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.

The porosity of cement mortars can be reduced by decreasing the water cement ratio with corresponding addition of superplasticizer to maintain workability. Further, the pore structure itself can be modified by the incorporation of pozzolanic admixtures such as Silica Fume, and Ground Granulated Blast Furnace Slag (GGBFS) powder. The reduced water cement ratio combined with refined pore structure increases the compressive strength in addition to enhancement in durability characteristics. Such cement mortars are termed as High Performance Mortars. The paper highlights the findings of a project which investigated the sorptivity characteristics of mortar mixes using (a) different percentages of GGBFS partially replacing OPC (b) reduced water cement ratios using superplasticizer admixture to improve the workability of mixes and (c) combination of superplasticizer admixtures and GGBFS. It is concluded that High Performance Mortars can be obtained by modifying a conventional high strength mortar mix by reducing the water/binder ratio and adding pozzolanic admixtures and superplasticizers.

Low permeability is an important characteristic of durable concrete. Concrete of low permeability minimizes the entry of moisture and aggressive chemicals. It provides better corrosion protection of steel reinforcement and limits freezing/thawing damage of concrete. A variety of test methods using gas or liquid have been developed to measure the permeability of concrete, but most of them are costly and suitable for use only in the laboratory. A simple device and test method developed by Zia and Guth at North Carolina State University measures air permeability of concrete. The Zia-Guth device, consisting of two concentric cylindrical chambers, is adhered to the concrete surface by vacuum and measures the rate of pressure increase in the inner chamber as air flows from the outer chamber through the concrete and into the inner chamber. The device is economical, and its compactness and quick response time make it suitable for nondestructive testing of in-place concrete in the field. Permeability of concrete depends not only on the microstructure of the concrete but also on the moisture content in the concrete. This paper presents the results of an experimental study undertaken to evaluate the effect of moisture content on the air permeability of concrete using the Zia-Guth testing device. Three different types of concrete varying in w/cm ratio and admixture content were tested. The influence of moisture content of the concrete on airflow was examined by testing slab specimens (400 x 400 x 75 mm) for each type of concrete under different moisture contents and at different concrete ages. Test results showed that the measured permeability index could vary by 10 to 300 percent depending on the moisture content and the type of concrete. Based on test results, a general methodology is proposed to account for the effect of the moisture content of concrete on the air permeability of different types of concrete.

This paper presents an overview on durability of reinforced concrete in marine environment in China and relevant test methods based on comparison of results from laboratory and exposure tests. The test results of the reinforced concrete specimens, including ordinary concrete and high-performance concrete containing silica fume and other anticorrosion measures are comprehensively analyzed. The test data of the specimens exposed 3, 9, and 20 years in-situ in the South Sea and 3, 8, and 16 years in Huanghai Sea of China are reviewed. A comparison of test results between the laboratory and long-term exposure is made for evaluating their common characteristics and differences. Based on the Fick’s Law, the chloride ion penetration and diffusion characteristics in the concrete specimens exposed 16-20 years in marine environment are used to estimate the service life of reinforced concrete structures in marine environment. Recommendations for ensuring and improving the durability of the reinforced concrete in marine environment are provided.

This study investigates the effectiveness of low shrinkage-high strength concrete (LS-HSC) using expansive additive and shrinkage-reducing agent with regards to the time-dependent structural performance of reinforced HSC flexural members. Design equation for evaluating the flexural crack width and deformation of RC beams considering the effect of shrinkage/expansion before loading are proposed on the basis of JSCE (Japan Society of Civil Engineers) Design Code of 2002. The results show that autogenous shrinkage of conventional HSC with no additives can significantly affect the time-dependent serviceability performance of the RC beams, while LS-HSC can markedly improve its serviceability performance. In addition, time-dependent flexural crack widths of reinforced LS-/conventional HSC beam, can be evaluated by the JSCE Code Equation, which takes into account the strain change in the reinforcement bars from the state where the stress in concrete at the depth of tension reinforcements is zero. Also, time-dependent as well as instantaneous curvatures of reinforced LS-/conventional HSC beam can be accurately calculated by the proposed equation. This equation takes into account the effect of the change in curvature due to the release of restrained-shrinkage/expansion stress at cracked section.