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Internal Curing with Lightweight Aggregates
(Return to Cement Hydration and Degradation Modeling Software)
The American Concrete Institute in 2010 defined internal curing as "supplying water throughout a freshly placed cementitious mixture using reservoirs, via pre-wetted lightweight aggregates, that readily release water as needed for hydration or to replace moisture lost through evaporation or self-desiccation" (American Concrete Institute, 2010). While internal curing has been inadvertently included in many lightweight concretes produced within the past 100 years, it is only within the first decade of the 21st century that this technology has been intentionally incorporated into concrete mixtures at the proportioning stage, using a variety of materials including pre-wetted lightweight aggregates, pre-wetted crushed returned concrete fines, superabsorbent polymers, and pre-wetted wood fibers. This report provides a state-of-the-art review of the subject of internal curing, first addressing its history and theory, and then proceeding to summarize published guidance on implementing internal curing in practice and published research on its influence on the performance properties of concrete. The ongoing exploration of extensions of the internal curing concept that employ the internal reservoirs to contain materials other than water are reviewed. Finally, the critical issue of sustainability is addressed. An extensive internal curing bibliography that is also available over the Internet is included in an appendix. The report is mainly focused on the utilization of pre-wetted lightweight aggregates as the internal reservoirs due to this being the current established practice within the U.S.
Uses
Mixture Proportioning with Saturated Lightweight Aggregates
Even in higher w/c ratio concretes, this form will calculate the LWA/water needed to compensate for the chemical shrinkage so that all pores in the cement paste remain water-filled during hydration. Autogenous shrinkage is not typically an issue with w/c > 0.45 concretes. For these higher w/c ratio concretes, it may be more efficient and practical to supply curing water via conventional external curing methods.
Estimation of Travel Distance of Internal Curing Water
To calculate how far the water present in the LWA can travel, the water flow rate is equated to the value needed to maintain saturation in the surrounding hydrating cement paste. It is assumed that the cement paste and water reservoirs are composed of a set of equi-size cylindrical pores. In the case of the water reservoirs, the pore size is fixed, while in the case of the cement paste, the pore size will decrease with continuing hydration.
Mixture Proportioning for Internal Curing with Lightweight Aggregates
In the given table, enter the particle size distribution of the aggregates in the original (normal weight) concrete mixture and the fraction (volume/number) of aggregates that are going to be replaced by lightweight aggregates. When the simulation is finished, you can view the water distribution in your model concrete, along with a table indicating the 'protected' paste volume as a function of distance from the LWA surfaces. If you provide your e-mail address, you will be notified when your simulation is complete and your results are ready for viewing. Computer codes are also available for exploring internal curing with ellipsoidal-shaped particles (e.g., fibers, etc.) and quantifying the three-dimensional spatial characteristics of such microstructures.