One of the things that occurred to me today as I was working on the new wall we are building is the fact that we are participating in an activity that humans have been pursuing for quite some time.
Concrete has been in use since Roman times. Many of the buildings that still exist in Rome were built using concrete. The Romans had not discovered using metal reinforcing in their concrete structures, but they used aggregate and rubble and cement to build their roads and the aqueducts. Some places on the web claim that the secret of making concrete was lost for many centuries and was not rediscovered until a British engineer rediscovered it in 1756. Frankly, I’m not buying this story because if you look around Europe you can see plenty of evidence of cement being used in the interim.
For example, in Ronda, Spain, the Puente Viejo (Old Bridge) was built in 1616, and it clearly shows evidence of being made using very similar construction techniques as Jim and I are using today.
Additionally, in Lisbon the Castelo de Sao Jorge has slip form construction all over.
This hill was initially fortified by the Romans, followed by the Visigoths and then the Moors. In 1147, the first king of Portugal, Alfonso Henriques, captured the castle and it was used as the royal palace for several centuries. I’m not sure exactly who built the walls in the next photos, or when, but it is obvious that cement was being utilized. Additionally, these arrow slits show that the builders were happy to use any material that was hauled up the hill to the building site.
This wall is a great example of the opportunistic use of materials in castle construction. Notice that they didn’t always bother to use worked stone for their walls, but when it was available it was used to good advantage. In the following picture you can see how the builders made the outside corner of the castle wall using the worked stone they had available. The rest of the wall has whatever rock they came across.
Our wall continues to grow nicely, and we have gotten better at the technique.
This whole exercise is sort of like going to the gym and doing squats for a few hours at the same time you are lifting light weights for many many reps. The difference is that when you are done with this kind of workout, you have something concrete to look at.
the havens 
I am anxious to see how the finished product will look!
Good luck with all the hard work.
Actually I do the squats so that when I do have to huck a rock or two I can pull it off. One reason, anyway.
Oh, chuckle, chuckle “something concrete to look at”
The photos are fascinating. It always amazes me that with nothing other than good old mathematics and some basic principles of physics, it’s possible to build something that lasts for centuries or millennia.
I miss Lisbon… 😦
I miss Seville. You wouldn’t believe how often Jim mentions it fondly. I think he wants to move to Spain.
I wonder how much of those old walls have been more recently ‘renovated’ though? The Spanish are rather keen on that – they don’t like their old buildings falling down and who can blame them, but it makes it much more difficult to determine just what is ‘original’ and what is a sympathetic restoration.
Similarly, I think that concrete and cement are counted as two separate substances: the one being a building material in and of itself and the other just the stuff which held larger blocks of stone and rock together and in place. The Romans certainly seem to have invented water-proof concrete (using it to great effect in the basement of the Colosseum, which was flooded in its early days so that mock sea battles could be staged in the arena) and that ‘secret’ wasn’t rediscovered til much later.
Sorry for being a pedant – I’m just completing a spread on Roman inventions and building techniques, so I’m metaphorically up to my eyes in this kind of trivia… 😉
Jim has been after me all week to learn the difference between cement and concrete. You are right about cement being an ingredient, the one that makes everything stick together once it has gone through its hydrolyzing reaction and cures. I am not sure that you can really say that cement and concrete are two separate substances in that if you don’t have cement in there you won’t get concrete but a pile of sand and gravel.
We are building a stone wall with mortar between the rocks. The mortar is a mixture of sand, water and cement. Concrete is a specific mixture of water, cement and aggregate. The quality of the aggregate is very important to the strength of the concrete formed in that particular mix. Apparently there is a maximum size your gravel can be and a particular distribution of sizes of particles with a ratio between the different sizes.
I did not know that the Romans flooded the basement of the Colosseum so they could have mock sea battles. Boy, they really did bread and circuses well!
Nothing wrong with being a pedant. God knows I spend enough time lecturing here, I have no problem hosting a guest lecturer!
I believe cement is a component of concrete.
Those Romans… they could have conquered the world if they hadn’t gotten so greedy and decadent. Oh, wait….
See my answer to Woo above. You are right.
Bread and circuses! We need more of that, right? The modern american version: Fast food and video games.