International Concrete Abstracts Portal

This paper presents the results of an experimental investigation of RPC (Reactive Powder Concrete) on shrinkage and creep under uniaxial compressive loading. The RPC are ultra-high strength concretes characterized’ by high silica fume content and steel fibers reinforcement. The present study focuses on RPC with a very low water/binder (0.17) ratio and a compressive strength at 28 days of 160 and 200 MPa after a 90°C heat-treatment. The thermogravimetric analysis shows that in RPC a high proportion of cement remains unhydrated, and the pozzolanic reaction becomes predominant two weeks after mixing. The autogenous shrinkage and creep of RPC were measured on sealed specimens. The stress level on the creep specimens represented 20 % of the concrete compressive strength at the time of loading. The basic creep kinetics of RPC is very rapid and does not differ from high strength concrete, whereas its magnitude can be twice as much. The basic creep amplitude and kinetics of RPC are strongly affected by the age of loading. After a heat-treatment of RPC at 9OC, the shrinkage becomes insignificant, and the basic creep is highly reduced.

In the past decades, cement-based materials have been increasingly used for the construction of radioactive-waste barriers. The design of durable structures for this specific application requires a precise knowledge of the evolution of the material engineering properties over a 1000-year period. Among the wide range of degradation phenomena to which the structure can be exposed upon its service life, the leaching of calcium appears to be the most critical. Given the intricate nature of the leaching process, a reliable prediction of the long term behavior of the concrete barriers can only be made through numerical modeling. In order to generate more quantitative information on the subject, a new accelerated leaching test has been developed. The operating principle of the test is quite simple. The leaching process is accelerated by applying an external electric field through the material. This paper details the different electrochemical phenomena involved during a LIFT experiment. It also presents several experimental data obtained for various neat paste samples. In this series of tests, the evolution of the hydrated cement paste microstructure was studied using various experimental techniques such as X-ray diffraction, DTA/TG analyses and scanning electronic microscopy. The advantages and limitations of this new procedure are discussed.

High fluidity concrete has been used to meet requirements for the marine construction thanks to its superior durability and ease of placing. High-fluidity concrete is, however, so viscous and has less bleeding to have the cold joint that may harm the uniformity of the structure. We have executed series of experiments to study the effect of interval and method of making joints on the strength of placing-joint of 5 types of high-strength and high-fluidity concrete and high-fluidity lightweight concrete for the marine construction . The strength of the placing-joint has shown no substantial degradation compared to those without placing-joint by rodding the joint within 120 minutes after the first placing under an ambient temperature of 20 C, while specimens without rodding, cured under the standard water bath, have shown 2/3 of the strength of those without placing-joint at an interval of placement less than 60 minutes.

In this paper, the authors present results of an experimental program carried out to study the pull-out behavior of a new type of high yield strength steel deformed reinforcing bars (fY = 830 MPa) embedded in high strength concrete (f, = 100 MPa). Influence of embedded length, concrete strength and yield steel strength, on bond strength has been investigated by means of pull-out tests. The final aim of this research program is to define design and specification requirements for this new material. Variations of the average ultimate bond strength with embedded length, for concretes with compressive strength from 40 MPa to 100 MI%, produce horizontal curves, which indicates that the mean ultimate bond stress is an appropriate bond strength indicator. Ultimate bond strength increases proportionally with both the increase of tensile strength and compressive strength of concrete. No significant effect of the yield steel strength of reinforcement on the value of the mean ultimate bond stress has been observed. In the case of a pull-out failure, the relationships between the ultimate mean bond stress and the main characteristics of the bond between steel and concrete (embedded length, mechanical strengths of concrete and yield steel strength) are similar to the ones of standard deformed reinforcement (fY = 500 MPa).

from Prince Edward Island, Canada’s smallest Transportation to and province, has been by ferry for the past century. The cost to operate the ferry system became an increasing burden for the Canadian government and a proposal call was solicited in 1987 to the private sector to construct and operate an alternate system to the Province of Prince Edward Island. A proposal was accepted for a private consortium to build a 12.9 km bridge from the mainland to Prince Edward Island. The bridge was completed in May, 1997. A precast concrete, post-tensioned segmental box girder structure was selected for the site. A requirement of the Government of Canada w as that the design and construction of the bridge provide a structure with a design life of 100 years. The bridge is located in a harsh marine environment, with some 100 annual cycles of freezing and thawing. Ice floes which originate in Northern waters pass through the Northumberland Strait in the winter and early spring months. Water temperatures vary from about -2 C in the winter months to +18 C in summer. The salinity of the water in the Northumberland Strait is approximately 3.5%. This paper presents some of the durability concerns which were considered during the design and construction of the bridge and describes how these concerns were addressed.