Search

Abstract The bond between prestressing strands and concrete within the dead-end zone of a post-tensioned concrete member significantly influences the effectiveness of the strand-concrete system. However, the existing code equations for determining development length rely on studies conducted on pretensioned concrete members rather than post-tensioned ones. As a result, the implementation of development length for prestressing strands with bulb-shaped dead end anchorage in post-tensioning slabs relies on common practice and former experience. Unfortunately, this can sometimes lead to concrete cracks or strand slippage at the dead end zone due to insufficient development length. This paper presents an experimental study on post-tensioning slab segments representing the dead end zone. The aim of this study is to assess the development length of prestressing strands with bulb-shaped dead end that shall guarantee full bond with concrete throughout the member’s service life. The Specimens were divided according to three different concrete compressive strengths 34 MPa, 48 MPa and 70 MPa. The parameters considered included slab thicknesses of 160 mm and 250 mm, as well as strand embedment lengths of 700 mm and 850 mm. Based on the test results, the sufficient development length was determined. Furthermore, a verification was carried out to assess the validity of applying predicted equations from an adopted bond model to determine the bond strength of strand with bulb-shaped dead end anchorage in concrete slabs.

Abstract Geopolymer concrete (GPC) has achieved a wide popularity since innovating it as an alternative to conventional concrete because of its superior mechanical characteristics and durability, in addition to being a green concrete due to its low negative impact on the environment. However, GPC still suffers from the problem of its poor workability which suppresses its spread in construction applications. This study investigated the most effective parameters on the workability of GPC including GGBFS content, water to binder ratio, and dosage of different types of chemical admixtures, Naphthalene-Based Admixture (NPA) and Polycarboxylate-Based Admixture (PCA), using Taguchi approach and Analysis of Variance (ANOVA) analysis considering the compressive strength at the different concrete ages. It was observed that NPA, in the geopolymer concrete, improved the compressive strength compared to PCA. The NPA-based mixes achieved the highest 28-day compressive strength, 69 MPa, with about 27.8% more than the highest 28-day compressive strength achieved by the PCA-based mixes, 54 MPa. The obtained results revealed that the NPA has achieved the best improvement for both the workability, in terms of initial slump value and slump loss rate, and the compressive strength of GPC mixes compared to PCA.

Abstract One-part alkali-activated materials (OP-AAM) have become a promising binder with low carbon and energy requirements associated with superior mechanical and durability characteristics. This study aims to employ commercial superplasticizers (naphthalene-based “Nb-SP” and polycarboxylate-based “PCb-SP”), as well as laboratory-prepared one (phenol–formaldehyde sulfanilate “PFS-SP”) in enhancing the properties of OP-AAM. The main problem of superplasticizers (SPs) in the AAM is their hydrolysis in the alkaline activator (NaOH) used in the activation reactions. Therefore, the thermo-chemical treatment process was utilized to mitigate the high activator alkalinity by impeding the NaOH in the aluminosilicate precursor matrix. The OP-AAM was fabricated from thermo-chemical treatment powder (TCT-P) resulting from sintering blast furnace slag (GGBFS) with 10 wt% NaOH at 300 and 500 °C. The XRD-pattern showed that NaOH was impeded in the GGBFS via sodium aluminum silicate phase formation after sintering at 500 °C. The results showed that the admixed OP-AAM prepared from TCT-P at 500 °C greatly enhanced the workability and mechanical properties. The PFS-SP proved its efficiency in improving the properties of OP-AAM prepared TCT-P at 300 and 500 °C, referring to its high stability in an alkaline medium. While PCb-SP reinforced the properties of OP-AAM prepared from TCT-P at 500 °C only, proving that PCb-SP promotes high capability in TCT-P-500 as well as in Portland cement.

Abstract Alkali-activated concrete (AAC) has attained great popularity since finding it as an alternative to Portland cement concrete due to its superior characteristics in terms of mechanical properties and durability, and its low negative environmental impact. This research investigated both experimentally and analytically the bond behavior between alkali-activated slag concrete (AASC) and steel rebars considering some important parameters (rebar diameter and development length-to-diameter ratio) before and after exposure to elevated temperature using beam-end bond testing technique. The obtained experimental results were compared with those obtained from applying the CEB-FIP model and the well-known available equations in the literature. A modified model was proposed for predicting the bond behavior of AASC. Results have showed that the CEB-FIP model provides more conservative values for bond strength compared to the experimentally obtained results which increases the safety level when estimating the bond strength for design purposes. The proposed modified model achieved a higher correlation with the experimental results than the CEB-FIP model at ambient temperature.

Abstract While several studies were conducted to investigate the current state of Open Educational Resources (OER) in several regions (e.g., Europe, America, Middle East and MENA), to the best of our knowledge, no study was conducted to cover the entire Arab region, specifically the twenty-two Arab countries. Therefore, to identify the OER gap in this region and then provide recommendations to facilitate OER adoption, this study investigates the current state of OER in the Arab region, specifically in twenty-two Arab countries. The obtained results showed that the OER progress is unbalanced within the Arab countries. Interestingly, several Arab countries are still lack behind when it comes to the application of OER in universities and schools. Finally, several recommendations are identified to several stakeholders, including policy makers and educators, to achieve social justice and facilitate the adoption and use of OER in the Arab region.

Abstract The number of disabled students is rapidly increasing worldwide, but many schools and universities have failed to keep up with their learning needs. Consequently, large numbers of disabled students are dropping out of school or university. Open Educational Resources (OER) and Open Educational Practices (OEP) contain several relevant features, including the possibility of reusing and remixing, which have led researchers to consider using OER and OEP to facilitate meeting the needs of disabled and functional-diverse students in order to increase their accessibility and e-inclusion capabilities in educational settings. The very limited research to date, however, has provided a limited holistic understanding of accessibility within OER and OEP in order to aid researchers in pursuing future directions in this field. Therefore, this paper systematically reviewed 31 papers to provide insights about functional diversity within OER and OEP. The results obtained highlighted that accessibility is still in its infancy within OER and that researchers should focus more on considering the four accessibility principles — perceivable, operable, understandable and robust — when providing OER. Additionally, while several researchers have focused on several issues related to accessibility within OER, limited focus has been given to assistive technologies using OER. Finally, this paper provides several recommendations to increase accessibility within OER and help design more accessible OER for students with functional diversity.

Urethral stricture management is a challenging surgery. Multiplicity of techniques means that none of them is ideal. No single technique is appropriate for all situations and the successful surgeon should have a store of operations to choose from according to each specific case. This review aims to provide an update on the different uses of buccal mucosal graft as a reconstructive and replacement tool for anterior urethral strictures management.

Aim: This study aims to compare the outcomes, morbidity and hospital stay in patients who underwent emergency surgery, and those who underwent percutaneous drainage for treatment of appendicular abscess. Patients and methods: From April 2013 to October 2014, we recruited 40 patients with appendicular abscesses for this study. These patients were randomized into two groups: group 1 (20 patients) for emergency surgery and group 2 (20 patients) for percutaneous drainage. Preoperative data, hospital stay, functional recovery and postoperative complications were analyzed. Results: Functional recovery was 2.2 ± 1 days in group 1 and 1 ± 0 day in group 2. Hospital stay in group 1 was 7.7 ± 3.5 days and in group 2 was 4 ± 1 days. Postoperative complications in group 1 were noted in 8 (40%) patients. No complications were recorded in group 2. Conclusions: Appendicular abscesses may be safely and effectively treated by US-guided percutaneous drainage with high technical and clinical success rates, low incidence of complications and shorter hospital stay.