Influence of Internal Curing on Properties and Performance of Cement-Based Repair Materials
Dale P. Bentz, Scott Z. Jones, Max A. Peltz, Paul E. Stutzman
Repair materials are playing an increasingly important role in the maintenance of our nations aging infrastructure. Understanding their properties and performance is critical to planning and executing appropriate repairs that will provide the requisite service life for critical systems and components. This study focuses on the dimensional stability of cement-based repair materials by examining the autogenous shrinkage of two representative materials, and its mitigation via the use of internal curing (IC). Three different IC agents are investigated in this regard: pre-wetted lightweight aggregates (LWA), a superabsorbent polymer-coated sand (PCS), and a superabsorbent polymer (SAP). Repair mortars with and without IC are also characterized via chemical shrinkage and setting time measurements, isothermal calorimetry, semi-adiabatic calorimetry, quantitative X-ray diffraction, and measurements of compressive strength, elastic modulus, shear slant bond, and drying shrinkage. As the IC agents have absorptions of pore solution that span two orders of magnitude, they have differing influences on mixture proportioning and subsequent performance. For the two materials investigated in the present study, the mortars using LWA to provide IC exhibited the highest compressive strengths and greatest relative reductions in autogenous shrinkage in comparison to the controls formulated without IC. Since a portion of the autogenous shrinkage in these repair mortars appears to be due to loss of internal restraint upon the dissolution of ettringite crystals (needles), the replacement of 5 % of the repair mortar with a limestone powder to stabilize a portion of this ettringite and further reduce the measured autogenous shrinkage was also investigated. For this application, a coarse (16 µm median diameter) limestone powder was found to be superior to a finer (2.2 µm) one in reducing autogenous shrinkage, while providing otherwise similar performance.
, Jones, S.
, Peltz, M.
and Stutzman, P.
Influence of Internal Curing on Properties and Performance of Cement-Based Repair Materials, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://doi.org/10.6028/NIST.IR.8076
(Accessed December 9, 2023)