Fresh and Hardened Properties

Internal Curing: Research Results and Two LADOTD Case Studies Zachary Collier, E.I.—Louisiana DOTD

Authors:

Tyson D. Rupnow, Ph.D., P.E.

Zachary Collier, E.I.

Patrick Icenogle, E.I.

Objective:

Determine if internal curing using prewetted

lightweight aggregate is a viable option to re-

duce cracking and decrease the need for labor

intensive wet curing on bridge decks.

Prewetted Lightweight Aggregate

Our research focused on the re-

placement of fine aggregate with

prewetted lightweight aggregate

Limited cost increase

5% to 25% replacement of fine ag-

gregate

Laboratory Study

Type I/II Portland cement

67 limestone and natural sand

600 lb. of cement, 60:40 aggregate ratio

Super plasticizer and air entraining agent used

0.35 and 0.45 w/cm

Specimens to be cured at both 50% and 100% RH

Determine effects on compressive strength

Determine effects on flexural strength

Determine effects on surface resistivity

What percentage of replacement is suitable?

Laboratory Mixes

Centrifuge West Congress Street Bridge

LTRC

Lab # Description

#67 Limestone

(lbs.)

Sand

(lbs.)

Expanded

Clay (lbs.)

Type I/II

Cement (lbs.) w/cm

Unit Weight

(pcf)

C-4061 0.45 control 1935 1255 -- 600 0.45 150

C-4062 0.45 5% LW 1935 1091 95 600 0.45 148

C-4124 0.45 10% LW 1939 934 186 600 0.45 147

C-4125 0.45 15% LW 1957 760 278 600 0.45 143

C-4126 0.45 20% LW 1915 644 371 600 0.45 141

C-4127 0.45 25% LW 1935 470 463 600 0.45 139

C-4128 0.35 Control 2004 1343 -- 600 0.35 151

C-4129 0.35 5% LW 2032 1152 97 600 0.35 151

C-4130 0.35 10% LW 2022 991 195 600 0.35 149

C-4131 0.35 15% LW 2031 819 291 600 0.35 147

C-4133 0.35 20% LW 2035 657 385 600 0.35 146

C-4134 0.35 25% LW 2018 504 485 600 0.35 140

Unit weight was decreased but still considered normal weight concrete

Slump, air, and set times were unaffected

Compressive strengths generally increase as more lightweight fines are introduced for the

0.45 w/cm ratio

Compressive strengths for the 0.35 w/cm ratio showed no changes

Overall flexural strength decreases with increased fines content. Although at 100% RH the

difference if within the error of the test.

The lower w/c ratio had higher resistance, we can also see that as the lightweight fines

content increases the resistivity generally increases

0.45 w/cm Compressive Strength

0.35 w/cm Compressive Strength Surface Resistivity

Flexural Strength

Parish line between Lafayette and Acadia parishes

13 in thick slab span structure

One 25 ft. center span, two adjacent 20 ft. spans, with a 10

ft. approach slab on each end

Each end slab was internally cured, as well as the east ap-

proach slab and south rail

Date Outside Temp.

(F)

SR 28-Day

(kΩ-cm)

Control 2/26/2016 50 9

IC Span 1 3/13/2015 75 8

IC Span 2 3/17/2015 77 10

Crack survey completed February 2016 (11

months from construction, about 9 months after

opening)

Bridge only has two cracks

Both longitudinal in the western control slab

Measured approximately 6 ft. and 16 in.

0.012-0.014 in width

Will Continue to monitor periodically

Future ICC bridge in Lafayette planned

U.S. 80 KCS Railroad Crossing Located in Bienville Parish, just east of Ada, LA

Incorporated two different IC concrete mixture designs in the

deck slab construction

150 pcy of lightweight fines 300 pcy of lightweight fines

Link slab construction, 300 ft. long pour with a 50 ft. wide deck

Each placement consisted of 350 cubic yards of ICC

Control section shows more random cracking even though it was

the last section poured

Conclusions

Internally cured concrete has the potential to increase service life of bridge

decks due to the reduction in cracking

Hardened concrete properties are adequate if not increased

No impact on fresh properties

Field monitoring will continue

An important part of producing ICC is determining the moisture state of the light weight

aggregate.

Quicker testing time

ASTM 1761, “Paper towel” method is slow at almost an hour and a half and subjective

Centrifuge methods take less than 15 minutes

Repeatable

Test method is repeatable across multiple users

2000 rpm for 3 minutes