The contractor last year filed a $21-million breach-of-contract lawsuit in state court against the supplier, Sacramento-based Elite Ready Mix, but terms of a November settlement were not disclosed.

Neither company could immediately be reached for comment.

A spokesman for Caltrans said that "the areas of highway with defective concrete were fixed" and that the project is set for completion this summer. Flatiron Dragados, the spokesperson added, has faced numerous complications including extensive weather-related excusable delays but remains ahead of its 2,000-day completion requirement.

What happened with those concrete shipments, however, is partly described in the lawsuit and other public records first revealed by Sacramento news outlet Abridged in December.

According to Flatiron's January 2025 lawsuit complaint, the concrete mix—which was contractually obligated to reach a compressive strength of 6,000 psi—was to be used in the stems and soffits of a viaduct frame at Elmhurst Street. Caltrans has strict requirements relating to material strength.

Faced with supply chain difficulties in obtaining Class F Fly Ash for the mix, Elite Ready Mix decided to instead use Class N natural pozzolan at its Bradshaw, Calif., plant without obtaining prior approval from Flatiron or Caltrans, the Flatiron lawsuit claimed.

The supplier initially responded to Flatiron's lawsuit in general terms, claiming that it had complied with the standard of care and industry standards, as well as all regulations and laws related to use and delivery of cementitious materials on Caltrans projects.

Class F fly ash is a byproduct of coal combustion that acts as a naturally occurring pozzolanic material, reacting with cement hydration products to improve strength and enhance durability in highway structures. Class N natural pozzolan performs a similar function but differs in chemical reactivity, particle characteristics and strength development rate. Different proportions and testing are often needed to meet exact project specifications.

But in a related breach-of-implied-warrantee cross-complaint filed by Elite Ready Mix against its pozzolan supplier Golden State Pozzolan, the concrete supplier spells out its thinking in more detail. It argues that Flatiron's design-build contract with Caltrans limited the amount of portland cement that could be used in project concrete and required that it be substituted for with cementitious materials that appeared on an approved agency list of materials and designated suppliers.

Elite: Materials Never Tested

While required to use only those materials, Elite Ready Mix argued that these were never tested by Caltrans "to consistently provide the necessary reactivity" needed for proper curing, strength and durability.

In a letter related to another project and quoted on the Abridged website, an Elite Ready Mix official explained that the use of the natural pozzolan on that project was needed “to ensure a steady, reliable product, without negatively impacting our customers’ schedules” and that [natural pozzolan sources] "are so close, they are often the most reliable during times with the worst supply chain issues.”

The 28-day compressive strength test revealed the problem, Flatiron stated. In July 2023 the contractor began demolition and replacement work on the bridge components. 

Neither Flatiron nor Elite Ready Mix has commented publicly on the resolution.

An attorney for Golden State Pozzolan said that his "client firmly disputes the allegations made by Elite Ready-Mix in its cross-complaint" and "our client’s response and evidence will be fully presented in court filings and proceedings."

Fly ash shortages have occurred as a result of the accelerating shutdown of coal-fired power plants combined with fragile long-distance logistics—conditions Elite Ready Mix cited for making the substitution.

Fly ash supply is now stable, according to industry analysts IMARC Group and ChemAnalyst, and substitute materials that achieve high performance strengths, including natural pozzolan, remain available.