| Scope and method of study. The losses in strength and permeability of plain cement, fly ash, and silica fume mortars and concretes, due to an interruption in moist curing, and subsequent regain in these properties due to recuring were investigated. In addition, the curing requirements of silica fume mortars and concretes were determined and compared with those of plain cement and fly ash mortars and concretes. The initial tests were performed on mortars (50-mm cubes), where the specimens were moist cured for 0, 3, 7, 14, and 28 days. After each moist curing period, the curing was interrupted by oven-drying the specimens at a temperature of 110{dollar}spcirc{dollar}C (230{dollar}spcirc{dollar}F) for 3 days. The specimens were then divided into two groups; one group was recured, while the curing of the other group was discontinued. At the end of the recuring period, both groups of specimens were tested for compressive strength and coefficient of absorptivity. The study was later expanded to include concrete mixes, typically used in highway construction. These tests utilized larger size specimens (100 x 200-mm cylinders), and a moderate environment (room-drying) for curing interruption.; Findings and conclusions. The data clearly demonstrate the detrimental effects of interrupted curing, particularly when the environment of curing interruption was harsh (oven-drying), the curing was interrupted at an early stage, or fly ash was used in the mortar or concrete. However, significant regain in the properties of mortars and concretes were achieved when the specimens were recured. Regression Equations developed from the data obtained in this study estimate the minimum lengths of curing for silica fume, fly ash, and plain cement (ASTM Type I) concretes as 3 days, 6.5 days, and 3.75 days, respectively. These results suggest that the current industry practice of over-curing silica fume concrete is unnecessary. |
