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Crack damage evolution in concrete coarse aggregates under microwave‑induced thermal stress

Yuan Yuan, Shao Zhushan, Qiao Rujia, Guo Xuan, Wang Weitao

Archives of Civil and Mechanical Engineering

2022

Vol. 22, no. 3

art. no. e108

Coarse aggregates of waste concrete can be efficiently separated from mortar under microwave irradiation. However, the microwave-induced damage in aggregates are restricting mechanical properties of the aggregates for replacing natural aggregates. Since damage evolution in rocks treated by microwave are influenced by mineralogy and microwave operating parameters, such as power and irradiation time, understanding the microwave weakening mechanism of rocks is necessary to assess and control the damage of aggregates for recovery of high-quality concrete coarse aggregates. This article develops an approach for evaluating crack damage evolution in aggregates exposed to microwave by combining theoretical analysis with experimental investigation. A theoretical heat source-matrix model based on electromagnetic and thermal properties of mineral components is established for microwave heated aggregates. Substituting microwave irradiating parameters and mineralogy of the aggregates into the model, corresponding temperature fields and thermal stress fields are solved. Cracks in aggregates after microwave exposure are observed using scanning electron microscopy (SEM) and quantified in terms of crack length, density and intensity. Crack damage varied with microwave energy is assessed by crack length and density. Crack propagation is further discussed by contrast of stress intensity factor (SIF) at the crack tip and fracture toughness of the aggregate. Cracking behavior analyzed by SIF of cracks is consistent with that obtained from quantitative analysis on SEM images. The results suggest that granite shows a stronger resistance to thermal stress damage compared with basalt under microwave exposure, and a multistage microwave treatment should be adopted for recovery of various aggregates.

Przyczynek do oceny stanu zarysowania belek z betonu zbrojonego prętami BFRP

Urbański M., Łapko A.

Budownictwo i Architektura

2014

Vol. 13, nr 3

201--208

W pracy przedstawiono analizę porównawczą doświadczalnych i obliczonych teoretycznie szerokości rys w jednoprzęsłowych belkach swobodnie podpartych zbrojonych prętami bazaltowymi BFRP (Basalt Fibre Reinforced Polymers). Belki typu BFRP wykonano z betonu C30/37 ze zbrojeniem dolnym na zginanie prętami bazaltowymi o średnicy 8 mm, dodatkowo wykonano belki referencyjne ze zbrojeniem stalowym tej samej średnicy. Badano ugięcia i zarysowania oraz nośność belek zbrojonych prętami BFRP, o cechach wytrzymałościowych określonych w testach na rozciąganie. Wykazano, że znacznie zredukowana sztywność elementów zbrojonych prętami bazaltowymi BFRP wywołuje kilkakrotnie większe szerokości rys w porównaniu z belkami zbrojonymi prętami stalowymi o tym samym przekroju poprzecznym.

This paper presents a comparative analysis of experimental and theoretical crack widths of simply supported beams reinforced with BFRP rebar (Basalt Fiber Reinforced Polymers). The tested BFRC model beams have been made of concrete class C30/37 and of bottom flexural basalt bars 8 mm in diameter. The reference RC beams with traditional flexural steel reinforcement have been additionally made of the same diameter. Beam deflections, concrete crack widths and strength capacity of beams reinforced with BFRP bars as well as with traditional steel bars have been registered. It has been shown that crack widths of beams reinforced with BFRP bars have been much (three to four times) higher than in the beams reinforced traditionally