National Concrete Consortium Embassy Suites, Indianapolis, In Measuring the Effectiveness of Cure Materials Dan G. Zollinger, Ph.D., P.E. Professor, Texas A&M University Zachry Department of Civil Engineering College Station, TX 77843-3136, USA
Content Outline Curing Compound Specification - ASTM C 156 New Test Protocol New Test Protocol and Application to the Field
Evaporation Factors
Importance of Curing Existence of water is essential for hydration process; Too much water loss results in high porosity, less abrasion resistance and low strength; Evaporation 80~90% rh High porosity exposes Stress Distribution concrete more Moisture Distribution ~98% rh vulnerable to moisture and chloride erosion Tensile Stress
CRC Construction
Curing Compound Specification Curing Qualification: ASTM C 156 (Tex 219F); ASTM C 309; ACI 305R Ambient Conditions, and Application Quality/Spray Technology Curing Compound Quality A good curing Practice is achieving a balance of these components! Curing Application Quality Ambient Conditions
Evaporation Retardant
Curing Compound Classification Classification: SealTight 2255: ASTM C 309, Type 2, Class B SealTight 1640: ASTM C 309, Type 2, Class A SealTight 1250: ASTM C 309, Type 2, Class B SealTight 1240: ASTM C 309, Type 2, Class B SealTight 1600: ASTM C 309, Type 2, Class A SealTight 2250: ASTM C 309, Type 2, Class B AHT : ASTM C 309, Type 1, Class B ECO cure : ASTM C 309, Type 2, Class B
Legend: Resin Pigment Mineral Spirits Surfactant Water PVC=Pigment Volumetric Concentration = Vpigment V + V pigment VOC=Volume of Mineral Spirit Concentration Water and Mineral Spirit evaporate resin Curing Compound layer Pavement Surface Prior to Breaking After Breaking
ASTM C 156 (Tex 219F) Measurements: weight loss of mortar Specimen dimension: top 6 by 12 in. bottom 5 1 / 4 by 11 3 / 4 in. thickness 2 in. Curing cabinet: Temperature: 100±2 ºF RH : 32± 2%
ASTM Water-Retention Limits total loss,kg/m^2 total loss, lbs/ft^2 total loss, 100% 24 hours 72 hours 24 hours 72 hours 24 hours 72 hours ASTM C 309, AASHTO M148 N/A 0.550 N/A 0.113 N/A 4.280% ACI 305 R N/A 0.390 N/A 0.080 N/A 3.025% Some other states N/A 0.250 N/A 0.051 N/A 1.939% TxDOT 219F 0.258 0.516 0.0528 0.106 2.000% 4.000% Note: in TxDOT specification, water loss is defined as : water loss from mortar specimen total water in mortar specimen
ASTM Test Conditions Curing cabinet: Temperature: 100±2 ºF RH : 32± 2% The PE for ASTM C 156 is 0.066 lb/ft 2 /hr. PE in Texas can go up to 0.600 lb/ft 2 /hr. Singular Test Conditions Lack of sensitivity to ambient conditions ACI 305 R
Mortar s Hardening Effects A special test Chamber Conditions: Temperature: 104 0 F (40 0 C) Relative Humidity: 30% Wind Speed: 10 mph PE: 0.395 lbs/ft^2/hr 6 diameter 2 thick plate 1250 Normal curing compound Application rate: 200 ft^2/gallon
Moisture Loss vs. Time The difference in the first 12 hours First 12 hours 12 hours ~ 24 hours Weight Loss, lbs/ft 2-1 -0.9-0.8-0.7-0.6-0.5-0.4-0.3-0.2-0.1 0 1 with cc without cc Stage I Weight Loss, lbs/ft 2-0.07-0.06-0.05-0.04-0.03-0.02-0.01 0 1 with cc without cc Stage II 24 hours ~ 48 hours 48 hours ~ 72 hours Weight Loss, lbs/ft 2-0.06-0.05-0.04-0.03-0.02-0.01 0 1 with cc without cc Stage III Weight Loss, lbs/ft 2-0.035-0.03-0.025-0.02-0.015-0.01-0.005 0 1 with cc without cc Stage IV
Moisture Loss vs. Strength Full sized cylinder strength has limited sensitivity to effects of moisture loss Moisture limit is indirectly related to curing quality. Fully Cured Sample Top Defected Sample Measuring strength of the whole cylinder may not reflect the strength loss of the thin top portion
New Lab Test Protocol Table 3 Mixture Proportion. Unit Weight (lb/ft 3 ) W/C Mixture Water Cement Sand 0.40 13.94 34.84 95.81
Monitoring Equipment Wind Speed Sensor Solar Radiation Sensor Ambient RH Sensor Filtered RH Chamber Curing Monitor System Sealed RH Chamber Concrete RH Sensor
Laboratory Equipment Weighing Scale Filtered Chamber Curing Compound Sprayer Test Setup
Typical Test Results 100 Surface RH Concrete RH Ambient RH 75 RH, % 50 25 0 0 10 20 30 40 50 60 Time Elapsed, hrs
Relative Humidity: Filtered 100 90 80 70 RH, % 60 50 40 30 WC LIC - Above LiRC RC HRRC-Cal LIC - Below 20 10 0 5 10 15 20 25 30 35 40 45 Time, hrs EI t = t e s t t us us Curing Compound 30 hr Equivalent Age, hrs Evaluation Index, EI RC 20.61 0.36 HRRC 23.56 0.55 LiC 26.75 0.82 LiRC 23.24 0.56 Note: t s = 29.16 hrs; t us = 15.85 hrs
Dielectric Measurements Permittivity Parameter Measurement 25
Dielectric Reading 35 30 25 DC 20 15 10 RC HRRC LiRC LIC WC 5 0 0 5 10 15 20 25 30 35 40 Time, hrs
Volume (m 3 ) Mass (kg) V p Air Voids Free Water (lost) w free_lost w free_tot V w Free Water w free w net Phys.-Bound Water Phase Subscripts: V HCP Gel Water Hydrated Cement M HCP w n c h p = porosity (air) c w = free (capillary) moisture V Cu Un-reacted Cement c u HCP = hydrated cement product V s Aggregate M s s = aggregates 27
Field Monitoring: Wax-Based 100.0 25 90.0 80.0 20 70.0 Relative Humidity, % 60.0 50.0 40.0 30.0 4:30pm 15 10 Dielectric Constant Sealed rh Cured rh amb rh ε pos #1 ε pos #2 ε pos #3 ε pos #4 20.0 5 10.0 0.0 0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 Time After 4:30 pm, hrs
Field Monitoring: Lithium Cure
Application Chart E 1 1 e filtered t e open R T Tr ; e β rh e sealed te open t EI = t = e t t
Curing Compound Spraying Technology Bob Coats Gomaco, Ida, Iowa Nozzles are replaceable and come in 2 sizes Spray bar height is adjustable Rate of Travel is adjustable Automate/retrofit: Rate of application Pressure/rate of travel Bar height Monitor application amount
Application Control Q = Flow Rate (gal/min) = 25gal =13.6 gal/min; 1:50 370ft V = =202 ft/min; 1:50m Q 13.6 gal / min = = = 1 / 371 V * w 202 ft / min*25 ft 2 AR gal ft pass Or 1 gal/185 sq ft Q 13.6 V = = = 163 ft/min per pass AR * w 1/ 300*25 163 level setting of 9; *9 = 7 202 AR = Application Rate (gal/ft ) = 1 per 200 ft w = pavement width (25 ft) 2 2
Summary
Volume-Dielectrics Relationship of Fresh PCC Fresh PCC defined as 5-phases system Volume Fraction Dielectric Constant Free water θ w w θ w = wnet net ε 1 Hydrated cement product Unreacted cement θ ( 1 f ) θα( t) = + hcp v c θ = θ 1 α ( ) uc c t ε 2 ε 3 Composite Dielectric Constant ( ε ) Aggregate θ agg (fixed) ε 4 Air voids ( ) θ 1 θ θ θ θ = + + + ε 5 ( = 1.0) air w hcp uc agg θ = θ + θ + θ + θ + θ = 1 i w hcp uc agg air
New Approach for Fresh PCC Self Consistent Model for PCC ε ε ε ε ε ε ε ε ε + + + + ε = + 2 + 2 + 2 + 2ε ε + 2ε 1 2 3 4 5 θ w θ hcp θ uc θ Agg θ Air ε1 ε ε2 ε ε3 ε ε4 5 0 Volumetric Relationship θ w ε ε ε ε ε3 ε ε ε + θ ( 1+ f ) α( t) + θ 1 α ( t) + θ ε + 2ε ε + 2ε ε + 2ε + 2ε 1 2 4 c v c Agg 1 2 3 ε 4 Free water HCP Unreacted cement Aggregate { ( ) } ε ε + 1 θ 1 5 w + fvα t θc θagg = 0 ε + 2ε Air 5
Table 1 Description of Volume Relationships and Dielectric Constant of Components. Dielectric Component Volume Relationship Remark Constant Free Water θ w ( t) θ w w = wnet net HCP θ ( 1 f ) θα( t) Unreacted Cement Aggregate Particle hcp v c ε 1 = + ε 2 ( ) Time-dependent - Time-dependent - f v 1.4 θuc = θc 1 α t ε 3 Time-dependent θ agg ε 4 Fixed amount Air Void θair 1 ( θw θhcp θuc θagg ) = + + + ε 5 Time-dependent Total (composite) θ i = 1 ε c ε ε ε ε ε ε ε ε θ + θ ( 1+ f ) α( t) + θ 1 α( t) + θ ε + 2ε ε + 2ε ε + 2ε ε + 2ε 1 2 3 4 w c v c Agg 1 2 3 4 ε ε + { θw + fvα( t) θc θagg} = ε + 2ε 5 1 1 0 5
Mercury Intrusion Porosimetry: Concrete Surface (MIP ASTM D 4284, D 4404, D 2873) Evaluate curing effectiveness based on porosity. Advantage: test the top concrete where curing quality matters. Customized sample dimension 1 in 1/4 in
MIP Test Conditions Basic Environmental Conditions: Temperature:100±2 ºF RH :32± 2% 1 2 Wind Speed, mph 0.00 10.00 20.00 PE, lbs/ft 2 /hr 0.07 0.33 0.60 Designed AR, ft 2 /gallon 60.00 90.00 180.00 Measured AR, ft 2 /gallon 55.32 103.36 180.18
Samples under Various PEs (a) high wind speed. (b) medium wind speed. (c) no wind. (d) sealed specimen
Mechanistic Curing Effectiveness Capillary Porosity, cc/g 0.02 0.015 0.01 0.005 0 120 Application Rate 90 60 Wind Speed 25 mph Wind Speed 10 mph Wind Speed 0 mph EI CE ) = EI ln( 1250 AR a b PE c Where, a, b, c, and d are regressed from MIP test results, EI1250 is the evaluation index of WR Meadow 1250, and EI is the evaluation index of the curing compound used in the field. d a b c d 179.744 4.223 0.968 1.192 EI AR = a ln( CE EI 1250 ) + d PE c 1/ b