Laboratory investigation and BP neural network modeling on heat-activated oil shale semi-coke attributable to the mechanical properties of concrete

Abstract

Concrete construction requires the consumption of large quantities of raw materials. If oil shale semi-coke can be used in concrete projects in a reasonable way, not only will it ease the shortage of raw materials for concrete, but it will also consume oil shale semi-coke and reduce its ecological impact. This investigation aims to study the feasibility of using semi-coke in concrete construction based on its mechanical properties. The chemical components and microstructures of four thermal activation temperature oil shale semi-cokes were first analyzed by X-Ray Fluorescence (XRF) and scanning electron microscope (SEM). Then, by replacing the cement with equal mass of semi-coke, the effect of heat-activated calcination temperature and the amount of semi-coke admixture on the mechanical strength of mortars sand and concrete was tested. Finally, a BP neural network was used to establish a strength prediction model for semi-coke concrete and the evolution of internal pores of semi-coke concrete was analyzed by nuclear magnetic resonance (NMR). The results show that semi-coke is mainly composed of SiO2 and Al2O3, which can be used as a concrete mineral admixture for volcanic ash reaction. The oil shale semi-coke is flaky with a porous surface, resulting in the semi-coke contributing more to the flexural strength of the mortar than to the compressive strength. At the calcination temperature of 500 ℃ and a semi-coke content of 15%, the concrete has the lowest porosity and the best mechanical properties, and is therefore recommended. The developed BP neural network prediction model has a high prediction level and can provide guidance for practical engineering. The increase in the amount of coke admixture leads to a continuous increase in the number of pores in the medium and large pore sizes inside the concrete, which is the main reason for the change in concrete strength due to semi-coke.