Early-age Properties of High-volume Fly Ash Concrete Mixes for Pavement: Volume 2

Abstract

High-volume fly ash concrete (HVFAC) is more cost-efficient, sustainable, and durable than conventional concrete. This report presents a state-of-the-art review of HVFAC properties and different fly ash characterization methods. The main challenges identified for HVFAC for pavements are its early-age properties such as air entrainment, setting time, and strength gain, which are the focus of this research. Five fly ash sources in Illinois have been repeatedly characterized through x-ray diffraction, x-ray fluorescence, and laser diffraction over time. The fly ash oxide compositions from the same source but different quarterly samples were overall consistent with most variations observed in SO3 and MgO content. The minerals present in various fly ash sources were similar over multiple quarters, with the mineral content varying. The types of carbon present in the fly ash were also characterized through x-ray photoelectron spectroscopy, loss on ignition, and foam index tests. A new computer vision–based digital foam index test was developed to automatically capture and quantify a video of the foam layer for better operator and laboratory reliability. The heat of hydration and setting times of HVFAC mixes for different cement and fly ash sources as well as chemical admixtures were investigated using an isothermal calorimeter. Class C HVFAC mixes had a higher sulfate imbalance than Class F mixes. The addition of chemical admixtures (both PCE- and lignosulfonate-based) delayed the hydration, with the delay higher for the PCE-based admixture. Both micro- and nano-limestone replacement were successful in accelerating the setting times, with nano-limestone being more effective than micro-limestone. A field test section constructed of HVFAC showed the feasibility and importance of using the noncontact ultrasound device to measure the final setting time as well as determine the saw-cutting time. Moreover, field implementation of the maturity method based on wireless thermal sensors demonstrated its viability for early opening strength, and only a few sensors with pavement depth are needed to estimate the field maturity.

High-volume Fly Ash Concrete for Pavements Findings: Volume 1

“…Based on the field test sections in Canton, Illinois, and complementary lab testing, the maturity method can successfully indicate the compressive strength of the in situ HVFAC pavement. Source: Baral, Roesler, and Fu (2021) In the lab or during a trial batch in the field, a maturity calibration curve must be constructed relating the compressive strength over time to maturity of the HVFAC. An example of a strength versus age for a HVFAC and control concrete (20% fly ash) is shown in Figure 26 for two patching mixes.…”

“…The noncontact ultrasound measurement device (Figure 28) developed by Tran and Roesler (2021) measures the energy of the leaky Rayleigh wave to determine concrete's final setting time in the field. The working principle of the noncontact ultrasound testing device (Tran and Roesler 2021) is described more in detail in the volume 2 report (Baral, Roesler, and Fu 2021). The evolution of the energy of the leaky Rayleigh wave over time for the concrete control and HVFAC mixes is shown in Figure 29.…”

“…The current characterization tests in ASTM C618 should continue to be run with the replacement of the loss on ignition (LOI) with the foam index test, which is outlined in this document and volume 2 (Baral, Roesler, and Fu 2021). The foam index test employed in this project does not exactly match the one described in ASTM C1827.…”

“…The evolution of empty area with number of drops of AEA addition for different times after stopping the shaking is shown in (b). Both figures use the same digital foam index test data.Source:Baral, Roesler, and Fu (2021)…”

“…Graph. Isothermal calorimetry results for a sample Portland cement with initial and final setting times of 3.3 hours and 6.5 hours, respectively.Source:Baral, Roesler, and Fu (2021)…”