- [기술동향]Riddle solved: Why w...
- Riddle solved: Why was Roman concrete so durable?An unexpected ancient manufacturing strategy may hold the key to designing concrete that lasts for millennia.David L. Chandler | MIT News OfficeJanuary6, 2023The ancient Romans were masters of engineering, constructing vast networks of roads, aqueducts, ports, and massive buildings, whose remains have survived for two millennia. Many of these structures were built with concrete: Rome’s famed Pantheon, which has the world’s largest unreinforced concrete dome and was dedicated in A.D. 128, is still intact, and some ancient Roman aqueducts still deliver water to Rome today. Meanwhile, many modern concrete structures have crumbled after a few decades.Researchers have spent decades trying to figure out the secret of this ultradurable ancient construction material, particularly in structures that endured especially harsh conditions, such as docks, sewers, and seawalls, or those constructed in seismically active locations.Now, a team of investigators from MIT, Harvard University, and laboratories in Italy and Switzerland, has made progress in this field, discovering ancient concrete-manufacturing strategies that incorporated several key self-healing functionalities. The findings are published today in the journal Science Advances, in a paper by MIT professor of civil and environmental engineering Admir Masic, former doctoral student Linda Seymour ’14, PhD ’21, and four others.For many years, researchers have assumed that the key to the ancient concrete’s durability was based on one ingredient: pozzolanic material such as volcanic ash from the area of Pozzuoli, on the Bay of Naples. This specific kind of ash was even shipped all across the vast Roman empire to be used in construction, and was described as a key ingredient for concrete in accounts by architects and historians at the time.Under closer examination, these ancient samples also contain small, distinctive, millimeter-scale bright white mineral features, which have been long recognized as a ubiquitous component of Roman concretes. These white chunks, often referred to as “lime clasts,” originate from lime, another key component of the ancient concrete mix. “Ever since I first began working with ancient Roman concrete, I’ve always been fascinated by these features,” says Masic. “These are not found in modern concrete formulations, so why are they present in these ancient materials?Previously disregarded as merely evidence of sloppy mixing practices, or poor-quality raw materials, the new study suggests that these tiny lime clasts gave the concrete a previously unrecognized self-healing capability. “The idea that the presence of these lime clasts was simply attributed to low quality control always bothered me,” says Masic. “If the Romans put so much effort into making an outstanding construction material, following all of the detailed recipes that had been optimized over the course of many centuries, why would they put so little effort into ensuring the production of a well-mixed final product? There has to be more to this story.”Upon further characterization of these lime clasts, using high-resolution multiscale imaging and chemical mapping techniques pioneered in Masic’s research lab, the researchers gained new insights into the potential functionality of these lime clasts.Historically, it had been assumed that when lime was incorporated into Roman concrete, it was first combined with water to form a highly reactive paste-like material, in a process known as slaking. But this process alone could not account for the presence of the lime clasts. Masic wondered: “Was it possible that the Romans might have actually directly used lime in its more reactive form, known as quicklime?”Studying samples of this ancient concrete, he and his team determined that the white inclusions were, indeed, made out of various forms of calcium carbonate. And spectroscopic examination provided clues that these had been formed at extreme temperatures, as would be expected from the exothermic reaction produced by using quicklime instead of, or in addition to, the slaked lime in the mixture. Hot mixing, the team has now concluded, was actually the key to the super-durable nature.“The benefits of hot mixing are twofold,” Masic says. “First, when the overall concrete is heated to high temperatures, it allows chemistries that are not possible if you only used slaked lime, producing high-temperature-associated compounds that would not otherwise form. Second, this increased temperature significantly reduces curing and setting times since all the reactions are accelerated, allowing for much faster construction.”During the hot mixing process, the lime clasts develop a characteristically brittle nanoparticulate architecture, creating an easily fractured and reactive calcium source, which, as the team proposed, could provide a critical self-healing functionality. As soon as tiny cracks start to form within the concrete, they can preferentially travel through the high-surface-area lime clasts. This material can then react with water, creating a calcium-saturated solution, which can recrystallize as calcium carbonate and quickly fill the crack, or react with pozzolanic materials to further strengthen the composite material. These reactions take place spontaneously and therefore automatically heal the cracks before they spread. Previous support for this hypothesis was found through the examination of other Roman concrete samples that exhibited calcite-filled cracks.To prove that this was indeed the mechanism responsible for the durability of the Roman concrete, the team produced samples of hot-mixed concrete that incorporated both ancient and modern formulations, deliberately cracked them, and then ran water through the cracks. Sure enough: Within two weeks the cracks had completely healed and the water could no longer flow. An identical chunk of concrete made without quicklime never healed, and the water just kept flowing through the sample. As a result of these successful tests, the team is working to commercialize this modified cement material.“It’s exciting to think about how these more durable concrete formulations could expand not only the service life of these materials, but also how it could improve the durability of 3D-printed concrete formulations,” says Masic.Through the extended functional lifespan and the development of lighter-weight concrete forms, he hopes that these efforts could help reduce the environmental impact of cement production, which currently accounts for about 8 percent of global greenhouse gas emissions. Along with other new formulations, such as concrete that can actually absorb carbon dioxide from the air, another current research focus of the Masic lab, these improvements could help to reduce concrete’s global climate impact.The research team included Janille Maragh at MIT, Paolo Sabatini at DMAT in Italy, Michel Di Tommaso at the Instituto Meccanica dei Materiali in Switzerland, and James Weaver at the Wyss Institute for Biologically Inspired Engineering at Harvard University. The work was carried out with the assistance of the Archeological Museum of Priverno in Italy.
2023.01.09
- [기술동향]World-first project t...
- Water treatment sludge could be used to prevent 117,000 kilometres of sewer pipes in Australia from cracking in future, without any intervention by humans, helping to save $1.4 billion in annual maintenance costs. A world-first project led by University of South Australia sustainable engineering expert Professor Yan Zhuge is trialling a novel solution to halt unprecedented levels of corrosion in the country’s ageing concrete pipelines.Corrosive acid from sulphur-oxidising bacteria in wastewater, along with excessive loads, internal pressure and temperature fluctuations are cracking pipes and reducing their life span, costing hundreds of millions of dollars to repair every year across Australia.Self-healing concrete, in the form of microcapsules filled with water treatment sludge, could be the answer.“Sludge waste shows promise to mitigate microbial corrosion in concrete sewer pipes because it works as a healing agent to resist acid corrosion and heal the cracks,” Prof Zhuge says.Researchers will develop microcapsules with a pH-sensitive shell and a healing agent core containing alum sludge – a by-product of wastewater treatment plants – and calcium hydroxide powder. The combination will be highly resistant to microbially induced corrosion (MIC).It will be embedded inside the concrete at the final step of mixing to protect it from breakage. When the pH value changes as acid levels build up, microcapsules will release the healing agents.“This technology will not only extend the lifetime of concrete structures, saving the Australian economy more than $1 billion, but it will promote a circular economy as well by reusing sludge that would normally end up in landfill,” Prof Zhuge says.Existing repairs of deteriorating concrete not only cost millions, but they are often short-lived, with 20 per cent failing after five years and 55 per cent failing after 10 years.Existing methods to contain acid corrosion in sewer pipes are unsuccessful for a variety of reasons.Chemicals can be added to wastewater to alter the sewer environment and stop corrosion, but they contaminate the environment and are also costly. Another option involves increasing the speed of sewage flow by amending the pipe hydraulics, but this is not always effective. Surface coating is another popular option, but it is time consuming, and the effect is temporary.“Improving the concrete mixture design is the preferred method for controlling microbially induced corrosion. Using self-healing concrete that can seal cracks by itself without any human intervention is the solution.”To be carbon-neutral by 2050, the construction industry is being forced to transit to a circular economy, Prof Zhuge says.“Industry by-products or municipal wastes that would normally be discarded in landfill sites, potentially generating pollution, may now be reused in the construction production chain.“Mainland Australia alone has about 400 drinking water treatment plants, with a single site annually generating up to 2000 tonnes of treated water sludge. Most of that is disposed of in landfill, costing more than $6 million each year, as well as causing severe environmental issues.”Disposing one tonne of sludge in landfill releases approximately 29.4 tonnes of carbon dioxide emissions – much higher than cement production – and leaches aluminium into the soil and water, a risk factor for Alzheimer’s disease.“We are confident this novel self-healing concrete based on advance composite technology will address issues of sewer pipe corrosion and sludge disposal in one hit,” Prof Zhuge says.The project is being partially funded by a $501,504 Australian Research Council grant and involves researchers from the University of South Australia and University of Queensland.Yan Zhuge is a Professor in Structural Engineering at UniSA STEM and a renowned expert in sustainable concrete material. Over the past five years she has attracted more than $4 million worth of grants, published 149 journal papers and in 2018 won the South Australian Innovation Award in Engineering for her research on using waste in concrete. Provided by University of south Australia Source : https://www.unisa.edu.au/media-centre/Releases/2022/world-first-project-to-self-heal-cracked-concrete-using-sludge-could-save-$1.4-billion-repair-bill-to-australias-sewer-pipes/
2022.12.13
- [행사정보]SMARTINCS’23 Confe...
- Source : https://smartincs.ugent.be/index.php/conference
2022.09.01
- [기술동향]Building the future w...
- After water, concrete is the most widely used substance on Earth. With applications from housing and industry to coastal defence and infrastructure, concrete and cement are at the cornerstone of life, quite literally. Unfortunately, the construction industry also has a major environmental impact. Cement production alone generates up to 8% of global carbon emissions, more than aviation (2.5%) although less than the agriculture sector (12%), according to one report.Innovative thinking is needed to make construction materials more sustainable, while keeping them affordable and versatile. Some in the industry are using new technologies to make concrete ultra-durable, while others are turning to biology to make sustainable biocement.New types of sustainable concrete are key to providing the foundations for other sustainable infrastructure, such as wind farms, said Professor Liberato Ferrara, a professor of structural analysis and design at the Polytechnic University of Milan in Italy.‘If we think of all the needs that we have now for the energy transition, I would say that we cannot do this without concrete,’ he said.Punishing settingsHe led a project called ReSHEALience, which set out to develop ultra-high-durability concrete (UHDC). Such concrete is able to withstand extreme conditions and self-heal when used for construction in punishing settings like marine environments and geothermal energy plants.‘These environments are among the most aggressive situations that you can have for concrete structures,’ said Prof Ferrara.The tailored recipes are what gives these concrete mixes their strength and durability, including components such as crystalline additives, alumina nanofibres and cellulose nanocrystals.Concrete inevitably cracks during its service life, but one of the features of crystalline mixtures is that they stimulate self-healing. By reacting with water and constituents in the concrete, they form needle-shaped crystals that grow to fill the cracks. The nanofibres mixed through it add mechanical strength to the material and help to enhance its toughness, allowing it to endure extreme conditions.UHDC has been tested as a durable substitute for traditional wooden rafts in mussel farming, and to make parts of floating wind-turbine platforms in coastal areas. It has also been tested in the harsh conditions of a geothermal power plant, where its performance improved on traditional methods of construction.Its use in the restoration of an old water tower in Malta demonstrates the concrete’s potential for the maintenance of heritage architecture.Sustainable material‘The pilots are matching expectations from all points of view,’ said Prof Ferrara. ‘We succeeded in demonstrating that UHDC is intrinsically a sustainable material. It allows the use of less material to build the same structure, so in the end the environmental footprint and economic balance is better.’The material slashes resource use both by reducing the amount of material needed in the first place and by lasting much longer, with Prof Ferrara predicting that it may have the potential to last up to 50 years before requiring significant maintenance.It can be produced in a wide variety of locations for many different applications using local materials. Moreover, crushed UHDC shows promise as a recycled constituent to produce new concrete with the same mechanical performance and durability as the parent concrete.The increasing urgency of meeting sustainability goals calls for fresh ways of looking ‘holistically’ at construction, Prof Ferrara added.‘It’s about spreading a new way of thinking for concrete structures’ that considers the whole value chain and service life of the planned structures, he said. ‘You have to think of the structural design, the procurement of materials, and the materials’ durability and life cycle. If you do not think like that, you will always have partial information and innovation will not break through.’BiocementElsewhere, researchers are looking at quite different ways of innovating in the construction sector, harnessing the natural processes of living organisms.For rail companies, the settlement of soils over time in embankments beneath railways can create serious problems and add to maintenance costs and passenger delays.Mechanical methods for firming up ground materials or chemical-based stabilisers are usually employed as a solution. However, these can be disruptive and costly, have environmental side-effects and generate carbon emissions.The NOBILIS project is therefore getting bacteria to do the work, viewing the ground as a living organism rather than a nondescript mass to be moved by bulldozers.The idea is that stronger soil, created through a process called ‘biocementation’, can reduce the need for earthworks and materials like concrete.Bacteria-builtIn the process of biocementation, the bacteria’s growth and metabolic activity are stimulated by providing them with nutrients and so-called cementing agents. The resulting enzymes produced by the bacteria catalyse reactions that ultimately form substances such as calcium carbonate, which bind the soil particles together.The technique has been recognised as having potential in soil with larger particles, such as sandy soils, including forming beach rocks to protect against coastal erosion and for other applications in civil or environmental engineering.However, a bigger challenge emerges with finer-grained soils like clay and peat, due to more restricted movement of bacteria, water and other substances. Undeterred, NOBILIS is seeking to explore ways to use biocementation on a wider range of soils.Recent work in East Anglia, UK has demonstrated the possibility of biocementing peat soils. The NOBILIS project will aim to scale up this work through trials in the field, said Professor Maria Mavroulidou, a geotechnical researcher and project lead at London South Bank University (LSBU).Paradigm shiftProf Mavroulidou said this kind of biology-inspired approach requires new ways of thinking and faith in unfamiliar techniques.‘To tell a practising civil engineer that you’re going to use bacteria to cement the ground raises eyebrows,’ she said, because it’s a paradigm shift for the industry.Wilson Mwandira, an environmental engineering researcher, also at LSBU, said NOBILIS is investigating techniques to lock up carbon dioxide in the soil as biocementation occurs, as well as looking at the potential of using more indigenous bacteria in the process.Using bacteria already present in the soil would avoid having a negative impact on organisms already in the environment, explained Mwandira. ‘If you bring new bacteria into a community, you are going to have a disruption in the system,’ he said.The hope is that such biocementation techniques will become more widely applicable to construction work in general. ‘We’re also trying to extend the technique more generally to other geotechnical materials found in foundations under buildings and civil-engineering construction,’ said Professor Michael Gunn, a geotechnical engineer also at LSBU. ‘All construction requires some form of ground improvement.’He thinks that it could take a number of years for the techniques to be used in a more routine way, but that it is essential such innovative methods are explored to address long-term challenges in construction.‘A significant proportion of greenhouse gas emissions in the form of carbon dioxide is down to the construction industry,’ he said. ‘So we need to move away from the traditional processes.’ Provided by Horizon Magazine : https://horizon.scienceblog.com/2102/building-the-future-with-self-healing-concrete-and-biocement/
2022.07.22
- 이메일 무단수집 거부에 대해 알려 드립니다.
- 자기치유 친환경 콘크리트 연구센터에 무차별적으로 보내지는 메일을 차단하기 위해 본 웹사이트에 게시된 이메일 주소가 전자우편 수집 프로그램이나 그밖의 기술적 장치를 이용하여 무단으로 수집되는 것을 거부하며, 이를 위반시 정보통신망법에 의해 형사처벌됨을 유념하시기 바랍니다.