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Reducing the Clinker Factor – Part 1

World Cement,

Advancing the cement industry’s carbon reduction goals

Cement manufacturers have committed to reducing the CO2 emissions associated with their product, but they are often constrained by the equipment used in cement making and the standardised chemistry of ordinary Portland cement. US start-up Solidia Technologies has joined forces with leaders in industry, government and academia to industrialise an innovative technology that could reduce the environmental footprint of cement in precast concrete applications while reducing concrete production costs and improving the performance of concrete-based building materials.

Cement and concrete production is ripe for disruption. But bringing a sustainable innovation to a market that dates back 2000 years, and whose last major product innovation was the development of Portland cement in the early 19th century, is no small order. Solidia is tasked not only with the development of a sustainable technology, but making that technology easy for the industry to adopt.

To that end, Solidia’s patented processes for producing sustainable cement and concrete use the industry’s existing infrastructure, raw materials, formulations, production methods and specifications.

Motivating a market

The incentive to ‘reduce the clinker factor’ in cement products is two-fold. The primary motivation is to reduce the energy consumption and CO2 emissions associated with cement clinker production in rotary kilns. It is generally accepted that the production of 1 t of ordinary Portland cement (OPC) creates over 800 kg of CO2. The secondary reason is to reduce the environmental impact of industrial byproducts such as flyash, slag and silica fumes. 

The strategy deployed to accomplish these goals is to replace a portion of the cement clinker used in cement production with industrial byproducts, without detrimentally affecting the performance of the cement.

Using Solidia’s patented processes in the production of concrete does not reduce the clinker factor, per se, but rather helps make clinker production and use more palatable from the carbon footprint and energy consumption perspectives.

A new class of sustainable cement and novel CO2-curing technology

Solidia has developed a new class of sustainable cement that reacts with gaseous CO2 rather than with water to form Solidia Concrete™. Produced with a non-hydraulic, lower-energy and lower-emission chemistry, Solidia Cement™ is more sustainable than ordinary Portland cement (OPC). The patented technology allows lower CO2 emissions in the cement production process and involves the use of CO2 as a curing agent in precast concrete manufacturing.

Solidia Cement is composed of a family of ‘green’, low-lime calcium silicate phases, similar, but not identical to the chemistry of OPC. As a result, it can be produced in existing cement kilns using the same raw materials that are used to make ordinary Portland cement, albeit in different proportions. Solidia Cement is produced using less limestone and at lower temperatures than are necessary for Portland cement. These factors translate into a reduction in the CO2 emissions during cement manufacturing, from 816 kg/t of OPC clinker to 570 kg/ t of Solidia Cement clinker.  This difference alone is equivalent to achieving a 30% reduction in the clinker factor.

To create Solidia Concrete products, water, aggregates and Solidia Cement are mixed, formed into the desired shape and then reacted with gaseous CO2 to produce a durable binding matrix. The curing process consumes up to 300 kg of CO2 per t of cement used. The CO2 is permanently and safely stored in solid carbonate form within the concrete. This difference is equivalent to an additional 37% reduction in the clinker factor.

Overall CO2 emissions associated with the production and use of cement can be reduced by up to 70%. ;Benefits realised by the concrete industry include reduced materials and water usage, shorter curing times and improved product durability.

Solidia Concrete can be produced by manufacturers of traditional concretes and can be designed to address any precast concrete application. These products, which include paving stones, concrete blocks, hollow-core slabs, railroad sleepers (ties), roof tiles, and pervious concrete, match or exceed the properties and characteristics of concrete products made using OPC. Additionally, the Solidia Concrete cures in less than 24 hours, compared to the up to 28 days required for traditional concrete products to reach full strength. As water is not consumed during the CO2-curing process, it can be collected and reused, with recycle rates of 60 to 80%.

This is part 1 of a three-part article written by Dr Nicholas DeCristofaro, Solidia Technologies, USA for World Cement’s September issue and abridged for the website. Subscribers can read the full issue by signing in, and can also catch up on-the-go via our new app for Apple and Android. Non-subscribers can access a preview of the September 2015 issue here.

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