Search

The aim of this study is to improve the mechanical and dimensional stability properties of 3D printable concrete by using fibers. Ten mixtures containing polypropylene fiber in three different lengths (3, 6, and 12 mm) and ratios (0.2%, 0.4%, and 0.6%) were prepared. Rheological properties, compressive strength, three‐point flexural strength, and drying‐shrinkage performance of 3D printable concrete mixtures were examined in this study. Strength properties were determined by perpendicular and lateral loading. Thixotropic properties of the mixtures were determined using three different approaches (structural build‐up development, hysteresis area and dynamic structural build‐up). The dynamic yield stress value increased with fiber addition up to 0.4% of the total volume. It was determined that this value decreases with the use of fiber above this rate. In terms of mechanical and dimensional stability properties of 3D printable concrete, the optimum fiber length and utilization ratio were 6 mm and 0.4%, respectively. This parameters were adversely affected when fiber utilization ratio was 0.6% and length was 12 mm. Also, there is a strong correlation between structural build‐up development and dynamic structural build‐up. [ABSTRACT FROM AUTHOR]

With the use of photocatalytic materials, it was understood that self-cleaning and anti-bacterial properties are gained in cementitious systems and indoor air quality is improved. It was determined that Nano-TiO2 (nT) is used as the most common photocatalyst due to its advantages. Anatase phase, which is one of the phases of nT, was found to be the most preferred photocatalyst because it has a faster photocatalytic effect. In this study, a detailed literature search was conducted on the photocatalysis process, the photocatalyst selection criteria, the materials used in the production of photocatalytic concrete and their mix design. In addition, the effects of the use of nT on the setting time, flow performance, rheological behavior, degree of hydration, pore structure and strength performance of cementitious systems were investigated. It was determined that nT is used at rates ranging from 1-10% for the production of photocatalytic concrete. It was observed that the hydration rate of cementitious systems increases with the increase in the use of nT, and the flow performance and rheological behavior are adversely affected. Also, it was emphasized that the use of nT improves the mechanical properties by reducing the void volume of the system. However, it was reported that the use of nT above a certain rate causes the strength performance of cementitious systems to be adversely affected. [ABSTRACT FROM AUTHOR]

In today's environment, where energy is desired to be used more efficiently, it has been understood that the interest in the use of lightweight concrete with superior performance in terms of thermal insulation properties has increased. On the other hand, it has been stated that construction waste increases rapidly, especially after severe earthquakes. In this context, encouraging the use of recycled concrete waste and efficient disposal of construction and demolition waste is of great importance for the European Green Deal. It is also known that pollutants such as COx and NOx stick to facades over time, causing environmental pollution and visual deterioration. It has been reported that materials with photocatalytic properties are used in lightweight concrete facade elements to prevent such problems. This study examines the effect of using recycled concrete aggregates on the thermal properties of self-cleaning lightweight concrete mixtures (SCLWC). For this purpose, an SCLWC containing 1% TiO2 and 100% pumice aggregate was prepared. By replacing pumice aggregate with recycled concrete aggregate at the rates of 15%, 25%, 35%, 45% and 50%, four different SCLWCs with self-cleaning properties were produced. High-temperature resistance, thermal conductivity performance, microstructure analysis and photocatalytic properties of the produced mixtures were examined. It has been understood that the unit volume weight loss of SCLWC mixtures exposed to high temperatures generally decreases due to the increase in the recycled concrete-aggregate substitution rate. However, it was determined that the loss of compressive strength increased with the increase in the amount of recycled concrete-aggregate replacement. Additionally, it was determined that the thermal-conductivity coefficient values of the mixtures decreased with the use of pumice. After SCLWC mixtures were exposed to 900 °C, small round-shaped crystals formed instead of C–S–H crystals. [ABSTRACT FROM AUTHOR]

In this study, a procedure for mixture design was proposed with the aim of meeting the requirements of extrudability, buildability, and shape stability in 3D printable concrete. Optimum water/binder ratio, sand/binder ratio, binder type, utilization ratio, aggregate particle distribution and quantity, and type and utilization ratio of chemical admixtures were determined for 3D printable concrete in terms of print quality and shape stability criteria. A total of 32 different mixtures were produced. It was determined that mixtures produced using a binder content with approximately 40% fly ash, a w/b ratio of 0.35, and aggregates with Dmax of 1 mm exhibit acceptable characteristics. Investigations were also conducted into the thixotropic behavior, rheological characteristics, and mechanical properties of the mixes that were deemed acceptable. As a result, it was determined that the increase in the amount of fly ash usage positively affected the buildability of the printed layers. Additionally, the dynamic yield stress ranging from 114 to 204 Pa, viscosity ranging from 22 to 43 Pa.s, and structural build-up value ranges suitable for the production of 3D printable concrete mixtures were determined. [ABSTRACT FROM AUTHOR]

In this study, photocatalysis technology was used to reduce water pollution. Decolorization of Reactive Black 5 using nano-TiO2 (NT) as a photocatalyst was investigated by adsorption and degradation experiments. Effects of NT particle size and utilization ratio on the time-dependent flow performance, compressive-flexural strength, and Bohme abrasion resistance of cementitious systems were investigated. In addition to the NT-free control mixture, a total of six photocatalytic self-cleaning mortar mixtures (PSCM) were prepared using NT in two different particle sizes (28 and 38 nm) and three different ratios (0.5%, 1%, and 1.5%). The PSCM sample containing 38 nm NT exhibited superior performance in terms of photocatalytic properties compared to the 28 nm state. It was observed that the flow performance of PSCM mixtures with NT substitution is adversely affected regardless of the NT type. Mixtures containing NT with a lower particle size (28 nm) had higher compressive and flexural strengths. [ABSTRACT FROM AUTHOR]

The biggest obstacle to become widespread 3D Printing Concrete (3DPC) is the insufficient interlayer-bonding strength (IBS). The parameters affecting the IBS are classified as physical effects such as cleanliness and roughness, effects caused by the material properties it contains, and printer-induced effects for instance interlayer interval time, nozzle shape and printing speed. However, it was stated that the rheological properties of 3DPC mixtures should also be examined in order to strengthen the IBS. In this article, the relationship between IBS and rheological properties of 3DPC mixtures is discussed. It was stated that the static yield stress and the structural build-up have an optimum value in terms of the effect on IBS of 3DPC mixtures. On the other hand, studies indicating that the IBS of 3DPC mixtures depends on surface moisture of the layers were also encountered. [ABSTRACT FROM AUTHOR]

It is known that 3D printable concrete mixtures can be costly because they contain high dosages of binder and that the drying-shrinkage performance may be adversely affected. Mineral additives and fibers are generally used to control these negative aspects. In this study, the use of silica fume, a natural viscosity modifying admixture, was investigated to improve the rheological and thixotropic behavior of 3D printable concrete mixtures reinforced with polypropylene fiber (FR-3DPC). The effect of increasing the silica fume utilization ratio in FR-3DPC on the compressive strength (CS), flexural strength (FS), and drying-shrinkage (DS) performance of the mixtures was also examined. A total of five FR-3DPC mixtures were produced using silica fume at the rate of 3, 6, 9, and 12% of the cement weight, in addition to the control mixture without silica fume. As a result of the tests, the dynamic yield stress value decreased with the addition of 3% silica fume to the control mixture. However, it was found that the dynamic yield stress and apparent viscosity values of the mixtures increased with the addition of 6, 9, and 12% silica fume. With the increase in the use of silica fume, the CS values of the mixtures were generally affected positively, while the FS and DS behavior were affected negatively. [ABSTRACT FROM AUTHOR]

Some properties of 3D Printing Concrete Mixtures (3DPC) need to be developed in order to make them widespread in the construction industry. The amount of cement used to provide extrudability in 3DPC mixtures is quite high compared to conventional concrete mixtures. This situation negatively affects the sustainability of 3DPC mixtures as it is not ecological and economical. In this article, the development, advantages and production process of 3DPC mixtures from past to present are mentioned. In addition, the use of mineral additives such as fly ash, silica fume, blast furnace slag and other waste materials instead of cement for the production of sustainable 3DPC mixtures was investigated. Also, the possibilities of using other aggregates such as recycled concrete aggregate and desert sand in 3DPC mixtures were investigated. Within the scope of the study, the rheological properties of 3DPC mixtures were examined. In addition, the interlayer adhesion properties, which is another obstacle to the widespread use of 3DPC mixtures and the parameters affecting the interlayer adherence were investigated. [ABSTRACT FROM AUTHOR]