Performance of Concrete Rehabilitation using Rapid …docs.trb.org/prp/14-1361.pdf · 1 Performance...

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Performance of Concrete Rehabilitation using 1

Rapid Setting CalciumSulfoAluminate Cement 2

at the Seattle-Tacoma Airport 3

4

July 28, 2013 5

6

Corresponding Author 7 Chris Ramseyer 8

University of Oklahoma 9 Associate Professor, Director Fears Structural Engineering Lab 10

202 W. Boyd, room 334 11 Norman, Oklahoma 73019 12

United States 13 Phone: 405-406-2330 14

Fax: 405-325-4217 15 Email: [email protected] 16

17 18 19

Co-Author 20

Shideh Shadravan 21

Cornell University 22

325 Hollister Hall 23

Ithica, New York 14850 24

United States 25

Phone: 405-974-8066 26

Email: [email protected] 27 28 29

number of words in text = 4377 30 31

number of figures, tables, or photographs = 12 32 33

34

TRB 2014 Annual Meeting Original paper submittal - not revised by author

1

Abstract 1

2

This paper summarizes the results from an experimental study on the behavior of concrete 3

pavement in a controlled environment. The test program characterizes the volume change or 4

dimensional properties of selected concrete materials, evaluating their performance as real 5

pavements in that they are exposed to the controlled environment on the top surface and to 6

the ground moisture on the bottom surface. The concrete mix designs examined included 7

normal-strength Portland cement concrete (PCC), high-strength concrete (HSC), concrete 8

using shrinkage reducing admixtures (SRA), and concrete using Calcium sulfoaluminate 9

cement (CSA). The data includes standard concrete material characterization test results, joint 10

movements, internal relative humidity and temperature over the pavement depth. It was found 11

that the concrete using CSA was very stable with no long term shrinkage, cracking or 12

warping, while typical PCC and HSC continued to show crack growth at over 600 days of 13

age. The concrete using SRA had a minor decrease in shrinkage and crack growth at an early 14

age, and while this decrease extended for the length of the testing no further decrease in the 15

shrinkage growth or sectional stability was noted when compared to normal PCC at the end 16

of approximately two years. 17

18

19


2

1. Introduction 1

Drying shrinkage is one of the common causes of cracking in concrete slabs-on-ground 2

including pavements. As concrete dries, the water mix in concrete begins to evaporate from 3

the top surface of concrete. Therefore, a moisture difference is generated between the top and 4

bottom surface of the slabs. This causes a dimensional or “shrinkage” gradient to develop 5

into the slabs (Carlson, 1938; Tremper and Spellman, 1963; Ytterberg, 1987). Because the 6

concrete surface is restrained by many factors such as friction between bottom surface of slab 7

and subgrade, form work or surrounding objects and moisture difference through the depth of 8

the slab, it resists the effects of shrinkage. Therefore, an additional tension applies to the 9

concrete. As the tensile stress in the concrete exceeds the tensile strength of the concrete, 10

cracking and warping occurs (ACI, 2008). 11

12

Shrinkage is the most important factor influencing warping, curling and cracking of slabs or 13

pavements (Mailvaganam et al., 2002). In this research, warping is defined as a phenomenon 14

occurring due to uneven moisture conditions in the slab, whereas curling is defined as a 15

phenomenon occurring due to the uneven temperature through the depth of a slab. Warping 16

and curling have major effects on serviceability and performance of the concrete slabs-on-17

ground, necessitating their maintenance and repair. Drying shrinkage, a type of shrinkage in 18

concrete, is one of the major causes of cracks in concrete particularly in slabs-on-ground. 19

Shrinkage does not begin at the time of loading or drying; rather, it starts immediately after 20

cement and water come in contact during the concrete mix (Ramseyer, 1999; Holt, 2001). 21

Prediction of drying shrinkage in concrete is difficult because many affecting factors are 22

involved. According to many researchers (Tremper and Spellman, 1963; Hansen, 1987; Hart, 23

1928; Meininger, 1966; Neville, 2000; Powers, 1959; Washa, 1955), the amount of water per 24

unit volume of concrete or the ratio of water to cement has a significant effect on the 25

shrinkage process of concrete. Also, the amount of cement per unit volume is one of the most 26

important factors contributing to shrinkage (Mailvaganam et al., 2002; Troxell et al., 1968; 27

Nagataki, 1970). Thus, concrete shrinkage increases with using more water and cement 28

(paste) in concrete. The moisture content of the sub-base has also an important effect on the 29

drying shrinkage and curling moment of the concrete (Nagataki, 1970; Suprenant, 2002). As 30

the shrinkage gradient rises the curling moment of concrete increases (Carlson, 1938; Keeton, 31

1979). Also, temperature and relative humidity at the surface of the slab, along with moisture 32

content in the sub-base, greatly affects the amount of curling at slab edges (Mailvaganam et 33

al., 2002; Suprenant, 2002). 34


3

1

As described in the preceding paragraphs, there have been numerous analytical and 2

experimental investigations to characterize drying shrinkage as a material property. There, 3

however, are not enough data to evaluate the strains and stresses within concrete subjected to 4

moisture gradients and restrained shrinkage. Given this gap, this research provides an 5

opportunity to improve our understanding of warping and our ability to predict its effects. 6

The general objectives of this research are: 7

8

(1) To provide reliable warping data in a controlled environment for typical Portland cement 9

concrete, high-strength concrete, Portland cement concrete with shrinkage reducing 10

admixture, and Portland cement concrete with calcium sulfoaluminate cement (also known as 11

“shrinkage compensating concrete”); 12

(2) To investigate a representative selection of shrinkage magnitude for concrete; 13

(3) To develop a better understanding of ASTM C 157 and C 878 test methods (ASTM, 14

2008) versus the “shrinkage from time zero” test method; and 15

(4) To characterize behavior of slabs-on-ground for the selected materials where shrinkage 16

and warping are a concern. 17

18

This paper summarizes the research for seven large-scale test specimens of slabs-on-ground 19

with the six selected concrete mixtures monitored for approximately 2 years. This research 20

follows the test protocol of Bissonnette et al. (2007) for slabs-on-ground with more realistic 21

conditions. The main variables of the investigation are the concrete composition (Portland 22

cement concrete, high-strength concrete, concrete with shrinkage reducing admixtures, and 23

concrete with calcium sulfoaluminate cement). The items monitored for the investigation 24

include visual observation of cracks; surface strains obtained using Demec target strain 25

gauges; interior relative humidity and interior temperature in 12.7 mm increments through the 26

depth of a slab; compressive strength; unrestrained and restrained expansion; and shrinkage 27

from time zero test results. This was done in order to obtain as much information as possible 28

for a better understanding of warping and shrinkage, to enhance the prediction of its effects, 29

and to compare the dimensional stability sensitivity of various materials. 30

31

32

33

34


4

2. Experimental program 1

2.1 Concrete mixtures and materials 2

Six concrete mixtures were selected for the investigation: normal-strength Portland Cement 3

Concrete (PCC), High-Strength Concrete (HSC), normal concrete mixes with two types of 4

Calcium SulfoAluminate cement [Komp I and Rapid Setting CSA Cement] (CSA and 5

RSCC), and normal concrete mixes with two types of common Shrinkage Reducing 6

Admixtures [Eclipse and Tetraguard] (SRA #1 and SRA #2). The only difference between 7

PCC and concrete mixes with SRAs is adding SRAs to the same PCC mixes. The concrete 8

mixes used in this research are summarized in Table 1. The mixtures (CSA and RSCC) using 9

two types of calcium sulfoaluminate cement, Komp I(CSA), a so-called shrinkage 10

compensating concrete and Rapid setting CSA cement (RSCC) which were made in the 11

mixer at the laboratory. The rest of the concrete mixtures (PCC and HSC) using normal-12

strength and high-strength concrete were provided by a local ready mix concrete company in 13

Oklahoma. 14

15

Table 1 Concrete mixes for slab specimens. 16

Materials

(kg/m3)

SRA #1 SRA #2 PCC HSC CSA-a CSA-b RSCC

Komp I - - - - 71.2 71.2 -

Portland Cement 211.1 210.5 210.5 322 219.4 219.4 -

Fly Ash 52.2 52.2 52.2 106.7 - - -

Rapid setting CSA Cement - - - - - - 390.2

Citric Acid - - - - - - 2.97

Course Aggregate 57 1097.1 1097.1 1097.1 1097.1 1037.8 1037.8 1050.8

Sand 867.6 867.6 867.6 709.2 779.8 779.8 775.1

Water 157.7 157.7 157.7 156.6 160.1 161.3 172

MR (Polyheed 1020 (L/m3)) - - - - 2.48 2.5 2.04

MR (Pozzolith 80 (L/m3)) 0.5 0.54 0.54 1.12 - - -

Eclipse (L/m3) 4.95 - - - - - -

Tetraguard (L/m3) - 4.95 - - - - -

Water-to-cement ratio 0.023 0.023 0.023 0.014 0.021 0.021 0.017

28 day compressive strength

(MPa) 26.2 23.8 21.7 36.2 41 39 69

17

18

19

20

21

22

23


5

2.2 Characterization tests for materials 1

A number of characterization tests, as listed in Table 2, were developed in the investigation to 2

typify the materials. The characterization tests followed ASTM standard tests such as 3

compressive strength test (ASTM C 39), length change test (ASTM C 157), and restrained 4

expansion test (ASTM C 878). Therefore, cylinders and prism test specimens were filled with 5

the concrete from each batch. The ASTM test measurements began at the first few hours after 6

placing concrete into the form according to the test method description. Also, the shrinkage 7

from time zero method was used for the purpose of characterizing the materials. Test 8

specimens were made 75 x 75 x 325 mm. A 25 mm plastic block was placed at one end of the 9

specimen. Therefore, concrete was free to move due to shrinkage at this end (free end). A 10

steel plate (form) on the other end of specimen restrained the concrete in shrinkage and 11

expansion provided fixed end (Figure 1). Two bolts were screwed at the center of the ends. 12

The bolts were 279 mm apart and were used as the original length of specimens for 13

calculating the strain 14

Table 2 Material characterization tests 15

Test description Lab RH & T

60% RH 21 °C 30% RH 21 °C

Compressive

strength (ASTM C

39)

+

–

Length change

(ASTM C 157) + +

Restrained

expansion (ASTM C

878)

+

–

shrinkage from time

zero test method

+

–

16

(Figure 1). A dial gauge was installed at the free end (the end with the plastic block) of each 17

specimen and the length change was recorded at the time “zero” which was immediately after 18

placing concrete into the form (Figure 1) and were continued for 110 days. The dial gauge 19

was connected to the bar and bar went through the hole and touched the back of the nut 20

(bolt). The specimens were placed in the chamber at 21°C and 60% relative humidity and 21

were wet cured by placing wet sponges on top of specimens for 7 days. Then the specimens 22

were demolded from the sides (not the ends). The concrete mixes used for the shrinkage from 23

time zero method were similar to the large-scale slab concrete used in this study with the 24

minor exception being due to the type of water reducer used on 4 of the samples. 25


6

1

Figure 1 Shrinkage from time zero test mold and shrinkage from time zero test specimen. 2

2.3 Slab experiments 3

Seven slab test specimens of 75 mm x 900 mm x 6000 mm were cast on 100 mm moist 4

compacted sand on the ground (Figure 2). Two slabs (CSA-a and CSA-b) produced with 5

calcium sulfoaluminate cement of Komp I and one slab per other combination of concrete 6

mixes (PCC, HSC, RSCC, SRA #1 and SRA #2) was cast. The slab specimens were located in 7

the test facility with a controlled environmental chamber. The laboratory relative humidity 8

and temperature are generally 60% and 21 ºC. The relative humidity was dropped to 30% for 9

the second year of the investigation as part of the experiment. The purpose of reducing 10

ambient relative humidity was to increase the moisture gradient into the slab due to a lower 11

relative humidity at the top surface of the slab. Slabs were cast in specially designed pits, 12

truly on-grade. The idea was that while the base is kept moist by ground water, the top of the 13

slabs are exposed to the low ambient relative humidity environment in the lab; this increases 14

the moisture gradient in the slab and increases warping. 15

16

Figure 2 (a) Slab on 102 mm moist-compacted sand on grade and (b) 225 mm of concrete 17

slab edge restrained by trusses 18


7

1

The slabs were fully restrained longitudinally by casting the test slabs around a transverse 2

steel truss that was attached to the edges and the test pits. The steel trusses shown in Figure 2 3

transfer all the loads to two D25 reinforcing bars (diameter = 25 mm), cast previously in the 4

existing floor along each edge of the test specimen. The test slab ends were thickened to 230 5

mm to accommodate this detail (Figure 2). A minimum longitudinal reinforcing steel for 6

temperature ( s = 0.0015) was used for all of the slabs. Four 6.35 mm diameter longitudinal 7

reinforcing bars were continuous through the joints. Upon casting the slabs, contraction joints 8

were saw cut 25 mm deep at 1500 mm from each end to provide a 3000 mm long central test 9

section. All the slab specimens except one (RSCC) were cured with wet burlap and a plastic 10

sheet for 7 days. The slab (RSCC) made with Rapid setting CSA cement was cured with 11

spraying water for 4 ~ 5 hours after casting. 12

13

Slab monitoring began after 7 days of moist curing. The monitoring consisted of the 14

following: (1) visual observation for surface cracking; (2) surface strain and joint opening 15

measurement in the longitudinal direction using Demec target strain gauges with 178 mm 16

gauge length; (3) internal relative humidity at 12.7 mm increments through the depth of the 17

slab (ASTM F 2170); (4) internal temperature at 12.7 mm increments through the depth of 18

the slab; and (5) ambient relative humidity and temperature. The slab monitoring represented 19

the behavior of slab exposed to the low relative humidity at the top surface and high relative 20

humidity at the bottom surface of the slab. Figure 3(a) shows the location of Demec target 21

strain gauges at mid-span at 1500 mm from the ends and the location of the RH (Relative 22

Humidity) meter at 375 mm from mid-span of the slab. Figure 3(b) shows a profile of the slab 23

deformation due to warping. It displays the end restraints and warping at joint opening. 24

25

26

27

28

29


8

1

(a) Top view of slab specimen 2

3

(b) Profile of slab deformation due to warping 4

Figure 3 Top view and profile of slabs-on-ground specimen (Note: 1 in. = 25 mm; 1 ft = 300 5

mm) 6

7

3. Test results and discussion 8

3.1 Characterization test results 9

The ASTM C 39 compressive strength results were recorded for one year, the ASTM C 157 10

length change results were recorded for approximately 2 years (Figure 4(a)), and the ASTM 11

C 878 restrained expansion results for CSA were recorded during the time the concrete 12

expanded due to the test method description. The ASTM C 157 method is a standard test 13

method for length change of hardened hydraulic-cement mortar and concrete, and the ASTM 14

C 878 method is a standard test method for restrained expansion of shrinkage compensating 15

concrete (CSA). Upon curing the specimens into the limestone and water (saturated water 16

with lime) for 7 days, measurement of length variations was initiated. From Figure 4(a), the 17

comparison between PCC and SRA #1 results represents that SRA #1 had a minimal impact 18

on shrinkage at short term and almost no impact at long term. Therefore, it can be concluded 19

that the shrinkage reducing admixture did not provide a noticeable improvement on reducing 20

over all shrinkage in normal concrete. The HSC shrank in a greater rate in comparison to the 21

other concrete mixes used in this research. The difference between HSC and PCC was due to 22

many issues that affect the shrinkage in HPC, like all types of concrete shrinkage (e.g., 23


9

autogenous shrinkage, porous system, capillary size, paste quantity, etc.) but the increased 1

paste volume in HSC is generally referenced as a leading contributor to the increase in 2

shrinkage (Mailvaganam et al., 2002; Troxell et al., 1968; Nagataki, 1970). 3

4

5

Figure 4 (a) Unrestrained expansion ASTM C 157 versus time (PCC, HSC and SRA #1) and 6

(b) restrained expansion ASTM C 878 versus time (CSA) 7

8

On the other hand, the CSA expanded more than 4 times greater than the other concrete 9

mixtures during the first 7 days of curing (Figure 4(b)). It can be expected that the large 10

expansion of CSA is able to offset the restrained shrinkage caused by drying shrinkage of 11

concrete at the long term and that the possibility of warping and cracking caused by drying 12

shrinkage is reduced. Note that shrinkage compensating cement concrete (CSA) was used for 13

two of the concrete specimens (CSA-a and CSA-b), and both concrete mixes exhibited similar 14

characteristics. Therefore, all the results showing CSA are the average of the data from the 15

two concrete specimens using CSA. It is noted that the ASTM C 878 method provides data 16

only for expansion of CSA; therefore, the shrinkage from time zero tests were additionally 17

conducted for an equal basis comparison as described in the following paragraphs. 18

19

The shrinkage from time zero test results were recorded for 28 days and 110 days. Comparing 20

the results from the shrinkage from time zero method to the ASTM C 157 unrestrained 21

0 50 100 150 200 250 300 350 400 450 500 550 600

Day

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

Str

ain

(%

)

SRA #1

HSCPCC

0 50 100 150 200 250 300 350 400 450 500 550 600

Day

-0.15

-0.1

-0.05

0

0.05

0.1

Str

ain

(%

)

CSA (Avg. of CSA-a & CSA-b)

SRA #1


10

expansion results shows that the trend after 7 days was the same for both testing methods 1

(Figure 5). The concrete specimens for the shrinkage from time zero method did not show 2

expansion in the first 7 days of curing because the expansion was restraind due to the steel 3

plate at the fixed end of the specimens (Figure 3), while the expansion was unrestrained for 4

the ASTM C 157 method.. It is noted that the shrinkage from time zero method was found 5

easier to perform in comparison with the ASTM C 157 and C 878 methods. Figure 5 is a 6

representative result comparing two testing methods for PCC and SRA #1. 7

8

9

Figure 5 Shrinkage from time zero test results for SRA #1 in comparison with those obtained 10

from ASTM C 157 11

12

The Shrinkage from time zero test results are also compared with those of the ASTM C 878 13

method for CSA in Figure 6. The shrinkage from time zero test results show the same general 14

trend when compared to that of the ASTM C 878 method. Both testing methods showed 15

expansion for the first 7 days of curing; however, the amount of expansion was different due 16

to the smaller stiffness of the rod used to restrain expansion of concrete for the ASTM C 878 17

18

Figure 6 Shrinkage from time zero test results for CSA in comparison with those obtained from ASTM C 878 19

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Day

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

Str

ain

(%

)

SRA #1 (Shrinkage from Time Zero)

SRA #1 (ASTM C 157)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Day

0

0.02

0.04

0.06

0.08

0.1

Str

ain

(%

)

CSA (Shrinkage from Time Zero)

Avg. of CSA-a & CSA-b (ASTM C 878)


11

method, compared with the stiffness of the steel frame used to restrain expansion of concrete 1

for the shrinkage from time zero method. Overall, there was little shrinkage in CSA for about 2

110 days of curing after the initial expansion, which verified the effectiveness of shrinkage 3

compensating concrete in reducing the drying shrinkage. 4

5

3.2 Slab monitoring results 6

3.2.1 Surface measurements and joint opening 7

The average joint opening data for the six concrete mixtures of seven slabs are represented in 8

Figure 7, with complete surface measurements for all the slabs provided in Figure 3. The 9

average of the east and west opening strains were used. The shrinkage was measured from the 10

point of initial set and continued for 600 days. This measurement is not exactly the same as 11

those from the ASTM C 157 and C 878 methods, because the slab bottom is exposed to the 12

moisture in the soil and the slab top is exposed to the relatively low humidity in a controlled 13

environment, while for the ASTM C 157 and C 878 methods, all sides of the specimens are 14

exposed to the controlled relative humidity. The relative humidity of the lab (air above the 15

top of the slab) was 60% for the first year and then was reduced to 30%. 16

17

Figure 7 Width of joint opening versus time 18

19

Figure 7 shows the average width of the joint opening versus time and illustrates that the use 20

of SRA only reduced shrinkage in the first week. After the first week the slope of the line 21

representing the SRA data matches the slope of the line for PCC. This once again indicates 22

that the use of SRA reduced shrinkage at short term but did not impact the shrinkage at long 23

term. Figure 7 also shows that HSC had the largest expansion/crack at the joints and CSA had 24

the smallest expansion/crack at the joints. When comparing the strain of control joints for 25

CSA with SRAs, it is found that shrinkage compensating concrete (CSA) had a positive effect 26

on reducing shrinkage of concrete at both short and long terms compared with all concretes 27

0 50 100 150 200 250 300 350 400 450 500 550 600

Day

0

1

2

3

4

5

6

7

8

Wid

th o

f Jo

int

Op

en

ing

(m

m)

0

1

2

3

4

5

6

7

8

Wid

th o

f Join

t O

penin

g (

mm

)

HSCPCC

SRA #2

SRA #1RSCC

CSA (Avg. of CSA-a & CSA-b)


12

including SRAs. Conversely, joint opening expansion continued over the long term (over 600 1

days) with PCC, HSC and SRAs. The comparison between HSC and PCC shows that the 2

cracks of HSC were wider than those of PCC, and HSC also shrank quicker than normal 3

concrete (PCC). The HSC shrank at a faster rate than other mixes during the first few weeks 4

(early age) after curing. Based on the discussion in this and the preceding paragraphs, it is 5

concluded that the use of CSA reduces warping in comparison to the other types of concrete 6

used in this research. 7

8

Table 3 summarizes the joint expansion (crack growth) for the mixes after 574 days. It can be 9

seen that, the slab using SRAs shows join expansion 2.1 to 2.4 times greater than CSA, PCC’s 10

joint expansion was 3.7 times greater than CSA, and HSC’s joint expansion was 4.6 times 11

greater than CSA. Therefore, it can be concluded that CSA is very stable with less crack and 12

warping at long term compared to other mixes in this research. 13

14

Table 3 Joint expansion at 574 days, 15

Mix Joint expansion (mm) Compared to CSA

CSA 1.6 -

SRA #1 3.4 231%

SRA #1 3.9 244%

PCC 5.9 367%

HSC 7.4 459%

16

17

3.2.2 Comparing slab monitoring with ASTM C 157 18

Figure 8 shows the slab behavior in comparison with the ASTM C 157 method for SRA #1, 19

PCC and HSC. A significant difference was observed between the slab behavior and the 20

ASTM C 157 results. Again, this might be due to the different conditions of humidity on each 21

face of the slab. In light of that, it appears that the ASTM C 157 method does not provide 22

accurate results for predicting slab-on-ground behavior. Conversely, the current slab-on-23

ground experiment reflects the realistic exposure conditions and actual dimensional and 24

material properties of concrete. 25


13

1

2

3

Figure 8 Strains at mid-span for SRA #1, PCC and HSC in comparison with those obtained 4

from ASTM C 157 5

6

3.2.3 Interior relative humidity and temperature 7

This subsection presents general results for internal temperature and relative humidity of 8

slabs-on-ground, measured after 1 year. Figure 9(a) shows that there were no temperature 9

changes through the depth of the slabs which means the ambient temperature remained 10

constant, whereas Figure 9(b) presents that the RH of the slabs within the top 12.5 mm of 11

concrete slab was higher than the ambient relatively humidity in the air. From the internal 12

relative humidity of slabs (Figure 9(b)), it is found that HSC had the highest moisture 13

gradient and CSA had the least moisture gradient. The PCC, SRA #1, SRA #2 and RSCC 14

0 50 100 150 200 250 300 350 400 450 500 550 600

Day

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

Str

ain

(%

)

Slab at Mid-Span

ASTM C 157

(a) SRA #1

0 50 100 150 200 250 300 350 400 450 500 550 600

Day

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

Str

ain

(%

)

Slab at Mid-Span

ASTM C 157

(b) PCC

0 50 100 150 200 250 300 350 400 450 500 550 600

Day

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

Str

ain

(%

)

Slab at Mid-Span

ASTM C 157

(c) HSC


14

moisture gradients were between CSA and HSC. There were almost no changes in the 1

moisture content at 63.5 mm depth in the slab. Most of the moisture content changes occurred 2

between 25 and 63.5 mm depth from the top surface of the slab. Similar trends were observed 3

after reducing the ambient RH (in the air) to 30% from 60%. The measured interior relative 4

humidity (RH) of the slabs-on-ground is directly related to warping. The materials RH 5

gradient is related to a strain gradient due to the materials tendency to swell of shrink due to 6

moisture. In this case CSA has less of a RH gradient which indicates it has less of a strain 7

gradient and as such it is less sensitive to warping than typical Portland cement concrete or 8

high-strength concrete, Shadravan (2011) reports the complete results for the slabs’ interior 9

temperature and relative humidity, as well as ambient temperature and relative humidity in 10

the air. 11

12

Figure 9 Interior slab temperature and relative humidity as a function of depth from slab top 13

surface, measured after 1 year of curing 14

15

The discussion in the preceding paragraph brings up two possible hypotheses. The first 16

possible hypothesis is that the porosity of the HPC is low since it is hard for moisture to get 17

in to the concrete from the bottom surface of the slab and it is much easier to dry it out from 18

the top. Thus, the least porous material has the lowest average relative humidity, The second 19

possible hypothesis is that HPC is the most porous material that has the lowest relative 20

humidity at the top surface (i.e., the concrete is drying further into its core). These two 21

hypotheses, however, would require further research to validate and may be influenced by 22

other factors such as the amount of paste in each mix. 23

24

25

26

67 68 69 70 71 72 73 74

Temperature (oF)

50 60 70 80 90 100

Relative Humidity (%)

-80

-70

-60

-50

-40

-30

-20

-10

0

Depth

(m

m)

-80

-70

-60

-50

-40

-30

-20

-10

0

Depth

(m

m)

(a) Interior Slab Temperature

RSCC

CSA

(Avg. of

CSA-a & CSA-b)

SRA #1, SRA #2, HSC and PCC (b) Relative Humidity

RSCCHSC

SRA #1 SRA #2

CSA (Avg.)PCC

[Air: 60% RH]

[Soil: 100% RH]


15

4. Conclusions 1

2

The main objective of this research was to provide reliable warping data based on the internal 3

strain measurements of pavement, ASTM C 157, ASTM C 878, and shrinkage from time zero 4

drying shrinkage measurements for the selected concrete mixtures in a controlled 5

environment. The main conclusions of the investigation are summarized as follows: 6

7

(1) Typical Portland cement concrete, high-strength concrete and concrete with SRAs 8

continued to exhibit increased crack growth at approximately 2 years. 9

10

(2) The shrinkage from time zero test method gets the same results, measures shrinkage more 11

accurately, and is easier to perform when compared to ASTM C 157 and C 878 method. 12

13

However, the shrinkage from time zero tests provide less accurate results for the prediction of 14

slabs-on-ground behavior when compared to the large-scale tests of actual slab-on-ground 15

exposed to realistic conditions. 16

17

(3) The ASTM C 157 method appears inadequate to assess slab shrinkage behavior because 18

the ASTM C 157 method and the actual slab-on-ground test method show significant 19

differences in the results. 20

21

(4) Based on the measured interior relative humidity of the slabs-on-ground, shrinkage 22

compensating concrete or concrete using calcium sulfoaluminate cement (CSA) was 23

inherently less sensitive to warping than typical Portland cement concrete or high-strength 24

concrete. 25

26

(5) Shrinkage compensating concrete or concrete using calcium sulfoaluminate cement was 27

extremely stable, with little or no long-term shrinkage, cracking or warping. This stability 28

was noted at both early age and at approximately 2 years. 29

30

(6) Shrinkage reducing admixtures decreased shrinkage and crack growth a small amount at 31

an early age but did not impact the rate of shrinkage growth or sectional stability after that 32

period of time. 33

34


16

1

Acknowledgements 2

The research lab construction and the materials used for the investigation has been financially 3

supported by CTS Cement Manufacturing Corporation. The views expressed are those of 4

authors, and do not necessarily represent those of the sponsors. 5

6

References 7

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23


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