This study points out the close relationship between several quality indicators of recycled aggregate and the performance of recycled aggregate concrete. Regarding the diversity in quality and composition of the recycled concrete products, three laboratory produced air-entrained-concretes with low, medium and high water-cement ratios and a non-air-entrained concrete with medium W/C were processed for recycling. Recycled aggregate concretes were produced with a water/cement of .55, and tested after 28 days of moist curing. Results of the capillary water immersion and permeable porosity tests indicate that structure and amount of adhered mortar as well as the recovery percent of original coarse aggregate and other physical properties of recycled coarse aggregate, especially the inclusion of recycled fine aggregate into the system are the mean reasons creating important differences in the permeable pore system and captivity of recycled aggregate concretes. Relatively low pore content of the non-air-entrained type adhered mortar compared with the air-entrained ones influences the concrete porosity in the same way. The volume of permeable pores in concrete produced with non-air entrained type of recycled aggregate seems to be reduced. Although entrained air pores of the adhered mortar increase the total volume of the permeable voids, they play a role of interrupting the capillaries. The findings of this research indicate that all possible variations in recycled aggregate properties must be taken into account to be able to design durable recycled aggregate concretes.

Within the framwork of the "BHP 2000" French National Project, a long-term experimental study is carried out in order to assess the durability of fifteen concretes with 28-day compressive strength ranging from 20 to 130 MPa. The properties of these concretes are first studied on sampled in laboratory conditions. Also, reinforced-concrete test specimens are monitored over the years at four different field exposure stations. The experimental results of compressive strength, gas permeability, and carbonation death obtained in the laboratory on the water-cured 28-day old samples are compared here with some of the available field data. The ranking of the different concretes with respect to their durability is deduced in both cases. Other laboratory measurements, such a chloride diffusivity, capillary coefficient, and deicing-salt scaling resistance, are also presented and discussed in this paper. For each type of concretes, the influence of mixture-parameters, such as the water-to-cement ratio, the presence of entrained air or of pozzolanic admixtures, on the different properties is analyzed. The influence of the environmental conditions on the field data is also discussed. The various trends observed on the durability-related properties are interpreted o the basis of the microstuctural characteristics of the materials. The paper focuses on the behavior of high-performance concretes. A superior ability to limit gas or liquid transfers within the material is observed for these concretes. But, it is found that the presence of entrained air increases their gas permeability, indicating an increased potential risk of corrosion of the reinforcement, without systemically enhancing the deicing-salt scaling resistance of the concrete. Most of the non-air entrained HPCs do not exhibit good performance when submitted to accelerated freezing and thawing cycles in the presence of slats. All of these results have to be confirmed by the long-term monitoring of the structural elements.

Concrete slabs containing uncoated reinforcing bars were cast with a concrete cover of 20 mm. The W/C was either .25, .40, and .60. A simulated crack .4-mm wide was formed transverse to the axis of the reinforcing bar. Three types of commercial corrosion inhibitors were added to concrete mixtures for corrosion protection. Slabs were placed in an accelerated exposure cabinet with four cycles of wetting and drying per day in simulated seawater. The corrosion rates were measured using the linear polarization technique. Some of the concrete slabs were broken open at the end of the exposure period and corrosion damage was evaluated. Water-soluble chloride content analysis in the rebar trace was performed at the end of the exposure period for all of the examined specimens. The various types of corrosion inhibitors showed a wide variation in performance and their effectiveness was also found to be particularly sensitive to addition rate. In general all had a greater effectiveness in reducing corrosion rate in a higher water-to-cement ratio concrete than in a lower water-to-cement ratio concrete. Only calcium nitrite at an addition rate of 25 L/m3 provided some level of consistent performance in reducing the corrosion rate in .60 and .40 water-to-cement ratio concrete for uncracked and precracked specimens.

The lack of natural fine aggregate in Japan is serious because the commitment to protect the natural environment is increasing. Many concrete engineers are eager to find fine aggregate sources other than the traditional river and sea sand. Copper slag fine aggregate is expected to be one of the alternatives although the location where the copper slag is available is limited. In this paper, some characteristics of concrete with copper slag will be clarified. The carbonated thickness, resistance to freezing and thawing, thermal resistance, shrinkage strain, creep and setting time have been examined. The strength, slump and durability of concrete with copper slag are not inferior to those of normal concrete. However, copper slag sometimes delays the setting time of concrete even if it produced at the same refinery. The delay of setting time is more than one week in some cases although the durability in concrete is not affected by it. The main reason will be determined and the solution will be given in this paper.

This paper describes a study on the long-term strength development of concrete cured under high-temperature conditions at an early age. The concrete specimens were made with normal portland cement, high-early-strength portland cement, and low-heat portland cement, and were cured under 26 different temperature conditions. The temperature conditions were set so as to give systematic variations in the maximum temperature and the initial curing time. The strength development of concrete was examined over a period from 1 to 365 days. It was clarified that a higher maximum temperature improved the strength development of concrete at an early age, but inhibited the strength development of concrete at later ages. A shorter initial curing time inhibited the strength development of concrete at later ages. A time dependence of the effect of curing temperature on the strength development of concrete was observed. For concrete made with normal portland cement, a higher temperature during the period from 0 to 12 hours after mixing results in lower strength development after 3 days. For concrete made with high-early -strength portland cement, a higher temperature during the period from 0 to 3 hours after mixing results in lower strength development after 1 day. For concrete made with low-heat portland cement, a higher temperature during the period from 0 to 12 hours after mixing results in lower strength development after 7 days, but a higher temperature after 72 hours results in greater strength development at later ages.