MPC – Magnesium Phosphate Cement
Use flyash = 40% of total binder (less or more lower strength) gave higher compressive strength than without flyash!
MAP – mono ammonium phosphate P
MKP – mono potassium phosphate P
MgO – Magnesium Oxide M
H2O – Potable water w
M/P ratio = 10 keep in range 10-16
Borax = 5% (keep in range 5-6.5%) by weight of P
w/b ratio = 0.1 weight water/weight binder
Mixes were produced using a MgO to MKP weight ratio of 1:3,4, similar to that indicated by the molar ratios in Equation 1. The FA content was taken as 50% by weight of the total binder. Prior studies by Wagh et al. [1,2] showed that binder containing 30 to 50% fly ash exhibited higher strength than a binder with only MgO and MKP. The required mixing water to achieve a workable mix varied based on the overall mix composition and earlier studies have shown that the water to binder ratio (w/b) will also affect the compressive strength of the resulting concrete. To control the reaction rate and retard the setting time, different admixtures were examined and use of a commercially available lignosulphonate admixture at 1.5% by weight of the MgO+MKP was added to the mixing water to achieve the desired rheological properties.
The incorporation of sodium tripolyphosphate (Na5P3O10), or
simply STPP, into the magnesium phosphate mixture has a beneficial
effect. The deflocculating characteristics of tripolyphosphate ions
suggests that they may play a significant role in enabling improved
compaction of the wet mix, reducing the porosity of the hardened
material13,14. Moreover, Abdelrazig et al.14 reported that the incorpo-
ration of STPP in mortars brought about an increase in compressive
strength and a decrease in total and coarse pore volumes.
A mixture capable of forming a hard, bonded cement composition when admixed with water comprising magnesium oxide; a water soluble phosphate; a retarder selected from the group consisting of polycarboxylic acids, polyphosphonic acids, and salts of such acids; and an essentially inert aggregate filler. The retarder is preferably selected from the group consisting of citric acid, sodium citrate (monobasic), sodium citrate (dibasic), tartaric acid, trimellitic acid, nitrilotriacetic acid trisodium salt monohydrate, Dequest 2000 and Dequest 2006. The phosphate is preferably monoammonium phosphate and the filler is preferably silica sand and fly ash which are essentially free of calcium oxide and calcium carbonate. The mixture is admixed with water at a job site and used to fill holes in roads and other structures and is capable of being worked for at least seven minutes before initial set.
Grancrete has only been available to the public for just over a year and in that time has undergone some major growing pains. For example some of the initial compressive testing data put Grancrete at 6,880 PSI after 28 days under the original mixing instructions. Now with lessons learned and a better way of mixing Grancrete is now getting 12,590 PSI after only 3 days. Some valuable installation lessons learned are to mix Grancrete by hand with a drill mixer at a very high speed slowly adding the powder to the water. The amount of water used in the formula is very key to the final strength. The best performance comes when 18 to 22% water is used by weight on the “PC” formula and down as low as 11% on the “B” formula. We have also found that mesh is another key component to preventing check cracking. Currently the color fades during curing under direct sunlight. If used outdoors or where sunlight will affect the final color we recommend using a synthetic finish. There are still more lessons to be learned from Grancrete and the best way so far has been on the ground by people who recognize Grancrete’s ultimate potential in changing the way people build. Grancrete is moving in the right direction and has produced some beautiful homes, countertops, fireplaces, bathrooms, floors and even as a fireproofing for steal. We feel that the surface of what Grancrete is capable of has only been scratched. We have a lot of on the ground experience with Grancrete and appreciate people like Plaster Jon who are willing to give Grancrete a chance and are sorry that things didn’t work out for him. If you have any questions please feel free to contact us at email@example.com
April 16th, 2008 at 11:39 pm
I agree wholeheartedly with Matt Ketchum. There has been a lot learned in the last year or so.
The mixing process AND amount of water is absolutely essential to success. Over at Brownhomes.org they have the water ratios posted. When trying to follow those ratios you may think they are crazy if you do not mix according to how Matt suggested.
First, put in the water. Then add GC until it’s a paste. Add a little more GC until it balls up into sub-pea-size balls or looks more like soil. Your normal instict will be to add more water. Resist that urge. Let the mixer do its work. Within 30 seconds or so the mixture will come back together and look more fluid. That’s the time to add more of the GC. Repeat this process until all of the measured GC is in the mixing bowl/container. Your mixer will work hard, but it will all come together.
A key tool to have and use is the thermal temperature gauge. As you mix the total amount of GC, you’ll see the mixture get thinner and note a corresponding rise in temperature. We’ve found that 90 degrees F is a good time to get that GC out of the mixer and onto/into its final place. You will be surprised how the mixture may look like bread dough, yet still have the self-leveling characteristics if you vibrate it.
For smaller batches for creating the psi testing blocks, we’re finding that the good ol’ KitchenAid mixer works quite well. Yeah, don’t put aggregate in that as it completely ruins the beater and causes your wife to want to beat you. We mix the GC rather nicely in the mixer to maybe 85 degrees, then dump that into the pail and mix in aggregate with the drill & mortal paddle until it reaches 90 degrees.
The fiberglass mesh is a huge addition! Ceramics handle certain things well, but certainly benefit from the additional different strength characteristics of the mesh. It’s amazing how hard one has to jump up and down on a piece of styrofoam coated with only, at MOST, 3/8″ of GC with a thin fiber mesh in order to get it to bust.
I hope this helps. I’m glad there are people posting their experiences.
April 24th, 2008 at 9:48 am Reading my post I realized I said, “thermal temperature gauge”. That’s a bit redundant, eh? I meant infrared temperature guage
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.