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CONTENTS
Volume 18, Number 5, November 2024
 

Abstract
The use of polymer concrete in the construction sector, together with the use of waste from nearby quarries, is an excellent alternative to traditional concrete to help achieve sustainability and environmental objectives. In this work, polymer concrete samples were prepared using a vinyl ester resin as binder and slate, granite and kaolin wastes as mineral fillers. The proportion between the components was varied, as well as the combination of mineral fillers, to study the viability of these wastes for the manufacture of polymer concrete. The influence of these factors on their processing, densification and mechanical properties of these materials has also been investigated. In addition to the rheological characterization of the resin, scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray fluorescence (WDXRF) techniques were used to study the morphology and characterization of the other components; the mechanical behavior of these materials has also been studied through their hardness, compressive strength and flexural strength properties. The results obtained will help to optimize the proportions of resin and fillers used in the production of polymer concrete, as well as the convenience of using certain combinations of these mineral fillers to obtain quality materials. All this will contribute to improving the use and management of quarry waste, as well as minimizing environmental impact and saving on production costs.

Key Words
densification; mechanical properties; mineral waste; polymer composite; polymer concrete

Address
(1) Gianluca Grimaldi, Caridad Díaz-Jiménez, Antonio Macías-García, Antonio Díaz-Parralejo:
Departamento de Ingeniería Mecánica, Energética y de los Materiales, Escuela de Ingenierías Industriales, Universidad de Extremadura, Avenida de Elvas s/n, 06006 Badajoz, España;
(2) Paulo Brito:
Polytechnic Institute of Portalegre, Escola Superior de Tecnologia e Gestão, Praça do Municipio 11, 7300-110 Portalegre, Portugal.

Abstract
This article presents the impact of accelerated curing on high-strength, high-performance nano concrete made from copper slag. The study utilized a combination of cement and silica fume nanoparticles as binders, with quartz powder particles acting as fillers. Industrial by-products from the copper smelting industry were used to replace traditional fine and coarse aggregates, promoting sustainability. To enhance the tensile strength and flexural stiffness of the concrete, micro steel fibers were incorporated based on the optimal design mix for compressive strength. Both conventional and accelerated curing methods were adopted during preparation of the specimen. Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) analyses were conducted on the optimal nano concrete blends to investigate their microstructure. The developed concrete was evaluated for various structural applications, incorporating micro steel fibers and nanofibers. The highest compressive strength achieved with 100% sand replacement by copper slag was 136 MPa under accelerated curing conditions. Flexure, direct tension, and split tension tests yielded maximum values of 11.78 MPa, 7.12 MPa, and 12.70 MPa, respectively. Nano-Concrete elements reinforced with a blend of carbon and steel fibers exhibited greater flexural capacity, along with delayed crack initiation and propagation. Accelerated curing facilitated the growth and uniform distribution of C-S-H gel, further improving the performance of the nano-concrete.

Key Words
accelerated curing; copper slag high strength high performance; nano-concrete; quartz powder; silica fume

Address
Easwari Engineering College, Chennai, Tamil Nadu, India.


Abstract
The utilization of alkali-activated green tuff to produce geopolymer mortar, using low molarity NaOH and curing temperature to reduce energy consumption is a key focus of this research. This article examines physical and chemical analyses of geopolymer mortar based on alkali-activated green tuff at different ages (7 to 180) under ambient temperature conditions (26 ± 3°C) The alkaline activators in the mortar consist of sodium hydroxide with two different molarities (4 and 6), and sodium silicate. Analytical results indicate that higher molarity leads to the generation of more cations in the ionic soup. In the short term, this accelerates geopolymer formation and enhances compressive strength; however, in the long run, it results in increased shrinkage and dimensional instability, leading to the development of cracks. The findings reveal that the compressive strength of the mortar containing alkali-activated green tuff with 4M NaOH(aq) at 180 days is approximately 58% higher than that of mortar containing Portland cement. XRD analysis further demonstrates that the predominant phases formed in the mortar with alkali-activated green tuff are C-A-S-H and N-A-S-H gels. The higher presence of C-A-S-H gel is attributed to the inclusion of slag, constituting half of the alkali-activated binder.

Key Words
alkali-activated; curing; geopolymer; green tuff; mortars; NaOH; N-A-S-H; slag

Address
(1) Parand Razeghi Tehrani, Azita Behbahaninia:
Department of Civil Engineering, Roudehen Branch, Islamic Azad University, Roudehen, Iran;
(2) Mohammad Ali Arjomand:
Department of Civil Engineering, Shahid Rajaee Teacher Training University, Tehran, Iran;
(3) Nargess Kargari:
Department of Environment, Takestan Branch, Islamic Azad University, Takestan, Iran.

Abstract
This paper conducts an in-depth investigation into the stability and instability responses of a nanocompositereinforced concrete disk, analyzed under unconventional boundary conditions. The study centers on the dynamic behavior and critical buckling features, influenced by the integration of nanomaterials into the concrete matrix. By employing both analytical techniques and numerical simulations, the research assesses the impact of nanocomposite reinforcement on the disk's structural performance across a range of loading scenarios. The non-classical boundary conditions, characterized by atypical constraints and support systems distinct from standard fixed or simply supported conditions, are shown to play a pivotal role in determining the disk's critical load and stability thresholds. Such boundary conditions, which frequently arise in practical applications, significantly influence the disk's stability and load-bearing capacity. The paper also delves into the material properties of the nanocomposites, highlighting their improved stiffness, toughness, and mechanical performance, which contribute to enhancing the structure's overall strength. Through a parametric study, the research thoroughly examines the effects of variables such as nanomaterial volume fraction, disk geometry, and boundary support type. The results indicate a complex interaction between reinforcement, geometry, and boundary conditions, which may lead to instability in specific configurations. This investigation provides valuable insights for optimizing the design of nanocomposite-reinforced concrete structures and offers recommendations for enhancing their structural stability and integrity in practical applications. The findings advance the punderstanding of the mechanical behavior of nanocomposite materials under non-standard boundary conditions.

Key Words
concrete disk; instability; nanocomposite reinforcement; non-classical boundary conditions; stability

Address
(1) Lian Xue:
School of Computer and Computing Science, Hangzhou City University, Hangzhou 310015, Zhejiang, China;
(2) Mostafa Habibi:
Universidad UTE, Facultad de Arquitectura y Urbanismo, Calle Rumipamba S/N y Bourgeois, Quito, 170147, Ecuador;
(3) Mostafa Habibi:
Department of Biomaterials, Saveetha Dental College and Hospital, Saveetha Institute of Medical and Technical Sciences, Chennai, 600 077, India;
(4) Mostafa Habibi:
Department of Mechanical Engineering, Faculty of Engineering, Haliç University, 34060, Istanbul, Turkey;
(5) Mostafa Habibi:
Institute of Research and Development, Duy Tan University, Da Nang, 550000, Viet Nam;
(6) Chaohai Ou:
Department of Mechanical Engineering, Engineering Saeed Group, Alkharj, Saudi Arabia.

Abstract
The influence of seawater upon high calcium fly ash alkali activated paste (AAP) on setting time and strength was studied. The materials included high calcium fly ash, sodium hydroxide (NaOH), sodium silicate (NS) and seawater. Setting time and compressive strength of the mixes were tested. The variables included seawater content, liquid to fly ash ratio, NaOH concentration, and NS/NaOH ratio. All mixes were cured at ambient temperature. Seawater was used instead of distilled water to prepare NaOH solution. The incorporation of seawater resulted in the shortening of setting time and increasing compressive strength. The strength enhancement was highly significant when the seawater is used with low NaOH concentration of 5 molar which is cost attractive. The use of seawater with short setting time and sufficiently high strength AAP is useful in applications such as patch repair of pavement and sidewalk, precast sections and other applications in places such as remote coastal areas and islands where fresh water is scarce.

Key Words
alkali activated paste; high calcium fly ash; seawater; setting time; strength

Address
(1) Athika Wongkvanklom:
Department of Civil and Environmental Engineering, Faculty of Science and Engineering, Kasetsart University, Chalermphrakiat Sakon Nakhon Province Campus, Sakon Nakhon 47000, Thailand;
(2) Patcharapol Posi, Chaiwat Bangsai:
Department of Civil Engineering, Faculty of Engineering, Rajamangala University of Technology Isan, Khon Kaen Campus, Khon Kaen 40000, Thailand;
(3) Pornnapa Kasemsiri, Piyawat Foytong:
Sustainable Infrastructure Research and Development Center, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002, Thailand;
(4) Sumrerng Rukzon:
Department of Civil Engineering, Faculty of Engineering, Rajamangala University of Technology Rattanakosin, Nakhon Pathom, 73170 Thailand;
(5) Prinya Chindaprasirt:
Sustainable Infrastructure Research and Development Center, Department of Civil Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002, Thailand, and Academy of Science, Royal Society of Thailand, Dusit, Bangkok 10300, Thailand.

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