Freeze-Thaw Durability Evaluation of

Shotcrete in Cold Climates

ZHIDONG ZHOU AND PIZHONG QIAO

DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING

WASHINGTON STATE UNIVERSITY

ZHIDONG.ZHOU@WSU.EDU, QIAO@WSU.EDU

AUG. 10, 2017

Introduction

Shotcrete is attractive for structures (retaining walls, soil nail/soldier pile fascia walls, etc.) due to its inherent cost and construction time saving potential

More strongly depends on the skills of nozzleman than normal concrete

Engineering issues:

Early-drying shrinkage cracking

Debonding from substrates

Long-term durability

Lack of suitable/effective test methods for evaluating related performance of shotcrete

Objectives

Development of a test plan for durability evaluation

Adopt the ASTM C666 (Freezing and thawing (F/T) conditioning) as

an accelerated conditioning test protocol

Propose the fracture energy test procedure to evaluate the long-

term performance of shotcrete

Develop a statistical prediction model for durability of shotcrete

Comparison with CIP concrete

Conduct comparative study on the durability performance between

shotcrete and CIP

Study Plan (Tasks)

ComparisonCompare shotcrete with Cast-in-Place (CIP) Concrete

Evaluation

Evaluate long-term durability performance

• Evaluate the internal damage due to freeze-thaw environment (ASTM C215 & C666)

• Conduct the fracture energy test to characterize durability of shotcrete

MaterialsFinalize the mix design and test methods

• Basic mechanical properties of fresh and hardened shotcrete

PredictionPredict the failure life of shotcrete in FT condition

Mix Design (from WSDOT)

Constituents UnitShotcrete Concrete (CIP)

Quantity

Cement lb/yd3 705 564

GGBFS lb/yd3 40 ---

Microsilica lb/yd3 50 ---

AEA oz/cwt 0.1-25 1-10

HRWRA or WRA oz/cwt 0.1-30 30-40

Water lb/yd3 267 246

Sand (Class 2) lb/yd3 2120 1860

Coarse

Aggregatelb/yd3 790 (3/8”) 1260 (1”)

Water/Cementitio

us Ratio (max)- 0.34 0.48

Test Methods

Properties Standards

Air Content ASTM C231

Slump ASTM C143

Compressive Strength ASTM C39

Modulus of Elasticity ASTM C469

Flexural Strength ASTM C78

Freeze-Thaw (Conditioning) ASTM C666

Dynamic Modulus ASTM C215

Fracture Test (Fracture Energy) RILEM 50-FMC

I. Finalize Mix DesignThe amounts of Air Entraining Admixture and HRWRA have to be adjusted within the given range in the mix design in order to obtain the optimal values:

ResultsShotcrete Concrete (CIP)

Measured optimal Measured optimal

Slump, in

5 (ensure the

pumpability, decreases

after shooting)

4-6 before

shooting

<3 after

shooting

4 3-6

Air

content,

%

10.2 (decreases after

shooting, ~half )

8 – 12

(fresh)***4.8 4-8

Density,

lb/yd3

137.7 (increases after

shooting)148.8

***“If air entrainment is to be used, an air content ranging from 8 to 12 percent prior to pumping is typical. The in-place shotcrete will have about one-half of the entrained air that was recorded at the pump.” Standard Practice for Shotcrete, US Army Corps of Engineers, 1993

Basic Mechanical Properties

Age,

days

Compressive

strength, psi

Modulus of

rupture, psi

Modulus of

Elasticity, ksi

7 4549 588 2669

14 5225 683 3150

28 6698 772 3501

Age,

days

Compressive

strength, psi

Modulus of

rupture, psi

Modulus of

Elasticity, ksi

7 3461 499 2950

14 --- 594 ---

28 4432 748 3400

Shotcrete (WSDOT)

CIP (WSDOT Class 4000)

II. Investigation of Durability

Freeze-Thaw Test (ASTM C666) – as accelerated conditioning protocol

◦ Specimen size : 3 x 4 x 16 inch prism

◦ Curing condition : moisture curing for 28 days

◦ No. of cycles : up to 600 cycles

◦ Temperature Range : 0 – 40 ° F (-18 – 4 ° C )

Dynamic Modulus Test (ASTM C215)

◦ Frequency of testing : Every 30 cycles

Cohesive Fracture Test (RILEM 50-FMC)

◦ Depth of Notch : Half the beam depth (2 inches)

◦ Interval of testing cycle : 0, 60, 120, 180, 240, 300, 450, 600

Rapid Freeze-thaw Test (ASTM C666)

o Being used to condition the concrete prism samples

o The temperature range: 0 to 40°F (-18 to 4°F)

o The cycle frequency is 6 cycles per day (or 4 hrs/cycle)

o 600 cycles of F/T corresponding to 10 years of service

Dynamic Modulus (ASTM C215)o Being used to evaluate the dynamic modulus of concrete prism samples under specific F/T conditioning cycles

oThe impact test method is used to measure the transverse frequency, and an accelerometer (output signal) is attached to one end of the beam

Dynamic Modulus (ASTM C215)

M is the mass of the sample; n is the

fundamental transverse frequency;

For a prism3

30.9464 LC T

bt

L is the length of the sample; and t and b

are the thickness and width of the sample,

respectively. T is a correction factor that

depends on the ratio of the radius of

gyration to the length of the specimen and

the Poisson's ratio, 1.41 in this study.

Relative Dynamic Modulus of Elasticity Damage 𝐷 = 1 −𝐸𝑑𝑦𝑛 (𝑁)

𝐸𝑑𝑦𝑛 0 𝐷 = 1 −

𝐸𝑑𝑦𝑛 (𝑁)

𝐸𝑑𝑦𝑛 0

Fracture Energy Test (RILEM 50-FMC)

Sample Preparation for Fracture Energy Test

Three point bending beam specimen

Typical load–deflection curve from

the fracture energy (GF) test.

W1

0W

W2

P

1P 0

Fracture Energy Test (RILEM 50-FMC)

Test setup

Surface Scaling Process

o Scaling of paste and mortar

mainly occurred at the bottom

surfaces and ends due to frost

actions

o More serious after 300 F/T cycles

o Small pieces of shotcrete at the

ends were spalled after 600 cycles

Mass Loss

o Mass loss percentage: 1.68% and 2.20% after 300 freeze-thaw

cycles for shotcrete and CIP concrete, respectively.

o Mass loss percentage: 2.81% and 2.90% after 600 freeze-thaw

cycles for shotcrete and CIP concrete, respectively.

Shotcrete exhibited less mass loss and lower mass loss

percentage than CIP concrete

Dynamic Modulus-Shotcrete

Cycles Frequency, HzDynamic Modulus,

ksiRDM, %

0.00 1753.03 3716.80 100.00

30.00 1748.17 3696.19 99.45

60.00 1747.13 3691.82 99.33

90.00 1742.63 3672.83 98.82

120.00 1743.07 3674.67 98.87

150.00 1737.23 3650.13 98.21

180.00 1729.23 3616.60 97.30

210.00 1725.07 3599.20 96.84

240.00 1712.53 3547.05 95.43

270.00 1704.73 3514.81 94.57

300.00 1700.97 3499.29 94.15 (DF)*

450.00 1665.30 3354.12 90.24

600.00 1609.83 3134.39 84.33

*DF: Durability Factor

Dynamic Modulus-CIP

Cycles Frequency, HzDynamic Modulus,

ksiRDM, %

0.00 2071.80 5208.02 100.00

60.00 2039.40 5022.08 96.43

120.00 2005.20 4833.67 92.81

180.00 1989.60 4732.29 90.87

240.00 1981.00 4660.93 89.50

300.00 1963.40 4573.47 87.82(DF)*

360.00 1949.10 4500.38 86.41

420.00 1942.60 4467.02 85.77

480.00 1922.10 4363.61 83.79

580.00 1904.30 4274.99 82.08

680.00 1896.60 4226.83 81.16

*DF: Durability Factor

Comparisons of dynamic modulus

Shotcrete shows much lower degradation rate of

dynamic modulus than CIP (reduction % of dynamic

modulus: 5.85% of shotcrete vs. 12.18% of CIP at 300 F/T

cycles)

ASTM limit

Load-Deflection Curves-Shotcrete

Load-Deflection Curves-Shotcrete

Fracture Energy-Shotcrete

CyclesPeak

load, NSTDEV

Relative

peak load,

%

Work

Energy,

N/mm

STDEV

Relative

fracture

energy, %

0 1329.33 119.09 100.00 105.3 3.11 100.00

60 1337.33 119.53 100.60 95.69 2.11 90.87

120 1320 113.33 99.30 94.71 1.97 89.94

180 1235.33 14.97 92.93 90.21 4.57 85.67

240 1127.33 66.43 84.80 88.14 6.83 83.70

300 1102 59.00 82.90 88.25 3.01 83.81(DF)

450 1034 13.45 77.78 85.46 8.29 81.16

600 945.67 42.02 71.14 74.5 4.66 70.75

Fracture Energy-CIP

Cycles Peak load, N STDEV

Relative

peak

load, %

Work

Energy,

N/mm

STDEV

Relative

fracture

energy, %

0 457.23 2033.86 100.00 164.53 12.69 100.00

60 484.79 2156.45 106.03 180.96 19.1 109.99

120 440.98 1961.57 96.45 164.76 19.23 100.14

180 406.72 1809.18 88.95 146.5 18.98 89.04

240 373.67 1662.17 81.73 140.33 21.61 85.29

300 374.62 1666.38 81.93 123.26 16.73 74.92(DF)

500 336.91 1498.65 73.69 100.63 14.39 61.16

700 312.97 1392.17 68.45 84.934 14.01 51.62

Comparisons of Fracture Energy

Shotcrete shows lower degradation rate of fracture energy than

CIP (reduction % of fracture energy: 16.19% of shotcrete vs.

25.08% of CIP at 300 F/T cycles)

Comparison between methods

Testing Method ASTM C666 Fracture Energy

Durability Factor (DF)

@ 300 F/T cycle

94.15 (Shotcrete) 83.81 (shotcrete)

87.82 (CIP) 74.92 (CIP)

Durability Factor (DF)

@ 600 F/T cycle

84.33 (Shotcrete) 70.71 (shotcrete)

81.98 (CIP) 55.54 (CIP)

Fracture energy test is more sensitive to indicate the

degradation rate when compared to dynamic modulus test

Dynamic Modulus Fracture Energy

Weibull Reliability Function

Probability of Failure

Probability of Reliability

𝐹𝑓 𝑁 = 1 − 𝑒𝑥𝑝 − 𝑁 − 𝛾

𝛼 𝛽

𝑅𝑓 𝑁 = 𝑒𝑥𝑝 − 𝑁 − 𝛾

𝛼 𝛽

Where α is the scale parameter (or characteristic life) that locates the life

distribution, β > 0 is the shape parameter (or slope) that serves as the

inverse measure of the dispersion in the F/T cycles) life results, and γ > 0 is

the location parameter (or the failure free life) also known as the minimum

life parameter.

III. Statistical Prediction Model

Reliability Prediction

Probability of Failure Probability of Reliability

Relative Dynamic of Modulus of Shotcrete

Fails @ 1250 F/T cycles

Reliability Prediction

Probability of Failure Probability of Reliability

Fails @ 760 F/T cycles

Relative Fracture Energy of Shotcrete

Conclusions

• The accelerated F/T conditioning protocol following ASTM C666 is

suitable for shotcrete durability evaluation.

• Both the dynamic modulus of elasticity and fracture energy tests are

capable of screening the material degradation by the F/T cycles.

However, fracture energy test method is more sensitive, since the

degraded material is prone to fracture.

• Shotcrete degrades slower than CIP at the end of 300 & 600 F/T

cycles (via both the dynamic modulus and fracture energy tests),

indicating shotcrete has better performance than CIP in cold

climates

Acknowledges

• Washington State Department of Transportation (WSDOT)

• Center for Environmentally Sustainable Transportation in Cold Climates (CESTiCC)

QUESTIONS???