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A special issue of Buildings (ISSN 2075-5309). This special issue belongs to the section "Building Materials, and Repair & Renovation".

Deadline for manuscript submissions: closed (20 July 2024) | Viewed by 16225

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Special Issue Editors

Dr. Fernando G. Branco

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ISISE, Department of Civil Engineering, University of Coimbra, R. Luís Reis Santos, 3030-788 Coimbra, Portugal
Interests: concrete; durability; sustainability; valorization of byproducts and industrial waste; building materials; mortar
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. José Marcos Ortega

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Guest Editor

Departamento de Ingeniería Civil, Universidad de Alicante, Ap. Correos 99, 03080 Alicante, Spain
Interests: concrete; durability; sustainability; microstructure; performance in aggressive environments; nondestructive techniques
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

It is with great pleasure that we present this Special Issue on “Advanced Studies in Concrete Research”. Concrete is one of the most widely used construction materials, and its continued development is essential for the growth and sustainability of the construction industry. This Special Issue aims to focus on various aspects of concrete research, including additive manufacturing, sustainability, numerical modeling, material characterization, and structural design.

Additive manufacturing is a rapidly growing field that has the potential to revolutionize the construction industry. In this issue, we aim to present studies that investigate the use of 3D printing in concrete construction, exploring the various benefits and limitations of the technique, as well as the challenges that must be overcome for its widespread implementation.

Sustainability is another crucial aspect of concrete research. As the construction industry becomes more environmentally conscious, there is a growing demand for sustainable building materials. The studies in this issue examine various sustainable practices and materials, including recycled aggregates, low-carbon cement, and bio-based additives.

Numerical modeling is an essential tool for predicting the performance of concrete structures. Studies that use numerical simulations to investigate the mechanical properties and durability of concrete and studies that provide valuable insights into the performance of concrete structures under various loading conditions are welcome in this Special Issue.

Material characterization is another important area of concrete research. We invite studies that provide a better understanding of the microstructure and properties of concrete, which are essential for the development of new materials and construction techniques. This issue will welcome submissions of research in this area, making use of use various techniques to analyze the properties of concrete, including X-ray diffraction, microscopy, and spectroscopy.

Last but not least, structural design is also a critical aspect of concrete research. This Special Issue will accept submissions on research about design techniques and methods for optimizing the performance of concrete structures. We welcome studies that explore the use of advanced materials, such as fiber-reinforced concrete and high-strength concrete, as well as modern construction techniques, such as prefabrication and modular construction.

In conclusion, this Special Issue aims to present a comprehensive overview of the latest advances in concrete research. We hope that the research papers collected in this issue will inspire further research and innovation in the field of concrete construction.

Dr. Fernando G. Branco
Prof. Dr. José Marcos Ortega
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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. Buildings is an international peer-reviewed open access monthly 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

development and characterization of special concrete mixtures
concrete durability
advanced numerical modeling
innovative solutions and pre-fabrication applied to concrete
concrete rehabilitation and structural reinforcement
concrete sustainability
concrete-based addictive construction processes
material characterization and quality assessment
3D concrete printing
lifecycle assessment

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Published Papers (13 papers)

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15 pages, 4887 KiB

Open AccessArticle

Effect of Exposure Environment and Calcium Source on the Biologically Induced Self-Healing Phenomenon in a Cement-Based Material

by Deividi Gomes Maurente-Silva, João Vitor Bitencourt Borowski, Vanessa Giaretton Cappellesso, Marilene Henning Vainstein, Angela Borges Masuero and Denise Carpena Coitinho Dal Molin

Buildings 2024, 14(12), 3782; https://doi.org/10.3390/buildings14123782 - 27 Nov 2024

Viewed by 98

Abstract

Microbially induced calcium carbonate precipitation (MICP) presents a sustainable, environmentally friendly solution for repairing cracks in cement-based materials, such as mortar and concrete. This self-healing approach mechanism enables the matrix to autonomously close its own cracks over time. In this study, specimens (50 mm in diameter and 25 mm in height) were exposed to submersion and a wet–dry cycle environment. The solution considered a nutrient-rich suspension with calcium lactate, urea, calcium nitrate, and Bacillus subtilis or Sporosarcina pasteurii in a biomineralization approach. The self-healing efficiency was assessed through optical microscopy combined with image processing, focusing on the analysis of the superficial crack closure area. S. and B. subtilis exhibited notable capabilities in effectively healing cracks, respectively, 8 mm² and 5 mm² at 35 days. Healing was particularly effective in samples placed in a submerged environment, especially with a 69 mM concentration of calcium lactate in bacterial suspensions containing B. subtilis, where 87.5% of a 4 mm² crack was closed within 21 days. In contrast, free calcium ions in the solution, resulting from anhydrous cement hydration, proved ineffective for S. pasteurii biomineralization in urea-rich environments. However, the addition of an external calcium source (calcium nitrate) significantly enhanced crack closure, emphasizing the critical role of calcium availability in optimizing MICP for bio-agents in cement-based materials. These findings highlight the potential of MICP to advance sustainable self-healing concrete technologies. Full article

(This article belongs to the Special Issue Advanced Studies in Concrete Materials)

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18 pages, 8845 KiB

Open AccessArticle

Study on the Mechanical Performance, Durability, and Microscopic Mechanism of Cement Mortar Modified by a Composite of Graphene Oxide and Nano-Calcium Carbonate

by Weicheng Su, Changjiang Liu, Wei Bao, Zhoulian Zheng, Guangyi Ma, Yaojun Deng and Weihua Ye

Buildings 2024, 14(7), 2236; https://doi.org/10.3390/buildings14072236 - 20 Jul 2024

Cited by 1 | Viewed by 888

Abstract

Nano-calcium carbonate (NC) is a novel ultrafine solid powder material that possesses quantum size effects, small size effects, surface effects, and macroscopic quantum effects that ordinary calcium carbonate lacks. As a nanomaterial with superior properties, graphene oxide (GO) has been studied extensively in the field of construction. In microscopic characterization, the reaction between NC and tricalcium aluminate (C₃A) formed a new hydration product, hydrated calcium aluminum carbonate (C₃A·CaCO₃·11H₂O), which enhanced the arrangement of hydration products and optimized the distribution of pore size in the mortar. Regarding the mechanical properties, the addition of GO and NC significantly enhanced the early-age mechanical performance of the mortar. In terms of durability, the incorporation of GO and NC significantly improved the water permeability, chloride ion permeability, and resistance to sulfate attack of the cement mortar. In this study, it was found that adding 1 wt% NC and 0.02 wt% GO not only improves the mechanical and durability properties but also promotes the hydration reaction according to the microstructure analysis. With the help of NC, compared with other studies, the amount of GO is reduced, while the cost is reduced, and the application of GO in the field of cement-based materials is promoted. Full article

(This article belongs to the Special Issue Advanced Studies in Concrete Materials)

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21 pages, 10974 KiB

Open AccessArticle

Numerical Evaluation on Thermal Performance of 3D Printed Concrete Walls: The Effects of Lattice Type, Filament Width and Granular Filling Material

by Kunda Chamatete and Çağlar Yalçınkaya

Buildings 2024, 14(4), 926; https://doi.org/10.3390/buildings14040926 - 28 Mar 2024

Cited by 1 | Viewed by 2138

Abstract

Three-dimensional concrete printing (3DCP) is of great interest to scientists and the construction industry to bring automation to structural engineering applications. However, studies on the thermal performance of three-dimensional printed concrete (3DPC) building envelopes are limited, despite their potential to provide a long-term solution to modern construction challenges. This work is a numerical study to examine the impact of infill geometry on 3DPC lattice envelope thermal performance. Three different lattice structures were modeled to have the same thickness and nearly equal contour lengths, voids, and insulation percentages. Additionally, the effects of filament width and the application of granular insulating materials (expanded polystyrene beads and loose-fill perlite) were also studied. Finally, the efficacy of insulation was established. Results show that void area affects the thermal performance of 3DPC envelopes under stagnant air conditions, while web length, filament width, and contact (intersection) area between the webs and face shells affect the thermal behavior when cavities are filled with insulating materials due to thermal bridging. The thermal efficiency of insulation, which shows the effective use of insulation, varies between 26 and 44%, due to thermal bridges. Full article

(This article belongs to the Special Issue Advanced Studies in Concrete Materials)

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29 pages, 6138 KiB

Open AccessArticle

Assessment of Contact Laws Accounting for Softening in 3D Rigid Concrete Particle Models

by Nuno Monteiro Azevedo, Maria Luísa Braga Farinha and Sérgio Oliveira

Buildings 2024, 14(3), 801; https://doi.org/10.3390/buildings14030801 - 15 Mar 2024

Cited by 1 | Viewed by 1765

Abstract

To obtain predictions closer to concrete behaviour, it is necessary to employ a particle model (PM) that considers contact softening. A bilinear softening contact model (BL) has been adopted in PM studies. Several limitations in PM predictions have been identified that may be due to BL assumptions. For this reason, this paper compares BL predictions with those obtained with more complex models to assess if PM predictions can be improved. As shown, it is possible to calibrate each contact model to reproduce the complex behaviour observed in concrete in uniaxial and biaxial loading. The predicted responses are similar, and the known PM limitations still occur independently of the adopted model. Under biaxial loading, it is shown that a response closer to that observed in concrete can be obtained (higher normal-to-stiffness ratio of ≈0.50, maximum contact compressive strength of ≈60 MPa, and 30% reduction in the number of working contacts). The BL contact model for PM concrete DEM-based simulations is shown to have (i) lower associated computational costs (15% to 50% lower); (ii) a reduced number of contact strength parameters; and (iii) similar responses to those predicted with more complex models. This paper highlights that the BL contact model can be used with confidence in PM fracture studies. Full article

(This article belongs to the Special Issue Advanced Studies in Concrete Materials)

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19 pages, 7251 KiB

Open AccessArticle

Impact Resistance of Rubberized Alkali-Activated Concrete Incorporating Recycled Aggregate and Recycled Steel Fiber

by Weixian Che, Lei Li, Zhongmin Chen, Donghua Liang and Yongchang Guo

Buildings 2024, 14(2), 322; https://doi.org/10.3390/buildings14020322 - 24 Jan 2024

Viewed by 1122

Abstract

Alkali-activated concrete (AAC) features excellent mechanical properties and sustainability. The incorporation of crumb rubber (CR), recycled concrete aggregates (RCAs), and recycled steel fibers (RSFs) can further enhance environmental sustainability. This paper mainly investigated the dynamic behaviors of a novel rubberized AAC incorporating RCAs and RSFs (RuAAC) through Split-Hopkinson Pressure Bar (SHPB) tests. The variables included three types of RSF content (1%, 2% and 3%), five types of rubber content (0%, 5%, 20%, 35% and 50%) and five impact pressures (0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa and 0.9 MPa). Dynamic stress–strain curves, dynamic strength, the dynamic increase factor (DIF), impact toughness and the synergistic effects of RSF and CR were discussed. The results show that increasing RSF and CR contents could improve the impact resistance of RuAAC under impact loading. The RuAAC exhibited significant strain rate sensitivity, and the sensitivity increased with larger contents of RSF and CR. The increase in strain rate sensitivity was more pronounced with higher CR contents, which was reflected in larger dynamic increase factor (DIF) values. Under high impact pressure, the impact toughness was obviously enhanced with higher RSF contents, while the contribution of increased CR content to impact toughness was not apparent, which may be attributed to the fact that this study only calculated the integral under the dynamic stress–strain curve before the peak stress to determine impact toughness, neglecting the potential contribution of CR particles after the peak point. The obvious strain sensitivity exhibited by the RuAAC in the SHPB tests indicated superior impact performance, making it particularly suitable for architectural structures prone to seismic or explosive impacts. Full article

(This article belongs to the Special Issue Advanced Studies in Concrete Materials)

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20 pages, 7574 KiB

Open AccessArticle

Evaluation of Chloride Ion Attack in Self-Compacting Concrete Using Recycled Construction and Demolition Waste Aggregates

by Lorena K. S. Peixoto, Marcos A. S. dos Anjos, Evilane C. de Farias and Fernando G. Branco

Buildings 2024, 14(2), 319; https://doi.org/10.3390/buildings14020319 - 23 Jan 2024

Cited by 1 | Viewed by 1053

Abstract

Construction and demolition waste (CDW) destined for recycling companies has great potential for use in civil construction, since it gives rise to recycled aggregates of different particle sizes that can be used in concrete. However, there is a lack of studies on the durability of concrete produced with recycled aggregates from CDW. This study analyzed the influence of incorporating recycled aggregates from CDW, sand, and gravel on the durability parameters of SCC mixtures, with and without the addition of metakaolin (MK), when subjected to two exposure conditions: outdoors and in cycles of attack by chloride ions. Five mixtures were produced: reference SCC, with natural sand and gravel; SCC with recycled sand and gravel; SCC with recycled sand and gravel and the addition of 10% MK; SAC with recycled sand, natural gravel, and the addition of 10% MK; and SCC with natural sand, recycled gravel and the addition of 10% MK. The water/binder ratio was kept constant for all mixtures and the additive dosage was adjusted according to the variation in the use of aggregates. The mechanical and durability properties were assessed using axial compressive strength, ultrasonic pulse velocity, chloride penetration, chloride ion diffusion, and electrical resistivity tests. The results showed the feasibility of using recycled aggregates from CDW in SCC. The addition of MK significantly improved the performance of SCC using these aggregates. The mixtures with added MK showed a low risk of corrosion and high resistance to chloride ion penetration, and, under highly aggressive attack conditions, it was observed that the chloride ions did not exceed the minimum cover thickness recommended for reinforced concrete structures. The addition of MK to the mix with recycled aggregates caused an 84.6% reduction in the Cl⁻ diffusion coefficient, there was also a 40.3% reduction in Cl⁻ penetration and an increase of up to 156.14% in electrical resistivity compared to the mix with recycled aggregates without the addition of MK. The SCC mix with recycled sand and metakaolin stood out positively compared to the others, achieving an axial compressive strength similar to the reference mix (55.10 MPa). We, therefore, conclude that it is possible to produce such a mix with acceptable performance and ensure good behavior under aggressive environmental conditions. Full article

(This article belongs to the Special Issue Advanced Studies in Concrete Materials)

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15 pages, 2959 KiB

Open AccessArticle

The Influence of Waste Perlite Powder on Selected Mechanical Properties of Polymer–Cement Composites

by Beata Jaworska, Dominika Stańczak and Paweł Łukowski

Buildings 2024, 14(1), 181; https://doi.org/10.3390/buildings14010181 - 10 Jan 2024

Cited by 1 | Viewed by 1265

Abstract

The subject of this paper is the influence of the partial substitution of cement with mineral additive on the properties of polymer–cement composites (PCCs). Although there is considerable research on the use of perlite in cement concrete, most of the previous studies were conducted with expanded perlite or ground waste perlite, and there is a lack of results evaluating its suitability with polymer–cement composites. To fill this gap, this paper presents the mechanical characteristic of PCC mortars containing waste perlite powder. The modification consisted of replacing part of the cement with waste perlite powder, a byproduct formed during the expansion and fractionation of perlite. The granulometric characteristics of the powder were compiled, and its specific surface area and density were determined. A chemical composition analysis was also carried out. An aqueous dispersion of styrene–acrylic copolymer was used as a polymer modifier. The proportions (by mass) between the contents of the PCC composite components, i.e., cement/polymer (0 to 20%) and cement/mineral powder (0 to 15%), were used as material variables. The technical characteristics tested included the compressive, flexural, and tensile strengths at 28 and 90 days of curing. The compositions of the tested composites were determined using the statistical planning of the experiment. At a low polymer-modifier content in PCC mortars (2.93%), the tested mechanical strengths decreased by five times, with a 6-fold increase in waste content. For mortars containing more than 10% of the polymer modifier, no effect of waste material powder on the flexural strength was observed, while with relatively minor reductions in compressive strength of 2% and 5% and tensile strength of 4% and 2% were observed after 28 and 90 days of curing, respectively. It was shown that it is possible to use waste perlite powder as an ingredient in construction polymer–cement composites, while there is a limiting waste content, above which there is a deterioration in mechanical properties. Full article

(This article belongs to the Special Issue Advanced Studies in Concrete Materials)

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19 pages, 4272 KiB

Open AccessArticle

Rheological Properties of Carbon Nanotube Infused Cementitious Composites with Various Amounts of CNT

by Eryk Goldmann, Grzegorz Cygan, Barbara Klemczak and Marcin Górski

Buildings 2023, 13(12), 2960; https://doi.org/10.3390/buildings13122960 - 28 Nov 2023

Cited by 1 | Viewed by 1073

Abstract

The addition of carbon nanotubes (CNTs), which are hydrophobic materials, significantly influences the rheology of cementitious materials but requires important mix modifications in order to provide proper flowability for further use. This paper investigates the influence of various dosages of carbon nanotubes (0.05 wt.%, 0.1 wt.%, 0.2 wt.%, 0.5 wt.%, and 1 wt.%) on the flowability, rheological parameters, air content, and volume density of cement mortars. The results show an increase in the yield stress parameter with an increment in CNT dosage up to the threshold of 0.5 wt.% for mixes with an increased amount of cement. For standard proportions, it was on a stable level for all mixes except for 0.2 wt.%. The plastic viscosity parameter also increased with the CNT dosage; mixes with standard proportions of components were not higher than the reference, and mixes with an increased amount of cement were lower than the reference for dosages up to 0.5 wt.% of CNT. The addition of a superplasticizer and modifications of the ratio of the components were employed to achieve proper flowability and measure the rheological parameters. The presented results show that regardless of the negative influence of carbon nanotubes on the properties of fresh mortar, it is possible to achieve a stable flow and workability using simple modifications of the composition. Full article

(This article belongs to the Special Issue Advanced Studies in Concrete Materials)

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16 pages, 6982 KiB

Open AccessArticle

Experimental Investigation on Interfacial Defect Detection for SCCS with Different Contact NDT Technical

by Fernando Antonio da Silva Fernandes, Joseph Salem Barbar, Dayriane do Socorro de Oliveira Costa and João Adriano Rossignolo

Buildings 2023, 13(10), 2549; https://doi.org/10.3390/buildings13102549 - 9 Oct 2023

Cited by 2 | Viewed by 925

Abstract

Knowledge about air-incorporating additives in concrete can favor civil construction with structures that are lighter and more economical. This study investigated the production of concretes with the addition of 1 to 3% of air-entraining additive via the Micro-CT imaging technique. From the microtomography obtained, it was possible to obtain two-dimensional and three-dimensional images of the analyzed samples. The analysis of these images, using FEI Avizo 9.0 image processing software, allowed for obtaining the volumes of concrete, mortar, voids, and porosities of concrete mortars, in addition to the quantities, shapes, and dimensions of pores (voids) present in the samples. The air contents of the concrete with incorporated air were higher than the reference concrete, directly proportional to the additive contents used, and very close to the mixes with the same additive contents. Both the standard and modified mixes showed an increase in air content as the additive content increased. The specific mass of the concretes decreased as the additive content increased in the standard and modified concretes. As for consistency, the air-incorporated concretes showed greater slumps compared to the reference concrete and increased as the additive content increased, demonstrating the action of the air-incorporating additive in improving workability. Full article

(This article belongs to the Special Issue Advanced Studies in Concrete Materials)

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20 pages, 6431 KiB

Open AccessArticle

Experimental Study on Mechanical Properties and Drying Shrinkage Compensation of Solidified Ultra-Fine Dredged Sand Blocks Made with GGBS-Based Geopolymer

by Ming Feng, Chaohua Jiang, Yixuan Wang, Yongqi Zou and Junxian Zhao

Buildings 2023, 13(7), 1750; https://doi.org/10.3390/buildings13071750 - 10 Jul 2023

Cited by 2 | Viewed by 1222

Abstract

As natural aggregates become increasingly scarce, attention has turned to ultra-fine dredged sand (UDS) generated in waterway regulation engineering. UDS is typically challenging to utilize due to its high clay content and high water demand. This article uses ground granulated blast-furnace slag (GGBS)-based geopolymer to solidify UDS, along with sodium silicate (SS) and sodium hydroxide (SH) as alkaline activators. This paper explores the effects of SS modulus (SiO₂/Na₂O molar ratio) and mass percentage content of Na₂O on the fluidity, setting time, mechanical properties, and shrinkage behavior of hybrid UDS-GGBS geopolymer (HUGG) paste. According to the research findings, increased SS modulus and Na₂O content lead to decreased fluidity and setting time. When the Na₂O content reaches 6%, flash coagulation occurs in the slurry, leading to more internal shrinkage cracks and pores. This has been confirmed by scanning electron microscope (SEM) analysis. When Na₂O content is 5%, and SS modulus is 1.0, the 90-day maximum compressive strength reaches 56.53 MPa, corresponding to a splitting tensile strength of 6.83 MPa, which can be considered the optimal formulation. Meanwhile, basalt and polypropylene fibers (BF and PPF) are chosen to compensate for the susceptibility to drying shrinkage. Both BF and PPF can significantly inhibit the linear drying shrinkage of the HUGG paste. The BF’s ability to enhance mechanical properties is more robust than PPF’s, which can make the paste more homogeneous. The research contributes an effective method for the resource utilization of UDS. Full article

(This article belongs to the Special Issue Advanced Studies in Concrete Materials)

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17 pages, 6540 KiB

Open AccessArticle

Long-Term Behavior Related to Water Ingress in Mortars Which Combine Expanded and Natural Cork Lightweight Aggregates and Eco-Friendly Cements

by José Marcos Ortega, Fernando G. Branco and Luís Pereira

Buildings 2023, 13(7), 1651; https://doi.org/10.3390/buildings13071651 - 28 Jun 2023

Cited by 2 | Viewed by 1466

Abstract

The water ingress plays an important role in building materials’ degradation. The use of lightweight aggregates is interesting in terms of sustainability, because they reduce the density of cement-based materials, among other advantages. The development and use of new lightweight aggregates, such as cork granulates, is a current research topic. In the present work, water ingress performance of sustainable mortars which combined expanded and natural cork aggregates and cements with slag, fly ash and limestone has been studied. Mortars produced with sand and expanded clay were also prepared. Bulk density, water absorption, drying capacity and gel and capillary pores were studied. Tests were carried out at 28 days and 1 year. A good behavior has been generally observed when an addition was incorporated to the binder, especially slag or fly ash. Regarding the new non-standardized lightweight cork aggregates, mortars with natural cork showed lower water absorption and lower volume of permeable pore space in the long term than mortars with expanded cork. At one year, natural cork mortars had an adequate water absorption performance compared to those with expanded clay, which may be due to the high volume of small capillary pores (100 nm–1 µm) in natural cork mortars. Full article

(This article belongs to the Special Issue Advanced Studies in Concrete Materials)

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16 pages, 2849 KiB

Open AccessArticle

Improvement of the Mechanical Properties of Mortars Manufactured with Partial Substitution of Portland Cement by Kaolinitic Clays

by Beatriz Astudillo, Domingo A. Martín, Jorge L. Costafreda, Leticia Presa, Miguel A. Sanjuán and José Luis Parra

Buildings 2023, 13(7), 1647; https://doi.org/10.3390/buildings13071647 - 28 Jun 2023

Cited by 1 | Viewed by 1246

Abstract

Presently, the search for urgent solutions to mitigate climate change has become a global priority. One of the most important challenges is the characterization, standardization, and technology of sustainable natural raw materials, which will significantly improve the quality of common types of cement, the production process of which emits large amounts of greenhouse gases into the atmosphere. This work is focused on the study of natural kaolinitic clays (NKC) from the eastern part of the Iberian Peninsula and its main objective is to define and normalize their properties as natural pozzolanic materials. This research consists of an initial study to determine the morphological and chemical properties using SEM and XRF. Furthermore, the physical properties of the samples were studied, such as thermic treatment (TT), Blane particle finesse (BPF), real density (RD) and apparent density (AD), porosity (P), volume stability (VS) and start and final setting time (SFST). On the other hand, technological analyses were carried out as follows: chemical analysis (CATQ), pozzolanicity (CAP), mechanical compression strength tests at 7, 28, and 90 days (MCST) as well as the ultrasonic pulse velocity (UPV). XRF results indicated that the SiO₂ content (49.9–51.0%) of kaolinitic clay in its natural state (NKC) increases to 57.41 and 58.10%, respectively, when calcined (CKC). The chemical analysis of pozzolanicity established that the NKC does not show pozzolanic activity during the first 8 and 15 days; however, once calcinated, its pozzolanic reactivity increases substantially. On the other hand, the results of the mechanical stress tests (MCST) indicate an exponential increase in mechanical resistance from 7 to 90 days, which is higher in mortars made with CKC; similarly, and according to the results of the calculation of the Resistant Activity Index (RAI), it shows that the substitutions of Portland cement (PC) by NKC are effective between the ranges of 10 and 25%, while in the case of the substitution of PC by CKC, all formulations (10, 25 and 40%) are effective. This research establishes that the kaolinitic clays of the east of the Iberian Peninsula can be considered quality pozzolanic materials, capable of partially replacing Portland cement. The results presented here could be used as guidelines for the understanding and application of natural pozzolanic materials contributing to the improvement of types of cement, mortars, and concretes, which would positively affect the quality and preservation of the environment as well as the sustainability of eco-efficient construction materials. Full article

(This article belongs to the Special Issue Advanced Studies in Concrete Materials)

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24 pages, 5028 KiB

Open AccessReview

The Application of Calcium-Based Expansive Agents in High-Strength Concrete: A Review

by Yulu Zhang, Yifan Pan, Tiezhen Ren, Hongtao Liang, Jianfeng Zhang and Dakang Zhang

Buildings 2024, 14(8), 2369; https://doi.org/10.3390/buildings14082369 - 1 Aug 2024

Cited by 1 | Viewed by 739

Abstract

In this study, comprehensive investigation of the shrinkage compensation mechanisms of calcium-based expansive agents (CEAs), their effects on the properties of (ultra) high-strength concrete (HSC/UHSC), and the existing problems in applying this methodology was conducted. Analyses showed that the rational use of CEAs under certain conditions could greatly or completely inhibit the development of autogenous shrinkage of HSC/UHSC and significantly reduce the risk of associated cracking. However, it was found that the hydration of the CEAs affected the hydration process of other binders, thereby altering the microstructure of concrete. This, in turn, led to a reduction in mechanical properties such as compressive strength, flexural strength, and elastic modulus, with the rate of reduction increasing as the amount of CEA used increased. Moreover, when attempting to improve the shrinkage compensation effects, increasing the amount of CEA presented a risk of delayed expansion cracking of the HSC/UHSC. Neither the expansion mechanism, expansion conditions, nor the inhibition methods have yet been fully clarified in the current stage. Lastly, newly proposed Ca–Mg composite EAs were outlined, and the research prospects of Ca–Mg composite EAs in HSC/UHSC were explored. Full article

(This article belongs to the Special Issue Advanced Studies in Concrete Materials)

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