History about MgO
The history of magnesium cements goes long back, magnesium phosphate cements made from animal faeces or fermented plant material and magnesia were used in the great wall and in many early buildings around the world. It is also likely that magnesium sulfate or chloride type cements were used before their western invention by Stanislaus Sorel. The oldest cement is probably magnesium phosphate type wherein insoluble magnesium phosphates are formed from a mixture of a soluble phosphate and magnesium oxide. The early magnesium cements were made with soluble phosphate from animal faeces or fermented plants and magnesia and optionally clays. “These natural cements bind naturally and exceptionally well to all things cellulose (i.e. plant fibers, wood chip, etc.) and are often referred to as “living cements.” This is in sharp contrast to Portland cement, which repels cellulose. Blends of magnesium oxide were used in ancient times in Germany, France, Mexico and Latin America, Switzerland, India, China and New Zealand, among other countries. The Great Wall of China and many of the Stupas in India, still standing today, were all made with magnesium-based cements. Ancient European artisans used a timber frame with magnesium oxide infill in constructing homes. No gaps are visible in these 800 – year – old walls that still remain in use.”
Magnesia reacts with soluble phosphates to precipitate almost totally insoluble magnesium phosphate.
MgO + H2O = Mg(OH)2
3Mg(OH)2 + 2H3PO4 = Mg3((PO)4)2 + 6H2O
If a cheap source of potassium hydrogen phosphate the active chemical in dung could be found then magnesium phosphate cements could make a valuable contribution to reducing global warming and improving building biology from the point of view of occupant health. A range of magnesium phosphate cements has been used including magnesium ammonium phosphate which is thought to be formed by an acid-base reaction between magnesia and di hydrogen ammonium phosphate. This results in an initial gel formation followed by crystallization into an insoluble phosphate, mainly magnesium ammonium phosphate hexahydrate, [NH4MgPO4.6H2O]. The magnesium oxide used in this system is produced by calcining at higher temperatures and is referred to in the industry as being “dead burned” and is not as reactive as magnesia made at lower temperatures. A set retarder, typically either borax or boric acid is also used to give a workable set time. Magnesium phosphate cements develop considerably greater compressive and tensile strengths compared to Portland cement, and given they could take less energy to produce it is a wonder why they are not more commonly used these days. The promotion and proliferation of Portland cement occurred when energy was cheap and health concerns of the public were simply not an issue.
Another advantage of Magnesium-based cements are that they have a natural affinity for cellulose materials, such as plant fibers or wood chips; Portland cement repels cellulose. So you can actually use wood chips as an aggregate to achieve lighter weight and more insulative products. Magnesium oxide when combined with clay and cellulose creates cements that breathe water vapor; they never rot because they always expel moisture.
Before the widespread 20th century use of Portland cement magnesium oxide and magnesium chloride based cements were numbered amongst the world’s popular cement products. Once the introduction of Portland cement essentially cornered the market in the latter part of the 19th century, serious public health issues began to be quietly recognized, documented, and scientifically verified as being directly linked to the use of limestone/gypsum based cement and concrete products. In contrast to this sobering reality magnesium cements have consistently proven to be superior in strength, versatility, and environmental integrity.
So why these magnesium cements were virtually abandoned over the past 175 years?
Whether we are discussing Portland cement or any other cement no one ever purposely set out to make a problematic cement; quite the opposite. When Joseph Aspdin invented his water-activated Portland cement in his Leeds England kitchen in 1824, it obviously seemed to be a viable and exciting advance in addressing the accelerated pace of the industrial revolution. And in many respects notably its convenience and availability it was! It was only as time went on and this nineteenth century cement/concrete innovation spread around the world that the previously unrecognizable, negative side effects would slowly but surely begin to become scientifically scrutinized. It’s also important to note that Portland cement manufacturers continuously allocate enormous amounts of R&D funding in a valiant effort to overcome these inherited deficiencies. Literally billions of dollars are spent in an effort to do what magnesium and phosphate-bonded cements do ‘naturally’.
To understand this dilemma a discussion of the history of magnesium cements, which will explain why these ancient magnesium/phosphate building materials are of such great historic importance. and more importantly why these same ‘cold-fired’ ceramic bonding techniques now hold the key to the future of worldwide, sustainable building practices. This currently available cement alternative (often referred to as ceramic cement) provides unique, short and long term solutions to the adverse effects of Portland cement. The quicker this fact is understood by both the cement/concrete industries and the general public, the quicker we can reverse the deleterious health and environmental effects caused by the contemporary concrete materials to which we are all subjected to.
Availability and Benefits of Magnesium/Phosphate based cements:
Magnesium deposits exist in abundance in every corner of the earth and cover roughly 8% of the world’s surface. Depending upon where they are mined, magnesium oxide and magnesium oxide/magnesium chloride cements require only 20%-40% of the energy required to produce Portland cement. Phosphates are available from many sources ranging from phosphoric rock to animal wastes and fermented plants, which historically were used to “react” with various oxides to produce these environmentally friendly, non-toxic cements.
