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Calculation of the concrete temperature in production phase is an important parameter to control the concrete quality, confining inconsistencies, and costly corrections. In order to obtain after mixing temperature of concrete, the before mixing temperature and weight of the constituent material as well as the moisture contents of the aggregates are collected. Using heat balance equilibrium of the concrete material is an easy and widely used method to calculate after-mixing temperature of the concrete. ACI 306R-10 has presented an equation to calculate the concrete temperature based on thermal equilibrium of the constituents. To evaluate the performance of the equation in estimation of the concrete temperature an experiment is conducted. In the experimental site test results of the output from a batching plant is recorded and graphed. The results of the after induction temperature were calculated using the formula presented in ACI. However, the proposed equation predicts smaller temperature values compared to the actual ones. In the final step the reasons for deviation in the results was discussed and an equation is derived to calculate the concrete temperature for post-mixing stages. The obtained equation was tested on other data and the results show that the method could predict the results reliably.

Fibre-reinforced concrete (FRC) has gained tremendous attention in many disciplines due to its high initial strength, favorable mechanical properties, structural lightness, and energy-absorbing properties. In this research, Barchip fibres, Forta, and Basalt are utilized to reinforce concrete under penetration effect loading to examine the energy absorption and impact strength characteristics. To determine the parameters of the percentage of fibres on the impact resistance properties, the Box–Behnken method as a subset of the response surface method (RSM) was used. A diagram of RSM is adopted to determine the optimal percentage of fibres for higher initial strength and energy absorption. Results obtained using Design-Expert software revealed an initial strength of 886.127 N and an optimal energy absorption of 4.9865 J. In addition, the calculated R2 values and normal probability graphs showed a fairy accurate correlation between the results of the experimental and mathematical approaches. Finally, this study evaluated the fracture surface, adhesion of the fibres to the concrete, and degradation modes of the fibres to pave the way for optimal utilization of these hybrid FRCs.

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Steel box-shaped columns are suitable structural members for structures with moment frames in two directions, but plate connections have several construction problems, including inaccessibility of inside of columns, welding difficulties, etc. ConXL connections are the new proposed details to reduce these problems. This connection consists of collar flange, collar corner, and collar web extension. In this paper, the seismic behavior of these types of connections is investigated using the numerical method. For this purpose, three samples of ConXL connections without concrete filler, with concrete filler and with concrete filler and stiffener plates inside the column were studied using Abaqus software. The results demonstrated that the ductility of the ConXL connection without concrete filler is more than the two other samples, while the strength of this connection is less than the strengths of the two other samples. It was observed that utilizing stiffener plate inside the column has no significant effect on the strength of the connection.