Lightweight Concrete Changes in the 2019 ACI 318

Lightweight Concrete Changes in the 2019 ACI 318 Code Fred Meyer 22 October 2019

Tony Fiorato, 2010: This is a no brainer—this should be easy!

August 2019, Concrete International

What Changed Code Commentary

What Changed

What changed Overview • New “LDP-friendly” technique added • Existing “difficult to use” technique remains • The “splitting tensile strength” technique was removed, but laboratory testing can still be used to determine a more accurate value of lambda for the specific mixture to be used in the structure • Lightweight concrete now defined as having equilibrium density of 90 -135 lb/ft 3 • The new lambda (l) is not universal • Other requirements to be aware of

What changed Two ways to determine lambda (l) 1. Table 19. 2. 4. 1(a) – New • Requires the LDP to have knowledge of the desired equilibrium density of the LWC in the proposed structure.

What changed Two ways to determine lambda (l) 2. Table 19. 2. 4. 1(b) – Existed previously Requires the LDP to have knowledge of the aggregate blend of the LWC mixture to be used in the proposed structure.

What changed The new lambda (l) is not universal for LWC! • 15. 4. 2. 3 – Joint shear strength, l = 0. 75 • 18. 8. 2. 3 – Longitudinal beam reinforcement through a beam-column joint, l = 0. 75 • 18. 8. 4. 3 – Nominal joint shear strength, l = 0. 75 • 22. 9. 4. 2 – Coefficients of friction, l ≤ 0. 85 • Table 25. 4. 2. 5 – Development length (T), l = 0. 75 • Table 25. 4. 3. 2 – Hooked bars in tension, l = 0. 75 • Table 25. 4. 9. 3 – Development length (C), l = 0. 75

What changed Other requirements • 26. 4. 2. 1(a)(15) – Submittal of volumetric fractions • 26. 4. 2. 2(h) – Determination of fresh density • 26. 12. 5 – Acceptance criteria for density of LWC • 26. 12. 5. 1 – Compliance requirements (a) Frequency of sampling IAW ACI 26. 12. 2 (b) Sampling at point of delivery IAW ASTM C 172 (c) Fresh density determined IAW ASTM C 138 (d) Range of fresh density is +/- 4 lb/ft 3

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