Embodied energy refers to the total energy consumed during a material's lifecycle, including extraction, manufacturing, and transportation. Fly ash is a waste byproduct from coal-fired power plants. Using it to replace a significant portion of Portland cement in concrete directly reduces the material's embodied energy, as cement production is an extremely energy-intensive process. This strategy, known as using supplementary cementitious materials (SCMs), is a primary method for lowering the carbon footprint and embodied energy of new construction. The other options primarily address operational energy, not embodied energy.

A. External shading: This strategy reduces solar heat gain, which lowers the building's cooling load and saves operational energy, not the energy embodied in the building's materials.

C. Aluminum sliding window: The production of aluminum is highly energy-intensive, giving it one of the highest embodied energy values among common construction materials. It is not an energy-saving choice in this context.

D. Waterproofing with SRI of 84%: A high Solar Reflectance Index (SRI) indicates that the material reflects solar heat effectively. This reduces cooling needs, saving operational energy, but does not relate to embodied energy.

1. Massachusetts Institute of Technology (MIT) OpenCourseWare. (2005). 1.018J / 7.30J / 10.021J / 1.963J Ecology I: The Earth System, Lecture 19 - Industrial Ecology and Life Cycle Assessment. Section on "Life Cycle Assessment of Concrete." This courseware explains how using industrial byproducts like fly ash in concrete reduces environmental impact and embodied energy. Available at: https://ocw.mit.edu/courses/1-018j-ecology-i-the-earth-system-fall-2009/resources/mit1018jf09lec19/

2. Glavinich, T. E. (2008). Contractor's Guide to Green Building Construction: Management, Project Delivery, Documentation, and Risk Reduction. John Wiley & Sons. Chapter 10, "Site and Building Envelope," distinguishes between embodied energy (related to materials like fly ash concrete) and operational energy (affected by shading and high-SRI surfaces).

3. Ochsendorf, J. (2013). Sustainable Engineering: Embodied Energy. University of Cambridge. This academic resource details the concept of embodied energy, highlighting that cement production accounts for 5-10% of global CO2 emissions and that replacing it with materials like fly ash is a key reduction strategy. It also lists aluminum as a material with very high embodied energy.