Good curing is now recognized as essential to achieving good durability of concrete and other cementitious material surfaces. However, it has not been easy to judge whether or not it has been achieved on site, so surface failures continue to occur. The Department of Civil Engineering at the Queen's University of Belfast is developing a number of test techniques to allow the measurement of surface strength, surface absorption and permeability, and surface abrasion-resistance of structures on site. These have been used to assess the performance of various curing regimes for concrete and mortar, first to see if the test methods can extract meaningful measurements of durability-related properties, and secondly to get an indication of the magnitude of the changes in these properties for different curing regimes and water-cement ratios. It is hoped that they may eventually provide a means to assess a surface in terms that could allow an objective judgment of its durability.

Five dormitory buildings on the Amherst College campus in Amherst, Massachusetts have essentially identical exposed aggregate precast concrete curtainwall panels. The panels on the three buildings that were constructed in 1963 are severely cracked and spalled; the buildings constructed in 1964 are relatively free of deterioration. The concrete used in the panels of all the buildings is composed of crushed quartz coarse and fine aggregate with strong and hard portland cement paste with low water-cement ratio and low void content. The significant difference between the materials used in the buildings is the amount of alkalies: the alkali content of the portland cement in the 1963 buildings is almost twice as high as in the 1964 buildings. A network of fine cracks developed in the panels due to alkali-silica reaction. These cracks allowed water to enter the panels and freeze during cold weather. The resulting progressive damage has led to disintegration of the cement paste, severe spalling, and corrosion of the reinforcing steel. The phased repair program, which began in the summer of 1989 and is expected to require several years to complete, involves removal and/or replacement of severely damaged panels, repair of damaged panels in place, modification of structural and waterproofing details to reduce exposure, and treating of undamaged panels to prolong their life.

The principal mechanism for the deterioration of concrete is transport of fluids either into or out of the pore structure of hardened body. The fluid transport occurs via a complex network of interconnected porosity incorporating both the cementitious matrix and matrix/aggregate interfacial regions. Paper describes the development of an experimental method and a mathematical background for a rapid water-permeability measurement method and a mathematical model relating porosity, described in terms of a log-normal distribution, to permeability.

The hydration and factors relating to the durability of hardened cement paste and concrete have been investigated. Both chemical and physical factors involved in the paste and concrete microstructure are governing factors in prediction of performance. This paper addresses the effects of cementitious materials modified by the presence of granulated blast furnace slag, fly ash, or silica fume. Special alkali-activated cements are also discussed. Initial structure developed in the fresh state is transmitted to the final structure, including the paste pore structure, and is important in resisting forces of degradation. Considerable advances have been made in understanding the mechanisms of degradation, such as shrinkage, freezing, and thawing, carbonation, intrusion of undesirable chemicals, or leaching of species to the environment.

The 100 m reinforced concrete open spandrel arch bridge over the Storms River Gorge was constructed in the mid-1950s, and in 1982 surface cracking of the concrete was noticed. Cores were obtained from the various members and laboratory testing confirmed that the concrete was suffering from the effects of alkali-aggregate reaction (AAR). In 1986, the decision was made to rehabilitate this bridge, consisting of two distinct stages, of which the first was widening and strengthening the superstructure, as well as strengthening the concrete arch rib itself. The second stage consisted of treating the concrete surfaces with a hydrophobic coating to halt any further effects of AAR. To assess the long-term effectiveness of the hydrophobic coating, the bridge was instrumented and strain gage readings were taken at regular intervals. The analysis of the readings show that the concrete has been shrinking since the strain readings were started, confirming that, to date, the silane hydrophobic coating is still effective.