PREDICTION OF EARLY STRENGTH DEVELOPMENT IN CEMENTITIOUS MATERIALS BY HEAT OF HYDRATION MEASUREMENTS. Aron Shonhiwa 4 SEPTEMBER 2012

Transcription

1 PREDICTION OF EARLY STRENGTH DEVELOPMENT IN CEMENTITIOUS MATERIALS BY HEAT OF HYDRATION MEASUREMENTS. Aron Shonhiwa 4 SEPTEMBER 2012

2 Contents Introduction AfriSam Product Portfolio Factors which affect strength development in cement Hydration reactions in cement and heat evolved Strength determinations and heat of hydration measurements Experimental data: Heat of hydration vs mortar strength Conclusion 4 September 2012 <Presentation Title> 2

3 INTRODUCTION CONCRETE IS ONE OF THE MOST COMMONLY USED CONSTRUCTION MATERIALS IN THE WORLD. Ref: Afrisam Technical Reference Guide 4 September 2012 <Presentation Title> 3

4 INTRODUCTION CEMENT MANUFACTURING Cement clinker is manufactured by sintering Limestone and Alumino Silicates at high temperature ( o C ). The reactions form Calcium alumino ferro silicate oxides. 4 September 2012 <Presentation Title> 4

5 INTRODUCTION MINERAL CONSTITUENTS OF CEMENT Major cement minerals Tricalcium Silicates C 3 S Dicalcium Silicates C 2 S Tricalcium Aluminates C 3 A Tetracalcium Aluminoferrite C 4 AF Clinker CEM I Various cement types Gypsum (CaSO 4.2H 2 O) CSH 2 Other mineral components C = CaO, S = SiO 2, A = Al 2 O 3, F= Fe 2 O 3, S =SO 3, H = H 2 O 4 September 2012 <Presentation Title> 5

6 CEMENT STRENGTH CLASSES PERFORMANCE SPECIFIED Ref: Afrisam Technical Reference Guide 4 September 2012 <Presentation Title> 6

7 NEW AFRISAM CEMENT PRODUCT PORTFOLIO All Purpose 32.5 R High Strength 42.5 R Roadstab 32.5 N Ref: Afrisam Technical Reference Guide Rapid Hard 52.5 N Eco Building 42.5 N 4 September 2012 <Presentation Title> 7

8 WHAT HAPPENS WHEN CEMENT IS MIXED WITH WATER? Hydration reactions responsible for strength development Hydration reactions are exothermic 4 September 2012 <Presentation Title> 8

9 MICROSTRUCTURAL DEVELOPMENT AND PHASE EVOLUTION DURING HYDRATION (K. Kurtis et al ) 4 September 2012 <Presentation Title> 9

10 DEVELOPMENT OF MICROSTRUCTURE AND HEAT OF HYDRATION Volume of capillary porosity inversely related to heat of hydration Young et al 1998 Porosity of mortar, p is inversely related to strength, f c f c =k(1-p) 3 K = strength of voidless mortar 4 September 2012 <Presentation Title> 10

11 FACTORS WHICH AFFECT STRENGTH DEVELOPMENT IN CEMENTITIOUS SYSTEMS Chemical / Mineralogical composition Fineness Water cement ratio Incorporation of admixtures Curing conditions Presence of supplementary mineral components 4 September 2012 <Presentation Title> 11

12 TRADITIONAL STRENGTH DETERMINATION SANS vs HEAT OF HYDRATION Sample preperation 30 min Curing 48 hr Data collection 30 min Total 49 hr Sample preperation 30 min Data collection 24 hr Data manipulation 30 min Total 25 hr 4 September 2012 <Presentation Title> 12

13 TAM AIR ISOTHERMAL MICROCALORIMETER Eight channel, isothermal, heat conduction calorimeter operating in the milliwatt range. (Temperature range 5 o C 80 o C) All eight channels are mounted together to form a calorimeter block housed in a temperature controlled thermostat. 4 September 2012 <Presentation Title> 13

14 INSTRUMENT CONFIGURATION/ OPERATION PRINCIPLE [1] Each calorimetric channel is constructed in a twin configuration with one side for the sample and the other side for reference. Within each calorimeter channel there are two heat flow sensors. Heat created by any physical or chemical reaction in the sample will flow rapidly to its surroundings Flow of heat caused by thermal gradient across the sensor, creates a voltage signal proportional to the heat flow. The voltage difference is a quantitative expression of rate of heat production in the sample. Exothermic reactions result in positive heat flow value (i.e exothermic is up). 4 September 2012 <Presentation Title> 14

15 TYPICAL HEAT OF HYDRATION PROFILES Pre Induction period Dormant period Deceleration period Acceleration period 4 September 2012 <Presentation Title> 15

16 TYPICAL CUMULATIVE HEAT OF HYDRATION PROFILES 4 September 2012 <Presentation Title> 16

17 CORRELATION OF 24 HOUR HEAT OF HYDRATION AND 2 DAY STRENGTH FOR COMPOSITE CEMENTS A & B Y = 0.195x R 2 = September 2012 <Presentation Title> 17

18 CORRELATION OF 24 HOUR HEAT OF HYDRATION AND 7 DAY STRENGTH FOR COMPOSITE CEMENTS A & B Y= 0.213X 2.87 R 2 = September 2012 <Presentation Title> 18

19 CORRELATION OF 24 HOUR HEAT OF HYDRATION AND 28 DAY STRENGTH FOR COMPOSITE CEMENTS A & B Y = X R 2 = September 2012 <Presentation Title> 19

20 COMPARING MEASURED STRENGTH AND PREDICTED STRENGTH AT 2 DAYS FOR COMPOSITES A & B Average Average Average Average September 2012 <Presentation Title> 20

21 COMPARING MEASURED STRENGTH AND PREDICTED STRENGTH AT 7 DAYS FOR COMPOSITES A & B Average Average Average Average September 2012 <Presentation Title> 21

22 COMPARING MEASURED STRENGTH AND PREDICTED STRENGTH AT 28 DAYS FOR COMPOSITES A & B Average Average Average Average September 2012 <Presentation Title> 22

23 CONCLUSION Heat liberated and strength development for cements made with clinker from same source have a linear relationship. Heat of hydration measurements can successfully be used to predict early strength (2 days) development in cementitious systems. The technique however becomes less reliable for predicting late strengths (7 and 28 days) due to the participation of other mineral components. Strength prediction by heat of hydration is faster (25hrs) compared to conventional strength determination (+ 48 hrs) and less labour intensive. This technique can be used as a quality predictive tool to detect any anomalies in clinker quality and also to estimate amount of mineral extender added in cement. 4 September 2012 <Presentation Title> 23