Search

The use of recycled concrete aggregates in structural concrete is a sustainable solution to reduce the extraction of natural resources and the detrimental impacts of waste concrete to the environment. The present study aimed to assess the compressive and flexural behaviour of recycled aggregate concrete (RAC) and normal concrete (NC) modified with silica fume and steel fibres or polypropylene fibres (PPFs). The coupling effects of the silica fume and fibres on the compressive strength, fracture toughness, modulus of elasticity, and failure mode of the RAC and NC were analysed following a series of axial compression and three-point bending tests. The results show that the thick steel fibre exhibited worse interfacial bonding with the cement paste than the PPF, but the addition of silica fume enhanced these interfacial bonds, resulting in an improvement in the compressive and flexural behaviour of the fibre-reinforced RAC. Additionally, the coupling effect of silica fume and steel fibre was better than that of the silica fume and PPF. Based on the synthetical consideration of the performance improvement and economic cost, 10% silica fume content by the equal quantity substitution of cement is optimal for the compressive and flexural strength of steel-fibre reinforced RAC. [ABSTRACT FROM AUTHOR]

This experimental and analytical investigation is conducted to develop a sustainable recycled concrete by incorporating ceramic waste as coarse aggregate. In order to achieve the designed goal, conventional aggregate is replaced by different amounts of ceramic waste aggregate. Fresh and hardened properties of conventional as well as ceramic waste aggregate concrete are assessed. Environmental impacts are also considered in terms of CO 2 footprints and consumption of volume of raw materials by concrete. Interfacial model is proposed at micro level to evaluate the behavior of ceramic waste and conventional aggregate with hydrated cement paste. Finally, sustainable concrete is selected which has the best performance with respect to compressive strength and environmental impacts. It is concluded that 30% partial replacement of ceramic waste aggregate with conventional aggregate provides the highest compressive strength, less environmental impacts and is selected as sustainable concrete, which is also verified by analytical hierarchy process (AHP) and technique for order preference by similarity to ideal solution (TOPSIS) [ABSTRACT FROM AUTHOR]

Recycled concrete aggregates (RCAs) have inferior qualities compared with natural aggregates, mainly attributed to the porous nature of the attached cement mortar. To improve the quality of the RCAs, an environmentally friendly and cost-effective method is proposed to treat RCAs in this study. In this method, RCAs are first soaked in acetic acid solution, in which the acetic acid reacts with cement hydration products attached to the surface of the RCAs. This reaction weakens the attached mortar, making it possible to remove it from the RCAs by mechanical rubbing later. The treated RCAs have lower water absorption and less cement mortar attached. Once used as aggregates in new concrete, these RCAs can enhance the compressive strength of the concrete at 28 days up to 25%. It is safe and clean to apply this new method since no dangerous chemical is used and no detrimental chemicals are introduced into the treated RCAs. More importantly, zero hazardous waste solution is generated since the waste solution of the treatment can be used to produce high value-added products, permanently store CO 2 , and regenerate acetic acid. As an example, the waste solution of the treatment was used as admixture for new concrete, which improved the strength of the concrete by 14%. [ABSTRACT FROM AUTHOR]

The Common Data Element (CDE) Project was initiated in 2006 by the National Institute of Neurological Disorders and Stroke (NINDS) to develop standards for performing funded neuroscience-related clinical research. CDEs are intended to standardize aspects of data collection; decrease study start-up time; and provide more complete, comprehensive, and equivalent data across studies within a particular disease area. Therefore, CDEs will simplify data sharing and data aggregation across NINDS-funded clinical research, and where appropriate, facilitate the development of evidenced-based guidelines and recommendations. Epilepsy-specific CDEs were established in nine content areas: (1) Antiepileptic Drugs (AEDs) and Other Antiepileptic Therapies (AETs), (2) Comorbidities, (3) Electrophysiology, (4) Imaging, (5) Neurological Exam, (6) Neuropsychology, (7) Quality of Life, (8) Seizures and Syndromes, and (9) Surgery and Pathology. CDEs were developed as a dynamic resource that will accommodate recommendations based on investigator use, new technologies, and research findings documenting emerging critical disease characteristics. The epilepsy-specific CDE initiative can be viewed as part of the larger international movement toward 'harmonization' of clinical disease characterization and outcome assessment designed to promote communication and research efforts in epilepsy. It will also provide valuable guidance for CDE improvement during further development, refinement, and implementation. This article describes the NINDS CDE Initiative, the process used in developing Epilepsy CDEs, and the benefits of CDEs for the clinical investigator and NINDS. [ABSTRACT FROM AUTHOR]

Alkali-silica reaction (ASR) is a chemical reaction that cause to cracking and led to deterioration of concrete in a short time because of led to huge expansion in the concrete. The increase of temperature, humidity and pressure increases these reactions. In this study, the alkali silica reaction (ASR) development was investigated in silica fume blended mortars produced with different aggregates. In the production of mortars, natural sand, crushed sand, waste concrete sand and waste marble sand were used. Silica fume was replaced with cement in ratio of 0%, 10%, 20%, 30% and 40% by weight in the in the mixtures. ASR test was conducted according to ASTM C 1260 standards. Mortar bars (25×25×285 mm) have been exposed to high alkali environment and high temperatures for 14 days. Then, the influence of aggregate type and silica fume was determined on the effect of ASR by measuring the length change of mortar bars. According to the results obtained, the maximum expansion was seen in mortars with the natural sand, and the minimum expansion was observed in mortars produced with limestone aggregate origin. On the other hand, by use of silica fume in ratio of 10%-30%, it was observed that expansion of all the mortars was significantly decreased. [ABSTRACT FROM AUTHOR]

The sol–gel method was applied to synthesise xerogels of C2AS and C2S at ambient temperature. Then they were thermally treated at 600, 900, 1100 and 1250°C and the crystallisation of C2S and C2AS was characterised using X-ray diffraction (XRD). The evolution of the heat of hydration of these samples was investigated at 70°C using a conduction calorimeter. The microstructure of the samples, separately cured under hydrothermal conditions (7 days at 70°C), has been examined by means of SEM. Calorimetric measurements of hydration heat evolution showed that C2AS and C2S, synthesised via sol–gel method are much more active during hydration than their related clinker minerals synthesised by the conventional method. Furthermore, hydration activity of samples depends chiefly on calcination temperature. While C2S calcined at 900°C has the most intense hydration rate, C2AS has the same aspect when calcined at 1100°C. The hydration products of C2S, heat treated at 600°C, are well crystallised as characterised by XRD analysis. Large gehlenite hydrate crystals were observed to form during the hydration C2AS prepared via sol–gel processing. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an experimental investigation for the mechanical behavior of confined concrete specimens made with different types of coarse aggregates and subjected to concentric loads. The response of the specimens varies with the variation in the properties of the aggregates. The effect of different levels of transverse reinforcement ratio on the behavior of the studied types of concrete is investigated and the results are analyzed and presented in the study. The study included forty-eight cylindrical specimens of 100 mm diameter and 650 mm height. The results of the study show considerable effect for the type of the used aggregate on the mechanical behavior of the specimens. The effect of changing the spacing of the stirrups and the configuration of the stirrup closure are also investigated and analyzed in the paper. [Copyright &y& Elsevier]

Experimental studies were conducted to investigate the application of fracture tough overlay welds for the upgrading of welded steel moment connections. The experimental program consisted of cyclic tests on three exterior connection specimens that were initially fabricated using pre-Northridge welding procedures. Two specimens were fabricated from small size sections and one was fabricated from an intermediate size section. Overlay welds were placed using self-shielded flux core arc weld (FCAW-ss) with a fracture tough electrode (E70T-8). The application of weld overlays to the small size specimens resulted in a significant improvement in their cyclic performance. The plastic rotation capacity of both specimens was either close to or exceeded 3%. The application of weld overlays to the moment connection of the intermediate size specimen also improved the rotation capacity. However, the upgraded specimen failed in the parent material of the beam flange, away from the weld region at a plastic rotation of 2.7%. [ABSTRACT FROM AUTHOR]