高温后页岩轻骨料混凝土断裂特性

为研究页岩轻骨料混凝土Ⅰ型断裂性能随温度的变化规律,对页岩轻骨料混凝土试件进行100,200,300,400 ℃加热处理,自然冷却至常温。采用三点弯曲梁法对15个缝高比为0.4的轻骨料混凝土小梁进行断裂试验,依据荷载-跨中挠度曲线计算断裂能及断裂韧度。结果表明:起裂韧度与失稳韧度均随温度升高先上升后下降,起裂韧度的转折点在200 ℃左右,失稳韧度的转折点在300 ℃左右; 黏聚韧度呈现下降—上升—下降的趋势,其随温度变化规律与起裂韧度、失稳韧度存在较大的关联性,当温度为300 ℃时裂尖端的黏聚力阻止裂缝扩展的能力最为显著; 断裂能呈现出基本不变—增大—减小的3个变化阶段,当温度为200 ℃左右时断裂能达到最大值,断裂能随温度变化规律的拟合曲线上升段为二次抛物线,下降段为直线; 在所研究的温度范围内,页岩轻骨料混凝土的断裂性能受高温影响较为显著; 所得结论为高温状态下轻骨料混凝土结构裂缝扩展研究和结构设计提供了试验依据。

Fracture Properties of Shale Lightweight Aggregate Concrete After High Temperature

In order to study the temperature effect on modeⅠfracture properties of shale lightweight aggregate concrete,the shale lightweight aggregate concrete specimens were heated at 100, 200, 300, 400 ℃ and then naturally cooled to room temperature. Three-point bending beam method was used to the fracture test for 15 lightweight aggregate concrete beams with seam-height ratio of 0.4. The fracture energy and fracture toughness were calculated according to the load-midspan deflection curves. The results show that the initiation toughness and the unstable toughness both rise firstly and then drop with the increase of temperature. The turning point of the initiation toughness is at about 200 ℃, and that of the unstable toughness is at about 300 ℃. The cohesion toughness shows a decrease-increase-decrease trend with elevated temperatures, and is largely related to the initiation and the unstable toughness. The cohesion force of crack tip significantly prevents crack extension at about 300 ℃. The fracture energy presents a hold-rise-decline three-stage and reaches the maximum value at about 200 ℃. The ascending part of the fitting curve of the fracture energy changing with temperature is a quadratic parabola and the descending part is a straight line. Within the temperature range of the study, the fracture behavior of shale lightweight aggregate concrete affected by high temperature is notable. It provides experimental basis for the study of crack propagation and structural design of lightweight aggregate concrete under high temperature condition.