Tag Archives: #concrete

What Are The Effects Of Fiber Addition On The Properties Of High-Performance Concrete? (Civil Engineering)

Szymon Grzesiak and colleagues investigated the influence of fiber addition on the properties of high-performance concrete. They showed that addition of fibers reduced compressive strength and the modulus of elasticity of the concrete. Their study recently appeared in the Journal Materials.

High performance fiber reinforced concrete (HPFRC) is developing quickly to a modern structural material with a high potential. HPFRC is a ductile concrete with high metallic fiber content (1% or more by volume), with uniform or hybrid fibers. Experimental tests showed that fiber dosage improves the energy absorption capacity of concrete and enhances the robustness of concrete elements. However, the addition of fiber does not have always have a positive effect on the mechanical properties. Besides, due to increasing costs of the produced fiber reinforced concrete there is a demand to analyze the necessary fiber dosage in the concrete composition.

Now, Szymon Grzesiak and colleagues investigated the influence of fiber addition on the properties of high-performance concrete.

“It is expected that the surface and length of used fiber in combination with their dosage influence the structure of fresh and hardened concrete.”

— they said

In order to determine the influence of fiber addition, they carried out tests on a mixture with polypropylene (PP) and polyvinyl alcohol (PVA) fiber with dosages of 15, 25, and 35 kg/m³ as well as with control concrete without fiber.

Fig 1. (A) Slump experiment for MasterFiber 401 (PVA). (B) Fresh concrete with MasterFiber 401 (PVA). (C) Fresh concrete with MasterFiber 235 SPA (PP). © Authors

They found that, due to the addition of fibers to the concrete mix, a significant difference was observed in the compressive strength of the concrete. The fiber addition of 15 kg/m³ in the concrete composition reduced the compressive strength from 83.2 MPa to 79.6 MPa. The higher fiber dosage showed a similar trend. Furthermore, it reduced bulk density and the modulus of elasticity of the concrete.

“Due to the higher air content in the fiber-reinforced mixtures compared to normal concrete, the compressive strengths differed from each other.”

— they said.

They also showed that, PP and PVA fibers are effective in increasing the splitting tensile strength of concrete, which allows better utilization of material capacities and has an impact on the production costs of Fiber Reinforced Concrete (FRC) members. The comparison showed that the dosage of fibers increased from 4.0 MPa to 5.0 MPa (for 15 kg/m³), 6.7 MPa (25 kg/m³), and 6.9 MPa (35 kg/m³).

Additionally, the fiber dosage improved the flexural properties of concrete. The flexural strength increased the maximal 31% for a fiber dosage of 25 kg/m³ in comparison to the plain concrete. The bending tensile strength of concrete with added fibers also increased by up to 18% compared to materials without fibers.

© Authors
Figure 2. Bending-tensile strength of concrete with different fiber types (MasterFiber 235 SPA and MasterFiber 401) for a fiber dosage of 35 kg/m³ in accordance with EN12467 © authors

Moreover, it has been shown from stress–deflection curves that long MasterFiber 235 SPA (PP) is better than short MasterFiber 401 (PVA). This is because the stress–deflection curve of fiber type MasterFiber 401 (PVA) revealed a higher increase in deflection compared to fiber type MasterFiber 235 SPA (PP), which may indicate unfavorable adhesion forces between PVA fiber and the matrix. Shorter fibers pull-out of the matrix faster than longer fibers. This is attributed to the bonding forces between the fibers and the concrete matrix.

“The 30 mm long fibers provided a better friction range than the 12 mm long fibers and also provided a better stress transfer in the matrix.”

Finally, the highest PP fiber dosage examined in the concrete composition amounted to 35 kg/m³. However, the addition of more than 25 kg/m³ of fibers to the concrete mix had less influence on the bending tensile strength of the concrete. This concrete mix had an overcritical fiber dosage and was characterized by tensile strain-hardening behavior. A comparison of the stress–deflection curves with the addition of 25 kg/m³ and 35 kg/m³ of fibers also revealed that the cracking behavior of concrete for these two fiber contents did not differ significantly.

Fig 3. Top: Typical failure modes for specimens with MasterFiber 235 SPA (PP). (A) Images of the tensile fracture face of a fiber. (B) Images of the pull-out fracture face of a fiber. Middle: Typical failure modes for specimens with MasterFiber 401 (PVA). (A) Images of the pull-out fracture face of a fiber. Bottom: Typical failure modes for specimens without fiber. © Authors

Funding: Their research was funded by the Master Builders Solutions Deutschland GmbH.

Featured image: (A) Polypropylene fiber MasterFiber 235 SPA (PP). (B) Polyvinyl alcohol fiber MasterFiber 401(PVA) used in the present study. © Authors


Reference: Grzesiak, S.; Pahn, M.; Schultz-Cornelius, M.; Harenberg, S.; Hahn, C. Influence of Fiber Addition on the Properties of High-Performance Concrete. Materials 2021, 14, 3736. https://doi.org/10.3390/ma14133736


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Researchers Uncover Fatal Flaw In Green Pigmented Concrete (Engineering)

As Xi’an Jiaotong-Liverpool University researchers completed their research on coloured architectural concrete, they found a surprising result—green pigmented cement had impurities that produced porous, poor quality concrete. Meanwhile, red and blue pigments had little effect.

The research was conducted by Mehreen Heerah, a graduate of XJTLU’s Department of Civil Engineering, Dr Graham Dawson of XJTLU’s Department of Chemistry, and Dr Isaac Galobardes of Mohammed VI Polytechnic University.

Pigmented architectural concrete is used as a visually appealing alternative to grey concrete, such as in Barcelona’s Ciutat de la Justícia, explains Dr Dawson. As the demand for pigmented architectural concrete grows, so does the importance of this research.

Not easy being green

“The characteristics of red and blue pigments used in the study were established in the existing research literature. However, the characteristics of the green pigment was not usual,” says Dawson.

“The results for the red and blue pigments were quite close to our expectation,” Heerah says. “On the other hand, we did not expect the drastic effect of green pigment on the properties of the mortar. In fact, we expected that a greater increment in strength with the green pigment compared to the other two.”

That’s because green pigment in products is based upon chromium oxide, which increases the strength of the mix when hydrated.

So why was green concrete found to be substandard?

The answer lies in how it was produced with damaging impurities, says Dr Dawson.

“Chemical products are used to produce pigments,” he explains. “Sometimes, pigments present simple chemical components and other combinations of them to obtain different colours.”

The offending impurity that weakened the green concrete was muscovite; a mineral used to produce green pigment for other industrial uses. When hydrated with cement, muscovite generated significant quantities of a component that causes excessive porousness, which results in a reduction in strength and longevity.

“However, other studies have found that there is no adverse effect when using green pigment consisting solely of chromium (III) oxide, with no muscovite,” says Heerah.

Mix it up

The cement samples were produced with three different pigments—blue cobaltous aluminate, green chromium oxide and red iron oxide pigment—at three different levels: 1, 5 and 10%. The researchers tested two types of cement to understand how these admixtures and by-products affect the properties of the resulting concrete.

The four-part experiment first tested water absorption to evaluate the change in physical properties, and then determined the hydration properties of the samples.

Next, the kinetics of hydration were studied through the evolution of the temperature of each mix. Finally, the researchers examined the flexural and compressive strength to understand the effect of pigment on mechanical strength.

The research established that the morphology of hydration products and kinetics was related to the samples’ compressive strength.

The poor performance of the green pigment stood out compared to the minimal effects of the red and blue.

The research also discovered that the cobaltous aluminate oxide (blue) and iron (III) oxide (red) pigments could be used with both Portland and Portland Composite cement without weakening the concrete’s strength.

Less impact

Researchers also improved upon an existing equation used for estimating the real-time compressive strength of the pigmented mortar, Heerah says.

Dr Galobardes explains: “Using this equation avoids making the destructive tests used to estimate the mechanical properties of concrete.

“This eliminates waste and lowers carbon dioxide emissions and costs related to the production of the samples used in the tests.”

While pigments themselves do not reduce carbon emissions produced by concrete, the research indicates that they are safe to use with eco-cements.

Cement mixes such as Portland Composite Cement, which includes ground granulated blast-furnace slag (GGBS) and fly ash are expected to achieve reduced carbon emissions in coming years.

The paper, “Characterisation and control of cementitious mixes with colour”, was published by Elsevier’s Case Studies in Construction Materials journal.


Provided by XJTLU

What Are The Effects Of Thermal Conductive Materials on The Freeze-thaw Resistance Of Concrete? (Material Science / Engineering)

Byeong-Hun Woo and colleagues studied the effects of thermal conductive materials on the freeze-thaw resistance of concrete. They performed two experiments: freeze-thaw and rapid cyclic thermal attack in order to evaluate the thermal durability of concrete with thermal conductive materials. They showed that the graphite had a negative effect on the freeze-thaw and rapid cyclic thermal attack. While, the use of silicon carbide (50%) and steel fiber significantly improved thermal durability of concrete. Their study recently appeared in the Journal Materials.

Cold regions have two kinds of threatening factors for vehicle users. One is black ice and the other is pot-holes caused by the freeze–thaw cycle. Black ice makes the surface of the road slippery and causes traffic accidents. To prevent the generation of black ice, people use chemical salts such as CaCl2. However, chemical salts cause deterioration of concrete and reduce the service life of the concrete. While, the water present in the concrete mix freezes and this freezing causes deterioration such as such as cracking, scaling etc. This is called freezing and thawing. This deterioration occurs due to lack of air on the surface layer of concrete mass. Study showed that the combination of both black ice and chemical salts accelerate deterioration of concrete.

However, to overcome this problem, many studies tried to enhance the thermal conductivity of the materials. Like, some suggested the use of carbon nanofibers and carbon nanotubes, while others suggested the use of graphene as they have good thermal conductivities. But, they have certain limitations such as properties and cost.

Thus, to overcome this limitation Byeong-Hun Woo and colleagues now applied a substitution method. The reason behind using substitution method is that, the aggregates occupies more than 65% of the volume fraction. They used silicon carbide (SiC) as the substituting material and substituted it for 50% and 100% of fine aggregate in order to improve the thermal conductivity.

“Silicon carbide was chosen as the substituting material of the fine aggregate; as silicon carbide has good thermal conductivity and hardness, it is considered sufficient as a fine aggregate substitution material.”

— they said

In addition, they used graphite at 5% of volume for enhancing the thermal conductivity, and the arched-type steel fiber for compensating the reduction in mechanical properties by the graphite. Furthermore, they used steel fiber (upto 1% vol. fraction) as the thermal conductive material because the steel fiber has a high level of thermal conductivity. However, there’s a risk if we apply all these various thermal conductive materials to the concrete, why? Because it would generate thermal damage by the difference in the thermal conductivity of each material in the cold environment, e.g., via freeze–thaw. Thus, it is necessary to verify or assess the thermal durability of concrete with thermal conductive materials, in conditions such as freeze-thaw.

For this reason, Byeong-Hun Woo and colleagues performed two experiments: freeze–thaw (FT) and rapid cyclic thermal attack (RCTA). Their concrete was made for application as road paving material, therefore, the FT resistance was important. In addition, cold regions usually change the air temperature very rapidly. Therefore, it was essential to performed RCTA test for assessing the thermal durability of concrete.

RCTA test concept © Woo et al.

They found that, Arched type steel fiber improves the mechanical properties of concrete due to the anchorage effect. On the contrary, it was demonstrated that using graphite brought about a negative effect on the mechanical properties. However, graphite is a good material for improving the thermal conductivity of concrete. Therefore, the decrease in mechanical properties caused by using graphite could be compensated by using arched type steel fiber.

They also found that, SiC is able to be used as fine aggregate and has sufficient thermal conductivity. In addition, it was demonstrated through the thermal conductivity results that the steel fiber could be used as a thermal conductive material. The combination of SiC and steel fiber maximized the improvement in the thermal conductivity of concrete. Adding graphite also brought about an increase in thermal conductivity.

“Using 100% silicon carbide was considered the acceptable range, but 50% of silicon carbide was the best. Graphite decreased all the properties except for the thermal conductivity.”

Finally, it has been demonstrated from the results of the FT test and RCTA test that use of graphite is not suitable for FT and RCTA resistance. However, the arched type steel fiber showed a remarkable improvement of the FT resistance and RCTA. In addition, SiC compensated for the negative effect of graphite on the FT and RCTA.

“We suggest the content of graphite and use of other conductive materials should be carefully consider in further studies”

— they concluded.

Featured image: Used thermal conductive materials. (a) Arched-type steel fiber; (b) SiC; (c) Graphite © Woo et al.


Reference: Woo, B.-H.; Yoo, D.-H.; Kim, S.-S.; Lee, J.-B.; Ryou, J.-S.; Kim, H.-G. Effects of Thermal Conductive Materials on the Freeze-Thaw Resistance of Concrete. Materials 2021, 14, 4063. https://doi.org/10.3390/ma14154063


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Tires Turned Into Graphene That Makes Stronger Concrete (Material Science)

Rice University lab’s optimized flash process could reduce carbon emissions

This could be where the rubber truly hits the road.

Rice University scientists have optimized a process to convert waste from rubber tires into graphene that can, in turn, be used to strengthen concrete.

The environmental benefits of adding graphene to concrete are clear, chemist James Tour said.

“Concrete is the most-produced material in the world, and simply making it produces as much as 9% of the world’s carbon dioxide emissions,” Tour said. “If we can use less concrete in our roads, buildings and bridges, we can eliminate some of the emissions at the very start.”

Recycled tire waste is already used as a component of Portland cement, but graphene has been proven to strengthen cementitious materials, concrete among them, at the molecular level.

While the majority of the 800 million tires discarded annually are burned for fuel or ground up for other applications, 16% of them wind up in landfills.

“Reclaiming even a fraction of those as graphene will keep millions of tires from reaching landfills,” Tour said.

The “flash” process introduced by Tour and his colleagues in 2020 has been used to convert food waste, plastic and other carbon sources by exposing them to a jolt of electricity that removes everything but carbon atoms from the sample.

Those atoms reassemble into valuable turbostratic graphene, which has misaligned layers that are more soluble than graphene produced via exfoliation from graphite. That makes it easier to use in composite materials.

Rubber proved more challenging than food or plastic to turn into graphene, but the lab optimized the process by using commercial pyrolyzed waste rubber from tires. After useful oils are extracted from waste tires, this carbon residue has until now had near-zero value, Tour said.

Rice scientists optimized a process to turn rubber from discarded tires into turbostratic flash graphene.  Courtesy of the Tour Research Group

Tire-derived carbon black or a blend of shredded rubber tires and commercial carbon black can be flashed into graphene. Because turbostratic graphene is soluble, it can easily be added to cement to make more environmentally friendly concrete.

The research led by Tour and Rouzbeh Shahsavari of C-Crete Technologies is detailed in the journal Carbon.

The Rice lab flashed tire-derived carbon black and found about 70% of the material converted to graphene. When flashing shredded rubber tires mixed with plain carbon black to add conductivity, about 47% converted to graphene. Elements besides carbon were vented out for other uses.

The electrical pulses lasted between 300 milliseconds and 1 second. The lab calculated electricity used in the conversion process would cost about $100 per ton of starting carbon.

The researchers blended minute amounts of tire-derived graphene — 0.1 weight/percent (wt%) for tire carbon black and 0.05 wt% for carbon black and shredded tires — with Portland cement and used it to produce concrete cylinders. Tested after curing for seven days, the cylinders showed gains of 30% or more in compressive strength. After 28 days, 0.1 wt% of graphene sufficed to give both products a strength gain of at least 30%.

“This increase in strength is in part due to a seeding effect of 2D graphene for better growth of cement hydrate products, and in part due to a reinforcing effect at later stages,” Shahsavari said.

Rice graduate student Paul Advincula is lead author of the paper. Co-authors are Rice postdoctoral researcher Duy Luong and graduate student Weiyin Chen, and Shivaranjan Raghuraman of C-Crete. Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of computer science and of materials science and nanoengineering at Rice.

The Air Force Office of Scientific Research and the Department of Energy’s National Energy Technology Laboratory supported the research.

Read the abstract at https://www.sciencedirect.com/science/article/abs/pii/S0008622321003249.

Featured image: A transmission electron microscope image shows the interlayer spacing of turbostratic graphene produced at Rice University by flashing carbon black from discarded rubber tires with a jolt of electricity. Courtesy of the Tour Research Group


Provided by Rice University

Self-healing Concrete For Regions With High Moisture and Seismic Activity (Civil Engineering)

Preparing regular concrete scientists replaced ordinary water with water concentrate of bacteria Bacillus cohnii, which survived in the pores of cement stone. The cured concrete was tested for compression until it cracked, then researchers observed how the bacteria fixed the gaps restoring the strength of the concrete. The engineers of the Polytechnic Institute of Far Eastern Federal University (FEFU), together with colleagues from Russia, India, and Saudi Arabia, reported the results in Sustainability journal.

During the experiment, bacteria activated when gained access to oxygen and moisture, which occurred after the concrete cracked under the pressure of the setup. The “awakened” bacteria completely repaired fissures with a width of 0.2 to 0.6 mm within 28 days. That is due to microorganisms released a calcium carbonate (CaCO3), a product of their life that crystallized under the influence of moisture. After 28 days of self-healing experimental concrete slabs retrieved their original compressive strength. In the renewed concrete, the bacteria “fell asleep” again.

“Concrete remains the world’s number one construction material because it is cheap, durable, and versatile. However, any concrete gets cracked over time because of various external factors, including moisture and repetitive freezing/thawing cycles, the quantity of which in the Far East of Russia, for example, is more than a hundred per year. Concrete fissuring is almost irreversible process that can jeopardize the entire structure.” Says engineer Roman Fediuk, FEFU professor. “What we have accomplished in our experiment aligns with international trends in construction. There is pressing demand for such “living” materials with the ability to self-diagnose and self-repair. It’s very important that bacteria healed small fissures-forerunners of serious deep cracks that would be impossible to recover. Thanks to bacteria working in the concrete, one can reduce or avoid at all technically complex and expensive repair procedures.”

Spores of Bacillus cohnii capable of staying alive in concrete for up to two hundred years and, theoretically, can extend the lifespan of the structure for the same period. This is almost 4 times more than the 50-70 years of conventional concrete service life.

Self-healing concrete is most relevant for construction in seismically risky areas, where small fissures appear in buildings after earthquakes of a modest magnitude, and in areas with high humidity and high rainfall where a lot of oblique rain falls on the vertical surfaces of buildings. Bacteria in concrete also fill the pores of the cement stone making them smaller and less water gets inside the concrete structure.

Scientists have cultivated the bacteria Bacillus cohnii in the laboratory using a simple agar pad and culture medium, forcing them to survive in the conditions of the pores of the cement stone and to release the desired “repair” composition. Fissures healing was assessed using a microscope. The chemical composition of the bacteria repairing life product was studied via electron microscopy and X-ray images.

Next, the scientists plan to develop reinforced concrete, further enhancing its properties with the help of different types of bacteria. That should speed up the processes of material self-recovery.

A scientific school of the scientific school of geomimetics run at FEFU. Engineers follow the principle of nature mimicking in the development of composites for special structures and civil engineering. Concrete, as conceived by the developers, should have the strength and properties of natural stone. The foundations of geomimetics were laid by Professor Valery Lesovik from V.G. Shukhov BSTU, Corresponding Member of the Russian Academy of Architecture and Construction Sciences.

Featured image: The slab of self-healing concrete is measured for its compressive strength. © FEFU press office


Reference: Sumathi, Arunachalam; Murali, Gunasekaran; Gowdhaman, Dharmalingam; Amran, Mugahed; Fediuk, Roman; Vatin, Nikolai I.; Deeba Laxme, Ramamurthy; Gowsika, Thillai S. 2020. “Development of Bacterium for Crack Healing and Improving Properties of Concrete under Wet–Dry and Full-Wet Curing” Sustainability 12, no. 24: 10346. https://doi.org/10.3390/su122410346


Provided by Far Eastern Federal University

Super Asphalt Lasts Longer (Civil / Engineering)

Asphalt concrete is a great material for road surfacing purposes but it’s not always the most sustainable of options. Sandra Erkens, professor of Pavement Engineering Practice, is looking for ways of predicting and extending the lifespan of both existing and new pavement materials. Epoxy asphalt may well hold the key to more durable road surfaces. The beginning of November should see the start of the construction of a trial section on a Noord-Holland road to put the new super asphalt through its paces.

©tudelft

The Netherlands has some 140,000 kilometers of paved roads, most of which are covered with asphalt, a mixture of sand, small pebbles and other fillers held together by bitumen binder. Asphalt concrete differs from other materials commonly used in civil and pavement engineering in a number of ways Sandra Erkens says. ‘The main difference is the viscoelasticity of asphalt which enables it to adapt to the movement of the soft Dutch soil. This capacity to ‘flow’ means the material is less likely to break. This viscoelastic property – which is lacking in concrete, for example- means it has the ability to self-heal. Small cracks in the asphalt can disappear without any outside intervention. This happens especially if the material is left in peace for a while. And in our ever-busier country that is getting less likely with time.’

Asphalt behaviour issues

Much is still unclear about the behaviour of asphalt, particularly in the longer term, Erkens says. ‘Asphalt is exposed to a wide range of temperatures and weather conditions, and the nature and amount of traffic also varies. An additional complication when making predictions about the behaviour of asphalt is that the chemical composition of the material varies as well. This variation in properties means you never know what the behaviour of a particular stretch of asphalt is going to be. But that’s what makes it so interesting. There is still a lot left to study and find out when it comes to the properties, lifespan and overall sustainability of asphalt. And while all the asphalt in the Netherlands is already being recycled, for instance as new pavement foundation, or as part of new asphalt mixtures, much more can be done.’

Not very sustainable- as yet

The top layer of the asphalt structure has to be replaced on average every ten to twenty years. That is expensive and not very sustainable, Erkens says. ‘The production of asphalt is done at very high temperatures and that makes it very energy intensive and high in CO2 emissions. So even if we do re-use all our asphalt and most new asphalt is made using old asphalt, we still have a long way to go to make the process truly sustainable. Only then will we be able to meet the energy and CO2 goals, and achieve more circularity.’

To help green the polluting asphalt industry TU Delft has joined forces with construction company Dura Vermeer. Together they have been developing a sustainable super asphalt. The magic ingredient: epoxy. Erkens: ‘By mixing epoxy resin with bitumen and letting it harden, the asphalt becomes less sensitive to external factors, such as the weather. It also keeps its stiffness and hardness under higher temperatures. Considering the rise in temperature because of climate change that is definitely an important property. The great challenge we are facing is to preserve the advantages of regular asphalt, such as its capacity for self-healing and its recyclability.’

Relatively expensive

The use of epoxy asphalt is not completely new, Erkens says. ‘There are places in the United States which have had epoxy asphalt pavements for over forty years, particularly on bridge decks. Intense traffic and the expansion of the metal structure in high temperatures take a heavy toll on bridges, and the authorities want to keep the need for maintenance to a minimum to avoid long diversion routes for drivers. The reason it is not used more often is cost. It is relatively expensive and to make it commercially viable it would have to last three to four times longer than ordinary asphalt. It looks as if this material fits the bill but we’ll find out for certain when we test it in practice.’

Lifespan

Testing the durability of epoxy asphalt is still mainly laboratory-based. ‘We use fatigue testing to ascertain how often epoxy asphalt can sustain a certain load. This will give us an indication of its lifespan. The lab results seems to indicate that epoxy asphalt is less susceptible to fatigue and wear and tear than ordinary asphalt and will last longer. With Dura Vermeer we are also investigating how best to re-use epoxy asphalt. The first results show that it can be recycled using current methods.’

Epoxy asphalt trial area

In order to find out if the lab results stand up in practice the Noord-Holland authorities have commissioned Dura Vermeer to cover a stretch of the N249 in epoxy asphalt. Erkens: ‘Our TU Delft team will be monitoring the trial area for a number of years. We will be using sensors to monitor stiffness, and we will also be looking at wear and tear at the surface and the occurrence of cracks. This is not the first trial area but it the first to be monitored in such detail using equipment.’

Not sustainable everywhere

Despite the promising potential of epoxy asphalt Erkens does not expect the entire road network of the Netherlands to be covered in it by the next decade. ‘It can only have its longer lasting effect if it is left in peace for long periods of time. In and around urban areas there are road works at least every ten years to replace cables or pipes. Epoxy asphalt is far too expensive for that and its application in that case would not be sustainable.’

Other asphalt innovations

Epoxy asphalt is not the only sustainable solution, Erkens emphasises. ‘The provincial authorities, Rijkswaterstaat, research institutes and particularly construction companies are participating in various regional and national programmes, such as Asfalt-Impuls, to investigate more sustainable production methods for asphalt, by using lower temperatures to reduce energy use, for instance, and upping re-use and introducing asphalt rejuvenation techniques for maintenance. We are also looking at bio asphalt development and the application of epoxy in ZOAB, or porous asphalt. So although there is less traffic, things are definitely moving as far as the asphalt is concerned.’

Provided by Tudelft

Concrete Structure’s Lifespan Extended By A Carbon Textile (Engineering)

Construction costs reduced by 40%, while improving fire resistance.

The Korea Institute of Civil Engineering and Building Technology (KICT) has announced the development of an effective structural strengthening method using a noncombustible carbon textile grid and cement mortar, which can double the load-bearing capacities of structurally deficient concrete structures and increase their usable lifespan by threefold.

Failure test of a concrete slab strengthened with TRM panel. ©Korea Institute of Civil Engineering and Building Technology (KICT).

More than 90% of infrastructures in South Korea, such as bridges and tunnels, as well as residential buildings were initially constructed out of concrete. For deteriorated or structurally deficient concrete structures in need of structural strengthening, carbon fiber sheets are typically applied to the surface of the concrete structure using organic adhesives. However, organic adhesives are susceptible to fire and cannot be applied to structures with wet surfaces. These carbon fiber sheets may detach and fall from the structure if they are exposed to moisture.

A research team in KICT, led by Dr. Hyeong-Yeol Kim, has developed an effective as well as efficient strengthening method for deteriorated concrete structures. With the developed method, thin precast textile reinforced mortar (TRM) panels, which are made of a carbon textile grid and a thin layer of cement mortar, are used. Furthermore, the TRM strengthening method can be applied in the form of cast-in-place construction. Employing KICT’s method, 20 mm-thick TRM panels are attached to the surface of the existing structure, and then the space between the existing structure and the panels is filled with cement grout, with the cement grout serving as the adhesive.

Both the carbon textile and cement mortar are noncombustible materials that have a high resistance to fire, meaning that they can be effectively used to strengthen concrete buildings that may be exposed to fire hazards. The construction method can also be applied to wet surfaces as well as in the winter, and the panels do not fall off even in the event of water ingress. Additionally, unlike steel reinforcing bars, the carbon textile does not corrode, and thus it can be effectively used to strengthen highway facilities and parking buildings, where deicing agents are often used, as well as to strengthen offshore concrete structures that are exposed to a chloride-rich environment.

Applied load versus vertical displacement. ©Korea Institute of Civil Engineering and Building Technology (KICT).

A failure test conducted in KICT indicates that the failure load of concrete structures strengthened with the TRC panel increased by at least 1.5 times compared to that of an unstrengthened structure. Furthermore, the chloride resistance of the TRM panel has been evaluated in order to assess its service life in a chloride-rich environment. The durability test and analysis of the TRM panel indicates that the lifespan of the panel is more than 100 years. This increase can be attributed to the cement mortar, developed by KICT, which contains 50% ground granulated blast furnace slag, an industrial byproduct generated at ironworks. The cement mortar, which has a higher fire resistance than conventional cement mortar, is also advantageous because its cost is half that of conventional mortar. In terms of economical efficiency, the newly developed method can reduce construction costs by about 40% compared to existing carbon sheet attachment methods.

The newly developed strengthening method uses thin TRM panels that are very versatile and can be used as building facades, repair and strengthening materials, and in other applications. In the future, if the panels can be fabricated with thermal insulators, it is expected that they will replace building insulation materials that are susceptible to fires.

Dr. Kim said, “For easier production and shipping, the TRM panels are manufactured in a relatively small size of 1 m by 2 m and must be connected at the construction site. A method for effectively connecting the panels is currently being developed, and performance tests of the method will be conducted by the end of 2020.”

References: Strengthening of Concrete Element with Precast Textile Reinforced Concrete Panel and Grouting Material”, Materials 2020, 13(17), 3856; https://doi.org/10.3390/ma13173856

Provided by Korea Institute of Civil Engineering and Building Technology (KICT)