International Concrete Abstracts Portal

This CD consists of 14 papers presented at the ACI Fall Convention, Toronto, Canada, October 2012, and sponsored by ACI Committees 130, Sustainability of Concrete; 213, Lightweight Aggregate and Concrete; and 231, Concrete Properties at Early Ages.These papers cover the following general topics: impact on sustainability, mixture proportioning, internal curing methods and their implementation, hydration impacts, volume change effects, mechanical properties, cracking tendency, durability aspects, life-cycle cost analysis, and case studies that document the use of internal curing in full-scale production applications. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-290

Over the last fifteen years there has been growing interest in using internally cured concrete. While the original intention of using internal curing was to reduce autogenous shrinkage, it has been observed that the internally cured concretes have additional benefits. For example, previous research has shown that internally cured concrete has lower water absorption than comparable conventional (plain) concrete mixtures. This paper presents results of chloride transport experiments performed using a conventional (plain) concrete mixture and an internally cured concrete mixture. Chloride transport performance was evaluated using a series of experimental techniques including: 1) resistivity, 2) rapid chloride penetration (RCP), 3) rapid chloride migration (the Nord Test), 4) migration cell testing (STADIUM cells) and 5) chloride ponding and profiling. The results indicate that internally cured concretes have similar or superior performance to plain concrete. Several testing artifacts are noted associated with the pre-wetted lightweight aggregate that overestimate the transport measures for the internally cured concrete. The experimental results suggest that by reducing the chloride transport rate the use of internally cured concrete can result in structures with improved durability (due to the time it takes chloride ions to cause corrosion at the reinforcing steel).

The internal curing process is often referred to as “curing concrete from the inside out”. This process is accomplished by using materials that absorb water, such as lightweight aggregate, to replace some of the normalweight aggregate in the freshly placed concrete mixture. This absorbed water can then be released from the aggregate into the paste fraction as the paste begins to desiccate. By doing this the hydration reactions of cement and supplementary cementitious materials are enhanced, and capillary stresses are reduced as the water is readily released from the absorbent materials. This paper gives a general overview of internal curing, and will show how internal curing plays a practical and economical role in today’s move toward sustainable concrete. The paper will explain how internal curing works, why internal curing is used, summarize the modern history of internal curing, and how it affects the carbon footprint of a concrete mixture. In addition, how to adjust the concrete mixture to provide appropriate amount of internal curing, and reduce the life-cycle costs of the concrete. Examples of real projects that have used internally cured concrete will then be highlighted.

Cellulosic or wood pulp fibers, like pre-wetted lightweight aggregates and superabsorbent polymers, can be used as internal curing agents in cementitious materials to mitigate autogenous shrinkage. While the internal curing abilities of different types of cellulose fibers have been demonstrated in mortar and concrete, relatively little fundamental research has examined the influence of fiber processing or “pulping” on their efficacy as internal curing agents. This is an important topic because even for fibers derived from the same type of wood, the morphology and composition of its pulp can be altered by processing, and these alterations can have important effects on the fibers’ internal curing capacity. This research examines the effect of variations in pulping process on the internal curing performance of eucalyptus pulp fibers grown in Southeast Asia. Variations in processing produced three fibers – unbleached soda pulp, unbleached kraft pulp, and semi-chemical pulp –which were compared as internal curing agents through standard autogenous shrinkage testing. These data were then compared based on fiber composition and morphology, using results from thermogravimetric analysis (TGA) and scanning electron microscopy, to better understand the complex roles of these factors – as influenced by processing – in providing internal curing to cement-based materials.

First noticed by T. C. Powers, et al in 1948, [22] as beneficial for hydration by supplying water internally, specifiers and contractors in 2012 have grasped how the process of internal curing is implemented, how hydration behaves, and how improvements in mechanical properties, durability, and cost may be beneficial. To meet the time-dependent hydration needs of the concrete, having sufficient water internally available, when, as, and where needed, is vital for achieving optimum characteristic qualities. There is lower life cycle cost with internal curing (IC) and frequently lower first cost. In 2012, the number of projects using internal curing is increasing at an escalating rate, because the process is simple and economically implemented. Pavements, bridges, buildings, and pervious parking lots are being started now in this recession, because specifiers and contractors are saving dollars, as they build longer lasting structures while costs and interest rates are low. Developed initially to reduce autogenous shrinkage in low water-cement ratio and high performance concretes, internal curing has been found to reduce drying shrinkage. Other benefits found include reduced permeability, increased compressive and flexural strengths, less warping, stronger interfacial transition zones, greater durability, and lower carbonation.