C. CONCRETE
- Concrete must meet all the requirements of Chapter 11 of the 2006 City of Lincoln Standard Specifications.
- Make a minimum of one set of 3, 6" by 12", test cylinders for each concrete mix to represent each day's construction. On large pours make a set of 3 cylinders to represent each ½ days work. Additional sets may be required at the direction of the Engineer.
- Notify the City Testing Lab prior to the start of each concrete placement of 100 cubic yards or more to allow for plant inspection.
- Each concrete placement of 100 cubic yards or more shall require air, slump, and concrete temperature tests in addition to one set of 3, 6" by 12" cylinders for each one half day's construction. Tests should be run after any adjustments to the mix at the project site and cylinders should be made after the tests to be representative of concrete incorporated into the structure.
- If concrete is pumped, tests must be run and cylinders fabricated from concrete sampled after the pump with the hose at approximately the same angle as required for the structure and not from the hose lying horizontal along the ground.
- Notify concrete plant personnel of test results as soon as possible after testing to allow for adjustments to the mix.
- If field tests indicate a need for a plant adjustment, additional tests should be run and cylinders fabricated after adjustment.
- On large pours, an initial one or two loads of concrete which is slightly out of the specification range for air and/or slump (+/- 0.5% air, or +/- 0.5 inch slump) may be incorporated into the structure as long as immediate action is taken to adjust the mix within the specification range on all subsequent loads and is verified with test results.
- If the air content of the concrete at the job site is less than the minimum specified, only one addition of air-entraining admixtures to a load is allowed. If the air content is then outside the limits specified, the load of concrete shall be rejected.
- Admixtures which are not incorporated into the mix at the plant shall not be added to individual loads of concrete at the job site to enhance work-ability or pump-ability without permission from the Engineer.
- Admixtures shall not be added to individual loads of concrete at the job site to reduce either air content or slump without permission from the Engineer.
- No Class "C" Fly Ash Modified Concrete is allowed in City of Lincoln concrete pours. Refer to Chapter 11 of the 2006 City of Lincoln Standard Specifications.
- Deliver each set of test cylinders to the City Testing Lab for compression testing on the day following fabrication or on Monday if the pour occurred on Friday or the weekend.
- Test cylinders delivered to the City Testing Lab shall be accompanied by a cylinder identification envelope (may be obtained from the City Testing Lab) containing the following information: date, time of fabrication, project number and location, test location within project, structure, method of cure of both structure and test cylinders, method of placement, weather conditions at the time of testing, mix, concrete plant, truck number, air, slump, and temperature tests if ran, amount of water, if any, added to the sample load represented by tests, in gal./cubic yard.
- Truck delivery tickets indicating mix, plant, batch size, aggregate moisture, material weights, and admixtures must accompany every load delivered to the project site on City of Lincoln concrete pours and a copy of this ticket representing the load tested must accompany the test cylinders delivered to the City Testing Lab.
- Each set of cylinders will be tested for compressive strength at 7 days and 28 days. The third cylinder will be an early break, tested prior to 7 days, depending on concrete mix and when made. If a specific age is desired, it should be indicated on the cylinder identification envelope. If more than one early break is desired, then additional cylinders should be fabricated and ages indicated on cylinder identification envelope.
- Cylinder break reports will be faxed from the City Testing Lab to the Engineer on a weekly basis.
