**Internal Curing of Concrete Bridge Decks \-\-- Demonstration of Early
Age Crack Mitigation and Evaluation of Enhanced Freeze-Thaw
Performance**

Proposal for a Transportation Pooled Fund (TPF) Study

VTRC Contact: Stephen Lane, 434-293-1953,
<Stephen.Lane@vdot.virginia.gov>

NIST Contact: Dale P. Bentz, 301-975-5865, <Dale.Bentz@nist.gov>

**Project Goals:** 1) Demonstrate the performance benefits of internal
curing provided by pre-wetted lightweight aggregates to concrete used in
transportation structures;

> 2\) Investigate hypothesized additional benefits such as slump
> retention and increased freeze-thaw durability.

**Deliverables:** 1) Interim report documenting the laboratory study;

> 2\) Guide document on evaluating lightweight aggregates for use as
> internal curing agents and proportioning and producing concrete with
> lightweight aggregate internal curing;
>
> 3\) Final report summarizing the effort and documenting the
> performance of the field projects.

**Estimated duration:** 36 months

**Proposed budget:** \$600,000

**Project Description:**

In numerous laboratory and a few large scale field studies, the
utilization of pre-wetted lightweight aggregates (LWA) to provide
internal curing to mortars and concretes has been verified (see
<http://ciks.cbt.nist.gov/~bentz/phpct/database/ic.html> for a listing
of relevant papers and reports). Experimental measurements have
indicated a substantial reduction (or even complete elimination) of
autogenous shrinkage, the maintenance of a higher internal relative
humidity throughout curing, and an increase in later age hydration and
compressive strengths, particularly under sealed curing conditions. The
first two of these should result in a substantial reduction in early-age
cracking, while the latter provides for a more complete utilization of
and may even allow for a reduction in the (most expensive) cementitious
components of the concrete. These improvements have been quantitatively
demonstrated for mortars and concretes based both on ordinary portland
cements and on blended cements (containing slag, silica fume, or fly
ash). Furthermore, three-dimensional x-ray microtomography studies have
conclusively indicated the movement of internal water from the LWA to
the surrounding hydrating cement paste during the first hours and days
of curing. In addition, there may be further benefits of utilizing
internal curing using pre-wetted LWA, such as the production of a
concrete with greater slump retention (workability) and a more robust
air void system, the latter due to the pores in the emptied LWAs
functioning as "physical" air voids in addition to any entrapped and
entrained air normally present in or proportioned into the concrete.

The purpose of the proposed three-year pooled-fund study would be
two-fold: to demonstrate the performance of internal curing utilizing
pre-wetted LWA in actual bridge decks and to investigate the
hypothesized supplementary benefits such as slump retention and
freeze-thaw durability. A technical advisory committee (TAC) will be
formed to provide guidance and oversight of the project and refine the
working plan. The TAC will meet at the beginning of the project to
provide detailed input and feedback for the proposed research plan, and
yearly thereafter. The Virginia Transportation Research Council will
provide project administration, coordination, and management.

In the 1^st^ phase of the study, the different LWAs to be employed will
be extensively characterized using the techniques listed below and an
existing mixture proportion for bridge deck concrete will be
appropriately modified to incorporate internal curing (different
mixtures for the different LWAs). In the 2^nd^ and 3^rd^ phases of the
study, both laboratory and field concrete specimens will be evaluated
for a variety of physical properties (see list below). Rheological
characterization as a function of the time elapsed since initial mixing
will be performed using a concrete rheometer (available at NIST).
Freeze-thaw testing will be performed at the Virginia Transportation
Research Council (VTRC) using conventional laboratory testing equipment
(ASTM C666, etc.) on the laboratory and field concretes, and on a
supplemental set of internally cured concretes in which the entrained
air content has been systematically varied (and characterized). Plastic
shrinkage and warping will be evaluated in a fashion similar to that
described in ASTM C1579-06. Projected outputs of the project include a
guidance document for evaluating lightweight aggregates as internal
curing agents and subsequently proportioning a mixture with internal
curing, a report contrasting the performance of the laboratory
concretes, and a final report that includes the performance of the field
concretes.

**Parameters to be Investigated in the Phase 1 and 2 Studies:**

Quantify influence of internal curing on properties of ready-mixed
concrete for bridge decks as a function of the size fraction of LWA
employed (fine, mid range to fill in a gap graded mixture, or coarse).
How well do the different size ranges of LWA accomplish the goals of
internal curing and providing various supplemental benefits?

**Description of Phase 1 Study:**

In the phase 1 study, lightweight aggregates will be obtained from
various producers, including those participating actively in the
pooled-fund study. Each source of aggregates will be characterized using
the following techniques:

Particle Size Distribution (sieving)

Specific Gravity (Saturated Surface-Dry) (ASTM standard methods C 127
and C 128)

Specific Gravity (dry) (helium pycnometer)

Absorption Rates (based on mass gain during immersion for various
periods of time)

Desorption Isotherms (exposure to saturated salt solutions at constant
temperature,

following protocols in ASTM standard method C 1498)

Low Temperature Calorimetry (NIST protocol) for examining pore sizes

Scanning Electron Microscopy (NIST techniques) or 3-D X-ray
microtomography for

pore sizes and connectivity

The above characterization will assist in the mixture proportioning of
the bridge deck concrete mixtures incorporating internal curing. In
addition, the cementitious (or mortar) component of the selected
existing mixture will be characterized with respect to its chemical
shrinkage using the ASTM standard method C 1608. Then, knowing both the
(curing) water demand of the concrete and the water supply available
from the LWA, appropriate mixture proportioning can be employed. The
projected mixture proportions will then be modeled using the NIST hard
core/soft shell (HCSS) model to estimate the effectiveness of the
different size range LWAs in delivering water to all of the cement paste
component of each concrete mixture. The LWA characterization and
(theoretical) mixture proportioning will comprise phase 1 of the study.
Phase 1 will culminate with the production of a report providing
guidelines for evaluating lightweight aggregates as internal curing
agents and determining appropriate mixture proportions for concretes
incorporating internal curing.

**Description of Phase 2 Study:**

At the end of the phase 1 study, a set of different (size range) LWAs
will have been characterized with respect to internal curing and
preliminary mixture proportions for each LWA established. In phase 2,
these concretes will be produced using conventional ready-mix concrete
equipment, and characterized in the laboratory with respect to the
following properties:

Compressive Strength (lab cylinders, sealed curing - 1, 2, 3, 7, 14, 28,
56, 90 d)

Static Modulus of Elasticity (3, 7, 28, and 90 d)

Splitting Tensile Strength (3, 7, 28, and 90 d)

Degree of Hydration (loss on ignition on sieved mortar fraction)

Heat Release (adiabatic or semi-adiabatic setup)

Isothermal Calorimetry (NIST- on sieved mortar fraction or separately
prepared mortars)

Autogenous Shrinkage (concrete dilatometer using concrete strength
cylinders)

Drying Shrinkage

Rapid Chloride Permeability (VTRC)

Sorptivity (NIST)

Freeze/Thaw Resistance (VTRC- ASTM standard method applied after
"sufficient"

curing)

Linear Traverse of "air void" parameters with/without inclusion of
"voids" in LWA

(VTRC)

Plastic Shrinkage/Warping

At the end of phase 2, a report will be produced detailing the final
mixture proportions for each LWA and comparing the properties that were
obtained with the different mixtures. Based on the results of phase 2,
one or more of the mixtures incorporating internal curing will be
selected for the phase 3 (field) study.

**Description of Phase 3 Study:** For phase 3, one or more job sites
will be identified for the construction of bridge decks incorporating
internal curing. It is envisioned that one bridge deck will be
constructed using the conventional mixture (without internal curing) and
one or more of the mixtures with internal curing evaluated in the phase
2 study will be used for the other bridge deck(s). The fresh concretes
will be evaluated for temperature, slump, unit weight, and air content,
and cores will be taken of the hardened concrete for the evaluation of
many of the properties included in the phase 2 study. In addition, the
skid resistance of the finished bridge decks will be evaluated during
the course of their first year of exposure. At the end of phase 3, a
final report will be produced detailing the initial performance of the
concrete bridge decks with and without internal curing and including
final recommendations for the concrete mixture proportioning and
construction of bridge decks with internal curing.

**Funding Requested:**

\$200 K per year for three years. (10 participants at \$20 K each). See
attached worksheet for details of timetable.

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                                     Year 1                                                Year 2                                                Year 3                           

  Task               1   2   3   4   5      6   7   8   9   10   11   12   1   2   3   4   5      6   7   8   9   10   11   12   1   2   3   4   5      6   7   8   9   10   11   12

  PHASE 1                                                                                                                                                                          

  Obtain LWAs                                                                                                                                                                      

  LWA                                                                                                                                                                              
  characterization                                                                                                                                                                

  Cement chem. Shr.                                                                                                                                                                

  Mixture                                                                                                                                                                          
  proportioning                                                                                                                                                                   

  Modelling                                                                                                                                                                        

  Phase 1 report                                                                                                                                                                   

  PHASE 2                                                                                                                                                                          

  Obtain concrete                                                                                                                                                                  
  materials                                                                                                                                                                       

  Preparation of                                                                                                                                                                   
  concretes                                                                                                                                                                       

  Evaluation of                                                                                                                                                                    
  properties                                                                                                                                                                      

  Phase 2 report                                                                                                                                                                   

  PHASE 3                                                                                                                                                                          

  Identification of                                                                                                                                                                
  job sites                                                                                                                                                                       

  Final trial                                                                                                                                                                      
  batches                                                                                                                                                                         

  Field concrete                                                                                                                                                                   
  placement                                                                                                                                                                       

  Coring and                                                                                                                                                                       
  Evaluation                                                                                                                                                                      

  Skid resistance                                                                                                                                                                  

  Final report                                                                                                                                                                     

                                                                                                                                                                                  

                                                                                                                                                                                  

  Cost estimates                                                                                                                                                                  

  Phase 1                                                                                                                                                                         

  \$220,500.00                                                                                                                                                                    

  Phase 2                                                                                                                                                                         

  \$189,000.00                                                                                                                                                                    

  Phase 3                                                                                                                                                                         

  \$189,000.00                                                                                                                                                                    

  Total                                                                                                                                                                           

  \$598,500.00                                                                                                                                                                    
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