Q. We are considering whether to bid to provide concrete storage tanks on a high-profile residential development project. The developer has opted to install a large septic system, rather than paying to hook up to the local waste water treatment system.
His decision has brought his development plan under the scrutiny of the local county sanitation department and opponents of the project. One of the requirements for the development's onsite treatment system is that pipe and tank connections must be free of leaks.
What standards can we provide the developer to help him assure the county engineer a quality connection will be the result?
A. ASTM Committee C-27 on Precast Concrete Structures recently approved a new standard covering this concern. C-1644-06, “Standard Specification for Resilient Connectors Between Reinforced Concrete On-Site Wastewater Tanks and Pipes,” provides guidance to the minimum performance and material requirements for connectors. This information is applicable to the connectors used on structures referenced in Specifications C 913 (Precast Concrete Water and Wastewater Structures) and C 1227 (Precast Concrete Septic Tanks).
The specification only covers the design, material, and performance of the connector. Field experience has demonstrated that a system's overall success also depends on properly selecting bedding and backfill, in addition to the care of the contractor's installation.
Nonetheless, the standard does provide the specifier assurance that resilient connectors meeting the testing requirements will provide a positive seal between the connector and the tank, and between the connector and the pipe in most applications.
Copies of the new standard specification are available for purchase at the ASTM Web site at www.astm.org.Determining Mix Design Adjustments
Q. We've just installed a new batching system at our ready-mix plant. After start-up we continued production using our old mix designs. After a few months, we noticed our 28-day cylinders are consistently breaking at higher compressive strengths. It seems that the new equipment has not helped us run smoother, but it has enhanced our quality.
We'd like to demonstrate to upper management that these higher breaks are part of a pattern. We'd like to suggest to our managers that we can economize our mix designs, without the risk of ruining any of the trust we've built with our customers.
What is our best approach to this problem?