Articles


CONCRETE OF THE FUTURE ABSTARCT Concrete as material, requires different sizes of solid particles (powdery Portland cement with mineral admixtures, granular fine and coarse aggregates) so that there is good packing density resulting in lower amount of voids, which has to be then filled by liquid portion of the concrete mix. This would result in high performance of the Portland cement matrix due to use of reduced water (which is the liquid portion of the concrete mix) and thereby economy also. Similar thing happens in one special concrete which is regarded as the concrete of the future namely Geopolymer concrete (GPC), where the liquid portion contain chemicals such as hydroxides and silicates of alkali which are costly. The solid material portion of Geopolymer is similar to Conventional Concretes (CCs) except that powdery portion consists of only mineral admixtures (fly ash, ground granulated blast furnace slag etc.,) without any presence of Portland cement. As the chemical reactions involved in creating binding actions in CCs and GPCs are different and chemical (and physical) properties of liquid medium are also different, it is necessary to look at the ingredients of the GPCs in a fresh way and make a decision on their selection. This paper discusses the ingredients of the GOCs in general. The actual proportioning of the ingredients is not covered here. Introduction Cement concrete is & can be considered as an artificial stone made by mixing Portland cement (P-C), water, sand (fine aggregate), and crushed stone aggregate (coarse aggregate) to produce a mouldable mixture. This has become one of the most important construction materials in the world. Concrete is used more than any other man-made material in the world. Per capita production of concrete being about a ton, makes it as the second most widely consumed substance on earth after water. But, the ‘Embodied Carbon Dioxide’ (ECO2) of concrete is high in the range of 75–176 kg CO2/tonne, depending upon the type and method of mix design. The ‘Embodied Energy’ (EE) content of concrete is also very high (400 to 600 kWH/m3). Therefore, there is an urgent need for making the concretes more eco-friendly so that both ECO2 and EE of concrete are reduced, since any developmental activities for improving quality of life involves always large construction activities which in turn require production of varieties of concretes. Therefore, development of concretes with more eco-friendly characteristics is taking up all over the world. The cement production is highly energy intensive next only to steel and aluminium, consuming significant amount of non-renewable natural resources such as lime stone deposits, coal, etc.). The ‘EE’ of P-C being about 1.3 kWh / kg, is a very high quantity. A tonne of P-C production involves emission of about a tonne of CO2 which is a greenhouse gas causing global warming. More than 7% of world CO2 production is attributed towards production of P-C. Moreover, among the greenhouse gases, CO2 contributes about 65% of global warming. Therefore, there is a need to find an alternate to P-C, but, the new binder should also possess strength and durability characteristics comparable, and preferably superior to those ‘conventional concretes’ (CCs) based on P-C. Geopolymer - an Alternate to P-C A new binder, known as ‘geopolymer’ (GP) was first introduced by Davidovits in 1978 to describe binders with chemical composition similar to natural or synthetic zeolites but with an amorphous microstructure [Davidovits]. He utilised silica (SiO2) and alumina (Al2O3) of the specially processed clay (metakaolin) to get inorganic polymeric system. Unlike ordinary Portland cement (P-C), geopolymers do not need calcium-silicate-hydrate (C-S-H) gel for strength, but utilise the polycondensation of silica and alumina precursors. Two main constituents of geopolymers are: geopolymer source materials (GSMs) and alkaline activator liquids. The GSMs should be rich in both silicon (Si) and aluminium (Al) and therefore, by-products such as fly ash, silica fume, slag, rice-husk ash, red mud, etc can form GSMs. Geopolymers are Inorganic Polymers with ceramic like properties but synthesised and hardened by curing at ambient temperatures The geopolymeric reaction occurs as a result of reacting alumino-silicate oxides with alkali (NaOH, KOH) and soluble alkali polysilicates. The synthesis of geopolymer consists of three steps – (i) dissolution of alumino-silicate under strong alkali solution, (ii) reorientation of free ion clusters, (iii) polycondensation. However, researchers describes the three stages as (a) deconstruction (dissolution in alkaline solution), (b) polymerization of alumina/silica–hydroxyl species and oligomers, and (3) stabilization, small gels formed are probably transformed into large networks through reorganization. Geopolymerisation involves the chemical reaction of alumino-silicate oxides with alkali polysilicates yielding polymeric Si–O–Al bonds. Polysilicates are generally sodium or potassium silicate supplied by chemical industry or manufactured fine silica powder as a by-product of ferro-silicon metallurgy26. Recently, Rangan and Hardijto, exploited silica and alumina of fly ash to produce three-dimensional polymeric chain and ring structure consisting of Si-O-. Geopolymers are unique in comparison to other aluminosilicate materials (e.g. aluminosilicate gels, glasses, and zeolites). The concentration of solids during geopolymerisation reactions is higher than that in aluminosilicate gel or zeolite synthesis [Rajamane et al]. It is now clear that any mineral containing reactive oxides of silicon and aluminium can be activated by suitably formulated highly alkaline liquid (called as Alkaline Activator System, AAS) to obtain inorganic polymeric binding material. Preliminary studies in this regard, were carried out at SERC in early 2000s; both fly ash and Ground Granulated Blast Furnace Slag (GGBS), (either individually or combined in certain proportions) were found to produce sufficient strength levels in geopolymer concretes (GPCs). The following materials can be used to produce GPCs [Refs. 4, 5 and 6]: (i) Fly ash (ii) Ground Granulated Blast furnace Slag (GGBS) (iii) Metakaolin (iv) Granite aggregates (v) Light Weight Aggregates (LWA) a. Sintered Fly Ash Aggregates (SFAAs) b. Bonded Fly Ash Aggregates (BFAAs) (vi) Alkali Activator Solution made of a) Sodium hydroxide flakes b) Sodium Silicate Solution c) DW (vii) River sand (viii) Water CONCLUDING REMARKS Significant work has been done in this area and geopolymer concretes of strength varying from M30 to M80 have been produced at Sri Jaychamrajendra College of Engineering, Mysore and at SERC, Chennai as a part of the ongoing M. Tech and Ph. D works. This geopolymer concrete can be used as an alternative to conventional concretes in all applications. Even though engineers may find it difficult initially to understand contributions of different ingredients of GPCs, as compared to Portland based concretes, sufficient information and data exist in various publications on GP technology for guiding the GPC mix design for the given application. This GPC is very popular and being used in many practical applications in western countries. In the days to come it is going to be one of the wide accepted eco-friendly concrete. REFERENCES 1. Davidovits J, (1994), Geopolymers: Man-Made Rock Geosynthesis and the Resulting Development of Very Early High Strength Cement, Journal of Materials Education, Vol. 16, No 2&3, pp 91-137. 2. Davidovits Joseph, (2011), Geopolymer chemistry and applications, 3rd Edition, Institute Geopolymere, ISBN 9782951482050. 3. Hadjito D, Wallah SE, Rangan B.V., (2002), Study on engineering properties of fly ash based geopolymer concrete, Journal of Austr. Ceram Soc, Vol.38, pp. 44-7. 4. Rajamane N. P., M. C. Nataraja, N. Lakshmanan, and P. S. Ambily, [2009a], “Geopolymer concrete –An ecofriendly concrete”, The Masterbuilder, , Vol.11, No. 11, November, pp 200-206 5. Rajamane N P, Nataraja M C, N Lakshmanan, and P S Ambily, [2009b], ‘Geopolymer Concrete - An Alternate Structural Concrete’, All India seminar on concrete Dams ConcDams'09, 2-3 October, Nagpur, organised by the Institute of Engineer (India), Nagpur Local centre and Indian Concrete institute, Nagpur centre, pp 274-278 6. Rajamane N. P., Nataraja M C, N Lakshmanan, and J.K Dattatreya, [2011a], “Pull-out tests for bond strengths of geopolymer concretes”. The Indian Concrete Journal. India.

CONCRETE OF THE FUTURE

ABSTARCT
Concrete as material, requires different sizes of solid particles (powdery Portland cement with mineral admixtures, granular fine and coarse aggregates) so that there is good packing density resulting in lower amount of voids, which has to be then filled by liquid portion of the concrete mix. This would result in high performance of the Portland cement matrix due to use of reduced water (which is the liquid portion of the concrete mix) and thereby economy also. Similar thing happens in one special concrete which is regarded as the concrete of the future namely Geopolymer concrete (GPC), where the liquid portion contain chemicals such as hydroxides and silicates of alkali which are costly. The solid material portion of Geopolymer is similar to Conventional Concretes (CCs) except that powdery portion consists of only mineral admixtures (fly ash, ground granulated blast furnace slag etc.,) without any presence of Portland cement. As the chemical reactions involved in creating binding actions in CCs and GPCs are different and chemical (and physical) properties of liquid medium are also different, it is necessary to look at the ingredients of the GPCs in a fresh way and make a decision on their selection. This paper discusses the ingredients of the GOCs in general. The actual proportioning of the ingredients is not covered here.

Introduction
Cement concrete is & can be considered as an artificial stone made by mixing Portland cement (P-C), water, sand (fine aggregate), and crushed stone aggregate (coarse aggregate) to produce a mouldable mixture. This has become one of the most important construction materials in the world. Concrete is used more than any other man-made material in the world. Per capita production of concrete being about a ton, makes it as the second most widely consumed substance on earth after water. But, the ‘Embodied Carbon Dioxide’ (ECO2) of concrete is high in the range of 75–176 kg CO2/tonne, depending upon the type and method of mix design. The ‘Embodied Energy’ (EE) content of concrete is also very high (400 to 600 kWH/m3). Therefore, there is an urgent need for making the concretes more eco-friendly so that both ECO2 and EE of concrete are reduced, since any developmental activities for improving quality of life involves always large construction activities which in turn require production of varieties of concretes. Therefore, development of concretes with more eco-friendly characteristics is taking up all over the world.
The cement production is highly energy intensive next only to steel and aluminium, consuming significant amount of non-renewable natural resources such as lime stone deposits, coal, etc.). The ‘EE’ of P-C being about 1.3 kWh / kg, is a very high quantity. A tonne of P-C production involves emission of about a tonne of CO2 which is a greenhouse gas causing global warming. More than 7% of world CO2 production is attributed towards production of P-C. Moreover, among the greenhouse gases, CO2 contributes about 65% of global warming. Therefore, there is a need to find an alternate to P-C, but, the new binder should also possess strength and durability characteristics comparable, and preferably superior to those ‘conventional concretes’ (CCs) based on P-C.

Geopolymer - an Alternate to P-C
A new binder, known as ‘geopolymer’ (GP) was first introduced by Davidovits in 1978 to describe binders with chemical composition similar to natural or synthetic zeolites but with an amorphous microstructure [Davidovits]. He utilised silica (SiO2) and alumina (Al2O3) of the specially processed clay (metakaolin) to get inorganic polymeric system. Unlike ordinary Portland cement (P-C), geopolymers do not need calcium-silicate-hydrate (C-S-H) gel for strength, but utilise the polycondensation of silica and alumina precursors. Two main constituents of geopolymers are: geopolymer source materials (GSMs) and alkaline activator liquids. The GSMs should be rich in both silicon (Si) and aluminium (Al) and therefore, by-products such as fly ash, silica fume, slag, rice-husk ash, red mud, etc can form GSMs. Geopolymers are Inorganic Polymers with ceramic like properties but synthesised and hardened by curing at ambient temperatures
The geopolymeric reaction occurs as a result of reacting alumino-silicate oxides with alkali (NaOH, KOH) and soluble alkali polysilicates. The synthesis of geopolymer consists of three steps – (i) dissolution of alumino-silicate under strong alkali solution, (ii) reorientation of free ion clusters, (iii) polycondensation. However, researchers describes the three stages as (a) deconstruction (dissolution in alkaline solution), (b) polymerization of alumina/silica–hydroxyl species and oligomers, and (3) stabilization, small gels formed are probably transformed into large networks through reorganization.
Geopolymerisation involves the chemical reaction of alumino-silicate oxides with alkali polysilicates yielding polymeric Si–O–Al bonds. Polysilicates are generally sodium or potassium silicate supplied by chemical industry or manufactured fine silica powder as a by-product of ferro-silicon metallurgy26.
Recently, Rangan and Hardijto, exploited silica and alumina of fly ash to produce three-dimensional polymeric chain and ring structure consisting of Si-O-. Geopolymers are unique in comparison to other aluminosilicate materials (e.g. aluminosilicate gels, glasses, and zeolites). The concentration of solids during geopolymerisation reactions is higher than that in aluminosilicate gel or zeolite synthesis [Rajamane et al].
It is now clear that any mineral containing reactive oxides of silicon and aluminium can be activated by suitably formulated highly alkaline liquid (called as Alkaline Activator System, AAS) to obtain inorganic polymeric binding material. Preliminary studies in this regard, were carried out at SERC in early 2000s; both fly ash and Ground Granulated Blast Furnace Slag (GGBS), (either individually or combined in certain proportions) were found to produce sufficient strength levels in geopolymer concretes (GPCs). The following materials can be used to produce GPCs [Refs. 4, 5 and 6]:
(i) Fly ash
(ii) Ground Granulated Blast furnace Slag (GGBS)
(iii) Metakaolin
(iv) Granite aggregates
(v) Light Weight Aggregates (LWA)
a. Sintered Fly Ash Aggregates (SFAAs)
b. Bonded Fly Ash Aggregates (BFAAs)
(vi) Alkali Activator Solution made of
a) Sodium hydroxide flakes
b) Sodium Silicate Solution
c) DW
(vii) River sand
(viii) Water

CONCLUDING REMARKS
Significant work has been done in this area and geopolymer concretes of strength varying from M30 to M80 have been produced at Sri Jaychamrajendra College of Engineering, Mysore and at SERC, Chennai as a part of the ongoing M. Tech and Ph. D works. This geopolymer concrete can be used as an alternative to conventional concretes in all applications. Even though engineers may find it difficult initially to understand contributions of different ingredients of GPCs, as compared to Portland based concretes, sufficient information and data exist in various publications on GP technology for guiding the GPC mix design for the given application. This GPC is very popular and being used in many practical applications in western countries. In the days to come it is going to be one of the wide accepted eco-friendly concrete.

REFERENCES
1. Davidovits J, (1994), Geopolymers: Man-Made Rock Geosynthesis and the Resulting Development of Very Early High Strength Cement, Journal of Materials Education, Vol. 16, No 2&3, pp 91-137.
2. Davidovits Joseph, (2011), Geopolymer chemistry and applications, 3rd Edition, Institute Geopolymere, ISBN 9782951482050.
3. Hadjito D, Wallah SE, Rangan B.V., (2002), Study on engineering properties of fly ash based geopolymer concrete, Journal of Austr. Ceram Soc, Vol.38, pp. 44-7.
4. Rajamane N. P., M. C. Nataraja, N. Lakshmanan, and P. S. Ambily, [2009a], “Geopolymer concrete –An ecofriendly concrete”, The Masterbuilder, , Vol.11, No. 11, November, pp 200-206
5. Rajamane N P, Nataraja M C, N Lakshmanan, and P S Ambily, [2009b], ‘Geopolymer Concrete - An Alternate Structural Concrete’, All India seminar on concrete Dams ConcDams'09, 2-3 October, Nagpur, organised by the Institute of Engineer (India), Nagpur Local centre and Indian Concrete institute, Nagpur centre, pp 274-278
6. Rajamane N. P., Nataraja M C, N Lakshmanan, and J.K Dattatreya, [2011a], “Pull-out tests for bond strengths of geopolymer concretes”. The Indian Concrete Journal. India.