Admixture tuning for high‐performance concrete for the production of novel precast pre‐stressed long‐span girders for highway overpasses

Abstract

The improvements observed in concrete technology in the last decades, namely the production of Portland cement CEM I 52.5 R, the development of third generation super-plasticizers, and the commercialization of additions with high pozzolanic properties, turned possible the development of new concrete products using high performance concrete (HPC). Nevertheless, their implementation in the production process of the conservative precast concrete industry is not yet a reality. In this paper, the development and characterization of a HPC exhibiting high workability in the fresh state and high compressive strength in hardened state is presented. This HPC aims at producing, on a competitive basis, precast pre-stressed long-span girders for highway overpasses. For this reason, the main goal was to maximize the abovementioned properties but using the constituents available at the concrete precast company supporting the research. A set of different commercial admixtures was gathered and their influence on both compressive strength and workability of concrete was experimentally investigated. Results show that the compatibility between the admixture and the cementitious material is of paramount importance. By selecting the best type of the considered super-plasticizers and by optimizing its dosage, it was possible to increase the workability from class S1 to S5 and, simultaneously, increase the compressive strength in circa 50%, up to 120 MPa, at 28 days of age.

Flexural behavior of slender long‐span precast prestressed high‐strength concrete girders

“…This defined the maximum bending moment and curvature of the cross section. Plots in Figure 16 show a sound agreement between experimental and analytical results within the complete curvature range, suggesting that the mechanical behavior of the hardened material, resulting from the mixture design published in, 14 is well described by the constitutive model recommended by Eurocode 2 13 and Model Code 2010 19…”

“…This defined the maximum bending moment and curvature of the cross section. Plots in Figure 16 show a sound agreement between experimental and analytical results within the complete curvature range, suggesting that the mechanical behavior of the hardened material, resulting from the mixture design published in, 14 is well described by the constitutive model recommended by Eurocode 2 13 and Model Code 2010. 19 Figure 17 depicts the deformed shape of specimen V2 for increasing load steps, obtained based on the records provided by the displacement transducers placed at the monitored sections, and interpolating between these.…”

“…As previously referred to, the mixtures' design is published in the study by Fernandes et al 14 For the current study, an economic concrete mix with mean compressive strength of circa 120 MPa and high workability (S5 class according to European Committee for Standardization 15 ) was adopted. The corresponding constituents and proportions are presented in Table 1.…”

“…At this point, it must be stressed out that, in this case, always considering the economic perspective, only raw materials already available at the precast plant were adopted. Therefore, the first part of the project was entirely dedicated at designing the concrete reference mixture, using only constituents available at the industrial plant, including the mechanical characterization of the adopted UHPC in the hardened state 14 . The present paper addresses the experimental characterization of the structural behavior of half‐scale specimens tested in bending up to failure.…”

Long‐term behavior of slender long‐span precast prestressed high‐strength concrete girders

“…For execution reasons, high workability (S5 class according to Reference 13) was required for the mixture in the fresh state. The mixture design and characterization in both fresh and hardened states of the concrete adopted to produce the new girders have been published in Reference 14.…”