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High and Ultra-High Performance Concrete for Sustainable Construction
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High and Ultra-High Performance Concrete for Sustainable Construction

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Construction and Building Materials".

Deadline for manuscript submissions: closed (31 August 2020) | Viewed by 43287

Special Issue Editor

Prof. Andrzej Cwirzen

E-Mail Website
Guest Editor
Division of Building Materials, Luleå Tekniska Universitet, Lulea, Sweden
Interests: concrete; nanomaterials; nanotechnology; alternative binders; durability; sustainable materials; mechanochemical activation; smart materials; ice research
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Concrete has come a long way since the invention of Portland cement at the end of the 19th century. The material was constantly improved, leading to the development of high and ultra-performance concrete, which opened new opportunities for architects and designers.

The performance of concrete can be determined in terms of mechanical properties or durability. High-strength concrete was first introduced in the 1990s. Its development was largely due to the appearance of silica fume, leading to compressive strength values exceeding 100 MPa and durability improved to levels not previously known. Countless structures around the world including bridges, high-rise buildings and oil platforms were built using this type of concrete. High strength was often the key parameter but in many cases, it was the improved durability that was decisive. Concrete with a compressive strength well exceeding 200 MPa, so-called ultra-high performance concrete, were the next step of the evolution process, as the density and homogeneity of the binder matrix had been further improved, resulting in even better durability, potentially elongating the life span of concrete structures far beyond 100 years.

This success stories have one drawback. Typically, high and ultra-high performance concrete contain large amounts of Portland cement leading to a substantial CO2 footprint. Worldwide research is trying to tackle this huge environmental problem. One of the recent trends is to increase the usage of alternative cementitious binders. Unfortunately, these novel ecological systems often have unknown durability and long-term performance. To close this knowledge gap, this Special Issue will deal with research leading to improved high and ultra-high performance concrete with the clear aim of sustainable construction.

It is my pleasure to invite you to submit a manuscript to this Special Issue. Full papers, communications, and reviews are all welcome.

Prof. Andrzej Cwirzen
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • strength
  • durability
  • sustainability
  • long-term performance
  • alternative cementitious binders
  • secondary cementitious binders

Published Papers (15 papers)

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Research

13 pages, 5528 KiB  
Article
The Effect of Incorporating Silica Stone Waste on the Mechanical Properties of Sustainable Concretes
by Saeid Abbasi, Mohammad Hemen Jannaty, Rabar H. Faraj, Shahriar Shahbazpanahi and Amir Mosavi
Materials 2020, 13(17), 3832; https://doi.org/10.3390/ma13173832 - 30 Aug 2020
Cited by 18 | Viewed by 2173
Abstract
Incorporating various industrial waste materials into concrete has recently gained attention for sustainable construction. This paper, for the first time, studies the effects of silica stone waste (SSW) powder on concrete. The cement of concrete was replaced with 5, 10, 15, and 20% [...] Read more.
Incorporating various industrial waste materials into concrete has recently gained attention for sustainable construction. This paper, for the first time, studies the effects of silica stone waste (SSW) powder on concrete. The cement of concrete was replaced with 5, 10, 15, and 20% of the SSW powder. The mechanical properties of concrete, such as compressive and tensile strength, were studied. Furthermore, the microstructure of concrete was studied by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy analysis (EDX), Fourier transformed infrared spectroscopy (FTIR), and X-Ray diffraction (XRD) tests. Compressive and tensile strength of samples with 5% SSW powder was improved up to 18.8% and 10.46%, respectively. As can be observed in the SEM images, a reduced number of pores and higher density in the matrix can explain the better compressive strength of samples with 5% SSW powder. Full article
(This article belongs to the Special Issue High and Ultra-High Performance Concrete for Sustainable Construction)
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26 pages, 8198 KiB  
Article
Elevated Temperature Performance of Reactive Powder Concrete Containing Recycled Fine Aggregates
by Hammad Salahuddin, Liaqat Ali Qureshi, Adnan Nawaz, Muhammad Abid, Rayed Alyousef, Hisham Alabduljabbar, Fahid Aslam, Summera Fahmi Khan and Rana Faisal Tufail
Materials 2020, 13(17), 3748; https://doi.org/10.3390/ma13173748 - 24 Aug 2020
Cited by 7 | Viewed by 2605
Abstract
This study examines the effect of elevated temperature on various properties of reactive powder concrete (RPC) containing varying percentages of recycled fine aggregates as sand replacement. Recycled fine aggregates were collected from two sources, i.e., demolished normal strength concrete and demolished RPC. The [...] Read more.
This study examines the effect of elevated temperature on various properties of reactive powder concrete (RPC) containing varying percentages of recycled fine aggregates as sand replacement. Recycled fine aggregates were collected from two sources, i.e., demolished normal strength concrete and demolished RPC. The specimens were prepared using 25%, 50%, and 75% replacement of natural sand with recycled fine aggregates, exposed to two different curing conditions and were subjected to four temperatures, i.e., 25, 200, 400, and 600 °C. Later, the specimens were tested for mass loss, compressive strength test, split-tensile strength test, flexural strength test, and water absorption test at all temperature ranges. Results determined that although the mechanical properties degraded with the temperature rise, the recycled aggregates can be employed as a partial replacement of natural sand in RPC without causing a significant decrease in the performance of RPC, and can help to produce more sustainable RPC by using recycled aggregates. Full article
(This article belongs to the Special Issue High and Ultra-High Performance Concrete for Sustainable Construction)
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21 pages, 6911 KiB  
Article
Effect of Fibre Material and Fibre Roughness on the Pullout Behaviour of Metallic Micro Fibres Embedded in UHPC
by Niels Wiemer, Alexander Wetzel, Maximilian Schleiting, Philipp Krooß, Malte Vollmer, Thomas Niendorf, Stefan Böhm and Bernhard Middendorf
Materials 2020, 13(14), 3128; https://doi.org/10.3390/ma13143128 - 14 Jul 2020
Cited by 21 | Viewed by 4071
Abstract
The use of micro fibres in Ultra-High-Performance Concrete (UHPC) as reinforcement increases tensile strength and especially improves the post-cracking behaviour. Without using fibres, the dense structure of the concrete matrix results in a brittle failure upon loading. To counteract this behaviour by fibre [...] Read more.
The use of micro fibres in Ultra-High-Performance Concrete (UHPC) as reinforcement increases tensile strength and especially improves the post-cracking behaviour. Without using fibres, the dense structure of the concrete matrix results in a brittle failure upon loading. To counteract this behaviour by fibre reinforcement, an optimal bond between fibre and cementitious matrix is essential. For the composite properties not only the initial surfaces of the materials are important, but also the bonding characteristics at the interfacial transition zone (ITZ), which changes upon the joining of both materials. These changes are mainly induced by the bond of cementitious phases on the fibre. In the present work, three fibre types were used: steel fibres with brass coating, stainless-steel fibres as well as nickel-titanium shape memory alloys (SMA). SMA fibres have the ability of “remembering” an imprinted shape (referred to as shape memory effect), triggered by thermal activation or stress, principally providing for superior performance of the fibre-reinforced UHPC. However, previous studies have shown that NiTi-fibres have a much lower bond strength to the concrete matrix than steel fibres, eventually leading to a deterioration of the mechanical properties of the composite. Accordingly, the bond between both materials has to be improved. A possible strategy is to roughen the fibre surfaces to varying degrees by laser treatment. As a result, it can be shown that laser treated fibres are characterised by improved bonding behaviour. In order to determine the bond strength of straight, smooth fibres of different metal alloy compositions, the present study characterized multiple fibres in series with a Compact-Tension-Shear (CTS) device. For critical evaluation, results obtained by these tests are compared with the results of conventional testing procedures, i.e., bending tests employing concrete prisms with fibre reinforcements. The bond behaviour is compared with the results of the flexural strength of prisms (4 × 4 × 16 cm3) with fibre reinforcements. Full article
(This article belongs to the Special Issue High and Ultra-High Performance Concrete for Sustainable Construction)
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16 pages, 2236 KiB  
Article
Comparative Fracture Properties of Four Fibre Reinforced High Performance Cementitious Composites
by Piotr Smarzewski
Materials 2020, 13(11), 2612; https://doi.org/10.3390/ma13112612 - 08 Jun 2020
Cited by 21 | Viewed by 1972
Abstract
This study investigates the fracture properties of high performance cementitious composites (HPCC) with four different types of fibres and with volume fraction content 3%. The four fibres are steel hooked end (S), polypropylene crimped (PP), basalt chopped (B), and glass (G) fibres. The [...] Read more.
This study investigates the fracture properties of high performance cementitious composites (HPCC) with four different types of fibres and with volume fraction content 3%. The four fibres are steel hooked end (S), polypropylene crimped (PP), basalt chopped (B), and glass (G) fibres. The tests were carried out in accordance with the RILEM recommendations. In order to examine the fresh properties of HPCC the slump flow tests were performed. Twelve fibre reinforced HPCC beam specimens with notch were cast and tested using central point loading experiments. In addition, experimental tests of the compressive strength and splitting tensile strength were carried out. The test results made it possible to obtain representative fracture parameters, such as the equivalent strengths, residual strengths, and fracture energy of fibre reinforced HPCC. The S fibre specimens showed the best performance in terms of workability, compressive strength, tensile splitting strength, and fracture energy at large deflection. On the other hand, G fibre specimens exhibited the best performance in terms of flexural strength, equivalent flexural strength at higher deflection, and residual flexural strength at lower deflection. In terms of equivalent flexural strength at lower deflection and residual flexural strength at higher deflection, basalt fibre specimens performed the best. On the contrary, polypropylene fibre reinforced beam specimens revealed the highest deflection capacity. Full article
(This article belongs to the Special Issue High and Ultra-High Performance Concrete for Sustainable Construction)
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13 pages, 7394 KiB  
Article
Geopolymer Based on Mechanically Activated Air-cooled Blast Furnace Slag
by Ilda Tole, Magdalena Rajczakowska, Abeer Humad, Ankit Kothari and Andrzej Cwirzen
Materials 2020, 13(5), 1134; https://doi.org/10.3390/ma13051134 - 04 Mar 2020
Cited by 15 | Viewed by 2988
Abstract
An efficient solution to increase the sustainability of building materials is to replace Portland cement with alkali-activated materials (AAM). Precursors for those systems are often based on water-cooled ground granulated blast furnace slags (GGBFS). Quenching of blast furnace slag can be done also [...] Read more.
An efficient solution to increase the sustainability of building materials is to replace Portland cement with alkali-activated materials (AAM). Precursors for those systems are often based on water-cooled ground granulated blast furnace slags (GGBFS). Quenching of blast furnace slag can be done also by air but in that case, the final product is crystalline and with a very low reactivity. The present study aimed to evaluate the cementitious properties of a mechanically activated (MCA) air-cooled blast furnace slag (ACBFS) used as a precursor in sodium silicate alkali-activated systems. The unreactive ACBFS was processed in a planetary ball mill and its cementing performances were compared with an alkali-activated water-cooled GGBFS. Mixes based on mechanically activated ACBFS reached the 7-days compressive strength of 35 MPa and the 28-days compressive strength 45 MPa. The GGBFS-based samples showed generally higher compressive strength values. Full article
(This article belongs to the Special Issue High and Ultra-High Performance Concrete for Sustainable Construction)
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13 pages, 2773 KiB  
Article
Fluorescence Microscopic Investigations of the Retarding Effect of Superplasticizers in Cementitious Systems of UHPC
by Johannes Arend, Alexander Wetzel and Bernhard Middendorf
Materials 2020, 13(5), 1057; https://doi.org/10.3390/ma13051057 - 27 Feb 2020
Cited by 5 | Viewed by 1915
Abstract
The adsorption of superplasticizer molecules to particle surfaces in cementitious systems is a very important aspect for the desired liquefaction of pastes and concretes. This way, the comb shaped polymers shield attractive forces between the particles and induce a well-dispersed, homogeneous suspension. These [...] Read more.
The adsorption of superplasticizer molecules to particle surfaces in cementitious systems is a very important aspect for the desired liquefaction of pastes and concretes. This way, the comb shaped polymers shield attractive forces between the particles and induce a well-dispersed, homogeneous suspension. These admixtures allow the usage of fine fillers even in combination with low amounts of mixing water, and thus, are the basis for modern high performance concretes. However, the adsorption does not cause beneficial effects only: The polymer covered particle surfaces, especially clinker, are hindered to interact with water, thus hydration is retarded. This is the reason for lower early strength and is very disadvantageous for certain applications. Today it is known that the molecular structure of the polymers, for instance the chain length and charge density, affects the retardation strongly. The complexity and diversity of cementitious systems is the main reason why research in this field is quite empiric and time as well as cost intensive. To investigate the adsorption of superplasticizers in various systems in-situ, a fluorescence microscopic approach was applied: By staining the polymers with fluorescent dye they become localizable and the adsorption quantifiable. This work shows the influence of molecular structure to adsorption characteristic of different polymers and the correlation to the retarding effect of superplasticizers, especially concerning the presence of silica fume, which is indispensable for ultra-high performance concrete (UHPC). Full article
(This article belongs to the Special Issue High and Ultra-High Performance Concrete for Sustainable Construction)
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11 pages, 1885 KiB  
Article
Effects of Steel Slag Powder and Expansive Agent on the Properties of Ultra-High Performance Concrete (UHPC): Based on a Case Study
by Shunkai Li, Shukai Cheng, Liwu Mo and Min Deng
Materials 2020, 13(3), 683; https://doi.org/10.3390/ma13030683 - 03 Feb 2020
Cited by 39 | Viewed by 3172
Abstract
In view of the performance requirements of mass ultra-high performance concrete (UHPC) for the Pang Gong bridge steel cable tower in China, the UHPC incorporating of steel slag powder and hybrid expansive agents is optimized and prepared. The effects of steel slag powder [...] Read more.
In view of the performance requirements of mass ultra-high performance concrete (UHPC) for the Pang Gong bridge steel cable tower in China, the UHPC incorporating of steel slag powder and hybrid expansive agents is optimized and prepared. The effects of steel slag powder and hybrid expansive agents on the hydration characteristics and persistent shrinkage of UHPC are investigated. The results indicate that 15 wt.% steel slag powder and 5 wt.% hybrid expansive agents can effectively reduce the drying shrinkage deformation of UHPC with a slight decrease of strength. Heat flow calorimetry results show that the incorporation of steel slag powder and expansive agents decreases the hydration heat at three days. Moreover, the obtained adiabatic temperature rise of UHPC is 59.5 °C and the total shrinkage value at 180 days is 286 με. The hydration heat release changes of large volume UHPC in the steel-concrete section of cable tower is agreed with the result of adiabatic temperature rise in the laboratory. Full article
(This article belongs to the Special Issue High and Ultra-High Performance Concrete for Sustainable Construction)
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19 pages, 12267 KiB  
Article
Experimental Study of the Mechanical Properties and Microstructures of Lightweight Toughness Cement-Based Composites
by Wenhua Chen and Zhiyi Huang
Materials 2019, 12(23), 3891; https://doi.org/10.3390/ma12233891 - 25 Nov 2019
Cited by 13 | Viewed by 2618
Abstract
The effects of cenospheres, an industrial waste residue, on the compressive strength, flexural strength, toughness, ductility, chemical component, microstructures, and micromechanics of lightweight toughness cement-based composites (LTCCs) by comprehensive experimental tests are explored in this paper. The results indicate that an increase in [...] Read more.
The effects of cenospheres, an industrial waste residue, on the compressive strength, flexural strength, toughness, ductility, chemical component, microstructures, and micromechanics of lightweight toughness cement-based composites (LTCCs) by comprehensive experimental tests are explored in this paper. The results indicate that an increase in the amount of cenospheres leads to a decrease in the compressive and flexural strength of LTCCs. However, the specific strength of LTCCs increases with increasing cenosphere content. LTCCs containing 20% cenospheres and 1% fiber volume have the best toughness and ductility. Significant strain hardening occurs during the four-point bending and uniaxial tensile process. Furthermore, the incorporation of cenospheres promotes the hydration reaction of LTCCs due to its high pozzolanic activity. The LTCC cement paste has a low bonding strength to the fiber, which helps the fiber to be pulled out to produce greater bending deformation and tensile strain. The elastic modulus and hardness of the LTCC cement paste decrease linearly with increasing cenosphere content, which also causes the LTCC microstructure to become loose and more ettringite to generate. The weak interfacial transition zone between the cenospheres and the cement matrix is the important reason for the decreasing compressive strength of the LTCC. In conclusion, LTCC incorporating cenospheres is suitable for long-span steel deck pavements due to its light weight and excellent toughness. The successful application of cenospheres in engineering construction can save natural resources and contribute to sustainable development. Full article
(This article belongs to the Special Issue High and Ultra-High Performance Concrete for Sustainable Construction)
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16 pages, 4808 KiB  
Article
Mechanical Properties of Carbon-Fiber RPC and Design Method of Carbon-Fiber Content under Different Curing Systems
by Xuejian Zhang, Lincai Ge, Yunlong Zhang and Jing Wang
Materials 2019, 12(22), 3759; https://doi.org/10.3390/ma12223759 - 15 Nov 2019
Cited by 10 | Viewed by 2610
Abstract
Natural, standard, and compound curing are adopted to study the effect of different curing systems on the reinforcement of carbon fiber in reactive powder concrete (RPC). This work systematically studies the changes in RPC compressive and tensile strengths under different curing systems. Taking [...] Read more.
Natural, standard, and compound curing are adopted to study the effect of different curing systems on the reinforcement of carbon fiber in reactive powder concrete (RPC). This work systematically studies the changes in RPC compressive and tensile strengths under different curing systems. Taking age, fiber content, and curing system as parameters, Scanning electron microscope (SEM) and X-ray diffraction (XRD) microscopic methods are used to study the influencing mechanism of carbon-fiber content and curing systems on RPC. The calculation methods of the RPC strength of different carbon-fiber contents are studied. Results show that the optimum carbon-fiber content of carbon-fiber RPC is 0.75% under the natural, standard, and compound curing conditions. In comparison with standard curing, compound curing can improve the early strength of carbon-fiber RPC and slightly affect the improvement of late strength. The strength is slightly lower in natural curing than in standard curing, but the former basically meets the requirements of the project and is beneficial for the practical application of this project. The calculation formula of 28-day compressive and splitting tensile strengths of carbon-fiber content from 0% to 0.75% is proposed to select the carbon-fiber content flexibly to satisfy different engineering requirements. Full article
(This article belongs to the Special Issue High and Ultra-High Performance Concrete for Sustainable Construction)
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19 pages, 8038 KiB  
Article
Reactive Powder Concrete Mix Ratio and Steel Fiber Content Optimization under Different Curing Conditions
by Yunlong Zhang, Bin Wu, Jing Wang, Mo Liu and Xu Zhang
Materials 2019, 12(21), 3615; https://doi.org/10.3390/ma12213615 - 04 Nov 2019
Cited by 16 | Viewed by 3770
Abstract
In this paper, a practical reactive powder concrete mixture ratio is created on the basis of an orthogonal experiment. Previous studies have combined the compressive and splitting tensile strengths of four categories of reactive powder concrete (RPC) for major materials. These categories include [...] Read more.
In this paper, a practical reactive powder concrete mixture ratio is created on the basis of an orthogonal experiment. Previous studies have combined the compressive and splitting tensile strengths of four categories of reactive powder concrete (RPC) for major materials. These categories include water/binder ratio, silica fume volume content, sand/binder ratio, and dosage of fly ash volume. The optimal mixing proportion of each factor was determined by analyzing the compressive strength of the RPC matrix. For this purpose, steel fiber was used as a reinforcing agent. The compressive and splitting tensile strength test results of steel fiber RPC were analyzed by comparing compound, standard, and natural curing. This was conducted to explore the improvement effect of different steel fiber contents on compressive performance, especially tensile strength of the RPC matrix. According to the results, the optimal steel fiber content was found to be 4% under the three curing conditions. The effect of compound curing on early strength was found to be greater in RPC than by natural or standard curing. However, the effect of late improvement is not obvious. Although standard curing is slightly stronger than natural curing, the performance under the latter can still meet engineering requirements. Full article
(This article belongs to the Special Issue High and Ultra-High Performance Concrete for Sustainable Construction)
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17 pages, 5109 KiB  
Article
Does a High Amount of Unhydrated Portland Cement Ensure an Effective Autogenous Self-Healing of Mortar?
by Magdalena Rajczakowska, Lennart Nilsson, Karin Habermehl-Cwirzen, Hans Hedlund and Andrzej Cwirzen
Materials 2019, 12(20), 3298; https://doi.org/10.3390/ma12203298 - 11 Oct 2019
Cited by 19 | Viewed by 2726
Abstract
It is commonly accepted that the autogenous self-healing of concrete is mainly controlled by the hydration of Portland cement and its extent depends on the availability of anhydrous particles. High-performance (HPCs) and ultra-high performance concretes (UHPCs) incorporating very high amounts of cement and [...] Read more.
It is commonly accepted that the autogenous self-healing of concrete is mainly controlled by the hydration of Portland cement and its extent depends on the availability of anhydrous particles. High-performance (HPCs) and ultra-high performance concretes (UHPCs) incorporating very high amounts of cement and having a low water-to-cement ratio reach the hydration degree of only 70–50%. Consequently, the presence of a large amount of unhydrated cement should result in excellent autogenous self-healing. The main aim of this study was to examine whether this commonly accepted hypothesis was correct. The study included tests performed on UHPC and mortars with a low water-to-cement ratio and high cement content. Additionally, aging effects were verified on 12-month-old UHPC samples. Analysis was conducted on the crack surfaces and inside of the cracks. The results strongly indicated that the formation of a dense microstructure and rapidly hydrating, freshly exposed anhydrous cement particles could significantly limit or even hinder the self-healing process. The availability of anhydrous cement appeared not to guarantee development of a highly effective healing process. Full article
(This article belongs to the Special Issue High and Ultra-High Performance Concrete for Sustainable Construction)
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19 pages, 6450 KiB  
Article
Cost-Effective High-Performance Concrete: Experimental Analysis on Shrinkage
by Barbara Kucharczyková, Dalibor Kocáb, Petr Daněk and Ivailo Terzijski
Materials 2019, 12(17), 2730; https://doi.org/10.3390/ma12172730 - 26 Aug 2019
Cited by 2 | Viewed by 2112
Abstract
This paper focuses on the experimental determination of the shrinkage process in Self-Compacting High-Performance Concrete (SCC HPC) exposed to dry air and autogenous conditions. Special molds with dimensions of 100 mm × 60 mm × 1000 mm and 50 mm × 50 mm [...] Read more.
This paper focuses on the experimental determination of the shrinkage process in Self-Compacting High-Performance Concrete (SCC HPC) exposed to dry air and autogenous conditions. Special molds with dimensions of 100 mm × 60 mm × 1000 mm and 50 mm × 50 mm × 300 mm equipped with one movable head are used for the measurement. The main aim of this study is to compare the shrinkage curves of SCC HPC, which were obtained by using different measurement devices and for specimens of different sizes. In addition, two different times t0 are considered for the data evaluation to investigate the influence of this factor on the absolute value of shrinkage. In the first case, t0 is the time of the start of measurement, in the second case, t0 is the setting time. The early-shrinkage (48 h) is continuously measured using inductive sensors leant against the movable head and with strain gauges embedded inside the test specimen. To monitor the long term shrinkage, the specimens are equipped with special markers, embedded into the specimens’ upper surface or ends. These markers serve as measurement bases for the measurement using mechanical strain gauges. The test specimens are demolded after 48 h and the long term shrinkage is monitored using the embedded strain gauges (inside the specimens) and mechanical strain gauges that are placed, in regular intervals, onto the markers embedded into the specimens’ surface or ends. The results show that both types of measurement equipment give a similar result in the case of early age measurement, especially for the specimens cured under autogenous conditions. However, the early age and especially long term measurement are influenced by the position of the measurement sensors, particularly in the case of specimens cured under dry air conditions. It was proven that the time t0 have a fundamental influence on the final values of the shrinkage of investigated SCC HPC and have a significant impact on the conclusions on the size effect. Full article
(This article belongs to the Special Issue High and Ultra-High Performance Concrete for Sustainable Construction)
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14 pages, 3972 KiB  
Article
Effect of Multi-Walled Carbon Nanotubes on Improving the Toughness of Reactive Powder Concrete
by Jintao Liu, Hang Jin, Xin Zhao and Cheng Wang
Materials 2019, 12(16), 2625; https://doi.org/10.3390/ma12162625 - 17 Aug 2019
Cited by 10 | Viewed by 2974
Abstract
Multi-walled carbon nanotubes (MWCNTs) have great potential to improve the strength and microstructure of traditional cement-based materials. In this research, different aspect ratios of MWCNTs (F-type and L-type) were dispersed into water using surfactants, and then incorporated into reactive powder concrete (RPC) for [...] Read more.
Multi-walled carbon nanotubes (MWCNTs) have great potential to improve the strength and microstructure of traditional cement-based materials. In this research, different aspect ratios of MWCNTs (F-type and L-type) were dispersed into water using surfactants, and then incorporated into reactive powder concrete (RPC) for improving mechanical and microstructure properties. With the addition of 0.025 wt.% F-MWCNTs, the 28 days compressive strength and initial-cracking flexural strength increased by 7.2% and 36%, respectively. Moreover, the first-cracking tensile strengths of the composites containing L-MWCNTs were improved by 16%. Energy absorption capability indices were formulated based on tensile load–displacement curves, and results showed that the energy absorption capabilities of RPC at initial cracking improved as a result of the incorporation of MWCNTs. Furthermore, microscopic analysis indicated that MWCNTs decelerate crack development at the nanoscale and improve the initial-cracking tensile strength of RPC. Full article
(This article belongs to the Special Issue High and Ultra-High Performance Concrete for Sustainable Construction)
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14 pages, 7661 KiB  
Article
Thermal Effectiveness Enhancement of Autoclaved Aerated Concrete Wall with PCM-Contained Conical Holes to Reduce the Cooling Load
by Atthakorn Thongtha, Aitthi Khongthon, Thitinun Boonsri and Chan Hoy-Yen
Materials 2019, 12(13), 2170; https://doi.org/10.3390/ma12132170 - 06 Jul 2019
Cited by 19 | Viewed by 2744
Abstract
This work investigates and improves the thermal dynamics of autoclaved aerated concrete (AAC) wall containing phase change material (PCM). The PCM is paraffin wax loaded into conical holes drilled into the AAC. Filled AAC with three different numbers of PCM-filled holes (2, 3, [...] Read more.
This work investigates and improves the thermal dynamics of autoclaved aerated concrete (AAC) wall containing phase change material (PCM). The PCM is paraffin wax loaded into conical holes drilled into the AAC. Filled AAC with three different numbers of PCM-filled holes (2, 3, and 4 conical holes, which are designated as AAC-2H, AAC-3H, and AAC-4H, respectively) as well as the unfilled original AAC were both tested under two different conditions: indoors (with controlled temperature) and outdoors (with actual weather). For the indoor experiment, a heater was used as a thermal source and set up to maintain the testing temperature at one of three levels: 40 °C, 50 °C, or 60 °C. The wall temperature was then measured on the surface with each horizontally-positioned wall as well as four different positions at various depths below the surface of the wall. It was found that AAC-4H was the optimum condition, which can produce outstandingly a time lag of approximately 27%, reduce a decrement factor of approximately 31%, and also decrease the room temperature. This reached approximately 9% when compared with that of ordinary AAC at the controlled testing temperature of 60 °C. All samples were further tested in actual weather to confirm the thermal performances of AAC-4H. Thermal effectiveness of AAC-4H was improved by extending approximately a 14.3% time lag, which reduces approximately a 4.3% decrement factor and achieving approximately 5% lower room temperature when compared with ordinary AAC. Full article
(This article belongs to the Special Issue High and Ultra-High Performance Concrete for Sustainable Construction)
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16 pages, 11018 KiB  
Article
Effects of High Temperature on the Burst Process of Carbon Fiber/PVA Fiber High-Strength Concretes
by Rui-dong Cao, Hui-wei Yang and Guo-yun Lu
Materials 2019, 12(6), 973; https://doi.org/10.3390/ma12060973 - 24 Mar 2019
Cited by 11 | Viewed by 3493
Abstract
This paper carried out burst tests on the carbon and polyvinyl alcohol (PVA) fiber high-strength concrete specimens to investigate the effects of fiber type, fiber content, water content, heating rate and test specimen size on the burst, and the whole burst process of [...] Read more.
This paper carried out burst tests on the carbon and polyvinyl alcohol (PVA) fiber high-strength concrete specimens to investigate the effects of fiber type, fiber content, water content, heating rate and test specimen size on the burst, and the whole burst process of fiber-high concrete was photographed and recorded. The results indicated that fiber addition will improve the high temperature burst behavior of the high-strength concrete, and the performance of PVA is greatly different from that of carbon fiber. The water content and heating rate have little influence on the burst of the PVA test specimen, but they will greatly affect the carbon fiber test specimen. The size of the test specimen has a great influence on the burst. For the PVA concrete test specimen, the large size test specimen bursts on the surface; as for the carbon fiber test specimen, the large size test specimen delays the initial burst time, but the burst becomes fiercer. Full article
(This article belongs to the Special Issue High and Ultra-High Performance Concrete for Sustainable Construction)
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