Paving the Way for More Durable and Sustainable Cements: Castle Rock Construction Company of Colorado


Sustainability continues to grow in significance as environmental stewardship is integrated into all elements of transportation design and construction.


The Challenge

As a recognized leader in promoting a healthy environment, Colorado issued its first climate action plan in 2007 for reducing greenhouse gas emissions. This plan—developed in response to the governor’s order to mitigate global warming concerns—directed state agencies to achieve a 20% and 80% reduction in greenhouse gas emissions by 2020 and 2080, respectively.

The number of vehicle miles driven by Coloradans increased by 69% from 1990 to 2004—the third fastest growth rate in the nation. With an estimated population increase of 47% by 2040, Colorado was facing high demand for increased mobility throughout the state.

Based on growing population trends and plans for new and improved road networks, the transportation sector was projected to account for about 33% of the state’s carbon dioxide emissions. To help meet the goals of the state’s climate action plan, Colorado was searching for innovative solutions to reduce the environmental impact of construction activities.


In response to the call to action for more ecologically friendly construction practices, Castle Rock Construction Company and Holcim collaborated with the Colorado Department of Transportation (CDOT) on the development of a new “green concrete” paving specification to help lower the carbon footprint of concrete with no compromise in quality and long-term durability.  

Adopted in 2008, the new CDOT specification allowed carbon-reducing alternatives to ordinary portland cement (OPC), such as portland-limestone cement (PLC) and fly ash, to be used in concrete paving projects. PLC contains between 6% and 15% limestone and has equivalent performance to OPC. With up to 15% of clinker replaced by limestone, PLC reduces carbon dioxide emissions by up to 10% in cement production. PLC used in combination with supplementary cementitious materials, such as fly ash, further reduces the carbon footprint of the built environment.

“Based on our innovative approach to product development and extensive testing, we were confident that PLC would provide the same level of performance as OPC in terms of concrete workability, set time, durability and strength development, while making a significant contribution to the state’s sustainable construction goals,” said Brooke Smartz, senior market manager of sustainable products for Holcim.


In May 2008, Castle Rock Construction used a concrete mix containing Holcim’s brand of PLC and 20% fly ash for the reconstruction of seven miles of pavement on U.S. Highway 287. The concrete achieved an average 28-day flexural strength of 695 psi, surpassing CDOT’s requirements of 650 psi.

Since this first project, Castle Rock Construction has used PLC in all their infrastructure paving work (over 600 lane miles). This includes the highway to Denver International Airport, which was recognized with a Triad Award from Public Works magazine for outstanding innovation and sustainability in using PLC. According to Ralph Bell, CEO of Castle Rock Construction, other notable megaprojects include 1.5-million square yards of concrete for 12 miles of express lanes on U.S. Route 36, and 1.2-million square yards of concrete for 12.5 miles of new express lanes on Colorado State Highway 470.  

“We have partnered with Holcim on more than thirty projects over the past decade, and Envirocore PLC has been an integral part of our intense effort to improve the quality and rideability of more than 600 lane miles of concrete pavement in Colorado,” said Bell. “Even more impressive has been the commitment, leadership and technical expertise put forth by the Holcim support teams, which are the best professionals our company has worked with in the industry.”

In the past decade, Castle Rock Construction has used more than 277,000 tons of PLC to build more than 250 lane miles of concrete pavement in Colorado. The resulting reduction in carbon dioxide emissions is equivalent to taking more than 2,700 cars off the state’s roadways, which is a tremendous contribution to reducing the carbon footprint of the transportation sector and helping Colorado meet its sustainable construction goals.