SYNTHESIS OF CEMENTITIOUSLY BONDED AGGREGATES

Open Access
Author:
Boyce, Joshua Merrell
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 18, 2008
Committee Members:
  • John Richard Hellmann Jr., Thesis Advisor
  • Barry Earl Scheetz, Thesis Advisor
Keywords:
  • cement
  • chemical bonding
  • proppants
  • AlPO4
Abstract:
Increasing material costs and environmental concerns surrounding greenhouse gas emissions have necessitated research into new proppant materials and manufacturing techniques. With bauxite and energy prices rising, there is a growing need for proppants manufactured using inexpensive raw materials and low temperature processing. Low temperature chemically bonded industrial by-products were investigated as sources to fabricate proppants with strengths comparable to sintered aluminosilicate proppants (100 MPa in diametral compression). Aluminum phosphate (AlPO4) derived proppants showed a maximum diametral compressive strength of 24 MPa. Strength evolution was shown to be a function of processing correlated to the evolution of the cristobalite polymorph of AlPO4. Hydrothermal processing and high temperature processing (to 1400 ºC) resulted in further cristobalite evolution and tailorable microstructures, but no increase in strength. When repeated efforts to suppress cristobalite formation failed, phosphate bonding efforts were abandoned in favor of portland-based cementitious systems. Strength enhancement of portland based systems was achieved via processing (pressure application as well as macro-defect-free processing) and chemistry adjustment using common pozzolanic materials (silica fume, fly ash, blast furnace slag, and metakaolin). Scaling of ball-on-ring strengths shows that proppants fabricated using the chemical bonding techniques utilized can meet or exceed the strength of commercially available sintered aluminosilicate proppants.