ACBM VIDEO: Hydration of Cement ACBM Cement Hydration • Water + Cement chemi cal reaction (Cement grains dissolve, di ffuse and precipitate) • Reaction is exothermic (heat released) • Heat signature can be i mportant to characterize material development ACBM Rate of Heat Evolution Heat of Hydration Final set hydrolysis I C3S reacts III nucleation dissolution II IV diffusion control V Initial set Time Stage I Rapid Heat Evolution (<15 mins) Stage II Dormant Period Important for transportation (2-4 hrs) Stage III Accelerating Stage Begins with initial set (4-8 hrs) Stage IV Deceleration Stage No longer workable (12-24 hrs) Stage V Steady State ACBM Typical Setting Times for Portland Cements Vicat apparatus (Gebhardt 1995 and PCA 1996). ACBM Conceptual View of Hydration Initial During Hydration w/c>0.32 100% Hydration w/c < 0.32 100% Hydration Portland Cement Grain (Un hydrated) Water Filled Capillary pores C-S-H Note: Calcium Hydroxide and Calcium Sulfoaluminates not shown • For complete hydration 1 g of PC requi res 0.32 - 0.36 g of water (i.e., equal volumes) ACBM Structure of H ydrated Cement Paste Calcium Silicate Hydrate (C-S-H) • 50-67% of solids volume (major product) • C/S ranges f rom 1.5~2 • Morphology - poorly crystalline to reticular network • Resembles tobermorite (naturally occurrin g mineral) Image is from Paul Stutzman, 2003 ACBM Structure of H ydrated Cement Paste Calcium Hydroxide - (CH, Portlandite) • • • • 20-25% of solids volume Known stoichiometry Ca(OH) 2 Morphology - hexagonal crystal plates Adverse effect on durabilit y C-SH C 3S CH 10 mm Image is from Jennings, 2003 ACBM Structure of H ydrated Cement Paste Calcium Sulfoaluminates (ettringite) • • • • 15-20% of solids volume Minor role in structural behavior Hexagonal plate crystal Ettringite (Aft) formation Unhydrated clinker grains • Cores of larger particles • Morphology - resembles clinker ACBM Relative Volume of Major Compounds in Hydrated Paste s Function of Time Locher, Richartz, and Sprung 1976 Function of Degree of Hydration Tennis and Jennings 2000 ACBM Water In H ydrated Cement Past e X X X X OO X X X X X X X O O X X XX X X XX X OO O X OO OO X X X X X X X X X X X O O OO O O O O O OO O O X O OO X X XX O X X X O X X X O O O O OO O O O OO X X X X X O O O X X X X O O X O O O O O X O O OOO X X X OO X **After Feldman and Serada 1970 Interlayer water (X) - Associated with C-S-H structure - Lost on drying below 11 % •Capillary water - Large voids - Free water, pores > 50 nm - Capillary tension, pores 5-50 nm Adsorbed water (O) - Held close to solid surface - Up to approx imately 6 layers Chemicall y combined w ater - Integral part that is not lost on heating ACBM Voids in H ydrated Cement Past e Interlayer space in C-S-H (gel void) à nm level • Small voids - probably 5-25Å Capillary voids à mm level • Popularly called porosity Air voids à mm level • Generally round • Entrapped air (as large as 3mm) • Entrained air (50 -200mm) Capillary Porosity Hydration Products Unhydrated Grain ACBM Dimensions of Solids & Pores Interparticle Spacing Between C-S-H Sheets Hexagonal Ca(OH) 2 Crystals Entrapped Air Entrained Air Capillary Void Aggregation of C-S-H Particle 0.001mm 0.01mm 0.1mm **After Monterio and Mehta Fig 2-7 1mm 10mm Max Air Spacing 100mm 1mm 10mm ACBM Volume of Products Effect of Time Consider 100 cm3 of cement with w/c = 0.63 (by wt.) Total Volume of Paste (cc) VWater VCementrCement w 100cc(3.14g / cc ) = = 0.63 = 200cc r Water c 1.0g / cc 300 Capillary Pores 200 Hydration Product 100 0 Initial Day 7 50% hyd. Day 28 75% hyd. Day 365 100% hyd. Anhydrous Cement ACBM Volume of Products Effect of w /c Ratio Capillary Pores 37% 300 30% 22% Hydration Product 11% 200 0% 100 Strength Total Volume of Paste (cc) Consider 100 cm 3 of cement with 100% hydration Complete Reaction = 200 cm 3 0 0.32 w/c 0.7 Vol. 320 0.6 288 0.5 257 0.4 225 0.32 200 w/c Conclusion: lower w/c has lower porosity, greater strength ACBM Calculation of Volume Changes Empirical equations deri ved by T.C. Powers from experiments Evaporable Water - Lost at 105°C Capillary and gel pores (interlayer pores) Non-Evaporable Water (wn) - Lost at 1000°C Approximate measure of combined water Capillary pores Increasing Hydration Gel pores Evaporable Water Hydration products (gel) Total ‘Solid Volume’ Unhydrated cement ACBM Calculation of Volume Changes Assumption: 1 g of cement requires 0.36 g of w ater for complete hydration ( 1 g of cement = 0.32 cm 3) Volume of gel: Vg = 0.68a cm 3/g, where a = % hydration Capillary Porosit y: VCP = w/c - 0.36a = 0.63 - 0.36*1 = 0.27 cm 3/g (if w/c = 0.63 and a = 1) Volume of CP = CP*rcement = 0.27*(100)*3.15 @ 85 cm 3 (for 100 cc of cement) Gel Space ratio = Volume of gel/Space ava ilable for gel = 0.68a/(w/c + 0.32a) Note: because of space requirements minimum w /c = 0.42 Solid space = 1 - capillary porosity ACBM Porosity, Gel Space, Strength, and Permeability Typical Capillary Porosity Typical Capillary Porosity Hydration Capillary Porosity 120 20 80 10 40 0 1.0 0.9 0.8 0.7 0.6 0 0.5 0.4 Solid/Space Ratio (1-P) Water/Cement Ratio 30 100% 75% 0.3 0.6 -12 ) 0.45 (cm/secx10 0.3 Permeability Coefficient (x10 3 psi) Compressive Strength 0 50% 25% 0.4 0.5 0.6 0.7 0 0.1 0.2 0.3 0.4 0.5 0.6 Capillary Porosity, Vol. Fraction P ACBM • • • • • Ways to Measure Porosity Electrical Measurements Image Analysis Nuclear Magnetic Resonance (NMR) Weight Loss Computer Simulations ( Virtual Cement and Concrete Testing Laboratory-VCCTL) • Mercury Intrusion Porosimetry ACBM Mercury Intrusion Porosimetry (MIP) Penetration Volume (cc/g) Hydration Pore Volume Pore Diameter 0.5 28 Days AGE 0.4 90 Days INCREASING w/c 0.3 365 Days 0.2 0.1 0 5000 2000 1000 500 200 100 Pore Diameter A ACBM Chemically Combined Water C B Adsorbed and Interlayer Water A Free Water Shrinkage Water Loss Water and Shrinkage C A B 100% Relative Humidity Loss of Water Note: Relationship between shrinkage and water loss is not unique, it depends on age and degree of hydration ACBM VIDEO: Microstructure of Concrete Images from Paul Strutman, 2003 Clinker, HF-etch, 300 mm FW 0.45 w/c, 7 d 30 mm FW 0.45 w/c, 1 d, 50 mm FW ACBM Key Ideas • How long are the stages of the hydrati on reaction? • What is the relative sizes of C-S-H crystals, capillary voids, entrained air and entrapped ai r? • What effect does w/c have on the microstructure … and other properti es?