3. Slump.
The slump test is a measure of concrete consistency.
For given proportions of cement and aggregate without admixtures, a higher slump correlates to a wetter mixture. Slump is indicative of workability when assessing similar mixtures. However, it should not be used to compare mixtures of totally different proportions. When used with different batches of the same mixture, a change in slump can indicate a change in consistency, aggregate grading, aggregate moisture content, cement or admixture properties, amount of entrained air, or temperature. Therefore, slump test values are indicative of hour-to-hour or day-to-day variations in the uniformity of a given concrete mix.
f. For superplasticized concrete ±2-1/2 in.
(±63 mm)
f. Flowable concrete achieved by the incorporation of high-range water reducers (HRWR) (superplasticizers) is difficult to control within tight tolerances at specified slumps of 7 in. (175 mm) or greater. In addition, it is difficult to accurately measure high slumps. Consideration should be given to eliminating a maximum slump requirement when an HRWR is used to achieve flo wable concrete.
4. Air Content.
If an air-entraining admixture is used, the air content shall be measured in accordance with ASTM C173 or C231 as applicable. Air content shall be tested periodically during the daily operation with a minimum of one daily check per mix design or when making strength test specimens.
Variations from the specified value of air content shall not exceed 1-1/2 percentage points to avoid adverse effects on compressive strength, workability, or durability.
A check on the air content shall be made when the slump varies more than ±1 in. (25 mm),
4. Air Content.
The volumetric method of measuring air content (ASTM C173) may be used on any type of aggregate, whether it is dense, cellular, or lightweight. The pressure method (ASTM C231) gives excellent results when used with concrete made with relatively dense, natural aggregates for which an aggregate corrections factor can be determined satisfactorily. It may not give accurate results for very harsh or low-slump mixtures. With such mixtures, the application of pressure to the surface of the concrete may not result in the expected compression of the air in the void system.
The volumetric method, ASTM C173, is not subject to this limitation and should produce accurate results on even the driest concrete. Although these tests
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temperature of the concrete varies more than
±10°F (6°C), a change in aggregate grading occurs, or there is a loss in concrete yield.
measure only air volume and not air-void characteristics, which can only be determined microscopically (ASTM C457), it has been shown by laboratory tests that these methods are generally indicative of the adequacy of the air-void system.
5. Unit Weight.
Unit weight tests of concrete in accordance with ASTM C138 shall be carried out at least once per week for each mix design regularly used, except for lightweight concrete, which shall be tested daily in accordance with ASTM C567 to confirm batching consistency. When the nominal fresh unit weight varies from the established value by more than ±2 lbs per cu ft (±32 kg/m3) for normal weight concrete or ±2%
for structural lightweight concrete, batch adjustments shall be made.
5. Unit Weight.
The unit weight is a quick and useful measurement for assessing quality. A change in unit weight generally indicates a change in either air content or aggregate weight. When unit weight measurements (ASTM C138 or C567) indicate a variation of the calculated fresh unit weight from the laboratory mix design of more than 2 lb per cu ft (32 kg/m3) for normal weight concrete, or ±2% for structural lightweight concrete, the air content should be checked first to establish whether the correct amount of air has been entrained. If air contents are correct, then a check should be made on the aggregates to ensure that the unit weight, gradation, moisture content, or proportions have not changed. Results of these checks generally will reveal the cause of the variations in unit weight of concrete and indicate what mix adjustments need to be made. After adjustments are made, the unit weight should again be measured.
The unit weight test results are used to calculate the volume or yield produced from known weights of materials and to calculate the cement content in pounds per cubic yard of concrete.
6. Temperature of Concrete.
The temperature of freshly mixed concrete shall be measured in accordance with ASTM C1064 and recorded when slump, air content, or compressive strength test specimens are made. This shall apply for every batch in hot or cold weather conditions and at the start of operations each day.
6. Temperature of Concrete.
Temperature of fresh concrete affects a number of properties of concrete. Warm concrete sets faster than cool concrete. Warm concrete requires more water per cubic yard than cool concrete to produce t h e same slump. For mixes of the same slump without admixtures, unless more cement is used in the warmer concrete, the concrete will have a higher water-cementitious material ratio. Warm concrete gains strength faster than cool concrete, but the strength at later ages may be lower than that of cool concrete. Knowledge of the temperature of fresh concrete permits the batch plant operator to adjust mixes. Concrete at higher temperatures requires more air-entraining agent to produce the same air content. Warm concrete tends to dry faster;
consequently, curing of warm concrete is even more important than curing of cool concrete. Also important is maintaining a given minimum temperature during cold weather concrete operations. This is to prevent freezing and ensure
appropriate strength gain, both during placement and during the initial cure time.
7. Air Temperature.
Ambient air temperature shall be recorded at the time of sampling for each strength test.
8. Welding.
Quality control shall verify welder’s quali-fication, make certain proper electrodes (oven dry) are used, and that a preheat temperature indicating device is on hand and used appropriately. Welder qualification shall be for the welding process, expected weld types, and position of welds to be performed. As a minimum, the welder shall be qualified for complete joint penetration groove welds and flare-groove welds.
The welder’s qualification shall be considered as remaining in effect indefinitely unless: (1) the welder is not engaged in a given process of welding for which the welder is qualified for a period exceeding six months, or (2) there is some specific reason to question a welder’s ability.
Personnel responsible for acceptance or rejection of welding workmanship shall be qualified. The following are acceptable qualification bases:
a. Current or previous certification as an AWS Certified Welding Inspector (CWI) in accordance with the provisions of AWS QC1.
b. Current or previous qualification by the Canadian Welding Bureau (CWB) to the requirements of the Canadian Standard Association (CSA) Standard W178.2.
c. An engineer or technician with training or experience in steel fabrication, inspection, and testing.
The qualification of the responsible personnel shall remain in effect indefinitely, provided such personnel remain active in inspection of welded steel fabrication, unless there is specific reason to question the personnel’s ability.
Inspectors shall have passed an eye examination with or without corrective lenses to prove: (1) near vision acuity of Snellen English, or equivalent, at 12 in. (305 mm); and (2) far
Visual inspection guidelines are given in AWS B1.11 while radiographic and ultrasonic testing procedures and limits are given in AWS D1.1 and D1.4. If required by specifications, radiographic
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vision acuity of 20/40, or better. Vision examination of all inspection personnel is required every three years or less if necessary to demonstrate adequacy.
testing (while very costly) is good, and ultrasonic testing is poor in detecting volumetric discontinuities, such as porosity. Ultrasonic testing is good for detecting planar discontinuities, such as incomplete sidewall fusion, while radiographic testing can miss such discontinuities unless oriented parallel or near parallel to the radiation direction.
Visual inspection for cracks in welds and base metal and other discontinuities should be aided by a strong light, magnifier, or other such devices, as may be found to be helpful.
Prior to welding, inspection shall include the following:
a. Review of welding drawings and welding procedure specifications.
b. Assuring that welding materials and con-sumables are in accordance with speci-fications.
c. Checking and identifying as -received materials against specifications.
d. Checking storage of filler material.
e. Checking welding equipment.
f. Checking weld joint preparations.
g. Checking for base metal discontinuities.
h. Establishing a plan for the recording of results.
Visual inspection during welding by the weld operator shall include:
a. Quality of weld root bead.
b. Joint root preparation, such as slag removal, prior to welding the second side.
c. Preheat and interpass temperatures.
d. Sequence of weld passes.
e. Subsequent layers for apparent weld qual-ity.
f. Cleaning between passes (use of a wire brush and chipping hammer to remove slag).
g. Conformance with the applicable pro-cedure, i.e., voltage, amperage, heat input, and/or speed.
Size, length, and contour of welds should be measured with suitable weld-size gauges. Groove welds should be measured for proper reinforcement on both sides of the joint. Quality control should compare the welds with three-dimensional
“workmanship samples” available from AWS.
These are actual welded samples, or plastic replicas of welded samples, that depict actual weld conditions.
The following items shall be inspected on at least 10% of all assemblies after welding to determine the quality of the welds:
a. Geometric imperfections. The fillet weld faces shall be slightly convex, concave, or flat, as shown in Figure 6.2.3(a) A and B.
Weld profiles exhibited in Figure 6.2.3(a) C are unacceptable. Figure 6.2.3(a) D and E
shows similar acceptable and unaccep-table profiles for groove type welds.
b. The weld metal and heat-affected zone of the base metal shall be free of cracks.
c. There shall be thorough fusion between weld metal, base metal, and successive passes in the weld.
d. All craters shall be filled to the full cross section of the weld, except for the ends of intermittent fillet welds outside the effective length.
e. Welds shall be free from overlap. Overlap is the protrusion of weld metal beyond the weld toe or root weld.
f. For materials less than 1 in. (25 mm) thick, undercut depth greater than 1/32 in.
(1 mm) in the solid section of the reinforcing bar or structural members shall not be allowed except at raised reinforcing bar deformation where 1/16 in. (1.5 mm) is permissible. For steel shapes or plates, refer to AWS D1.1 for the requirements of the specific structure type.
g. For reinforcing bars, the sum of diameters of piping porosity in flare-groove and fillet welds shall not exceed 3/8 in. (10 mm) in any linear inch (25 mm) of weld and shall not exceed 9/16 in. (14 mm) in any 6 in.
(150 mm) length of weld. For steel shapes or plates, refer to AWS D1.1 for the requirements of the specific structure type.
h. Incomplete joint penetration.
i. Slag inclusions.
j. Amount of distortion.
The size, length, location, and type of all welds shall be as shown on approved drawings. No welds shall be omitted or added without approval.
Weldments shall be checked after fabrication for brittleness by striking at least one out of every 50 pieces with a 3-lb (1.3-kg) hammer.
Brittle weldments will break under a hammer blow. When such brittle weldments are found, all assemblies made using similar procedures shall be considered suspect and checked for acceptance.
Deficient welds shall be corrected by rewelding or removal in accordance with specified procedures.