Recently, the quality of the surface layer of concrete has been recognized as an important index to relate the durability of concrete structures. However, an appropriate assessing method has not yet been achieved. The assessment of the change in the quality of the surface layer should be made from the viewpoint of not only the mechanical property but also other physical and chemical properties, such as pore structure, carbonation and so on. Attaching importance to the simplicity of tests on site, the authors have proposed that the pull-off tensile strength by the pull-off method is applicable to the former and the recovering speed in the rapid air permeability test to the latter. This study describes the results of tests on the surface layer of concrete using specimens exposed in both inland and seashore locations in the cold district of Japan. Then, the capabilities of two specific tests are examined to assess the properties of the surface layer of concrete due to weathering and other environmental attacks.

The use of nondestructive testing in the laboratory is well-documented and standard specifications are available. However, when these nondestructive testing methods are used on site, additional factors have to be taken into consideration to enable meaningful interpretation of measurements obtained. This aspect of knowledge has not received sufficient attention for standard specifications to be drafted. Suggestions are put forward in this paper on precautions to be taken when applying nondestructive testing on site. The methods of testing discussed include the magnetic method of concrete cover or bar size determination, the rebound hardness, ultrasonic pulse velocity and the penetration resistance (Windsor Probe) test. The methods of calibration in the laboratory are reviewed and the ways to check on equipment and its calibration during site work are proposed. The information to be recorded and the interpretation of data are discussed. The need for trained personnel to carry out site testing, as well as experienced professionals to interpret test results, is emphasized.

The work described in this paper is part of a research program aimed at quantifying and, if possible, modelizing, the contribution of metallic glass fibers to the durability of thin concrete repairs (about 5 cm) cast on horizontal surfaces. The tests that have been carried out up to now on fresh concrete overlays (0 to 24 hr) indicate that metallic glass fibers can decrease the magnitude of swelling during the first hours after casting. The tests carried out on hardened concrete overlays (on composite specimens kept under Toulouse natural climatic conditions) indicate significant differences between fiber reinforced concrete overlays and plain concrete overlays. Replicas examined with a scanning electron microscope show that microcracks near the interface between the overlay and the base concrete are less numerous when fiber reinforced concrete is used as a repair material instead of plain concrete. Ultrasonic pulse velocity test results are in agreement with these microscopic examinations. A field experiment was also carried out in Quebec, Canada. This experiment proved that normal mixing procedures are sufficient to disperse these fibers if a proper mixing sequence is used (no balling problems occurred). In spite of correct curing conditions, cracks developed after only 2 weeks in the plain concrete overlays, but the fiber concrete overlays are still uncracked after more than 6 months of exposure.

The evaluation of early-age strength of shotcrete is very important for some kinds of applications, for example, tunnel linings. However, until now there has been no suitable procedure for this purpose. This paper provides information on a test program carried out to establish an experimental procedure to evaluate the compressive strength of shotcrete at early age (to 8 MPa). Results obtained using the Meynadier needle and the constant energy penetrometer are shown. The first test was employed for very low-strength concrete (less than MPa) and the second covered a higher range (1 to 10 MPa). The influence of mixture proportions on the test results was evaluated.

The last few years have seen the cost of repairs and rehabilitation of major constructions become an urgent concern. In particular, the ever increasing use of reinforced concrete in corrosive and marine environment for the construction of bridges, tunnels, causeways, canals, dams, docks, retaining walls, multistory parking facilities, etc., has resulted in severe premature deteriorations. It has been established that these deteriorations are due mainly to the corrosion of the steel reinforcement in the concrete. This obviously has led many building codes to adopt a more stringent view on the durability of reinforced concrete against corrosion in specific constructions. Many procedures and techniques such as dense and latex concrete covers, epoxy-coated reinforcing steels, synthetic membranes, etc., have been used more or less successfully to meet these requirements. All these techniques, however, are expensive and their long-term efficiency is questionable. Therefore, the need for a more positive alternative to replace conventional steel reinforcing bars, at least for some applications, becomes conspicuous. This has led to the development of a new composite fiber glass rod. This new product has been evaluated in terms of mechanical properties and structural behavior as a reinforcing element and the results are presented in this paper. Immediate as well as long-term applications are discussed in terms of experimental as well as theoretical and economical considerations.