Ecological, fresh state and long-term mechanical properties of high-volume fly ash high-performance self-compacting concrete

Abstract

In this work, the ecological efficiency, fresh state and long-term mechanical properties of high-volume fly ash (HVFA) high performance self-compacting concretes (SCCs) were evaluated. SCCs were prepared with 40–60% replacement of Portland cement by three fly ashes from two sources, with different finenesses. The rheological properties of the SCCs were evaluated by concrete workability tests. The efficiency of the fines to promote fresh state stability was also investigated. The compressive strength, modulus of elasticity and binder index were determined at 28, 91, 180 and 365 days. In addition, life-cycle assessment (LCA) analysis was performed to evaluate the influence of cement replacement by the fly ashes on the CO2 emission of concrete production. The results showed that cement replacement by fly ash reduced the viscosity and superplasticizer content of the SCCs, and improved their passing ability. The SCCs required a minimum surface area of fines of 120 × 106 m2/m3 of concrete to achieve fresh state stability. The finest fly ash obtained by grinding was the most efficient in promoting stability and resulted in the highest compressive strengths at all ages. The concretes showed significant compressive strength and modulus of elasticity increases up to 180 days. SCCs containing fly ash achieved a binder index of 5.8 kg.m−1.MPa−1 at 180 days and 5.6 at 365 days, lower than the 6.0 index of the reference at 28 days. The use of HVFA resulted in CO2-eq emissions (kg CO2-eq/m3 of concrete) and CO2-eq intensities (kg CO2-eq/MPa.m3 of concrete) up to 46 and 30% lower than the reference, respectively. Ground ash presented the best CO2-eq intensity indices, surpassing the additional energy spent to grind it.