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Final Report: An Alternative Concrete Chemistry with Significantly Enhanced Durability, Sustainability, Economy, Safety and Strength

EPA Contract Number: EPD17021
Title: An Alternative Concrete Chemistry with Significantly Enhanced Durability, Sustainability, Economy, Safety and Strength
Investigators: Balachandra, Anagi
Small Business: Metna Co.
EPA Contact: Richards, April
Phase: II
Project Period: March 1, 2017 through February 28, 2019 (Extended to September 30, 2019)
Project Amount: $300,000
RFA: Small Business Innovation Research (SBIR) - Phase II (2016) Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Building Materials

Description:

A new class of sustainable hydraulic cements was developed, which are distinguished by the primary aspect of their processing. These hydraulic cements offer significant advantages over conventional Portland cement in terms of carbon footprint, energy content, performance, cost, and safe use of industrial byproducts. The distinct approach to processing of these hydraulic cements allows for expanding their chemistry and selection of raw materials. Some hydration mechanisms considered included through-solution polycondensation of alkali aluminosilicates, and formation of more stable binders from the metastable phases of cement. The approach adopted for processing of hydraulic cements enables the use of diverse byproduct and natural primary raw materials. The byproducts considered were rich in aluminosilicates, and included metallurgical slags, biomass combustion ash, landfilled coal ash, mine tailings, and the brick constituent of construction & demolition wastes. Abundant aluminosilicate- and carbonate-rich natural materials were also evaluated, including limestone, clay, and igneous rocks (granite, etc.). Besides these primary raw materials, supplementary constituents were also used to enable activation of and compounding with the primary raw materials.

The sustainable hydraulic cements were developed to meet performance-based standard requirements for hydraulic cements, and also to act as the major constituent in blended cements that meet relevant standard requirements. Given the prevalence of industrial byproducts in formulation of the new hydraulic cements, special attention was given to their safety for general infrastructure applications.
 
Fundamental investigations were undertaken in order to provide insight into the structure of hydraulic cements, and their hydration mechanisms. Quantitative analyses were made in order to evaluate the advantages offered by the new hydraulic cements in terms of carbon footprint, energy content, cost and performance.
 
Significant efforts were devoted to scale-up of the production process of hydraulic cements. For this purpose, a comprehensive experimental program was designed and implemented in order to optimize the processing condition and develop empirical models that guide scale-up of the production process.
 
Advanced mix design techniques were employed for effective use of the new hydraulic cements towards production of concrete materials. Experimental investigations were conducted in order to evaluate the mechanical, physical and durability characteristics of the concrete materials. The results were used to identify the performance advantages of these concrete materials versus conventional Portland cement concrete. Field demonstration projects were conducted in order to verify compatibility of concrete materials incorporating the new hydraulic cements with industrial-scale concrete production and construction methods.

Summary/Accomplishments (Outputs/Outcomes):

It is possible to transform abundant industrial byproducts and natural raw materials into hydraulic cements without resorting to excessively high temperatures. These hydraulic cements have about 75% less carbon footprint and energy content, and their production cost is about half that of Portland cement. The weathering resistance and chemical stability of the new hydraulic cements magnify their sustainability and cost benefits when evaluated from a life-cycle point of view. The new hydraulic cements meet the performance-based requirements for general-used hydraulic cements. They also suit utilization as the primary constituent of blended cements. The approach to processing of the sustainable hydraulic cements developed in the project is scalable. These cements actually benefit from scale-up which improves their quality and rate of product. The new hydraulic cements are compatible with the procedures developed for design of Portland cement concrete mixtures. Concrete materials incorporating the new hydraulic cements can be produced using common industrial-scale methods of concrete production, and are compatible with the prevalent methods of concrete construction. The physical, mechanical, barrier and durability characteristics of concrete materials prepared with the new hydraulic cements match or surpass the corresponding properties of Portland cement concrete.

Conclusions:

  • It is feasible to transform abundant byproduct and natural materials into hydraulic cements that meet standard requirements via input of mechanical energy in the presence of relatively small concentration of supplementary materials that complement their chemistry and/or facilitate their mechanical activation.
  • The cement chemistries considered for processing via input of mechanical energy include alkali aluminosilicates and carbonates. Activation via disturbing the crystalline structures as well as chemical compounding under input of mechanical energy are the prevalent mechanisms in transformation of the blends of raw materials into hydraulic cements.
  • Diverse raw materials suit transformation into hydraulic cement, in the presence of supplementary materials, via input of mechanical energy. The primary byproduct raw materials evaluated for this purpose include metallurgical slags, mine tailings, landfilled coal ash, and the brick constituent of construction & demolition waste. These industrial byproducts were used as aluminosilicate precursors (some of which also include alkali or alkaline earth metals). Some abundant natural raw materials used in the process included sedimentary rocks (limestone), clay, and different igneous rocks (e.g., granite). These natural materials were used either as sources of aluminosilicates (with or without alkali metals) or carbonates.
  • Some supplementary materials used successfully in formulation of hydraulic cements for processing via input of mechanical energy included sodium carbonate, sodium sulfate, sodium hydroxide, potassium hydroxide, gypsum, lime, and quick lime.
  • The mechanically processed hydraulic cements based on alkali aluminosilicate chemistry are effective in stabilizing any heavy metals constituent of the aluminosilicate-rich industrial byproducts used as primary raw materials in their processing.
  • The mechanical approach to processing of hydraulic cements developed in this project is scalable, and actually benefits from scale-up that raises the intensity of mechanical energy input via impact. At any scale, measures that raise the intensity of mechanical energy input enhance the efficiency of the process and the end product quality.
  • While our current state of understanding the transformation of raw materials into hydraulic cements via input of mechanical energy is not adequate for theoretical simulation of the process, the semi-empirical models developed in the project can guide further scale-up of the process for industrial implementation.
  • Conventional and advanced methods of Portland cement concrete mix design are applicable when the new hydraulic cements replace Portland cement; the relationship between water/cement ratio and strength needs to be adjusted when using the sustainable hydraulic cements developed in the project.
  • High-performance concrete materials matching or surpassing the mechanical, physical, barrier and durability characteristics of Portland cement concrete can be prepared with the sustainable class of hydraulic cements developed in the project.
  • Conventional methods of industrial-scale concrete production and field construction suit concrete materials prepared with the new class of hydraulic cements.
  • Guidelines were developed for implementation of the mechanical approach to processing of sustainable hydraulic cements in a continuous mode of operation that facilitates industrial-scale implementation.
  • The optimum approach to transformation of the more inert raw materials (e.g., crystalline rocks and soils) into hydraulic cements may require exposure of raw mateirals to moderately elevated temperatures to supplement input of mechanical energy.
  • Quality control procedures were developed to facilitate production of the sustainable hydraulic cements to reliably meet standard requirements and to reach their potential in terms of sustainability, economy and production throughput.
  • The new class of hydraulic cements promise to reduce the carbon footprint and energy content of normal Portland cement by about 75%, and lower its product cost by about 50%. The potential to tailor existing cement manufacturing plants towards production of the new hydraulic cements further add to their market appeal.

Commercialization

market adoption of the new class of hydraulic cements developed in the project. The new class of hydraulic cements can be used in the mainstream concrete construction projects either as full replacement for Type I Portland cement or in blended cement where the new hydraulic cements are used together with a minor dosage of Type I Portland cement.

The prospects for high-impact market transition of the technology benefit from the potential to convert existing cement manufacturing plants for production of the new hydraulic cements, and major reduction of the capital investment in new plants dedicated to production of the new hydraulic cements. The option of tailoring existing cement manufacturing plants towards production of the new hydraulic cements would benefit from the potential for continued use of the primary raw materials currently used in production of normal Portland cement.
 
While many alternative hydraulic cement chemistries have been proposed and developed, the reliance on raw materials with limited and/or local availability has mitigated their widespread market acceptance. The robust chemistry of the new hydraulic cements allows for the use of locally (and globally) abundant raw materials for their production, thus removing a key obstacle for successful market transition.
 
Cement industry is highly risk-adverse because there are major liabilities associated with malfunction of the hydraulic cement used in concrete construction, and also because of the high capital intensity of the industry. This reality should be considered in efforts aimed at accelerated market transition of the new hydraulic cements. Validation of the statistical consistency of the new hydraulic cements and demonstration of their reliability through implementation of field demonstration projects are among the measures that need to be taken to build trust in the technology among the cement industry. Emphasis on the sustainability advantages of the technology would also be important in efforts to address the risk-adverse nature of the cement industry understanding the pressure on the industry to reduce their significant carbon footprint and energy use.
 
The sustainable hydraulic cements have been developed in this project to meet the performance-based standard requirements for hydraulic cements that suit mainstream (general use) concrete construction applications. Performance-based standards thus provide a natural basis for market transition of the technology. While performance-based standards are now available in the United States and across the globe, their actual market adoption varies from region to region. Standards for blended cements, on the other, have been adopted broadly across the globe (and in the United States). These circumstances would rationalize initial market introduction of the technology in certain regions as the primary component of blended cement. In the long term, however, performance-based standards should be viewed as the primary basis for transition of the new hydraulic cements to concrete construction markets.
 
The theoretical and semi-empirical models developed in the project would provide key guidance towards industrial-scale implementation of the new hydraulic cement production in a continuous mode of operation that is vital to their successful adoption by cement manufacturers.
 
The global trend towards integration within the cement industry has led to the creation of a limited number of global firms that account for a major fraction of cement production capacity. These firms also possess significant resources for scaled-up validation and field demonstration of alternative hydraulic cement chemistries, which can facilitate implementation of steps that can move the technology from its current state of development towards market transition. Efforts have been launched to make effective use of these resources for accelerated commercialization of the technology.
 
The ability to insure projects utilizing the new class of hydraulic cements is critical to their market adoption. Insurance companies have always been considered to be even more conservative than consulting engineers. While the untried and unproven status of alternative cements for concrete still exists, insurance companies also understand that the nature of risk has changed. Environmental awareness and the need to shift to a low-carbon economy mean that the weight of different factors in providing an overall risk profile for construction has changed substantially. Insurance companies are realizing that any business risk could be balanced by the probability that alternative products replace ordinary Portland cement, and they need to maintain their market share by understanding of the rise profile. Similar to consulting engineers and architects, there is an initial opportunity for insurance companies to grow their business through innovation.


SBIR Phase I:

An Alternative Concrete Chemistry with Significantly Enhanced Durability, Sustainability, Economy, Safety and Strength  | Final Report

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