In the fall of 2022, the construction of Waco ISD’s replacement high school began. The new 370,000 square foot building is located on the same site as the existing 60-year-old facility. Besides the expected challenges of building a replacement school on a tight site, the project team encountered a very significant cost impact for fly ash, one of the concrete mix ingredients. None was available. To minimize a schedule delay, the Construction Manager At-Risk (CMAR) recommended the design team approve a 100% cement mix for the concrete, a very traditional approach, to resolve this issue. At the same time, cement prices were at an historic high. This change had a significant impact on the cost of construction. With two more projects beginning, the architect and consulting team began investigating other options for concrete mixes.
The architect approached the school district with a proposed internally cured concrete mix design that could be used on the upcoming school projects, Kendrick Elementary School and South Waco Elementary School. The architect also introduced the concrete consultant that they had been working with to help Waco ISD and the construction teams learn about ways to use this new concrete mix and its potential benefits. District leadership discussed these benefits, which included a reduced reliance on imported fly ash and cement to reduce cost, reducing the amount of water used during placement and the amount of time needed for curing. These benefits, as discussed, would allow the work to proceed more efficiently.
Waco ISD District leadership and the Board of Trustees supported investigation of this new technology and its benefits, with the condition that local suppliers and contractors be able to propose on the work. Understanding that there was considerable resistance to change from local contractors and ready-mix companies, the architect and structural engineer, the concrete consultant, and the district developed a plan for outreach and education to the local contracting community. The first step in the outreach plan was the mockup event, which was necessary to qualify the contractors to propose on the concrete for the upcoming bids for the two elementary school projects.
In the fall of 2023, all was ready at the mockup site at the Waco ISD Maintenance Facility. Three 20’ x 20’ x 4” forms had been built for testing of three different admixtures. Three different ready-mix suppliers were engaged to provide the cement and aggregate. Trucks were scheduled to arrive every 45 minutes. Finishers and concrete polishing companies were on site to see and take part in this new process. One concrete pumping truck was on site, ready for trucks to arrive. The local news channel was there along with the newspaper and the Associated General Contractors representative. All of the CMARs working for Waco ISD were also present.
The three test slabs were completed, though the pump truck driver refused to pump the mix halfway through the first truck, insisting that it would clog his machine. The ready-mix trucks were late and the drivers were adding water on the way to the test site, which altered the mix design. Contractors were giving conflicting direction to the pump truck driver and the concrete truck drivers. Though the planning team spent a great amount of time on the technical requirements of this mockup, we did not take into account human behavior and resistance to change. A great deal was learned on this day.
After the discouraging outcome of the mockup event, the architect, consultants and the district decided to hold a town hall meeting to hear the concerns and ideas from the local community. It was held at the Waco ISD Operations facility and many of the same people and companies that attended the mockup were in attendance. Concerns of the community and the actual people who would be providing and installing this new material were expressed. Lessons learned from across the nation were shared with the group and myths were verbalized so that they could be addressed. After the meeting, one of the local CMARs agreed to take the lead in implementing a mockup event at his construction yard. This was a turning point in favor of the new technology.
With the CMAR’s leadership and relationships with the subcontractors and suppliers, the next mockup was successful. Several more mockups were performed at the CMAR’s site and they, along with their subs and suppliers, became convinced that it could work for Kendrick Elementary School. The team finally had a way forward using internally cured concrete, no fly ash, 20% reduced cement and reduced water, and potential for schedule compression.
As of September of 2024, all of the structural concrete for Kendrick Elementary School is complete and the project is 4 to 6 months ahead of schedule. This process has yielded a higher quality concrete and polished finish than any other Waco ISD project, along with reducing water use and carbon impact.
This was not an easy process. There were many issues along the way that required problem solving and support from everyone on the team from the Vice President of the CMAR, the ready-mix company and their drivers, pump truck operator, concrete placers and finishers, concrete polishing company, admixture provider, architect, structural engineer, material testing company and the District. It took everyone to make this goal of higher quality and lower cost to happen.
Waco ISD, through the leadership of their architectural partner, was educated on the benefits of internally cured concrete. These benefits included decreasing the carbon impact of the project, reducing water usage, and improving the quality of the final product for lower cost than the traditional concrete design. As stewards for the stakeholders of Waco ISD, the District is committed to exploring innovations that are sustainable and educating our local contractors. Together, we can control cost, maintain quality and make a positive impact on our community.
“Do the best you can until you know better. Then, when you know better, do better.”
Maya Angelou
