Sensitivity of Hydration Heat to Autogenous Shrinkage in Full-Scale High-Performance Concrete Beams

Abstract

High-performance concrete is more susceptible to cracking at an early age. During hydration, various forces come into play, including heat generated by hydration, forces driving the growth of hydration products, and forces contributing to the reduction of pore number and size. Heat hydration is one of the things highlighted as the cause. The investigation of full-scale beam hydration heat aims to address the challenge of producing crack-free HPC. This research was carried out experimentally on full-scale prestressed beams measuring 200´600´3000 (mm) with a compressive strength (fc') of 60 MPa. Shrinkage and temperature in the concrete were measured using vibrating wire-embedded strain gauges. Four gauges were installed at 1030 mm from each end, and another four were placed in the middle of the beam. After casting, the beam were immediately covered with burlap sacks to keep them consistently moist. Strain and temperature observations were recorded every 15 minutes starting immediately after casting. Eight autogenous shrinkage phenomena were identified in full-scale beams. Phenomena 1 and 6 showed no sensitivity to hydration heat release. Phenomenon 1 occurred within the first 3 hours, during which the surrounding temperature still influenced the concrete temperature. Phenomenon 6 took place at 20.5-20.7 hours, indicating a sudden jump in autogenous shrinkage not accompanied by heat of hydration. The critical period, from age 9.5 to 16 hours, sees the highest values of temperature and shrinkage in the concrete. At this time the beams can be given special treatment.  A growth sketch of the hydration product has been proposed.

Keywords: Autogenous shrinkage, Beam, Concrete, Hydration heat

DOI: 10.7176/CER/15-3-06

Publication date:December 31^st 2023