Women in Concrete

I'm talking women in the business of concrete, not women actually in concrete, that would be injurious to their health (for those who don't know; concrete mix burns and can kill you if you get too much of it on your skin). There are many good women in concrete, one I recently read about owns Tec-Crete Transit-Mix Corp of Queens, New York, NY.

http://teccretenyc.com/pages/about-us/

Founded in 1998, owner Ms Linda Gisonda won a Women Business Enterprise (WBE) award in 2013. Yay. 

Tec-Crete have a total of 4 dry batch plants across two locations. As their name suggests, this will be an operation where the ingredients for the concrete are discharged into the truck, water is then added to the agitator on the back of the truck and the mix is completed while the truck drives to the site (alternatively, a dry batch may make its way to the job site with water and the mix completed at the destination). What dry batching allows for is longer delivery distances, however that generally comes at the expense of payload, as a heavier truck is required to do the mixing.

Another way of doing things, very popular this, is to completely mix at the plant, the mix is then discharged into the agitator on the back of the truck. This type of plant is called central mix. The advantage of this is fast batching, and the mix can be discharged into anything, even a dump truck. Another advantage is smaller trucks fitted with lighter agitators can be used to deliver the same or greater payload, however they can only do so over a much shorter distance compared to transit mix. 

So there we have the age-old quandary, tyranny of distance vs capital cost vs operating costs. Which is better? My father always preferred central mix and spoke of its advantages often. Transit mix certainly comes into its own if distance is a factor (or waiting times before discharging loads), which is often the case in Australia for instance.

Like this:

Distance or waiting times, lower cost of batching plant, heavier trucks required (less payload), higher cost of running trucks = Transit Mix.

Short distance or waiting times, higher cost of batching plant, lighter trucks (more payload), lower cost of running trucks - Central Mix.

Sand Wars

I watched the documentary Sand Wars on al Jazeera recently, it was interesting but ultimately came up short, and that's because the documentary lacked balance and became emotive.

I know something about sand. Some may call me an expert on the subject but I wouldn't go that far, I'd call myself a specialist. That said there are several things to consider about sand and where to find it, how to process it. Sand is critical for construction, the oceans, and our coastlines. We can't have a civilisation without sand and our environment is jeopardised if we extract too much ot it. So what is the answer? That's what I'm going to deal with here:

1. Natural or Man-made?

The above documentary never once considered quarried rock being transformed into sand. They did have someone at an aggregate trade show or conference saying that all the natural deposits of sand and gravel had been taken away. That is nonsense.

There is a rule in the sand business; first find a natural deposit. This can be quite difficult as a lot of factors need to be considered when searching for a suitable extraction pit. Such things as distance to market or end-user, ease with which the resource can be extracted, the physical properties of that resource having a bearing on just how much processing is involved, water sources and so on. But increasingly regulation and the NIMBY effect come into it as well. There is a lot of natural, clean sand out there, you're just not allowed to touch it because of that last factor.

So what now then? You have to manufacture that sand at your already operationally consented rock quarry. This is not an easy exercise and involves complex machinery which can be very expensive. Even when set up the end-product can be of much lesser quality than the natural equivalent. It doesn't have to be, but man is fallible and they don't always get it right.

Is sand running out? The short answer is No.

2. Sand from the Sea or Beach.

This is generally not the answer as salt comes with the sand. Sand dredged from below the sea is not as heavy with salt as beach sand is, but this source of sand still requires further processing, or thorough washing before it can be used in construction. The documentary said that buildings in Tangiers may fall down because they're built with sand from the sea. If the sand is salt ridden then the structures would be weakened over time due to the rusting of the reinforcing steel inside the concrete. The buildings would be fine if that sand had been washed sufficiently or simply came within specification without further processing.

How much sand comes from dredging operations? Much less than you're led to believe. Ships are a pain in the arse and you can't see below the water. Even land based dredging from wet pits or lakes is thwart with difficulty. I've seen the figures on this and sand dredging is still the little bedfellow on the block in terms of the whole.

3. Recycling and Blending.

Not just glass, but concrete can be recycled also. Valuable sand and other aggregates can be re-extracted. This extends the life of existing in-ground resources. But also overlooked is blending the sand. That is, taking some man-made, some natural and maybe some recycled resource and blending them together. A pugmill or similar process can do this most effectively.

4. Concrete

There are few alternatives to this amazing stuff called Portland Cementous Concrete. Our world does not function without it and we have got to learn to manage it. People talking about straw bale houses is not the answer. Yes we can use wood and steel and such but what the Romans knew all along and the rest of the world woke up to in the nineteenth century is that Concrete is the answer. If in doubt concrete it.

If you have a sand deposit and don't know what to do with it, or need help in any way, then please contact me using the contact form on this page. I'm here to help.

Concrete To Revolutionize Heating

Interesting stuff from the Swiss, Ettringite concrete, reported below from DW TV. Concrete blocks are made which heat when exposed to water. Copper pipes are threaded through the blocks, which act as a heat exchanger. The hot water then circulates through the house, heating it. 

DW TV Video

It would take only a few blocks to heat an average size home all winter. Would these blocks last? It appears they will, at least as long as the home will, which has got to be something worth considering. Are they expensive to produce? Simple answer - I don't know, but the process looks a little complicated, the blocks heat up when made, can they explode if you get the recipe wrong?

One of the guys featured in the video can be found here...

Frank Winnefeld of Empa - the Swiss Federal Laboratories for Materials Science and Technology