International Concrete Abstracts Portal

Permeability is now recognized to be one of the key properties influencing the durability of concrete structures. The focus of this paper is the determination of the role and effectiveness of combinations of pozzolanic and cementitious cement replacement materials on the air/gas permeability of concrete. The apparatus used to determine the gas permeability consisted of a permeability cell, and air was forced to flow only in the vertical direction. Six different concrete mixtures were used; all the mixtures had the same water-binder ratio of 0.45, but two different total cementitious contents of 350 kg/m3 and 450 kg/m3 were investigated. Fly ash or slag was used in combination with silica fume. The test specimens were exposed to three different curing conditions prior to carrying out the permeability test. The results show that air permeability of concrete is highly dependent on the curing history of the concrete. There was no well-defined correlation between air permeability and compressive strength, but a reasonable correlation existed between air permeability and the threshold pore parameter obtained from pore structure studies.

Standard test results indicate that the quality of new epoxy coated reinforcement has been improved, but the question in regard to the real durability of these systems in practice has not yet been determined. Therefore, the Institute for Building Materials Research has carried out some investigations to evaluate the durability of the corrosion protection of two different coatings. The results can be summarized as follows: the adhesion test is able to differentiate between effective and non-effective coatings. An evaluation of the durability of the corrosion protection, for the improved coating types with a chromation layer, was not possible within the duration of these tests. The initial results of the Electrochemical Impedance Spectroscopy tests indicate that the coating Type 2 avoids corrosion reaction, if the coating is undamaged. The undamaged coating Type 1 extends the service life because the resistance against the charge transfer through the coating is an order of magnitude higher than that of the reference steel plates. In the case of local damages, both coatings were effective. Considering the initial test results, an extension of service life, compared to uncoated reinforcement by means of a durable limitation of the cathodic area, seems to be possible.

In the study reported in this paper. the permeability of normal portland cement (PC) and fly ash (FA) concretes containing 15%. 30% and 45% FA were investigated. These were compared on an equal 28 day strength basis (and therefore had increasing binder contents and reducing W/B with increasing FA content at a given design strength). A further series of FA concretes (45%), combined with two active early strength cements to overcoming low early strength were also considered. The results followed expected behaviour in terms of strength/permeability relationships. It was also found that the permeabilities of FA concretes were lower than those of PC concrete. with greater differences at increasing FA level. The permeability of all concretes cured in water was significantly lower than those of concrete cured in air, but the differences reduced with increasing FA level. suggesting that this concrete may be less sensitive to limited moist curing. Long-term curing in water lead to reductions in permeability for all concretes, while that in ai r generally lead to slight increases. Comparison between pemeabilities of high FA content concretes indicated similar performance between these. although the exact ranking varied slightly depending on the curin g conditions. It was found that the performance of high FA concrete was better than PC concrete under a wide range of temperature and moisture curing conditions, but this may be reversed under low temperature, cold curing conditions. A ranking of the FA concretes to illustrate their potential durability is provided.

Water penetration and premature deterioration are widespread problems in reinforced concrete structures, particularly in the tropics. Many different chemical and mineral admixtures have been proposed as possible solutions. This paper examines high quality concretes modified with fly ash, silica fume, polypropylene fibre or certain chemical admixtures so as to reduce the permeability and hence make concrete more durable and watertight. Experiments were conducted at the National University of Singapore using different combinations of these admixtures supplied by four local manufacturers. A total of 39 mixtures were tested for pressure penetration and water absorption as well as compressive strength. The results show significant variation in the penetrability characteristics of the different concretes tested. Most products had some beneficial effect on pressure penetration, but little influence on absorption. One proprietary ingredient tested was found to greatly reduce both pressure penetration and absorption producing a concrete that was virtually completely watertight.

Granulated ground blast furnace slag is widely used as a partial substitute for normal portland cement in concrete. Among others, one of the perceived benefits is that slag cement improves the durability of reinforced concrete structures. Numerous investigations have reported enhanced resistance to steel reinforcement corrosion. There are two aspects to enhancing resistance to reinforcement corrosion. The first is the ability of the concrete to resist the penetration of chlorides. The second is the degree of corrosion once the chlorides have reached the reinforcing steel. This presentation considers the performance of specimens once chlorides have reached the depth of steel reinforcement. The Ministry of Works & Agriculture has monitored the performance of 96, 100 by 100 by 300 mm reinforced concrete specimens for ten years; exposed to the Bahrain environment. The environment is classified as an ultra hot climate with extreme temperature, extreme solar radiation and extreme chloride salt concentrations in the air and seawater. The specimens were cast with three types of cementitious material: 1) normal portland cement, 2) site-blended slag cement, consisting of 30 percent portland cement and 70 percent slag and 3) preblended slag cement, typically consisting of 30 percent portland cement and 70 percent slag. The exposure program includes two concrete mixtures (220 and 330 kg/m3 cementitious material), two curing regimes (good and poor) and two depths of cover (10 mm and 20 mm). The concrete was contaminated with 0.4 percent chloride and 1.5 percent sulfate by weight of cementitious material. The exposure specimens made with the slag cements had substantially greater carbonation depths and steel corrosion losses than the specimens made with normal portland cement. This is the result regardless of curing regime,cover to reinforcement and content of cementitious material.