Effect of Fly Ash on Leaching Characteristics of Cement-Stabilized Macadam Base

Shrinkage and Durability of Waste Brick and Recycled Concrete Aggregate Stabilized by Cement and Fly Ash

To study the shrinkage and freeze-thaw durability of cement-fly-ash-stabilized brick and concrete reclaimed gravel mixture (CFRBCA), recycled gravel was used to replace 100% of the natural gravel in cement-and-fly-ash-stabilized gravel (CFRCA). Five different mixture ratios of recycled brick and recycled concrete were designed. Dry shrinkage tests, temperature shrinkage tests, freeze-thaw cycle tests, ultrasonic tests, and microscopic analyses were then conducted. The test results showed that the water loss rate, dry shrinkage strain, and dry shrinkage coefficient of CFRBCA increased as the age and brick content increased and tended to be stable by approximately the 40th day of age. The reclaimed gravel content had a great influence on the temperature shrinkage of CFRBCA: the temperature shrinkage coefficient first increased and then decreased as the temperature decreased and reached a peak at −10 to 0 °C. The microstructure analysis showed that as the number of freeze-thaw cycles increases, cracks appear and extend in the CFRBCA, hydration products gradually change from dense to loose, and the Ca/Si ratio increases. Through these experiments, the logarithmic relationship model between ultrasonic wave velocity and CFRBCA strength damage, which can better predict the strength loss caused by CFRBCA variation with freeze-thaw cycles, was established. The brick content is the key parameter affecting the durability of the freeze-thawed CFRBCA, and thus the brick slag content should be properly controlled in engineering applications.

Durability of Glass Fiber Reinforced Cement (GRC) Containing a High Proportion of Pozzolans

Glass fiber reinforced cement (GRC) is an excellent composite for architects and engineers because it can be molded to produce laminar panels or to create complicated designs. GRC is a fine concrete reinforced with alkali-resistant glass fibers at 3–5% per mass. However, fiber durability is limited because of the aggressiveness of the alkaline medium produced during Portland cement hydration (effect of portlandite). The objective of this study is to assess GRC with high Portland cement replacement with pozzolans (ground fly ash or a mixture of ground fly ash and sonicated silica fume) in order to reduce the corrosion of the fibers. The selected high-content pozzolan (60% replacement) composites were tested under different conditions: aging, drying–wetting, freezing–thawing, and chemical attack (ammonium chloride and sulfuric acid). The modulus of rupture and toughness were determined. Composite behavior showed that the samples with pozzolans not only better resisted aging, but also physical and chemical attacks, and specimens presented a better modulus of rupture and toughness than the samples prepared with 100% Portland cement (control specimens). Due to the good behavior in durability terms, the high pozzolan content GRC products are suitable in potential corrosive environments for sunscreens, drainage channels, cable trays, sound barriers, or pavements.