Although ultra high-performance concrete (UHPC) has great performance in strength and durability, it has a disadvantage in the environmental aspect; it contains a large amount of cement that is ...responsible for a high amount of CO
emissions from UHPC. Supplementary cementitious materials (SCMs), industrial by-products or naturally occurring materials can help relieve the environmental burden by reducing the amount of cement in UHPC. This paper reviews the effect of SCMs on the properties of UHPC in the aspects of material properties and environmental impacts. It was found that various kinds of SCMs have been used in UHPC in the literature and they can be classified as slag, fly ash, limestone powder, metakaolin, and others. The effects of each SCM are discussed mainly on the early age compressive strength, the late age compressive strength, the workability, and the shrinkage of UHPC. It can be concluded that various forms of SCMs were successfully applied to UHPC possessing the material requirement of UHPC such as compressive strength. Finally, the analysis on the environmental impact of the UHPC mix designs with the SCMs is provided using embodied CO
generated during the material production.
•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.
Laser cutting of intrusive rocks, including granite, gabbro, and diorite, is carried out in order to assess the cut characteristics through geometrical measurements, such as kerf width, melting ...width, and penetration depth. The absorption rate for each specimen at the wavelength of 1064 nm is measured using a spectrophotometer. A multimode fiber laser is used in this study with the power of 9 kW and different cutting speeds. Furthermore, nitrogen gas at 13 bar is applied as the assistant gas in order to remove the melted material effectively. As a result of the experiment, the relationship between the cutting speed and geometrical measurements is investigated. Furthermore, variations of penetration depth are performed in accordance with the number of laser cuts. In addition, through energy dispersive X-ray (EDX) element mapping, minerals that comprise the rocks are classified and characterized. Subsequently, the changes in the microstructure and chemical composition of each specimen, before and after laser cutting, are compared using scanning electron microscope (SEM) and EDX analyses. Experimental results demonstrate that the cutting characteristics vary, depending on the types of minerals that make up the rock. Based on a series of tests, it is identified that volume energy of more than 3.06E + 13 Formula: see text is required to fully cut intrusive rocks that have a thickness of 25 mm.
This paper investigates the effect of silica fume on the mechanical properties of metakaolin-based geopolymers with different silicon-to-aluminum molar (S/A) ratios. Geopolymer has been extensively ...studied as an alternative to traditional cementitious material because of its low CO
2
emissions. Previous studies revealed that the application of silica fume can improve the compressive strength of geopolymer, however, the optimum dosages are different. To examine the reason for the different optimum dosages of silica fume, this study prepares geopolymer specimens of which variables are the S/A ratio and silica fume dosage, and conducts compressive strength and initial setting time tests. To examine whether the strength degradation is caused by the expansion due to the added silica fume in geopolymer, the volume and dynamic modulus are also measured. The results show that a part of silica fume dissolves and changes the S/A ratio of geopolymer, and that a part of silica fume remains in the geopolymer matrix. These combined effects of silica fume result in an irregular compressive strength trend, and, thus, an optimum dosage of silica fume can vary depending on the S/A ratio. Furthermore, the volume expansion of geopolymer with silica fume is observed, however, no sign of damage on the compressive strength is found.
The amendment of cementitious binders with waste materials aids as a path to reduce the volume of waste and carbon emission. This review summarizes the current state of practice for cementitious ...binder fabrication in favor to the utilization of waste materials such as waste concrete powder (WCP), coal bottom ash (CBA) and steel slags. These materials have the potential to be employed as cementitious material, however much of the application is still up to the laboratory scale. This manuscript will serve as the support to understand the utilization of mentioned waste as nontraditional cementitious products. The highlighted areas likely need more refinement and research with indication on possible negative impact on application of wastes. The use of the aforementioned wastes for blending with OPC (ordinary Portland cement) can reduce carbon emissions from cement manufacturing. Additionally, it can also reduce the use of natural resources during clinker production.
This experimental research investigated the applicability of the liquid crystal display (LCD) by-product of the refining process as a sustainable and alternative alkali activator for ground ...granulated blast-furnace slag (GGBFS) blended cement concrete. Three levels of binder replacement using the industrial by-product, and four water/binder ratios were considered in order to evaluate the effects of the replacement in fresh and hardened properties of the blended concrete. XRD and TG analyses confirmed that the by-product that contains abundant alkali compounds promotes the reactivity of GGBFS. The test results indicated that the incorporation of the by-product results in delayed setting and degraded workability due to the highly porous nature of the by-product, yet shows rapid early-age strength development of the blended concrete as conventional alkaline activators for GGBFS. These characteristics shed light on a simple yet effective and practical means of reusing the industrial by-product as an alternative alkaline activator.
This experimental research highlights the applicability of laser cutting to cement-based materials using multimode fiber lasers. A 9 kW multimode fiber laser is used, and the experimental variables ...are the water-to-cement ratio, laser speed, and material compositions such as cement paste, cement mortar and ultra high performance concrete (UHPC). The laser cutting performance on the cement-based materials is investigated in the downward laser direction. The kerf width and penetration depth of the cement-based materials are quantitatively evaluated with the parameters in the surface and cross section of the specimens after the laser cutting. Moreover, the material removal zone of each specimen is compared in terms of the penetration shapes in the cross-sectional view. Based on experimental observations, the interaction mechanism between the laser and cement-based materials is proposed.
The vibration-reducing ability of construction materials is generally described by the damping ratio of the materials. Previously, many studies on the damping ratio of concrete have been done, such ...as the addition of rubber, polymer, fiber, and recycled aggregates in the concrete. However, the application of these materials in construction is limited due to their drawbacks. This paper investigated the effect of the replacement ratio and the size of the hollow glass microspheres (HGM), cenospheres (CS), and graphite flakes (GF) on the damping ratio of mortar. Furthermore, rubber particles (RP), aluminum powder (AP), and natural fiber (NF) were investigated to find if they have a combination effect with HGM. The half-power bandwidth method was conducted to obtain the damping ratio at 28 days of curing, and the compressive and flexural strength tests were also conducted to study the mechanical properties of mortar that contained HGM, CS, and GF. The results show that increases in the size of HGM and the replacement ratio of sand with HGM lead to an increase in the damping ratio. Moreover, RP and NF do not provide a combination effect with HGM on the damping ratio, whereas the application of AP results in a drastic compressive strength decrease even with an increase in damping ratio when incorporated with HGM. Besides, an increase in the replacement percentage of CS also leads to an improvement in the damping ratio, and a smaller size and higher replacement ratio of GFs can improve the damping ratio compared to other additives. As a result, CS and GF are more effective than HGM. 50% replacement ratio of CS slightly reduced the compressive strength by 6.4 MPa while improving the damping ratio by 15%, and 10% replacement ratio of samller GF can enhance the flexural strength by over 4.55% while increasing the damping ratio by 20.83%.
Cement-based materials are the most prevalent construction materials, and the conventional cutting techniques are still mostly used for fabricating the materials. However, these conventional cutting ...methods could generate undesirable micro-cracks and remove unintentional structural sections. This experimental study aims to evaluate the effects of the new fabricating method using laser on the microstructural characteristics of the cement-based materials. The experimental variables are laser cutting speed, water to cement ratio and material compositions. In order to compare the microstructure before and after the laser interaction, the microstructure of the cut surface is observed through scanning electron microscopy/energy dispersive X-Ray (SEM/EDX). After the laser interaction, the Material Removed Zone (MRZ) and Heat Affected Zone (HAZ) are observed on the cut surface. In MRZ, it is found that the glassy layer is thickened by an increasing amount of silicate-based materials in cement-based materials. In addition, it concluded that the amount of silicate-based material mixed in the cement-based materials affects the laser cutting quality.
This numerical study investigates the structural performance of railway sleepers made of ultra high-performance concrete (UHPC). First, numerical concrete sleepers are developed, and the tensile ...stress-strain relationship obtained from the direct tension test on the UHPC coupons is used for the tensile constitutive model after applying a fiber orientation reduction factor. The numerical sleeper models are validated with the experimental data in terms of the force and crack-width relationship. Second, using the developed models, a parametric study is performed to investigate the performance of the UHPC sleepers while considering various design/mechanical/geometrical parameters: steel fiber contents, size of the cross-section, and diameter and strength of prestressing (PS) tendons. The simulation results indicate that the size of the cross-section has the most impacts on the performance, while the effect of yielding strengths of PS tendons is minimal among all the parameters. Engineers need to pay attention to efficiency and an economical factor when using a larger cross-section, since sleepers with larger cross-sections can be an over-designed sleeper. This study suggests an economical design factor for engineers to evaluate what combination of parameters would be economical designs.
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