Severud Associates Consulting Engineers PC

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Severud Associates Consulting Engineers PC

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Typical Concrete Strength and Stiffness Specs for High Rise (Over 500 feet) in NYC

Spec concrete strength 6 ksi to 12 ksiActual concrete strength 6 ksi to 19 ksiSpecified E value 4.7Mpsi to 6.6MpsiActual E value 8Mpsi maxNo. concrete mixes 10 - 20w/c ratio 0.29 to 0.35 (verified by microwave test)

Concrete Placement Rules

95% max water content added at the plant. Max 5% water available for addition at the site.

5% held water added on site only to raise the slump of the concrete.

Superplasticizer to be made available on site during all concrete placing operations, for re-dosage as required. All trucks delivering to the site shall be supplied with a re-dosage chart.

All concrete trucks arriving to the jobsite will have a computerized batch ticket to be given to the inspector for review prior to pouring concrete.

The batch ticket must indicate truck number, total batch size, strength in psi, time of discharge, amounts of materials added at the plant, percentage of moisture in the aggregate.

Trucks arriving on site without the computerized batch ticket shall be rejected.

Concrete Placement Rules (cont.)

Pre-approved design mixes and admixtures only. A pre-approved mix is defined as one having the exact same constituent proportions and constituent sources. Any truck arriving on site with a mix or admixture that is different than the approved design mixes shall be rejected.

Pour time limit = 90 minutes after leaving plant, with a possible extension to 120 minutes (pending the temperature of the concrete).

However, if the mix is provided with a hydration control admixture that has been pre-approved, this time limit may exceed 120 minutes.

Lab shall measure concrete temperature after 90 minutes.

700F < Temperature < 900F : Inspector’s or Engineer’s call

Temperature > 950F : concrete is rejected regardless of mix time

Temperature < 500F : concrete is rejected regardless of mix time

Concrete Placement RulesTime > 120 minutes : concrete is rejected (unless the mix is provided with a pre-approved hydration control admixture)

Slump exceeds max value shown on design mix (with tolerances): concrete is rejected

No concrete placement without both Severud and the testing lab present

An insulated coring box with sufficient room to place all the required samples shall be provided on site.

A microwave oven will be provided at the site to verify the moisture content in the concrete in accordance with the specifications.

Slump tests for every 50 yards of concrete placed, and at any time upon a request from Severud, at the point of discharge (at the truck).

The contractor will be responsible for delivering the required samples from the point of placement to the concrete inspector on request every 150 cubic yards if concrete is placed using a pump.

Typical 8,000psi Mix – Vertical Elements

Typical 8,000psi Mix – Vertical Elements

Typical 10,000psi Mix – Vertical Elements

Typical 10,000psi Mix – Vertical Elements

Typical 12,000psi Mix – Vertical Elements

Typical 12,000psi Mix – Vertical Elements

Modulus E Chart for Test Cylinders

Modulus of Elasticity and Poisson’s Ratio: ASTM C469 / C469M–14

Microwave Oven Testing

• Used to test water content and water cementitious ratio of discharged concrete at the site

• AASHTO T318 for Guidelines• One test per every five trucks (or fifty yards), typically• Used for verification of water content, not for rejection*

• * if it is a frequent issue, rejection and remediation will be required

Microwave Test Equipment(Courtesy of National Concrete Pavement Technology Center)

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