Analysis of flexural failure mechanism of ultraviolet cured-in-place-pipe materials for buried pipelines rehabilitation based on curing temperature monitoring

Flexural properties is one of the important parameters for the evaluation of buried pipeline ultraviolet cured-in-place pipe (UV-CIPP) rehabilitation effectiveness. The flexure failure mechanism of UV-CIPP materials under the influence of different construction parameters (curing time, UV lamp irradiation intensity, curing distance, and material thickness) is unclear. In this paper, a method was proposed to approximate evaluation of the curing quality by monitoring the surface temperature of UV-CIPP material during the curing process. The flexure failure process and the causes of flexure failure of UV-CIPP materials were analyzed by considering the effects of construction parameters, combined with the monitored material surface peak temperature, and using a three-point bending test incorporating HD video and SEM observations, and sensitivity analysis of construction parameters was carried out by using random forest, and the flexural properties of UV-CIPP materials were predicted by support vector machine. The results showed that matrix cracking, debonding delamination and fiber pull-out fracture are the main reasons for the flexural failure of UV-CIPP materials. Under the influence of a single variable, the exothermic temperature of curing reaction on the surface of UV-CIPP material increases with the increase of curing time, UV lamp power and material thickness within a certain range, and decreases with the increase of curing distance. With the increase of curing time, UV lamp irradiation intensity and curing distance within a certain range, the flexural strength and flexural modulus show a trend of first increase and then decrease, but gradually decrease with the increase of material thickness. The monitoring and analysis results of the curing reaction exothermic temperature show that curing time and UV lamp irradiation intensity are still important factors affecting the curing performance of the material, and the flexural properties of the pipeline UV-CIPP material and the surface curing reaction exothermic temperature satisfy a nonlinear decreasing function relationship, and excessive curing reaction temperatures can reduce the flexural properties of UV-CIPP materials and accelerate its flexural failure.