Construction activities have been a primary cause for depleting natural resources and are associated with stern environmental impact. Developing concrete mixture designs that meet project specifications is time-consuming, costly, and requires many trial batches and destructive tests that lead to material wastage. Computational intelligence can offer an eco-friendly alternative with superior accuracy and performance. In this study, coal waste was used as a recycled additive in concrete. The flexural strength of a large number of mixture designs was evaluated to create an experimental database. A hybrid artificial neural network (ANN) coupled with response surface methodology (RSM) was trained and employed to predict the flexural strength of coal waste-treated concrete. In this process, four influential parameters including the cement content, water-to-cement ratio, volume of gravel, and coal waste replacement level were specified as independent input variables. The results show that concrete incorporating 3% recycled coal waste could be a competitive and eco-efficient alternative in construction activities while attaining a superior flexural strength of 6.7 MPa. The RSM-modified ANN achieved superior predictive accuracy with an RMSE of 0.875. Based on the experimental results and model predictions, estimating the flexural strength of concrete incorporating waste coal using the RSM-modified ANN model yielded superior accuracy and can be used in engineering practice to save the effort, cost, and material wastage associated with trial batches and destructive laboratory testing while producing mixtures with enhanced flexural strength.

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A microwave electrothermal thruster (MET thruster) has been constructed, consisting of a microwave plasma chamber 12 cm long and 8 cm in inner diameter and a micronozzle 10 mm long with 1 mm in diameter. The microwave plasma is produced by 2.45 GHz microwave frequency at a power of 1 kW, and the feed gas is Ar at a pressure of 10^-3mTorr. Microwave energy is transmitted into the cavity and electrons sre connected to the wave's electric field. Thus, the electrons are accelerated by microwave electric fields. Microwave plasma discharge is formed based on the interaction of electrons with neutral gas particles. Then, the plasma acts as a resistive load and absorption of microwave energy, raises the temperature of the gas or plasma. Gas heating increases the gas pressure and is released through the nozzle. The plasma density and electron temperature are 2.35×〖10〗^17 m^(-3) and 1.2 eV, respectively. The thrust and specific impulse are 10 mN and 100 s.