About the author:
Kurt Chirbas is western regional manager for GeoTree Solutions. Chirbas can be reached at [email protected].
by Kurt Chirbas
undefinedCaltrans maintenance departments throughout California — the Golden State — are always striving to improve their highway maintenance programs in order to meet current and future regulations, increase safety during maintenance activities for the public, minimize worker exposure and improve long-term performance while reducing maintenance cost.
One specific product being used for the departments’ toolbox fixes for erosion control, soil stabilization, fire protection, vegetation control, invert culvert repairs and water quality issues is a geosynthetic concrete composite mat (GCCM) in accordance with ASTM D4439-18 Standard Terminology for Geosynthetics.
GCCM is an easy-to-use roll product that consists of a flexible, three-dimensional fiber matrix impregnated with cement that hardens when hydrated with water forming a durable abrasion resistance concrete protective layer that is used for soft and hard amor applications. The fiber matrix helps to reinforce the concrete and prevents crack propagation while providing a safe plastic failure mode. The PVC backing provides additional protection for water migration into subsurface soils.
Caltrans already has several locations throughout the state that have installed a specific GCCM called Concrete Cloth, which is supplied by GeoTree Solutions. The applications included: Relining a concrete drainage ditch, slope protection, vegetation control under guard rail, enhance quality runoff water and directing runoff water away from the highway with installations carried out either by Caltrans maintenance crews or by a Caltrans contractors.
Caltrans Maintenance Superintendent Craig Bettencourt for the Delta Region, Walnut Creek Ca. opted to use GCCM for a slope paving application under a bridge. The GCCM was selected because it would minimize worker exposure, minimize/eliminate disruption to traffic or pedestrians during installation, enhance the performance of the repair by eliminating it as a maintenance issue, increase hydraulic capacity and slope stability, improve storm water quality and it can be installed rapidly with Caltrans crews versus other traditional conventional methods for this project.
Shanelle Wilson, owner of Brishan Inc., a distributor in California, explains that when comparing GCCM to conventional methods (such as riprap, revetment mats, articulate blocks, shotcrete, or poured concrete) for repairing erosion, soil stabilization, drainage channel, enhance water quality, vegetation control and other maintenance repairs, GCCM offers other values including; lower overall cost, quick installation with minimum surface preparation, adaptable to different climates, environmental conditions, soils and/or surface conditions, and it can be used for multiple applications.
A recent GCCM installation for Caltrans was for a sloped paving area on an existing bridge on I-680/Concord Avenue in Walnut Creek California.
The GCCM was installed for erosion control, enhance water quality runoff, slope stabilization, maintaining a safe pedestrian walkway, aesthetics and to minimize/eliminate long term maintenance costs. The slope length was approximately 27 feet long with a gradient ranging from 3:1 to 1.5:1. The slope width was approximately 200 linear feet. The GCCM was deployed up the slope from the toe by unrolling the GCCM from a stationary spreader bar system.
Installation Process
The product is secured to the surface by either anchor trenches, spikes, percussion anchors, and/or concrete anchors to depending on existing surface conditions and the application.
For this project, the GCCM was fastened and secured to the ground using 10-inch metal spikes with washers at 6-foot spacing interval along the overlap seams to develop the tensile resistance for live and dead loads that would be applied to the GCCM. Caulk was applied to all overlaps panels and screwed together to develop a watertight and mechanical fastening seam. After deploying and securing the GCCM to the surface and terminating at the sidewalk (with an anchor trench or securing it an existing edge boarder along the walkway) and the bridge foundation at top of the slope, the GCCM was hydrated with a water hose supplied by a water truck.
The installation took a day and a half with a small maintenance crew without causing any disruption to pedestrian or road traffic while minimizing worker exposure to vehicle traffic.
Geosynthetic cementitious composite mats, and onshore/offshore RenewWrap structural strengthening products can be applied to culverts, sewers, slopes, berm and tank containment areas, and civil structure repairs such as pilings, bridges, wharfs, silos, tanks, buildings, monuments and towers.
