Effect of freezing-thawing on concrete behavior

This study aims to determine the effect of change of temperature (freezing-thawing cycles) on the behavior of the mortar and the concrete. Also, the evaluation of the effect of air entering for improving the durability of the mortar and concrete was discussed. 23 mixes were cast to evaluate the purpose of this study. Cement types (Portland cement and limestone cement), aggregate types (dolomite and gravel), dosages of air entering 0.01, 0.1, 0.15 and 0.2% of cement weight and freezing thawing cycles (50, 100, 150, 200, 300 and 400 cycles) were considered. Relative dynamic modules of elasticity which is illustrated the internal cracks growth, durability factor and losses of weight were evaluated. Empirical correlations were formulated. The results showed that; 0.15% air entrained of cement weight improve the durability in term of freezing-thawing; where the durability factor for the mixes was ≥ 85% that exposed to freezing-thawing cycles in range 0-200. Up to 200 cycles of freezing-thawing cycles did not effect on the compressive strength of the mixes and the durability of the mortar and the concrete. It is recommended that more than 300 freezing-thawing cycles must be avoided

BEHAVIOUR OF HIGH STRENGTH CONCRETE COMPOSITE SLABS WITH DIFFERENT END ANCHORAGES

This study is performed to investigate experimentally the behaviour of steel deck composite slabs with different end anchorages. End anchorage as a type of shear connection for composite slabs plays an important role to prevent relative slip between concrete and steel deck. The presented composite slab specimens are made of high strength concrete and loaded at a specific shear span. Objectives of this study is to evaluate experimentally load carrying capacity, end slip, mode of failure, shear bond capacity, and the end anchorage contribution to the whole composite slab behaviour. Research also presents a comparison between the experimental results and the theoretical results derived according to m-k and partial shear connection methods included in these standards (BS 5950-4:1994, CSSBI S3-2003, and EC4 EN 1994-1-1:2004)

Increasing safety and productivity on Egyptian building sites

Safety and productivity in construction industry of Egypt still suffers from ignorance. This low consideration of safety importance caused escalation of accident rate in construction projects. The paperaims to identify the safety factors most related to productivity, and determine their relative importance as perceived by the target audience. The questionnaire was implemented directly; included 4 specific answers (agree, strongly agree, disagree, and strongly disagree) and consists of 47 questions divided into 7 groups: inspection, monitoring, training, etc. These questions were selected from the previous questionnaires and the questions inspired by the topic of this research. The questionnaire was distributed to 67 target audiences of different categories, including Consultants, Site engineers, Site managers and Workers. The duration of their experience ranges from 0 to more than 15 years, as well as their scientific degrees from Ph.D., Masters, and Bachelor. The following factors are the most important factors of safety and productivity. “Working 7 days per week will increase productivity”, ” increase productivity , Rework will decrease safety , Incentives based on productivity decreases safety , “Compressed schedules affect negatively safety . The results indicated that worker problems are the most important among the groups of productive factors followed by personal protective equipment , supervisors and subcontractors , monitoring , communication skills . The target audience is advised to work strategically to protect workers by continuing to identify, assess and mitigate hazardous conditions and activities in work sites to achieve the highest levels of safety and productivity

Pre- and Post-Fire Strength Assessment of Ferrocement beams

The results of an experimental investigation on the behavior of ferrocement beams after exposed to fire are presented in this paper. Different types of steel meshes are used compared with conventional reinforcement. The experimental program comprised casting and testing of eighteen beams having the dimensions of 100mm×100mm×1000mm. Three beams were reinforced as a conventional reinforcement. Each control beam was reinforced with two steel bars of diameter 8 mm in tension, two steel bar of diameter 6mm in compression and stirrups of 6 mm diameter placed at 200 mm intervals. The ferrocement beams were reinforced with steel meshes without any stirrups. Two types of steel meshes were used to reinforce the ferrocement laminate. These types are: square welded wire fabric, and expanded wire mesh. Single layer, double layers and three layers of square welded wire mesh were employed. Single layer and double layers of expanded wire mesh were employed. The experimental program was classified into three groups. First group was tested without exposure to fire, the second group was tested after exposure to fire for six hours and the last group was tested after exposure to fire under loading. All specimens were tested under 4-points flexural loadings. The performance of the test beams in terms of strength, stiffness, cracking behavior and energy absorption was investigated. The results showed that high serviceability and ultimate loads, crack resistance control, and better deformation characteristics could be achieved by using the proposed ferrocement forms

Study of Optical, Electrical and Photocatalysis Properties of SrMnO3 Synthesized by Solid-State Reaction

SrMnO3 was prepared by solid-state reaction method to obtain powder then thin films by a thermal evaporation method. XRD diffraction, Optical and electrical properties were investigated. Photocatalysis process was implemented as an interesting application of SrMnO3. XRD diffraction results were used to study the compound structure and to calculate some other parameters such as crystallite size, D, microstrain, e, and dislocation density, d. XRD results revealed that SrMnO3 has a polycrystalline structure such as hexagonal structure for SrMnO3 phase and tetragonal structure for MnO2 phase. The optical energy band for the powder and thin film were equal to 2.28 eV and 2.92 eV respectively, which candidates this compound to be a solar cell transparent window, especially for deposited thin films. The electrical resistivity behaved as semiconductor-like where it decreases with the temperature with electrical activation energy equal 0.960 eV when heating and 0.663 eV when cooling. The result of the Methylene blue absorption showed that the SrMnO3 powder does work very well as a Photocatalyst. The efficiency of the powder of SrMnO3 as a Photocatalyst increases with the illumination time and its best value is about 56% at 120 min

Study of Optical, Electrical and Photocatalysis Properties of SrMnO3 Synthesized by Solid-State Reaction

SrMnO3 was prepared by solid-state reaction method to obtain powder then thin films by a thermal evaporation method. XRD diffraction, Optical and electrical properties were investigated. Photocatalysis process was implemented as an interesting application of SrMnO3. XRD diffraction results were used to study the compound structure and to calculate some other parameters such as crystallite size, D, microstrain, e, and dislocation density, d. XRD results revealed that SrMnO3 has a polycrystalline structure such as hexagonal structure for SrMnO3 phase and tetragonal structure for MnO2 phase. The optical energy band for the powder and thin film were equal to 2.28 eV and 2.92 eV respectively, which candidates this compound to be a solar cell transparent window, especially for deposited thin films. The electrical resistivity behaved as semiconductor-like where it decreases with the temperature with electrical activation energy equal 0.960 eV when heating and 0.663 eV when cooling. The result of the Methylene blue absorption showed that the SrMnO3 powder does work very well as a Photocatalyst. The efficiency of the powder of SrMnO3 as a Photocatalyst increases with the illumination time and its best value is about 56% at 120 min

Insights into the Exfoliation Process of V2O5\ub7 nH2O Nanosheet Formation Using Real-Time 51V NMR

Copyright \ua9 2019 American Chemical Society. Nanostructured hydrated vanadium oxides (V2O5\ub7nH2O) are actively being researched for applications in energy storage, catalysis, and gas sensors. Recently, a one-step exfoliation technique for fabricating V2O5\ub7nH2O nanosheets in aqueous media was reported; however, the underlying mechanism of exfoliation has been challenging to study. Herein, we followed the synthesis of V2O5\ub7nH2O nanosheets from the V2O5 and VO2 precursors in real time using solution- and solid-state 51V NMR. Solution-state 51V NMR showed that the aqueous solution contained mostly the decavanadate anion [H2V10O28]4- and the hydrated dioxovanadate cation [VO2\ub74H2O]+, and during the exfoliation process, decavanadate was formed, while the amount of [VO2\ub74H2O]+ remained constant. The conversion of the solid precursor V2O5, which was monitored with solid-state 51V NMR, was initiated when VO2 was in its monoclinic forms. The dried V2O5\ub7nH2O nanosheets were weakly paramagnetic because of a minor content of isolated V4+. Its solid-state 51V signal was less than 20% of V2O5 and arose from diamagnetic V4+ or V5+.This study demonstrates the use of real-time NMR techniques as a powerful analysis tool for the exfoliation of bulk materials into nanosheets. A deeper understanding of this process will pave the way to tailor these important materials. \ua