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