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Homedan C.,French Institute of Health and Medical Research | Homedan C.,University of Angers | Laafi J.,French Institute of Health and Medical Research | Schmitt C.,University Paris Diderot | And 20 more authors.
International Journal of Biochemistry and Cell Biology | Year: 2014

Acute intermittent porphyria (AIP), an inherited hepatic disorder, is due to a defect of hydroxymethylbilane synthase (HMBS), an enzyme involved in heme biosynthesis. AIP is characterized by recurrent, life-threatening attacks at least partly due to the increased hepatic production of 5-aminolaevulinic acid (ALA). Both the mitochondrial enzyme, ALA synthase (ALAS) 1, involved in the first step of heme biosynthesis, which is closely linked to mitochondrial bioenergetic pathways, and the promise of an ALAS1 siRNA hepatic therapy in humans, led us to investigate hepatic energetic metabolism in Hmbs KO mice treated with phenobarbital. The mitochondrial respiratory chain (RC) and the tricarboxylic acid (TCA) cycle were explored in the Hmbs-/- mouse model. RC and TCA cycle were significantly affected in comparison to controls in mice treated with phenobarbital with decreased activities of RC complexes I (-52%, ** p < 0.01), II (-50%, ** p < 0.01) and III (-55%, * p < 0.05), and decreased activity of α-ketoglutarate dehydrogenase (-64%, * p < 0.05), citrate synthase (-48%, ** p < 0.01) and succinate dehydrogenase (-53%, * p < 0.05). Complex II-driven succinate respiration was also significantly affected. Most of these metabolic alterations were at least partially restored after the phenobarbital arrest and heme arginate administration. These results suggest a cataplerosis of the TCA cycle induced by phenobarbital, caused by the massive withdrawal of succinyl-CoA by ALAS induction, such that the TCA cycle is unable to supply the reduced cofactors to the RC. This profound and reversible impact of AIP on mitochondrial energetic metabolism offers new insights into the beneficial effect of heme, glucose and ALAS1 siRNA treatments by limiting the cataplerosis of TCA cycle. © 2014 Elsevier Ltd.

Karim Z.,French Institute of Health and Medical Research | Karim Z.,Laboratory of excellence | Lyoumi S.,French Institute of Health and Medical Research | Lyoumi S.,Laboratory of excellence | And 15 more authors.
Clinics and Research in Hepatology and Gastroenterology | Year: 2015

The hereditary porphyrias comprise a group of eight metabolic disorders of the heme biosynthesis pathway. Each porphyria is caused by abnormal function at a separate enzymatic step resulting in a specific accumulation of heme precursors. Porphyrias are classified as hepatic or erythropoietic, based on the organ system in which heme precursors (δ-aminolevulinic acid [ALA], porphobilinogen and porphyrins) are overproduced. Clinically, porphyrias are characterized by acute neurovisceral symptoms, skin lesions or both. However, most if not all the porphyrias impair hepatic or gastrointestinal function. Acute hepatic porphyrias present with severe abdominal pain, nausea, constipation, confusion and seizure, which may be life threatening, and patients are at risk of hepatocellular carcinoma without cirrhosis. Porphyria Cutanea presents with skin fragility and blisters, and patients are at risk of hepatocellular carcinoma with liver iron overload. Erythropoietic protoporphyria and X-linked protoporphyria present with acute painful photosensitivity, and patients are at risk of acute liver failure. Altogether, porphyrias are still underdiagnosed, but once they are suspected, early diagnosis based on measurement of biochemical metabolites that accumulate in the blood, urine, or feces is essential so specific treatment can be started as soon as possible and long-term liver complications are prevented. Screening families to identify presymptomatic carriers is also crucial to prevent overt disease and chronic hepatic complications. © 2015 Elsevier Masson SAS.

Brousse V.,University Hospital Necker Enfants Malades | Brousse V.,French Institute of Health and Medical Research | Brousse V.,Laboratory of Excellence | Brousse V.,University of Paris Descartes | And 4 more authors.
British Journal of Haematology | Year: 2015

Sickle cell disease induces specific brain alterations that involve both the macrocirculation and the microcirculation. The main overt neurovascular complications in children are infarctive stroke, transient ischaemic attack and cerebral haemorrhage. Silent cerebral infarction, cognitive dysfunction and recurrent headache are also common. Cerebrovascular disease selectively affects children with the HbSS or HbS-β0 genotypes (i.e. sickle cell anaemia). The incidence of stroke peaks between 2 and 5 years of age (1·02/100 patient-years) and increases with the severity of the anaemia. Most strokes can be prevented by annual transcranial Doppler screening from 2 to 16 years of age and providing chronic blood transfusion when this investigation shows elevated blood-flow velocities. The role for hydroxycarbamide in children with abnormal transcranial Doppler findings is under investigation. After a stroke, chronic blood transfusion is very strongly recommended, unless haematopoietic stem cell transplantation can be performed. Routine magnetic resonance imaging shows that more than one-third of children have silent cerebral infarction, which is associated with cognitive impairments. Screening for silent infarcts seems legitimate, since their presence may lead to supportive treatments. The role for more aggressive interventions such as hydroxycarbamide or chronic blood transfusion is debated. © 2015 John Wiley & Sons Ltd.

Lasocki S.,Angers University Hospital Center | Piednoir P.,Groupe Hospitalier Paris Nord Val Of Seine | Couffignal C.,French Institute of Health and Medical Research | Couffignal C.,University Paris Diderot | And 15 more authors.
Critical Care Medicine | Year: 2016

Objective: To compare the oxidative stress induced by IV iron infusion in critically ill patients and in healthy volunteers. Design: Multicenter, interventional study. Setting: Two ICUs and one clinical research center. Subjects: Anemic critically ill patients treated with IV iron and healthy volunteers. Interventions: IV infusion of 100 mg of iron sucrose. Measurements and Main Results: Thirty-eight anemic patients (hemoglobin, median [interquartile range] = 8.4 g/dL [7.7-9.2]) (men, 25 [66%]; aged 68 yr [48-77]; Simplified Acute Physiology Score II, 48.5 [39-59]) and 39 healthy volunteers (men, 18 [46%]; aged 42.1 yr [29-50]) were included. Blood samples were drawn before (H0) and 2, 6, and 24 hours (H2, H6, and H24) after a 60-minute iron infusion for the determination of nontransferrin bound iron, markers of lipid peroxidation-8α-isoprostanes, protein oxidation-advanced oxidized protein product, and glutathione reduced/oxidized. Iron infusion had no effect on hemodynamic parameter in patients and volunteers. At baseline, patients had much higher interleukin-6, C-reactive protein, and hepcidin levels. 8α-isoprostanes was also higher in patients at baseline (8.5 pmol/L [6.5-12.9] vs 4.6 pmol/L [3.5-5.5]), but the area under the curve above baseline from H0 to H6 was not different (p = 0.38). Neither was it for advanced oxidized protein product and nontransferrin bound iron. The area under the curve above baseline from H0 to H6 (glutathione reduced/oxidized) was lower in volunteers (p = 0.009). Eight patients had a second set of dosages (after the fourth iron infusion), showing higher increase in 8α-isoprostanes. Conclusions: In our observation, IV iron infusion does not induce more nontransferrin bound iron, lipid, or protein oxidation in patients compared with volunteers, despite higher inflammation, oxidative stress, and hepcidin levels and lower antioxidant at baseline. In contrary, iron induces a greater decrease in antioxidant, compatible with higher oxidative stress in volunteers than in critically ill patients. © 2016 by the Society of Critical Care Medicine and Wolters Kluwer Health, Inc.

Arnaud-Cormos D.,University of Limoges | Kohler S.,University of Limoges | Bessieres D.,University of Pau and Pays de l'Adour | O'Connor R.P.,University of Limoges | And 3 more authors.
IEEE Transactions on Plasma Science | Year: 2014

In this paper, a device for accurate electrical measurements for nanosecond repetitive pulsed discharges (NRPDs) is presented. The experimental setup developed is based on an interelectrode system integrated in a transverse electromagnetic cell. This setup allows synchronizing the voltage and current measurements with a 4-GHz frequency bandwidth, corresponding to 250-ps pulse duration. A coaxial-shaped sharp metallic needle serves as a probe for current measurements. The needle probe is also the point electrode of a point-to-plane system used to generate discharges. The experimental setup was used to electrically characterize NRP corona and diffuse discharges, in negative polarity. Discharge current pulses with rise times less than 1 ns and amplitudes up to 120 mA were measured. The energy deposited by discharges was also determined. © 1973-2012 IEEE.

Deplanque G.,Saint Joseph Hospital | Demarchi M.,Besancon University Hospital Center | Hebbar M.,University Hospital | Flynn P.,Park Nicollet Institute | And 21 more authors.
Annals of Oncology | Year: 2015

Background: Masitinib is a selective oral tyrosine-kinase inhibitor. The efficacy and safety of masitinib combined with gemcitabine was compared against single-agent gemcitabine in patients with advanced pancreatic ductal adenocarcinoma (PDAC). Patients and methods: Patients with inoperable, chemotherapy-naïve, PDAC were randomized (1:1) to receive gemcitabine (1000 mg/m2) in combination with either masitinib (9 mg/kg/day) or a placebo. The primary endpoint was overall survival (OS) in the modified intent-to-treat population. Secondary OS analyses aimed to characterize subgroups with poor survival while receiving single-agent gemcitabine with subsequent evaluation of masitinib therapeutic benefit. These prospectively declared subgroups were based on pharmacogenomic data or a baseline characteristic. Results: Three hundred and fifty-three patients were randomly assigned to receive either masitinib plus gemcitabine (N = 175) or placebo plus gemcitabine (N = 178). Median OS was similar between treatment-arms for the overall population, at respectively, 7.7 and 7.1 months, with a hazard ratio (HR) of 0.89 (95%CI [0.70; 1.13]. Secondary analyses identified two subgroups having a significantly poor survival rate when receiving single-agent gemcitabine; one defined by an overexpression of acyl-CoA oxidase-1 (ACOX1) in blood, and another via a baseline pain intensity threshold (VAS > 20 mm). These subgroups represent a critical unmet medical need as evidenced from median OS of 5.5 months in patients receiving single-agent gemcitabine, and comprise an estimated 63% of patients. A significant treatment effect was observed in these subgroups for masitinib with median OS of 11.7 months in the 'ACOX1' subgroup [HR = 0.23 (0.10; 0.51), P = 0.001], and 8.0 months in the 'pain' subgroup [HR = 0.62 (0.43; 0.89), P = 0.012]. Despite an increased toxicity of the combination as compared with single-agent gemcitabine, side-effects remained manageable. Conclusions: The present data warrant initiation of a confirmatory study that may support the use of masitinib plus gemcitabine for treatment of PDAC patients with overexpression of ACOX1 or baseline pain (VAS > 20mm). Masitinib's effect in these subgroups is also supported by biological plausibility and evidence of internal clinical validation. © The Author 2015.

Akoussan K.,CNRS Study of Microstructures, Mechanics and Material Sciences lab | Boudaoud H.,University of Lorraine | El-Mostafa D.,CNRS Study of Microstructures, Mechanics and Material Sciences lab | El-Mostafa D.,Laboratory of Excellence | Carrera E.,Polytechnic University of Turin
Mechanics of Advanced Materials and Structures | Year: 2015

This work deals with the vibration of orthotropic multilayer sandwich structures with viscoelastic core. A finite element model is derived from a classical zigzag model with shear deformation in the viscoelastic layer. The aim of the present work is to establish numerical models and develop numerical tools to design multilayer composites structures with high damping properties. To fulfill this purpose, a finite element model has been developed for vibration analysis of a sandwich plate (elastic orthotropic)/(viscoelastic orthotropic)/(elastic orthotropic). A numerical study from the variation of the damping properties of the structures was performed according to the faces materials fibers orientation. © 2015 Copyright © Taylor & Francis Group, LLC.

News Article | October 27, 2015

Climate change undoubtedly affects all organisms but researchers have found that reptiles are particularly vulnerable as their body temperature is directly affected by temperature in the environment. In a study published in the journal PLOS Biology, researchers examined what would happen to a populations of common lizards (Zootoca vivipara) should the climate warm by 2 degrees Celsius, the predicted world temperature by the end of the century. According to the results of their research, Elvire Bestion and colleagues were able to show that many of the common lizard populations will disappear quickly if warmer temperatures persist. To study the lizards, the researchers used a Metatron, a system of semi-natural enclosures that allowed for temperature manipulation, creating two distinct climates: one simulating present conditions and the other warmer by 2 degrees Celsius. There were 18 common lizard populations utilized in the study, each one placed in either a "present" or "warmed" enclosure for more than two years. The populations were then surveyed for another year, allowing the researchers to observe how warmer climates had an impact on the lizards in terms of demographic parameters like survival, reproduction and growth rate. Bestion said the warmer climate was actually beneficial to the lizards at first as it led to earlier access to reproduction (some adult females also engaged in second reproduction event in a year when they typically only have one annually) and faster growth rates in juveniles but it led to lower survival in the adults of the species. "A model of population dynamics showed that the increased adult mortality would lead to decreased population growth rates, and ultimately rapid population extinctions in around 20 years," she added. While the results of the study appear dramatic, it does not predict that common lizards will become extinct at the level of the species, clarified Julien Cote, the study's co-lead author. However, it is suggested that common lizard populations at the southern end of the species' distribution range should be tracked specifically as they will be the likeliest to suffer from the effects of a warmer climate. Depending on carbon emission scenarios, the study showed that 14 to 30 percent of common lizard populations in Europe will be threatened by a warming climate. The study received funding support from "TULIP," a French Laboratory of Excellence project.

News Article | February 1, 2016

The dark-colored hydrocarbon solid known as kerogen gives rise to the fuels that power many of our daily activities: Petroleum is the source of gasoline and diesel fuels, and natural gas is used for cooking, heating, and increasingly for producing electricity. And yet, kerogen’s basic internal structure has remained poorly understood — until now. A new analysis, by a joint team of researchers at MIT, the French government research organization CNRS, and elsewhere, has revealed kerogen’s internal structure, in detail down to the atomic level. Their results were just published in the journal Nature Materials in a paper by MIT postdoc Colin Bousige, visiting scientist Benoit Coasne, senior research scientist Roland J.-M. Pellenq, professor Franz-Josef Ulm, and colleagues at MIT, CNRS, and other institutions. The findings reveal important details about how gas and oil move through pores in formations deep underground, making it possible to estimate the amount of recoverable reserves more accurately and potentially pointing to better ways of extracting them. Kerogen is a mixture of organic materials, primarily the remains of dead microbes, plants, and animals that have decomposed and been buried deep underground and compressed. This process forms a carbon-rich, rock-hard material riddled with pores of various sizes. When transformed as a result of pressure or geothermal heat, hydrocarbon molecules in the kerogen break down into gas or petroleum. These flow through the pores and can be released through drilling. It turns out that the formula, known as the Darcy equation, that the petroleum and gas industries have traditionally used to describe the way these fluids move underground is not accurate when the hydrocarbon fluids are inside kerogen. The new understanding could change the interpretation of how some gas and oil reservoirs, often found in shale formations, actually behave. As these fluids move through pores in the deep rock, “the flux in these nanopores, what we call the transport properties, are not what is given by the macroscale physics of liquids,” says Pellenq, a senior research scientist in the Department of Civil and Environmental Engineering at MIT and co-director, with Ulm, of the joint MIT-CNRS program called MultiScale Materials Science for Energy and Environment. In many situations where the standard formula predicts that oil or gas will flow, in reality — and as predicted by the new model — the flow stops. The pore sizes in the rock are often smaller and less interconnected than expected, the study shows, so the individual molecules of oil or gas no longer behave collectively as fluids. Instead, they get stuck in place, like a large dog trying to crawl through a cat door. This understanding of the nanoscale structure of pore spaces in kerogen is “a true new idea, it’s a game changer,” says Pellenq. Previously it had been assumed that the pore spaces in these deep underground formations were larger — microscale rather than nanoscale — and thus would allow the petroleum or gas to flow more easily through them. “Those nanopores were not expected by the industry,” he says. What that reveals, he explains, is that “those molecules trapped in those pores are really trapped.” Although researchers had generally assumed that these molecules could be released from the rock simply by applying more pressure or better solvents, “these nanopores are really a big part of the porosity of kerogen,” he says, and essential for understanding the recoverability of reserves. Right now, industry practices extract fluids from the few big pores in the fracture, Pellenq says. However this fracking process “is not even touching the real treasure, which is in the walls, in the pores of the wall.” A better approach, the research suggests, might be to replace the conventional water-based hydrofracking solutions. “Those formations, and especially those pores, are hydrophobic, so the hydrofracking is not touching those nanopores,” Pellenq says. But “if you were change the fluids from water-based to carbon-dioxide based, we know that CO will go into those nanopores, because those pores are CO -philic” (that is, carbon-dioxide attracting). This would force out at least the lighter molecules, such as the methane that is the main component of natural gas, though perhaps not the heavier molecules of petroleum. Moving away from the use of water would be “good news” because it would reduce the need for using and then cleaning or disposing of contaminated water, according to Pellenq. In addition, it might even be a way of sequestering some carbon dioxide, he says, providing another potential bonus. Jean-Noël Rouzaud, the CNRS research director at the geology laboratory of the Ecole Normale Supérieure in Paris, who was not involved in this research, says this work “appears me very original and of really good scientific quality.” He adds that it brings “an essential contribution to the study of non-conventional sources of hydrocarbons such as oil and gas shales. [This work] should allow people to envisage more effective and environment-friendlier techniques of recovery of hydrocarbons.” The study also included researchers from Oak Ridge National Laboratory; the Institut de Science des Materiaux de Mulhouse in Mulhouse, France; Schlumberger-Doll Research in Cambridge, Massachusetts; the European Synchrotron Radiation Facility in Grenoble, France; and Aix Marseille University in Marseille, France. It was supported by the MIT Energy Initiative, as part of the X-Shale project funded by Shell and Schlumberger, and by the French National Research Agency through the Laboratory of Excellence (Labex) ICoME2.

News Article | August 22, 2016

An MIT-led team has defined the nanoscale forces that control how particles pack together during the formation of cement “paste,” the material that holds together concrete and causes that ubiquitous construction material to be a major source of greenhouse gas emissions. By controlling those forces, the researchers will now be able to modify the microstructure of the hardened cement paste, reducing pores and other sources of weakness to make concrete stronger, stiffer, more fracture-resistant, and longer-lasting. Results from the researchers’ simulations explain experimental measurements that have confused observers for decades, and they may guide the way to other improvements, such as adding polymers to fill the pores and recycling waste concrete into a binder material, reducing the need to make new cement. Each year, the world produces 2.3 cubic yards of concrete for every person on earth, in the process generating more than 10 percent of all industrial carbon dioxide (CO ) emissions. New construction and repairs to existing infrastructure currently require vast amounts of concrete, and consumption is expected to escalate dramatically in the future. “To shelter all the people moving into cities in the next 30 years, we’ll have to build the equivalent of several hundred New York cities,” says Roland Pellenq, senior research scientist in the MIT Department of Civil and Environmental Engineering (CEE) and research director at France’s National Center for Scientific Research (CNRS). “There’s no material up to that task but concrete.” Recognizing the critical need for concrete, Pellenq and his colleague Franz-Josef Ulm, professor of CEE and director of the MIT Concrete Sustainability Hub (CSHub), have been working to reduce its environmental footprint. Their goal: to find ways to do more with less. “If we can make concrete stronger, we’ll need to use less of it in our structures,” says Ulm. “And if we can make it more durable, it’ll last longer before it needs to be replaced.” Surprisingly, while concrete has been a critical building material for 2,000 years, improvements have largely come from trial and error rather than rigorous research. As a result, the factors controlling how it forms and performs have remained poorly understood. “People always deemed what they saw under a microscope as being coincidence or evidence of the special nature of concrete,” says Ulm, who with Pellenq co-directs the joint MIT-CNRS laboratory called MultiScale Material Science for Energy and Environment, hosted at MIT by the MIT Energy Initiative (MITEI). “They didn’t go to the very small scale to see what holds it together — and without that knowledge, you can’t modify it.” Cement: the key to better concrete The problems with concrete — both environmental and structural — are linked to the substance that serves as its glue, namely, cement. Concrete is made by mixing together gravel, sand, water, and cement. The last two ingredients combine to make cement hydrate, the binder in the hardened concrete. But making the dry cement powder requires cooking limestone (typically with clay) at temperatures of 1,500 degrees Celsius for long enough to drive off the carbon in it. Between the high temperatures and the limestone decarbonization, the process of making cement powder for concrete is by itself responsible for almost 6 percent of all CO  emissions from industry worldwide. Structural problems can also be traced to the cement: When finished concrete cracks and crumbles, the failure inevitably begins within the cement hydrate that’s supposed to hold it together — and replacing that crumbling concrete will require making new cement and putting more CO  into the atmosphere. To improve concrete, then, the researchers had to address the cement hydrate — and they had to start with the basics: defining its fundamental structure through atomic-level analysis. In 2009, Pellenq, Ulm, and an international group of researchers associated with CSHub published the first description of cement hydrate’s three-dimensional molecular structure. Subsequently, they determined a new formula that yields cement hydrate particles in which the atoms occur in a specific configuration — a “sweet spot” — that increases particle strength by 50 percent. However, that nanoscale understanding doesn’t translate directly into macroscale characteristics. The strength and other key properties of cement hydrate actually depend on its structure at the “mesoscale” — specifically, on how nanoparticles have packed together over hundred-nanometer distances as the binder material forms. When dry cement powder dissolves in water, room-temperature chemical reactions occur, and nanoparticles of cement hydrate precipitate out. If the particles don’t pack tightly, the hardened cement will contain voids that are tens of nanometers in diameter — big enough to allow aggressive materials such as road salt to seep in. In addition, the individual cement hydrate particles continue to move around over time — at a tiny scale — and that movement can cause aging, cracking, and other types of degradation and failure. To understand the packing process, the researchers needed to define the precise physics that drives the formation of the cement hydrate microstructure — and that meant they had to understand the physical forces at work among the particles. Every particle in the system exerts forces on every other particle, and depending on how close together they are, the forces either pull them together or push them apart. The particles seek an organization that minimizes energy over length scales of many particles. But reaching that equilibrium state takes a long time. When the Romans made concrete 2,000 years ago, they used a binder that took many months to harden, so the particles in it had time to redistribute so as to relax the forces between them. But construction time is money, so today’s binder has been optimized to harden in a few hours. As a result, the concrete is solid long before the cement hydrate particles have relaxed, and when they do, the concrete sometimes shrinks and cracks. So while the Roman Colosseum and Pantheon are still standing, concrete that’s made today can fail in just a few years. Laboratory investigation of a process that can take place over decades isn’t practical, so the researchers turned to computer simulations. “Thanks to statistical physics and computational methods, we’re able to simulate this system moving toward the equilibrium state in a couple of hours,” says Ulm. Based on their understanding of interactions among atoms within a particle, the researchers — led by MITEI postdoc Katerina Ioannidou — defined the forces that control how particles space out relative to one another as cement hydrate forms. The result is an algorithm that mimics the precipitation process, particle by particle. By constantly tracking the forces among the particles already present, the algorithm calculates the most likely position for each new one — a position that will move the system toward equilibrium. It thus adds more and more particles of varying sizes until the space is filled and the precipitation process stops. Results from sample analyses appear in the first two diagrams in Figure 1 of the slideshow above. The width of each simulation box is just under 600 nanometers — about one-tenth the diameter of a human hair. The two analyses assume different packing fractions, that is, the total fraction of the simulation box occupied by particles. The packing fraction is 0.35 in the left-hand diagram and 0.52 in the center diagram. At the lower fraction, far more of the volume is made up of open pores, indicated by the white regions. The third diagram in Figure 1 is a sketch of the cement hydrate structure proposed in pioneering work by T.C. Powers in 1958. The similarity to the center figure is striking. The MIT results thus support Powers’ idea that the formation of mesoscale pores can be attributed to the use of excessive water during hydration — that is, more water than needed to dissolve and precipitate the cement hydrate. “Those pores are the fingerprint of the water you put into the mix in the first place,” says Pellenq. “Add too much water, and at the end you’ll have a cement paste that is too porous, and it will degrade faster over time.” To validate their model, the researchers performed experimental tests and parallel theoretical analyses to determine the stiffness and hardness (or strength) of cement hydrate samples. The laboratory measurements were taken using a technique called nanoindentation, which involves pushing a hard tip into a sample to determine the relationship between the applied load and the volume of deformed material beneath the indenter. The graphs in Figure 2 of the slideshow above show results from small-scale nanoindentation tests on three laboratory samples (small symbols) and from computations of those properties in a “sample” generated by the simulation (yellow squares). The graph on the left shows results for stiffness, the graph on the right results for hardness. In both cases, the X-axis indicates the packing fraction. The results from the simulations match the experimental results well. (The researchers note that at lower packing fractions, the material is too soggy to test experimentally — but the simulation can do the calculation anyway.) In another test, the team investigated experimental measurements of cement hydrate that have mystified researchers for decades. A standard way to determine the structure of a material is using small-angle neutron scattering (SANS). Send a beam of neutrons into a sample, and how they bounce back conveys information about the distribution of particles and pores and other features on length scales of a few hundred nanometers. SANS had been used on hardened cement paste for several decades, but the measurements always exhibited a regular pattern that experts in the field couldn’t explain. Some talked about fractal structures, while others proposed that concrete is simply unique. To investigate, the researchers compared SANS analyses of laboratory samples with corresponding scattering data calculated using their model. The experimental and theoretical results showed excellent agreement, once again validating their technique. In addition, the simulation elucidated the source of the past confusion: The unexplained patterns are caused by the rough edges at the boundary between the pores and the solid regions. “All of a sudden we could explain this signature, this mystery, but on a physics basis in a bottom-up fashion,” says Ulm. “That was a really big step.” “We now know that the microtexture of cement paste isn’t a given but is a consequence of an interplay of physical forces,” says Ulm. “And since we know those forces, we can modify them to control the microtexture and produce concrete with the characteristics we want.” The approach opens up a new field involving the design of cement-based materials from the bottom up to create a suite of products tailored to specific applications. The CSHub researchers are now exploring ways to apply their new techniques to all steps in the life cycle of concrete. For example, a promising beginning-of-life approach may be to add another ingredient — perhaps a polymer — to alter the particle-particle interactions and serve as filler for the pore spaces that now form in cement hydrate. The result would be a stronger, more durable concrete for construction and also a high-density, low-porosity cement that would perform well in a variety of applications. For instance, at today’s oil and natural gas wells, cement sheaths are generally placed around drilling pipes to keep gas from escaping. “A molecule of methane is 500 times smaller than the pores in today’s cement, so filling those voids would help seal the gas in,” says Pellenq. The ability to control the material’s microtexture could have other, less-expected impacts. For example, novel CSHub work has demonstrated that the fuel efficiency of vehicles is significantly affected by the interaction between tires and pavement. Simulations and experiments in the lab-scale setup shown in Figure 3 of the slideshow above suggest that making concrete surfaces stiffer could reduce vehicle fuel consumption by as much as 3 percent nationwide, saving energy and reducing emissions. Perhaps most striking is a concept for recycling spent concrete. Today, methods of recycling concrete generally involve cutting it up and using it in place of gravel in new concrete. But that approach doesn’t reduce the need to manufacture more cement. The researchers’ idea is to reproduce the cohesive forces they’ve identified in cement hydrate. “If the microtexture is just a consequence of the physical forces between nanometer-sized particles, then we should be able to grind old concrete into fine particles and compress them so that the same force field develops,” says Ulm. “We can make new binder without needing any new cement — a true recycling concept for concrete!” This research was supported by Schlumberger; France’s National Center for Scientific Research (through its Laboratory of Excellence Interdisciplinary Center on MultiScale Materials for Energy and Environment); and the Concrete Sustainability Hub at MIT. Schlumberger is a Sustaining Member of the MIT Energy Initiative. The research team also included other investigators at MIT; the University of California at Los Angeles; Newcastle University in the United Kingdom; and Sorbonne University, Aix-Marseille University, and the National Center for Scientific Research in France. This article appears in the Spring 2016 issue of Energy Futures, the magazine of the MIT Energy Initiative.

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