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Revision of current Article 8.13 for SDCs C and D to Design example for grouted duct connection in SDC A
Article 8.15 for precast bent cap connection design (minimum joint reinforcement)
· Attachment DE3: SDC A Design Example--Cap Pocket
Other proposed articles for the AASHTO LRFD Bridge Connection
Design Specifications (4th Edition) are as follows (29): Design example for cap pocket connection in SDC A
(minimum joint reinforcement)
· Attachment DS16: Revised Article 5.10.11.4.3--Column · Attachment DE4: SDCs B, C, and D Design Flow Chart
Connections Flow chart for design of precast bent cap connections in
Revised Article to ensure AASHTO LRFD SGS is used SDCs B, C, and D
for emulative precast bent cap to column connection · Attachment DE5: SDC B Design Example--Grouted Duct
design. Connection
· Attachment DS17: Proposed Article 5.11.1.2.4--Moment Design example for grouted duct connection in SDC B
Resisting Joints (minimum joint reinforcement)
Revised Article to ensure AASHTO LRFD SGS is used for · Attachment DE6: SDC B Design Example--Cap Pocket
emulative precast bent cap to column connection design. Connection
Design example for cap pocket connection in SDC B
3.4 Design Flow Charts (minimum joint reinforcement)
· Attachment DE7: SDCs C and D Design Example--Grouted
and Design Examples
Duct Connection
Design flow charts and design examples have been devel- Design example for grouted duct connection in SDCs
oped for the systems and connections investigated under this C and D (additional joint reinforcement)
project. The design flow charts and design examples illustrate · Attachment DE8: SDCs C and D Design Example--Cap
the design process, including proper application of the design Pocket Connection
specifications, for all SDC levels using precast bent cap to col- Design example for cap pocket connection in SDCs
umn connections with practical reinforcement and detailing. C and D (additional joint reinforcement)
Two design flow charts are provided, one for SDC A and · Attachment DE9: SDCs C and D Design Example--Hybrid
another for SDCs B, C, and D. Consolidation of SDCs B, C, and Connection
D into one flow chart highlights the fact that the amount Design example for hybrid connection in SDCs C and D
and type of joint shear reinforcement are based on the deter- · Attachment DE10: SDCs C and D Design Example--
mination of the principal tensile stress and that, even for SDC Integral Connection
B, the likelihood of joint shear cracking should be determined. Design example for integral connection in SDCs C
Finally, as required, the effects should be mitigated through the and D
use of joint shear reinforcement.
Design examples are provided for SDC A, SDC B, and
SDCs C and D. The examples include extensive commentary 3.5 Development of Construction
and figures and list applicable references to the LRFD SGS Specifications
and LRFD BCS. The design examples for SDCs C and D illus- This section provides the basis for proposed Article 8.13.8--
trate the case in which additional joint shear reinforcement is Special Requirements for Precast Bent Cap Connections to be
required (i.e., principal tensile stress, pt, 0.11 fc or larger). added to AASHTO LRFD Bridge Construction Specifications,
The SDC B and SDC A examples illustrate the case in which 2nd Edition, 2004 with 2006, 2007, 2008, and 2009 Interims
minimum joint reinforcement governs. Special consideration (LRFD BCS) (35) to address nonintegral precast bent cap sys-
is given to clarity, completeness, and accuracy. tems using grouted duct and cap pocket connections.
Design flow charts and design examples are provided as Proposed construction specifications are based on specifica-
attachments to this report (available online at www.trb.org/ tions developed by Matsumoto et al. (8) together with results
Main/Blurbs/164089.aspx), as follows: from the experimental test results. Major sections of the
construction specification address the following:
· Attachment DE1: SDC A Design Flow Chart
Flow chart for design of precast bent cap connections in · Materials
SDC A portland cement concrete for the precast bent cap and
· Attachment DE2: SDC A Design Example--Grouted Duct cap pocket fill
Connection hydraulic cement (non-shrink) grout
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corrugated metal duct Hybrid connections use grouted duct connections to
lock-seam, helical corrugated steel pipe anchor column longitudinal reinforcement. Unbonded post-
connection hardware tensioning is also used in the section to resist lateral demands.
· Contractor submittal including a precast bent cap place- The integral connections must provide a stable flexural con-
ment plan nection between the superstructure and substructure. These
· Construction methods including grouting of grouted duct connections can include systems with discontinuous girders
connections and concreting of cap pocket connections at the bent cap made continuous through longitudinal post-
(trial batch, placement, material testing) tensioning.
In Article 8.13.8, the term "column bars" refers to column
In addition, a grout specification for the grouted duct con- bars, column dowels, and pile dowels.
nection from Matsumoto et al. (8) is presented.
Most of this section is incorporated within the proposed
3.5.2 Materials
specification as code and commentary. Proposed specifica-
tions are set off from the main text. The following sections use Materials used for precast bent cap connections include
the same outline as that used in the proposed specifications. Portland cement concrete for the precast bent cap, connec-
References to articles within this section refer primarily to tion hardware, and materials specific to each connection type.
existing or proposed Articles of the LRFD BCS. Grouted duct connection materials include hydraulic cement
grout (non-shrink) and corrugated metal ducts. Cap pocket
connection materials include Portland cement concrete for
3.5.1 General
the cap pocket fill and the steel (corrugated) pipe. Hybrid
This article addresses construction of precast bent cap connections use grouted duct connections in combination
connections: with post-tensioning.
The proposed specification states the following:
This article describes special requirements for integral
and nonintegral emulative and hybrid precast bent cap The materials and manufacturing processes used for
connections using the grouted ducts or cap pockets. precast concrete bent caps shall conform to the require-
ments of Article 8.13.3 except as those requirements are
These special requirements are intended to ensure pre- modified or supplemented by the provisions that follow.
cast bent cap connections studied are constructible and also
provide the expected seismic performance, durability, and Portland Cement Concrete for Precast Bent Cap
economy.
The grouted duct connection uses corrugated ducts embed- Bent cap concrete is required to satisfy provisions for
ded in the precast bent cap to anchor individual column lon- normal-weight Portland cement concrete and provide a
gitudinal bars. The ducts and bedding layer between the cap strength margin between the cap and the connection. The
and column or pile are grouted with high-strength, non-shrink specified compressive strength of the connection grout or con-
cementitious grout to complete the precast connection. Ducts crete fill is required to exceed the expected bent cap concrete
are sized to provide adequate tolerance for bent cap fabrication compressive strength by at least 500 psi to help ensure that the
and placement and should be accounted for in sizing the bent connection does not become a weak link in the system:
cap to minimize potential congestion.
The cap pocket connection uses a single, helical, corrugated Portland cement concrete for the precast bent cap
steel pipe embedded in the precast bent cap to form the cap shall conform to the provisions of Article 8.2.2 for
normal-weight concrete. The concrete mix design for
pocket, which anchors the column longitudinal bars. This pipe,
the precast bent cap shall conform to the requirements
placed between top and bottom bent cap longitudinal re- of Articles 8.13.8.3.2a and 8.13.8.3.3a to achieve the
inforcement, serves as both a stay-in-place form and as joint required 500 psi strength margin between the bent
transverse reinforcement. Special forming is required above cap compressive strength and the specified compres-
and below the pipe to form the cap pocket void through the full sive strength of the connection grout or cap pocket
depth of the bent cap. A flowable CIP concrete is used to fill the concrete fill.
void and complete the precast connection. The pipe diameter
is sized to provide adequate field tolerance for placement of the Lightweight concrete can provide significant advantages
precast bent cap over column longitudinal bars, and the pipe for a precast bent cap system. However, its use should be
thickness is sized to satisfy transverse joint reinforcement based on relevant research including research on its effect on
requirements. the seismic performance of the connection.
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Use of lightweight concrete shall be based on appli- Proposed LRFD BCS Table 8.13.8-1 is shown as Table 3.4 of
cable research of connection performance, including this report. This table includes provisions intended to ensure
seismic effects, and approval by the Engineer.
that the grout used in the connection develops mechanical,
compatibility, constructability, and durability properties that
Grouted Duct Connection help ensure that the grout is placed efficiently, achieves per-
formance for rapid construction, and does not become a weak
Hydraulic Cement Grout (Non-Shrink). Grout for the
link in the system under the various limit states. For example,
grouted duct connection is carefully specified:
Table 3.4 requires the 28-day grout compressive strength to
have a minimum 500-psi margin over the 28-day expected
Grout used in grouted duct connections shall consist of
prepackaged, cementitious, non-shrink grout in accor- bent cap concrete compressive strength. This margin accounts
dance with ASTM C1107 and the additional perfor- for the likelihood that the actual concrete strength will exceed
mance requirements listed in Table 8.13.8-1, including its specified strength as well as the possibility of a low grout
the following properties: mechanical, compatibility, strength. The 1.25 factor applied to f ce_cap in Table 3.4 accounts
constructability, and durability. Table 8.13.8-1 require-
for the higher 2-in grout cube compressive strength compared
ments shall govern over ASTM C1107 requirements.
Grout shall contain no aluminum powder or gas- to standard concrete cylinder compressive strength.
generating system that produces hydrogen, carbon Grout should be selected with a compressive strength based
dioxide, or oxygen. Grout using metallic formulations on water required for fluid consistency using the ASTM C939
shall not be permitted. Grout shall be free of chlorides. Flow Cone Test. Grouts mixed to a flowable or plastic consis-
No additives or admixtures, including retarders, shall be
tency in accordance with ASTM C230 achieve a higher com-
added to prepackaged grout. Extension of grout shall
only be permitted when recommended by the manu- pressive strength but possess inadequate fluidity for filling voids
facturer and approved by the Engineer. in a precast bent cap system and therefore should be avoided.
At a minimum, grout compressive strength and flowa- Prepackaged grouts are proprietary mixes, and thus no addi-
bility shall be established during trial batches per Article tives should be used in the grout. Additives may adversely affect
8.13.8.5.4a. Laboratory testing shall be permitted to
grout properties and void manufacturer warranties.
establish other properties listed in Table 8.13.8-1.
Grouted joints shall not exceed 3 in. in thickness for Modification of prepackaged grout, including extension
structures located in Seismic Design Categories B, C, with small-size aggregate, is discouraged because of the
and D. additional uncertainty introduced in achieving the required
Table 3.4. Grout specification for grouted duct connection (8).
Property Value
Mechanical Age Compressive strength (psi)
Compressive strength 1 day 2,500
(ASTM C109, 2" cubes) 3 days 4,000
7 days 5,000
28 days Maximum
[6000, 1.25 ( ) + 500]
Compatibility
Expansion requirements Grade B or Cexpansion per ASTM C1107
(ASTM C827 & ASTM C1090)
Modulus of elasticity 2.8-5.0×106 psi
(ASTM C 469)
Coefficient of thermal expansion 3.0-10.0×10-6/deg F
(ASTM C 531)
Constructability
Flowability Fluid consistency efflux time: 2030 sec
(ASTM C939 Flow Cone)
Set Time (ASTM C191)
Initial 2.55.0 hrs
Final 4.08.0 hrs
Durability
Freeze Thaw (ASTM C666) 300 cycles, relative durability factor 90%
Expansion at 26 weeks < 0.1%
Sulfate Resistance (ASTM C1012)
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properties and the potential risk in resolving liability if the Cap Pocket Connection
quality of grouted connections is believed to be deficient. For
Portland Cement Concrete for Cap Pocket Fill. Portland
example, ASTM C33 No. 8 Hard Pea Gravel or Hard Aggregate
cement concrete for the cap pocket fill has additional require-
Chips may contain excessive fines that adversely affect the flow
ments beyond that of typical normal-weight concrete:
of the prepackaged grout.
Clear spacing between the reinforcing and the formed sur-
Portland cement concrete for the cap pocket fill shall
faces should be at least three times the top size of the aggre- follow the provisions of Article 8.2.2 for normal-weight
gate to ensure adequate flow of grout to fill all voids. concrete and Article 8.3 for associated materials. The
mix design for the concrete fill shall be based on achiev-
Corrugated Metal Duct. Corrugated metal ducts used to ing a concrete compressive strength at least 500 psi
anchor column bars within the bent cap are specified as follows: greater than the expected concrete strength of the
precast bent cap.
The use of ducts in a grouted duct connection shall Lightweight concrete shall not be used.
conform to the requirements of Article 10.8.1 except as Concrete shall satisfy Article 8.13.8.5.5a to ensure
those requirements are modified or supplemented by pocket and bedding layer are completely filled and
the provisions that follow. without voids.
Ducts used to provide holes in the precast bent cap
concrete shall be formed with semi-rigid steel ducts The probable concrete strength for the cap pocket fill is
that are cast into the concrete. Ducts shall be galva- required to provide a minimum 500-psi margin over the
nized ferrous metal per ASTM A653 and shall be fab-
expected bent cap concrete compressive strength to ensure that
ricated with either welded or interlocked seams.
Ducts shall be corrugated with a minimum wall thick- the cap fill concrete is not the weak link in the connection. This
ness of 26 gage for ducts less than or equal to 4-in margin accounts for the likelihood that the actual bent cap
diameter and 24 gage for ducts greater than 4-in compressive strength will exceed its specified strength as well
diameter. Rib height of the corrugation shall be at least as the possibility of a low compressive strength of the fill.
0.12 in. Use of lightweight concrete is not permitted in the cap
Plastic ducts shall only be used based on applicable
research and when approved by the Engineer.
pocket because it may pose an unnecessary risk in the seismic
Duct diameter shall be based on fabrication and place- performance of the connection.
ment tolerances established for the job. Concrete should be sufficiently flowable to fill the pocket
Placement and anchorage of ducts shall conform to and bedding layer and to flow out of air vents at the top of the
the requirements of Article 10.4.1.1. bedding layer. In addition, clear spacing between the reinforc-
ing and the formed surfaces should be at least three times the
Corrugated galvanized steel ducts for grouted duct connec- top size of the aggregate to ensure adequate flow of concrete to
tions have been successfully used in seismic and nonseismic fill all voids, including the bedding layer.
research as well as in practice. Steel ducts provide excellent
mechanical interlock with the bent cap concrete and connec- Steel Pipe. The steel pipe, which serves a critical dual
tion grout as well as confinement for the grouted column bar. purpose in fabrication and seismic reinforcement, is specified
When steel ducts with the minimum specified duct thickness as follows:
and corrugation rib height are used together with grouts satis-
fying Table 8.13.8-1, excellent bond develops and column bars The steel pipe used to form the void in the precast bent
cap concrete shall be a lock seam, helical corrugated pipe
can be safely anchored in a grouted duct within the relatively
cast into the concrete. The steel pipe shall satisfy the
short anchorage length given in Article 8.15.2.2.2 of the 2009 requirements of ASTM A760, Standard Specification for
LRFD SGS (1). Corrugated Steel Pipe, Metallic-Coated for Sewers and
Use of plastic ducts can have a significant impact on the Drains, and the lock seam shall satisfy the requirements
behavior, failure mode, and strength of grouted duct con- of AASHTO T 249, Standard Method of Test for Helical
Lock Seam Corrugated Pipe. The pipe shall satisfy the
nections and should not be used without investigation and
thickness required by Article 8.15.3.2.2 of the AASHTO
approval of the Engineer. Brenes et al. (36) provide guide- Guide Specifications for LRFD Seismic Bridge Design.
lines for use of high-density polyethylene and polypropylene Where required, coupon testing to determine ma-
ducts in grouted duct connections, including minimum duct terial properties shall be conducted in accordance
wall thickness, corrugation rib height, and maximum spac- with ASTM A370.
Plastic pipe shall not be used.
ing between ribs. An increase in development length of approx-
The pipe diameter shall be based on fabrication and
imately 30% was recommended for plastic ducts tested under placement tolerances established for the job.
monotonic tension. However, tension cyclic tests were not Placement and anchorage of steel pipe shall conform
conducted. to the requirements of Article 10.4.1.1.
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Lock seam, helical corrugated steel pipe has been successfully layer for hybrid precast connections. Therefore, the following
used in seismic research as well as in practice for precast cap article is recommended for hydraulic cement grout in hybrid
pocket connections. These pipes provide excellent mechanical precast connections:
interlock with the bent cap concrete and connection concrete
fill and also serve as joint reinforcement. When the steel pipe is Grout used in grouted duct connections in conjunction
designed in accordance with Article 8.15.3.2.2 of the AASHTO with hybrid precast connections shall meet the require-
ments of Article 8.13.8.3.2a. Polypropylene fibers shall
Guide Specifications for LRFD Seismic Bridge Design and is used
be added to the grout matrix during mixing at a 3 lb/cu
together with concrete satisfying Article 8.13.8.3.3a, excellent yd fraction. Fibers shall meet the requirements of ASTM
bond is expected to develop and column bars are expected to be C1116.
anchored in the pipe within the relatively short anchorage
length given in Article 8.15.2.2.2 of the AASHTO Guide
Integral Precast Connections with Vertical Joints
Specifications for LRFD Seismic Bridge Design (1).
Plastic pipe should not be used because it cannot serve as The integrity of vertical closure joints in integral precast
seismic reinforcement. connections is essential to satisfactory flexural response. To
promote joint integrity, a high-quality, non-shrink grout
Connection Hardware. Connection hardware is speci- containing fiber reinforcement is necessary. The following
fied as follows: article is therefore recommended:
All connection hardware such as friction collars, shims,
Grout used in grouted duct connections shall consist
falsework, or other support systems shall be in accor-
of prepackaged, cementitious, non-shrink grout in
dance with the requirements shown in the plans.
accordance with ASTM C1107 and the additional per-
formance requirements listed in Table 8.13.8-1, includ-
Friction collars and shims may be used to support the cap ing the following properties: mechanical, compatibility,
during placement. When shims are used, compressible shims constructability, and durability. Table 8.13.8-1 require-
such as those made of plastic are preferred over steel shims to ments shall govern over ASTM C1107 requirements.
Grout shall contain no aluminum powder or gas-
help ensure that load eventually transfers to the hardened bed-
generating system that produces hydrogen, carbon diox-
ding layer grout. Plastic shims should be made of engineered ide, or oxygen. Grout using metallic formulations shall
multipolymer, high-strength plastic with a modulus of elastic- not be permitted. Grout shall be free of chlorides. No
ity slightly less than the hardened grout at the time of load additives or admixtures, including retarders, shall be
transfer. Steel shims have a stiffness at least five times that of added to prepackaged grout. Extension of grout shall
only be permitted when recommended by the manufac-
the bedding grout and therefore can act as hard points
turer and approved by the Engineer.
between the column and bent cap. Calculations should be At a minimum, grout compressive strength and flowa-
made to determine the potential effect of shims in the com- bility shall be established during trial batches per Article
pression zone of the bedding layer. Where steel shims are used, 8.13.8.5.4a. Laboratory testing shall be permitted to
additional cover should be provided for corrosion protection. establish other properties listed in Table 8.13.8-1.
Specific measures to prevent movement of shims during Polypropylene fibers shall be added to the grout matrix
during mixing at a 3 lb/cu yd fraction. Fibers shall meet
cap placement should be detailed in the plan sheets. To facil- the requirements of ASTM C1116.
itate complete grouting of the bedding layer, the total shim Grouted joints shall not exceed 3 in for structures
plan area should be limited and shims should be placed away located in Seismic Design Categories B, C, and D.
from the exposed surface of the bedding layer unless shim
removal is planned.
3.5.3 Contractor Submittal
As explained in Matsumoto et al. (8), the contractor should
Hybrid Precast Concrete Connections
provide a detailed submittal to ensure successful construction
Hybrid connections constructed with precast components of the precast bent cap connection:
use a combination of column longitudinal reinforcement and
unbonded post-tensioning. The connection of column longi- In advance of the start of precast bent cap placement
tudinal reinforcement is traditionally made using a grouted operations in the field, to allow the Engineer not less
than a 30-calendar-day review period, the Contractor
duct connection. The construction specifications for grouted
shall submit the following documents: (1) Precast Bent
duct connections shall therefore be implemented for these Cap Placement Plan per Article 8.13.8.4.2, (2) Design
connections. However, experimental testing described in Calculations for Construction Procedures per Article
Chapter 2 indicated a need to place fibers within the bedding 8.13.8.4.3, and (3) Shop Drawings per Article 8.13.8.4.4.
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Bent caps shall not be set until the Engineer has Design calculations shall be submitted for friction col-
approved all required submittals. Any subsequent devi- lars, shims, falsework, erection devices, formwork, or
ation from the approved materials and/or details shall other temporary construction that will be subject to cal-
not be permitted unless details are submitted by the culated stresses.
Contractor and approved by the Engineer in advance of Design of the friction collars, shims, and falsework or
use. Two sets of the Precast Bent Cap Placement Plan, erection devices for all bent cap concrete, duct grout,
calculations, and required drawings shall be submitted or cap pocket concrete shall be completed under the
and resubmitted if and as necessary until approved by the direction of and sealed by a registered Professional
Engineer. The specified number of distribution copies Engineer.
shall be furnished after approval. Post-tensioned precast bent caps shall also follow the
provisions of Article 8.16.3.2.
Precast Bent Cap Placement Plan Shop Drawings
The Precast Bent Cap Placement Plan is specified as follows: Detailed shop drawings are specified as follows:
The Precast Bent Cap Placement Plan, at a minimum, The Contractor shall submit detailed shop drawings
shall contain the following items: for approval in accordance with the contract docu-
(a) Step-by-step description of bent cap placement ments. The shop drawings shall follow the provisions of
for each bent, including placement of the bent cap on Article 8.16.3.3, with the following additions:
the columns or piles and the proposed method for form- (a) Shop drawings shall completely describe the pro-
ing the bedding layer, placing grout in ducts or concrete posed construction sequence and shall show enough
in cap pockets, and ensuring that grout or concrete is detail to enable construction of the bent cap without
properly consolidated in the connection and bedding the use of the plan sheets.
layer. (b) Size and type of ducts or pipes for all bent cap
(b) Method and description of hardware used to connections shall be clearly detailed. Duct or pipe sup-
hold bent cap in position prior to connection grouting ports, tremie tubes, air vents, and drains shall be shown,
or concreting. Hardware shall be permitted to consist of including size, type, and locations.
friction collars, plastic or steel shims, shoring, or other (c) Bedding layer reinforcement, as well as its loca-
support systems. A hardware submittal shall consist of tion within the bedding layer and its location relative
product information, material descriptions, and draw- to the first hoop at the top of the column or pile, shall
ings for friction collars and shims and shop drawings for be shown.
shoring if used. (d) Spacing between the first hoop at the top of the
(c) For grouted duct connections, manufacturer's column or pile and the bedding layer hoop shall be
product information for at least two candidate grouts, shown. This spacing shall not exceed the spacing used for
including a description of the performance characteris- hoops in the plastic hinge region. The concrete cover
tics as specified in Table 8.13.8-1, mixing requirements, above the first hoop at the top of the column shall be
working time, curing requirements, and other informa- permitted to be less than that specified in Article 5.12.3
tion related to grouting of precast connections utilizing of the AASHTO LRFD Bridge Design Specifications.
ducts. For cap pocket connections, concrete fill mix (e) A table showing elevations and geometry to be
design, description of the method to achieve concrete used in positioning the bedding layer collar for bent
consistency for filling the pocket and bedding layer, cur- cap placement shall be provided.
ing requirements, and other information related to con- (f) For the grouted duct connection, details of grout-
creting precast connections using a steel pipe should be ing equipment, grout mix design, and method of mix-
provided. ing, placing, and curing grout shall be provided.
(d) Hardware and equipment associated with grout- (g) For the cap pocket connection, details of concrete
ing grouted duct connections or concreting cap pocket fill mix design and method of mixing, placing, and cur-
connections. ing concrete fill shall be provided.
(e) A mitigation plan to repair any voids observed (h) Other required submittals shown on the plans or
within the bedding layer, coordinated and approved by requested by the Engineer relating to successful instal-
the Engineer. lation of precast bent caps and associated hardware
(f) Other required submittals shown on the plans or shall be provided.
requested by the Engineer relating to successful instal-
lation of precast bent caps and associated hardware. As discussed in Chapter 2, uniform spacing between hoops
at the top of the column and the bedding layer is critical to
ensuring that system ductility is not compromised. A smaller
Design Calculations for Construction Procedures
cover than that used for typical column applications is permit-
Design calculations related to construction procedures are ted for the top hoop because the bedding layer provides addi-
specified as follows: tional cover after placement of the precast bent cap. Plan sheets
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should show the intended placement of the first hoop at the top Specifications address general grouting issues, trial batches,
of the column. This requirement for design is addressed in the grout placement, and grout testing. Matsumoto et al. (8) pro-
proposed Article 8.8.14 of the AASHTO Guide Specifications for vide further background and details on these provisions.
LRFD Seismic Bridge Design.
General Issues. General issues are specified as follows:
3.5.4 Construction Methods The preparation and use of grout for precast bent
cap connections shall conform to the requirements of
General Article 10.9 except as those requirements are modified
or supplemented by the provisions that follow.
Construction of precast bent cap systems must account for Prepackaged, cementitious, non-shrink grout shall
tolerances: be used in strict accordance with manufacturer's
recommendations.
All tolerances shall be established on a project- Per Article 8.13.8.3.2a, additives or admixtures, includ-
specific basis. Combined tolerances shall include, but ing retarders, shall not be added to grout. However, it
are not limited to, fabrication of the bent cap and shall be permitted to adjust the temperature of mixing
columns or piles and placement of the bent cap over water or substitute ice for water to extend the working
the columns or piles, including location of column time and pot life.
bars or other dowels within the corrugated metal Addition of water to previously mixed grout or remix-
ducts or steel pipe. ing of grout shall not be permitted. Water exceeding
All form release agents and curing membranes shall manufacturer's recommendations shall not be added to
be completely removed from areas of the cap that will the grout to increase flowability.
be in contact with bearing seat and connection grout.
Trial Batch. The trial batch is a key step in achieving the
Combined fabrication and placement tolerances should be required installation and performance of a grouted duct con-
established for each project. The following issues should be con- nection. The purposes of a trial batch are to do the following:
sidered: differences in tolerances for longitudinal and transverse
· Determine the required amount of water to be added to a
directions; accuracy of column bars or dowels within corru-
particular grout brand to achieve acceptable flowability per
gated ducts or steel pipes; size, type, location and orientation of
Table 3.4 and pot life under the temperature and humidity
ducts or pipe to account for cap slope; plumbness of column
conditions expected in the field;
bars or dowels; and provisions for out-of-tolerance substruc-
· Determine the grout cube strength corresponding to the
ture elements.
flow achieved;
Handling and placement are specified as follows: · Examine grout for undesirable properties such as segregation;
· Establish the adequacy of proposed grouting equipment
Handling of precast bent caps shall satisfy the provi-
such as the mixer, pump, tremie tubes, and vent tubes;
sions of Article 8.16.7.4.
· Provide jobsite personnel experience in mixing and han-
The Contractor is solely responsible for ensuring the
stability of the bent cap prior to and during grouting or dling grout prior to actual connection grouting; and
concreting operations. · Help the contractor to make a judicious decision regarding
All grades, dimensions, and elevations shall be deter- grout brand and its use.
mined and verified before the bent cap is placed. The
contractor shall verify proper alignment between the The trial batch is specified as follows:
columns or piles, including column bars, dowels, corru-
gated metal ducts, steel pipes, and other connection
At least 2 weeks prior to grouting of connections, a
hardware cast into the bent cap.
trial batch of grout shall be prepared to demonstrate
All loose material, dirt, and foreign matter shall be
grout properties per Article 8.13.8.3.2a and adequacy
removed from the tops of columns or piles before the
of equipment and to familiarize job site personnel with
cap is set.
grouting procedures.
A batch of grout shall be the amount of grout sufficient
Grouting of Grouted Duct Connection to complete an entire connection or number of connec-
tions and is limited to the amount of grout that can be
Grouting is a crucial operation for use of a precast bent cap placed within the pot life determined in the trial batch.
system using the grouted duct connection. Because it involves For continuous placement using a grout pump, a batch
shall be defined as one connection or one bent cap.
procedures, operations, and equipment that may not be famil- Partial batches will not be allowed and shall be discarded.
iar to the Contractor, specifications provide sufficient detail The Contractor shall establish grout flowability by
to ensure that connections are properly made in the field. measuring efflux (flow) time of the grout with a standard
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flow cone according to the Corps of Engineers Flow Cone grouting. Vent tubes shall have a minimum 1/2-in. inner
Method, CRD-C 611 and ASTM C939. The flow time shall diameter and shall be flush with the top of the bedding
be determined twice: (1) immediately after mixing and layer. Vents shall not be plugged until a steady stream
(2) at the expected working time corresponding to the of grout flows out.
pot life of the grout. The ambient temperature and Grout shall be deposited such that all voids in the
mixing water temperature at the time of trial batch bedding layer and bent cap are completely filled. Grout
mixing shall be within +/- 5 deg F of that expected at shall be consolidated at intervals during placement
the time of grout placement. The Contractor shall estab- operations as needed. All connections shall be grouted
lish that the grout flow time satisfies the limits prescribed in a manner that deposits the grout from the bedding
in Table 8.13.8-1. layer or bottom of connection upward. When pumping
Observation of segregation, clumps of grout, or other is used, grout shall be placed through ports located at
anomalies in the final trial batch shall be cause for rejec- the bottom of the bedding layer. To prevent introduc-
tion of the proposed brand of grout. Samples used for ing air into the system, when continuous flow grouting
testing shall be taken from the middle of the batch. is not possible, shutoff valves shall be required.
One set of six (6) grout cubes shall be prepared as All exposed grout surfaces shall be cured in accor-
specified in Article 8.13.8.5.4c to verify the compressive dance with manufacturer's recommendations.
strengths shown in Table 8.13.8-1. All grout surfaces shall be inspected post-grouting
The Contractor shall validate the proposed grout in coordination with the Engineer. Any voids shall be
placement technique by using the trial batch grout and repaired as specified in the mitigation plan in Article
grout equipment in a sample grouting operation simi- 8.13.8.4.2.
lar to the proposed connection grouting. Pumping shall Grout shall not be disturbed and connections shall
be validated in the trial batch in cases where it is pro- not be loaded until final acceptance of the connection.
posed for field placement. Adequacy of the mixer, pump, Final acceptance of the connection shall be after the
tremie tubes, vent tubes, and other grouting equipment grout has reached a compressive strength in accordance
shall be established. The contractor shall demonstrate with the "Final Strength" shown in the plans or as
that the equipment is adequate for mixing the grout approved by the Engineer.
and grouting the connection within the pot life of the
batch and does not introduce air into the grout or con-
Grout Testing. Grout testing is specified as follows:
nection. A wire mesh shall be used to filter out poten-
tial clumps when transferring grout between the mixer
and containers. The compressive strength of the grout for "Beam
Setting Strength" and "Final Strength" shall be deter-
Grout Placement. Grout placement is specified as follows: mined using grout cubes prepared and tested in accor-
dance with ASTM C109. The contractor shall prepare a
minimum of six (6) cubes per batch. A Commercial
All equipment necessary to properly perform grouting
Testing Laboratory approved by the Engineer shall test
operations shall be present before actual grouting oper-
the specimens for "Beam Setting Strength" and "Final
ations begin. All grouting operations shall be performed
in the presence of the Engineer in accordance with the Strength." Grout failing to meet the minimum required
Precast Bent Cap Placement Plan. Grouting operations compressive strength may be cause for rejection of the
shall be performed under the same weather limitations connection, grout removal, and re-grouting of the con-
as cast-in-place concrete and as required by the grout nection by means approved by the Engineer.
manufacturer. Grout pumping shall be required for con-
nections that cannot be completed by other methods Protection of the grout cube specimens in the field is criti-
within the pot life established for the grout during the cal and should be performed as required by ASTM C942. Prior
trial batch.
All additional materials required to ensure proper to testing, all cubes should be measured for mass determina-
connection of bent cap to column, such as but not lim- tion. The typical break pattern is also to be noted. Curing and
ited to bedding layer hoops, shall be properly placed ambient temperatures are to be reported as well as flow deter-
according to shop drawings. minations per ASTM C939.
All surfaces to be in contact with the grout shall be
cleaned of all loose or foreign material that would in any
way prevent bond prior to setting bedding layer forms. Concreting of Cap Pocket Connection
Bedding layer forms shall be drawn tight against the
existing concrete to avoid leakage or offsets at the joint. Concreting of cap pocket connections addresses similar
All previously hardened concrete surfaces that will be in
issues as grouting of the grouted duct connection: trial batch,
contact with the grout shall be pre-wetted to a surface-
saturated moist condition when the grout is placed. concrete placement, and concrete testing.
Drain ports or holes shall be provided to allow residual
water from pre-wetting to drain prior to grouting. The handling and placing of concrete for the cap
Forms for the closure pour between the cap and column pocket fill in precast bent cap connections shall con-
shall be adequately vented to allow air to escape during form to the requirements of Article 8.7 except as those
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requirements are modified or supplemented by the used in the field placement. Adequacy of the mixer,
provisions that follow. pump, tremie tubes, vibrators, vent tubes, and other
concreting equipment shall be established. The contrac-
tor shall demonstrate that the equipment is adequate
Trial Batch. The trial batch is a key step in achieving
for mixing, placing, and consolidating the concrete in
the required installation and performance of a cap pocket the connection within the pot life of the batch and does
connection. The purposes of a trial batch are to do the not introduce air into the connection.
following:
Concrete Placement. Concrete placement in the cap
· Determine the required amount of water and admixtures pocket is specified as follows:
required to achieve acceptable flowability and pot life
under the temperature and humidity conditions expected All equipment necessary to properly perform con-
creting operations shall be present before actual con-
in the field; creting operations begin. All concreting operations
· Determine the corresponding cylinder strength; shall be performed in the presence of the Engineer in
· Examine the concrete for undesirable properties; accordance with the Precast Bent Cap Placement Plan.
· Establish the adequacy of proposed concreting equipment Concreting operations shall be performed under the
such as the mixer, pump, tremie tubes, vibrators, and vent same weather limitations as cast-in-place concrete.
Concrete pumping shall be required for connections
tubes; that cannot be completed by other methods within
· Provide jobsite personnel experience in mixing, placing, the pot life established for the concrete during the trial
and consolidating the concrete in the connection prior to batch.
actual connection concreting; and All additional materials required to ensure proper
· connection of bent cap to column, such as but not lim-
Help the contractor to make a judicious decision regarding
ited to bedding layer hoops, shall be properly placed
concrete mix and associated operations. according to shop drawings.
All surfaces to be in contact with the cap pocket con-
The trial batch for cap pocket concrete is specified as crete shall be cleaned of all loose or foreign material
follows: that may in any way prevent bond prior to setting bed-
ding layer forms.
Bedding layer forms shall be drawn tight against
At least 2 weeks prior to concreting of connections, a the existing concrete to avoid leakage or offsets at
trial batch of concrete shall be prepared to demon- the joint. All previously hardened concrete surfaces
strate concrete properties per Article 8.13.8.3.3a and that will be in contact with the cap pocket concrete
adequacy of equipment and to familiarize jobsite per- shall be pre-wetted to a surface-saturated moist con-
sonnel with concreting procedures. dition when the concrete is placed. Drain ports or
A batch of concrete shall be the amount of concrete holes shall be provided to allow residual water from
sufficient to complete an entire connection or number pre-wetting to drain prior to concreting. Forms for
of connections and is limited to the amount of concrete the closure pour between the cap and column shall be
that can be placed within the pot life as determined in adequately vented to allow air to escape during con-
the trial batch. For continuous placement using a con- creting. Vent tubes shall be flush with the top of the
crete pump, a batch shall be defined as one connection bedding layer and have an inner diameter adequate
or one bent cap. Partial batches will not be allowed and for venting air and allowing concrete to flow out.
shall be discarded. Vents shall not be plugged until a steady stream of
The Contractor shall establish concrete flowability concrete flows out.
using AASHTO T 119, Slump of Hydraulic Cement Concrete shall be deposited such that all voids in
the bedding layer and bent cap are completely filled.
Concrete. The Contractor shall establish that the slump
Concrete shall be deposited through the top opening
satisfies the requirements of Article 8.13.8.3.3a during
of the cap pocket in a manner that deposits the con-
all stages of placement of the concrete fill.
crete from the bedding layer or bottom of connection
Observation of segregation or other anomalies in
upward. Concrete in the pocket shall be vibrated in
the final trial batch shall be cause for rejection. Samples accordance with Article 8.7.3. All exposed cap pocket
used for testing shall be taken from the middle of the concrete surfaces shall be cured in accordance with
batch. Article 8.11.
One set of six (6) cylinders shall be prepared and All concrete surfaces shall be inspected post-concreting
tested in accordance with Article 8.5.7 to verify the in coordination with the Engineer. Any voids shall be
compressive strengths required by Article 8.13.8.3.3a. repaired as specified in the mitigation plan in Article
The Contractor shall validate the proposed concrete 8.13.8.4.2.
placement technique by using the trial batch concrete Concrete shall not be disturbed and connections
and concreting equipment in a sample concreting oper- shall not be loaded until final acceptance of the con-
ation similar to the proposed connection concreting. nection. Final acceptance of the connection shall be
Pumping shall be validated in the trial batch if it is to be after the cap pocket fill concrete has reached the
