•Silica powder in UHPC was replaced to coal bottom ash and nano slag.•Replacement of coal ash did not decrease in workability and strength.•Autogenous shrinkage of UHPC was not affected by ...by-products.
This experimental research addresses the physical properties of eco-friendly Ultra High Performance Concrete (UHPC) incorporating industrial by-products including coal bottom ash, fly ash and two types of slag powder. Slump flow, compressive strength development, porosity, setting time, autogenous shrinkage and thermogravimetric analysis of UHPC are characterized. The experimental results indicate that coal bottom ash and fly ash are promising industrial by-products by effectively replacing silica powder in UHPC without significant losses in workability and strength development. It is revealed that normal-sized and finer-sized ground granulated blast furnace slag can be effectively used without additional activator to partially substitute cement and silica fume, respectively, which results in enhanced workability and comparable compressive strength, albeit relatively slow strength development. Furthermore, it is found that the adoption of various forms of industrial by-products in UHPC does not play a significant role in affecting autogenous shrinkage, porosity and capillary water absorption of UHPC.
•Decreasing size of bottom ash may promote their utilization in cement composites.•Bottom ash powders could improve in workability of high-strength mortar.•Bottom ash powders improve hydration of ...mortar at early-age compared to fly ash.
In the present study, sieved and ground coal bottom ash powders were utilized in high-strength mortar as a coarse binder to help improve workability. The chemical and physical characteristics of the powders were evaluated. The hydration heat of blended binders was measured. The workability, hydration kinetics, compressive strength, and autogenous shrinkage of the mortar were investigated. The workability of the high-strength paste and mortar mixtures with bottom ash powders was significantly higher than that of mixtures including only cement and fly ash. Owing to their higher pozzolanic reactivity, the mortar containing bottom ash powders exhibited a higher degree of hydration and similar compressive strengths at 3 and 28days compared to the mortar with fly ash.
The hydration kinetics and shrinkage of carbon nanotube (CNT)/cement composites were investigated experimentally. The effect of CNTs mixed in a paste matrix was evaluated in terms of the degree of ...hydration and heat of hydration to evaluate the overall hydration kinetics. Furthermore, the microstructure and the reaction products were characterized using mercury intrusion porosimetry, X-ray diffraction, and chemical shrinkage for further analysis. Autogenous and dry shrinkages were measured, and the results were analyzed based on the hydration kinetics. The experimental results show that pure CNTs are not capable of activating or delaying the hydration products; rather, they offer a micro-filler capability. In addition, autogenous shrinkage increased despite the amount of added CNTs in some cases.
•CNT/cement composite could be used as chloride sensor in concrete structure.•Conductivity of the CNT/cement composite was influenced mainly by the sodium chloride content.•A CNT content in the ...composite was an important factor on the chloride monitoring accuracy.
A novel non-destructive method of monitoring chloride penetration in reinforced concrete structures prior to corrosion is proposed. By measuring the change in the electrical characteristics induced by chloride in cement composites containing carbon nanotubes (CNTs), chloride penetration in the structures could be monitored in real time. To evaluate the feasibility of this method, cement composites containing various amounts of CNTs and sodium chloride were fabricated and their electrical characteristics were measured. Although the conductivity of the composite without CNTs fluctuated as a result of both reinforcement and moisture content, that of the composites with CNTs was seldom influenced by these factors, and the conductivity generally increased with increasing chloride content. The chloride content in the composites was estimated via regression analysis based on the electrical characteristics, implying that the CNT/cement composite could be used as a sensor for chloride penetration monitoring.
Graphene quantum dots (GQDs) are carbon-based zero-dimensional materials that have received considerable scientific interest due to their exceptional optical, electrical, and optoelectrical ...properties. Their unique electronic band structures, influenced by quantum confinement and edge effects, differentiate the physical and optical characteristics of GQDs from other carbon nanostructures. Additionally, GQDs can be synthesized using various top-down and bottom-up approaches, distinguishing them from other carbon nanomaterials. This review discusses recent advancements in GQD research, focusing on their synthesis and functionalization for potential applications. Particularly, various methods for synthesizing functionalized GQDs using different doping routes are comprehensively reviewed. Based on previous reports, current challenges and future directions for GQDs research are discussed in detail herein.
•Steel fibers on surfaces of UHPC immersed in chloride solution were corroded after a year.•Flexural strength of thin UHPC panel (10 mm) was decreased by fiber corrosion.•Fiber corrosion on surface ...led no substantial strength decrease of thick UHPC panel.
The results of experimental investigation of ultra-high performance concrete (UHPC) by evaluating the flexural response are presented in order to qualitatively evaluate the effects of chloride-induced corrosion. The third-point bending test is carried out using the hydraulic servo-controlled testing machine. The experimental variables are thickness of specimen (10, 25 and 50 mm), immersion duration, and mixture design of UHPC. The specimens are immersed in 10 wt% NaCl solution up to a year to induce corrosion. The effect of chloride-induced corrosion of steel fiber of UHPC is evaluated in terms of compressive strength, flexural strength and flexural toughness. The experimental results indicate that there is no significant loss in flexural strength and toughness for the specimens which were thicker than 25 mm over a period up to 365 days of immersion in chloride solution; whereas, the specimen with thickness of 10 mm showed about 10% decrease in maximum stress and corresponding toughness after 180 days of the immersion. Furthermore, it is revealed by comparing the compressive strength with and without fibers that the presence of steel fibers in UHPC under corrosive environments do not lead to substantial strength decrease.
This experimental research investigates the mechanical properties and shrinkage of ultra high performance concrete (UHPC) incorporating coarser fine aggregates with maximum particle size of 5 mm. To ...adequately design UHPC mixtures using various sizes of solid constituents, particle packing theory was adopted. UHPC mixtures containing either dolomite or basalt, and four fiber volume fractions up to two volume percent were investigated. Uniaxial tension test was performed to evaluate the first cracking tensile strength, ultimate tensile strength, tensile strain capacity and cracking pattern. The UHPC mixtures with dolomite and steel fibers with more than one volume percent achieved more than 150 MPa of compressive strength at the age of 56 days, and showed strain hardening behavior and limited decrease in tensile strength compared to typical UHPC without coarser fine aggregates. The experimental results highlight the potential of dolomite used as coarser fine aggregate in UHPC.
•Mine tailings could substitute silica powder and sand in UHPC.•Characteristics of UHPC were varied by the shape and size of tailings.•Leaching of toxic elements in tailings was highly controlled by ...UHPC matrix.
High production cost and scarcity of raw materials may hinder the application and accessibility of ultra-high performance concrete (UHPC). In the present study, mine tailings, mineral waste products from mining sites, were applied to mitigate these problems. Two types of quartz-based mine tailings produced in South Korea were used to substitute silica powder and silica sand by half and fully in UHPC. The characteristics of UHPC with the tailings, including the compressive strength, workability, water absorption, and leachability of toxic elements, were experimentally evaluated. The effects of the tailings on the characteristics of UHPC varied according to the shape and size of particles of the tailings. The leaching of toxic trace elements from the tailings was highly controlled due to the chemical and physical capsulation of UHPC.
•Calcined oyster shell (COS) waste was utilized as an additive for high volume slag cement binder.•Addition of COS had a positive effect on strength development of high volume slag cement binder.•COS ...increased the percentage of Ca2+ leading to higher cumulative heat evolution.•Incorporation of COS refined the pore structure of high volume slag cement binder.•Increased degree of hydration and mean chain length was observed for binder mixes containing COS powder.
The present study investigates the effect of calcined waste oyster shell powder as additive on the fresh, hardened and microstructural properties of high volume slag cement. The results provide that addition of calcined oyster shell powder enhanced the early age compressive strength. The hydration of calcined oyster shell powder resulted in additional portlandite formation during the initial reaction stage. The observations drawn from porosity measurements indicated that calcined oyster shell powder decreased the porosity of binder matrix at early and elongated duration of curing. Furthermore, by 29Si NMR it was observed that the hydration of high volume slag cement was also benefited by calcined oyster shell powder as indicated by increased degree of hydration and chain length. However, excess addition of calcined oyster shell powder caused decreased compressive strength development. Considering the results, calcined oyster shell powder can be used as additive in high volume slag cement.
Experimental results on the effects of chloride content of ultra high performance concrete (UHPC) are presented. The experimental variables are the amount of sodium chloride, ranging from zero to ...3.0% per cement weight, and matrix strength, including normal mortar and high strength mortar. Sodium chloride is directly mixed with cement matrix in order to simulate harsh environments by promoting the corrosions of fibers and matrix. The effects of chloride content are evaluated in terms of visual observation, electrical resistivity change, compressive strength, bending strength, and dynamic Young's modulus. The experimental results show that UHPC has the superior capability to resist chloride ions due to its dense microstructures, which prevent the growth of rust crystals. Furthermore, the experimental findings suggest that the potentials for corrosion of steel fibers and for corrosion-induced matrix cracking are inconsequential in UHPC even if chloride ions penetrate into UHPC.
