From The University of Cambridge (UK)
5.22.24
Sarah Collins
sarah.collins@admin.cam.ac.uk
Construction workers pouring concrete. Credit: Jung Getty via Getty Images
Materials Processing Institute
Researchers from the University of Cambridge have developed a method to produce very low-emission concrete at scale – an innovation that could be transformative in the transition to net zero.
The method, which the researchers say is “an absolute miracle”, uses the electrically-powered arc furnaces used for steel recycling to simultaneously recycle cement, the carbon-hungry component of concrete.
Concrete is the second-most-used material on the planet, after water, and is responsible for approximately 7.5% of total anthropogenic CO₂ emissions. A scalable, cost-effective way of reducing concrete emissions while meeting global demand is one of the world’s biggest decarbonisation challenges.
The Cambridge researchers found that used cement is an effective substitute for lime flux, which is used in steel recycling to remove impurities and normally ends up as a waste product known as slag. But by replacing lime with used cement, the end product is recycled cement that can be used to make new concrete.
The cement recycling method developed by the Cambridge researchers, reported in the journal Nature, does not add any significant costs to concrete or steel production and significantly reduces emissions from both concrete and steel, due to the reduced need for lime flux.
Fig. 1: Chemical analysis of the clinkers produced over molten steel.
a, Ternary diagram pair presenting the oxide composition of the slags studied in the SiO2–CaO–Al2O3 and SiO2–CaO–Fe2O3 systems measured using XRF. Every oxide composition was analysed by X-ray diffraction, and the resulting crystallographic composition is shown as a pie chart. Right, a detail of the SiO2-CaO-Al2O3 ternary diagram on the left. b, Percentage of gehlenite in the slag and the fraction of alite over total alite and belite in the tested systems both as a function of (C/S)*, the available lime-to-silica ratio for the formation of silicate phases. The method for calculating (C/S)* is given in the Methods. The grey shaded region represents the range of C/S for which both Alite and Belite can form. c, Diffractograms and phase compositions of selected slags produced in this work. γ, C2S-γ; β, C2S-β; m, C3S-monoclinic; g, ghelenite; a, C3A cubic; c, graphite; and q, quartz. d, Comparison between the tested slags and compositions reported in the literature. The literature used to create this figure is given in Supplementary Table 3. Med., medium; Com., commercial; a.u., arbitrary units.
See the science paper for further instructive material with images.
Recent tests carried out by the Materials Processing Institute, a partner in the project, showed that recycled cement can be produced at scale in an electric arc furnace (EAF), the first time this has been achieved. Eventually, this method could produce zero emission cement, if the EAF was powered by renewable energy.
The world’s first process for making zero emissions cement.
“We held a series of workshops with members of the construction industry on how we could reduce emissions from the sector,” said Professor Julian Allwood from Cambridge’s Department of Engineering, who led the research. “Lots of great ideas came out of those discussions, but one thing they couldn’t or wouldn’t consider was a world without cement.”
Concrete is made from sand, gravel, water, and cement, which serves as a binder. Although it’s a small proportion of concrete, cement is responsible for almost 90% of concrete emissions. Cement is made through a process called clinkering, where limestone and other raw materials are crushed and heated to about 1,450°C in large kilns. This process converts the materials into cement, but releases large amounts of CO₂ as limestone decarbonates into lime.
Over the past decade, scientists have been investigating substitutes for cement, and have found that roughly half of the cement in concrete can be replaced with alternative materials, such as fly ash, but these alternatives need to be chemically activated by the remaining cement in order to harden.
“It’s also a question of volume – we don’t physically have enough of these alternatives to keep up with global cement demand, which is roughly four billion tonnes per year,” said Allwood. “We’ve already identified the low hanging fruit that helps us use less cement by careful mixing and blending, but to get all the way to zero emissions, we need to start thinking outside the box.”
“I had a vague idea from previous work that if it were possible to crush old concrete, taking out the sand and stones, heating the cement would remove the water, and then it would form clinker again,” said first author Dr Cyrille Dunant, also from the Department of Engineering. “A bath of liquid metal would help this chemical reaction along, and an electric arc furnace, used to recycle steel, felt like a strong possibility. We had to try.”
The clinkering process requires heat and the right combination of oxides, all of which are in used cement, but need to be reactivated. The researchers tested a range of slags, made from demolition waste and added lime, alumina and silica. The slags were processed in the Materials Processing Institute’s EAF with molten steel and rapidly cooled.
“We found the combination of cement clinker and iron oxide is an excellent steelmaking slag because it foams and it flows well,” said Dunant. “And if you get the balance right and cool the slag quickly enough, you end up with reactivated cement, without adding any cost to the steelmaking process.”
The cement made through this recycling process contains higher levels of iron oxide than conventional cement, but the researchers say this has little effect on performance.
The Cambridge Electric Cement process has been scaling rapidly, and the researchers say they could be producing one billion tonnes per year by 2050, which represents roughly a quarter of current annual cement production.
“Producing zero emissions cement is an absolute miracle, but we’ve also got to reduce the amount of cement and concrete we use,” said Allwood. “Concrete is cheap, strong and can be made almost anywhere, but we just use far too much of it. We could dramatically reduce the amount of concrete we use without any reduction in safety, but there needs to be political will to make that happen.
“As well as being a breakthrough for the construction industry, we hope that Cambridge Electric Cement will also be a flag to help the government recognise that the opportunities for innovation on our journey to zero emissions extend far beyond the energy sector.”
The researchers have filed a patent on the process to support its commercialisation. The research was supported in part by Innovate UK and the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI). Julian Allwood is a Fellow of St Catharine’s College, Cambridge.
See the full article here .
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The University of Cambridge (UK) [legally The Chancellor, Masters, and Scholars of the University of Cambridge] is a collegiate public research university in Cambridge, England. Founded in 1209 Cambridge is the second-oldest university in the English-speaking world and the world’s fourth-oldest surviving university. It grew out of an association of scholars who left the University of Oxford (UK) after a dispute with townsfolk. The two ancient universities share many common features and are often jointly referred to as “Oxbridge”.
Cambridge is formed from a variety of institutions which include 31 semi-autonomous constituent colleges and over 150 academic departments, faculties and other institutions organized into six schools. All the colleges are self-governing institutions within the university, each controlling its own membership and with its own internal structure and activities. All students are members of a college. Cambridge does not have a main campus and its colleges and central facilities are scattered throughout the city. Undergraduate teaching at Cambridge is organized around weekly small-group supervisions in the colleges – a feature unique to the Oxbridge system. These are complemented by classes, lectures, seminars, laboratory work and occasionally further supervisions provided by the central university faculties and departments. Postgraduate teaching is provided predominantly centrally.
Cambridge University Press a department of the university is the oldest university press in the world and currently the second largest university press in the world. Cambridge Assessment also a department of the university is one of the world’s leading examining bodies and provides assessment to over eight million learners globally every year. The university also operates eight cultural and scientific museums, including the Fitzwilliam Museum, as well as a botanic garden. Cambridge’s libraries – of which there are 116 – hold a total of around 16 million books, around nine million of which are in Cambridge University Library, a legal deposit library. The university is home to – but independent of – the Cambridge Union – the world’s oldest debating society. The university is closely linked to the development of the high-tech business cluster known as “Silicon Fe”. It is the central member of Cambridge University Health Partners, an academic health science centre based around the Cambridge Biomedical Campus.
By both endowment size and consolidated assets Cambridge is the wealthiest university in the United Kingdom. The central university – excluding colleges – has a total income of over £2.5 billion of which over £600 million is from research grants and contracts. The central university and colleges together possess a combined endowment of over £7 billion and overall consolidated net assets (excluding “immaterial” historical assets) of over £12.5 billion. It is a member of numerous associations and forms part of the ‘golden triangle’ of English universities.
Cambridge has educated many notable alumni including eminent mathematicians, scientists, politicians, lawyers, philosophers, writers, actors, monarchs and heads of state. Nobel laureates, Fields Medalists, Turing Award winners and British prime ministers have been affiliated with Cambridge as students, alumni, faculty or research staff. University alumni have won many Olympic medals.
History
By the late 12th century, the Cambridge area already had a scholarly and ecclesiastical reputation due to monks from the nearby bishopric church of Ely. However, it was an incident at Oxford which is most likely to have led to the establishment of the university: three Oxford scholars were hanged by the town authorities for the death of a woman without consulting the ecclesiastical authorities who would normally take precedence (and pardon the scholars) in such a case; but were at that time in conflict with King John. Fearing more violence from the townsfolk scholars from the University of Oxford started to move away to cities such as Paris, Reading and Cambridge. Subsequently enough scholars remained in Cambridge to form the nucleus of a new university when it had become safe enough for academia to resume at Oxford. In order to claim precedence, it is common for Cambridge to trace its founding to the 1231 charter from Henry III granting it the right to discipline its own members (ius non-trahi extra) and an exemption from some taxes; Oxford was not granted similar rights until 1248.
A bull in 1233 from Pope Gregory IX gave graduates from Cambridge the right to teach “everywhere in Christendom”. After Cambridge was described as a studium generale in a letter from Pope Nicholas IV in 1290 and confirmed as such in a bull by Pope John XXII in 1318 it became common for researchers from other European medieval universities to visit Cambridge to study or to give lecture courses.
Foundation of the colleges
The colleges at the University of Cambridge were originally an incidental feature of the system. No college is as old as the university itself. The colleges were endowed fellowships of scholars. There were also institutions without endowments called hostels. The hostels were gradually absorbed by the colleges over the centuries; but they have left some traces, such as the name of Garret Hostel Lane.
Hugh Balsham, Bishop of Ely, founded Peterhouse – Cambridge’s first college in 1284. Many colleges were founded during the 14th and 15th centuries but colleges continued to be established until modern times. There was a gap of 204 years between the founding of Sidney Sussex in 1596 and that of Downing in 1800. The most recently established college is Robinson built in the late 1970s. However, Homerton College only achieved full university college status in March 2010 making it the newest full college (it was previously an “Approved Society” affiliated with the university).
In medieval times many colleges were founded so that their members would pray for the souls of the founders and were often associated with chapels or abbeys. The colleges’ focus changed in 1536 with the Dissolution of the Monasteries. Henry VIII ordered the university to disband its Faculty of Canon Law and to stop teaching “scholastic philosophy”. In response, colleges changed their curricula away from canon law and towards the classics; the Bible; and mathematics.
Nearly a century later the university was at the centre of a Protestant schism. Many nobles, intellectuals and even commoners saw the ways of the Church of England as too similar to the Catholic Church and felt that it was used by the Crown to usurp the rightful powers of the counties. East Anglia was the centre of what became the Puritan movement. In Cambridge the movement was particularly strong at Emmanuel; St Catharine’s Hall; Sidney Sussex; and Christ’s College. They produced many “non-conformist” graduates who, greatly influenced by social position or preaching left for New England and especially the Massachusetts Bay Colony during the Great Migration decade of the 1630s. Oliver Cromwell, Parliamentary commander during the English Civil War and head of the English Commonwealth (1649–1660), attended Sidney Sussex.
Modern period
After the Cambridge University Act formalized the organizational structure of the university the study of many new subjects was introduced e.g. theology, history and modern languages. Resources necessary for new courses in the arts architecture and archaeology were donated by Viscount Fitzwilliam of Trinity College who also founded the Fitzwilliam Museum. In 1847 Prince Albert was elected Chancellor of the University of Cambridge after a close contest with the Earl of Powis. Albert used his position as Chancellor to campaign successfully for reformed and more modern university curricula, expanding the subjects taught beyond the traditional mathematics and classics to include modern history and the natural sciences. Between 1896 and 1902 Downing College sold part of its land to build the Downing Site with new scientific laboratories for anatomy, genetics, and Earth sciences. During the same period the New Museums Site was erected including the Cavendish Laboratory which has since moved to the West Cambridge Site and other departments for chemistry and medicine.
The University of Cambridge began to award PhD degrees in the first third of the 20th century. The first Cambridge PhD in mathematics was awarded in 1924.
In the First World War 13,878 members of the university served and 2,470 were killed. Teaching and the fees it earned came almost to a stop and severe financial difficulties followed. As a consequence, the university first received systematic state support in 1919 and a Royal Commission appointed in 1920 recommended that the university (but not the colleges) should receive an annual grant.
Following the Second World War the university saw a rapid expansion of student numbers and available places; this was partly due to the success and popularity gained by many Cambridge scientists.
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