considered “standardization”, which is a simplified form of calibration. The process determines the correction to be applied to the result of a measuring device when compared to a reference standard. Standardization does not address all of the elements of uncertainty and does not lead to traceable measurements.

According to AASHTO PP57-06, this process is termed “verification of standardization“, a process that establishes whether the results of a previously standardized measurement device are in control.

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— Structural Engineer in Oakland, California

Answer:    Possibly.

AWS D1.1 – 2.17 Prohibited Joints and Welds
2.17.1 One-Sided Groove Welds. Groove welds, made from one side only without backing or made with backing, other than steel, that has not been qualified in conformance with Section 4 shall be prohibited….

We aren’t talking about “One-Sided Groove Welds”, so this restriction does not apply.

In an attempt to mitigate this situation, from an administrative point of view, we designate the prequalified joint configuration to be TC-U4b-GF, similar to the TC-U4a-GF joint configuration.

Next, we look at “D1.1 – Fabrication”. We cannot prohibit the contractor from using his own “methods and means” to produce welds, as long as they are within the limitations of the code.

The contractor uses the TC-U4b-GF joint configuration, elects to use the widest “As Fit-Up” root opening allowed, uses ceramic backing, and cites the following:

“AWS D1.1 – 5.10 Backing
Roots of groove or fillet welds may be backed by copper, flux, glass tape, ceramic, iron powder, or similar materials to prevent melting through.

Since the weld is to be back-gouged and welded, as an inspector, I would have to allow this, verifying that the groove angle was within the tolerances of the 45° bevel preparation and not the 30° that may be used in the case of the TC-U4a-GF joint configuration.

(After back-gouging, the other side of partially welded joints should resemble a prequalified U- or J-joint configuration at the joint root, and, for administrative purposes, would require an additional WPS.)

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— Special Inspector from Southern California

The UBC Standard 21-16 as referenced in previous CBC’s is no longer applicable in the 2007 CBC. The new code section for structural testing of masonry (1708.1) is adapted from the ACI 530/ASCE 5/TMS 405 reference, which does not require any field mortar testing for quality assurance. The rational of the reference is that mortar is specified based on long standing prescriptive proportioning or property testing performed in a laboratory enviroment that must meet ASTM C270. In either case, material certifications and/or test records should be provided prior to construction to confirm the materials meet the standard and the Special Inspector is responsible for verifying the proper use and proportioning of the material in the field. Per 2007 CBC, Section 2105A.5, essential facilities (schools and hospitals) still require verification testing according to ASTM C1586 for the first three successive days and once every week thereafter for strength requirements only.

11/08 – Response prepared by Jeffry Cannon, the Materials Technical Discipline Leader at Kleinfelder, Inc.

ASTM C1586 specifically states that ASTM C780 should be used to sample and test mortar from project sites (not C270), but goes on to say strength verification of field-sampled mortar should not be performed because strengths of test specimens do not equate to actual strengths of the in-place mortar (Section 5.5).

These conflicts between the CBC and the ASTM stadards that are referenced in the code have not been rectified to date. It is suggested that if field sampled mortar specimens are obtained for strength testing, specimens are fabricated and tested in accordance with C780. Some member firms are adding a statement on their reports of laboratory test results indicating that the strengths of the test specimens may not be indicative of the in-place mortar.

One side note to ASTM C780 is that after initial curing in the field, compression specimens must be cured in moist closets or moist rooms until they are tested. The use of water tanks (curing tanks) is not allowed.

— Bob McCormick, Field Service Manager at Raney Geotechnical, Inc.

You are correct, the averaging calculations for thickness measurements as mentioned in ASTM E605 section 8.1.2.1 do not apply when measuring thickness for a density sample. Section 8.1 of E605 specifies how to correctly measure the thickness of SFRM for the purpose of determining the average thickness, and areas of excessive thickness are dealt with in section 8.1.2.1. By limiting the measured thickness to a maximum of ¼′” over the design thickness, uneven application will not significantly skew the average thickness calculation to a “false high” reading.

When measuring density, IBC 2006 refers us to section 8.2 of E605. Section 8.2.3 deals with thickness measurements for determining density, and quizzically refers to section 7.1, which has no practical meaning on thickness measurement. However, this section does note that 12 thickness measurements are to be taken, and no statement is made regarding adjusting the average of the 12 measurements.

From a practical viewpoint, the use of actual measurements for density calculations prevents “false high” density calculations. For a given weight of SFRM, a limited average thickness/lower volume (as determined by section 8.1.2.1) would generate an erroneous higher density than the actual higher thickness/higher volume measurements would. Thickness measurements are concerned with the application of the SFRM, while the density measurements pertain to the product itself.

For SFRM to provide the required level of protection both the minium average thickness and the density requirements must be met.  “Understating” the average thickness by disregarding a false high point does not result in an understatement of protection.  However, if we use thicknesses as determined by a maximum of the design thickness +1/4” (as used for average thickness determination) and not the actual thickness, we would be overstating the density.  This would result in an overstatement of the protection level, which must be avoided. 

When this question was asked of Luke Woods of W.R. Grace & Co. – Conn. He stated the following:

“The density test in Section 8.2 states that the thickness of the sample shall be determined by averaging the thickness of 12 measurements. I do not believe the 25% – ¼ inch allowance is applicable to these measurements. Also I would encourage you and your team to use the displacement method for determining density, Section 8.3.”

It’s very appropriate to mention the alternate displacement method for determining the in-place density stated, in ASTM E605 Section 8.3 as a referee method. This method measures the volume of the material without the need for thickness or area measurements. It can be used to retest a sample that may be in question.  It reduces some of the measuring and sampling variables that are inherent with other methods.

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— Anonymous

When determining the density of SFRM the Special Inspector is referred to ASTM E605 Standard Test Method for Thickness and Density of Sprayed Fire-Resistive Materials (SFRM) Applied to Structural Members. Section 8.4.1.2 states that when the calculated average density of the SFRM is less than that allowed by the respective fire resistance design see Note 4 & 5. And Note 4 states the following: “A thickness to density correction formula is contained in certain fire resistance rating criteria or is available from some SFRM manufacturers. Consult the rating criteria….before citing for deficiency.” In some cases it has been determined that an increase in thickness will compensate for the deficient density, so what duty does the special inspector/agency/laboratory have in such a case? If we go back to the IBC 1704.10.4 the laboratory is to determine the density according to E605. It makes no reference to Note 4 in using a correction formula. 1704.10.4 states, “The density of the sprayed fire-resistant material shall not be less than the density specified in the approved fire-resistant design.” Unless the fire-resistant design mentions a correction formula and the design professional performs this calculation, the as-measured low density is a non-compliance. From the point of view of the special inspector /agency/laboratory it should be reported in a timely manner to the contractor as a discrepancy for correction.

The concept of a correction formula has a valid basis and should not be considered as a loop hole or an easy way out. It is based on the same design concept of the original tested assembly but it is up to the design professional to determine if the increase in thickness compensates for the low density of the SFRM. As special inspectors or agency/laboratory we report our findings, and the interpretation and revisions are at the discretion and approval of others.

It would be appropriate to mention the alternate method for determining the in-place density stated, in ASTM E605 Section 8.3 as a referee method. This method measures the volume of the material without the need for thickness or area measurements. It can be used to retest a sample that may be in question.  It reduces some of the measuring and sampling variables that are inherent with other methods.

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— Anonymous

The new IBC replaces the Technical Manual 12A, Standard Practice for the Testing and Inspection of Field Applied Sprayed Fire-Resistive Materials  with ASTM E605 as a reference standard. However the user should be cautious as to the extent of the reference. The IBC uses E605 for thickness determination but has wording that supersedes E605 on the rate of testing. E605 conducts thickness testing at a Rate of one bay per floor or one bay for each 10,000 sq. ft., whichever provides the greater number of tests. On the other hand, IBC 1704.10.3.1 would have the inspector take the average of “not less than four measurements for each 1000 sq. ft. of sprayed area on each floor or part thereof”. With such a conflict we refer to IBC 102.4 “Where differences occur between provisions of this code and referenced codes and standards, the provisions of this code shall apply”. So, when writing an SOP for performing thickness determination the following could be adopted:

“Layout a 12 inch square every 1000 square ft of sprayed floor area and take four random symmetrical measurements within that square, one each of the following: valley, crest, and sides, and report as an average”.

NOTE: This change has drastically increased the amount of testing on fluted decks.

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— Unknown

The IBC uses E605 for thickness determination but has wording that supersedes E605 on the rate of testing. E605 conducts thickness testing at a rate of one bay per floor or one bay for each 10,000 sq. ft., whichever provides the greater number of tests. On the other hand, IBC 1704.10.3.1 would have the inspector take the average of “not less than four measurements for each 1,000 sq. ft. of sprayed area for floor decking and 25% of the other protected elements per floor. With such a conflict we refer to IBC 102.4 “Where differences occur between provisions of this code and referenced codes and standards, the provisions of this code shall apply.”

A sample Operating Procedure follows:

FLOOR, ROOF AND WALLS
Sprayed fire-resistive material (SFRM) thickness, applied to the listed members whall be determined in accordance with ASTM E605.

For every 1,000 sq. ft. of SFRM applied, four measurements shall be taken in accordance with ASTM E605 and averaged for determination of the thickness.
NOTE:  The number of tests per square footage differs from ASTM E605.

STRUCTURAL FRAMING
Thickness shall be determined on 25% of the members on each floor in accordance with ASTM E605.
NOTE:  The number of tests per floor may differ from ASTM E605.

— Special Inspector in San Francisco

Though a common rule-of-thumb is “three threads past the nut”, it is just that – a rule-of-thumb, with no basis in fact, In order to arrive at the right answer, we need to follow the reference document chain.

If we start with the 2012 IBC, Section 1705.2.1 states “… Special inspection for structural steel shall be in accordance with quality assurance inspection requirements of AISC 360”, which is a very broad statement. Chapter 35 is a little more specific by designating AISC 360-10 “Specification for Structural Steel Buildings”.

Section N5 (6) uses the provisions of RCSC Specification for Structural Joints Using Gigh Strength Bolts to confirm materials, procedures and workmanship. Thus, we have arrived at the collect specifying document, Specification for Structural Joints Using High Strength Bolts, hereafter referred to as the RCSC 2009.

Section 2.3.2 of the RCSC 2009 states, “The bolt length used shall be such that the end of the bolt extend beyond or is at least flush with the outer face of the nut when properly installed.” So while the old rule-of-thumb won’t hurt, the short bolts will work just fine,

Reference Documents

2009 RCSC “Specification for Structural Joints Using High Strength Bolts”
http://www.boltcouncil.org/files/2009RCSCSpecification.pdf

AISC 360-10 Specification for Structural Steel Buildings
http://www.aisc.org/WorkArea/showcontent.aspx?id=26516

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— San Francisco Structural Engineer

The typical standard used to reference shrinkage limits for a project is ASTM C157 “Length Change of Hardened Hydraulic-Cement Mortar and Concrete”. This test method is a very sensitive laboratory test based on specific criteria for mixing, sampling, curing and measuring. Some criteria may vary, such as storage, allowing for either water or air, which can have significant influence on the test results. SEAONC developed a modified procedure to C157 in the 1960’s commonly referenced in project specifications that make several changes that include sample size (4x4x11 vs. 3x3x11), initial curing (7 days vs. 28 days wet cure) and air drying (50% RH). It is this modified procedure that most project specification limits are based. As with interpreting and analyzing any test results, it is critical to make sure you are comparing apples to apples.

Although every project would like to limit shrinkage to the least possible amount, it is important that limits be specified only when necessary and if the proper quality control, including laboratory testing, can be established. Local materials or mix proportions may not be able to meet shrinkage requirements without the addition of costly admixtures that can affect other properties of the mix. Lab test values should be used as a basis to determine the acceptability of materials and proportions and should not be used categorically. Furthermore, as with concrete compression testing, the results from shrinkage testing are not necessarily representative of the performance of the mix in-place because of the complexity of the factors that influence shrinkage. Similarly, field cast shrinkage samples are typically found to be greater than lab cast samples. Some specifications allow for 15% to 25% higher tolerances, while the SEAONC “Supplementary Recommendations for Control of Shrinkage in Concrete” gives maximum ranges for differenct classes of concrete at 21 days drying for lab from .036 to .060, while field cast specimens are in the range of .048 to .080.

Given the factors noted above, field-testing data can give some indication of the quality of the shrinkage characteristics, however reliance on this information for material acceptance should be avoided. The bottom line is that, in the absence of a new ASTM for field-testing or modified specifications, there is no substitute for laboratory trial batching to determine the shrinkage limits of a specific mix.

— Steve Marcki, Construction Inspection Manager, Youngdahl Consulting Group, Inc.

The intent of ASTM Subcommittee E06.21 when writing E-736 was to outline a standard method to measure the combined bond strength from cohesion and adhesion of SFRM when applied to a structural member. Cutting around the cap down to the substrate will isolate the bond strength to only adhesion and may thereby indicate why your project sounds hollow but would not be a standard method to substantiate an unacceptable application of SFRM.

Since you suspect an improper application, it would be prudent to test the SFRM in the standard method and to also cut around the cap and test just for adhesiveness and report the findings to the design professional.

www.wordnet.princeton.edu/perl/webwn defines cohesion as the intermolecular force that holds together the molecules in a solid or liquid. They further define adhesion as the property of sticking together (as glue or wood) or the joining of surfaces of different composition.

Is ACI certification required for both concrete and masonry special inspectors?

— Anonymous

Many years ago, ASTM C94 Standard Specification for Ready-Mix Concrete included a certification requirement for the technician sampling fresh concrete.  Specifically, Section 16.2 reads, “Tests of concrete required to determine compliance with this specification shall be made by a certified ACI Concrete Field Testing Technician, Grade I or equivalent.  Equivalent personnel certification programs shall include both written and performance examinations as outlined in ACI CP-1.”

For the most part, building officials throughout the State of California interpreted this to mean the ACI certification only.  By mutual agreement with the three Greater Bay Area ICC (formerly ICBO) Chapters, CCTIA included the ACI Grade I certification as a requirement in its Guidelines for Issuing Identification Cards for Special Inspectors for both Reinforced Concrete and Pre-Stressed Concrete Technicians.  This certification is also required by ICC in order to become fully certified as a Reinforced Concrete Special Inspector and Pre-Stressed Concrete Special Inspector.

Sampling masonry grout is another matter.  Note 8 in ASTM C1019 Standard Test Method for Sampling and Testing Grout states, “The field technician sampling, making, and curing specimens for acceptance testing should be certified (American Concrete Institute Field Testing Technician – Grade I, National Concrete Masonry Association Masonry Testing Technician, or equivalent).  Equivalent certification programs should include both written and performance examinations.”

As we know from a previous FAQ (reference number 10.002), the language contained in the “Notes” of an ASTM Standard are not considered mandatory. In addition, the language of the note suggests a recommendation as opposed to a requirement with the use of the word “should” as opposed to “shall.”

As the ACI Grade I certification has nothing to do with the proper methods or procedures for fabricating masonry grout samples, it would be inappropriate to require this certification for masonry inspectors. This certification is not a requirement of ICC in order to become fully certified as a Structural Masonry Special Inspector.

COMMENTS

Today, most of the testing laboratories have to meet the requirements of Practice C1077 Laboratories Testing Concrete and Concrete Aggregates for Use in Construction and Criteria for Laboratory Evaluation (through CCRL) and Standard Specification E329 Agencies Engaged in Construction Inspection and/or Testing. Practice C1077 in Section 6.1.6 states “Concrete field technician shall possess current technician certification.” And continues to say ACI or NICET can satisfy this requirement. Specification E329 in Section 13.1.2 states “The agency shall comply with the most recent edition of Practice C1077 for tests of concrete and aggregates.” Under PERSONNEL in E329 the requirement for inspector or technician is a little vague. Section 6.2.4 states the technician must be able to demonstrate competence for the test which is being conducted either by oral or written examination or both.” So certification is one means of showing competence but this section does not require certification. But with the requirement to meet C1077, certification is required. It’s interesting that Specification C94 also requires the testing laboratory to meet C1077.
A quick look at Practice C1093 Accreditation of Testing Agencies for Unit Masonry does not mention field personnel nor does it require meeting any other Standard.

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We are trying to determine if the electrode they are using meets the specifications, which specifically call for E80 electrodes. We’re attempting to contact Lincoln Electric directly to get their opinion but we could use some outside advice, especially since the testing agency for the project seems reluctant to suggest anything and is looking to us for direction. Have you ever encountered a similar situation and if so how was it resolved? Please let me know what you would suggest.

— Structural Engineer from Oakland, CA.

Strictly speaking, “E80” is not explicity defined in any AWS document that I am aware of, although it clearly suggests an 80 ksi minimum UTS electrode. If the specification did not specify a consumable classification, then “matching” requirements for an ASTM A913, Grade 60 or 65 would be the classifications listed in AWS D1.1, Table 3.1, Group III. These do not all start with “E80”, although they are nominally 80 ksi minimum UTS. If the consumable manufacturer states in writing that the particular electrode meets the properties of an E8XTX-X classification, then the Engineer could accept it. I would not expect any inspector or test lab to accept a classification unless it is shown as such on the consumable manufacturer’s literature or it was approved by the Engineer.

2/07 – Response prepared by Dave Palfini, Principal, ASNT Level III, AWS SCWI, Testing Engineers, Inc., San Leandro

AWS A5.29-98 classifies the Lincoln NR-311 Ni electrode a E70T7-K2 indicating that it has a minimum tensile strength to 70,000 psi. To add value to his or her service, the special inspector should have researched the contractor’s claim that this electrode met the requirements of the specifications. The special inspector, or his or her support personnel at the inspection agency’s laboratory, should have gone to the Lincoln Electric Company’s website (www.lincolnelectric.com) and downloaded information for this electrode from the manufacturer’s catalog as well as the electrode’s Certificate of Conformance. Both of these documents indicate that the electrode meets the requirements of the specifications, 80,000 psi minimum tensile strength, as wells as FEMA 353 requirements. These documents then should have been forwarded to the EOR for review, and either approval or rejection.

— Structural Engineer from Houston, TX.

There are no general requirements for NDT of fillet welds in the 2001 CBC, AWS D1.1, AWS D1.8, or the AISC Specifications. The requirements in CBC Section 1703 apply only to the welds noted, and are the minimum NDT requirements. The Engineer has the option of requiring testing beyond the minimum requirements, including NDT of fillet welds, as part of the Statement of Special Inspections prepared by the responsible design professional. However, such testing is not specifically required by code.

Appendix Q of the 2005 AISC Seismic Provisions for Structural Steel Buildings (AISC 341) now lists specific locations where NDT is required for connections resisting seismic forces. The only connections that could potentially involve fillet welds are welds within the “k-area” of the section and repairs within the plastic hinge region of reduced beam section (RBS) moment frame connections. These provisions have not yet been adopted into the California Building Code.

FEMA-353 recommends the Engineer to develop a Quality Assurance Plan and indicate the appropriate Seismic Weld Demand Category and Seismic Weld Consequence Category for each welded joint on the design drawings. Magnetic particle testing is specified for fillet and PJP welds in all but two categories.

If desired, Magnetic Particle Testing (MT) should be used to test fillet welds. Ultrasonic Testing (UT) should not be specified for fillet welds.

— Structural Engineer from Oakland, CA.

Puddle welds are typically used to join sheet metal to underlying structural steel elements. These welds are generally completed by using high heat settings to allow for burning through of the sheet metal. With the higher heat required for this welding technique, a larger weld puddle is formed than would typically be created with the use of a lower heat (amperage) setting.

The connection strength of the puddle metal is a function of the perimeter area of the weld. With the larger puddle area of a puddle weld versus that of a linear weld or plug weld, and the higher heat of the molten metal, the application of a puddle weld is governed by gravity. The forces of gravity do not allow for the creation of a larger weld puddle as is common for a puddle weld in any position other than the flat position.

1/17/07 – Response prepared by Dave Palfini, Principal, ASNT Level III, AWS SCWI, Testing Engineers, Inc., San Leandro

Arc spot (puddle) welds and arc seam welds are only done in the flat position. See AWS D1.3-98, Table 1.2. It is almost impossible to do them in any other position.

1/17/07 – Response prepared by Doug Williams, Consulting Metallurgical and Welding Engineer

The simple answer is that if the contractor won’t do it, it’s not going to get done – regardless of theory.

See D1.3-98 Table 4.1 for standard joints. #4.4, Arc spot weld-sheet to supporting structural member is only shown for F, i.e., flat welding only. #4.5B is only shown for the horizontal position.

The relevant all-position weld might be #4.5, the arc plug weld.

Yes, it is possible. However, it will have to be done with an all position welding electrode. The fact that it is possible does not relieve any inspector from following the code for the acceptance of the weld requirements. AWS D1.3 has tolerances that limit out of position puddle welds

— Structural Engineer from Oakland, CA.

The two most common types of Gas Metal Arc Welding (GMAW) metal transfer are short-circuit and spray transfer. Both processes use constant voltage and direct current. In the short-circuit process, which uses both a constant voltage and constant current, the filler wire contacts the base metal causing a short-circuit. The short circuit processes sufficient heat to melt the filler wire where the wire is in contact with the base metal.

Spray transfer is a process where the filler metal wire melts above the base metal and is projected across the arc as globules or as fine droplets of molten metal. Spray transfer can be accomplished using conventional constant voltage constant current or pulse current techniques and equipment.

Pulsed arc welding, also known as pulsed spray welding, is a spray-transfer form of GMAW. Pulsed arc welding process is also a constant voltage direct-current process where the current is not held constant but is pulsed. Melting of the filler wire occurs at the higher current associated with the electrical pulse wave, with the droplets of molten filler metal projected across the arc from the wire to the weld puddle. Thus the spray-transfer of the filler metal.

The spray transfer process has the ability to make high-deposition welds on thick carbon steels when using larger diameter filler wire. The current AWS Welding Code D1.1 precludes the use of short-circuiting for welding of structural steel and stipulates that the spray transfer method be used for GMAW.

An advantage of the pulse method of GMAW versus that of conventional spray transfer GMAW, as cited by suppliers of the equipment, is that the average current of pulse arc is equal to and often less than that of conventional spray transfer. The pulse method of welding can result in increased penetration with less heat buildup in the joint. Spray transfer, and in particular the pulsed arc method, is also identified with better root fusion than the short circuit method of GMAW. Another advantage of the pulse method of GMAW is the reduction in spatter over that of the steady current short-circuit method.

References:

RobotWorx
370 W. Fairground St.
Marion, OH 43302
www.robots4welding.com

Considering the Benefits of Pulse Spray Transfer GMAW
By Paul Niskala, Contributing Writer
Practical Welding Today®
www.thefabricator.com
October 25, 2002

— Anonymous

Let’s talk about the different types of adhesives first. There are two primary types of adhesives: pure epoxies, which depend on the physical mixing of the two parts (resin and hardener) and vinyl esters and acrylics, which depend on a polymeric chemical reaction between two parts (resin and initiator). There are fast set and standard (slower) set versions of epoxies. The vinyl esters and acrylics typically gain strength quickly and can have load applied accordingly. Acrylics work well at low temperatures. Some products do not have good long term creep performance, which is an issue when constant loads are applied.

The application drives what is specified.

The chemical formulations provide the performance characteristics and they can vary greatly. So it’s not just a matter of load-carrying capacity when looking to determine an “equal” or “equivalent” epoxy. The application drives what is specified. In some cases it may not make any difference which product is used (e.g., a hold down inside a wall). In others it is critical (e.g., a suspended ceiling). Therefore the issue of “or equal” for adhesives is something that only the specifier (project engineer) who knows what is needed for the specific application, can answer.

It should also be noted that when a specification included on Approved (Building Department approved) plans includes an allowance of an “approved equal” or “approved equivalent” the responsible design professional must provide the Approval. Where the plans include a simple allowance of an “equal” or “equivalent” the responsible design professional should be requested to provide their approval for a proposed substitution based on the variable performance characteristics of the numerous epoxies available as discussed above.

What concerns me about the specification is that I’m sure that the differences between AWS D1.1 and FEMA-353/D1.8 were not taken into account when the provision was written. That’s why I need the clarification. Should we be using D1.8 or D1.1 or both?

— Structural Engineer from Oakland, CA.

AWS D1.1 has two ultrasonic testing procedures and acceptance criteria. The primary one, used for decades and most commonly accepted, is contained in Section 6, Part F.

Annex K, referenced in FEMA-353, UT Examination of Welds by Alternate Techniques, is relatively new. Since FEMA-353 was not specified for ultrasonic testing in the project documents, AWS D1.1, Section 6, Part F would be the procedure to be used. Some reasons for this are as follows:

FEMA-353, Section 5.8.3 allows the engineer the option of either AWS D1.1 Annex K or Table 6.2 (Section 6, Part F).

Annex K (moved to Annex S in 2006), states, “This annex is non-mandatory unless specified in the contract documents.”

AISC 341s1-05 and AWS D1.8-06 specify AWS D1.1, Section 6, Part F unless alternative procedures are approved by the engineer.

7/23/06 – Response prepared by Doug Williams, Consulting Metallurgical and Welding Engineer

If given the choice, I prefer the D1.1 criteria, primarily because there are precious few UT technicians that can accurately and reliably size flaws in 3 dimensions. As the welding inspector suggests in his original request, the FEMA-353 criteria may not be as conservative as D1.1, particularly considering the lower probability of detection and accuracy of sizing for technicians whose experience is predominantly with the D1.1, Sec. 6, Parts C & F criteria and methods.

— Anonymous

According to the Concrete Reinforcing Steel Institute (CRSI) in a similar FAQ, they state “Rust actually improves bond because it increases the roughness of the surface. However – and this is the exception – if there is so much rust that the weight of the bar is reduced or the height of the deformation is reduced, then the rust is considered harmful.”

Check out the following references:

CRSI Engineering Data Report #54 Field Inspection of Reinforcing Bars Page 3 Surface Conditions of Bars, “A light surface coating of rust on reinforcing steel should not be a cause for rejection by the inspector”

ACI 318 Building Code and Commentary – Section 7.4.2, “Except for prestressing steel, steel reinforcement with rust and mill scale, or a combination of both, shall be considered satisfactory, provided the minimum dimensions and weight of a hand-wire-brushed test specimen comply with applicable ASTM specifications.” Section 7.4.3, “Prestressing steel shall be clean and free of oil, dirt, scale, pitting and excessive rust. A light coating of rust shall be permitted.”

ASTM A615 Standard Specification for Deformed and Plain Carbon Steel Bars for Concrete Reinforcement – Section 12.2, “Rust, seams, surface irregularities, or mill scale shall not be cause for rejection, provided the weight, dimensions, cross-sectional area and tensile properties of a hand wire brushed test specimen are not less that the requirements of this specification.”

ASTM A706 Standard Specification for Low-Alloy Deformed and Plain Bars for Concrete Reinforcement – Section 11.2, “Rust, seams, surface irregularities, or mill scale shall not be cause for rejection, provided the weight, dimensions, cross-sectional area and tensile properties of a hand wire brushed test specimen are not less that the requirements of this specification.”

CALTRANS – Standard Specifications M ay 2006 Section 52-1.05 CLEANING, “Before concrete is placed, the reinforcement to be embedded shall be free of mortar, oil, dirt, excessive mill scale and scabby rust and other coatings of any character that would destroy or reduce the bond.”

Conclusion

As noted in documents issued by ASTM, ACI, CRSI, and Caltrans, some rusting of the reinforcing steel is acceptable and advantageous. The difficulty in addressing this issue is the subjectivity of a visual evaluation as suggested by CRSI (“A light surface coating…”) and Caltrans (“…free of …excessive mill scale and scabby rust and other coatings of any character…’). Common sense and fabrication tolerances should be used. Where there is readily visible pitting or scale associated with rust (not mill scale) and where the engineer or inspector have cause for concern that the deformations and/or cross sectional area of the bar have been reduced, the degree of rusting may need to be determined by laboratory testing. As always, the project specifications, where more stringent than the published standards, shall prevail over all else.

— Anonymous

The FF and FL numbers represent a statistical calculation of the flatness and levelness of a concrete slab as determined with slope measuring equipment. Testing is performed in accordance with ASTM E1155 Standard Test Method for Determining FF Floor Flatness and FL Floor Levelness Numbers. The higher the F-number the better the characteristic of the floor.

The straightedge method specifies that the gap observed under a free-standing or leveled 10 ft. long straightedge shall not exceed 1/8″. The problem with this method is that there is no standard method for taking measurements (i.e., number of tests, location, direction) or quantitative procedure for establishing compliance of a test surface.

The following excerpts from ACI help clarify some of the industry guidelines:

ACI 302 Guide for Concrete Floor and Slab Construction
Section 8.15.1.1 – It is recommended that both flatness and levelness requirement be described by Face Floor Profile Number. Two separate F-numbers are required to define the required floor flatness and levelness of the constructed floor surface.

Section 8.15.1.2 – The older method of using a 10-ft. straightedge can also be used to measure floor flatness, but it is much less satisfactory that the F-number system. There is no nationally accepted method for taking measurement or for establishing compliance of a test surface using the tolerance approach. This can often lead to litigation.

ACI 117 Standard Specifications for Tolerances for Concrete Construction and Materials
Section 4.5.6 – Floor finish tolerance as measured in accordance with ASTM E1155 Standard Test Method for Determining Floor Flatness and Levelness Using the F-Number System.

Section 4.5.7 – Floor finish tolerance as measured by placing a freestanding (unleveled) 10 ft. straightedge anywhere on the slab and allowing it to rest upon two high spots within 72 hr after slab concrete placement. The gap at any point between the strightedge and the floor (and between the high spots) shall not exceed:
Conventional
Bullfloated …………… 1/2 inch
Straightedged ………… 5/16 inch
Very flat ……………… 1/8 inch

CONCLUSION

The 1/8 inch in 10 ft specification has been a common specification. However, it is seldom measured and rarely enforced due to its unscientific and non-repeatable method. It is approximately equivalent to an FF of 50, which is a very flat floor, not normally required for typical concrete slab surfaces. Most convenventional slabs have flatness readings (FF) between 20 and 30.

The F number system is the preferred method of specifying and verifying compliance of floor finish tolerances and should be used in lieu of the archaic 1/8″ in 10 ft.

— From the October 2001 Inspection Division Quarterly Newsletter,
City of Santa Clara, CA.

The International Residential Code (R319.3) and the International Building Code (2304.9.5) have similar requirements for fasteners used with treated wood. The IRC states, “Fasteners for pressure-preservative and fire-retardant-treated wood shall be of hot-dipped zinc coated galvanized steel, stainless steel, silicon bronze or copper. The coating weights for zinc-coated fasteners shall be in accordance with ASTM A153. Exceptions: 1) One-half inch (12.7 mm) diameter or greater steel bolts. 2) Fasteners other than nails and timber rivets shall be permitted to be of mechanically deposited zinc-coated steel with coating weights in accordance with ASTM B695, Class 55, minimum.”

The codes do not discriminate between types of preservatives and do not take into account exposure conditions, nor do they contain provisions for other hardware such as connectors or flashing.

The potential for corrosion of hardware in contact with treated wood occurs when metals in the preservative (such as copper) are different from the metals in the hardware (the iron in steel, or aluminum). In a wet environment these dissimilar metals create a small electrical current that triggers a chemical reaction resulting in galvanic corrosion.

In damp or wet exposure, hardware in contact with pressure-treated wood must be corrosion resistant. Hardware includes fasteners (e.g. nails, screws, and bolts) and all connectors (e.g. joist hangars, straps, hinges, post anchors, and truss plates).

Regardless of exposure condition, fasteners and connectors should be specified in compliance with the hardware manufacturer’s recommendations and the building codes for their intended use.

A conclusion from the above would indicate that shear wall nailing to a pressure-treated sill plate requires galvanized nails.

Also, does a PQR for a groove weld qualify a WPS for a fillet weld of the same size?

— Unknown

Yes, WPS qualification of a complete joint penetration (CJP) groove weld (butt joint) qualifies tee and corner (CJP and PJP) joints within the limits of the qualified WPS. It also qualifies fillet welds within the limits of AWS D1.1 Table 4.1 and 4.2 Note 4. Most fillet welds are afforded pre-qualified status per AWS D1.1 Section 3.9.

6/16/06 – Response prepared by Dave Palfini, Principal, ASNT Level III, and AWS SCWI, Testing Engineers, Inc., San Leandro

When responding to frequently asked questions, the apparent code answer is not always what the inquirer may be seeking. When reviewing and approving welding procedure specifications, the Engineer has the authority to “relax” code requirements or enforce more stringent requirements. In this case, it is possible that the project team was looking for a more comprehensive analysis due to a critical connection required by their design. Following is an interpretation of the code with that thought in mind.

1. For a complete joint penetration (CJP) groove weld, at first glance, yes. AWS D1.1-06, Section 4.9.1.1 Corner or T-Joints states “Test specimens for groove welds in corner or T-joints shall be butt joints having the same groove configuration as the corner or T-joint to be used on construction….”

However, AWS D1.1-06, Table 4.3, Note 2. states “If a PJP bevel- or J-groove weld is to be used for T-joints or double-bevel- or double-J-groove weld is to be used for corner joints, the butt joint shall have a temporary restrictive plate in the plane of the square face to simulate a T-joint configuration.”

Welding Procedure Specifications (WPSs) requiring qualification by test, resulting in Performance Qualification Test Records (PQR), are typically done to qualify an unproven joint configuration, base metal, weld metal combination. The ability of a/any welder to accomplish a sound weld during construction using this type of WPS is very important

It is recommended that WPSs that are not pre-qualified for T-joints and/or corner joints with J-grooves or double-bevel groove or double-J-groove, whether CJP or PJP, be qualified using a temporary restrictive plate, prior to approval by the Engineer.

2. Yes. AWS D1.1-06, Table 4.2, Note 4. states “CJP groove weld qualification on any thickness or diameter shall qualify any size fillet or PJP groove weld for any thickness.”

Excerpt from Section 5.1, ASTM C511, Standard Specification for Mixing Rooms, Moist Cabinets, Moist Rooms, and Water Storage Tanks Used in the Testing of Hydraulic Cements and Concrete:

“The recording thermometer shall be calibrated at least every six months or whenever there is a question of accuracy.

Perform the verification of the recording thermometer by comparing the temperature reading of the recording thermometer with the temperature reading of a reference thermometer during the normal operation of the moist cabinet or moist room.

The thermometer used as the reference thermometer must be accurate and readable to 0.5°C.”

— Unknown

I posed this question to the ASTM staff member in charge of C511, who asked Mr. Ray Kolos of CCRL to respond. Mr. Kolos stated that the intent of the standard is that verification of the recording thermometer will be conducted every six months using a reference thermometer. Section 5.1 uses the term “calibrated” even though verification is intended. Mr. Kolos will ask the chairman of the ASTM Committee C1.95, Mr. Dave Norris, to consider modification to correct the error.

— Unknown

A quick look at the “Scope” of ASTM A307 Standard Specification for Carbon Steel Bolts and Studs, 60,000 psi Tensile Strength, indicates that Grade Cs are non-headed anchor bolts, either bent or straight, and having properties conforming to Specification A36. This seems to answer our question in a very straightforward manner

If we look at the Standard Specification ASTM A36 for Carbon Steel the mechanical properties listed in Table 3 for bars are as follows:

Tensile strength, ksi           58 – 80
Yield point, min, ksi           36
Elongation, in 2 inch, %     23

and Section 3.1of A36 states “When components of a steel structure are identified with this ASTM designation but the product form is not listed in the scope of this specification, the material shall conform to one of the standards listed in Table 1 unless otherwise specified by the purchaser.”

So, in Table 1 of A36, for anchor bolts, we find the designated specification of ASTM F1554 Standard Specification of Anchor Bolts, Steel, 36, 55, and 105-ksi Yield Strength with the following Note:

“The specifier should be satisfied of the suitability of these materials for the intended application. Composition and/or mechanical properties may be different that specified in A36/A36M.”

The mechanical property requirements for ASTM F1554 Grade 36 anchor bolts are identical to A36 and A307 Grade C.

Conclusion:   ASTM A307 designates F1554 as the controlling specification and the mechanical properties of A307 Grade C are identical to that specified for F1554 Grade 36.

Discussion:   ASTM F1554 Standard Specification of Anchor Bolts, Steel, 36, 55, and 105-ksi Yield Strength was introduced in 1999. It marked the first time that hooked, headed and threaded and nutted rods in multiple grades were fully addressed in one specification. F1554 grades 36, 55, and 105 are essentially the anchor-rod equivalent of the generic rod specification ASTM A36, A572 Grade 55, and A193 Grade B7, respectively. The benefits of F1554 are clear: there is no other specification that brings all requirements for anchor-rods together into one place – mechanical, chemical, threading, manufacturing, and dimensional. Compared to older “material-only” specifications like A36, F1554 eliminates confusion about what product is required.

— Unknown

The ACI Concrete Laboratory Testing Technician – Grade 1 certification includes capping and testing concrete cylinder specimens for compressive strength, but does not include flexural strength testing. Certification for this test may be obtained by the Concrete Strength Testing Technician or Concrete Laboratory Testing Technician – Grade 2 certifications. If certification for performing only compression tests is required, the Concrete Laboratory Testing Technician – Grade 1 certification should be sufficient.

— Unknown

There is no requirement in the UBC or ASTM standards that requires reporting concrete test results. Project specifications typically address the required 28-day compressive strength, with some specifications also including a 7-day compressive strength. On projects where the concrete compressive strength is specified at an age of 28 days, a 7-day compressive strength test may provide an indication of the 28-day strength. Many laboratories consider concrete with a 7-day strength of less than 65% of the 28-day strength to be suspect (see FAQ 10.004). Most laboratories consider it good business to notify their clients of 7-day compressive strength results that are less than 65% of the 28-day strength, and to include the 7-day strength when reporting the 28-day results.

— Unknown

UBC Section 1924.10 states that shotcrete with maximum nominal aggregate larger than 3/8-inch shall be tested using 3-inch diameter cores or 3-inch cubes. Shotcrete with maximum nominal aggregate of 3/8-inch or smaller shall be tested using 2-inch diameter cores or 2-inch cubes.

ASTM C1140 requires shotcrete be tested as drilled cores or sawed cubes, and references C42 and C513, respectively, for obtaining the specimens. Cores shall be at least 3.70-inches in diameter for load bearing structural shotcrete. Cores for non-load bearing shotcrete, or when it is impossible to obtain cores with length-diameter ratios greater than or equal to 1, are not prohibited. Cubes shall be 2-inches to 4-inches in size, with no size requirement based on aggregate size.

COMMENTS
ASTM Subcommittee C09.46, who has jurisdiction over C1140 will be replacing the requirements of C42 with a new ASTM designated as C1604-05 Standard Test Method for Obtaining and Testing Drilled Cores of Shotcrete. This new standard has the following requirements:

8. CORES FOR COMPRESSIVE STRENGTH

8.1 Diameter – The diameter of core specifications for the determination of compressive strength in load bearing structural members shall be at least 3.0 in. [75 mm] (see Note 4).

Core diameters less than 3.0 in. [75 mm] shall be permitted as directed by the specifier of the tests.

Note 4 – The compressive strengths of 2-in. [50-mm] diameter cores are known to be somewhat lower and more variable than those of 3-in. [75-mm] diameter cores. In addition, smaller diameter cores appear to be more sensitive to the effect of the length-diameter ratio.

This new standard will bring us better into alignment with IBC, UBC and CBC

— Unknown

— Unknown

The short answer to your question is that there is no UBC limitation on the maximum drop height of concrete during placement. Although factually there is no UBC requirement to limit concrete drop height, there are implied practical limits. The Code refers to the issue of concrete segregation during conveying and depositing of concrete. In referencing UBC Section 1905.10 you correctly cited the Code but left out an important element of the Code provision. Section 1905.10 states “Concrete shall be deposited as nearly as practical in its final position to avoid segregation [emphasis added] due to rehandling or flowing.” Section 1905.9.2 states “Conveying equipment shall be capable of providing a supply of concrete at site of placement without separation of ingredients…”. These two provisions show intent to maintain concrete quality to the point of final deposit by preventing or avoiding separation of materials. Experience has shown that free falling of concrete through close spaces with obstructions, such as reinforcing steel and embeds, can cause segregation of concrete. Based on this experience and the absence of specific limits on free-fall drop heights in the UBC, a specific provision was added to Title 24 of the California Building Code. CBC Section 1905A.10.9 states “In depositing concrete in columns, walls or thin sections of considerable height, concrete shall be placed in a manner that will prevent segregation… unless otherwise approved by the enforcement agency, the unconfined vertical drop of concrete… to the placement surface shall not be greater than 6 feet (1829 mm).” The American Concrete Institute also addresses placement of concrete in several publications, including ACI 304R-00. ACI 304R-00 states that “… if forms are sufficiently open and clear so that concrete is not disturbed in a vertical fall into place, direct discharge without the use of hoppers, trunks, or chutes is favorable.” In summary, though not specifically limited, drop height has been shown to have practical limits based on the conditions where the concrete is being placed. The drop height should be limited to that where concrete quality can be maintained and segregation is prevented.

COMMENTS
Historically, drop heights of 10-20 feet have been referenced as the maximum allowable. Studies of the impacts of free-fall placement of concrete in large diameter drilled cast-in-place piers (also referred to as cast-in-drilled-hole caissons) up to 150 feet deep indicate concrete can free fall great distances without appreciable problems. Because of this, reference to maximum drop heights has been removed from many current specifications, including those of the Federal Highway Administration (FHWA). The trend towards removal of controlling concrete drop height based on these studies and the advocacy of less control on concrete placement techniques by contractor-based organizations may not be well founded for concrete placement in structures other than large uncongested structural elements. It should be understood that the studies conducted involved large diameter piers or caissons, which allowed for minimal impact with reinforcing steel. Though the FHWA has been quoted as stating that “the general expectation that (concrete) striking of the rebar cage will cause segregation or weakening of the concrete is invalid,” it is important to recognize that the dynamics of the concrete falling into place, even when striking rebar in a large diameter caisson, are very different than in a close space, such as a wall, thin section or small diameter column. The studies cited by contractor-based organizations, such as the American Society of Concrete Contractors, advocating unrestricted fall heights for concrete, are all based on large diameter caissons. They do not refer to studies of more restrictive structural elements, such as walls and smaller diameter caissons or columns, though they are advocates of applying the unrestricted free-fall practice to other structural elements, including walls and columns.

The reader may wish to closely examine position paper #17 from American Society of Concrete Contractors, which does note than “Concrete placing operations are often planned to allow for the free fall of concrete. This planning must also consider any segregation that might occur when the concrete free falls into place.” The paper may be viewed at www.ccagc.org/tech_info.php or purchased online at www.ascconline.org.

— Unknown

Rather than address the subject of hardness and what might be a reasonable tolerance, let’s discuss the point of authority that the evaluator is quoting. According to an ASTM document “Form and Style for ASTM Standards” Section A27.1 “Notes in the text shall NOT include mandaroty requirements. Notes are intended to set explanatory material apart from the text itself, either for emphasis or for offering informative suggestions not properly part of the standard.” Therefore, I would suggest that the Subcommittee C09.61 on “Testing Concrete for Strength” feels that a comment on hardness is appropriate but cuts short of mandatory language. The subcommitee has recommended a hardness number of 55 HRC. A slight difference from the recommended would not be a violation of the intent of C39 but a reasonable tolerance is not given.

The same document mentioned above also discusses Footnotes in Section A26.1. “Footnotes referenced in the text are intended ONLY for reference and shall never include any informaton or instructions necessary for the proper application of the method. Table footnotes area a part of the table.” Therefore, again, we see that no mandatory language should be outside of the main text of the document.

— Unknown

The rule of 85% can be best explained by ASTM C42-04 Section 3.5: “There is no universal relationship between the compressive strength of a core and the corresponding compressive strength of standard-cured molded cylinders. The relationship is affected by many factors such as the strength level of the concrete, the in-place temperature and moisture history, and the strength gain characteristics of the concrete. Historically, it has been assumed that core strengths are generally 85% of the corresponding standard-cured cylinder strengths, but this is not applicable to all situations.”

The commentary of ACI 318 Section R5.6.5 also states “Core tests having an average of 85% of the specified strengths are realistic. To expect core tests to be equal to f’c is not realistic, since differences in the size of specimens, conditions of obtaining samples, and procedures for curing, do not permit equal values to be obtained.”

NOTE: According to ACI 214.4R-03 “Guide for Obtaining Cores & Interpreting Compressive Strength Results” the preceding method is NOT an option when evaluating for structural capacity.

For further information ASTM references Neville, A., “Core Tests: Easy to Perform, Not Easy to Interpret”, Concrete International, Vol.23 No. 11 November 2001, pp. 59-68.