LTC Implementation of LADOTD Mass Concrete & Maturity Testing Specifications. Presented by. Mark A. Cheek, PE, FACI Vice-President

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1 Implementation of LADOTD Mass Concrete & Maturity Testing Specifications Presented by Mark A. Cheek, PE, FACI Vice-President LTC 2018

2 Definition of mass concrete any volume of concrete with dimensions large enough to require that measures be taken to cope with generation of heat from hydration of the cement and attendant volume change to minimize cracking American Concrete Institute (ACI 207.1R-05)

3 What is mass concrete? Not all mass concrete placements are enormous pours! For most state DOT s, it is defined as any concrete placement where the smallest dimension exceeds 3-4 ft. Even thin placements like slabs and columns can qualify ACI commentary provides the following recommended limits: Thickness 4 ft Cementitious content 660 pcy

4 Industry Trends Larger concrete elements in structural applications Flowable / SCC High-strength concrete Rapid construction Service life requirements All of these are leading to more concrete placements being mass concrete. If not properly considered, can contribute to an increased risk of thermally induced damage!

5 Why do we care? High internal concrete temperatures can cause delayed ettringite formation (DEF)

6 High temperature differentials within a concrete placement can cause thermal cracking Early Ages Late Ages Hot Cool Cool Cool 6

7 Typical Specification Limits Maximum Temperature: Typical maximum temperatures range from 154 F to 160 F. If SCM s are used, limits sometimes increase to 170 F or higher. Maximum Temperature Differential: Typical limits range from 35 F to 38 F. More advanced modeling techniques allow for this to exceed typical limits (Performance based) 7

8 Thermal Control Plans Placement plans developed to decrease the risk of thermal issues. Typically include: 8 Thermal modeling Mix design Concrete & ambient temperature Element dimensions Thermal control measures Detailed placement plan Mix design Thermal control measures Embedded thermocouples to monitor placement

9 Concrete Mix Design Limit cementitious materials content Use supplementary cementitious materials Use fly ash and slag to lower temperature rise Fly ash up to 40-50% replacement typical Slag up to 70% replacement typical Silica fume can increase the temperature rise 9

10 Thermal Control Measures Passive: Surface insulation Blankets, form liners, foam insulation Precool the concrete Ice, cold water, liquid nitrogen Active: Cooling Tubes Passive measures typically require longer periods until the placement can be accessed than active control measures 10

11 LOUISIANA Standard Specifications for Roads and Bridger 2016

12 MASS CONCRETE Description Mass concrete is defined as a structural concrete placement having a least dimension of 48 inches or greater, or if designated on the plans or in the project specifications as being mass concrete. Drilled shafts are exempt from mass concrete requirements General Submit proposals for the mass concrete mix design, analysis, temperature monitoring, and control, including insulation and methods, to the Department for review and acceptance a minimum of 30 days prior to the placement of any mass concrete Materials The structural class designation for mass concrete is Class MASS (A1, A2, or A3) as shown in Table

13 Cement/Cementitious Combination Use Type II portland cement. Replace portland cement with fly ash at 20 percent to 50 percent by weight or replace with slag cement at 50 percent to 70 percent by weight or a ternary mix meeting specification requirements. Certify that the cementitious combination generates a heat of hydration of not more than 70 calories/gram (290 kj/kg) at 7 days as determined by ASTM C186.

14 Construction Produce a structure free from thermal cracks. Place mass concrete continuously to eliminate cold joints. Control differential temperatures by appropriate use of insulated forms, curing blankets, or other acceptable methods. If during the first 48 hours after placement, the temperature differential nears 35 ºF (20 ºC), take corrective measures immediately to remain within the limits. Furthermore, revise the plan to maintain the limits on differential temperature on any remaining placements of mass concrete. Obtain the engineer's acceptance of the revised plan prior to implementation. Strength gain and cooling of the mass concrete placements can take a long time. Take all such time and strength considerations into account when planning construction activities.

15 Analysis and Monitoring Submit an analysis to the engineer of the projected thermal developments within the mass concrete elements for the anticipated concrete and ambient temperatures, along with the proposed mix design and construction methods. Include a copy of model results, with site and element specific data, and any electronic files. Describe the measures and procedures intended to maintain, monitor, and control the temperature differential between the interior and exterior of the mass concrete elements. A maximum temperature during curing of 160 º F (70 º C) and a maximum differential temperature of 35 F (20 C) is allowed. An abbreviated submittal may be allowed for previously approved mass concrete mix designs.

16 Monitoring Devices Provide temperature-monitoring devices to record temperature development between the interior and the exterior of the element at points acceptable to the engineer. Monitor a minimum of two independent sets of interior and exterior points for each element to provide redundancy. Locate the monitoring points at the geometric center of the element for the interior point and two inches from the surface along the shortest line from the geometric center to the nearest surface of the element for the exterior point.

17 Monitoring devices shall be automatic sensing and recording instruments that record information at a maximum interval of one hour. Calibrate monitoring devices to the manufacture s recommendations. These devices shall operate within the temperature range of 0 to 180 ºF (-18 to 82 ºC) with an accuracy of ± 2 ºF (±1 C). Take readings and record the temperature data at intervals no greater than 6 hours to ensure that the automatic devices are working properly and that the temperatures are within allowable limits. The intervals of one and six hours shall begin immediately after casting is complete and shall continue until the maximum temperature differential is reached and begins to drop. Transmit these readings to the engineer daily. Prior to the placement of mass concrete, perform a test of the automatic and manual thermal sensing and recording equipment to ensure they are operational.

18 Macarthur Interchange Completion - Phase 1B (H )

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21 Mass Elements - 31 Footing (range in height from 5 to 8 ) Pier Placements (range in width from 5 to 25 ) 10 out of 39 Caps (range in depth from 4 to 7.5 )

22 Mix Design Cement Type I/II 162 lbs/yd 3 Slag Cement Grade lbs/yd 3 Water 238 lbs/yd 3 Coarse Aggregate 1879 lbs/yd 3 Fine Aggregate 1164 lbs/yd 3 Air Content 5% Chemical Admixtures ASTM C 494 Type A, HRWR W/CM 0.44

23 Thermal Model for 5 Thick Footing

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29 Installation Geometric center of the element for the interior point Two inches from the surface along the shortest line from the geometric center to the nearest surface of the element for the exterior point. At each location use a minimum two logger.

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31 Logger Types Cable Lengths 4ft to 200ft MAT-02-1H180D MAT-02-1M2D TPL-02-1H28D TPL-02-15M28D

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36 Insulation Recommendations Install blankets preferable before placement Blankets must completely cover all portions of the formwork and any portion that extends above or beyond the limits of the placement Blankets should be held tightly against the formwork to prevent air movement between the blankets and forms Protruding steel should be insulated Insulation for the placement should extend a minimum of 3 ft. onto any adjoining existing concrete

37 Monitoring Field Monitoring

38 Remote Monitoring Watch real time in your office and Text notifications

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47 Maturity Meters for Any-Time Strength Measurements

48 Brief History of the Maturity Method The maturity concept was proposed in the late 1940s and early 1950s as a technique to account for the combined effects of time and temperature on the strength development of a concrete mixture (Nurse 1949; McIntosh 1949; Saul 1951). Carino and Tank

49 Specifications ACI 301 Standard Specifications for Structural Concrete (paragraph 2.3.4) 318 Building Code Requirements for Structural Concrete (paragraph 6.2)

50 Specifications ACI 228.1R In-place Methods of Estimating Concrete Strength (paragraph 2.7) 306 Cold Weather Concreting (paragraph 6.4)

51 Specifications FHWA SA Guide to Non-destructive Testing of Concrete ASTM C 1074 Practice for Estimating Concrete Strength by the Maturity Method

52 Used by DOT s State Alabama Alaska Arizona Arkansas California Colorado Conneticut Delaware Florida Georgia Hawaii Idaho Illinois Indiana Iowa Kansas Kentucky Louisiana Maine Maryland Massachusetts Michigan Minnesota Mississippi Missouri Allows Mat Montana Nebraska Nevada New Hampshire New Jersey New Mexico New York North Carolina North Dakota Ohio Oklahoma Oregon Pennsylvania Rhode Island South Carolina South Dakota Tennessee Texas Utah Vermont Virginia Washington West Virginia Wisconsin Wyoming District of Columbia

53 Benefits of Using the Maturity Method (to the project) Accelerate construction schedules Reduce man-hours Reduce test specimen cost =

54 Remove shoring and re-shoring sooner Allows earlier form removal and with confidence that the operation is safe; rented forms can be returned sooner Post-tensioning tendons can be stressed earlier Open roadways to traffic in less time

55 Engineering Benefits of Using the Maturity Method Provides a better representation of in-place concrete strength gain (compressive or flexural) than laboratory or field cured specimens Enables any-time in-place strength measurements Enables in-place strength measurements at lowest strength (youngest concrete) locations Enables in-place strength measurements at critical stress locations

56 Maturity Rule Concrete of the same mix at the same maturity (reckoned in temperature-time) has approximately the same strength whatever combination of temperature and time go to make up that maturity. A.G.A. Saul, 1951

57 Maturity Functions Temperature-time Factor (Nurse-Saul) M = Σ (T a T o ) Δt Equivalent age (Arrhenius) t e = Σe Q [ 1/T a 1/T s ] Δt

58 Nurse Saul Function (Temperature time factor) M = Σ (T a T o ) Δt M = the temperature time factor (TTF) at age t, degree hours T a = average concrete temperature during time interval, Δt Δt = a time interval, hours T o = 0 C or 32 F

59 Datum Temperature T o = 0 C Traditionally, the datum temperature has been the temperature below which strength gain ceases, which has been assumed to be about 0 C (32 F)

60 In-Place Concrete Temperature (T a ) Ambient conditions Types & amounts of cementitious materials Admixtures Size and shape of the structure Formwork & Insulation

61 Implementing the Concrete Maturity Method Strength-Maturity Relationship Compressive Strength (psi) y = Ln(x) R 2 = Maturity Index (TTF) (C-hrs)

62 1. Develop a mixture specific calibration curve 2. Embed maturity loggers into plastic concrete 3. Take maturity (TTF) measurements 4. Use the calibration curve to estimate strength from maturity (TTF) measurements

63 Laboratory Test Data

64 Developing a mixture specific curve

65 Developing a mixture specific curve

66 Strength - Maturity Relationship 4000 Compressive Strength (psi) Day 3 Day 7 Day 14 Day 28 Day Maturity Index (TTF) (C - hrs.)

67 Strength-Maturity Relationship 4000 Compressive Strength (psi) Maturity Index (TTF) (C-hrs) Y = Ln(x) R 2 =

68 Maturity equation defines the strength-maturity relationship (logarithmic best fit curve) Y = Ln(x) The R 2 value indicates the reliability of the strength-maturity relationship R 2 =

69 Using the Strength-Maturity Relationship Curve Strength-Maturity Relationship 6000 Compressive Strength (psi) psi 4029 C-H Maturity Index (TTF) (C-hrs)

70 Utilizing Maturity for form Removal On average forms were removed 4 days earlier! Warm weather removed in 5 days Cold weather removed in 7 days

71 Questions