11/19/2013. Types of concrete. Concrete based On alternative binders Special concretes. Normal strength concrete. High strength concrete (>60MPa)

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1 Types of concrete Normal strength concrete Concrete based On alternative binders Special concretes. High strength concrete (>60MPa) High performance concrete Ultra high strength concrete (>150MPa) Ultra high performance concrete 1

2 Content: Introduction Alkali activated binders Magnesium based binders Fillers, secondary binders... Metakaolin Red mud Fly ash Blast Furnace Slag Fly ash 2

3 Alkali activated binders (geopolymers) Content History Difference between hydration and geopolymerisation Geopolymerisation process Commonly used raw binders Effects of binder combinations Effects of activators 3

4 History Egyptians advanced to the discovery of lime and gypsum mortar as a binding agent for building such structures as the Pyramids. Geoplymers used for Pyramids?... X-Rays Analysis and X-Rays Diffraction of casing stones from the pyramids of Egypt, and the limestone of the associated quarries., Davidovits J., Science in Egyptology; A.R. David ed.; 1986; Proceedings of the Science in Egyptology Symposia ; Manchester University Press, UK; pp History Multistory building were made in Ukraine in the 70s using alkali activated BFS binders Buildings are in service still at present time and not problems were recorded so far 4

5 Portland cement vs. Alkali activated binders Portland cement + Blast Furnace Slag + Fly Ash Metakaolin + Water Water Activator Water Activator + Hydration reactions Geopolymerisation C-S-H Ca(OH) 2 AFm/AFt C 4 AF Mostly C-S-H Some Hydrocalcite Aluminosilicate gel Aluminosilicate gel and/or Zeolites Geopolymerisation process React amorphous silica and alumina rich solids with a high alkaline solution to form amorphous to semi-crystalline aluminosilicate inorganic polymers The chemical composition of geopolymers is similar to that of natural zeolitic materials, but they are usually amorphous instead of crystalline Three-dimensional silico-aluminate structures consisting of linked SiO 4 and AlO 4 tetrahedral by sharing all the oxygen atoms 5

6 Geopolymerisation process Three-dimensional silicoaluminate structures consisting of linked SiO 4 and AlO 4 tetrahedral by sharing all the oxygen atoms Si/Al ratio of 3, and silicate links with a Si/Al ratio of >3. A general formula for the chemical composition of geopolymers is as follows: A general chemical formula Geopolymerisation process 6

7 Geopolymerisation What are geopolymers and geopolymerisation Geopolymerization can be divided into three essential stages: The generation of reactive species or alkali activation, which is the dissolution of amorphous phases (e.g., aluminosilicates) by alkali to produce small reactive silica and alumina Reorientation, which is the transportation, orientation, or condensation of dissolved precursor ions (e.g., Al3+, Si4+) into monomers Setting reaction, polycondensation process leading to the formation of amorphous or semi-crystalline aluminosilicate polymers 7

8 Possible alkali activators Water glass Sodium silicate The most efficient alkali activator for FA, BFS. MK and their combinations Problems related to rapid stiffening cause major problems with application especially in in-situ concrete Sodium hydroxide Na(OH) 2 Often used alkali activator but less efficient in comparssion with water glass Less strength Need for high concentrations Potassium Carbonate Sodium sulphate Less commonly used Very efficient in some applications SODIUM HYDROXIDE 8

9 NaOH commonly used as an alkaline activator in geopolymer production The concentration and molarity determines the paste properties. High NaOH additions accelerate chemical dissolution, it depresses ettringite and CH (carbon-hydrogen) formation during binder formation. Higher concentrations of NaOH promote higher strengths at early stages of reaction, but the strength of aged materials were compromised Geopolymers activated with sodium hydroxide develop greater crystallinity which improves stability in aggressive environments of sulfates and acids Sodium hydroxide buffers the ph of pore fluids, regulates hydration activity and directly affects the formation of the main C-S-H product in geopolymer pastes SODIUM SILICATE (WATER GLASS) 9

10 Sodium (or potassium) silicates are manufactured by fusing sand (SiO 2 ) with sodium or potassium carbonate (Na 2 CO 3 or K 2 CO 3 ) at temperatures in excess of 1100 C and dissolving the product with high pressure steam into a semi-viscous liquid referred to as water glass Rarely used alone Commonly mixed with NaOH or KOH as a fortifying agent to enhance alkalinity and increase overall specimen strength The most common alkaline liquid used in geopolymerization is a combination of sodium hydroxide or potassium hydroxide and sodium silicate or potassium silicate. Powdered waterglass leads to lower performance compared to the liquid form For best results, a silicate solution with a SiO 2 to Na 2 O ratio (by mass) of 2.0 mixed with an 8 16 M activator 24 hours prior to use is recommended [6]. Modulus denotes mass ratio of SiO 2 to Na 2 O, which is commercially available in the range of 1.5 to 3.2 Soluble silicates reduce alkali saturation in pore solution and promote greater interparticle bonding with both geopolymer binders and the included aggregate material Activators containing little or no soluble silicates produced significantly lower compressive strengths of mortars and concretes than those activated with high doses of soluble silicates Increasing temperatures decreased strength while those containing only a base activator (NaOH, KOH) produce higher strengths. 10

11 Possible raw materials Metakaolin Fly ash Red mud Blast Furnace Slag Any material consisting of mostly amorphous silica or alumina is a possible source for geopolymer production Each material will produce different geopolymers with different properties Activation energies of raw materials will specify heat treatment procedures FLY ASH 11

12 Geoploymers based on Fly Ash Fly ash is a industrial by product Non-reactive if mixed with water Rather large variations in chemical composition Carbon content can strongly affect the properties of produced geopololyer Fly ash a) the initial chemical attack at one point on the surface of a particle Descriptive model of the alkali activation of fly ash. b) expands into a larger hole exposing smaller particles, whether hollow or partially filled with other yet smaller ashes, c) reaction product is generated both inside and d) outside the shell of the sphere, until the ash particle is completely or almost completely consumed e) Due to massive precipitation of reaction products is that a layer of these products covers certain portions of the smaller spheres. This crust prevents their contact with the alkaline medium A. Fernandez-Jimenez et al. / Cement and Concrete Research 35 (2005)

13 Effect of heat treatment duration Fly ash activated with 8 M NaOH for 20 h at 85 8C; (a) reaction process of a large sphere, (b) singular details of the reaction of some small spheres. Fly ash activated with NaOH 8 M and cured 60 days at 85 C. 13

14 Effect of Na 2 concentration and water glass modulus on compressive strength Ceramics Silikáty 49 (3) (2005) Ceramics Silikáty 49 (3) (2005) 14

15 FA geopolymer in acid exposures Extremely good durability in acids!!! Ceramics Silikáty 49 (3) (2005) 2009 Technology Summary for Innovative Technique Award, Japan Society of Civil Engineers ECOSULFUR anticorrosion method 15

16 FA geopolymer in freeze-thaw conditions Ceramics Silikáty 49 (3) (2005) FA geopolymer in fire Ceramics Silikáty 49 (3) (2005) 16

17 BLAST FURNACE SLAG Alkali activated BFS produced both geopolymer and CSH-like products The CSH-like products include Na-A-S-H and Ca-A-S-H BFS can be also alkali activated by OPC Much more stabile chemical composition in comparison with eg FA resulting in more predictable and repeatible 17

18 BFS geopolymer heat development D. Krizan, B. Zivanovic / Cement and Concrete Research 32 (2002) BFS geopolymer strength development 18

19 BFS microstructure vs OPC BFS microstructure (KOH activator) 19

20 BFS porosity of ITZ vs OPC Effect of curing on compressive strength of BFS concrete 20

21 COMBINED: BLAST FURNACE SLAG+FLY ASH Based on combining two or more raw materials Recently common combination if FA+BFS and FA+BFS+OPC and FA+MK Hardened binder matrix is formed due to both geopolymerisation and hydration reaction Obtained properties can be tailored to certain applications by adjusting proportions of raw materials and using different combinations of alkali activators 21

22 Example results FA/BFS Compressive strength (MPa) FA/BFS AHD AHW ANW AND Compressive strength (MPa) PC RHW RNW RND RHD Time (days) Time (days) RED MUD 22

23 Bauxite, contains between 30 50% alumina, the rest being silica, various iron oxides, and titanium dioxide. The alumina must be purified before it can be refined to aluminum metal. Bayer process, where bauxite is digested in a hot sodium hydroxide solution. This converts the alumina to aluminium hydroxide, which dissolves in the hydroxide liquor. The other components of bauxite do not dissolve. The solution is clarified by filtering off the solid impurities. This bauxite residue is a mixture of solid impurities and is called red mud. With a worldwide annual production of 120 millions of tonnes and a total inventory of 2.7 billion of tonnes, stored in huge holding ponds, red mud poses a significant hazardous problem Red mud Red mud is usually left untreated in reservoirs, which is cheaper than treating it with acid but can cause great damage to the environment if it leaks out, as happened in Hungary in 2010 when a spill of around one million cubic meters killed several people and injured many more. 23

24 Red mud Red mud 24

25 Magnesium concrete Reactive magnesium oxide As additive to cement As replacement of cement As alternative binder (no Portland cement) 100% PC 20% PC + 80% MgO Visible densification of microstructue A. Cwirzen, K. Habermehl-Cwirzen, Effects of reactive magnesia on hydration of Portland cement, submitted to Advanced Cement Research Cwirzen A. Habermehl-Cwirzen, K., Reactive magnesium oxide as alternative secondary binder for Portland cement, In proceedings of Nordic Concrete Research, Hämenlina, Finlaand

26 Summary Search for alternative binder to PC is strengthened by requirements to reduce carbon dioxide foot print Alternative binder such are SF, FA, and BFS are well know, established and regulated additions to PC Usage of FA, BFS as full substitute for PC is rather problematic due to current regulations except for Australia Alkali activation of FA, BFS, MK produces concrete having comparative performance as concretes based on PC Durability of alkali activated binders is still a point of dispute and ongoing research Concretes based on magnesium oxide are novel experimental material without ready use due to a limited amount of data especially regarding durability 26