Technical Questions and Answers

A student from Portugal asked the following questions

1. Does Eco-Cement maintain the same dimensional stability and durability as regular cement?
 
2. Does the fire resistance of Eco-Cement match regular cements?
 
3. Please describe the thermal dilation behaviour of Eco-Cement?
 

1. The dimensional stability of Eco-Cements is at least as good as that of ordinary Portland cement concretes.

2. Hydrated magnesium carbonates such as nesquehonite are well known fire retardants.

3. The dimensional changes with temperature of Eco-Cements have not yet been characterised.

Making foamed concrete using Tec and Eco-Cement formulations

Foaming using magnesia in the formulation works very well as there is usually enough CO2 in the air pockets to carbonate the magnesia whereby nesquehonite is formed. As nesquehonite looks a bit like a sea urchin it adds tremendous microstructural strength.

The magnesium ion also imparts a pseudo elastic viscosity to the mix which helps hold the bubbles (see Rheological and Shrinkage Reduction Affects of Adding Reactive Magnesia to Concretes.) and we have not found that it interferes with any of the common foaming agents (See newsletter 29).

The addition rate will depend on what else is in the mix and may be anywhere between 5 and 75%

Making Panels using TecEco Technology

Could any TecEco cements be used to produce similar boards to those on the market today coming out of China that are made from either magnesium oxychloride or sulfate bonded fibre, perlite etc and coated in magnesium phosphate to render them waterproof?

If boards could be made with your cements could they be made thinner, say less than 25 mm (1 inch) and used to build an entire house without any additional structural support, like posts and beams?

MgO compounds are highly suitable for the manufacture of composite boards in some ways but not others. A very important reason for their use is their ability to bond extremely well to just about anything. The reason for this strong bonding capacity is explained on our web site at http://www.tececo.com/technical.nanocomposites.php

A downside of current state of the art magnesium oxysulfate or magneisum oxychloride boards is that they are not waterproof and this is why they generally have a magnesium phosphate coating. A good look at the atomic structure in the first graphic on the above web page should give the reader insight into why magnesium oxychlorides and sulfates have an innate weakness and that is that their layered structure tends to delaminate. Each ionically bonded layer is polar bonded to the one above and below and these polar bonds tend to break with strong polar solvents like water. On the other hand the same bonding capacity is why such "Sorel" type cements bond so well to many other materials.

Magnesium phosphate, like most phosphates is insoluble and can therefore be used to waterproof magnesium oxychloride and sulfate panels. Like most magnesium compounds, because of the high charge density of magnesium, magnesium phophate has a differential charge density of the surface and will polar bond to other magnesium compounds such as oxychlroide or oxysulfate as well as other materials. The problem with phosphate is its high cost.

At TecEco we believe we can do better with a Mg carbonate Ca silicate/aluminate system. It would have the advantage of lower cost, the bonding power of brucite and it's carbonates, the microstructural advantage of the carbonates, the sequestration advantage and the early strength advantage of the aluminates. All of course do not de-laminate so would not require the addition of a chemically precipitated phosphate layer which would be a further advantage given the shortage of phosphate globally.

The answer to the second part of the question is to design with structure to overcome the innate lack of strength of such a thin board. With good design it should be possible to build to several stories.

Cooling Concrete using Liquid Nitrogen

We are considering the use of liquid nitrogen to cool concrete in a fairly large project in Ecuador.

There has not been any experience here with it, and our gas supplier has the equipment available, but we need to estimate nitrogen volume, we need to cool about 20 F, about 300 cy day, any suggestion?

Jose Arce in the forum at (www.aggregateRESEARCH.com)

I totally agree with Ken Day. Fixing the problem is much better than mitigating it with liquid hydrogen.

You will also find adding a small percentage of highly reactive MgO will not only reduce heat but make placement easier and improve long term strength through the release of chemical water for more complete hydration of PC. Water related shrinkage can also be reduced to nil and placement will be easier

There is some precident for adding MgO for dams see Du, C. (2005). "A Review of Magnesium Oxide in Concrete - A serendipitous discovery leads to new concrete for dam construction." Concrete International (December 2005): 45 - 50. Note however that our contribution is that highly reactive material works much better and has other advantages.

Iron Oxide

Has anyone heard about adding
iron oxide to concrete for other purposes
than coloring?

Erez Sariel in the forum at (www.aggregateRESEARCH.com)

I (John Harrison) call my self a geochemist and am the inventor of Tec and Eco-Cement. Geochemists are a bit broader minded than cement chemists!

I have done some experimental work with iron oxide and my summation is that it will mop up chloride and sulfate increasing the resistance to corrosion of embedded steel reinforcing.

Iron oxychloride and oxysulfate complexes would form.

I have not studied US patent 5110360 but it came up in a search on the subject.

It would be interesting to see if anybody has observed this increased durability when coloring iron oxides are used.

Evaporative Cooling

Tell us how permecocrete or any other pervious pavement cools the surrounds through evaporation

According to Wikipedia "Evaporative cooling is a physical phenomenon in which evaporation of a liquid, typically into surrounding air, cools an object or a liquid in contact with it. Latent heat describes the amount of heat that is needed to evaporate the liquid; this heat comes from the liquid itself and the surrounding gas and surfaces." Molecules or atoms in a gaseous state have more energy than in a liquid or solid state. During evaporation this energy is extracted from the molecules remaining in the liquid and the surrounds as only higher energy molecules escape the liquid. Evaporative cooling is most effective if the humidity is low.

Differential Calcination of Dolomite

Can dolomite be used to make Eco-Cement?

Dolomite can be differentially calcined to give MgO plus CaCO3. Fluxes such as common salt make this easier.

There are ways of separating MgO from dolomite but they involve a lot of processing and rely on the different solubilities of the two ions or differing reactions.

Renders for Straw Bale Construction

Tell us about Eco-Cement renders for a straw bale home

Eco-Cements are easy to use and ideal for straw bale construction for a number of reasons. Probably most important are the high workability, low sag and high stick that they have. The reasons for these advantageous properties are related to the rheological properties which are strongly influenced by the high surface charge on the magnesium ion and the particle packing of the material. It is also worth noting that with most aggregates a little magnesium oxide goes a long way with 1:2: 12-18 mixes not being uncommon.

Accelerators

What accelerators work for Eco-Cement

A range work. As to which work the best that is proprietary information.

Setting time Eco-Cement

Can the setting time for Eco-Cement be reduced as it can in Portland cement by using accelerators?

The short answer is yes and most of the so called "accelerators" for PC work with MgO. Be wary however as many of them actually take part in reactions and have product that remains in the concrete. Sulfate for example forms magnesium oxy sulfate with magnesium.

Setting time Eco-Cement

How does the setting time for Eco-Cement compare with portland cement?

Somewhat slower with the rate depending on the proportion reactive magnesia and permeability.

Please provide samples

Please send formulations so we can make Eco-Cement

Unless the aggregates for Eco-Cement concretes are properly graded to allow CO2 access they will not strengthen. It follows that making good Eco-Cement concretes requires an understanding of particle packing, carbonation kinetics and a number of other issues as well as how to handle concrete. Making Eco-Cement concretes is something even the British Research Establishment (BRE) could not successfully achieve so we do recognise we have a problem.

To resolve the issue we can currently provide advice and finances permitting will provide software to allow licensed users to formulate successful Eco-Cements.

To become a licencee of TecEco it will be necessary to first approach us and if we agree to sign the Testing Agreement with Option to Licence and Confidentiality Agreement under legal on our web site.

Chemical Reactions ?

Can Eco-Cement be a net carbon sink with the inclusion of organically derived fibres such as hemp?

Absolutely - have a look at our LCA under tools on the web site and you will see that it can be a carbon sink even without.

Chemical Reactions ?

Why do magnesium and calcium carbonate form more readily in permeable concretes made using TecEco Eco-Cements containing magnesia than in concretes containing only Portland cement (PC) as the binder?

We think this is because the CSH lattice provides nucleation sites with access for carbonation. i.e an open structure on which nculeation can occur that provides access to CO2 .

Chemical Reactions ?

Does a higher short term pH contribute to more affective pozzolanic and other silicification reactions, and, if so, why?

Most reactions occur in solution as diffusion reaction mechanisms are hopelessly slow. The solubility and hence reactivity of silica is entirely dependent on the pH as any pH solubility curve would show. More silica is soluble at very low and very high pH.

Chemical Reactions ?

What chemical reaction takes place between Eco-Cement and soil during the formation of Eco-Cement Mud Bricks?

If you only knew how complex this question is. The reactions depend totally on the components in the soil and in particular the kinds of clays. Pozzolanic CSH, brucite and nesquehonite form. We also suspect magnesium look alike's to ettringite or hydrogarnet.

Cellulose Fibre

Will your Eco-Cement etc.be able to use agricultural by-product like hemp and bagasse fibre and still be structural?

Our cements are fundamentally suited for this purpose because they are low alkali (See newsletter 41)