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

One strategy for achieving excellent long-term performance of concrete bridge decks is to combine low permeability with minimal early-age cracking. Low permeability can be achieved through the use of concretes with low water-cement ratios; however, topical curing techniques are usually insufficient to maximize hydration and minimize autogenous shrinkage effects. This autogenous shrinkage causes stresses in restrained concrete, which can lead to deleterious early-age cracking. Curing effectiveness can be enhanced through the implementation of prewetted lightweight fine aggregates. Internal curing is provided as the aggregate water gradually desorbs into the surrounding paste. A study of the early-age behavior of internally cured concrete is described in this paper. Internal curing was provided by means of expanded shale, clay, and slate lightweight fine aggregates. Ten mixtures with water-cement ratios of 0.42, 0.36, and 0.30 were investigated. Compressive and tensile strengths of the internally cured concretes were similar to or slightly greater than the strengths of their non-internally cured counterparts, and concrete stiffness decreased as expected in the internally cured mixtures. Autogenous shrinkage strains and stresses were found to increase as the water-cement ratio decreases. However, the autogenous effects were reduced or eliminated in the internally cured concretes.

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.

This paper reports results from a series of experiments performed in an ongoing FHWA research program that is investigating the potential for using more fly ash in transportation structures. The paper focuses on test results from five mortar mixtures: a water-to-cement ratio (w/c) of 0.30 and water-to-cementitious materials ratio (w/cm) of 0.30 with 40% and 60% fly ash by volume with and without internal curing. A reduction in early age autogenous shrinkage is observed for HVFA mixtures. While initial autogenous shrinkage is reduced in HVFA mixtures, they are more prone to higher rates of shrinkage and cracking at later ages (after seven days). This can be related to pore size distribution as well as continued effects of hydration and the pozzolanic reaction. Chemical shrinkage and isothermal calorimeter results are shown to describe the rate of fly ash reaction at early ages. Internal curing can reduce the propensity for cracking.

In this research, ten different high performance concrete (HPC) mixtures internally cured by pre-wetted lightweight fine aggregate (LWFA) and/or shrinkage reducing admixture (SRA) were cast and their drying shrinkage strain was monitored using the ASTM C157 test. The data collected was used to evaluate six shrinkage prediction models, namely, ACI 209 model, CEB90 model, AASHTO model, B3 model, GL2000 model and ALSN model. The study finds that the GL2000 model shows the best overall performance in predicting shrinkage strain for internally cured HPC. However, more accurate long-term shrinkage prediction can be achieved based on the current ACI 209 model with experimental measurements. This proposed procedure is capable to predict long-term drying shrinkage for concrete using local materials mixture by using short-term experimental measurements.