Slump Requirements per ACI 301
Q. ACI 301-101 calls for the slump to be proportioned
to 2 to 4 in. (50 to 100 mm) prior to a high-range
water-reducing admixture (HRWRA) being added
and calls for a maximum slump of 8 in. (200 mm) at the point
of delivery after the addition of the admixture. How is this
handled when a HRWRA is added at the batch plant prior to
arriving at the site?
A.ACI 301-10 has been replaced—the current version
of the specification is ACI 301-16.2 Section 188.8.131.52
of the current specification directs the specifier to
select a target slump or slump flow “at the point of delivery for
all concrete mixtures.” The upper limit on the target slump is
9 in. (230 mm), and the upper limit on the target slump flow is
30 in. (750 mm). These values are to be enforced for the duration
of the project, and slump is to be determined per ASTM C143/
C143M3 and slump flow per ASTM C1611/C1611M.4 Also,
slump and slump flow tolerances must meet the requirements of
ACI 1175 and ASTM C94/94M,6 respectively.
Section 184.108.40.206 also states that if slump measured at the
point of discharge from the transportation unit is greater than
specified in Section 220.127.116.11, a check test is required on a new
sample. If the check test also fails, the concrete fails to meet
the requirements of ACI 301-16. When the measured slump is
lower than specified in Section 18.104.22.168, adjustments can be
made in accordance with ASTM C94/C94M, unless specified
otherwise. If slump measured on the adjusted mixture fails,
72 MAY 2019 | Ci | www.concreteinternational.com
the concrete fails to meet the requirements of ACI 301-16.
As for slump adjustments, Section 22.214.171.124 states that if
slump is lower than required, it may be adjusted by adding
chemical admixtures or water and measured after the
adjustment to verify compliance with specified requirements.
The water is to be added in accordance with ASTM C94/
C94M and must not result in a water-cementitious materials
ratio greater than the specified maximum value. Also, water
must not be added to concrete delivered in equipment not
acceptable for mixing.
1. ACI Committee 301, “Specifications for Structural Concrete (ACI
301-10),” American Concrete Institute, Farmington Hills, MI, 2010, 77 pp.
2. ACI Committee 301, “Specifications for Structural Concrete (ACI
301-16),” American Concrete Institute, Farmington Hills, MI, 2016, 77 pp.
3. ASTM C143/C143M-15, “Standard Test Method for Slump of
Hydraulic-Cement Concrete,” ASTM International, West Conshohocken,
PA, 2015, 4 pp.
4. ASTM C1611/C1611M-14, “Standard Test Method for Slump Flow
of Self-Consolidating Concrete,” ASTM International, West
Conshohocken, PA, 2014, 6 pp.
5. ACI Committee 117, “Guide to Design of Slabs-on-Ground (ACI
117-10) (Reapproved 2015),” American Concrete Institute, Farmington
Hills, MI, 2010, 76 pp.
6. ASTM C94/C94M-15, “Standard Specification for Ready-Mixed
Concrete,” ASTM International, West Conshohocken, PA, 2015, 14 pp.
Roughening of Existing Concrete
to 1/4 in. Amplitude per ACI 318
Q. When does ACI 318-141 require a 1/4 in. (6.4 mm)
amplitude on existing concrete before new
concrete is placed against it?
A. Generally, roughening a surface to 1/4 in.
amplitude is an option that the designer may use to
get higher shear strength values between new and
existing concrete. ACI 318-14, Section 126.96.36.199(c), requires
the designer to put information on “roughening of hardened
concrete surface, where concrete is to be placed against
previously hardened concrete” in the construction documents.
The Code requires roughening of the surface to 1/4 in.
amplitude (condition (b) in Table 188.8.131.52) in two instances.
One is in Section 184.108.40.206 for contact surfaces in
construction joints in structural walls. The other is in Section
220.127.116.11 for contact surfaces in construction joints in
1. ACI Committee 318, “Building Code Requirements for Structural
Concrete (ACI 318-14) and Commentary (ACI 318R-14),” American
Concrete Institute, Farmington Hills, MI, 2014, 519 pp.