Browsing by Author "Ashour, Ashraf"

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Exploring the Flowability, Physical, and Mechanical Properties of Eco-Friendly Colored Cement Mortars With Metakaolin Under Sulfuric (H 2 So 4 ) and Nitric Acid (Hno 3 ) Attacks
(Elsevier, 2024) Akbulut, Zehra Funda; Guler, Soner; Osmanoglu, Faruk; Kivanc, Mehmet Riza; Ashour, Ashraf
This article aims to investigate the flowability, physical, mechanical, and durability properties of metakaolin (MK) -added colored cement mortars exposed to the effects of H 2 SO 4 sulfuric acid (SA) and HNO 3 nitric acid (NA). MK was used in 20 % replacement with cement, and yellow (YP) and red pigments (RP) were added to the mixtures at 1 % and 3 % of the cement by weight. According to the results, although MK reduced the workability and, therefore, the flow diameter (FD) of mortars, thanks to the void -filling feature of MK, filling the voids in the microstructure caused the samples ' apparent porosity (AP) and relative dynamic modulus of elasticity (RDME) to decrease. Additionally, MK significantly improved the residual compressive (RCS) and residual flexural strengths (RFS) of the samples thanks to the calcium -silicate -hydrate ( C - S - H) bonds it formed in the interior structure, owing to its high pozzolanic efficiency. Moreover, this improvement of MK is more remarkable in samples that remain subject to SA and NA attacks for more time. Furthermore, while YP reduces the workability of mortars and, therefore, the FD value due to its needle -tipped grain structure, RP increases the FD value of the mortars with its spherical grain structure. However, YP and RP contributed to reducing the AP of the samples and increasing RCS and RFS capacities at a meager rate by showing a micro -filling effect. In addition, there were significant increases in the total color changes ( Delta E) of YP and RP -added colored mortar samples, especially after longer SA and NA attacks.
Nonlinear Structural Performance of a Historical Brick Masonry Inverted Dome
(Taylor & Francis inc, 2020) Ozturk, Sehabettin; Bayraktar, Alemdar; Hokelekli, Emin; Ashour, Ashraf
Traditional domes are obtained by double curvature shells, which can be rotationally formed by any curved geometrical plane figure rotating about a central vertical axis. They are self-supported and stabilized by the force of gravity acting on their weight to hold them in compression. However, the behavior of inverted domes is different since the dome is downward and masonry inverted domes and their structural behaviors in the literature received limited attention. This article presents a nonlinear finite element analysis of historical brick masonry inverted domes under static and seismic loads. The brick masonry inverted dome in the tomb of scholar Ahmed-El Cezeri, town of Cizre, Turkey, constructed in 1508 is selected as an application. First, a detailed literature review on the masonry domes is given and the selected inverted dome is described briefly. 3D solid and continuum finite element models of the inverted masonry dome are obtained from the surveys. An isotropic Concrete Damage Plasticity (CDP) material model adjusted to masonry structures with the same tensile strength assumed along the parallel and meridian directions of the inverted dome is considered. The nonlinear static analyses and a parametric study by changing the mechanical properties of the brick unit of the inverted masonry dome are performed under gravity loads. The acceleration records of vertical and horizontal components of May 1, 2003 Bingol earthquake (Mw = 6.4), Turkey, occurred near the region, are chosen for the nonlinear seismic analyses. Nonlinear step by step seismic analyses of the inverted dome are implemented under the vertical and horizontal components of the earthquake, separately. Static modal and seismic responses of the inverted masonry dome are evaluated using mode shapes, minimum and maximum principal strains and stresses, and damage propagations.
Review of Current Design Guidelines for Circular Frp-Wrapped Plain Concrete Cylinders
(Asce-amer Soc Civil Engineers, 2016) Guler, Soner; Ashour, Ashraf
With the widespread use of fiber-reinforced polymer (FRP) composites in the construction sector as a strengthening technique, the development of design guidelines for the field application of externally bonded FRP systems is ongoing in Europe, Japan, Canada, and the United States. The main goal of this study is to evaluate the current seven international design guidelines and four other design models for the prediction of confined concrete compressive strength of FRP-wrapped plain concrete cylinders against the experimental results of a large database of 812 specimens reported in the literature. The results clearly show that the reliability of predictions of confined concrete compressive strength of FRP-wrapped plain concrete cylinders by the design guidelines significantly varies for different ranges of unconfined concrete compressive strength. For example, the gain in confined concrete compressive strength of FRP-wrapped low- and medium-strength concrete cylinders is larger than that of high- and ultrahigh-strength concrete cylinders. Furthermore, a simplified model for the prediction of design/characteristic-confined concrete compressive strength is developed based on the design-assisted-by-testing approach. The developed simplified model accounts for the variation in confinement effectiveness for different ranges of unconfined concrete strengths.
Strength Prediction Models for Steel, Synthetic, and Hybrid Fiber Reinforced Concretes
(Ernst & Sohn, 2019) Guler, Soner; Yavuz, Demet; Korkut, Fuat; Ashour, Ashraf
This paper proposes new strength models to predict compressive, splitting tensile and flexural strengths of steel, synthetic and hybrid fiber reinforced concretes. The strength models depending on fiber reinforcing index, concrete compressive strength, and fiber volume fraction have been developed by multiple regression analyses of the experimental results obtained from a comprehensive experimental program. Twenty-five concrete batches, one control and 24 fiber reinforced concrete with target compressive strength of 40MPa were produced. Steel and synthetic fibers, namely hooked-end steel (HF) and polyamide (PA) synthetic fibers of total volume of 0.25, 0.5, and 0.75% were added in single and hybrid forms to concrete mixes. Moreover, the predictions of the proposed strength models have been compared with the existing strength models in the literature. The test results clearly showed that the predictions of the proposed strength models are more accurate than the existing strength models for compressive, splitting tensile and flexural strengths of all the fiber types. Although the existing strength models may be applicable to the prediction of compressive strength of steel, synthetic, hybrid fiber reinforced concrete (FRC), they may not be safely used for splitting tensile and flexural strength of steel, synthetic and hybrid FRC.