Hamed Hemmati Pourghashti, Malek Mohammad Ranjbar and Rahmat Madandoust
The purpose of this paper is to conduct a laboratory investigation on measuring the tensile strength of recycled concrete using a double punch test. Furthermore, one of the main…
Abstract
Purpose
The purpose of this paper is to conduct a laboratory investigation on measuring the tensile strength of recycled concrete using a double punch test. Furthermore, one of the main goals of this study is to compare the tensile and compressive strengths of recycled concrete samples.
Design/methodology/approach
Recycled concrete samples were made with variables such as aggregate type (natural stone and aggregate recycled concrete), different water-to-cement ratios and different treatment conditions in the first stage. In the next stage, the double punch test was performed on them, and finally the results obtained from experiments were analyzed and investigated.
Findings
According to the above tests, it was concluded that: first, according to the laboratory results, the strength of concrete containing recycled aggregates becomes closer to the strength of concrete containing natural aggregates whenever the water-to-cement ratio is higher. Second, upon investigating the treatment conditions, it was observed that the treatment had a greater effect on the strength of the recycled concrete. However, this effect was less tangible in tensile strength. Third, upon investigating the results of tensile strength, it can be said that the Barcelona test results were closer to the direct tensile test results compared to the Brazilian test results. This indicates the higher viability of Barcelona’s test results. Fourth, the results obtained from the Barcelona tensile test for recycled concrete were closer to the results of the direct tensile test compared to the concrete containing natural aggregates, which suggests that the Barcelona test is more suitable as a tensile test for recycled concrete. Fifth, the effects of various factors on tensile strength were somewhat less compared to the compressive strength, although very close. Sixth, the relationships provided by the regulation for concrete tensile strength on compressive strength were highly inconsistent with the results obtained from the direct tensile test, for which the consistency was higher for concrete containing natural aggregates compared to recycled concrete. Seventh, the dispersion of results obtained from tensile tests was higher for recycled concrete compared to concrete containing natural aggregates, but lesser of this dispersion was observed in the compressive strength.
Originality/value
According to the laboratory results, the strength of concrete containing recycled aggregates becomes closer to the strength of concrete containing natural aggregates whenever the water-to-cement ratio is higher. Upon investigating the treatment conditions, it was observed that the treatment had a greater effect on the strength of the recycled concrete. However, this effect was less tangible in tensile strength. On the basis on the results of the tensile strength, it can be said that the Barcelona test results were closer to the results of the direct tensile test compared to those of the Brazilian test. This indicates the higher viability of Barcelona’s test results. The results obtained from the Barcelona tensile test for recycled concrete were closer to the results of direct tensile test compared to the concrete containing natural aggregates, which suggests that the Barcelona test is more suitable as a tensile test for recycled concrete. The effects of various factors on tensile strength were somewhat less compared to the compressive strength, although very close. The relationships provided by the regulation for concrete tensile strength on compressive strength were highly inconsistent with the results obtained from the direct tensile test, for which the consistency was higher for concrete containing natural aggregate compared to recycled concrete. The dispersion of results obtained from tensile tests was higher for recycled concrete compared to concrete containing natural aggregate, but lesser of this dispersion was observed in the compressive strength.
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Mostafa Esmaeili, Hamed Hashemi Mehne and D.D. Ganji
This study aims to explore the idea of solving the problem of squeezing nanofluid flow between two parallel plates using a novel mathematical method.
Abstract
Purpose
This study aims to explore the idea of solving the problem of squeezing nanofluid flow between two parallel plates using a novel mathematical method.
Design/methodology/approach
The unsteady squeezing flow is a coupled fourth-order boundary value problem with flow velocity and temperature as the desired unknowns. In the first step, the conditions that guarantee the existence of a unique solution are obtained. Then following Green’s function-based approach, an iterative method for solving the problem is developed.
Findings
The accuracy of the method is examined by comparing the obtained results with existing numerical data, indicating excellent agreement between the two. In addition, the effects of nanoparticle shape and volume fraction on the flow and heat transfer characteristics are addressed. The results reveal that although the nanoparticle shape strongly affects the temperature distribution in the squeezing flow, it only has a slight impact on the velocity field. Furthermore, the highest and lowest Nusselt numbers belong to the platelets and spherical nanoparticles, respectively.
Originality/value
A semi-analytical method with computational support is developed for solving the unsteady squeezing flow problem. Moreover, the existence and uniqueness of the solution are discussed for the first time.
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Asal Neshatbini Tehrani, Hossein Farhadnejad, Amin Salehpour and Azita Hekmatdoost
This study aims to investigate the association of vitamin D intake and the risk of depression, anxiety and stress among Tehranian female adolescents.
Abstract
Purpose
This study aims to investigate the association of vitamin D intake and the risk of depression, anxiety and stress among Tehranian female adolescents.
Design/methodology/approach
This cross-sectional analysis included 263 participants. A valid and reliable food frequency questionnaire was used to determine dietary intake of vitamin D. Depression, anxiety and stress scores were characterized by Depression Anxiety Stress Score-21 questionnaire. Multivariable logistic regression was used to estimate the odds ratio (OR) for the occurrence of depression, anxiety and stress according to the tertiles of vitamin D intake.
Findings
The mean ± standard deviation age and body mass index (BMI) of participants were 16.2 ± 1.0 years and 22.2 ± 4.1 kg/m2, respectively. Mean score of depression, anxiety and stress of participants were 9.8 (low-grade depression), 8.4 (low-grade anxiety) and 14.0 (borderline for stress), respectively. In the final model, after adjustment for age, BMI, physical activity, mother/father’s education level, dietary fiber and total energy intake, the OR for depression in the highest compared to the lowest tertile of vitamin D intake was 0.53 (95% confidence interval [CI], 0.24–0.98) (p for trend: 0.040). Moreover, based on the fully adjusted model, participants in the highest tertile of vitamin D intake had lower odds of stress (OR: 0.49; 95% CI: 0.23–0.93), in comparison to those in the lowest one (p for trend: 0.021).
Originality/value
To the best of the authors’ knowledge, this is the first study to assess the association of vitamin D intake and risk of psychological disorders, including depression, stress and anxiety in Middle East and North Africa region’s female adolescents.