Concrete Placement Inspection 3

[wehr6]

Does anyone have a list of things they look for during a concrete pour (placement), including what they will allow and will not allow, any rules of thumb as to how the conrete slump and strength is effected by adding water?

 

[SlideRuleEra]

Here is a general purpose checklist for a contractor's placement preparation

http://www.concreteconstruction.net/pclinic/pc_template.asp?ProbClinicID=J950758A

As an engineer, be very careful about "on-the-spot" direction of a contractor (under the terms of many contracts this action can relieve the contractor of responsibility). If properly prepared, the drawings and specifications should speak for themselves - all you have to do is see that they are enforced.

As for water added to the concrete (at the jobsite); added water typically increases slump and decreases strength. One "trick" that many contractor's may try is to sample the concrete for test cylinders, THEN add water. My advice in this situation: If they choose to add water, have the contractor take another sample for a replacement set of cylinders. Discard the old ones.

http://www.SlideRuleEra.net

 

[crossframe]

SlideRuleEra makes an extremely important point about directing the work of the Contractor and the subsequent liability.

When I was in that situation, I used the mix design to determine the maximum amout of water that "could" be added to a given mix and still meet the specifications. I would then let the Contractor add all the water he wished. I said it was up to him to decide how much if any to add, but if he exceeded that maximum, I would rejected the entire load. If, after water was added (AND the drum rotated enough times at a proper mixing speed), the concrete looked the least bit suspicious, I would take my cylinders then.

After a while, you'll begin to get a feel for the tolerance of the mix.

 

[techmaximus]

ACI SP-2 --- ACI Manual of Concrete Inspection
Chapter 23 - Checklist of Inspection

This chapter provides a complete list of items to inspect before concreting, during concreting, and after concreting.


Techmaximus

 

[techmaximus]

FYI, the rule of thumb on addition of water at the job site is 1 gallon, or roughly 10 lb. (5 liters or 5kg), of water added to 1 cubic yard (cubic meter) of concrete increases the slump about 1” (25mm). If this added 1 gallon water is in excess of the design mixing water the strength of the mix will be decreased about 200 PSI or about 5% on average. The addition of water over the design mixing water decreases strength and increases susceptibility of cracking. Per ASTM C94, water can be added to the mix when the truck arrives on the jobsite as long as the specified slump and/or W/C ratio is not exceeded.

Techmaximus

 

[techmaximus]

Also, the National Ready Mixed Concrete Association sells a neat little package of informative articles called a CIP (Concrete in Practice). It’s only $20 and each article is packed with good info. Info on this series of articles can be found at:

http://www.nrmca.org/aboutconcrete/cips/default.asp

Techmaximus

 

[techmaximus]

This info might be helpful....

From the ICC Concrete Manual

TABLE 25.1
SPECIAL INSPECTOR JOB TASKS FOR REINFORCED AND PRESTRESSED CONCRETE
I. GENERAL REQUIREMENTS
1. Duties and Responsibilities
Review approved plans and specifications for special inspection requirements. Comply with special inspection requirements of the enforcing jurisdiction.
2. Notification of Discrepancies
Notify the contractor of deviations from approved plans and specifications. If the deviations are uncorrected, notify the architect or engineer of record and the building official of deviations.
3. Inspection Reports
Submit progress reports to the architect or engineer of record and the building official, describing tests which were performed and compliance of work. Submit final summary report stating whether work requiring special inspection was in conformance with the approved plans and applicable provisions of the building code.
II. CONCRETE QUALITY
1. Mix Verification
Verify that individual batch tickets indicate delivery of the approved mix as specified. Verify that concrete ingredients conform to acceptable quality standards. Verify time limits of mixing, total water added, and proper consistency and workability for placement.
2. Testing
Determine the required type, quantity and frequency of tests to be performed on fresh and hardened concrete. Observe sampling of concrete, field testing of fresh concrete, and making of test specimens. Verify that the required concrete strength has been attained prior to tendon stressing.
3. Specimen Handling and Protection
Provide or arrange for proper specimen identification, site storage and protection, and transportation to the testing laboratory.
4. Test Reports
Provide or arrange for communication of field testing results to the architect or engineer of record and to the building official.
III. REINFORCEMENT
1. Quality
Verify that reinforcing and prestressing steel are of the type, grade and size specified and are in conformance with acceptable quality standards. Verify that the prestressing tendon system is fabricated in conformance with acceptable quality standards. Ensure that reinforcing and prestressing steel are free of oil, dirt, and flaking rust and that steel is properly coated and/or sheathed as specified.
2. Tolerances
Verify that reinforcing and prestressing steel are located within acceptable tolerances, and are adequately supported and secured to prevent displacement during concrete placement.
3. Cover
Verify that minimum concrete cover is provided.
4. Placement
Verify that placement of reinforcing and prestressing steel (or ducts) complies with required spacing, profile and quantity requirements, as indicated by both the approved plans and placing drawings, or installation drawings.
5. Details
Verify that hooks, bends, ties, stirrups and supplemental reinforcement are fabricated and placed as specified.
6. Splices
Verify that required lap lengths, stagger and offsets are provided. Verify proper installation of approved mechanical connections per the manufacturer’s instructions and/or evaluation reports. Ensure that all weldments are as specified, and have been inspected and approved by an approved welding inspector.
7. Prestressed Rock and Soil Anchors
Verify that prestressed rock and soil anchors are fabricated and installed in accordance with national standards or with project specifications.
IV. PRESTRESSING AND GROUTING
1. Stressing
Inspect for proper equipment calibration. Verify that proper stressing (or tensioning) sequences are used, proper jacking forces are applied, and acceptable elongations are attained and recorded.
2. Anchorage Protection
Verify that tendons and anchorages are properly sealed or otherwise protected from corrosive environments.
3. Posttensioning Ducts/Grouting
Verify that ducts are of the required size, are mortar-tight, and are nonreactive with concrete, tendons and grout materials. Verify that proper grout materials, strength and grouting pressures are used as specified by the manufacturer.
V. FORMWORK, JOINTS AND EMBEDS
1. Formwork Construction
Verify that formwork will provide concrete elements of the specified size and shape.
2. Construction Joints
Verify that the location and preparation of construction joints are in accordance with the approved plans, specifications and building code requirements.
3. Embeds
Verify that the type, quantity, spacing and location of embedded items are as specified.
VI. CONCRETE PLACEMENT, PROTECTION AND CURING
1. Preplacement
Verify acceptable condition of the place of deposit before the concrete is placed.
2. Placement
Verify that methods of conveying and depositing concrete avoid contamination and segregation of the mix.
3. Consolidation
Verify that concrete is being properly consolidate during placement.
4. Protection
Verify that concrete is protected from temperature extremes and that proper curing is initiated.


Techmaximus