The role of supplementary cementing materials on sustainability. Anıl DOĞAN

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1 The role of supplementary cementing materials on sustainability Anıl DOĞAN

2 SUSTAINABILITY «meeting the needs of the present without compromising the ability of future generations to meet their needs»

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4 It is impossible to walk through cities without seeing concrete in some form Buildings Side walks Roads Dams Bridges Marine structures Industrial plants Infrastructure etc. Concrete is inescapable Concrete = cement + water + aggregate requires substantial amount of energy and releases large amount of CO 2

5 The demand for cement-based materials is expected to continue growing, and under current technology will require a continuous increase in cement production. Environmentally and economically viable mitigation strategies are needed. Sustainability of a material depends on Energy required to produce the material CO 2 emissions resulting from the material s manufacture Toxicity of the material Transportation of the material during its manufacturing and delivery Degree of pollution resulting from the material at the end of its useful life Maintenance required and the materials required for maintenance Lifetime of the material and its potential for reuse if the building is demolished.

6 EMBODIED ENERGY is the amount of energy required to produce a material. extraction of the raw material process and manufacture Embodied energy is directly proportional to CO 2 production The main greenhouse gas emission affecting the sustainable development of the world is CO 2

7 The estimated carbon dioxide concentration was about 380 ppm in The concentration of the CO 2 is expected to increase at an exponential rate resulting in rapid temperature rise of the earth. GLOBAL WARMING!! T of CO 2 is released to produce equal amount of clinker 65% from CaCO 3 30% from fossil fuels

8 The worldwide cement production accounts for almost 7 % of the total world CO 2 emissions. Cement has been marked as a possible threat to the sustainability of concrete. In order to reduce the impact of concrete on the environment; increase the efficiency of production reduce the amount of cement in the concrete mix Cement can be replaced in part by supplementary cementing materials.

9 In order to reduce the large amount of CO 2 emission and high energy consumption during the cement production, replacement of clinker with supplementary materials, usage of alternative energy sources, energy efficient processing systems, and carbon capture and storage are the main precautions proposed (World Business Council for Sustainable Development, International Energy Agency (IEA) 2009).

10 The clinker factor (CF) is defined as the percentage of the clinker in a cement and a pozzolan or an inert material, such as limestone powder, substitution appears to be the most efficient way today to reduce the CF. When the life-cycle assessment (LCA) of cement production is considered 25% pozzolan substitution with clinker seemed to have a reduction of 21.6% in the environmental impact (Huntzinger et al. 2009).

11 The pozzolans used for this purpose can be natural ones, such as volcanic ashes, pumice, zeolitic tuffs, opaline, rice husk ash and bentonite clay, or by-products of industries, such as fly ash, blast furnace slag, silica fume. World average CF was 0.77 in 2010 (Schneider et al. 2011) and it is predicted to be reduced down to 0.71 in 2050 (World Business Council for Sustainable Development, International Energy Agency (IEA) 2009).

12 Supplementary cementing materials A pozzolan: is a siliceous or alumino-siliceous material (similar chemistry to cement) that, in finely divided form and in the presence of moisture, chemically reacts with the calcium hydroxide released by the hydration of Portland cement to form calcium silicate hydrate and other cementing compounds. They have little or no cementing property on their own

13 Fly ash, Ground granulated blast-furnace slag, Silica fume Natural pozzolans, calcined shale calcined clay or metakaolin,

14 Chemical Analysis of Typical Fly Ash, Slag, Silica Fume, Calcined Clay, Calcined Shale, and Metakaolin Class F fly ash Class C fly ash Ground slag Silica fume Calcined clay Calcined shale Metakaolin SiO 2, % Al 2 O 3, % Fe 2 O 3, % CaO, % SO 3, % Na 2 O, % K 2 O, % Total Na eq. alk, %

15 Traditionally, fly ash, slag, silica fume and natural pozzolans such as calcined clay and calcined shale were used in concrete individually. Today, due to improved access to these materials, concrete producers can combine two or more of these materials to optimize concrete properties. Mixtures using three cementing materials, called ternary mixtures, are becoming more common.

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17 Used Additives Admixture type Portland Limestone Cement Strength class S: Granulated Blast Furnace Slag P: Natural Pozzolana Q:Natural calcined Pozzolana V: Siliceous fly ash W: Calcareous fly ash T: Burnt shale L: Limestone D: Silica fume A: Low admixture B: High admixture C: Very high admixture Strength classes: R 32.5, Yüksek 42.5, 52.5 erken mukavemet R: High özelliğini early gösterir strength (rapid) N Yüksek erken mukavemet N: Ordinary özelliği olmadığını early strength gösterir (normal)

18 FLY ASH: Fly ash, also known as Pulverized Fuel Ash (PFA), is an industrial ash created when coal is burned to create electrical power. As the gaseous emissions of burning coal cool, some of its chemical constituents solidify into spherical granules, forming fly ash. A fine, glassy powder, its chemical components vary but usually include oxides of silicon (SiO 2 ), aluminum (Al 2 O 3 ), iron (several kinds), and calcium (CaO). It is found in power plant chimneys and has several industrial uses, the most noteworthy being as an additive to cement

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20 Reactivity depends on composition, morphology, fineness and the amount of glass phase The ash itself may be cementitious (high calcium). Fly ash may contain sulphates that react with cement in the same way as the gypsum added to Portland cement does. Reduces the water demand for a certain workability due to spherical and smooth surface of the particles. The fly ash cement mortar may contain less water as a consequence of the presence of fly ash, and this will influence the rate of stiffening. Fly ash particles may act as nuclei for crystallization of cement hydration products

21 Influence of replacement of cement by fly ash on the workability of concrete Influence of partial replacement of cement by fly ash on the yield stress and plastic viscosity of concrete

22 Effect on temperature rise and strength

23 Effect on shrinkage The use of fly ash in normal proportions does not significantly influence the drying shrinkage of concrete.

24 Effect on permeability

25 Effect on carbonation

26 Effect on resistance to freezing-thawing cycles

27 Effect on resistance to sulphate attack 1937 Sulphate expansion of concretes containing low-calcium fly ash (10 % soak test)

28 Effect on resistance to AAR

29 Effect on corrosion of reinforcing steel

30 GRANULATED BLAST FURNACE SLAG: Metallurgical industry produces slag as by-products. They are formed either in glassy texture used as a cementitious materials or in crystalline forms used as aggregates. If a molten slag with a temperature between 1400 and 1600 O C is cooled slowly in the air, a stable solid and crystalline material is obtained. They have little or no pozzolanic properties and used as aggregates in concrete or as base materials for road construction. In the rapid cooling process, slags are formed as granular glassy materials higher in energy than the crystalline materials. Crystallization is avoided by the usage of large quantities of water (100 m 3 per t of slag) or spraying jets under pressure (Water, 3 m 3 per t of slag) for rapid cooling of molten slag.

31 Fineness of granulated blast furnace slag is a major factor affecting the strength of mortars and concretes. It is reported that slag particles less than 10 µm contribute to early strength development up to 28 days. Most standard specifications limit the proportion of particles greater than 45 µm. The Blaine surface area of granulated blast furnace slag ranges between 4000 and 6000 cm 2 /g in order to obtain satisfactory strength development in concrete.

32 Slow cooled slag has no or very little cementitious or hydraulic properties. Granulated slag has also little cementitious properties but with some activator. The activators are lime, Portland cement, alkalis such as sodium, calcium or magnesium. Some hydraulic moduli of granulated slags derived from chemical analysis

33 1 in Germany 1.4 in Japan MgO 18 wt.% CaO 11 wt.% efficient The effect of Al 2 O 3 on the development of strength for a hydraulic modulus (C + M)/S= 1.4 Thermal treatment can accelerate the hydration of slags. Active slags rich in alumina do not need a long thermal treatment due to the rapid formation of hydrated aluminate crystals.

34 Effect on fresh properties It is believed that unlike Portland cement the slag cement particles absorb little water during initial mixing. Comparison of vibration time for full compaction of concretes with and without slag

35 The partial replacement of cement with slag generally increases setting time of concrete. Lower temperatures would further extend the setting time. Results on time of setting of concretes incorporating a pelletized slag and two different granulated slags carried out by CANMET

36 Effect on strength Chemical composition, Physical properties (fineness is of major importance if high volume is used), Activity index, Mixture design and Moist curing period affect the strength of slag cement concretes.

37 In a study, higher tensile strength was observed for slag concrete in comparison with no slag concrete on the basis of equal compressive strength of 70 MPa. This increase is probably due to the stronger bonds in the slag cement aggregate system because of the shape and surface texture of the slag particles.

38 Effect on shrinkage Results on the drying shrinkage of slag cement concretes are conflicting. Slag properties Cement properties Curing conditions Test methods In an investigation a greater shrinkage was observed in concretes containing various slag cement blends when compared with no slag cement concretes. This increase in shrinkage is attributed to the increase of volume of cement paste in concretes containing slag with lower density and on equal replacement level by weight

39 Effect on Microstructure, Porosity and Permeability Measurement of porosity and pore size distribution of slag cement paste by mercury intrusion porosimetry shows that the pore structure in blended cements is characterized by relatively large but discontinuous and thinwalled pores Pore refinement effect and reduction in the porosity of slag cement concretes will result in lower permeability of the mix especially in well cured concretes

40 Effect on carbonation The rate of carbonation of slag cement concrete has been reported to be higher than that of Portland cement concretes especially at high slag replacement levels Curing of concrete is very important in reducing the carbonation depth especially in slag cement concretes. Effect of moist curing on the depth of carbonation

41 Effect on chloride attack The incorporation of granulated blast furnace slag in concrete increases its resistance to chloride ion diffusion especially at later ages It also improves the chloride binding capacity of the concrete. The reason for reduction in chloride penetration is not simply the lower permeability of concretes containing slag; even badly cured slag cement concrete has shown a better resistance to chloride ion intrusion. This suggests that chemical resistance of concrete containing slag might be a reason for that. Chemical reaction of chloride ions with hydration products of slag cement increases the chloride binding capacity of the slag cement pastes.

42 Effect on sulphate attack The level of improvement depends upon the amount of slag replacement, the alumina content of slag (high alumina content may result in lower resistance to sulfate attack) the C 3 A content of the cement and permeability of concrete. Expansion of mortars containing various amounts of slag in sodium sulfate solution

43 Effect on AAR The first report showing the effect of slag on suppressing alkali silica reaction was published in The use of slag will change the alkali-silica ratio, dissolution and consumption of the alkali species, reduction in calcium hydroxide to support the reaction, and direct reduction of available alkali in the system. The permissible value of alkalis (Na 2 O equivalent) in cement when the aggregates used in concrete are potentially reactive Pyrex glass

44 Effect on resistance to freezing-thawing cycles As with all Portland cement concretes, proper air content and bubble spacing is necessary for adequate protection against freezing and thawing. Higher dosage of air entraining admixture is needed for higher slag concretes to achieve similar frost resistance as type I and type II Portland cement concretes. Slag Cement Association suggests limiting the replacement percentage between 25 and 50 % with water to cementing materials ratio of 0.45.

45 SILICA FUME (MICROSILICA): First collected 1947 in Norway First tests in concrete in Industrial recovery developed early 1970 s Increasing use and availability of standards for microsilica and its use in concrete. More than 10 million m 3 of microsilica concrete are produced annually.

46 Microsilica production Quartz, coke and wood as raw materials Smelting plant with furnaces, coolers and baghouse 2000 degrees electric arc furnace Microsilica Silicon or ferro-silicon

47 More than 95 % of the particles are less than 1 m Spherical shape with a mean diameter of 0.2 m It consists essentially of an amorphous silica structure with very little crystalline particles. The reaction of silica fume with lime is very rapid Silica fume containing about 85 % of silica combines most of the available lime within 28 days while other natural pozzolans and fly ashes containing about % silica are capable combining about % of the lime in the limepozzolan mixture micrograph of Portland cement grains (left) and silica fume particles (right) at the same magnification

48 How Microsilica Transforms Concrete Crystals produced by the hydration reaction grow away from each cement particle. Finer, stronger crystals grow from both cement particle and Nucleation Centres of well dispersed microsilica. When hydration is complete, the extended crystal structure remains weak and permeable. A strong, impermeable dense microstructure develops - improving continually for years to come.

49 Effect on fresh properties Addition of very fine particles of silica fume to the concrete mixtures increases the cohesiveness of the mixture and makes it slightly stiffer. Due to the cohesiveness of silica fume concrete mixture, it will show lower slump than the similar normal concrete mixture. The difference between the two concretes can be measured by two point test method. Very fine particles of silica fume in concrete mixtures also reduce the size of flow channels and causes segmentation in the bleed water routes. That is the reason why silica fume concretes usually have little or no bleeding. Final finishing of this concrete should be started earlier than the normal concrete.

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51 Effect on shrinkage Effect on creep

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53 Effect on carbonation Similar to other pozzolanic materials, silica fume consumes the calcium hydroxide of the cement paste. This may increase the risk of carbonation in the silica fume mortar and concrete. On the other hand silica fume addition will reduce the permeability of concrete which may result in lower carbonation. Some researchers tried to relate the depth of carbonation of silica fume concretes to their compressive strengths. They concluded that for a given strength of concrete below 40 MPa, carbonation of concrete is higher in silica fume concrete than in normal concretes. Concretes having the strength above 40 MPa, corresponding to a low water cement ratio, show little or no change in the carbonation rate

54 Effect on chloride attack Use of silica fume in concrete slightly reduces the alkalinity of pore water and will cause a reduction in the threshold value of chloride necessary for the initiation of corrosion of steel bars On the contrary, the use of silica fume reduces the permeability and chloride diffusion of concrete. The use of silica fume has significantly reduced the chloride ions diffusion of the cement paste.

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56 Effect on sulphate attack It has been reported that silica fume increases resistance of Portland cement to sodium sulfate attacks especially at higher level of replacements

57 Effect on AAR Very fine particles of silica fume react with the alkalis in cement paste to form alkali silicates. This reduces the available alkalis in the pore solution and would prevent attack on reactive siliceous aggregates. Mixtures containing silica fume are also less permeable and prevent the penetration of water necessary for the alkali aggregate reaction Silica fume should be dispersed thoroughly in the mixture otherwise it may even cause the ASR problem.

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59 Tunnel from Somerset to Newton Circus in Singapore Concrete lining cast in 1986 Pictures taken after 15 years in service

60 Corrosion potential

61 Effect on resistance to freezing-thawing cycles The published data on the freezing and thawing of mortars and concretes containing silica fume are contradictory. Some authors reported that silica fume reduces the frost resistance of non air entrained concretes but improves that of air entrained one. It seems that the combination of silica fume and air entraining admixture is a good option. Salt scaling resistance of a concrete containing silica fume and air entrainment in a long term test was similar to the normal concrete mixture without silica fume.

62 Troll platform Troll A metres high - the largest moveable structure ever built. At tow-out it weighed 1.2 million T. It took 2000 workers 4 years to cast 245,000 m 3 concrete and 100,000T of reinforcement (about 15 Eiffel towers) into this impressive structure. The rig operates in water over 300 m deep.

63 The Øresund bridge

64 JJ Hospital Flyover, Mumbai First 75 MPa precast project in India m long, 7.9m high, 16.2m wide, 34.5m spans 20,000m 3 of HPC 500 kg OPC + 50 kg silica fume, w/b = d = 80 MPa, 90d = 87 MPa, 1 year = 95 MPa Drying Shrinkage = % Rapid Chloride (ASTM 1202) < 240 coulombs

65 Tsing Ma bridge

66 RECOMMENDED SPECIFICATION FOR REINFORCED CONCRETE IN MARINE ENVIRONMENT The main features of the recommended specification are summarized as follows : The minimum characteristic strength of the concrete mix shall be 45 MPa. The maximum water/cementitious ratio shall not exceed Condensed silica fume is to be added to reduce the permeability of the concrete. The cementitious content shall be within kg/m 3, of which the dry mass of condensed silica fume shall be within 5-10% range by mass of the cementitious content. The cover to all reinforcement in all exposure zones shall be 75 mm. For flexural crack width design and control purpose, the allowable crack width, taken to be 0.1 mm for marine structures, may be increased by a factor of Quoted from: PORT WORKS DESIGN MANUAL, PART 1; General Design Considerations for Marine Works Civil Engineering Office, Civil Engineering Department The Government of the Hong Kong Special Administrative Region (first published May 2002)

67 Typical clauses: 100 year design Concrete shall contain a combination of PC (Portland cement), ggbfs (granulated blast furnace slag) or pfa (pulverised fly ash), and MS (microsilica) in accordance with the latest EN Standards. The concrete, when tested at 28 days, shall have the following performance: ASTM C1202: Mean coulomb value less than 800, with no individual test result above 1,000. Chloride diffusion coefficient to be less than 1x10-12 m 2 /sec when tested to international standards acceptable to the engineer. Permeability, when tested to DIN 1048 shall be less than 5/10mm.

68 Compressive Strengths: 45 to 80MPa Minimum Cement: kg/m 3 (MSRPC + FA + SF) W/C ratio: 0.34 Flow (at site): > 600mm Water Penetration <10mm (BS EN ) Water Absorption <1.5% (BS 1881:122) RCPT <1200 (AASHTO T-277) Water Permeability <5mm (Din 1048) Compressive Strengths (150mm cubes - averages) 7 days 40.5 MPa 14 days 51.5 MPa 28 days 64.5 MPa 56 days 75.5 MPa Tensile Strength (300 x 150mm cylinders - averages) 14 days 28 days 3.75 MPa 4.35 MPa

69 Water Penetration (10mm) Zero Water Absorption (1.5%) 0.7% RCP Test (1200) 590 Water Permeability (5mm) Zero

70 Silica fume is a waste product (recycling!) Even with collection and processing it has a very small carbon footprint many times less than cement gate value ~4kg/t High reactivity potential replacement of cement with microsilica means greatly reduced cement. Increased strength, giving modified designs, means less concrete volume. Faster turnaround means less impact on the environment. Longer lifetimes mean less repairs, less re-building and hence reduces the use of natural resources. Better concrete = better environment = better economics = better all around.