Concrete inFocus - Fall 2017 - OC13

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ENGINEERING:

Specifying for Performance
Karthik Obla, Ph.D., P.E., FACI, NRMCA Vice President, Technical Services and
Colin Lobo, Ph.D., P.E., NRMCA Executive Vice President, Engineering

T

his article is an advisory to the engineer to minimize prescriptive requirements and to consider performance alternatives
for concrete mixtures in project specifications (1, 2, 3). An
important step is to assign exposure classes to structural members
consistent with ACI 318 (and ACI 301). It is noted that the current
version of AIA MasterSpec does not address the ACI 318 durability
exposure requirements. Consider performance alternatives as needed
for performance and serviceability of specific structural member types.
Overly conservative specification requirements that are invoked when
not applicable to different member types and exposures can increase
cost and detract from sustainability initiatives.

CONCRETE MATERIAL REQUIREMENTS
The Building Code Requirements for Structural Concrete, ACI
318-14, covers requirements for concrete mixtures in Chapter 19, primarily for durability. Some details are covered in Chapter 26. The engineer
of record is required to assign durability exposure classes based on an
assessment of the severity of exposure to concrete members for each ACI
318 Exposure Category: F for freezing and thawing; S for exposure to
water soluble sulfates in soil; W for concrete members in contact with
water requiring low permeability; C for concrete members requiring
protection from corrosion of reinforcement. Review the definitions of
Exposure Categories in Appendix A. The ACI 318-14 Code has very
few prescriptive concrete material requirements. Section 1.10 of the
ACI 318-14 states that performance alternatives to prescriptive code
requirements such as w/cm need approval from the building official.

(ACI 318-14) Table 19.3.3.1 - Total Air Content for Concrete
Exposed to Cycles of Freezing and Thawing
Nominal
Maximum
Aggregate Size, in
	3/8
	½
	¾
	1
	1½
	2
	3

Target Air Content, Percent
F1

F2 and F3

	6
	5.5
	5
	4.5
	4.5
	4
	3.5

	7.5
	7
	6
	6
	5.5
	5
	4.5

(ACI 318-14) Table 26.4.2.2(b) - Limits on Cementitious Materials
for Concrete Assigned to Exposure Class F3
Maximum Percent of
Total Cementitious
Materials by Mass

Cementitious Materials
Fly ash or other pozzolans conforming to
ASTM C618
Slag cement conforming to ASTM C989
Silica fume conforming to ASTM C1240
Total of fly ash or other pozzolans and
silica fume
Total of fly ash or other pozzolans,
slag cement, and silica fume

25
50
10
35
50

Freeze Thaw Exposure
In accordance with ACI 318-14 select w/cm, air content and compressive strength for members assigned Exposure Classes F1, F2 and F3,
(ACI 318-14) Table 19.3.2.1 - Requirements for
Concrete by Exposure Class
Exposure Max Min ƒ´c , Additional Requirements Limits on
psi
SCM
Class
w/cm(1)
Air Content
F0
N/A
2500
N/A
N/A
F1
0.55
3500
Table 19.3.1.1
N/A
F2
0.45
4500
Table 19.3.1.1
N/A
Table 19.3.1.1
26.4.2.2(b)
F3
0.40(2) 5000(2)
 he maximum w/cm limits in Table 19.3.2.1 do not apply to
T
lightweight concrete.
(2)
For plain concrete, the maximum w/cm shall be 0.45 and the
minimum fc' shall be 4500 psi.
(1)

respectively. Limits on the quantity of supplementary cementitious
materials (SCM) are applicable to exposure class F3, i.e. concrete with
frequent exposure to water and deicing chemicals.
Note that the w/cm and strength requirements for exposure class
F3 are intended for structurally reinforced and prestressed concrete
members and are intended to be consistent with the requirements for
exposure class C2. Refer to the definition of "plain concrete" in ACI 318.
Specified air content can be reduced by 1% when ƒ´c >5000 psi.

Performance Requirement
Scaling is generally related to timing and procedures used for
finishing. A performance alternative may be used if higher quantities of SCMs are needed. The performance alternative might be to
evaluate the deicer salt scaling resistance measured in accordance with
ASTM C672 with a "Visual rating less than or equal to 2." Experience
concrete INFOCUS

ı

OC13


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Table of Contents for the Digital Edition of Concrete inFocus - Fall 2017

From the President’s Desk
Corporate Suite
Enviroscene
2017 National Ready Mixed Concrete Association Fleet Benchmarking and Costs Survey
The Root Causes of Poor Communication
Insulating Concrete Forms for Commercial Construction
Engineering: Specifying for Performance
View from Capitol Hill: State of Play of U.S. Infrastructure
2017 Service & Supply Buyers’ Guide
2017 Products & Services Suppliers Guide
Index of Advertisers
Concrete inFocus - Fall 2017 - Intro
Concrete inFocus - Fall 2017 - bellyband1
Concrete inFocus - Fall 2017 - bellyband2
Concrete inFocus - Fall 2017 - cover1
Concrete inFocus - Fall 2017 - cover2
Concrete inFocus - Fall 2017 - 3
Concrete inFocus - Fall 2017 - 4
Concrete inFocus - Fall 2017 - 5
Concrete inFocus - Fall 2017 - 6
Concrete inFocus - Fall 2017 - 7
Concrete inFocus - Fall 2017 - 8
Concrete inFocus - Fall 2017 - From the President’s Desk
Concrete inFocus - Fall 2017 - 10
Concrete inFocus - Fall 2017 - Corporate Suite
Concrete inFocus - Fall 2017 - 12
Concrete inFocus - Fall 2017 - 13
Concrete inFocus - Fall 2017 - Enviroscene
Concrete inFocus - Fall 2017 - 15
Concrete inFocus - Fall 2017 - 16
Concrete inFocus - Fall 2017 - 17
Concrete inFocus - Fall 2017 - 2017 National Ready Mixed Concrete Association Fleet Benchmarking and Costs Survey
Concrete inFocus - Fall 2017 - 19
Concrete inFocus - Fall 2017 - 20
Concrete inFocus - Fall 2017 - 21
Concrete inFocus - Fall 2017 - 22
Concrete inFocus - Fall 2017 - 23
Concrete inFocus - Fall 2017 - 24
Concrete inFocus - Fall 2017 - 25
Concrete inFocus - Fall 2017 - The Root Causes of Poor Communication
Concrete inFocus - Fall 2017 - 27
Concrete inFocus - Fall 2017 - 28
Concrete inFocus - Fall 2017 - 29
Concrete inFocus - Fall 2017 - Insulating Concrete Forms for Commercial Construction
Concrete inFocus - Fall 2017 - 31
Concrete inFocus - Fall 2017 - 32
Concrete inFocus - Fall 2017 - 33
Concrete inFocus - Fall 2017 - 34
Concrete inFocus - Fall 2017 - 35
Concrete inFocus - Fall 2017 - 36
Concrete inFocus - Fall 2017 - 37
Concrete inFocus - Fall 2017 - 38
Concrete inFocus - Fall 2017 - 39
Concrete inFocus - Fall 2017 - Engineering: Specifying for Performance
Concrete inFocus - Fall 2017 - 41
Concrete inFocus - Fall 2017 - 42
Concrete inFocus - Fall 2017 - 43
Concrete inFocus - Fall 2017 - View from Capitol Hill: State of Play of U.S. Infrastructure
Concrete inFocus - Fall 2017 - 45
Concrete inFocus - Fall 2017 - 46
Concrete inFocus - Fall 2017 - 2017 Service & Supply Buyers’ Guide
Concrete inFocus - Fall 2017 - 48
Concrete inFocus - Fall 2017 - 49
Concrete inFocus - Fall 2017 - 50
Concrete inFocus - Fall 2017 - 2017 Products & Services Suppliers Guide
Concrete inFocus - Fall 2017 - 52
Concrete inFocus - Fall 2017 - Index of Advertisers
Concrete inFocus - Fall 2017 - 54
Concrete inFocus - Fall 2017 - cover3
Concrete inFocus - Fall 2017 - cover4
Concrete inFocus - Fall 2017 - OC1
Concrete inFocus - Fall 2017 - OC2
Concrete inFocus - Fall 2017 - OC3
Concrete inFocus - Fall 2017 - OC4
Concrete inFocus - Fall 2017 - OC5
Concrete inFocus - Fall 2017 - OC6
Concrete inFocus - Fall 2017 - OC7
Concrete inFocus - Fall 2017 - OC8
Concrete inFocus - Fall 2017 - OC9
Concrete inFocus - Fall 2017 - OC10
Concrete inFocus - Fall 2017 - OC11
Concrete inFocus - Fall 2017 - OC12
Concrete inFocus - Fall 2017 - OC13
Concrete inFocus - Fall 2017 - OC14
Concrete inFocus - Fall 2017 - OC15
Concrete inFocus - Fall 2017 - OC16
Concrete inFocus - Fall 2017 - OC17
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