Concrete Corrosion and Slab Heaving in a Sabkha Environment: Long Beach-Newport Beach, California

Abstract

The Long Beach to Newport area which coincides with the Downey and Santa Ana River flood plains, is an area of shallow (2.9 m to 3.2 m), brackish ground water. This area experiences a 2 to 3 m rise in water levels during heavy (0.91 m) winter rains. This shallow ground water evaporates causing precipitation of gypsum and halite. The area is a sabkha, a nearly level coastal or continental salt flat which is only occasionally inundated by sea, rain, and/or terrestrial waters. In the early 1960's, the area was mostly dairy land, but now is blanketed with homes, apartments and business complexes. During the mid-1980's, the early constructed homes experienced concrete corrosion and slab heaving. Engineering studies did not identify the problem, suggesting either inadequate grading or poor construction. The Long Beach–Newport Beach area exhibits many characteristics of a typical sabkha, including evaporation exceeding precipitation, high salinity of ground water, high ground-water levels, fine- to medium-grained sand, and salt precipitation. The concentration of salts results in corrosion of normal concrete at the air-water interface. The growth of gypsum crystals resulted in heaving of slabs, allowing more corrosion. Identification of sabkha conditions are important to construction. Those homes built in the early 1960's were repaired at a cost of about six million dollars. Repair methods include replacing existing concrete slabs with new slabs of Type V concrete with a moisture barrier under the slab. As ground-water levels rise again in response to heavy winter rains, additional destruction may occur from the lack of early recognition of sabkha conditions.