Evaluation of Sustainable High-Volume Fly Ash Concretes
Alejandro Duran-Herrera, Cesar Juarez, P Valdez, Dale P. Bentz
This article presents results of an experimental research work oriented to develop practical tools for the regional concrete industry, as well as to illustrate the potential benefits of the synergistic effect of an ASTM C 618 Class F fly ash (FA) produced in the Northeast of México and a polycarboxylate superplasticizer (SP) in the production of conventional concrete. The different concretes considered in this study were produced with water/binder (w/b) ratios between 0.5 and 0.6, mass substitutions of cement by FA between 15 % and 75 %, and a target slump of 20 cm. Sustainability is a key issue in this work; in this regard, the approach was to improve the ability of concrete to diminish its ecological impact, and is based on two main aspects: the highest water reduction through the use of an optimum SP dosage that resulted in reductions of 18%, 15% and 11% respectively for the reference mixtures of w/b=0.5, w/b=0.55, and w/b=0.6, which leads to the same reductions of cement; and the use of conventional to high volumes of FA. Key parameters in the fresh and hardened states were characterized to establish tools that can facilitate the use of these concretes in practice. Heat release and heat flow were analyzed through isothermal and semi-adiabatic calorimetry, illustrating that heat release per unit mass of cement is independent of w/b, contrasting with the time of setting results that vary by several hours between the three different w/b. The paper highlights the beneficial effect of the SP in terms of cement reduction and slump retention. Correlations between the FA substitution and slump loss, setting times, compressive strength and static modulus of elasticity (E) were established and they represent very useful potential tools for practical applications. Compressive strength developments up to an age of 56 d are also reported, as well as correlations between the modulus of rupture and compressive strength or splitting tensile strength at an age of 28 d.
, Juarez, C.
, Valdez, P.
and Bentz, D.
Evaluation of Sustainable High-Volume Fly Ash Concretes, Fuel, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=904699
(Accessed December 7, 2023)