Effect of Alumina Additives on Mechanical and Fresh Properties of Self-Compacting Concrete: A Review

Influence of Various Nanomaterials on the Rheology and Hydration Kinetics of Oil Well Cement

Nanomaterials have great potential to influence the properties of cement-based materials due to their small particle size and large specific surface area. The influences of Nano-SiO2 (NS), gamma-nano-Al2O3 (GNA), alpha-nano-Al2O3 (ANA), and nano-TiO2 (NT) on the rheology and hydration kinetics of class G cement at 30 °C were investigated in this study. The nanomaterials were added in dry powder form at dosages of 1, 2, 3, 5, and 7% by weight of cement (bwoc), and their dispersion was accomplished using polycarboxylate superplasticizer (PCE) at a dosage of 1.6% bwoc. PCE provides a uniform dispersion of nanoparticles in the cement matrix, enhancing the efficiency of nanomaterials. The w/c ratio varied between 0.718 and 0.78 to form a constant-density slurry of 1.65 g/cm3. Our test results showed that NS and GNA caused significant increases in the rheology of the cement slurry, with this effect increasing with dosage, while ANA and NT tended to reduce the rheology of the slurry. Compared to a well-suspended and well-dispersed cement slurry generated by the use of PCE and diutan gum, all nanomaterials can accelerate early hydration by reducing the induction time, with GNA having the strongest influence, while NS was the only nanomaterial that further increased the long-term hydration heat release at 7 days. The stronger effect of NS and GNA on the cement slurry properties can be attributed to their higher chemical reactivity. The dosage effect on total hydration extent was relatively strong for ANA, NT, and NS from 3% to 5% but weak for GNA in the range from 3% to 7%.

Optimal Roving Winding on Toroidal Parts of Composite Frames

Frames made of polymer composites are increasingly used in the aerospace, automotive, and agricultural industries. A frequently used technology in the production line of composite frames is winding rovings onto a non-load-bearing frame to form the structure using an industrial robot and a winding head, which is solidified through a subsequent heat-treatment pressure process. In this technology, the most difficult procedure is the winding of the curved parts of a composite frame. The primary concern is to ensure the proper winding angles, minimize the gaps and overlaps, and ensure the homogeneity of the wound layers. In practice, the curved frame parts very often geometrically form sections of a torus. In this work, the difficulty of achieving a uniform winding of toroidal parts is described and quantified. It is shown that attaining the required winding quality depends significantly on the geometrical parameters of the torus in question. A mathematical model with a detailed procedure describing how to determine the number of rovings of a given width on toroidal parts is presented. The results of this work are illustrated with practical examples of today's industrial problems.

Effects of Fiber and Surface Treatment on Airport Pavement Concrete against Freeze-Thawing and Salt Freezing

Airport pavement concrete often suffers from freeze-thawing damage in high latitude and cold areas. In addition, the use of aircraft deicer makes the airport pavement concrete suffer from salt-freezing damage. To improve the durability of airport pavement concrete, modified polyester synthetic fiber (FC), cellulose fiber (CF), and basalt fiber (BF) reinforced concrete were prepared in this paper. The mechanical strength, pore structure, and frost resistance (freeze-thawing and salt freezing) of fiber-reinforced concrete were investigated. The effects of the combined action of fiber (fiber type and content) and surface treatment methods (spraying silane and impregnating silane) on the frost resistance of concrete were investigated. The results show that the flexural strength of concrete is positively correlated with the elastic modulus of fiber, but has little effect on the compressive strength. Fiber can reduce mass loss and dynamic modulus loss of concrete subjected to frost damage. FC more effectively improved the frost resistance of concrete than CF. After 30 cycles of salt freezing, the spalling amount of concrete sprayed or soaked with silane was decreased by 65.5% and 55.5%, respectively. Adding fiber and impregnating silane reduced the spalled concrete by up to 70.5%. Spraying silane treatment is better than impregnating silane treatment in enhancing the frost resistance of concrete because a better silane condensation reaction is achieved with spraying silane.

Koloor SS, Kumar D, Yahya MY. On Laminated Object Manufactured FDM-Printed ABS/TPU Multimaterial Specimens: An Insight into Mechanical and Morphological Characteristics

Fused deposition modeling (FDM) printing of commercial and reinforced filaments is a proven and well-explored method for the enhancement of mechanical properties. However, little has hitherto been reported on the multi-material components, fused or laminated together into a single specimen by using the laminated object manufacturing (LOM) technique for sustainable/renewable polymers. TPU is one such durable and flexible, sustainable material exhibiting renewable and biocompatible properties that have been explored very less often in combination with the ABS polymer matrix in a single specimen, such as the LOM specimen. The current research work presents the LOM manufacturing of 3D-printed flexural specimens of two different, widely used polymers available viz. ABS and TPU and tested as per ASTM D790 standards. The specimens were made and laminated in three layers. They were grouped into two categories, namely ABS: TPU: ABS (ATA) and TPU: ABS: TPU (TAT), which are functionally graded, sandwiched structures of polymeric material. The investigation of the flexural properties, microscopic imaging, and porosity characteristics of the specimens was made for the above categories. The results of the study suggest that ATA-based samples held larger flexural strength than TAT laminated manufactured samples. A significant improvement in the peak elongation and break elongation of the samples was achieved and has shown a 187% increase in the break elongation. Similarly, for the TAT-based specimen, flexural strength was improved significantly from approximately 6.8 MPa to 13 MPa, which represents a nearly 92% increase in the flexural strength. The morphological testing using Tool Maker’s microscopic analysis and porosity analysis has supported the observed trends of mechanical behavior of ATA and TAT samples.

Investigating the Behavior of Waste Alumina Powder and Nylon Fibers for Eco-Friendly Production of Self-Compacting Concrete

Self-compacting concrete (SCC) incorporating secondary raw materials has been extensively used around the globe due to its improved fresh, mechanical and durability properties. This study was planned to evaluate the suitability of locally available waste alumina powder (AP) and nylon textile fibers (NF) as a partial replacement for fine and coarse aggregates with the ultimate goal to locally produce SCC with desired properties. The used AP was acquired from a local market and NF was collected from a local textile factory. Various dosages of AP (10%, 20%, 30%, 40% and 50% by volume of fine aggregates) and NF (1% and 2% by volume of coarse aggregates) were studied. Tests including slump flow, V-funnel and J-ring tests were performed for examining the fresh properties of developed SCC. Results showed that the addition of AP has an insignificant effect on the superplasticizer dosage for maintaining a constant flow of 70 cm. However, a higher dosage of superplasticizer was required for a mixture with increasing dosages of NF to sustain a constant flow. Similarly, slump flow time (for a spread of 50 cm) and V-funnel time increased for mixtures with higher dosages of AP and NF. Tested SCC mixtures incorporating 40% and 50% of AP with 1% and 2% of NF showed an extreme blocking assessment due to their increased interparticle friction, the higher water absorption capacity of used AP and NF leading to increased flow resistance and hence, showed lower passing ability. The compressive strength was 16% higher for specimens incorporating 40% of AP due to the filling effect of AP which fills the micro-pores, leading to a more dense and compact internal micro-structure, confirmed through scanning electron microscopy analysis. An ultrasonic pulse velocity test conducted on hardened specimens verified the findings of the compressive strength results. Moreover, it was observed that NF has an insignificant effect on the compressive strength; however, flexural strength was increased due to the incorporation of NF, especially at higher dosages of AP.

Study on Impact Compression Performance and Constitutive Model of Aluminum Oxide Fiber-Reinforced Concrete

In order to explore the impact compression performance of aluminum oxide fiber concrete, the impact compression test of aluminum oxide fiber concrete with different contents is carried out by using the split Hopkinson pressure bar (SHPB) comprehensive test system with a diameter of 100 mm. Our intent was to explore the influence law of different contents of aluminum oxide fiber on the impact compression performance of concrete matrixes, and to optimize and establish a constitutive model based on damage theory and stress residue. The results show that adding alumina short-cut fiber to concrete changes its mechanical properties of impact compression to a certain extent. When the volume content of fiber is 0.2%, the characteristics of strength, deformation, and energy are the best, and the excess aluminum oxide fiber reduces the original performance due to agglomeration and other factors; the strength characteristics, peak deformation characteristics, and energy characteristics of aluminum oxide fiber concrete are significantly affected by strain rate and impact velocity. Based on the Zhu-Wang-Tang non-linear viscoelastic model (ZWT model), the complexity coefficient is optimized and the residual stress term is added to construct the prediction model of aluminum oxide fiber concrete. The parameters in the model have a good prediction effect on the stress-strain curve under different strain rates.

The effect of nanosilica incorporation on the mechanical properties of concrete exposed to elevated temperature: a review

Exposing concrete to high temperatures leads to harmful effects in its mechanical and microstructural properties, and ultimately to total failure. In this sense, various types of waste materials are exploited not only to tackle serious environmental issues but also to enhance the thermal stability of concrete exposed to elevated temperatures. Furthermore, nanomaterials have been incorporated in concrete as admixtures to reduce the thermal degradation of concrete due to exposure to high temperatures. In the present study, the effects of nanosilica (NS) incorporation on the properties of concrete subjected to elevated temperature are discussed in several sequential sections. The process mechanism of concrete deterioration due to fire exposure and the important factors that could affect the performance of concrete under fire were evaluated. Moreover, brief highlights on the effect of elevated temperature on concrete containing waste materials are included in this review paper. Reviews and summaries of the available and updated literature regarding concrete containing NS are considered. According to the findings of the studies under review, the addition of nanosilica to concrete contributed in reduced strength loss, minimized internal porosity, and enhanced matrix compactness in concrete.

Special Issue on “Multifunctional Hybrid Materials Based on Polymers: Design and Performance”

Hybrids and composite materials offer a synergic combination of polymer and inorganic features [...]

Temperature Impact on Engineered Cementitious Composite Containing Basalt Fibers

Engineered cementitious composite (ECC) is a new generation of fiber-reinforced concrete with high ductility and exceptional crack control capabilities. However, ECC can suffer a substantial reduction in ductility when exposed to elevated temperatures resulting in a loss of crack-bridging ability. In this study, the effect of adding basalt fiber (BF), which is an inorganic fiber with high-temperature resistance for the production of ECC, was studied. Moreover, the change in the mechanical properties of ECC, including compressive, tensile, and flexural strength, was experimentally investigated under elevated temperatures up to 400 °C. The results showed that the addition of BF to reinforced ECC improved the tensile and flexural strength of concrete effectively, but compressive strength marginally decreased. A significant decrease was observed in the range from 300 to 400 °C, while it increased smoothly when heated up to 300 °C. The compressive and flexural strength diminished after a slight strain gained when heated up to 100 °C. This work paves the way for future investigations focusing on the development of high-temperature resistance ECC.

Experimental Study on the Effect of Basalt Fiber and Sodium Alginate in Polymer Concrete Exposed to Elevated Temperature

Polymer concrete contains aggregates and a polymeric binder such as epoxy, polyester, vinyl ester, or normal epoxy mixture. Since polymer binders in polymer concrete are made of organic materials, they have a very low heat and fire resistance compared to minerals. This paper investigates the effect of basalt fibers (BF) and alginate on the compressive strength of polymer concrete. An extensive literature review was completed, then two experimental phases including the preliminary phase to set the appropriate mix design, and the main phase to investigate the compressive strength of samples after exposure to elevated temperatures of 100 °C, 150 °C, and 180 °C were conducted. The addition of BF and/or alginate decreases concrete compressive strength under room temperature, but the addition of BF and alginate each alone leads to compressive strength increase during exposure to heat and increase in the temperature to 180 °C showed almost positive on the compressive strength. The addition of BF and alginate both together increases the rate of strength growth of polymer concrete under heat from 100 °C to 180 °C. In conclusion, BF and alginate decrease the compressive strength of polymer concretes under room temperature, but they improve the resistance against raised temperatures.