Smart Rock Plus Maturity Training Presented by Jaden
Smart. Rock™ Plus Maturity Training Presented by: Jaden Texeira, EIT Giatec Scientific
Session Overview 1. Strength Testing Methods & Standards 2. Maturity Equations 3. Maturity Calibration 4. Validation & Limitations 5. Where to Monitor Maturity & Strength Giatec Scientific 2
In-Place Strength of Concrete Field strength of concrete is required for critical operations such as: § Formwork removal § Post-tensioning § Tilt-up § Curing optimization § Saw cutting § Opening roads to traffic Giatec Scientific 3
Methods for Testing Concrete Strength Ø Field-cured specimens – ASTM C 31 Ø Cast-In-Place Cylinders – ASTM C 873 Ø Penetration Resistance – ASTM C 803 Ø Pullout Strength – ASTM C 900 Ø Rebound Hammer – ASTM C 805 Ø Maturity Method – ASTM C 1074 Giatec Scientific 4
Introduction to Maturity Skyline Towers in Fairfax County, 1973. § Progressive collapse from the 23 rd floor § 14 workers were killed § Premature removal of formwork (NBS and OSHA investigation) Cooling Tower in Willow Island, 1978. § Scaffolding systems anchored to a partially competed shell § 51 workers were killed § NBS commence in-depth study based on the urgent need for standards on estimating early age strength. Giatec Scientific 5
What is Maturity? Non destructive method to estimate the real-time strength development of the in-place concrete, specifically at early ages less than 14 days. § Uses the temperature and time to calculate maturity, correlated with historical strength data § Requires a calibration prior to use § Maturity calibration is specific for a mix design § Optimal for critical operations such as formwork removal, post-tensioning, curing optimization, saw cutting and opening roads traffic. Giatec to Scientific 6
What is Maturity? ASTM C 1074 - Maturity Method: “a technique for estimating concrete strength that is based on the assumption that samples of a given concrete mixture attain equal strengths if they attain equal value of maturity. ” C 40/50 – Sample 1 C 40/50 - Sample 2 = 1000 if M 1 = M 2 f 1 = f 2 Giatec Scientific 7
What is Maturity? A unique relationship between the Maturity Index (a function of concrete temperature) and Concrete Strength for each concrete mixture 40 Compressive Strength (MPa) 35 30 25 20 15 10 5 0 0 Giatec Scientific 2000 4000 6000 Maturity (ºC-hrs) 8000 10000 12000 8
North American Standards § ASTM C 1074, ASTM C 918 § ACI 318 -6. 2, ACI 228. 1 R, ACI 306 R § AASHTO T 325 § Accepted by majority of DOTs § CSA A 23. 1, 2 Giatec Scientific 9
Session Overview 1. Strength Testing Methods & Standards 2. Maturity Equations 3. Maturity Calibration 4. Validation & Limitations 5. Where to Monitor Maturity & Strength Giatec Scientific 10
Strength - Maturity Equations § Temperature-Time Factor, TTF (Nurse. Saul) § Equivalent Age (Arrhenius) § Weighted Maturity (NEN 5970) Giatec Scientific 11
Maturity Function Temperature-Time Factor (Nurse. Saul) Linear relationship between temperature and strength gain ü Most common ü Conservative ü Least complicated Giatec Scientific 12
Datum Temperature-Time Factor (Nurse. Saul) T 0 Time Giatec Scientific t 13
Datum Temperature (Td) Definition: The temperature at which the concrete stops developing strength. ASTM C 1074 states that; "For Type I cement without admixture and a curing range between 0 to 40°C, the recommended datum temperature is 0°C". Typical datum temperature can vary from -10 to 0°C. Giatec Scientific 14
What Td Should be Used? § Estimate Td= 0°C Conservative approach especially if the temperature falls below freezing (most common). § Estimating a lower Td This approach can overestimate the result if the temperature profile falls below the real datum temperature but can overall provide more accurate results in colder temperature. § Calculate the actual datum temperature by following ASTM C 1074. Full procedure requirements: Ø Minimum 63 mortar cubes ( 50 mm/ 2 in) Ø Select 3 curing temperatures (max, min and average) Ø Mortar must have same properties as the concrete Giatec Scientific 15
Maturity Function Equivalent Age (Arrhenius) Exponential relationship between temperature and strength gain ü Less common ü More accurate (if right assumptions) ü More complicated Giatec Scientific 16
Session Overview 1. Strength Testing Methods & Standards 2. Maturity Equations 3. Maturity Calibration 4. Validation & Limitations 5. Where to Monitor Maturity & Strength Giatec Scientific 17
How to Perform a Maturity Calibration? • Step 1: Prepare a minimum of 17 cylinders (2 for temperature and 15 for strength monitoring) • Step 2: Provide same curing condition for all the cylinders (constant temperature & moisture condition) • Step 3: Break 2 cylinders for every age, use the average strength value. Test the third cylinder if the difference in strength exceeds 10% of the average) • Step 4: Calculate average maturity at every age and develop maturity curve Giatec Scientific 18
How to Calculate Maturity? Use the Smart. Rock™ Plus app to calculate maturity. § Step 1: Use the Smart. Rock™ Plus sensors to monitor the temperature in the two cylinders. § Step 2: Assign a pouring time and a random mix to your sensor. (The mix must have the same datum temperature) § Step 3: The maturity will be calculated for you, view or export the data to get the maturity value at any given age. (Discard the strength value) Giatec Scientific 19
Compressive Strength Calibration Continued 1 2 3 5 Age 7 Temperature 30 28. 5 27 25. 5 24 22. 5 21 19. 5 18 0 20 40 60 Age Giatec Scientific 20
Calibration Results Maturity (ºC-hrs) (from app data) Strength (MPa) (from cylinder compression test) Day 1 690 5. 7 Day 2 1220 10. 2 Day 3 1708 15. 7 Day 5 3221 19. 0 Day 7 4531 21. 4 Time Giatec Scientific 21
Calibration Results Plotted 40 Compressive Strength (MPa) 35 30 25 20 fc = a + b log(M) 15 10 5 0 0 Giatec Scientific 2000 4000 6000 Maturity (ºC-hrs) 8000 10000 12000 22
RILEM International Union of Laboratories and Experts in Construction Materials, Systems and Structures FS = s * fc *Cv s = a parameter based on the safety margin adopted in practice according to the different situations For determining the period of curing s=0 For determining the time to strip form work s=1 For determining the time to apply prestressing s= 1. 5 fc = the mean measured strength in the calibration figure (PSI or N/mm 2) Cv = the coefficient of variation for a given production location and process. Obtained from the producer Giatec Scientific 23
RILEM Safety Factors Original Values Maturity (C-hrs) 493 Strength (MPa) 20. 7 964 28. 0 1445 32. 0 3405 40. 0 6769 46. 7 Maturity vs. Strength 50. 0 45. 0 40. 0 Factor of Safety: 3. 347 Parameters s 1 fc 33. 47 Cv 0. 1 With Factor of Safety Maturity (C-hrs) Strength (MPa) 493 17 964 25 1445 29 3405 37 6769 43 Giatec Scientific Strength (MPa) 35. 0 30. 0 25. 0 Original With Factor of Safety 20. 0 15. 0 10. 0 5. 0 0. 0 10000 Maturity (C-hrs) 24
Session Overview 1. Strength Testing Methods & Standards 2. Maturity Equations 3. Maturity Calibration 4. Validation & Limitations 5. Where to Monitor Maturity & Strength Giatec Scientific 25
Validation Before performing critical operations, ensure that the strength measurement obtained from your strength-maturity calibration has the same potential strength as your concrete pour. Section 9. 5 of ASTM C 1074 -17 provides multiple options: 1. Use other techniques to determine the strength of the cast in-place (ASTM C 873), penetration resistance test (ASTM C 803), or pullout test (ASTM C 900). 2. Standard-cured compressive strength test following ASTM C 918. 3. Accelerated curing compressive strength test following ASTM C 1768. 4. Additional cylinders to compare actual strength and strength obtained from maturity calibration. Giatec Scientific 26
How to Perform a Validation? Cast your regular field cured cylinders Compare strength data from breaks and the strength obtained from maturity in the extra cylinder Validation 6000 +10% + Cast an additional cylinder for temperature monitoring Giatec Scientific Keep in the same curing conditions Strength (psi) 5000 -10% 4000 3000 2000 1000 0 0 5000 10000 15000 20000 25000 30000 Maturity(°F-hrs) 27
Limitation – Same Mixture The in-place concrete mixture is assumed to be the same mixture as the one used for the calibration. Mitigation If possible, use the concrete from the truck instead of a lab mix to build the calibration; it is more representative of your pour. Build the curve for a specific mix with the high end of air and slump (water) as a conservative measure or build more than one curve for a mix. Giatec Scientific 28
Limitation – Curing Conditions The maturity method takes into consideration that the in-place concrete has enough moisture to allow cement hydration. Proper on-site curing is required. High temperatures at early ages can affect the long-term strength of concrete. Additional tests, such as ASTM C 918, can be performed for better predictions of later-age strength. Mitigation Revision to the ASTM C 1074 standard for curing conditions. Giatec Scientific 29
Limitation - Estimations If they are not experimentally calculated, an acceptable estimate for datum temperature and activation energy must be made to obtain acceptable accuracy. If there is a change of material in the mix, the maturity calibration must be verified or the mix re-calibrated. Mitigation The most common cause of changes to a mixture is the addition of retarders or accelerators. If this is a common practice, verify your mix or have a second calibration done to include the retarders and accelerators. Giatec Scientific 30
Limitation – Early Strength The goal of this method is to replace field-cured specimens at early ages (less than 14 days). The standard lab-cured specimen approval for 28 -day strength is still required for quality control of concrete. For critical operations, additional tests must be performed. Giatec Scientific 31
Additional Water Added A lot of time additional water is added last minute on site by the driver mainly for workability. How would this affect your in-place strength results obtained by maturity? Original mix from plant Original w/c Original slump test Transportatio n Slump loss + evaporation Mix arrive on site w/c could have slightly reduced in the summer because of evaporation + Lower slump due to time of transportation Tampering Potential very small increase of w/c for workability ( higher slump) Pouring Final w/c Use this mix for calibration Always perform validation Giatec Scientific 32
Accelerator § When in the year are you pouring your concrete? – Winter § Would it potentially require some accelerator? -Yes § Would the accelerator change your overall concrete performance? – If yes, you need a calibration 120 Temperature (°F) Accelerator will: - Reduce setting time - Accelerate strength gain at early age Perform a validationrecalibration might be required Giatec Scientific With Accelerator 110 Original Accelerator 100 90 80 70 60 0 4 8 12 16 Time (hr) 20 24 33
Retarder § When in the year are you pouring your concrete? - Summer § Would it potentially require some retarder? - Yes § Would the retarder change your overall concrete performance? – If yes, you need a calibration With Retarder will: - Increase setting time - Slow strength gain at early age Perform a validationrecalibration might be required Giatec Scientific Temperature (°F) 120 110 Original Retartder 100 90 80 70 60 0 4 8 12 Time (hr) 16 20 24 34
Session Overview 1. Strength Testing Methods & Standards 2. Maturity Equations 3. Maturity Calibration 4. Validation & Limitations 5. Where to Monitor Maturity & Strength Giatec Scientific 35
Where to Monitor Maturity & Strength One sensor per 100 m 3 Minimum of 2 sensors per pour (<100 m 3) Recommendations: 1. What are the coldest (exposed) areas on the structural element? 2. What is the pour size (start and end time)? 3. What are the critical locations on the structural element (max deflection & slab-column connections & edges)? 4. If a mass concrete element (surface and core). Giatec Scientific 36
Slabs Critical locations (maximum moments) and pour size (start and end time) Giatec Scientific 37
Post- Tensioned Elements Coldest areas (edges/corners) and critical locations (maximum moment) Giatec Scientific 38
Vertical Elements Coldest area (top of the wall) and critical locations (connections) column Giatec Scientific wall 39
Mass Concrete Center and surface, installation at the bottom and edges might be required. Installation must follow the design specifications (Thermal Control Plan) Giatec Scientific 40
Temperature Difference Limit ACI 207. 2 R Where: f’t = tensile strength CTE = coefficient of thermal expansion E = modulus of elasticity R = degree of restraint, and C = creep factor Giatec Scientific 41
Temperature Difference Limit Giatec Scientific 42
Smart Concrete Testing Technologies™ Giatec Scientific
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