Concrete Construction Online Magazine: Specifications & Testing

Floor Slab-on-grade Thickness

Fri, 15 Mar 2013 02:55:00 EST

Is the tolerance for the thickness of a floor-on-slab grade +3/8 inch and -1/4 inch?

Testing for Air in concrete

Mon, 1 Oct 2012 04:10:46 EST

Air content of concrete is usually tested with a pressure meter.

Too Much Air?

Fri, 16 Dec 2011 01:21:34 EST

The specifications for entrained-air content always include both minimum and maximum limits. I know that having too little entrained air reduces the concrete's resistance to freeze/thaw and deicer damage.

The Importance of Reading Blueprints

Wed, 15 Dec 2010 04:51:32 EST

In Part 1 of our series on the importance of being able to read contract specifications, we look at reading blueprints.

Nondestructive Strength Testing

Sun, 12 Dec 2010 08:46:38 EST

Is there a way to determine the compressive strength of concrete in-place, without removing samples for laboratory testing?

Controlling Moisture in Concrete Slabs

Sun, 12 Dec 2010 08:42:14 EST

Controlling moisture in concrete slabs can be tricky, but it's one of the most important factors a contractor needs to focus on.

What Caused This Scaling?

Sun, 12 Dec 2010 08:58:12 EST

Home builders here in the Denver area recently have had a rash of scaling driveways. Literally hundreds of driveways constructed over the past two to four years are showing isolated to widespread scaling. Our firm and others have met with the builders to help determine the causes. We have conducted petrographic analysis and chloride ion testing, and have generally concluded that the concrete was of lower quality, poorly placed, finished, and cured, as well as having poor air content or air spacing. Can you comment on this?

Testing SCC in the Field

Fri, 10 Dec 2010 06:15:35 EST

Questions about field tests for SCC are answered.

Standardized tests for SCC

Fri, 10 Dec 2010 06:10:38 EST

We are thinking about proposing the use of self-consolidating concrete on an upcoming project, but one challenge we face is coming up with acceptance criteria everybody feels comfortable with. What’s going on with the development of standardized tests for SCC?

Calibration and certification

Fri, 10 Dec 2010 06:05:43 EST

Do you have to be certified to calibrate equipment used for air pressure in concrete?

Air Test Variability

Fri, 10 Dec 2010 06:05:51 EST

Is it common to get different air readings when using a pressure meter and a roll-a-meter or volumetric meter? I continually get a difference of about 0.8% to 1%, but I feel very sure my meters are calibrated correctly. The higher reading is from the pres

Concrete Too Salty?

Fri, 10 Dec 2010 06:05:57 EST

Does the water for concrete have to be completely void of salt (from seawater)? What happens if it is not?

Core Test at 85%

Fri, 10 Dec 2010 06:04:37 EST

ACI 301-99, Section 1.6.7.3, regarding core test results, maintains that concrete represented by core tests is considered adequate when the average compressive strength of the cores is equal to at least 85% of the specified strength. I’m looking for any information that explains the basis for this claim.

SCC for Piles

Fri, 10 Dec 2010 06:04:44 EST

We are considering using self-consolidating concrete in bored cast-in-place piles up to 20-m deep. How can we check the level of compaction? Are there clear specifications for testing SCC and test specimens preparation? We cannot locate any ASTM or similar standards or material and workmanship specifications for SCC.

Slump Test Outdated?

Fri, 10 Dec 2010 06:04:01 EST

I seem to remember reading that testing for slump was very outdated and that there is really no difference between a 5-inch slump and 61/2-inch slump. Is this true?

Excessive Water Beneath Slab

Fri, 10 Dec 2010 05:58:22 EST

Our home is 2.5 years old, and the basement slab is constantly wet. Water is moving from the subgrade through the concrete. We did a pH test on the moisture, and it has a considerable acid content. The carpet, which was glued to the concrete, has come loose. What can we do about this problem?

Use Pad Caps When Testing Cores?

Fri, 10 Dec 2010 05:59:57 EST

ASTM C 42-99, Standard Test Method for Obtaining and Testing Drilled Cores and Sawed Beams of Concrete, requires measuring the length of the capped specimen to the nearest 0.1 inch (2 mm) and using this length to compute the length-to-diameter ratio prior

Effect of Concrete Strength and Slab Thickness on Floor Strength

Fri, 10 Dec 2010 05:59:51 EST

The specification for the floor of a maintenance building called for a 6-inch slab thickness and concrete with a design compressive strength of 3000 psi. The actual average cylinder strength for the floor concrete was 3630 psi. Four months after the floor

Gas from Concrete?

Fri, 10 Dec 2010 05:59:11 EST

We're building a concrete home for an owner who heard that concrete emits gas as it cures.

Vertical Rebar Placement in Footings

Fri, 10 Dec 2010 05:56:22 EST

When placing vertical rebar in a residential footing, is it necessary to tie them in place before the concrete pour, or can workers just "stab" them in after the concrete has been placed and struck off?