International Concrete Abstracts Portal

SP-228CD This CD-ROM of Special Publication 228 contains the papers presented at the Seventh International Symposium on the Utilization of High-Strength/High- Performance Concrete that was held in Washington, D.C., USA, June 20-24, 2005. The symposium continued the success of previous symposia held in Stavanger, Norway, (1987); Berkeley, California (1990); Lillehammer, Norway, (1993); Paris, France, (1996); Sandefjord, Norway, (1999); and Leipzig, Germany, (2002). The symposium brought together engineers and material scientists from around the world to discuss topics ranging from the latest applications to the most recent research on high-strength and high-performance concrete. In the years since the first symposium was held in Stavanger, there has been worldwide growth in the use of both high-strength and high-performance concrete. In addition to more research and applications of traditional types of high-performance concrete, the use of self-consolidating concrete and ultra-high-performance concrete has moved from the laboratory to practical applications. This publication offers the opportunity to learn the latest about these developments.

Concrete bridge structures in Canada experience exposure to extreme environmental conditions, such as prolonged low temperatures, frequent freezing and thawing cycles, and, in urban maintenance conditions, extensive use of deicing salts. In addition, windy conditions combined with a very low relative humidity increase the potential for concrete cracking. The intensity of shrinkage of high performance concrete (HPC) is affected not only by the type and duration of the fresh concrete curing but also by high cement content, low water/cementitious materials ratio (w/cm), and the use of silica fume. The amount of unrestrained shrinkage, as identified by laboratory tests, does not always properly characterize the performance of HPC mixes. The restrained shrinkage test in accordance with the provisional AASHTO standard may provide better prediction of early age shrinkage (tendency to crack). In the study described in this paper, the effect of mix parameters and curing regime was researched extensively. The impact of shrinkage reducing admixtures in comparison with moist curing was assessed for cast-in-place concrete and precast concrete. Based on the results of this study, optimum mix design parameters, curing conditions, and w/cm ranges were determined to satisfy both durability and structural performance of HPC.

In this paper, a composite admixture for reducing shrinkage (CARS) was used to make high strength concrete (HSC) with a water-binder ratio of 0.25 for reducing shrinkage. The effectiveness of CARS on reduction of shrinkage was experimentally investigated, and the influence of CARS on the behavior of autogenous shrinkage and drying shrinkage strains in HSC under different curing conditions and replacement dosage of CARS are discussed. Furthermore, mechanical properties such as compressive strength and Young’s modulus of HSC with CARS were experimentally investigated, and compared with those of HSC without CARS. CARS is effective in reducing autogenous and drying shrinkage of HSC. When replacement dosages of CARS were 5% and 8% of the cement content, the autogenous shrinkage strains of concrete could be reduced by 25% and 50%, respectively; the drying shrinkage could be reduced by 22% and 34% when dried at the age of 3 days, and by 10% and 28% while drying started at the age of 7 days. Compressive strength of concrete at the age of 28 days was reduced by 7%-12% due to the addition of CARS, while Young’s modulus was reduced by 10%-15%.

The microstructure of concrete, especially of High Performance Concrete/High Strength Concrete (HPC/HSC), usually shows many microcracks. The aim of this research project is to investigate the reasons for microcracking in HSC, especially the influence of different curing methods. Different specimens were stored at 20 °C/65 % r.h., under water, in a 40 °C furnace and under 40 °C hot wind. Additionally, the HSC was made with and without silica fume to determine the effect on the structure and on the formation of microcracks. Compressive strength of the investigated concretes ranged from 80 - 100 MPa. The main result is, that the wet curing led to a higher number of microcracks in HSC, than the curing at 20 °C/65 % r.h. and also a higher number than the curing method in the furnace or under a hot wind. Additionally, the effects of microcracking on servicability and durability were investigated. The results showed that the number of microcracks did not influence mechanical properties like compressive strength and splitting tensile strength nor water permeability. Specimens with high number of microcracks showed in these tests also higher values of Young´s modulus.

Early-age bridge deck cracking is the single most prevalent distress on bridges reported by all of the state DOTs. Although there have been many studies performed with regard to the cause of early-age deck cracking, the problem still exists. The early-age deck cracking due to restraint thermal stresses can be predicted using the 3-D finite element program DIANA. It simulates hydration of young concrete, shrinkage, and cracks due to the environmental conditions during the construction period and the restraint of the girders and adjacent structural elements. The analysis covers two stages. The first stage covers the construction period before the bridge is opened to traffic. The second stage starts after removing the formwork including just the bridge self-weight. Simulation results including time and crack initiation enable the understanding of cracking mechanism in young concrete as a first step to avoid early-age bridge deck cracking.