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CONTENTS
Volume 11, Number 4, April 2021
 


Abstract
This study aims to trace the response of twelve one-way sustainable concrete hollow-core slabs made by reducing cement content and using replacement of coarse aggregate by plastic aggregate. The trial mixes comprise the 25, 50, 75, and 100% replacement of natural coarse aggregate. The compressive strength of the resulting lightweight concrete with full replacement of coarse aggregate by plastic aggregate was 28 MPa. These slabs are considered to have a reduced dead weight due to using lightweight aggregate and due to reducing cross-section through using voids. The samples are tested under two verticals line loads. Several parameters are varied in this study such as; nature of coarse aggregate (natural or recycled), slab line load location, the shape of the core, core diameter, flexural reinforcement ratio, and thickness of the slab. Strain gauges are used in the present study to measure the strain of steel in each slab. The test samples were fourteen one-way reinforced concrete slabs. The slab's dimensions are (1000 mm), (600 mm), (200 mm), (length, width, and thickness). The change in the shape of the core from circular to square and the use of (100 mm) side length led to reducing the weight by about (46%). The cracking and ultimate strength is reduced by about (5%-6%) respectively. With similar values of deflection. The mode of failure will remain flexural. It is recognized that when the thickness of the slab changed from (200 mm to 175 mm) the result shows a reduction in cracking and ultimate strength by about (6% and 7%) respectively.

Key Words
hollow core slabs; recycled aggregate; PVC plastic aggregate; reinforced concrete; experimental tests; steel reinforcement

Address
Adel A. Al-Azzawi: Department of Civil Engineering, Al-Nahrain University, Baghdad, Iraq
Mustafa S. Shallal: Department of Civil Engineering, Al-Nahrain University, Baghdad, Iraq

Abstract
This study focused on experimental evaluation of mechanical properties of pervious concrete mixtures with the aim of achieving higher values of strength while considering the associated costs. The effectiveness of key parameters, including cement content, water to cement ratio (W/C), aggregate to cement ratio (A/C), and sand replacement was statistically analyzed using paired-samples t-test, Taguchi method and one-way ANOVA. Taguchi analysis determined that in general, the role of W/C was more significant in increasing strength, both compressive and flexural, than cement content and A/C. It was found that increase in replacing percent of coarse aggregate with sand could undermine specimens to percolate water, though one-way ANOVA analysis determined statistically significant increases in values of strength of mixtures. Cost analysis revealed that higher strengths did not necessarily correspond to higher costs; in addition, increasing the cement content was not an appropriate scenario to optimize both strength and cost. In order to obtain the optimal values, response surface method (RSM) was carried out. RSM optimization helped to find out that W/C of 0.40, A/C of 4.0, cement content of about 330 kg/m3 and replacing about 12% of coarse aggregate with sand could result in the best values for strength and cost while maintaining adequate permeability.

Key Words
pervious concrete; taguchi analysis; t-test; ANOVA; cost analysis; Response Surface Method (RSM)

Address
Bahram M. Taheri: School of Civil Engineering, College of Engineering, University of Tehran, Iran
Amir M. Ramezanianpour: School of Civil Engineering, College of Engineering, University of Tehran, Iran

Abstract
The alkali-silica reaction (ASR) is a highly complex chemical reaction which causes damage to concrete and thus adversely affects the durability and service life. Significant damage can occur in concrete structures due to cracking because of the chemical reactions taking place. Various mineral and chemical additives have been used so far to mitigate ASR and/or to reduce its adverse effects. In this study, ground trachyte and rhyolite provided from Rize-Çağrankaya region, Turkey, were used to investigate their effectiveness in controlling ASR-induced damage by substituting them with cement at certain ratios. In this context, initially the possible use of trachyte and rhyolite as pozzolanas was determined in accordance with BS EN 450-1 and TS 25 standards by considering their pozzolanic activities and then their effectiveness in mitigating the ASR was evaluated as per ASTM C 1567-13. In experimental study, blends of trachyte and rhyolite were prepared by substituting them by cement at 25%, 35%, and 50% percentage. Totally 7 mixes were prepared and three samples of 25 mm mortar bars were prepared from each batch. The length changes of the mortar bars were determined at the end of 3, 7, 14 and 28 days of exposure. SEM, along with XRD analyses were performed to examine and elementally determine the ASR products that have been formed. The results obtained have shown that ground trachyte and rhyolite used in this study can be used as pozzolanas in concrete and they can also significantly mitigate ASR-induced damage as the substitution ratio increases.

Key Words
trachyte; rhyolite; alkali-silica reaction; pozzolanic properties; expansion

Address
Vahiddin Alperen Baki: Department of Architecture and Civil Engineering, University of Bath, Bath, United Kingdom
Safa Nay: Department of Civil Engineering, Karadeniz Technical University, 61080, Trabzon, Turkey
Şakir Erdoğdu: Department of Civil Engineering, Karadeniz Technical University, 61080, Trabzon, Turkey
İlker Ustabaş: Department of Civil Engineering, Recep Tayyip Erdoğan University, 61080, Rize, Turkey


Abstract
Activated hwangtoh (ACT) is a natural resource abundant in South Korea, approximately 15.0% of soil. It is an efficient mineral admixture that has activated pozzolanic properties through high-temperature heating and rapid cooling. The purpose of this study is to improve a curb mixture that can reduce NOx outside and investigate durability performance. To this end, mortar curb specimens were manufactured by replacing OPC with ACT. The ACT substitution ratios of 0.0, 10.0, and 25.0% were considered, and mechanical and durability tests on the curb specimens were conducted at 28 and 91 days of age. Steam curing was carried out for three days for the production of curbs, which was very effective to strength development at early ages. The reduction in strength at early ages could be compensated through this process, and no significant performance degradation was evaluated in the tests on chloride attack, carbonation, and freezing and thawing. The mortar curb with an ACT of 10.0~25.0% replacement ratio exhibited clear NOx reduction through photocatalytic (TiO2) treatment. This is due to the increase in physical absorption through surface absorption and the photocatalyst-containing TiO2 coating. In this study, the reasonable range of the ACT replacement ratio for NOx reduction was quantitatively evaluated through a comprehensive analysis of each test.

Key Words
Activated Hwangtoh (ACT); chloride attack; freezing and thawing; carbonation; curb; NOx reduction

Address
Hyeok-Jung Kim: Industry Academic Cooperation Foundation, Hankyong National University, 327 Jangang-ro, Anseong, 17579, South Korea
Jang-Hyun Park: Korea Institute of Future Convergence Technology, Hankyong National University, 327 Jangang-ro, Anseong, 17579, South Korea
Yong-Sik Yoon: Department of Civil and Environmental Engineering, Hannam University, 70 Hannam-ro, Daedeok-gu, Daejeon, 34430, South Korea
-Jun Kwon: Department of Civil and Environmental Engineering, Hannam University, 70 Hannam-ro, Daedeok-gu, Daejeon, 34430, South Korea

Abstract
In this article, an analytical solution of the dynamical behavior in an orthotropic non-homogeneity elastic material using for elastodynamics equations is investigated. The effects of the magnetic field, the initial stress, and the non-homogeneity on the radial displacement and the corresponding stresses in an orthotropic material are investigated. The analytical solution for the elastodynamic equations has solved regarding displacements. The variation of the stresses, the displacement, and the perturbation magnetic field have shown graphically. Comparisons are made with the previous results in the absence of the magnetic field, the initial stress, and the non-homogeneity. The present study has engineering applications in the fields of geophysical physics, structural elements, plasma physics, and the corresponding measurement techniques of magneto-elasticity.

Key Words
non-homogeneous; magnetic field; an orthotropic material; elastodynamics equations; dynamical behavior

Address
Ahmed Ramady: GRC Department, Faculty of Applied studies, King Abdulaziz University. Jeddah 21589, Saudi Arabia;Department of Mathematics, Faculty of Science, Beni-Suef University, Beni-Suef, Egypt
H.A. Atia: Mathematics Department, Arts - Rabigh& College of Sciences, King Abdulaziz University, Rabigh 25732, Saudi Arabia
S.R. Mahmoud: GRC Department, Faculty of Applied studies, King Abdulaziz University. Jeddah 21589, Saudi Arabia

Abstract
The main objective of this study is to characterize and evaluate the hydrophobic performance of polymer-based water-repellent coatings on cementitious mortar surfaces. Different concentrations of poly(vinyl acetate) (PVAc) and poly(1,4- butylene adipate) (PBA) were prepared in the laboratory and their applicability and performance was tested experimentally by water absorption test and analysis of surface contact angles of cementitious mortar specimens. According to the results of this study, it can be stated that incorporation of nano polymer particles on the surface of cementitious mortar specimens can enhance contact angles and reduce water absorption by increasing hydrophobicity. However, a dosage limit exists for polymer materials in coating, and observed hydrophobic improvements decreases when polymer dosage reached beyond the limit. Additionally, it is observed that water absorption of polymer coated cementitious mortars is closely related with the results of surface contact angle.

Key Words
concrete; cementitious mortar; hydrophobic; water contact angle; water absorption

Address
Irem Sanal: Department of Civil Engineering, Faculty of Engineering and Natural Sciences, Bahcesehir University, 34353, Besiktas, Istanbul, Turkey
Bestenur Yalcin: Department of Medical Laboratory Techniques, Vocational School of Health Services, Bahcesehir University, 34353, Besiktas, Istanbul, Turkey
Ibrahim Ertugrul Yalcin: Department of Civil Engineering, Faculty of Engineering and Natural Sciences, Bahcesehir University, 34353, Besiktas, Istanbul, Turkey
Lutfi Arda: Department of Mechatronics Engineering, Faculty of Engineering and Natural Sciences, Bahcesehir University, 34353, Besiktas, Istanbul, Turkey

Abstract
It is known from the literature that there are relatively few studies on the engineering properties of ultra-high performance concrete (UHPC) in early age. In fact, in order to ensure the safety of UHPC during construction and sufficient durability and long-term performance, it is necessary to explore the early behavior of UHPC. The test parameters (test control factors) investigated included the percentage of cement replaced by silica fume (SF), the percentage of cement replaced by ultrafine silica powder (SFP), the amount of steel fiber (volume percent), and the amount of polypropylene fiber (volume percentage). The engineering properties of UHPC in the fresh mixing stage and at the age of 7 days were investigated. These properties include freshly mixed properties (slump, slump flow, and unit weight) and hardened mechanical properties (compressive strength, elastic modulus, flexural strength, and splitting tensile strength). Moreover, the effects of the experimental factors on the performance of the tested UHPC were evaluated by range analysis and variance analysis. The experiment results showed that the compressive strength of the C8 mix at the age of 7 days was highest of 111.5 MPa, and the compressive strength of the C1 mix at the age of 28 days was the highest of 128.1 MPa. In addition, the 28-day compressive strength in each experimental group increased by 13%-34% compared to the 7-day compressive strength. In terms of hardened mechanical properties, the performance of each experimental group was superior to that of the control group (without fiber and without additional binder materials), with considerable improvement, and the experimental group did not produce explosive or brittle damage after the test. Further, the flexural test process found that all test specimens exhibited deflection-hardening behavior, resulting in continued to increase carrying capacity after the first crack.

Key Words
ultra-high performance concrete; mix design; early-age mechanical properties

Address
Chao-Wei Tang:Department of Civil Engineering & Geomatics, Cheng Shiu University No. 840, Chengching Rd., Niaosong District, Kaohsiung City, Taiwan R.O.C.;Center for Environmental Toxin and Emerging-Contaminant Research, Cheng Shiu University, No. 840, Chengching Rd., Niaosong District, Kaohsiung 83347, Taiwan;Super Micro Mass Research & Technology Center, Cheng Shiu University, No. 840, Chengching Rd., Niaosong District, Kaohsiung 83347, Taiwan

Abstract
To address the limitation of the commonly used steam curing of reactive powder concrete (SC-RPC) in engineering, a preparation technology of normal curing reactive powder concrete (NC-RPC) is proposed. In this study, an experimental comparative research on the mechanical properties of NC-RPC and SC-RPC under uniaxial tension is conducted. Under the premise of giving full play to the ultra-high performance of RPC, the paper tries to explore whether normal curing can replace steam curing. The results show that various mechanical indexes of NC-RPC (e.g., tensile strength, ultimate tensile strain, elastic modulus and deformation performance) could basically reach the mechanical index values in steam curing at 28d age, some performance is even better at a longer age. So it affirms the feasibility of normal curing. In this paper, the influence of normal curing age on the tensile properties of RPC is discussed, and the relationship between each index and age is introduced in detail. Based on the experimental data, the tensile mechanism of RPC is analyzed theoretically, and two kinds of tensile constitutive models for RPC are proposed, one is curvilinear model, and another one is polygonal line model. The validity of the two models is further verified by the test results of others.

Key Words
reactive powder concrete RPC; normal curing; axial tensile test; stress-strain curve; curing age; tensile strength; ultimate tensile strain; elastic modulus; axial tensile toughness ratio

Address
Min Guo: School of Civil Engineering, Beijing Jiaotong University, 3 Shangyuan Village, Haidian District, Beijing 100044, China
Ri Gao: School of Civil Engineering, Beijing Jiaotong University, 3 Shangyuan Village, Haidian District, Beijing 100044, China


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