Contrary to ordinary concrete, where penetration of chlorides is caused by sources outside the concrete, recycled aggregate concrete has an additional source of chlorides, when chloride-contaminated concrete is used as aggregate inside the new concrete. Therefore special specimens were developed to simulate the transport of water and chlorides from recycled aggregate to the surrounding concrete matrix. Conventional methods like weighing and chemical analysis were used to measure the chloride and water transport. It was established, that the pretreatment of recycled aggregate (e.g. moistening) has a large effect on the quantity and the speed of redistribution of chlorides between recycled aggregate and the new matrix. Additional tests with conventional concrete corrosion cells, where individual chloride contaminated recycled aggregates were placed near the embedded steel, showed intense pitting corrosion already after 90 d. The results of rapid chloride migration tests and capillary suction tests are pre- sented for the penetration of chloride and water from outside. For these investigations the composition of the recycled aggregate concrete, especially the type and the proportion of recycled aggregate were varied. The results indicate that the quantity of recycled aggregate has a minor influence on chloride ingress. However, the concrete composition and the type of recycled aggregate can enhance the chloride ingress into recycled aggregate concrete.

Concerning the durability of concrete, Annex F of European Standard EN 206-1 gives recommendations for limiting values of concrete composition. These values are based on the assumption of an intended working life of the structure of 50 years. The in-situ and laboratory performance of eight concrete mixtures have been measured. The composition of these mixtures fulfills the limiting values of differenct carbonation-induced corrosion and chloride-induced corrosion exposure classes, as defined in EN 206-1. Two cements were tested a portland cement and a pozzolanic cement. The results present a set of laboratory and in-situ values that can he used as a basis for defining the performance-related design methods with respect to durability.

This paper illustrates the effect of silica fume, ultra fine fly ash and ground gran- ulated blast furnace slag on the compressive strength, shrinkage and the development of pore structure of high performance concrete. Shrinkage measurements were carried out using a modified version of ASTM C-341, as proposed by Tarawa and Mirawaya. The experimental data obtained demonstrates how the material composition, the water to binder ratio, and the distribution of pore volume influence strength, autogenous, drying and total shrinkage. High strength mixtures containing ultra fine fly ash, silica fume and ordinary Portland cement exhibited an increased drying shrinkage rate, when compared with the slag mixture. By using a 10% replacement of UFFA, a large improvement with respect to autogenous shrinkage, relative to a 10% silica fume replacement in high strength concrete occurs, without any noticeable effect on compressive strength. The pore structure of the matrix paste at early ages of hydration appears to have a strong effect on autogenous shrinkage.

Concrete members were once considered as maintenance free. However, it is clear that some have deteriorated and required maintenance work. This paper attempts to evaluate the factors influencing the total cost of RC members during their service life when structures gradually deteriorate and require maintenance work. The form of deterioration considered here is salt attack, and the repairing method involves restoration of the member to its original cross-section. Total maintenance cost is expressed as present cost based on the coefficient of current price. The main factors calculated in the paper are the deterioration ratio of RC members at the repair stage, the actual interest ratio (including the capital ratio and the price fluctuation ratio), and the cost loss for expected structural failure. Calculation results indicate that the life cylce cost of a structure is greatly affected by these factors (especially the actual interest ratio), and that they have to be decided cautiously.

Corrosion of steel reinforcement is the most important cause of premature failure in reinforced concrete structures. The use of corrosion inhibitors seems to offer a simple and cost effective prevention technique against chloride induced corrosion: nevertheless, performance of commercial inhibitors available on the market is only partially satisfactory. This paper deals with a basic study on organic substances, that present inhibiting effect on carbon steel corrosion. Two years electrochemical test results, obtained in simulated concrete pore solutions and concrete slabs, on the effect of functional groups are presented and discussed. The inhibition effect on corrosion initiationnd propagation was evaluated by means of two electrochemical parameters: potential and polarisation resistance. Tests on concrete specimens confirmed the effectiveness of some organic substances in delaying corrosion initiation and increasing the chlorides concentration threshold.