Hydration and air entrainment of fly ash concrete

Baral, Aniruddha

Permalink

https://hdl.handle.net/2142/117517 Copy

Description

Title

Hydration and air entrainment of fly ash concrete

Author(s)

Baral, Aniruddha

Issue Date

2022-07-28

Director of Research (if dissertation) or Advisor (if thesis)

Roesler, Jeffery R

Doctoral Committee Chair(s)

Roesler, Jeffery R

Committee Member(s)

• Lange, David
• Garg, Nishant
• Ley, M. Tyler

Department of Study

Civil & Environmental Eng

Discipline

Civil Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

fly ash, foam index, deep learning, limestone, calorimetry, hydration kinetics, setting time, maturity, non-contact ultrasound

Abstract

Replacing cement with a higher amount of fly ash can further reduce the concrete material unit cost, increase concrete durability, and improve sustainability. However, higher volume fly ash concrete (HVFAC) can adversely impact the fresh and early-age properties of concrete by decreasing its air content and delaying the hydration reactions, which can lead to longer setting times and lower strength gain rates. This thesis develops tools and material solutions for improving HVFAC air entrainment control, accelerating setting times, and monitoring concrete setting time and strength gain in the field. To increase test repeatability and minimize operator error associated with the traditional foam index test, the digital foam index test (D-FIT) was developed. For the D-FIT, a series of videos were acquired of the evolving foam layer through sequentially adding higher amounts of air-entraining agent (AEA). A deep learning-based computer-vision technique quantified the empty areas over time to characterize the fly ash-cement and AEA interactions. The amount of AEA required to produce a metastable foam was defined as the foam stability dosage. The AEA addition required to achieve a foam layer covering the entire container surface beyond the foam stability dosage was called the foam efficiency dosage. The foam index is the summation of the foam stability and foam efficiency dosage. The vinsol resin-based AEA foam efficiency was higher than the sulfonate–based AEA, but the foam stability dosage was greater for the sulfonate–based AEA. To accelerate the setting times of HVFAC, various replacement levels of cement with micro-and nano-limestone were explored for mixes with or without chemical admixtures. Limestone replacement accelerated the setting times with nano-limestone being more effective than micro-limestone because of its higher surface area. Both limestone types acted as nucleation sites for accelerated CSH precipitation. The addition of water-reducing admixture or superplasticizers increased the setting time of HVFAC. By replacing 5% of cement with micro limestone in HVFAC mixes with the same chemical admixture decreased the setting times. XRD tests showed HVFAC samples with chemical admixture and 5% micro limestone replacement had higher portlandite and ettringite content than HVFAC mixes containing chemical admixtures and no micro limestone. These hydration phases suggested the chemical admixtures were adsorbed by limestone. A non-contact ultrasonic device was used to estimate HVFAC setting time in the field by measuring leaky Rayleigh wave energy transmission along with the maturity method for in-place strength estimation. Two concrete pavement test sections were constructed, a high early strength concrete mix with 25% (control) and 40% replacement of cement with fly ash, for monitoring of the concrete’s setting time, sawcut timing, and strength gain. The field setting time of the control mixture measured 4.2 hours, which was shorter than the lab isothermal calorimeter estimate of 5.4 hours at 22C. The HVFAC mixture had a lab setting time of 14 hours, which was even longer than the control and would need acceleration for future field applications. Field saw-cutting for these two mixtures was initiated too early and caused significant joint raveling, reinforcing the importance of in situ setting time measurement for initiating field construction activities. The maturity method was successfully implemented with embedded wireless temperature sensors that rapidly and easily estimated the in-place compressive strength at early ages for HVFAC.

Graduation Semester

2022-12

Type of Resource

Thesis

Copyright and License Information

© 2022 Aniruddha Baral

Owning Collections