15 September 1999
The RRMS system has been used extensively to provide cost effective support to a variety of
structural and architectural systems for varying site conditions. This system has had limited use
worldwide. Most Corps projects using RRMS are located in the Southwestern Division. While
competent structural performance has been achieved, many RRMS projects have experienced
significant cosmetic cracking of floor slabs. Although these cracks have no significant structural
or functional consequence, users have expressed dissatisfaction with the extent of cracking in
high visibility areas.
5. SLAB CRACKING. Excessive shrinkage cracking
in concrete slabs has been
problem. A small percentage of moderate to severe slab cracking is experienced on RRMS
projects resulting from volumetric shrinkage during concrete curing. Cracking remains a
universal problem with reinforced slabs of large lateral dimensions. ACI 224R, ACI 302.1R, and
ACI 360R present criteria for crack sizes permissible in engineering practice. Due to additional
lateral restraint created by the stiffening beams, slabs for RRMS foundations have greater
cracking potential than flat slabs. These cracks do not affect RRMS performance, but can be
unsightly. Several factors contribute to increased potential for cracking; these factors are as
a. High concrete mix water/cement ratio.
b. Large slab placement dimensions.
c. Minimal slab reinforcement percentage.
d. Large, widely spaced reinforcement.
e. Small aggregate in the concrete mix.
f. High range water reducer additives.
g. High cement content.
h. Addition of water during placement.
i. Substitution of membrane curing in lieu of the specified wet mat curing.
6. RRMS DESIGN. There are several items presented in this document as minimum design
and construction criteria. Final design values are those developed during the design process
based on sound engineering principles and judgment. This document presents data that should
form a base line for design and construction.