Modern Building Design - Nano Lime Technology
In week 2 of the FutureLearn Modern Building Design course, they mentioned nano lime technology as a possible solution for reducing CO2 emissions produced by cement making.
I think a nice place to start is Jason Bolton’s blog post Nano-lime repairs of historic lime mortars and plasters,
“Nano-limes have been around for over fifteen years, but there are relatively few technical and practical studies to draw on.”
“Nano-limes are very small particles of calcium hydroxide suspended in an alcoholic medium, developed as a calcium-based consolidant and initially presented for the conservation of wall paintings and frescoes, and later extended to calcareous stones such as limestones.”
“Research into the application and use of nano-limes have focused on conservation of wall plaster and natural stones.”
The post is also useful as it referred me to the Building Limes Forum Ireland, which had more information about the basics of lime:
“Lime has been used as the principal binder for mortars and plasters for the past 10,000 years. The earliest surviving example dates from around 8000 BC in a floor in Turkey. It was only the introduction of cement in the middle of the 19th century, which led to the decline in the use of lime, culminating in its virtual disappearance by the mid 20th century. Emerging evidence in the 1970s of the damage caused to historic buildings by the use of cement mortars and modern plasters has led to a revival in the use of lime over the past 20 years, not only for conservation but also for new build.”
But, their focus was on traditional lime, not necessarily nano lime technology, so I had to do some more exploring. But even Wikipedia left me high and dry with a search for “nano lime.” The closest I got was a link on the lime page to “eco-cement.” Which in turn led me to two informative news articles.
First, A rock and a hard place: Eco-cement yet to cover ground in the building industry -
“Imagine a city that functions like a rainforest, soaking up greenhouse gases instead of emitting them. It is an unlikely scenario in a world that seems powerless to halt the spread of carbon dioxide in the atmosphere. But John Harrison, a Tasmanian inventor, says this can be achieved just by changing the mix of the cement we use.
Portland cement, invented nearly two centuries ago by a Yorkshire stonemason, is ubiquitous. Last year, a quarter of a tonne was manufactured for each human being on the planet. And every tonne of cement produces a tonne of carbon dioxide. Cement production accounts for more than 5% of all greenhouse gasses emitted in Europe and America, and more than 10% in China.
Cement, essentially a mixture of chalk, clay, and calcium, must be cooked in a kiln at 1450C. This provokes chemical reactions that give the material its strength but also release carbon dioxide. Substitute magnesite for calcium, says Harrison, and the result is "eco-cement", a product with all the structural qualities of Portland cement that produces almost no carbon dioxide.”
So, this isn’t nano lime technology, but it is an arguably more environmentally sustainable alternative to traditional cement. Why, then hasn’t it taken off?
“An independent scientific appraisal by Fredrik Glasser, a materials expert at the University of Aberdeen, found that eco-cement was strong, workable, cheap, resistant to corrosion and more environmentally friendly than Portland cement. It can be made using the the industry's existing facilities. Yet Harrison is finding it hard to make headway in the commercial market. "The building materials industry is intensely conservative," says Glasser. "Innovation is the exception, not the rule."
The greatest obstacle is that eco-cement's key ingredient, magnesite, while abundant in the earth's crust, is rarely mined - until now it had few obvious uses. Given economies of scale, eco-cement should be cheaper than Portland cement because less energy is required for production.”
The other article, The King of Green Investing, is about venture capitalist Vinod Khosla, and it mentions his eco-cement venture Calera. And this eco cement DOES use nano lime technology:
“The Calera process for the capture and conversion of CO2 takes its lead from nature. The earth’s atmosphere has had higher concentrations of CO2 in the past and nature dealt with these high levels of CO2 by a mineralization process whereby marine organisms use CO2 to form calcium carbonate structures that deposit on the ocean floor over time. It is estimated that up to 100 million billion tonnes of CO2 is stored in the geological record in the form of calcium carbonate.
The special form of calcium carbonate that Calera produces in its process mimics the form of calcium carbonate that marine organisms use to make their shells and other structures. The special form of calcium carbonate is a binder that creates structures with high strength and toughness.
Calcium carbonate exists in nature in different forms or polymorphs. The Calera process results in the production of the vaterite polymorph which is stable when stored in the absence of water. When water and other proprietary additives are added to the vaterite polymorph, a cement reaction occurs in which the vaterite transforms via a dissolution and reprecipitation reaction to form another polymorph of calcium carbonate known as aragonite. This conversion of vaterite to aragonite results in a material with high strength, just as natural systems like nacre (mother of pearl) are also constructed from the aragonite polymorph of calcium carbonate.”
To understand how this relates to lime, turns out I needed a quick primer from Wikipedia after all.
Lime is technically calcium oxide, CaO, or calcium hydroxide, Ca(OH)2. However, “the rocks and minerals from which these materials are derived, typically limestone or chalk, are composed primarily of calcium carbonate. They may be cut, crushed or pulverized and chemically altered.”
Limestone is “a sedimentary rock, composed mainly of skeletal fragments of marine organisms such as coral, forams and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3).”
And it’s that CaCO3 that is exactly what the vaterite polymorph is that Calera is using. Vaterite is simply “a polymorph of calcium carbonate. It was named after the German mineralogist Heinrich Vater. It is also known as mu-calcium carbonate (μ-CaCO3).” The whole mu/μ/micro thing just means it’s itty-freaking-bitty, aka “nano.”
And if you want to get into the real nitty gritty of nano lime research, here’s a few articles to get you started:
Study the Effect of Adding Nano Fly Ash and Nano Lime to Compressive Strength of Mortar
Influence of Nano-lime and Nano-silica Consolidants in the Drying Kinetics of Three Porous Building Materials
Can Nanolime Stone Consolidation offer a Feasible Conservation Method for Limestone Ecclesiastical Buildings?
Nano-Lime for Consolidation of Plaster and Stone
Nano-lime - a new material for the consolidation and conservation of historic mortars
Effect of clay and lime nano-additives on the freeze–thaw durability of hot mix asphalt
Functional Method of Using the Nano Lime in the Properties of Recycled Cold Asphalt Mixture with Bitumen Emulsion
Moisture Susceptibility of Warm-Mix Asphalt Mixtures Containing Nanosized Hydrated Lime
