Influence of Surface Sealers on the Properties of Internally Cured Cement Mortars Containing Saturated Fine Lightweight Aggregate Yudong Dang, Ph.D. 1 ; Xianming Shi, Ph.D., P.E., M.ASCE 2 ; Stephen Mery 3 ; Ning Xie, Ph.D. 4 ; Andrew Benson 5 ; and Zhenghong Yang, Ph.D. 6 Abstract: To date, internal curing (IC) has been widely accepted as a promising way to mitigate the autogenous shrinkage of high- performance concretes (HPCs). While extensive studies have confirmed the benefits of internal curing to HPCs cured under sufficient moisture, the durability implications of early-age drying remain unclear for internally cured cement-based materials. As such, this work investigates the influence of early-age drying on the properties of internally cured cement mortars containing saturated fine lightweight aggregate (LWA). The tests conducted on cement mortars with or without internal curing include: drying shrinkage, moisture loss, com- pressive strength, splitting tensile strength, water absorption, and gas permeability. Additionally, two surface sealers were individually applied to mortars and evaluated for their effectiveness in reducing the risk of early-age drying. The results reveal that early-age drying significantly offsets the advantages of internal curing of LWAwith respect to shrinkage reduction and microstructure densification. In this case, the presence of surface treatments can preserve and enhance the benefits of internal curing of cement mortar. Observations made using a scanning electron microscope suggest that coverage and integrity of the sealer film define its effectiveness in retaining moisture. Further studies on concrete specimens with larger cross sections and with various curing conditions are recommended in order to practically evaluate the effect of early- age drying on internally cured concrete. DOI: 10.1061/(ASCE)MT.1943-5533.0001306. © 2015 American Society of Civil Engineers. Author keywords: High performance concrete; Early-age curing; Internal curing; Surface treatment; Drying shrinkage. Introduction Shrinkage in volume is one of the major physical mechanisms that compromise the integrity of cement-based materials and lead to their deterioration (Dyer 2014). It may be attributable to the ten- dency for moisture to evaporate out of originally water-filled pores in the cement-based matrix, in the case of plastic shrinkage and drying shrinkage. It may also be attributable to the intrinsic volume reduction during cement hydration (autogenous shrinkage), as free water turns into chemically bound or absorbed water on cement hydrate surfaces (Kovler and Zhutovsky 2006). The shrinkage can induce marked tensile stress if it is restrained, and once it ex- ceeds the local tensile strength of the concrete, it would lead to formation and propagation of microcracks. Cracks pose a signifi- cant risk for the durability of concrete, as they not only impair the mechanical performance of concrete but also reduce the depth of protective cover and provide a preferential ingress path for deleteri- ous species (Wang et al. 1997; Liu and Shi 2012). For concrete with proper moist curing during the first 24 h (prior to final setting of cement), drying shrinkage and autogenous shrink- age from final setting to latter ages are two main forms of shrinkage that are of great interest. For conventional concrete, drying shrink- age (due to external moisture loss) is generally the main concern as autogenous shrinkage (due to internal moisture loss) is negligible. High performance concretes (HPCs) featuring high binder content and a low water-to-binder ratio, however, are known to be more susceptible to autogenous shrinkage and more likely to crack (Kovler and Bentur 2009). Various methods have been explored to mitigate the risk of excessive autogenous shrinkage due to self- desiccation (Kovler and Zhutovsky 2006). One example, known as “internal curing, ” entails the inclusion of lightweight aggregate (LWA) particles or super absorbent polymer (SAP) into the con- crete to serve as an internal reservoir of water and to compensate for the water lost by self-desiccation (Bentz and Snyder 1999; Jensen and Hansen 2001; Philleo 1991). For HPCs that typically feature low permeability, internal curing is especially beneficial as external curing has little effect on hydration inside the concrete matrix (Castro et al. 2010). Over the past two decades, the influences and benefits of internal curing on HPCs have been extensively studied (Bentz and Snyder 1999; Bentz 2009; Bentz and Stutzman 2008; Byard et al. 2011; 1 Postdoctoral Fellow, Key Laboratory of Advance Civil Engineering Materials of Ministry of Education, Tongji Univ., Cao’an Rd. 4800, Shanghai 201804, China. E-mail: dangyudong@gmail.com 2 Associate Professor, Dept. of Civil and Environmental Engineering, Laboratory for Advanced and Sustainable Cementitious Materials, Washington State Univ., Sloan 101, P.O. Box 642910, Pullman, WA 99164-2910 (corresponding author). E-mail: xianming.shi@wsu.edu 3 Undergraduate Student, Western Transportation Institute, Montana State Univ., P.O. Box 174250, Bozeman, MT 59717. E-mail: stephen .mery@msu.montana.edu 4 Research Associate, Western Transportation Institute, Montana State Univ., P.O. Box 174250, Bozeman, MT 59717; and School of Transporta- tion Science and Engineering, Harbin Institute of Technology, Harbin 150090, China. E-mail: ning.xie@coe.montana.edu 5 Undergraduate Student, Western Transportation Institute, Montana State Univ., P.O. Box 174250, Bozeman, MT 59717. E-mail: andrew .benson@msu.montana.edu 6 Professor, Key Laboratory of Advance Civil Engineering Materials of Ministry of Education, Tongji Univ., Caoan Rd. 4800, Shanghai 201804, China. E-mail: yzh@tongji.edu.cn Note. This manuscript was submitted on September 8, 2014; approved on February 6, 2015; published online on April 3, 2015. Discussion period open until September 3, 2015; separate discussions must be submitted for individual papers. This paper is part of the Journal of Materials in Civil Engineering, © ASCE, ISSN 0899-1561/04015037(9)/$25.00. © ASCE 04015037-1 J. Mater. Civ. Eng. J. Mater. Civ. Eng. Downloaded from ascelibrary.org by WA State Univ Libraries on 04/07/15. Copyright ASCE. 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