"Composite concrete" question 2

[PresidentEvil]

I found this in a book, and it puzzled me, with regards to how a composite cement is defined:

Composite cements are cements in which a proportion of the Portland cement clinker is replaced by industrial by-products, such as granulated blastfurnace slag (gbs) and power station fly ash (also known as pulverized-fuel ash or pfa), certain types of volcanic material (natural pozzolanas) or limestone.

...

According to statistics supplied by the association of European cement manufacturers (Cembureau) the average proportion of ‘pure’ Portland cement delivered in European Union countries was 38% in 1999 the remainder being ‘composite cements’. The proportion of composite cements in the UK is at present very much lower, and the UK also differs from most European countries in that the addition of ground granulated blastfurnace slag (ggbs) and fly ash at the concrete mixer is well established.

Currently (2002), although there are regional variations, most of the ready-mixed concrete produced in the UK contains either ggbs (at ~50% level) or fly ash (at ~30% level).

I don't get it. In the sections I put in bold:
1. They suggest UK does not use very much composite cement.
2. They say that adding ggbs or pfa at the mixer is commonplace in the UK. Doesn't that make the cement composite, suggesting composite cement is also commonplace?
3. They say most of the ready-mixed concrete in the UK contains either ggbs or pfa. Doesn't that also suggest that composite cement is commonplace in the UK?

What am I missing? It must be in the definition of composite cement, but I thought that was defined clearly at the start.

Thanks.

 

[hokie66]

I think someone didn't proofread the text. If you substitute "higher" for "lower" in the first of your bold sentences, the quote reads coherently.

What they call "composite cement" is normally referred to as "blended cement" in the US and Australia.

 

[Ron]

I get something a bit different from the bolded statement. It would appear to me that someone is comparing the production of "composite" cement in 1999 to the present, with production of the composite declining after a probable peak.

Agree with hokie66 on terminology. In the US it is a blended cement.

Blending in the US is most commonly done at the batch plant, not at the cement clinker level. The reason for this is the amount of control afforded the designer of the mix. If the designer wants to use 30% GGBFS and 12% Fly Ash with 58% Type I or other portland cement, he can do so. When the cement is produced as a blend, the designer has no control over the percentages of blend constituents.

As for the proportion of concrete mixes that contain some blend of cements or cementitious materials, it is quite high, mainly because of the cost of production of portland cement and the occasional production lapses (real, created or imagined) in the portland cement business.

 

[msquared48]

The word "Composite" is used in the US in the term "Composite Concrete", where metal studs are welded to the top flanges of steel beams and cast into a concrete slab, effectively increasiong the section properties of the steel beam to support additional "live" or "superimposed" loads.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[hokie66]

All gobbledygook, isn't it? Title of the OP's thread says "composite concrete", then the text goes on to talk about "composite cement". The paragraphs are confusing and contradictory...wish these UK writers would learn a bit of English.

 

[Ron]

Best post of the day, hokie!!!

 

[PresidentEvil]

Sorry, the title of the thread should have been "composite cement". (Believe me, I usually wouldn't confuse the two. Perhaps it's due to the fact I spent so long searching for a "concrete" forum, but it's pretty inexcusable. I just can't seem to find a way to edit it.)
Everything in the quote however is directly from the textbook "Advanced Concrete Technology: Constituent Materials" edited by John Newman and Ban Seng Choo.

Thanks for all your quick responses.

 

[IDS]

It seems to me that the quote in the OP is differentiating between adding the slag or fly ash to the cement, thus forming a composite or blended cement, and adding it directly to the mixer.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[hokie66]

On rereading (for about the third time), I believe you are right, Doug. I wasn't aware they did it that way in the UK, so my brain wouldn't process that option.

 

[concretemasonry]

There is the common practice of intergrinding Portland Cement with other production materials (fly ash, pozzolanics, etc.) to produce a uniform, controled cement for different ASTM specifications or needs. In the U.S, it is usually refered to a interground to meet a specific standard, but there are different words used elsewhere.

With this, there is less need to add resort too much of the dosing and changing at the batch plant.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.