Concrete Q&A: Definition of Brackish Water and Finding Voids


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Title: Concrete Q&A: Definition of Brackish Water and Finding Voids

Author(s): Terry Holland, Nick Carino, Bernie Hertlein

Publication: Concrete International

Volume: 32

Issue: 11

Appears on pages(s): 71-72


Date: 11/1/2010

1.We’re designing a concrete foundation that will be in contact with groundwater. Table 4.2.1 in ACI 318-081 indicates that Exposure Class C2 applies to concrete exposed to moisture and an external source of chlorides from deicing chemicals, salt, brackish water, seawater, or spray from these sources. Table 4.3.1 requires a maximum water-cementitious material ratio (w/cm) of 0.4 and a minimum specified compressive strength of 5000 psi, along with the related provisions of Section 7.7.6. The commentary to Section 7.7.6 states:Where concrete will be exposed to external sources of chlorides in service, such as deicing salts, brackish water, seawater, or spray from these sources, concrete should be proportioned to satisfy the requirements for the applicable exposure class in Chapter 4. These include minimum air content, maximum w/cm, minimum strength for normal-weight and lightweight concrete, maximum chloride ion in concrete, and cement type. Additionally, for corrosion protection, a specified concrete cover for reinforcement not less than 2 in. for walls and slabs and not less than 2-1/2 in. for other members is recommended.The language in ACI 318-08 implies that brackish water is a source of chlorides. We’re having the water tested, but what chloride concentration in brackish water constitutes a basis for designing to the much more demanding strength and w/cm requirements of Exposure Class C2? 2.We have reason to suspect that the concrete in a structural wall was not fully consolidated. Are there nondestructive methods to locate potential voids? What are the relative advantages and disadvantages of these methods?