International Concrete Abstracts Portal

This paper reports results of an investigation in which the effect of moisture condition of concrete at the time of application of silane on permeation and durability characteristics of concrete was determined. T h e permeation properties (i.e. air permeability and sorptivity) were measured with the Autoclam permeability system, an apparatus developed at Queen’s University of Belfast. The durability characteristics were determined in terms of chloride penetration and carbonation. Also, a comparison of the performance of silane was made with that of a controlled permeability formwork system. The results indicated that the moisture condition of concrete at the time of application of silane does not affect its protective properties to any significant degree. Silane’s performance was comparable with, or better than, that of the controlled permeability formwork in terms of sorptivity and chloride penetration at three moisture conditions included in the investigation. However, silane was found to have relatively little benefit in terms of carbonation resistance in accelerated tests, surface tensile strength and air permeability of the near surface concrete. The use of controlled permeability formwork resulted in improvements in these properties as well.

The results on the relatively high level of protection provided to the top steel in a reinforced concrete slab when the bottom steel is just adequately protected are presented in this paper. The steel reinforcement corrosion was accelerated with the use of chloride contaminated concrete. The chloride gradient within the specimen was created by inserting a relatively higher chloride bearing macrocell. Current reversal technique was used to monitor the corrosion protection level. The results showed that the presence of a higher chloride gradient requires a higher protection current density and potential. An instant-off potential of 632 mV CSE and a 4-hour decay potential of 100 mV were sufficient to protect steel reinforcement against corrosion in chloride rich concrete (19 kg/m3). The protection level at the top steel is significantly high when the bottom steel is just adequately protected from the anode source located above the top steel. In a chloride bearing concrete with the chloride gradients of 3.0 and 1.5, the top steel received 103 and 59 mA/m2 cathodic protection current densities compared to the current densities of 42 and 31 mA/m2, respectively required to protect the bottom steel. The instant-off potential of 730 mV CSE and the decay potential of 128 mV for the top steel also indicate a relatively high level of protection of the top steel. In a two-layer steel reinforced concrete slabs, it is necessary to develop a mechanism, specially in new construction, to facilitate the flow of current to the bottom steel. The current reversal technique used in the test was effective in determining the protection level against corrosion.

The electrical chloride test was developed some years ago and is carried out by driving chlorides through concrete samples using electric fields with high voltages up to 60 V. In the test, the total current passing through the sample in a few hours is used as an estimate of the transport properties of the chlorides in the concrete. This test has major advantages that it is rapid, and can be used insitu; and, it has been accepted by the ASTM. It has been criticised in the literature and has, for example, been found to give misleading results when pozzolanic materials are present. It has been pointed out by the author that if silica fume is added to the concrete, the current falls during the test. However, in plain concretes it normally rises. This paper is based on the premise that the current test procedure only makes use of part of the available data . Therefore, it provides only part of the possible results for evaluation and analysis. By analys in the shape of the current-time curve, mu’c h more information about the constituents and properties of the concrete may be obtained. For the data presented in this paper, a large number of samples were tested and computer analysis of the shape of the current-time transients was used to identify the causes of the different attributes of the current-time transients. This analysis is of particular importance in Europe where new Eurocodes for cement permit addition of pozzolanic materials to almost all cements.

Cathodic protection is an highly reliable protection method mostly suitable for concrete structures exposed to salt-attacked conditions, such as the splash zone and above in marine environments. Nevertheless, there has been no effective method to prevent salt-induced damage for reinforced concrete structures situated in tidal zones. The applicability of cathodic protection for structures in tidal zones is evaluated both by ease of execution and protective efficiency under wave and tidal action. This paper describes the results of a study on the use of a new cathodic protection method for concrete structures located in the tidal zones. The new method was developed using anode panels together with an injection material applied to gaps between the panels and concrete surface. Using a tidal water pool, exposure tests were conducted on test specimens treated with this method. From a series of exposure tests, it is concluded that the new cathodic protection method was suitable for concrete structures in a tidal zone in marine environments.

air-entrained concretes were made using a silica fume blended cement and six lightweight aggregates having a wide range of absorption values. The properties of the fresh concrete, including the autogenous temperature rise were determined. Concrete specimens were subjected to the determination of the compressive, flexural and splitting-tensile strengths, Young’s modulus of elasticity and drying shrinkage; the resistance to the freezing and thawing cycling, chloride-ion penetration and carbonation were also determined. The tests for the freezing and thawing resistance were performed on concretes made using dry and saturated lightweight aggregates. Small reinforced concrete beams made using three of the lightweight aggregates, and some incorporating polypropylene fibres, were tested for hydrocarbon-fire resistance. The target compressive strength at 28 days (60 to 65 MPa) was generally reached with five of the lightweight aggregates used. As expected the mechanical properties of the concrete were somewhat related to the degree of absorption of the lightweight aggregates. All the concretes investigated demonstrated excellent resistance to chloride-ion penetration at 28 days, negligible depth of carbonation after 448 days of air drying, and excellent performance in the freezing and thawing cycling. Based on the visual evaluation, the use of the polypropylene fibres improved considerably the performance of the high-strength semi-lightweight concrete in hydrocarbon fire.