Editor’s note: Despite the recent buzz about roller-compacted concrete (RCC), it is not a new material. In a recent editorial, CC Editor Bill Palmer noted that he had written an article about a Denver RCC project in 1986. This drew a response from TJ Peltz that Peltz Construction (Alliance, Neb.) had been the contractor on that project and is still a leader in RCC construction today. To learn what has changed in RCC over the past nearly three decades, Palmer interviewed Peltz Construction President Terry Peltz (TJ’s father). Although much has changed, the basics remain the same.
Terry Peltz: The Denver Intermodal Terminal project you wrote about was our first RCC job. Since then, our company and the original owners have constructed the majority of the major RCC paving projects in the U.S. Two things that haven’t changed since then are the thought that anyone can do RCC and the name Peltz. RCC looks simple but it requires experience to provide the owner with the quality he expects.
Bill Palmer: How have the materials changed since 1986?
TP: Some changes but nothing major. The strength of the mix remains highly dependent on the cement content and use of quality aggregates. Some designers are specifying fly ash and the use of more admixtures but our company has not seen the positives out weighing the negatives. Any savings in material cost with ash are typically neutralized by the need for additional equipment and labor. The fly ash can also be inconsistent, create color variations, be hard to control mix quantity, and may also retard the set, resulting in increased rolling time which can make it difficult to maintain time limits.
Typical aggregate gradations specified today are smaller on the top size: down from 1 to 11/2 inches to 5/8 to 3/4 inch. Non-gap-graded materials remain the norm but our company has also had great success with two-part aggregates consisting of ASTM #67 stone as the coarse aggregate and manufactured sand as the fines. We still don’t typically use any admixtures.
BP: Are you using different equipment today?
TP: Our core equipment is still much the same: ARAN continuous mix pugmills, ABG pavers (now owned by Volvo) with High Density Duo-tamp fixed screeds. Some major concrete suppliers are entering the market with centralized weigh batch pugmills and some specs are leaning toward this type of equipment, but from our experience, the mix is no better and production is being compromised. What has changed is that the equipment is more user-friendly (computerized) and there have been many safety improvements added over the years. Electronic automated steering has greatly increased the finished product.
BP: What has changed in your construction methods?
TP: For the larger paving projects, which have always been our focus, there has been very little change in the process. We still mix in continuous mix pugmills, haul in dump trucks (tandem or tri-axle or off-road), place with high-density pavers, and roll for final compaction and smoothness. The biggest difference is probably using white pigmented curing compound—exclusively. Another change is more use of material transfer vehicles to feed the paving machine. This allows the paver to run continuously, which improves rideability and production.
There are different thoughts on whether it’s better to pave short runs to eliminate longitudinal cold joints or pave long strips to eliminate transverse cold joints. Joints have always been a major concern with RCC, but using the right mix design and equipment and having experienced tradesmen has allowed us to reduce or eliminate many of the problems of the past. Our joints today are much better than those of the 1980s.
For us, paving wide, long strips, which eliminates many longitudinal joints, gives the best finished product to the owner and allows the highest production. We try to run continuously, matching mix production with feeding the machine to help with trucking. We run the paver at no more than 8 feet per minute with maximum density out of the machine which reduces the amount the roller is used—typically two or three passes with a static roller (no vibration). This results in much higher production rates and less surface grinding than for our competition. We also usually have multiple pavers on site to assist with changing widths and breakdowns, which is not common to the industry.
BP: Is RCC use going to increase over the next few years?
TP: Projects not conducive to RCC and projects constructed with inadequate equipment and personnel have continually provided setbacks to the promotion of RCC. Some people expect it to look like a troweled or broom finish and that will never happen. But today, with many more receptive engineers and owners, with more experienced contractors, and with more promotion from the national material organizations, we see a bright future for RCC.
For more information, please visit www.peltzco.com.