architecural concrete is black

http://www.merriam-webster.com/dictionary/architectural%20concrete

that was really hard....

architectural concrete wears glasses with bold, chunky frames

an alternative to architectural concrete would be rammed earth.

It is a heavy, rough building material made from a mixture of broken stone or gravel, sand, cement, and water, that can be spread or poured into molds and that forms a stonelike mass on hardening used as a structural and decorative material.

I think the distinction you are looking for is between architectural and structural concrete. Architectural concrete usually has some additional specific specifications for finish because it will be exposed along with the typical specifications for concrete strength and mix that is only structural. It might be things like pattern, grind, stain, seal, tie holes filled ect. 

What JonathanLivingston said.

But also this: 

Concrete is the most careless, promiscuous stuff until it is committed, when it becomes fanatically adamant. Liquid rock, concrete is born under a sign of paradox and does not care. It doesn't care about anything, lazy and in love with gravity but only half in love. Pour concrete on the ground and it will start to puddle and spread, in rapture to gravity but then will think better of it: enough spreading! Concrete can't be bothered; it heaps up on itself in lazy glops, sensual as a frog.  

- from Peter Schjeldahl's Concrete and Scott Burton. It goes on and on like this.

I've seen the term "architectural concrete" often used to describe concrete flatwork with a specialty finish texture and/or color, such as an exposed pebble aggregate, or embedded sand finish.  It usually refers to an upgraded finish, as opposed to a simple floated slab.

The American Concrete Institute defines architectural concrete and has more stringent requirements for it than structural concrete in ACI 301 Section 6. It is more than just picking formwork and plugging tie holes. It also gets into requirements for concrete placement, etc. as well that most contractors don't know about and don't follow. 

Also see ACI 303.1 Standard Specification for Cast-in-Place Architectural Concrete.

For getting examples ... I would start talking to contractors and asking them for examples of their architectural concrete. This will give you a much better idea of what you can expect in your particular area for quality and workmanship. Even then, require a mockup.

concrete that is used exclusively for architecture :)

Ooh, as Everyday Intern brings up: I am familiar with a project in which a significant proportion of the lower level CIP concrete walls are visible (sloped site). The specs say that the front wall, most visible as one approaches the building, is to be done in a continuous pour with no cold joints. Of course the contractor ignored this, and when formwork was pulled there was a big highly visible cold joint ruining the front wall. This is the kind of situation that doesn't matter in structural concrete, but architectural concrete specs will address.

Thanks Donna. Do you know if the concrete was actually specified as "architectural concrete" and not simply structural concrete with some added language for continuous pours, no cold joints, etc.? Either way the contractor ignored the specs (which is a contract administration problem). I'll point out that the references I gave above address that type of situation and it wouldn't need to be spelled out in the specs if the standards are referenced. 

ACI 303.1 Standard Specification for Cast-in-Place Architectural Concrete sections 2.3.2.6 through 2.3.2.9 cover specific requirements for placement in max. 3 foot high layers for consolidation, vibration of concrete overlapping zones of influence min. 50%, not hitting the face of the formwork with the vibrator, re-vibrating the top 6 inches between lifts if there is a delay in placement as long as the vibrator can penetrate the surface under it's own weight up to 30 min., etc.

However, not only is it important to specify the architectural concrete correctly, but you also need to be sure the contractor is aware of what is in the specifications. This is why seeing examples and getting a mockup are important. Probably also a good idea to have a pre-installation conference. Better yet would be to also bring it up during a pre-con or pre-bid meeting.

In my experience, when we talk about architectural concrete in my office, no one really understands the level of effort and detail that need to go into it to get it right. Everyone wants the look, but no one wants to pay for it (in both time and money). It takes time for the designer to design and document it correctly. It takes time for the contractor to construct it. It takes money to get it right, or to tear it out and do it again to get it right the second time, if a client is really serious about the aesthetics.