Presents the results of the effect of temperature on cathodic protection level needed for effective control of chloride corrosion of reinforcing steel in concrete structures. The chloride levels in the concrete were 8 and 32 lb/yd 3, and chloride gradients were 1.5 and 2.0. Chloride gradient was created by embedding in the concrete specimen a relatively higher chloride-bearing macrocell and thereafter connecting the macrocell steel and the main steel through an external resistor. Current reversal technique was used to establish the protection level needed for effective control of reinforcing steel corrosion. Two sets of specimens were used: the first set of reference specimens were kept at the controlled room temperature of 25 C, and the second set of temperature-treated specimens were kept in a temperature chamber with a peak value of 60 C. The corrosion activity of the reinforcing steel increased with an increase in the temperature to which concrete is exposed. Increased corrosion activity at a higher temperature exposure of 60 Required an increased level of cathodic protection as indicated by the higher protection current density, higher instant-off protection potential, and marginally higher decay potential at the beginning of the polarization period. The 60 C temperature effect requires about 20 percent higher level of protection in terms of current density and about 20 to 30 mV higher instant-off potential/delay potential for an initial polarization period of two months. Thereafter, no additional protection is required against the temperature effect. The subsequent reduction in the level of cathodic protection required at higher temperature is indicative of a dominant influence of the electromigration factor in the interactive relationship between corrosion activity and the beneficial effect of electromigration of ions caused by higher temperature.

Laboratory concrete made under different curing conditions was evaluated using electron-optical techniques. Differences in microstructure and strength were observed in relationship to water-cement ratio, wet/dry curing, temperature of curing, presence of supplementary materials, and mode of preheating. This presentation highlights the partial results of the microstructural evaluation.

The best time to place quality concrete is during cold weather, as long as the concrete is prevented from freezing. Why is it so hard to place quality concrete during hot climate conditions? The culprits are concrete temperature, air temperature, humidity, and wind velocity. There are secrets that can drastically improve the present quality of concrete placed in hot climates. This paper discusses how to cope with hot weather conditions and still produce high-quality concrete. Concrete in hot climates is affected by water demand, rapid setting times, and the resulting ultimate strength reduction. Understanding these detrimental effects and how to overcome them can result in high-quality, durable concrete. Many of these effects can be overcome by using the proper chemical or mineral admixture, but using techniques slightly different than the usual. There may be times when an accelerating admixture, or insulation, may be used effectively even in hot climates. Relatively high concrete temperatures may be appropriate to obtaining durable concretes.

Performance properties of mortars made with ordinary portland cement (OPC) and pozzolanic cements containing either fly ash (PFA) or granulated blast furnace slag (GBS) have been measured after exposing the mixes to laboratory-simulated hot dry environments. The simulated environments were: 20 C at 70 percent relative humidity; 35 C at 70 percent relative humidity; and 45 C at 30 percent relative humidity. Specimens were cured for different lengths of time before testing. The tests carried out to assess the performance properties and thus the durability of the mortars were: total porosity, pore size distribution, and gas permeability using oxygen. The tests showed that performance of the mortar mixes is enhanced by increased curing time. Uncured specimens subjected to hot dry environments (45 C at 30 percent relative humidity) were strongly affected by their durability characteristics as shown by the deterioration of the performance indicators. OPC mortars were severely affected by the hot dry environments independent of the length of curing. Pozzolanic mortars subjected to curing periods of 1 day or more in hot dry environments exhibited better properties than equivalent mortars cured at normal temperature.

Numerous methods are available to improve the surface durability of concrete. The most commonly used techniques are improved curing practices and the application of surface treatments. A new technique that employs a controlled permeability formwork liner (CPF) has been introduced in the U.K. This paper describes the results of an investigation to compare the effect of the controlled permeability formwork liner with that of various curing techniques and the absorption of silane in relation to the air permeability, sorptivity, water permeability, and strength of the cover concrete. Also, the resistance to carbonation has been studied. Results indicate that, in general, the use of CPF improves the surface properties compared with conventional steel formwork. The effect of variation of curing methods was marginal for concrete with CPF.