Concrete 3D printing is a novel construction method that can bring new horizons to the construction industry. However, there are still many challenges that limit its capabilities. Despite the huge ...research efforts, to date, there are still no standardized acceptance criteria and guidelines for the evaluation of printing concrete. Therefore, the main objective of this research was to develop 3D printing mixes with different aggregate-to-binder (a/b) ratios (1.2, 1.5, and 1.8) and evaluate it in terms of its fresh printing properties, which include the workability, extrudability, setting time, open time, and buildability. The compressive strengths of cast and printed specimens were also tested to determine the effect of the layering process. The workability was evaluated using commonly used devices in the construction industry (slump and flow table test) and was monitored over time along with the penetration test to indicate the structuration rate of concrete. From the experimental results and observations, the flow test resulted in the best indication of the structuration rate (thixotropy) of concrete, followed by the penetration and slump tests. The a/b ratio affected all the investigated properties of the printing concrete. Higher a/b ratios resulted in increased structuration rate, buildability, and compressive strength of cast specimens. However, for printed specimens, the compressive strength decreased with the increase in a/b ratio due to increased thixotropy. Therefore, from the results of the present investigation, it can be concluded that high a/b ratios (>1.5) are not desirable for printing concrete.
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•Effect of fiber addition on mechanical and durability characteristics of SCC was evaluated.•Effect of early wetting/drying cycles on FRSCC mechanical properties was investigated.•Microstructural ...analysis of FRSCC and correlation with macro-properties was conducted.•Low chloride permeability was achieved confirming adequate durability of FRSCC.
In this paper, an investigation of the mechanical properties and durability aspects of steel, synthetic, and hybrid fiber-reinforced self-compacting concrete exposed to early wet/dry cycles are presented and discussed. The experimental program consisted of two phases. Phase I involved tests on specimens for workability, mechanical properties, Rapid Chloride Penetration (RCP), and Scanning Electron Microscopy (SEM). The evaluation of mechanical properties included compressive, flexural and splitting tensile strengths, and modulus of elasticity. In Phase II, specimens were exposed to wet/dry cycles, and the effect of moisture on mechanical properties was investigated. All mixes in Phase I achieved a cube compressive strength of 70±5MPa. Furthermore, it was observed that exposure of Fiber-Reinforced Self-Compacting Concrete (FRSCC) to early wet/dry cycles improved the mechanical properties of all mixes; an increase in compressive strength of 10MPa compared to non-exposed specimens was observed. The microstructure of Synthetic Fiber-Reinforced Self-Compacting Concrete (SyFRSCC) and Steel Fiber-Reinforced Self-Compacting Concrete (SFRSCC) was different, which explains the difference in their respective crack-resistance mechanisms.
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In this paper, shear strength of fiber reinforced recycled concrete was investigated. A Self Consolidated Concrete (SCC) matrix with 100% coarse recycled aggregate and different types of fibers were ...used in the study. Steel (3D and 5D), synthetic and hybrid fibers with a volume fraction of 0.75% were added to the concrete matrix to prepare eight beams. In addition, two beams were cast without fibers as control specimens. All beams were prepared without shear reinforcement and were tested to evaluate concrete contribution to the shear capacity. In addition, optical images were captured to allow for full-field displacement measurements using Digital Image Correlation (DIC). The results showed about 23.44–64.48% improvement in the average concrete shear capacity for fiber-reinforced beams when compared to that of the control specimens. The percentage improvement was affected by fiber type and the steel fiber beams achieved the best performance. The addition of the fiber delayed the crack initiation and improved the post-cracking and ductile behavior of all beams. Moreover, the experimental results were compared to those predicted by codes and proposed equations found in the literature for concrete strength with and without fibers.
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This volume brings together state-of-the-art research on the development of infrastructure management, assessment, and rehabilitation techniques. It sheds light on pioneering work on innovative ...3D-printed concrete, novel methods for assessment of bridge decks, and advanced computer vision-based maintenance of civil infrastructure. The book is essential reading for infrastructure owners, engineers, and contractors, allowing them to gain insights into groundbreaking research that is paving the way toward sustainable and resilient infrastructure.
This article describes a technique to separate parts of cemented implant-supported restorations with a screw hole. A device was designed by using a computer-aided design (CAD) program and was milled ...in a milling center. The restoration was heated to 400 °C and then subjected to controlled mechanical force with the help of the device to separate the cemented parts.
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Concrete is a heterogeneous material that consists of cement, aggregates, and water as basic constituents. Several cementitious materials and additives are added with different volumetric ratios to ...improve the strength and durability requirements of concrete. Consequently, performance of concrete when exposed to elevated temperature is greatly affected by the concrete type. Moreover, post-fire properties of concrete are influenced by the constituents of each concrete type. Heating rate, days of curing, type of curing, cooling method, and constituents of the mix are some of the factors that impact the post-fire behavior of concrete structures. In this paper, an extensive review was conducted and focused on the effect of concrete constituents on the overall behavior of concrete when exposed to elevated temperature. It was evident that utilizing fibers can improve the tensile capacity of concrete after exposure to higher temperatures. However, there is an increased risk of spalling due to the induced internal stresses. In addition, supplementary cementitious materials such as metakaolin and silica fume enhanced concrete strength, the latter proving to be the most effective. In terms of the heating process, it was clear that several constituents, such as silica fume or fly ash, that decrease absorption affect overall workability, increase the compressive strength of concrete, and can yield an increase in the strength of concrete at 200 °C. Most of the concrete types show a moderate and steady decrease in the strength up until 400 °C. However, the decrease is more rapid until the concrete reaches 800 °C or 1000 °C at which it spalls or cannot take any applied load. This review highlighted the need for more research and codes’ provisions to account for different types of concrete constituents and advanced construction materials technology.
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This paper discusses the suitability of producing concrete with 100 % recycled aggregate to meet durability and strength requirements for different applications. Aggregate strength, gradation, ...absorption, specific gravity, shape and texture are some of the physical and mechanical characteristics that contribute to the strength and durability of concrete. In general, the quality of recycled aggregate depends on the loading and exposure conditions of the demolished structures. Therefore, the experimental program was focused on the evaluation of physical and mechanical properties of the recycled aggregate over a period of 6 months. In addition, concrete properties produced with fine and coarse recycled aggregate were evaluated. Several concrete mixes were prepared with 100 % recycled aggregates and the results were compared to that of a control mix. SEM was conducted to examine the microstructure of selected mixes. The results showed that concrete with acceptable strength and durability could be produced if high packing density is achieved.
In this paper, concrete mixes utilizing two sizes of natural aggregate and two sources of lightweight and recycled aggregates were used to investigate the effect of aggregate type and specimen size ...and shape on the compressive strength of concrete. In addition, samples from ready-mix concrete producers with different strengths were evaluated using standard size cylinders and cubes. Results were obtained on the 7th, 28th, and 90th day. In addition, flexural strength, split tension, and modulus of elasticity were evaluated on the 28th and 90th day. Statistical analyses were conducted to examine the significance of the difference between the compressive strength values for each two mixes using tests of hypotheses. Moreover, other mechanical properties as a function of compressive strength were discussed and compared to those predicated by the American Concrete Institute (ACI) specifications. Results indicate specimen shape has a noticeable effect on the compressive strength as the Cylinder/Cube ratio on the 90th day was ranging between 0.781 and 0.929. The concrete compressive strength and modulus of elasticity were significantly affected by the aggregate type. The flexural strength and split tensile strength were less affected by the aggregate type, which was also confirmed by the values predicted with the ACI equations.
The advancement of high-power microwave technology has indeed brought about the possibility of E-bombs, also known as electromagnetic pulse (EMP) bombs. These weapons emit an electromagnetic pulse ...that can disable electrical circuitry within a specific radius. As the frequency spectrum becomes more congested with various technologies operating in similar frequency bands, the need for shielding against interference becomes crucial. One promising solution is the use of conductive concrete, which is created by incorporating conductive components into a traditional concrete mixture. This conductive concrete has shown excellent shielding properties and improved electrical characteristics. To assess and quantify its effectiveness, the relative complex permittivity of the concrete mixture needs to be estimated. In this paper, the authors propose a method for estimating the relative complex permittivity of the concrete mixture. This was achieved by measuring the scattering parameters of concrete samples using a rectangular waveguide within the C-band frequency range. The scattering parameters provide valuable information about how electromagnetic waves interact with the concrete. A dielectric mixing model was developed to determine the relative complex permittivity. This model takes into account the volume percentage and the dielectric properties of the individual constituents present in the concrete mixture. By applying this model and obtaining the complex permittivity of the mixture, it becomes possible to calculate the required thickness of the conductive concrete mix needed to achieve the desired levels of electromagnetic attenuation and shielding.
The deterioration module (DM) is one of the four major modules necessary for any bridge management system (BMS). Environmental conditions, structural systems, bridge configuration, geographic ...location, and traffic data are some of the major factors that affect the development of deterioration modules. This emphasizes the need for the development of deterioration models that reflect the local conditions. In this article, some of the most important factors that could help in developing deterioration models in the Gulf Cooperation Council (GCC) were identified. The research was conducted in three phases; in the first phase, an extensive literature search was conducted to identify factors adopted in different deterioration models, and in phase two, the most relevant factors to the GCC environment were selected and these factors were further reduced based on input from local bridge experts. The result from the second phase is a list of factors identified by the experts. The identified list was utilized in phase three, which was focused on conducting a survey targeting bridge engineers to help identify the final selection and rank the factors according to their importance level. The results indicate that steel reinforcement protection, design load, chloride attack, type of defect, and age are the most important factors impacting bridge deterioration in the GCC. In addition, the time of rehabilitation; average daily truck traffic, ADTT; and average daily traffic, ADT, are the second most important factors. Factors with medium importance level are deck protection, services under the bridge, and inspection gap. The least important set of factors include temperature and wind load.
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