Analysis of Dowel Action in Reinforced Concrete Beams with Shear Reinforcement

The shear transfer mechanism was examined to view the contributions of different components of shear transfer such as aggregate interlocking, dowel force and uncracked compression zone. Understanding the role of various shear transfer components with transverse reinforcement provided was complex due to traditional difficulties involved in detail assessment of accompanying kinematics during the failure. In the present paper, the issue was addressed by employing sixteen specimens and grouped under two categories representing conventional beams and beams with preformed cracks and were tested under four - point bending load with a shear span to depth ratio of 1.26 by increasing the characteristic strength of concrete. From the results obtained, empirical formulas proposed were also evaluated and it was concluded that the results were consistent and contribution of shear transfer across uncracked compression zone was maximum in shear resistance with transverse reinforcement provided. Later structural behaviour was also assessed and it was concluded that beams with preformed cracks had exhibited greater stiffness thus nullifying the effect of aggregate interlocking in shear transfer.

Experimental Evaluation on Components of Shear resistance of Reinforced Concrete Beams with Shear Reinforcement Provided

The contribution of aggregate interlocking and dowel force in shear strength of reinforced concrete beams was topic of research for many years. The precise forecasts of shear behavior were challenging to determine due to complication involved. The existing theories had focused on aggregate interlocking force and shear resistance arising due to concrete compression zone, neglecting the contribution of dowel force despite considering as significant constituent in shear transfer mechanism. The present investigation focuses on cogitating all components in shear transfer mechanism by providing shear reinforcement and keeping clear cover and effective span to depth ratio constant. Sixteen specimens were considered for parametric study by employing suitable variables such as increase in strength of concrete and variation in flexural reinforcement. Eight specimens were conventional beams and the remaining eight specimens were provided with preformed cracks. Moment vs. displacement curvature and strain vs. moment curvature were plotted to evaluate shear at uncracked compression zone and accordingly aggregate interlocking force and dowel force were determined based on the empirical formulas proposed. From the result it was confirmed that contribution of aggregate interlocking force and dowel force were insignificant and shear resistance due to uncracked compression zone is the sole contributor in shear transfer mechanism. Structural behavior of concrete beams was also studied and it was confirmed that beams with preformed cracks exhibited better structural behavior when related to conventional beams.

The Suitability of Bailey Method for Design of Local Asphalt Concrete Mixture

The study investigated the behaviour of asphalt concrete mixes for aggregate gradations, according to the Iraqi specification using the Bailey method designed by an Excel spreadsheet. In mixing aggregates with varying gradations (coarse and fine aggregate), The Bailey method is a systematic methodology that offers aggregate interlocking as the backbone of the framework and a controlled gradation to complete the blends. Six types of gradation are used according to the bailey method considered in this study. Two-course prepared Asphalt Concrete Wearing and Asphalt Concrete binder, the Nominal Maximum Aggregate Sizes (NMAS) of the mixtures are 19 and 12.5 mm, respectively. The total number of specimens was 240 for both layers (15 samples) for each Chosen Unit Weight (CUW). The Marshall Test results show the increase in stability and decrease in flow and bulk density when the rise in CUW for both courses. In volumetric properties, VMA increases when the increase in CUW. When an increase in CUW air void increases gradually. The permanent deformation for the coarse aggregate (95, 100, 105% CUW) has more resistances than the fine aggregate (80, 85, 90%) wearing and binder coarse. The CUW (105%) blend of wearing, and binder course has a high value of stability and resistance to permanent deformation (11.9, 11.1 kN). The CUW above mentioned is considered a good design aggregate structure and produces improvement to the Marshall properties, leading to better performance for pavement roads and higher resistance to distresses. Doi: 10.28991/cej-2021-03091693 Full Text: PDF

Fluorine-induced aggregate-interlocking for color-tunable organic afterglow with a simultaneously improved efficiency and lifetime

Through the fluorine-induced aggregate-interlocking (FIAI) strategy, the designed afterglow materials showed both improved quantum yields and prolonged lifetimes by breaking through the intrinsic bottlenecks of organic afterglow.

Mechanical Testing and Modeling of Interlayer Bonding in HMA Pavements

After premature de-bonding failures of several roads in Germany, researchers at the Technische Universität Dresden developed a new testing device, the Dresden Dynamic Shear Tester (DDST), for quality control and characterization of the interlayer bond. The DDST is used to quantify the shear stiffness of the interlayer bond between asphalt layers at different temperatures, stress levels, and frequencies. The DDST was designed to avoid some limitations of common interlayer bond static tests (i.e., Leutner tests, torque bond tests, etc.) by simulating the dynamic loads experienced by real pavements and determining material parameters which can be used within mechanistic models. The paper presents the philosophy and methodology behind the DDST as well as the post-processing of the test data to obtain a master curve of shear stiffness of the interlayer bond. The master curve is determined by back-calculation of testing data by coupling a Fourier assisted finite element method with an optimization algorithm. The results of experiments showed that the shear stiffness at the interlayer zone was strongly influenced by the temperature, frequency, and normal load. At high temperatures the adhesion of the tack coat did not contribute to the layer bond. It was deduced that at high temperature and with no axial load shear stiffness was achieved only through aggregate interlocking and, when normal pressure was applied, through friction between the surfaces of the asphalt layers.