Characterization of high strength mortars with nano alumina at elevated temperatures

In this study, the effect of elevated temperatures on chemical composition, microstructure and mechanical properties of high strength mortars with nano alumina was investigated. Mortars with 1, 2 and 3% nano alumina as cement replacement were prepared and then exposed to 100 °C, 200 °C, 300 °C, 400 °C, 600 °C, 800 °C and 1000 °C. XRD, DSC and SEM tests were carried out to identify chemical composition and microstructure changes in the cement matrix after being exposed to elevated temperatures. Residual compressive strength, relative elastic modulus and gas permeability coefficient of samples were also obtained. A brittleness index was defined to monitor changes in brittleness of samples after being exposed to elevated temperatures. Nano alumina enhanced compressive strength of samples up to 16% and improved residual compressive strength. An increase in the relative elastic modulus, higher energy absorption and lower permeability were also observed when 1% nano alumina was added

Development of nanotechnology in high performance concrete

Concrete is the most widely used building material all around the world which has been undergoing many changes aligned with technological advancement. The most recent available type of concrete is high performance concrete which is produced employing different admixtures both chemical and mineral to enhance mechanical and durability qualities. As sustainability emerged as an indispensable factor in concrete industry, many researchers targeted micro sized mineral admixtures such as silica fume, fly ash, rice husk ash, slag and so on in order to replace Portland cement which is known to be responsible for almost 7% of carbon dioxide emission into atmosphere. Recently, technology has made it easy for scientist to study nanoscale admixtures and their effect on structure of concrete. This paper reviews nanomaterials in cement composites and how they can improve different properties of concrete

Characterization of mechanical and microstructural properties of palm oil fuel ash geopolymer cement paste

This study delineates activation of palm oil fuel ash (POFA) by a combination of sodium silicate and sodium hydroxide at 60 °C to be used as a geopolymer binder. Qualitative observations as well as compressive strength were recorded to assess the viability of POFA utilization. Also, XRD, SEM/EDX, DSC, FTIR tests were conducted to investigate underlying mechanisms of geopolymerization. The post-test observations revealed that activation of POFA is applicable and compressive strength of up to 32.48 MPa at the age of 28 days was achieved. Chemical tests indicated that formation of calcium silicate hydrate was the dominant cause of geopolymerization

Incorporation of Mineral Admixtures in Sustainable High Performance Concrete

Concrete is a widely used construction material around the world, and its properties have been undergoing changes through technological advancement. Numerous types of concrete have been developed to enhance the different properties of concrete. So far, this development can be divided into four stages. The earliest is the traditional normal strength concrete which is composed of only four constituent materials, which are cement, water, fine and coarse aggregates. With a fast population growth and a higher demand for housing and infrastructure, accompanied by recent developments in civil engineering, such as high-rise buildings and long-span bridges, higher compressive strength concrete was needed. At the beginning, reducing the water-cement ratio was the easiest way to achieve the high compressive strength. Thereafter, the fifth ingredient, a water reducing agent or super plasticizer, was indispensable. However, sometimes the compressive strength was not as important as some other properties, such as low permeability, durability and workability. Thus, high performance concrete was proposed and widely studied at the end of the last century. Currently, high-performance concrete is used in massive volumes due to its technical and economic advantages. Such materials are characterized by improved mechanical and durability properties resulting from the use of chemical and mineral admixtures as well as specialized production processes. This paper reviews the incorporation of mineral admixtures in binary, ternary and quaternary blended mortars in concrete

Evaluation of Residual Flexural Behavior of Corroded Fiber-Reinforced Super Workable Concrete Beams

This Study Investigates the Effect of Macro Synthetic Fiber (MSF) Volume and Crack Widths on Corrosion of the Reinforcing Bars and Residual Flexural Behavior of Fiber-Reinforced Super-Workable Concrete (FR-SWC) Beams Exposed to Accelerated Corrosion. FR-SWC Beams Prepared with 0, 0.33%, and 0.66% MSF Were Pre-Cracked at 0.2-, 0.4-, and 0.75-Mm Widths Before Corrosion Testing. the Controlled Crack Width Was Initiated in One Set of Beams that Were Then Unloaded. the Crack Width Was Maintained for Another Set of Beams during Corrosion Testing by Inserting a Shim. Test Results Showed that the Use of 0.33% and 0.66% MSF Reduced Crack Development and Crack Propagation, Delayed Corrosion Initiation Time, and Significantly Increased the Residual Flexural Strength of Beams Subjected to Accelerated Corrosion. the Beams Reinforced with 0.66% MSF Enhanced Residual Ultimate Load, Residual Yield Load, and Residual Flexural Toughness by 10%–45%, 38%–113%, and 42%–150% Compared to the Corresponding Non-Fibrous Beams. the Improved Flexural Performance of Beams Made with MSF after Accelerated Corrosion Can Be Attributed to the Ability of MSF to Reduce Crack Width Due to Corrosion Damage. Crack Width Lower Than 0.2 Mm Showed No Significant Effect on the Residual Flexural Behavior of Beams after Corrosion Testing. However, the Pre-Crack Width over 0.2 Mm Showed a Significant Influence on the Crack Initiation and Residual Flexural Behavior after Accelerating Corrosion. the Pre-Cracked Beams with a 0.75 Mm Crack Width Retained the Ultimate Load of 65%–76%, Yield Load of 47%–80%, and Toughness of 38%–83%, Respectively, compared to their Corresponding Uncracked Beams Subjecting to Accelerated Corrosion. the Un-Shimmed Beams Allowed Partial Closure of Cracks Due to the Presence of MSF after Initial Loading and Increased the Residual Ultimate Load, Yield Load, and Flexural Toughness by 7%–45%, 27%–82%, and 3%–56%, Respectively, Compared to their Corresponding Shimmed Beams. a Correlation between the Residual Flexural Behavior and the Rate of Cross-Sectional Area Loss of Reinforcing Bars Due to Corrosion Was Developed. Furthermore, a Mechanism Was Proposed to Explain the Effect of MSF in Improving the Residual Flexural Performance in the Cracked FR-SWC Beams

Behavior of high-strength concrete cylinders repaired with CFRP sheets

This study aims to investigate the behavior of damaged high-strength concrete cylinders repaired using carbon fiber reinforced polymer (CFRP) sheet. The experimental work on CFRP-wrapped concrete cylinders with various predamage levels indicated that CFRP can precisely resist the axial aggravated deformation of cylinders caused by damaging under uniaxial loading. The findings also revealed that the energy absorption of the damaged specimens confined with CFRP was restored approximately three times more than that of the undamaged specimens without confinement. Therefore, an empirical relationship exists between the pre-damage levels and the uniaxial compressive strength reduction of the concrete cylinders

FRP sheets contribution in common repair techniques of concrete structures with emphasis on concrete columns

The history of composites dates back to few thousand years ago. Actually, natural fibrous composites were used by ancient Egyptians to build small houses. Numerous studies have revealed that Fibre Reinforced Polymer (FRP) is a convenient material for repair and strengthening of concrete structures compared to the traditional materials. Since the presentation of fibre reinforced polymer (FRP) in the concrete structures, the need for practice codes containing FRP in field of strengthening and repair has emerged. Many parts of structures are usually replaced simply, instead of repair due to the lack of knowledge about the techniques of repair. Hence, in this review, advantages and disadvantages of FRP repair, different types of FRP repair systems, repair stages and principles of repair theory for concrete structures with FRP are reviewed. In addition, modern repair techniques are reviewed in detail for different damaged levels of concrete structures. Recent developments in the field of repair with FRP have highlighted the need for assessment of repaired concrete columns. Thus, in one part of this review, the authors emphasise different damaged concrete column repaired with CFRP. Finally, the recent needs for further researches in field of repair with FRP are discussed

FRP Sheets Contribution in Common Repair Techniques of Concrete Structures with Emphasis on Concrete Columns

The history of composites dates back to few thousand years ago. Actually, natural fibrous composites were used by ancient Egyptians to build small houses. Numerous studies have revealed that Fibre Reinforced Polymer (FRP) is a convenient material for repair and strengthening of concrete structures compared to the traditional materials. Since the presentation of fibre reinforced polymer (FRP) in the concrete structures, the need for practice codes containing FRP in field of strengthening and repair has emerged. Many parts of structures are usually replaced simply, instead of repair due to the lack of knowledge about the techniques of repair. Hence, in this review, advantages and disadvantages of FRP repair, different types of FRP repair systems, repair stages and principles of repair theory for concrete structures with FRP are reviewed. In addition, modern repair techniques are reviewed in detail for different damaged levels of concrete structures. Recent developments in the field of repair with FRP have highlighted the need for assessment of repaired concrete columns. Thus, in one part of this review, the authors emphasise different damaged concrete column repaired with CFRP. Finally, the recent needs for further researches in field of repair with FRP are discussed

Effect of halloysite nanoclay on mechanical properties, thermal behavior and microstructure of cement mortars.

Many studies have targeted the application of clay in cement composites and declared some enhancement on the properties of concrete. However there is little knowledge on nanoclays and their effect on the mechanical properties and durability of cement composites. Halloysite nanoclay is one of the subcategories of nanoclay that has been undeservedly ignored in the production of cement composites. Chemically, the outer surface of the halloysite nanotubes has properties similar to SiO2 while the inner cylinder core is related to Al2O3 which together may improve the cement matrix. In this study the mechanical properties, flowability, thermal behavior and durability of mortars containing 1, 2, 3% halloysite nanoclay were studied. Compressive strength and gas permeability of samples with 3% and 2% nanoclay were improved up to 24% and 56%, respectively. SEM, XRD, DSC tests were carried out to investigate the microstructure and chemical composition change in samples with halloysite nanoclay

Reinforcement benefits of nanomodified coir fiber in lime-treated marine clay

In this study, reinforcing effect of nanomodified coir fibers with ferric hydroxide, Fe(OH)3, and aluminum hydroxide, Al(OH)3, on shear strength of limed marine clay soil was investigated. Accordingly, triaxial compression strength (TCS) testing was carried out to determine the shear strength parameters of the reinforced soil. Also, wetting/drying cycle testing was conducted to assess the durability of samples. The results from the experimental investigation show that the lime and nanomodified fibers improved the shear strength and durability through the intended modification on natural coir fiber. Moreover, an increase in the effective stress internal friction angle and the cohesion intercept were observed. To confirm the morphology alteration in fibers, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) tests were performed. Nanomodification of fibers increased their tensile strength and caused a better interaction with the limed matrix by an enhanced interfacial adhesion. The tensile strength and friction at the interface was the dominant mechanism controlling the reinforcement benefit