Effect of Low Mixing Speed on the Properties of Prolonged Mixed Concrete

The mixing process of concrete consists of dispersing the constituent ingredients (i.e. cement, admixtures, sand, and gravel) in water to homogeneous and solid product. The properties of the final product depend on mixing parameters such as mixing time and mixing speed. Ready Mixed Concrete (RMC) should be mixed for a long time with limited speed until delivered to the working site. This long time depends on long transport distances and traffic conditions. The present study investigated the effects of long mixing time on the properties of concrete without any change in its proportions during the mixing process and the effects of using the chemical admixtures: super plasticizers and retarders on its effectiveness, using a drum batch mixer. It has two directions of rotation: one for mixing concrete and the other for discharging it. This research identified concrete mixtures with local available materials i.e. cement, sand as fine aggregates, dolomite as coarse aggregates, water and chemical admixtures. Mixtures were prepared with the same cement and water content with constant sand to dolomite ratio with different dosages of chemical admixtures. Chemical admixtures were used to keep concrete flow during mixing. Mixtures were prepared with low mixing speed 1rpm for identified long mixing times more than 90 minutes from adding water to other components Slump and compressive tests were used as measurement tools of fresh and hardened concrete Retempering with extra water or chemical admixtures was prevented through mixing, so mixtures were extracted without target slump value. Findings showed that low mixing speeds made mixtures more effective for long times, the exceeding mixing time led to minimize water to cement ratio due to reduction of water content, and there was an inverse relationship between slump flow and compressive strength in case of no re-tempering. Therefore, slump flow of mixtures decreased by time, but on the other hand, compressive strength enhanced i.e. stiffening took place. The present study proved that the properties of the final product depends on mixing parameters such as mixing time and mixing speed, and that Ready Mixed Concrete (RMC) would be more effective if mixed for a long time with limited speed until transported to the work site. In addition, chemical admixtures with prolonged mixed concrete should be used to improve workability rather than compressive strength

Effect of piles on the seismic response of mosques minarets

Minarets seismic behavior is not similar to other known structures, because of their unique characteristics such as slenderness, shape, and supporting system. This study is devoted to investigate pile foundation effects on minarets dynamic response. An advanced finite element models were employed to simulate this sophisticated problem. The analysis procedure is essentially 2-D model enhanced to satisfy the requirements of 3-D problems, using transmitting and viscous boundaries. Root mean square procedure is implemented to minimize the needed computer memory. The model has a main advantage of considering the full interaction between soil, foundation, and structure. Three artificial earthquakes’ time histories were used as control motions at the bedrock surface. Minaret (60.0-m height) was studied to investigate the effects of soil stiffness, pile length, diameter, and arrangement, on the minaret and pile dynamic behavior. Comparison between study results and conventional analysis method is illustrated. Study results, discussion, and conclusion are given

Lateral displacement and pile instability due to soil liquefaction using numerical model

Pile instability due to liquefaction of loose sand is considered one of the most important causes of bridge failures during earthquakes. In this study, the 3D finite element program DIANA 9.3 is implemented to study the seismic behavior of piles penetrated into liquefiable sandy soil. This model is supported by a special Line–Solid Connection element to model the interface between pile and surrounding soil. Extensive studies were performed to investigate the effects of soil submergence, pile diameter, earthquake magnitude and duration on pile lateral deformation and developed bending moment along pile shaft. Study results show that earthquake magnitude and time duration have a particular effect on the pore water pressure generation and hence pile lateral deformation and bending moments. They also show the benefits of using relatively large piles to control the lateral displacement. Recommendations are presented for designers to perform comprehensive analysis and avoid buckling and plastic hinge failures

Mutual seismic interaction between tunnels and the surrounding granular soil

At areas subjected to earthquake activity, strategic and vital underground structures should be designed to withstand both seismic and permanent loadings. This study aims to investigate the seismic interaction between tunnels and the surrounding granular dry soil. An advanced non-linear dynamic finite element model has been used to simulate such sophisticated problem, considering the full seismic interaction between tunnel, surrounding soil and bedrock motion. Extended Masing model is employed to simulate the nonlinearity and hysteresisty of the soil. Dynamic analysis is based on step-by-step integration schemes. Three artificial earthquake time-histories are used as control motions at the bedrock surface. Extensive comprehensive studies are carried out on a circular tunnel having diameters varying between 6 and 10 m, surrounded by homogenous sand layer of 30 m total thickness. The effect of sand layer relative density is examined using relative density range between 25% and 90%. The effects of lining thickness as well as tunnel embedment depth are also investigated. Study results show that the maximum exerted straining actions in tunnel lining are directly proportional to the relative stiffness between tunnel and surrounding soil (lining thickness and soil shear modulus). Moreover, it is highly affected by the peak ground acceleration and the tunnel location (embedment depth). A comprehensive study is performed to show the effect of tunnel thickness and tunnel diameter on both the induced bending moment and lining deformation. In general, it is concluded that seismic analysis should be considered in regions subjected to peak ground acceleration greater than 0.15g

An <i>in vivo</i> study of <i>Hypericum perforatum</i> in a niosomal topical drug delivery system

<p>The active compounds present in <i>Hypericum perforatum</i> L. (Hypericaceae) include hyperforin, hypericins and flavonoids, which are assumed to be responsible for the activity of the extract in the treatment of wounds and scars. The present study aimed to incorporate <i>H. perforatum</i> extract standardized to a known content of phloroglucinols, naphthodianthrones and polyphenolic compounds into an effective transdermal drug delivery system capable of entrapping both lipophilic and hydrophilic constituents in the form of niosomal gels for wound treatment. An 80% ethanol extract (HE) was prepared on a pilot scale using DIG-MAZ. An HPLC-DAD holistic profile was established for HE and was standardized to contain 3.4 ± 4 rutin, 1.1 ± 3 chlorogenic acid, 0.5 ± 2 quercitrin, 2.8 ± 2 hyperforin, and 0.51 ± 3% w/w total hypericins. Niosomes were prepared using the modified reverse phase evaporation technique (REV). The wound healing effect of the gel was tested on 16 adult mongrel dogs. A significant decrease in the inflammatory cell count (18.4 ± 5.3) was recorded in the niosomal gel 1.5% NaCMC-treated group at the 7th day post wounding. It induced a marked regression in the inflammatory phase and enhanced the early beginning of the proliferative phase of wound healing. After 21 days, it showed complete re-epithelization, formation of new matrix fibers and significant reduction in the wound size, compared to the control and the Panthenol® 2% cream treated groups. This is the first study of <i>H. perforatum</i> in a niosomal topical drug delivery system.</p