ABSTRACT
In Eastern Canada, RCC usually contains entrained air for protection against damage induced by freeze-thaw cycles. While air entrainment improves RCC freeze-thaw durability, it also affects some RCC fresh and hardened properties. The research project aims at assessing the effects of air entrainment on the workability and strength of Roller Compacted Concrete (RCC) for dam construction. The experimental program was designed to evaluate the effect of air entrainment on workability (Vebe time) and compressive strength at 28-d and 91-d. The test program involves the production of 16 RCC mixtures having a constant W/B ratio of 0.75. It includes four non-air-entrained reference mixtures made with two types of binders (50% and 60% Class F fly ash) and two binder dosages (125 kg/m3 and 150 kg/m3). The air-entraining agent dosage for each of the four reference mixtures was adjusted to produce approximately 2%, 4%, 6%, and 8% air in fresh RCC. Overall, the workability (Vebe time) of the 16 mixtures ranged from 4 s to 38 s and the 91-d compressive strength ranges from 5 MPa to 19 MPa. The results show that increasing the air content systematically improves RCC workability. A general relationship was found between the workability (Vebe time) and the RCC volumetric paste content. In this relationship, the paste content is the sum of the volumes of the cement, water, and air per cubic meter of RCC. Adding more than approximately 3% air in nonair-entrained RCC systematically decreases the 28-d and the 91-d compressive strength. However, adding a small volume of air to a non-air-entrained RCC, bringing the final air content to less than approximately 4%, yields no strength loss and can even slightly increase the compressive strength at all ages. The production of a limited air void system in RCC increases the paste volume and, consequently, the workability of fresh RCC. This higher workability yields better compaction of fresh RCC, which, in turn, increases density and strength of hardened RCC. The plastifying effect of a low entrained-air volume (approximately 3% to 4%) can lead to a reduction of the total binder dosage without decreasing workability and strength. Experimental data shows that, for the RCC tested, air entrainment allows a reduction in the total binder content of 25 kg/m3 to 30 kg/m3 (15% to 20%).
