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, for our International Society for Concrete Pavements (ISCP) Members, and for the transferring and sharing technology/research through our concrete paving industry.
The ISCP “STUDENT RESEARCH SPOTLIGHT” for September 2022 is Sumit Nandi, a Ph.D. candidate in civil engineering at Indian Institute of Technology Roorkee (Roorkee, India).
BIO:
Mr. Sumit Nandi is currently pursuing his Ph.D. degree in Civil Engineering under the supervision of Professor G.D. Ransinchung R.N. at Indian Institute of Technology Roorkee (IITR), Uttarakhand, India. He received his M. Tech. degree in Civil Engineering (Transportation Engineering specialization) from National Institute of Technology Agartala (NITA), Tripura, India, in 2017. During his M. Tech. study at NIT Agartala he was awarded the Post Graduate Gold Medal from the Department of Civil Engineering for academic excellence.
He is a student member of American Concrete Institute (ACI), American Society of Civil Engineers (ASCE) and Transportation Research Group (TRG) of India and a RILEM Young member. His research interests include pavement materials characterization, recycled aggregates, sustainable concrete paver blocks and concrete pavements.
TITLE:
Utilization of RAP for Development of Sustainable Concrete Paver Blocks Fabricated Using a Time-Controlled Dual-Source Compaction Technique
Gradual depletion of good quality natural aggregate reserves and restrictions on quarrying activities to preserve the natural topography of the environment has compelled researchers in the fields of construction materials to search for reliable alternative sources of supply. Although substantial efforts to explore the feasibility of alternative aggregate sources in the form of copper slag, steel slag, and recycled concrete aggregates have been put up, the production and availability of such recycled aggregates stand out to be very less for developing countries like India relative to other countries. Even if available, the transportation costs associated with the same are usually very high, especially for infrastructure development in hilly terrains. Given this scenario, reclaimed asphalt pavement (RAP) could serve as a potential recyclable aggregate source. RAP is a recycled material generated in large amounts when deteriorated asphalt pavements are milled or demolished for repair, rehabilitation, and reconstruction activities. According to the annual asphalt pavement industry survey, jointly conducted by the Federal Highway Administration (FHWA) and the National Asphalt Pavement Association (NAPA) on recycled materials and warm-mix asphalt usage, approximately 85.1 million tons of RAP remained stockpiled nationwide in the United States by the end of 2015.
For developing countries like India, a similar or even higher percentage of RAP is generated after every monsoon season, which finds its way to landfills or is stockpiled in open farms, creating ecological and environmental concerns.
Although RAP could be predominantly reused for hot mix asphalt mixes, much of it still remains unutilized, and hence, there is a growing interest among researchers and academicians to explore the possibility of using RAP as an alternative aggregate source in cement concrete pavement mixes. Successful utilization of RAP in the pavement industry can offer socio-economic and environmental benefits like safe disposal of an enormous amount of pavement solid waste, minimize the use of natural aggregate sources and pollution related to quarrying activities, and incur cost savings associated with the purchase and transportation of natural aggregates (on spot utilization). However, the main hurdle to implement the use of RAP for concrete pavement applications remains the presence of asphalt film adhered to the aggregates, which interferes with the bonding at the interface of cement mortar matrix and RAP aggregates and results in inferior strength characteristics for RAP-based concrete. In addition to the asphalt film, the presence of agglomerated particles (fine-RAP clusters) has been reported as another contaminant responsible for more than 70% reduction in concrete strength.
Sumit’s doctoral research aims to promote maximum utilization of RAP through its effective incorporation in special types of concrete pavement applications like concrete paver blocks (CPBs). Using RAP in its as-received state (with stiff asphalt coating, dust impurities, and agglomerated particles) and a higher proportion of coarse aggregates in the paver block mix design were some of the barriers tried to overcome during the study. The mix proportions formulated for CPB mix consisted of natural coarse and fine aggregates partially or fully replaced by an equivalent volume of the individual and combined fractions of coarse and fine RAP. Since CPB mixes are zero-slump or stiff in nature, utilization of RAP for these mixes using a design methodology that promotes the development of a dense microstructure seems promising.
Therefore, taking cognizance of the presence of agglomerated particles in RAP (which needs refinement) and the necessity to achieve a dense microstructure, the concrete specimens were fabricated by implementing a design methodology that included staged mixing of concrete ingredients and time-controlled dual-source compaction in layers.
The staged mixing approach (initial prewetting of aggregates followed by binder coating and final wet mixing) provided prolonged mixing time, giving chances of separating agglomerated RAP particles loosely bonded by aged asphalt film and even caused mechanical roughening of RAP aggregates to some extent. This creates windows for better chemical interaction between cement mortar matrix and RAP aggregate surface. Again, the primary motive behind implementation of a time-controlled dual-source compaction technique was to provide an additional chance to separate RAP agglomerates that may have escaped during the mixing stage by harnessing impact pressure and vibratory compaction energy from two different sources (vibratory hammer and table vibrator). It was observed that the adopted design methodology could successfully produce different classes of CPBs (with varying RAP proportions and cement content of 380 kg/m3), which manifested a great potential to be used for pavement applications having medium to very heavy traffic as per ASTM C936/C936M and IS 15658 standards. Even a better surface finish could be achieved with a higher proportion of coarse aggregates in the aggregate skeleton.
Presently, we are researching to optimize the RAP dosage for CPBs based on the effectiveness of different curing regimes. This has been taken up since precast products like CPBs, owing to their mass production and lack of indoor storage facilities, cannot strictly follow standard curing procedures and are either cured in the air or are subjected to a combination of water and air curing. It is envisaged that the outcomes of the ongoing research will help understand the possible utilization of RAP in the precast concrete industry from an economic perspective.
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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
ALL SPOTLIGHTS:
DECEMBER 2021—Inaugural: 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/
JANUARY 2022: Aniruddha Baral, Ph.D. Candidate-Department of Civil and Environmental Engineering, University of Illinois-Urbana-Champaign: www.concretepavements.org/2022/01/15/student-research-spotlight-jan-2022/
FEBRUARY 2022: Jordan Ouellet, Tech, BEng, MASc, PhD Candidate, Teaching and Research Assistant, University of Illinois at Urbana-Champaign: www.concretepavements.org/2022/02/26/student-research-spotlight-february-2022/
MARCH 2022: Sampath Kumar Pasupunuri, Ph.D. candidate, Pavement Engineering-School of Civil Engineering, University of Nottingham, UK: https://www.concretepavements.org/2022/03/31/student-research-spotlight-march-2022/
APRIL 2022: Anupam B R, Pursuing his doctorate-Indian Institute of Technology Bhubaneswar, India: https://www.concretepavements.org/2022/04/15/student-research-spotlight-april-2022
MAY 2022: Andréia Posser Cargnin, Ph.D. Candidate, Polytechnic School, University of São Paulo (São Paulo, Brazil): https://www.concretepavements.org/2022/05/09/student-research-spotlight-may-2022/
JUNE 2022: Charles Donnelly, Ph.D. Candidate, Department of Civil and Environmental Engineering, University of Pittsburgh (Pittsburgh, USA): https://www.concretepavements.org/2022/06/24/student-research-spotlight-june-2022/
JULY 2022: Amir Malakooti, Ph.D. Candidate, Department of Civil and Environmental Engineering, Iowa State University (Ames, Iowa, USA): https://www.concretepavements.org/2022/07/30/student-research-spotlight-july-2022/
AUGUST 2022: Haoran Li, Ph.D. Candidate, Department of Civil and Environmental Engineering, University of Pittsburgh (Pittsburgh, USA): https://www.concretepavements.org/2022/08/24/student-research-spotlight-august-2022/