Early-age shrinkage and temperature optimization for cement paste by using PCM and MgO based on FBG sensing technique

• Phase change of paraffin can offset the hydration heat in the fresh cement paste.
• Volumetric expansion of the paraffin can compensate early-age shrinkage in cement.
• MgO and paraffin can reduce the influence of early-age shrinkage and thermal accumulation.

Accompanying with hydration progress, early-age performance involving drying shrinkage and thermal expansion are becoming big challenges for ordinary Portland cement. Stress concentration induced by shrinkage can lead to cracking which definitely affect durability of engineering structures especially for large volume concrete structures such as dams, tunnels, nuclear reactor and deep foundation. To overcome this issue, a large amount of studies have been conducted to eliminate the influence of early-age shrinkage and thermal expansion in concrete after casting. Cooling tubes are generally embedded in a large volume concrete before casting. Stress concentration will occur around the pipe which is becoming a potential risk to the in-service structures. In this study, the authors proposed a new method to add paraffin and magnesium oxide in fresh matrix. A relatively new sensing technology was employed to measure the internal strain and temperature simultaneously. A series of test was executed to determine the addition of phase change materials and expansive. Finally, the experimental results were analyzed and discussed. It can be concluded from the test results that paraffin and magnesium oxide can be used as admixtures which can significantly reduce early-shrinkage and thermal accumulation.