Wasit Journal of Engineering Sciences

This paper presents an experimental investigation on the effects of incorporating coarse recycled concrete aggregates (RCA) on the punching and flexural behaviour of reinforced concrete two-way slabs. For this purpose, four concrete mixes were designed with various substitution ratios of natural coarse aggregates (NCA) by RCA 0% (reference mix), 25, 50 and 75%. Subsequently, fourteen 800 × 800 mm × variable thickness reinforced concrete slabs (two per concrete type) were cast and subjected to punching and flexural tests. Different parameters that affect the behavior of two-way slabs were studied including type of failure, replacement ratios of NCA by RCA, amount of main reinforcement, thickness and loading patch size. In order to investigate the effect of RCA incorporation on hardened concrete properties (compressive strength Fcu, tensile Ft strength, flexural Fr strength and modulus of elasticity Ec), different replacement ratios were considered, while the quantity of cement was kept equaled for all the mixes (with and without RCA). Hardened concrete samples results showed that Fcu, Ft, Fr and Ec were decreased by (8.62, 13.54 and 19.12%), (13.08, 17.63 and 25.46%), (10.02, 21.67%, and 34.30%) and (9.69, 15.65 and 16.62%) respectively, for the (25, 50 and 75%) replacement ratios compared with samples made from SCC without RCA. The experimental results of slabs showed that the cracking and ultimate load (11% maximum reduction ratio) and moment (19.5% maximum reduction ratio) capacities of slabs were decreased compared with slabs made from SCC without RCA. Moreover, the load deflection curves were almost identical with proportional increase to the RCA content. From the general behavior, ultimate capacity, deflections, failure angle and crack pattern results, it can be concluded that the recycled concrete aggregate can be used as a partial replacement of natural coarse aggregate to produce self-compacting concrete mixes, where the behavior of two-way slabs cast with SCC containing RCA can considered acceptable.

The importance of sustainability in road construction using and renewing the Reclaimed Asphalt Pavement (RAP) resulting from the reconstruction or periodic maintenance of roads is a challenge that requires the use of regenerative additions to restore the characteristics of the old bitumen in pure rap, in order to improve the performance properties of these renewable mixers. As there are many promising studies in this regard. The objective of this study is to recycle and restore RAP using two types of renovators; Waste Cooking Oil (WCO) and Asphalt Cement (AC (85-100)). Five percentages (1, 1.5, 2, 2.5 and 3) % by weight of both types of renovators were added to the RAP, separately, for the purpose of rejuvenation. Marshall Test was performed on the renovated samples to obtain the optimum percentages, which will be adopted in subsequent tests, which include; indirect tensile strength (ITS), tensile strength Ratio (TSR) and Duple Punch Shear Strength Test (DPSST) to evaluate the performance of rejuvenated RAP mixes and compare them with the original RAP. The outcomes indicated that (1.5 and 2.5) % are the optimal percentages for (WCO and AC (85-100)), respectively. In addition, the results of the performance tests indicated that the renovated RAP mixes are better than the original RAP in terms of stability, temperature susceptibility, stripping resistance and resistance to moisture damage, as well as achieving the specification requirements for the surface course. This indicates that the recycling process is of economic, environmental benefit and industrial sustainability.

Refrigeration and air conditioning systems consume high rates of electrical energy of the total global power consumption. The major part of this energy is used by compressor which is the main equipment in vapor compression refrigeration systems. In this study, the performance of a variable speed chilled water refrigeration system with electronic expansion valve (EEV) is experimentally investigated. The system is composed of variable speed rotary compressor, water cooled condenser, electronic expansion valve, and evaporator with refrigerant R410a for one tone cooling capacity. The results showed that the EEV opening was related to the compressor speed at limits of refrigerant subcool and system stability to achieve better performance. Refrigerant superheats increased with closing the EEV at constant compressor speed. Moreover, the degree of superheat was inversely proportional to the compressor speed at constant EEV opening. The coefficient of performance (COP) was improved by about 2.2 to 4.0% by controlling the EEV at constant compressor speed. Increasing compressor speed from 1200 to 3600 rpm resulted in decreasing system COP from 5.2 to 2.35 due to the increase of the power consumed by compressor.

Organic Rankine cycle (ORC) is one of the renewable energy to generate power at low temperatures; however, the thermal and physical properties data of the working fluid in this system are limited. In this regards, the experimental study by using R-141b as the working fluid and hot water (i.e. 50°C and 90°C) on the ORC system was conducted in order to evaluate the ORC performance via changing temperatures. Further, the air compressor was modified to act as a multi-vane expander in the ORC system. Energy and exergy analysis of ORC system was done by using Engineering Equation Solver (EES) program.

It was found that the performance of the expander is acceptable and suitable for operating conditions. In addition, the heat source temperature has a direct effect on expander performance. The higher temperatures of the heat source led to an increase the expander inlet temperature. This system satisfied maximum thermal and exergy efficiency and they found equal to 1.8 % and 21%, respectively. Moreover, the rotation speed and power of expander are equal to 1200 RPM and 2.331 kW respectively. It was concluded that the working fluid R-141b is suitable for ORC system due to consider the working fluid that do not need high temperatures to evaporate.

Forced convective heat transfer in a vertical channel symmetrically heated with a constant heat flux, and packed with saturated porous media, has been investigated experimentally in the present work. The channel was padded with spherical glass of three diameter (1, 3 and 10 mm) in a range 0.0416 < (particle diameter / inner channel radius) <0.416. The experimental setup, using a copper tube as a packed bed assembly with (48 mm) inside diameter and (1150 mm) heated length with a constant heat flux boundary condition. The test section was vertically oriented with water flowing against gravity and packed with glass spheres (1, 3 and 10 mm) diameter respectively. The results show that local Nusselt number increased at 34% with increasing Reynolds number at 65% while increased at 11% with increasing heat flux at 71%. Heat transfer rate increase as the particle diameter increase at the range of (1 – 3) mm but decrease with increasing particle diameter at the range (3 – 10) mm. Pressure drop through channel minimize at 97% as porosity increase at 23%.Many empirical relations, obtained experimentally.