Fly ash and PLC: The right prescription
for Batson Children’s Hospital
Finding themselves in dire need of expansion, Batson Children’s Hospital in Jackson, Mississippi, initiated the construction of a new seven-story medical tower and an adjacent five-level parking garage. With concrete representing a significant portion of the structures, the use of sustainable materials in the high-performance mixes was paramount to the project team.
The concrete used in the project incorporated PLC and 20 to 30 percent fly ash to meet durability requirements for moderate sulfate resistance and chloride exposure. It also included strengths of 31,026 kPa (4500 psi) for the foundations, 34,473 kPa (5000 psi) for the elevated decks, and 41,368 kPa (6000 psi) for the structural columns. The mix was also designed to achieve a high early strength in the elevated decks to keep the project on schedule.
The hospital expansion project was completed on schedule in October 2020. All application-specific performance targets aimed at durability, permeability, and strength were consistently met with the PLC/fly ash mix designs, and the embodied carbon of the concrete was reduced by as much as 35 percent.
New low-carbon concrete developments
To meet increasing demands to reduce embedded carbon in building materials, some cement producers have developed new low-carbon concrete products that offer 30 to 100 percent less carbon emissions than ordinary concrete. Up to 80 percent less carbon is achieved primarily with lower CO2 intensive materials. For a fully carbon-neutral solution, the last 20 percent is reached through offsets, with certified carbon projects. Where conditions allow, the low-carbon concrete can integrate construction and demolition waste, which closes the material cycle completely.
Washington, D.C., and Boston, Massachusetts, have pledged to be carbon neutral by 2050. Every large building under construction in these cities is a flagship project which requires the structural performance of high-quality concrete, aligned with the most advanced sustainability certifications from LEED. With concrete representing up to 80 percent of the mass of these buildings, the shift to low-carbon mixes played a key role in their sustainability profile by saving more than 700 tons (635 tonnes) of CO2. This is equivalent to taking 140 cars off the roadways for an entire year.
Exceeding LEED Platinum status in Washington, D.C.
Georgetown University is deeply committed to reducing the carbon footprint of its built environment. With the school pursuing LEED v4 Platinum status for its new student residence hall near the U.S. Capitol, the project team worked to achieve high levels of sustainability in construction.
The fast-track construction of the 12-story building by John Moriarty & Associates required the completion of one post-tensioned concrete floor deck each week. The challenge was to come up with a sustainable high-performance concrete solution that would consistently hit a high early strength of 20,684 kPa (3000 psi) in two to three days and a specified strength of 34,473 kPa (5000 psi) at 28 days.
To meet the specified strengths in the time needed while reducing the embodied carbon, the project team worked with the university to develop a low-carbon, high early strength mix containing high levels of SCMs. The high-performance concrete performed up to speed by hitting the specified high early strength, reduced the embodied carbon of concrete by 40 percent, and made a strong contribution to achieving the goal of LEED v4 Platinum certification.
The photo caption to this story has incorrect information: the project One Dalton is located in Boston, Massachusetts – not Washington DC and it is LEED certified Silver, not platinum.
Thanks a lot for pointing that out. We have modified the caption of the photo.