Final Report: Value-Added Use of Milled Mixed-Color Waste Glass as a Supplementary Cementitious Material in Environmentally Friendly and Energy-Efficient Concrete Building Construction

EPA Contract Number: EPD11070
Title: Value-Added Use of Milled Mixed-Color Waste Glass as a Supplementary Cementitious Material in Environmentally Friendly and Energy-Efficient Concrete Building Construction
Investigators: Balachandra, Anagi
Small Business: Technova Corporation
EPA Contact: Manager, SBIR Program
Phase: II
Project Period: May 1, 2011 through April 30, 2013
Project Amount: $225,000
RFA: Small Business Innovation Research (SBIR) - Phase II (2011) Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Green Buildings

Description:

The purpose of the work reported herein was to develop value-added use for milled (mixed-color) waste glass, as partial replacement for cement, in concrete. Another consideration in project was to use the qualities rendered by milled waste glass to concrete towards overcoming the drawbacks of using recycled aggregate (demolished concrete) in concrete.

Summary/Accomplishments (Outputs/Outcomes):

Based on experimental investigations of the structure and properties of concrete materials, it was found that waste glass, when milled to micro-scale particle size, undergoes pozzolanic reactions with cement hydrates, forming secondary calcium silicate hydrate (C-S-H). These reactions bring about favorable changes in the structure, including pore system characteristics of the hydrated cement paste and the interfacial transition zones in normal and recycled aggregate concrete.
 
Use of milled waste glass, as partial replacement of cement, produced significant gains in the resistance to moisture sorption and chloride permeation, durability under freeze-thaw and abrasive effects, dimensional stability and mechanical properties of normal and particularly recycled aggregate concrete. Milled waste glass also was found to suppress alkali-silica reactions. Unlike normal pozzolanic reactions, those involving glass do not reduce the alkalinity of cement paste; this is favorable to the chemical stability of concrete and its protection of reinforcing steel against corrosion. Field investigations confirmed the compatibility of recycled glass concrete with conventional concrete production and construction techniques, and verified the excellent performance of pavement sections made with recycled glass concrete after 2 years of natural weathering.
 
Numerical studies were conducted to predict the service lives of concrete pavements and bridge decks exposed to sulfate or freeze-thaw attack in different climatic conditions. Partial replacement of cement with milled waste glass in normal and recycled aggregate concrete produced significant gains in service life due to the improved resistance of concrete to the transport of moisture and deleterious ions.   
 
Recycling of waste glass in concrete can divert large quantities of the market-limited (mixed-color) waste glass from landfills for value-added use as partial replacement for cement, enable effective use of recycled aggregates in concrete, yield major cost and energy savings, and enhance the long-term performance, the life-cycle economy and the sustainability of concrete-based infrastructure systems.

Conclusions:

Manufacturing of cement, a key ingredient for the production of concrete, is responsible for 5–8 percent of the anthropogenic CO2 emissions, with production of each ton of cement resulting in emission of one ton of CO2 to the atmosphere. Besides, cement production is an energy-intensive process accounting for about 5 percent of the global industrial energy consumption.
 
Each year, about 50 percent of the total construction and demolition (C&D) waste produced (300 million tons), and about 77 percent of the total waste glass produced (12.2 million tons) are landfilled in the United States. Growing environmental concerns, rising energy costs and increasing tipping fees coupled with shortage of quality aggregates near construction sites encourage value-added recycling of the waste glass and concrete.
 
The recycled aggregate obtained from demolished concrete exhibits higher moisture absorption due to the old (porous) mortar clinging to its surface. This hampers effective use of recycled aggregate in new concrete which would have relatively high moisture absorption and thus drying shrinkage. The waste glass found in the solid waste stream has limited market value owing to its mixed color, increased degree of contamination and higher breakage percentage that limit its use towards production of new glass. Waste glass, on the other hand, has favorable chemical composition for use as partial replacement for cement in concrete. The favorable chemistry of waste glass can be used effectively towards production of concrete as far as the waste glass is milled to about the particle size of cement; the reactions of milled waste glass with cement hydrates occur largely during the active period of cement hydration. The resulting calcium silicate hydrate improves the pore system and the structure of hydrated cement paste as well as the interfacial transition zones in recycled aggregates and new concrete. The use of milled waste glass as partial replacement for about 20 wt. percent of cement in recycled aggregate concrete leads to effective reduction of moisture sorption and thus improvement of the dimensional stability, durability and mechanical properties of the resulting concrete. Similar benefits can be realized by using milled waste glass as partial replacement for cement in normal concrete. Major environmental, energy and economic benefits can be realized by diverting landfill-bound (mixed-color) waste glass for use as partial replacement for cement in recycled aggregate and normal concrete. The enabling role of waste glass towards value-added use of recycled aggregate in concrete adds to the environmental, energy and cost benefits of the practice.
 
A comprehensive experimental program was undertaken to study the effects of milled waste glass on the structure and properties of cement paste, mortar and concrete. The aggregates considered in concrete mixtures included recycled, virgin and 50:50 blends of recycled and virgin aggregates. Field investigations also were undertaken to verify the scalability of the practice and the concrete performance under natural weathering. Numerical studies also were conducted to assess the effects of recycled aggregate and milled waste glass on the service life of concrete-based infrastructure systems. Major findings and conclusions of this research are as follows:
 
  1. Replacement of about 20 wt. percent of cement will milled waste glass results in significant improvement of the structure of hydrated cement paste and interfacial transition zone. Pozzolanic reactions of milled waste glass with cement hydrates convert calcium hydroxide to calcium silicate hydrate, thereby producing a more stable chemical structure and a refined (and less continuous) capillary pore system.
  2. Milled waste glass, as replacement for about 20 wt. percent of cement, as significantly benefits the resistance of normal and especially recycled aggregate concrete to moisture sorption, which reflects on the refined and less continuous pore system in the presence of milled waste glass. The rate of water sorption and the cumulative sorption were reduced to about one-half by introduction of milled waste glass as partial replacement for cement. Milled waste glass proved to be more effective than Class-F and Class-C fly ash in these regards.
  3. An increase in workability (slump) of fresh concrete mixtures was observed when about 20 wt. percent of cement was replaced with milled waste glass. This effect was attributed to the relatively low moisture sorption of milled waste glass when compared with cement.
  4. Partial replacement of cement with milled waste glass lowered the volume of voids in hardened concrete. This reduction, which can be attributed to the pozzolanic reactions of milled waste glass, were comparable to those obtained with partial replacement of cement with Class-F fly ash, and better than those obtained using Class-C fly ash as partial replacement for cement.
  5. Mean compressive strengths of concrete materials incorporating milled waste glass as replacement for about 20 wt. percent of cement were comparable to those of control concrete materials (without milled waste glass) at 28 days of age. At 90, 156 and 300 days of age, the strengths of recycled glass concrete materials were higher than those of the corresponding control concrete materials at different water/cement ratios. The long-term gains in compressive strength is a typical feature of the pozzolanic reactions, which tend to occur when adequate quantities Ca(OH)2 become available upon hydration of cement. The significant gains in the long-term compressive strength of recycled aggregate concrete upon introduction of milled waste glass as partial replacement for cement point at the synergy of milled waste glass with recycled aggregate were notable. At 90, 156, and 300 days of age, partial replacement of cement with milled waste glass produced more gains in compressive strength than corresponding replacements of cement with Class-F and Class-C fly ashes.
  6. Beyond 28 days of age, replacement of about 20 wt. percent of cement with milled waste glass benefited the flexural strength of normal and recycled aggregate concretes made with different water/cement ratios. These benefits of milled waste glass were superior to those obtained using Class-F and Class-C fly ash as partial replacement for cement.
  7. The long-term split tensile strength of normal and recycled aggregate concretes benefited from the introduction of milled waste glass as replacement for about 20 wt. percent of cement. Milled waste glass performed similar to Class-F fly ash in normal concrete; in recycled aggregate concrete, milled waste glass produced superior gains in split tensile strength when compared with Class-F fly ash.
  8. At 90 days of age, the modulus of elasticity (chord modulus) of concrete benefited from replacing 20 wt. percent of cement with milled waste glass. Milled waste glass performed similar to Class-F fly ash and better than Class-C fly ash in this regard. The effects of pozzolanic reactions on the pore system characteristics of hydrated cement paste and the interfacial transition zone explain the benefits of milled waste glass to elastic modulus.
  9. Significant reductions of drying shrinkage in normal and recycled aggregate concrete were realized by replacing 20 wt. percent of cement with milled waste glass. This is a major achievement because excess drying shrinkage is a key hurdle against widespread use of recycled aggregate in concrete production. Milled waste glass reduce the drying shrinkage of concrete primarily through reduction of moisture sorption through capillary pores in hydrated cement paste and the interfacial transition zone.
  10. Chloride permeability of normal and recycled aggregate concretes dropped to about one-half upon replacement of 20 wt. percent of cement with milled waste glass. This effect of milled waste glass was superior to that of Class-F fly ash, which reduced chloride permeability by about one-third. The refined and discontinuous capillary pore system produced by the pozzolanic reactions of milled waste glass are key to the corresponding gains in resistance to chloride permeation.
  11. The favorable effects of milled waste glass (as replacement for 20 wt. percent of cement) on the resistance of concrete to moisture sorption benefited the durability of normal and recycled aggregate concretes under repeated freeze-thaw cycles.
  12. Significant improvements in the abrasion resistance of normal and recycled aggregate concretes was realized by replacing 20 wt. percent of cement with milled waste glass. These effects of milled waste glass were found to be comparable to those of Class-F fly ash.
  13. A thorough investigation of alkali-silica reactions (ASR) pointed at significant benefits of milled waste glass, as partial replacement for cement, in reduction of alkali-silica reactions with different aggregate types. The milled waste glass exhibited an innocuous behavior with major suppressing effects on ASR-related expansions. The fine particle size of milled waste glass promotes rapid pozzolanic reactions with cement hydrates and eliminates any potential deleterious long-term reactions involving glass. Scanning electron microscope investigations of ASR test specimens revealed a dense and uniform microstructure that did not exhibit any manifestations of ASR reactions.
  14. Unlike other pozzolans, milled waste glass did not reduce the pH of hydrated cement paste. This benefits the chemical stability and the protective qualities of recycled glass concrete against corrosion of embedded (reinforcing) steel.
  15. Numerical analysis of the service life of concrete pavements and bridge decks exposed to freeze-thaw and sulfate attack in different climatic conditions pointed at significant gains in service life of normal and recycled aggregate concrete systems realized by replacing about 20 wt. percent of cement with milled waste glass. These improvements result from the improved resistance of concrete to ingress of moisture and aggressive ions upon partial replacement of cement with milled waste glass.
  16. Field investigations confirmed the compatibility of recycled glass concrete with industrial-scale concrete production and construction techniques. Partial replacement of cement with milled waste glass produced concrete pavement sections with excellent performance under weathering effects (after 2 years of performance).

 

Supplemental Keywords:

concrete-based infrastructure, mixed-color waste glass, supplementary cementitious material, durability, impermeability


SBIR Phase I:

Value-Added Use of Milled Mixed-Color Waste Glass as a Supplementary Cementitious Material in Environmentally Friendly and Energy-Efficient Concrete Building Construction  | Final Report