Oregon

Building Distinct Concrete Bridges
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Building Distinct Concrete Bridges

Decorative concrete bridges preserve communities’ cultural identities. Oregon has... More

The Concrete Prodcuer 2014 Survey Round-Up
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The Concrete Prodcuer 2014 Survey Round-Up

Here are the articles and web extras from the 2014 The Concrete Producer Survey. More

The Concrete Producer Survey: A Rebuilding Year
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The Concrete Producer Survey: A Rebuilding Year

Producers try to make the most of an improving economy by focusing on core... More

Family-owned producer expands operations.
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Family-owned producer expands operations.

Molalla Redi-Mix & Rock Products is a small family-owned producer that knows the... More

Health Impacts of Products are new Focus in LEED v4
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Health Impacts of Products are new Focus in LEED v4

The USGBC's release of version 4 of the LEED rating system (LEED v4) includes new... More

Sustainable Strengths
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Sustainable Strengths

A new study brings home concrete's greenest assets. More

Reducing Emissions Pays Off
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The Rush to Build Bridges
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Fly Ash in Concrete Pavement

What are the effects of using fly ash in concrete pavements? Does it have an impact on abrasion resistance of the mix? Are case studies or field data available, especially where more than 30% fly ash was used in the mix? More

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Does Intermediate Rounding Decrease Accuracy?

I have a further question regarding the rounding of compressive strength results (ôHow Precisely Should Labs Round off Compressive Strength Results?ö April, page 26).At our lab, we test 4x8-inch and 6x8-inch concrete cylinders for compressive strength, and we round to the nearest 10 psi according to ASTM C 94, ôSpecification for Ready Mixed Concrete.ö We also test 2x2-inch cement cubes, which are the subject of my question.According to ASTM C 109/C 109M, ôStandard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or [50-mm] Cube Specimens),ö when calculating compressive strength of the cubes, a technician must average the compressive results of three test specimens. If the deviance of a specimenÆs result strays from the average by more than a specified maximum, it should be discarded. The average of the remaining two is taken, and the calculation procedure is repeated, but the maximum specified deviance from the average is lower between two specimens than among three specimens. In other words, after we round the compressive values from the 3 cubes, additional calculations often follow. Why intermediately round after determining the ratio of applied load and surface area (compressive strength) when I can measure the cubes to 0.001 accuracy, and our loading machine measures to the nearest 1 psi? DoesnÆt intermediate rounding introduce greater and unnecessary error? I understand rounding to the nearest 10 psi on the final result when no other calculations will be needed. It seems like this goes against everything we learn in the classroom about significant figures and propagation of error. Jack LaphamEngineering, Oregon State University More

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