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.

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.

Presents an evaluation of the effects of temperature and type of superplasticizer--high-range water-reducing admixture) (HWRA)--on there rate of chloride-ion diffusion through hydrated superplasticized ordinary portland cement (OPC) pastes and opc + fly ash (PFA) pastes. OPC pastes and OPC/PFA pastes with a water-cementitious materials ratio of 0.31 containing a HRWRA were prepared in the laboratory and cured at 21, 30, and 45 C for different lengths of time, so as to obtain approximately identical compressive strengths. Five different types of HRWRA were used in the study. At the end of the curing period, the specimens were placed in diffusion cells maintained at 30 C and the amount of chloride passing through the pastes was measured. Measurements of total porosity and pore-size distribution were made using helium pycnometry and mercury-intrusion porosimetry. The variations of chloride diffusion coefficients arising from changes in the temperature of curing and type of HRWRA are presented and discussed.

Focuses on the damaging implications of the daily temperature fluctuations in the aggressive climatic conditions of hot-arid regions due to strain incompatibility resulting from widely differing coefficients of thermal expansion of the local crushed limestone aggregate and the hardened cement paste. The data strongly indicate that temperature fluctuations cause microcracking in concrete, which increase its permeability and lower its tensile strength and cracking time. In this investigation, concrete specimens with water-cement ratios of 0.40, 0.50, and 0.65, with cement content of 550 lb/yd 3 were subjected to cyclic heating in programmed ovens which carried out 120 temperature fluctuations, each simulating the temperature regime of a typical summer day in eastern Saudi Arabia. The thermal regime was characterized by a temperature swing from 27 to 60 C within a 24 hr period. This included the effect of concrete surface heating by direct solar radiation. Pulse velocity, permeability, and time-to-cracking data were developed in reference to cyclic heat-treated specimens at 20, 40, 60, 80, and 120 heating cycles. The cyclic heat-treated specimens had a significantly reduced pulse velocity, a noticeably increased permeability, and, depending on water-cement ratio, a 55 to 70 percent reduction in cracking time due to reinforcing bar corrosion. This implies that a significant degree of microcracking is induced in concrete due to the thermal incompatibility of concrete components.

Concrete quality and strength are strongly affected by the curing procedures used in the initial days after concrete is cast. The relative advantage of any particular method and the strength-gain relations must be understood to assess concrete strength and quality adequately. In the present study, the strength gain with age of concrete up to 1 year with different compressive strengths and under different initial and subsequent curing conditions in warm and high-humidity climates was determined. The initial curing techniques evaluated were those most widely used in practice and were intended to represent actual, imperfect construction practice. The subsequent curing conditions were artificially modeled to simulate dry and rainy climates. Of the curing methods evaluated, ponding was found to be the most effective, followed by intermittent sprinkling, unsealed plastic covers, and curing compound. An initial period of three days can develop adequate concrete strength in Puerto Rico's climate; this has a good influence on concrete strength gain with age. Slabs that were kept indoors, and had no contact with water, showed in all cases a decrease in strength under saturated conditions at an age of 1 year, while those maintained outdoors with a rainy climate showed a continuous gain in strength with increasing slope at all times and developing strengths higher than the 28-day strength.