SiC BLAST – Concrete Durability and IBC Changes

Concrete durability and IBC Chapter 19 changes

The durability requirements for structural concrete have been DELETED from IBC, Chapter 19 and replaced by a reference to the durability provisions of ACI 318-14. Other durability provisions, weathering probability map and minimum concrete strength tables have also been deleted in favor of the new durability requirements for structural concrete contained in Part 6 of ACI 318-14. Listed below is a partial Table 19.3.2.1 of Chapter 19 of ACI 318-14. Only the “F Classes” of concrete are listed here.

F classes are classes of concrete that are exposed to freeze/thaw cycles with exposure to water except the FO class which is not exposed to water (slab on grade or elevated slabs inside the structure). All of the concrete on every project must comply with Table 19.3.2.1 exposure class criteria. Be aware of the dramatic CHANGES in the F1, F2 and F3 classes from the previous concrete code cycles of the past 25 years. Previously, the criteria for F1, F2 and F3 were almost identical and allowed the same concrete mix design to comply with all three (F1, F2, F3) classes. The new F class criteria is different from previous concrete codes and each F class of concrete will require a separate individual concrete mix because maximum w/c ratio and minimum strength criteria have changed with ACI 318-14. Be alert for F2 and F3 class concrete mixes which have higher w/c ratios than allowed by the new CODE and Table 19.3.2.1.

Special inspectors should review IBC section 1904.2 nonstructural concrete because this section requires minimum compressive strengths of 2500 psi for FO, 3000 psi for F1, 3500 psi for F2 and F3 classes. IBC section 1904.2 also requires that nonstructural concrete be AIR ENTRAINED. ACI 318 does not have durability requirements for nonstructural concrete; therefore, these IBC limits are not exceptions to the ACI 318 code but rather are a distinct set of requirements by IBC section 1904.2.

ACI 318-14 Chapter 19, Section 19.3.1.1. The licensed design professional engineer shall assign exposure classes in accordance with the severity of the anticipated exposure of members for each exposure category in Table 19.3.1.1.

Section 19.3.2.1 Based on the exposure classes assigned from Table 19.3.1.1, concrete mixtures shall conform to the most restrictive requirements in Table 19.3.2.1.