19-11-2012, 04:35 PM
BEST PRACTICES MANUAL
PRACTICEMANUAL.pdf (Size: 1,009.65 KB / Downloads: 167)
Introduction
This manual provides guidance on material selection,
manufacturing techniques, testing and installation to
attain structurally sound, watertight precast concrete
septic tanks and related components for on-site
wastewater treatment systems. It is not intended for
use as a regulatory code or minimum design standard,
but rather as an aid to manufacturers, engineers,
contractors and owners.
This manual will be most effective when used in
conjunction with a complete review of local codes
and design considerations before designing or
manufacturing any on-site wastewater treatment tank
or system.
It is impossible for a manual of this type to be all
inclusive, and the recommendations are not intended
to exclude any materials or techniques that will help
achieve the goal of producing structurally sound and
watertight precast concrete tanks. Attention to detail,
appropriate materials, proper training of workers and
quality control throughout a repeatable process will
ensure that the concrete tanks meet the needs of
specifiers, contractors and owners while protecting the
environment.
Structural Design
Loading Conditions
A properly designed precast concrete on-site
wastewater treatment tank must be able to withstand
a variety of loading conditions, which vary during
manufacture, installation, testing and service. Tanks
must be designed to withstand these loading conditions
with rational mathematical design calculations
performed by a qualified professional engineer or by
proof load testing in accordance with ASTM C1227,
“Standard Specification for Precast Concrete Septic
Tanks.”
Consider the following in the design:
• Surface surcharge
• Concentrated wheel loads
• Lateral loads
• Presumptive soil bearing capacity
• Buoyant forces
• Connections and penetrations
• Point load
Design precast concrete tanks for on-site
applications in accordance with one or more of the
following applicable industry codes and standards
or as required by the authority or authorities having
jurisdiction:
Concrete Thickness
The concrete thickness must be sufficient to meet
minimum reinforcement cover requirements and
withstand design loading conditions.
Concrete Mix Design
Concrete must have a minimum compressive
strength of 4,000 psi at 28 days. Consider methods to
reduce permeability, improve durability and increase
strength. Maintaining a low water-cementitious ratio is
one way to achieve this and must not exceed 0.45.
Reinforcement
Proper reinforcement is critical to withstand
the loads applied to an on-site wastewater tank.
Reinforcement must be sufficient to provide adequate
strength during early-age handling, installation and
service, including temperature and shrinkage effects. All
reinforcement must meet applicable ASTM International
specifications.