The International Society for Concrete Pavements (ISCP) “STUDENT RESEARCH SPOTLIGHT” January 2022 is
Aniruddha Baral, Ph.D. Candidate, Department of Civil and Environmental Engineering-University of Illinois-Urbana-Champaign
Bio:
Aniruddha Baral is a Ph.D. candidate studying Construction Materials in the Department of Civil and Environmental Engineering at University of Illinois at Urbana-Champaign (UIUC). He earned his master’s degree and bachelor’s degree in Civil Engineering at University of Illinois, and Indian Institute of Technology Kanpur, respectively.
Aniruddha’s research field deals primarily with investigating sustainable
construction materials such as photocatalytic concrete,
concrete containing high supplementary cementitious materials,
and concrete made from municipal waste incinerator ash for pavement
and other structural applications.
The topic of his thesis is
“Hydration and air Entrainment of High-volume Fly Ash Concrete”.
Hydration and Air Entrainment of High-volume Fly Ash Concrete (HVFAC)
Research by:
Aniruddha Baral, Ph.D. Candidate-Construction Materials-Department of Civil and Environmental Engineering-University of Illinois at Urbana-Champaign– Email id: abaral2@illinois.edu
Replacing cement with fly ashes has been common practice for decades with the primary objectives being to reduce the concrete material unit cost, increase material durability, and improve sustainability. However, concrete with high fly ash content (replacement level > 30%) 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 higher setting times and lower strength gain rates. State agencies have limited the adverse early age properties of fly ash replacement by mostly limiting the fly ash replacement rates and tight specifications on fly ash properties. Although limiting fly ash replacement rate in concrete lowers the potential risk of early-age problems of fly ash concrete, it restricts the possible improved sustainability value and cost-benefit associated with high volume fly ash concrete. This research aims to develop a test for better quality control of fly ashes for air-entrainment, modification of HVFAC mix design to accelerate setting times and show the feasibility of using advanced monitoring tools such as non-contact setting time and maturity method for HVFAC pavement.
Digital Foam Index Test
The digital foam index test aims to improve the recently approved ASTM C1827 foam index test. The ASTM test involves adding a diluted AEA to a fly-ash cement mix sequentially and shaking it until the surface is entirely covered by a stable layer of foam. The digital foam index test uses a video camera to monitor the foam layer to better understand the fly ash air-entraining agent interaction.
CLICK EACH PHOTO TO ENLARGE: Figure 1: Digital foam index test set up
(a) consisting of a video camera, foam index container, and a laptop for data storage.
(b) A representative image of the foam layer is shown with the empty area manually annotated.
Accelerating HVFAC Hydration with Nano-limestone Replacement
Limestone is the most abundant material used in cement production and is also added as a filler material nowadays, e.g., Portland limestone cement. Even though limestone is generally considered an inert material, it can react with the aluminate phases and form monocarbonate and hemicarbonates, thus reducing the optimal gypsum content in the system. In general, class C fly ash has a negligible amount of calcium sulfate present, but it may have a significant amount of aluminate phases, which may lead to a shortage of sulfate in HVFAC. The lower amount of gypsum present in the under-sulfated HVFAC system causes a longer final setting time compared to a well-sulfated system. Limestone addition can help with accelerating the setting time of high-volume fly ash systems by reducing the optimal gypsum content. Moreover, the filler effect of limestone also accelerates the setting time based on its particle size.
Figure 2: CLICK TO ENLARGE: Effect of limestone replacement on the hydration heat flow rates of HVFA mixes.
Heat flow rates for nano-limestone replacement for Fly Ash 1 (class C) and Fly Ash 4 (class F) are shown in (a) and (b) respectively;
Heat Flow Rates for micro-limestone replacement for Fly Ash 1 and Fly Ash 4 in (c) and (d), respectively.
Field Test-Sec5on with HVFAC
CLICK TO ENLARGE: Figure 3: HVFAC Field test section
(a) with dowelled joints,
(b) example of embedded, wireless temperature sensors, and
(c) non-contact setting time prototype device.
Developing tools and methods that help engineers evaluate the early age concrete pavement properties, such as setting time and strength gain, are necessary to adopt new concrete mixes, such as HVFAC. In this project, two concrete pavement test sections were constructed, a high early strength concrete mix with 25% (control) and 40% replacement of cement with fly ash (HVFAC) along with monitoring of the concrete’s setting time, sawcut timing, and strength gain. A non-contact ultrasound device developed in my research group was used to estimate setting time by measuring leaky Rayleigh wave energy. Based only on construction personnel experience, saw-cutting for these mixtures was initiated too early and caused significant joint raveling, reinforcing the importance of in situ setting time measurement. The maturity method was successfully implemented with embedded wireless temperature sensors that rapidly and easily estimated the in-place compressive strength and improved opening time determination for concrete with high cement replacement levels.
ISCP would like to feature a “STUDENT RESEARCH SPOTLIGHT” each month, or every other month. If you would like to nominate a student, or if you are a student and would like to nominate yourself or a colleague, please send ISCP an email to: newsletter@concretepavements.org
STUDENT SPOTLIGHT: Each month, or every other month, a student will provide a 1-page illustrated abstract of the research they are currently conducting. This is a wonderful opportunity for the student, our ISCP Members, and technology/research transfer to our concrete paving industry.
Prior SPOTLIGHTS:
Inaugural December 2021: Katelyn Kosar, Phd Student-Department of Civil and Environmental Engineering-University of Pittsburgh (Pitt): www.concretepavements.org/2021/12/14/new-at-iscp-student-research-spotlight/