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

Highway bridges and parking structures, subject to coupled effects of mechanical loads and corrosion, often show early signs of distress such as concrete cracking and rebar corrosion leading to reduced structural performance and shortened service life. One solution to this problem is to use low-shrinkage low-permeability high-performance concrete (HPC) for bridge decks exposed to de-icing salts and severe loading conditions. A new HPC was formulated to achieve low shrinkage and low permeability, high early-strength, and 28-day compressive strength over 60 MPa (8,700 psi). Its mechanical performance and durability were tested both in the lab and field under severe test conditions, including restrained shrinkage, cycling loading, freezing and thawing cycles, and application of de-icing salts. Models were developed and calibrated to predict structural performance and service life of concrete bridge decks under severe exposure conditions. Prediction models indicate that bridge decks designed with low-shrinkage HPC can achieve a service life up to 100 years. Compared to normal concrete decks, short-t t-to-medium span bridge decks using low-shrinkage HPC could be built at a comparable initial construction cost, but at less than 35% of the life-cycle cost.

High performance concrete (HPC) mixtures may be prone to early-age cracking. While uncracked HPC can protect steel reinforcement from corrosion reasonably well, cracking can dramatically accelerate the corrosion of reinforcement and reduce the service-life of structures. Several approaches have been developed to reduce the risk of cracking. One of these approaches is internal curing (IC) which uses prewetted lightweight aggregate. This paper describes a series of experiments performed using full-scale restrained concrete elements in an effort to quantify the performance of internally cured concrete on reducing the early-age shrinkage cracking thereby increasing the resistance to corrosion. The results show that concrete made using internal curing experienced a slight swelling at early-ages and experienced very little shrinkage. As a result the IC concrete did not crack while the conventional concrete cracked. Upon exposure to a chloride solution, extensive and nearly immediate corrosion activity was detected in the plain specimen while the internally-cured concrete did not exhibit any cracking or signs of corrosion during the time of this study (approximately 1 year). The benefits of internal curing are reduced cracking as well as reduced transport properties.

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.