Spatiotemporal Monitoring and Analysis of Hydration Heat in Ultra-Long Water Treatment Tank Slabs Based on Densely Distributed UWFBG-Finite Element Coupling

To address the early-age cracking issue of the ultra-long base slab in coal mine water treatment tanks caused by hydration heat accumulation and structural constraints， this study integrated densely distributed ultra-weak fiber Bragg grating （UWFBG） sensing with ABAQUS finite element simulation. This approach was used to conduct spatiotemporal monitoring and analysis of hydration heat and strain in a 106.6 m long， 500 mm thick C40 concrete base slab. Distributed temperature sensing （DTS） and distributed strain sensing （DSS） optical cables were deployed in the top and bottom protective layers of the base slab， enabling monitoring at a spatial resolution of 1 m and a sampling interval of 10 min. A coupled hydration heat-shrinkage model was established using the HETVAL subroutine， the FILM subroutine， and a shrinkage subroutine. The results showed that the peak temperature of the lower protective layer ranged from 54.90 to 59.90 ℃， which was higher than the range of 46.9 to 51.58 ℃ observed in the upper protective layer， with a maximum temperature difference of 8 ℃. The rebar strain exhibited a three-stage characteristic： tensile strain of （170-190）×10^-6 during the heating phase， transition to compressive strain during the cooling phase， and stabilization from -46×10^-6 to -62×10^-6 after 200 hours. The errors for both temperature and strain indicators are kept within 8%. The maximum principal tensile strain of concrete （38-42）×10^-6 was lower than the 7-day allowable value of 46×10^-6. Due to the implementation of post-pour strip measures， no risk of early-age cracking was observed.