Using Isothermal Calorimetry to Predict early Mortar Strengths. Lasse Frølich Engsig April 2014

Transcription

1 Using Isothermal Calorimetry to Predict early Mortar Strengths Lasse Frølich Engsig April 2014

2 Outline 2 Part 1 Testing critical parameters that will affect HoH/strength relationship Part 2 Routine testing of mill samples 1 day strength vs HoH Part 3 Miscellaneous measurements

3 3 Part 1 Parameter study

4 Experimental 4 Isothermal calorimetry Calmetrix ICal 2000 HPC isothermal conduction calorimeter Pre conditioning of water for min. 2 h Hand mixing 20 sec. Cement pastes prepared with 50 g cement and 25 g water Mortars Standard mortars prepared according to EN 196 and cured at 20 C. 24 h strength measurements

5 Data analysis 5 Excluding energy before 90 min Energy P1: Alumina and gypsum forms forms dddafm and AFt phases P2: Slow hydration reactions P3: Alite reaction and ettringite dddformation P4: Decreasing rate of reaction P5: Sulphate depletion 90 min 24 h

6 Parameter study test series Mix nr. Composition 6 Reference cement CEM I 42.5 N 1 day mortar strength app. 10 MPa C 3 S CEM I 52.5 R added C 3 S of cement app. 77 % Fineness Further grinding in laboratory scale mill Filler Limestone filler added Blaine app cm 2 /g C 3 A synthetic C 3 A added App. 94 % cubic and < 60 µm Alkali Different response between Sodium strength Hydroxide added and Chloride heat expected Calcium Chloride added Sulphate Hemihydrate added 1 Reference cement % high C 3 S cement % high C 3 S cement % high C 3 S cement 5 High C 3 S cement cm 2 /g in Blaine cm 2 /g in Blaine % Filler % Filler % Filler % C 3 A (cubic) % C 3 A (cubic) % Na 2 O eq % Na 2 O eq % Cl % Cl % SO % SO 3

7 Heat flow graphs 7

8 Correlation - strength and energy 8 High C 3 S cement Reference Linear regression line R 2 = 0,90 (excluding C 3 A and SO 3 ) +25 % filler

9 Correlation - strength and energy 9 + SO 3 + C 3 A

10 C 3 A content variations 10

11 Sulphate content variations 11

12 Alkali content variations 12

13 Chloride content variations 13

14 C3S content variations 14

15 Statistics 15 Mortar strengths Coefficient of variation for 1 day mortar strengths is 3,5 % for the given laboratory Isothermal calorimetry Coefficient of variation for isothermal calorimetry 24 h measurements is assumed to be 3,5 % Correlation From the predicted compressive strengths from the regression line, the CV of the residuals should be below 4,9 % Results All measurements CV of residuals = 6,5 % Excluding C 3 A and SO 3 CV of residuals = 5,3 % Excluding C 3 A, SO 3 and alkalis CV of residuals = 4,7 %

16 16 Part 2 Mill samples

17 Heat flow 17 Energy before set excluded in data analysis 27 samples

18 Rutine testing of cement mill samples 18

19 Rutine testing of cement mill samples 19 Regression line from parameter study Regression line from mill samples

20 Statistics 20 CV of residuals = 4,0 % (Standard deviation of residuals divided by mean strengths of mortar) CV < 4,9 % indicate same level of uncertainty as mortar Mix nr Sample 1 D HoH Regression line Residual Mpa J/g Mpa Mpa , ,5 0, , ,2-0, , ,1 0, , ,1 0, , ,5 0, , ,0-0, , ,9-0, , ,1 0, , ,0 0, , ,1-0, , ,4-0, , ,1-1, , ,6-0, , ,7 0, , ,7-0, , ,1 0, , ,9-0, , ,1 0, ,8 148,6 12,7-0, ,23 148,2 12,6 0, , ,9 11,5-0, , ,9 11,9-0, ,31 142,3 11,6 0, , ,3 11,3 0, , ,7 12,2-0, , ,9 11,0 0, ,39 136,1 10,6 0,2 St dev 0,49 Mean strenght 12,2 Stdev/mean 0,040

21 Conclusions 21 Isothermal calorimetry can be used to predict 1 day mortar strengths without compromising the precision Isothermal calorimetry will at the same time provide extra information on the hydration process Extra information from HoH can be used to look for unconformities due to undesired reactions

22 22 Part 3 Miscellaneous measurements

23 Miscellaneous measurements during past 2 years samples 10 different cement types Ages 1-7 days 10% deviates more than 2,5 Mpa from regression line

24 Miscellaneous measurements cement types 24

25 Discussion 25 Air 1% increase in air in EN196 mortar corresponds to approx 5% decrease in compressive strength. Variable air do not affect calorimetry significantly Calorimetry will give true chemical response while for compressive strength the effect of air is just noise". Calorimetry potential Replace compressive strength testing as a QC method for cement production, especially when the variations in C3A, SO3 and alkali are expected to be minor. Calorimetry would be most attractive for plants that does not have a dedicated compressive strength testing lab on site, or for plants who simply would like to use calorimetry as a source for complementary information to the compressive strength testing. (to detect potential variability in cement reactivity, or in compressive strength testing, etc)