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Suitability of excavated London clay as a supplementary cementitious material

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Fragkoulis Kanavaris discusses the potential of producing supplementary cementitious materials (SCMs) using London Clay excavated from construction activities of the High Speed 2 rail project. A trade-off between enhancing reactivity versus decomposition of impurities (e.g., pyrite, carbonates) present in different London Clay samples was considered in selecting the calcination temperature.

Image courtesy of interviewee. January 25, 2024

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The speaker discusses a major infrastructure project in London, focusing on the extensive excavation required due to tunneling that generates significant waste consisting mainly of London clay. Traditionally, this clay has been removed and used as landfill, leading to high costs and carbon emissions. The goal of the study was to explore innovative uses for this excavated London clay, particularly as a replacement for Portland cement in concrete, thereby reducing waste and embodied carbon.

The research involved detailed characterization of London clay and investigating its potential for transformation through calcination (heating) to create a reactive material usable in concrete. Despite the clay's low carbonate content, which poses a challenge for its reactivity, the study found that good quality concrete could be produced with 50-70% replacement of Portland cement using London clay, achieving strengths of 40-60 megapascals.

The most significant conclusion of the research indicates that waste clays, which are often discarded, can be effectively repurposed as supplementary cementitious materials, paving the way for further exploration of less reactive materials in concrete production. This video video offers a sustainable solution to using excavation waste while maintaining concrete quality.

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The motivation behind it, behind this work,

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was the fact that we were working

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and we have been still working,

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on a major infrastructure project development in, in the UK

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and specifically in, in London.

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And that's part of that major infrastructure project.

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We're talking about several kilometers of, of,

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high speed railway lines and several kilometers of tunnels.

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Um, which as part of the construction

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of these infrastructure assets, there is a lot,

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a vast majority of excavated material that is going

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to be generated because we have tunnel boring machines,

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for example, operating as part of,

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of the tunneling construction process.

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And that generates a significant volume of,

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of excavation waste.

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And that excavation waste

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because of the, the location

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that we are situated in London is predominantly London clay.

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And that brings us to the, question

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or answering the question of what London Clay is.

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And London Clay is a marine geological formation.

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Essentially, it's a soil, it's a clay.

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That whole lot of London is sitting on that clay.

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So nobody knows where bedrock is in London.

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And of course I'm saying this with,

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joking matter.

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Uh, but there's abundant

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clay present in London that normally during these kind

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of excavation operations,

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this clay is being extracted from the ground,

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removed from the ground, and,

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repurposed somewhere else as landfill.

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And we know that this operation of repurposing the clay,

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excavating the clay from London

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for infrastructure development

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and repurposing it somewhere else as landfill is associated

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with significant embodied carbon

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and significant, significant cost.

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Um, so what we are doing in, in this as part of this study,

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we thought, okay, we need to think out of the box

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and try to find ways to, repurpose that excavated clay,

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the excavation waste,

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in high value application rather than landfill it

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and transporting kilometers away from London.

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The focus of that study was London Clay itself.

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So we first thought, okay, what can we do with London Clay?

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London Clay is a, a clay.

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So that takes us a step back to consider

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what can we do with clays?

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And very important,

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research accomplishment over the past years, in, in,

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in the material science field

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or construction material science field was the utilization

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of clays for the replacement

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of Portland's men concrete in order

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to reduce concrete symboled carbon.

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So what we did in this case, we thought, okay,

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we can use other clays which are suitable

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for replacing Portland's main concrete.

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Why should we not try and use London clay for that purpose?

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That was never tried before, never tried before.

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Um, so it was a bit of uncharted territory for us.

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And, we took, a very detailed approach

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to towards characterization of that material.

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Uh, so we started with collaboration with,

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different reputable, academic institutions

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and, also, consultancies.

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And, we derived a detailed plan,

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which involves material characterization,

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micro structural material characterization

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of the raw clay itself.

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And then we investigated methodologies to convert that clay

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to a usable material in concrete.

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And the way to do this is to heat up the clay

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or cal signate as we call it, in scientific terms.

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And, that material converts itself

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through calcination from, an inert material

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to a reactive material for using concrete.

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So we did this study of trying to identify

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or determine which are the suitable temperature ranges

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or, particle size distributions, grinding,

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and so on, which are optimum for converting the raw clay.

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The as excavated clay from the infrastructure construction

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works to a usable material

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and concrete with, some requirements

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for for performance.

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So at first when we started this investigation on the

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reactivity of lung and clay, I think it's worth mentioning

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that, a metric

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or a criterion for describing the reactivity of clays.

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And there's suitability for use as,

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Portland cement replacement in concrete is the carbonite

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content, which is a mineralogical,

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phase within, within clays.

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Uh, so carbonite is quite key in, in,

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in its presence in clays

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because it improves the reactivity of these clays.

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So the material characterization showed

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that London clays are low in carbonate content, let's say

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below 30%.

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And that could be somewhat problematic for achieving,

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for producing a very good, good quality

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cal sign clay material for using s for using instead

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of portal cementing concrete.

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Uh, but what we found through our trials

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and concrete development activities was

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that we could produce, good quality concrete

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by good quality, I mean, 40 to six megapascal strengths

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of, of concrete.

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And this is been considered

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as a relatively good quality concrete in, in the world

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of civil engineering, with, 50%

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to 70% replacement of Portland cement

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with, with London clay.

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So that was extremely encouraging with respect

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to the suitability of using this excavation waste

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as a low cost, low carbon cement replacement in concrete.

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I think one of the most important conclusions,

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and at least the one that makes me feel the most excited

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is that we can

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Use, waste clays which are not

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so rich in called an A content.

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So waste clays, which would, nobody wants

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to use them essentially.

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Uh, we convert them in a usable supplementary cement tissue

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material for using concrete.

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And this is really, really a research breakthrough

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because over the past decade

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or even 15 years, we have seen several studies

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that are focusing on quite reactive clay.

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But I think our study really paved the way forward

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for looking into less reactive materials,

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more excavation wastes

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and their utilization in the

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production of structural concrete.

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So I think that this is the most important conclusion,

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and we can go down to more details in the conclusions of,

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the reactivity of material

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or the production of, of concrete strength.

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But as a key takeaway, I would like to say

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00:06:55.405 --> 00:07:00.135
that we can produce good quality concrete, so up to,

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40 or six megapascal strengths on a consistent manner,

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achieving good radiology,

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00:07:07.985 --> 00:07:10.855
using this excavation waste, material.

Repurposing London Clay in Infrastructure Projects

00:00:00 - The motivation behind it, behind this work, was the fact that we were working and we have been still working, on a major infrastructure project development in, in the UK and specifically in, in London. And that's part of that major infrastructure project. We're talking about several kilometers of, of, high speed railway lines and several kilometers of tunnels. which as part of the construction of these infrastructure assets, there is a lot,
00:00:34 - to be generated because we have tunnel boring machines, for example, operating as part of, of the tunneling construction process. And that generates a significant volume of, of excavation waste. And that excavation waste because of the, the location that we are situated in London is predominantly London clay. And that brings us to the, question or answering the question of what London Clay is.
00:01:04 - Essentially, it's a soil, it's a clay. That whole lot of London is sitting on that clay. So nobody knows where bedrock is in London. And of course I'm saying this with, joking matter. but there's abundant clay present in London that normally during these kind of excavation operations, this clay is being extracted from the ground, removed from the ground, and,
00:01:33 - And we know that this operation of repurposing the clay, excavating the clay from London for infrastructure development and repurposing it somewhere else as landfill is associated with significant embodied carbon and significant, significant cost. so what we are doing in, in this as part of this study, we thought, okay, we need to think out of the box and try to find ways to, repurpose that excavated clay,
00:02:03 - in high value application rather than landfill it and transporting kilometers away from London. The focus of that study was London Clay itself. So we first thought, okay, what can we do with London Clay? London Clay is a, a clay. So that takes us a step back to consider what can we do with clays? And very important, research accomplishment over the past years, in, in, in the material science field
00:02:35 - of clays for the replacement of Portland's men concrete in order to reduce concrete symboled carbon. So what we did in this case, we thought, okay, we can use other clays which are suitable for replacing Portland's main concrete. Why should we not try and use London clay for that purpose? That was never tried before, never tried before. so it was a bit of uncharted territory for us.

Repurposing London Clay for Sustainable Concrete

00:03:05 - to towards characterization of that material. so we started with collaboration with, different reputable, academic institutions and, also, consultancies. And, we derived a detailed plan, which involves material characterization, micro structural material characterization of the raw clay itself. And then we investigated methodologies to convert that clay to a usable material in concrete.
00:03:37 - or cal signate as we call it, in scientific terms. And, that material converts itself through calcination from, an inert material to a reactive material for using concrete. So we did this study of trying to identify or determine which are the suitable temperature ranges or, particle size distributions, grinding, and so on, which are optimum for converting the raw clay.
00:04:10 - works to a usable material and concrete with, some requirements for for performance. So at first when we started this investigation on the reactivity of lung and clay, I think it's worth mentioning that, a metric or a criterion for describing the reactivity of clays. And there's suitability for use as, Portland cement replacement in concrete is the carbonite content, which is a mineralogical,
00:04:40 - so carbonite is quite key in, in, in its presence in clays because it improves the reactivity of these clays. So the material characterization showed that London clays are low in carbonate content, let's say below 30%. And that could be somewhat problematic for achieving, for producing a very good, good quality cal sign clay material for using s for using instead of portal cementing concrete.
00:05:15 - and concrete development activities was that we could produce, good quality concrete by good quality, I mean, 40 to six megapascal strengths of, of concrete. And this is been considered as a relatively good quality concrete in, in the world of civil engineering, with, 50% to 70% replacement of Portland cement with, with London clay. So that was extremely encouraging with respect
00:05:46 - as a low cost, low carbon cement replacement in concrete. I think one of the most important conclusions, and at least the one that makes me feel the most excited is that we can Use, waste clays which are not so rich in called an A content. So waste clays, which would, nobody wants to use them essentially. we convert them in a usable supplementary cement tissue material for using concrete.

Utilizing Excavation Waste for Quality Concrete

00:06:15 - because over the past decade or even 15 years, we have seen several studies that are focusing on quite reactive clay. But I think our study really paved the way forward for looking into less reactive materials, more excavation wastes and their utilization in the production of structural concrete. So I think that this is the most important conclusion,
00:07:07 - the reactivity of material or the production of, of concrete strength. But as a key takeaway, I would like to say that we can produce good quality concrete, so up to, 40 or six megapascal strengths on a consistent manner, achieving good radiology, using this excavation waste, material.

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