INTRODUCTION:

The occurrence of high performance concrete (HPC); the durability and strength of concrete have been improved largely. However, due to the restriction of the manufacturing process and the raw materials, some inherent disadvantages of Portland cement are still difficult to overcome. The environmental issues associated with the production of OPC are well known. The amount of the carbon dioxide released during the manufacture of OPC due to the calcinations of limestone and combustion of fossil fuel is in the order of one ton for every ton of OPC produced. In addition, the extent of energy required to produce OPC is only next to steel and aluminum. When used as a partial replacement of OPC, in the presence of water and in ambient temperature, fly ash reacts with the calcium hydroxide during the hydration process of OPC to form the calcium silicate hydrate (C-S-H) gel. The development and application of high volume fly ash concrete, which enabled the replacement of OPC up to 60% by mass is a significant development. On the other hand, the abundant availability of fly ash worldwide creates opportunity to utilize this by-product of burning coal, as a substitute for OPC to manufacture cement products. The geopolymer technology is proposed by Davidovits and gives considerable promise for application in concrete industry as an alternative binder to the Portland cement. In terms of reducing the global warming, the geopolymer technology could reduce the CO₂ emission in to the atmosphere, caused by cement and aggregate industries about 80%. In this technology, the source material that is rich in silicon (Si) and Aluminum (Al) is reacted with a highly alkaline solution through the process of geopolymerisation to produce the binding material. The term “geopolymer describes a family of mineral binders that have a polymeric silicon-oxygen-aluminum framework structure, similar to that found in zeolites, but without 2 the crystal structure. The polymerization process involves a substantially fast chemical reaction under highly alkaline condition on Si-Al minerals that result in a three-dimensional polymeric chain and ring structure consisting of Si-O-Al-O bonds. Geopolymer concrete is emerging as a new environmentally friendly construction material for sustainable development, using flash and alkali in place of OPC as the binding agent. This attempt results in two benefits. i.e. reducing CO₂releases from production of OPC and effective utilization of industrial waste by products such as flash, slag etc by decreasing the use of OPC

LITERATURE REVIEW:

[1]In 1978, Davidovits (1999) proposed that binders could be produced by a polymeric reaction of alkaline liquids with the silicon and the aluminum in materials of geological origin or by-product materials such as fly ash and rice husk ash. He termed these binders as geo polymers. [2]In 2008 Djwantoro Hardjito, Chua Chung Cheak and Carrie Ho Lee Ing proposed Geopolymer is a novel binding material produced from the reaction of fly ash with an alkaline solution. In Geopolymer mortar, Portland cement is not utilized at all. In this research, the influence of various parameters on the short term engineering properties of fresh and hardened low-calcium fly ash-based Geopolymer mortar were studied. Tests were carried out on 50 x 50 x 50mm cube Geopolymer mortar specimens. The test results revealed that as the concentration of alkaline activator increases, the compressive strength of Geopolymer mortar also increases. Specimens cured at temperature of 65o C for 1 day showed the highest 28 days compressive strength. The mass ratio of activator/fly ash of 0.4 produced the highest 28 days compressive strength for the specimen. The obtained compressive strength was in the range of 1.6MPa – 20MPa. [3]In 2009 S. Mandal and D. Majumdar proposed the development of alkali-activated binders seems to present a greener alternative to OPC. The present study has been made on the low calcium fly ash with alkali activator as an alternative binding material as mortar. The mortar has been prepared with encore sand and Indian fly ash mixed with alkali activator fluid consisting of sodium silicate and sodium hydroxide of different concentrations. The effect of various parameters such as fluid to fly ash ratio, concentration of alkali activators, curing temperature and duration of curing on the compressive strength of mortar at different ages of 3,7, 28 days has been incorporated. 48 hours curing at about 60-700 C seems to be optimum for the present alkali activated fly ash mortar [4]In 2001 Mehta and Burrows Proposed Cement is also among the most energy-intensive construction materials, after aluminum and steel. Furthermore, it has been reported that the durability of ordinary Portland cement (OPC) concrete is under examination, as many concrete structures, especially those built in corrosive environments, start to deteriorate after 20 to 30 years, even though they have been designed for more than 50 years of service life [5]In 2011Anuradha introduced a new Design procedure was formulated for Geopolymer Concrete which was relevant to Indian standard (IS 10262-2009). The applicability of existing Mix Design was examined with the Geopolymer Concrete. Two kinds of systems were considered in this study using 100% replacement of cement by ASTM class F flyash and 100% replacement of sand by M-sand. It was analyzed from the test result that the Indian standard mix design itself can be used for the Geopolymer Concrete with some modification.

EXPERIMENTAL PROGRAM:

An attempt has been made to verify the possibility of preparing low calcium (ASTM Class F) fly ash based geopolymer concrete economically to suit the Indian conditions. In order to develop the fly ash based geopolymer concrete technology, therefore, a rigorous trail-and error process was adopted. In order to simplify the development process, the compressive strength was selected as the benchmark parameter. The focus of the study was mainly on the engineering properties of fly ash based geopolymer concrete and also for partial replacement of fly ash with cement. The current practice used in the manufacture and testing of Ordinary Portland Cement (OPC) concrete was followed, even for geopolymer concrete. It is to ease the promotion of this „new material to the concrete construction industry. Although geopolymer concrete can be made from various source materials, in the present study only low-calicum (ASTM class F) dry fly ash was used, as it is easily available at low price in India. Also, as in the case of OPC, even in the geo-polymer concrete, the aggregates occupy 50-75 % of the total mass of matrix.

MATERIALS:

Fly Ash:

The Fly ash was used as a partial replacement for cement. The fly ash used in the experiments was from Ramagundam thermal power station (NTPC). The specific gravity was 2.17. The fly ash had a silica content of 63.99%, silica+ alumina +iron oxide content of 92.7%, Calcium oxide of 1.71% , Magnesium oxide of 1.0%, Sulphuric anhydride of 0.73% , water and soluble salts of 0.04%, ph value of 10 and a loss on ignition of 2.12

Alkaline Liquid:

In the present study we have used a combination of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solutions. The sodium hydroxide solids were either a technical grade in flakes form (3 mm), 98% purity, and obtained from National scientific company, Vijayawada, or a commercial grade in pellets form with 97% purity, obtained from National Scientific centre, Vijayawada.

Sodium Silicate and Sodium Hydroxide Solution:

The sodium hydroxide (NaOH) solution was prepared by dissolving either the flakes or the pellets in the Potable water. The mass of NaOH solids in a solution varied depending on the concentration of the solution expressed in terms of molar, M. Molar concentration or molarities is most commonly in units of moles of solute per litre of solution. For use in broader applications, it is defined as amount of solute per unit volume of solution.

Aggregates:

Fine aggregate:

The fine aggregate conforming to Zone-2 according to IS: 383[1970] was used. The fine aggregate used was obtained from a nearby river source. The bulk density, specific gravity and fineness modulus of the sand used were 1.43g/cc, 2.62 and 2.59 respectively.

Water

Potable water was used in the experimental work for both mixing and curing.

Cement

Cement used in the investigation was 53 Grade Ordinary Portland cement confirming to IS: 12269[1987]. The specific gravity, standard consistency, initial setting time and final setting time values were respectively 3.14, 32%, 42min and 235min.

Galvanized Iron mesh:

Galvanized Iron Wire mesh: The galvanized iron wire mesh of square grid fabric is used in the Ferro cement Moulds

a) Cubes: Standard cube moulds of 100 x100 x 100mm made of cast iron were used for casting and testing specimens in compression.

b) Thin plates: Standard cast iron moulds of size 500x100x25mm were used for casting and testing specimen for flexural strength of concrete.

Casting:

For casting the specimens of geopolymer concrete, the following procedure was adopted. The fine aggregate were prepared in saturated-surface-dry condition, and were batched and were kept in the gunny bags just before casting. The solids constituents of the fly ash-based geopolymer concrete, i.e the fine aggregate and the fly ash, were dry mixed in the pan mixer for about three times. Then the liquid part of the mixture, the alkaline solution was added to the initially mixed fly ash and the fine aggregate. The whole mix is thoroughly mixed for about 5 to 10 minutes. The above procedure is done casting the geopolymer specimens when fly ash was partially replaced by cement. The fresh fly ash-based geopolymer concrete was dark in color and shiny in appearance. The mixtures were usually cohesive. The fresh concrete in the moulds was compacted by applying sixty manual strokes per layer in three equal layers. The ferrocement mesh was kept in the layers along with mortar. After compaction the top surface was leveled with a trowel. Then the specimens were cured at room temperature.

Curing:

Preliminary tests also revealed that fly ash based geo polymer concrete did not harden immediately at room temperature was less than 300c, the hardening did not occur at least for 24 hours. The handling time is a more appropriate parameter (rather than setting time used in case of OPC concrete) for fly ash based geo polymer concrete.

The demoulded specimens were left in sunlight until tested without any special curing regime. For each set of parameter, 3 prisms were cast, three each for determining 28 days strengths. Detention period. After the curing process, the moulds are taken out and cooled at room temperature for 1 day before demoulding for test.

RESULTS AND DISCUSSIONS:

The effect of various salient parameters on the compressive strength and flexural strength of low-calcium fly ash based geopolymer ferrocement concrete are discussed. And also the structural behavior of geopolymer concrete is discussed.

Calculations of Mortar cubes:

Size of the cube=7.07cm

Volume of the cube=3.53*10-4m3

Density of geo polymer concrete=2200kg/m³

Weight required= density*volume =3.53*10-4*2200kg/m³

=0.777kg (take 800gms)

Take fly ash to sand ratio as 1:3

Fly ash =200gms

Ennore sand=600gms

Take Ennore sand as a combination of grade1, grade 2, grade 3. Each 200gms

Take sodium silicate to sodium hydroxide in different ratio as 1.5, 2, 2.5, 3, 3.5.

Make the alkaline solution 24hrs before the preparation of mortar cubes

One day oven curing is there to get strength (60ºc)

FOR CEMENT MORTAR PLATES and GEO POLYMER BASED FERRO CEMENT PLATES

Size of the mortar cube=0.5*0.1*0.025=1.25*10-3m3

Density of geo polymer mortar=2200kg/m³

Weight of plate=2200*1.25*10-3=2.75 kg

FOR 1:1 RATIO OF FLYASH and FINE AGGREGATE

Fly ash= 1.375kg , Fine aggregate = 1.375 kg

Alkaline/Fly ash = 0.38;

Sodium Silicate/Sodium Hydroxide=2.5

Alkaline Solution = 522 ml

Sodium Silicate = 372.8 ml

Sodium Hydroxide = 149.14 ml

Weight of NaOH = 47.72 gms (taking Molarity as 8M)

FOR 1:1.5 RATIO OF FLYASH and FINE AGGREGATE

Fly ash= 1.1kg Fine aggregate = 1.65 kg

Alkaline/Fly ash = 0.42;

Sodium Silicate/Sodium Hydroxide=2.5

Alkaline Solution = 462 ml

Sodium Silicate = 330 ml

Sodium Hydroxide = 132 ml

Weight of NaoH = 42.24 gms (taking Molarity as 8M)

FOR 1:2 RATIO OF FLYASH and FINE AGGREGATE

Fly ash= 0.9166 kg Fine aggregate = 1.8344 kg

Alkaline/Fly ash = 0.45;

Sodium Silicate/Sodium Hydroxide=2.5

Alkaline Solution =412.47 ml

Sodium Silicate = 294.62 ml

Sodium Hydroxide = 117.84 ml

Weight of NaoH = 37.70 gms (taking Molarity as 8M)

Table 3: Comparison of Cement Mortar Specimens of Different Layers

Material	Proportions	Layers	Flexural Strength (MPa)	Toughness (N-mm)
Cement	1:1	1	8.422	3914.28
		2	7.701	6575.846
		3	8.487	12904.25
	1:1.5	1	5.991	5634.51
		2	6.307	4202.58
		3	8.619	6681.4
	1:2	1	3.679	9167.773
		2	5.045	2015.567
		3	6.727	6546.632

Table4: Comparison of Geopolymer based ferrocemnt Specimens of Different layers

Material	Proportions	Layers	Flexural Strength (MPa)	Toughness(N-mm)
Polymer	1:1	1	6.202	29255.722
		2	6.436	2770.177
		3	15.768	29625.8
	1:1.5	1	4.415	9611.422
		2	6.2020	8236.60
		3	11.668	23617.398
	1:2	1	4.204	1481.87
		2	5.256	2897.18
		3	5.466	11089.288

DISCUSSIONS:

Consistency test:

The consistency for geo polymer made with varying ratio of sodium silicate to sodium hydroxide (Na ₂ SiO ₃ /NaOH) is presented in table no 1 .With the increase in the ratio of alkaline solution (Na ₂ SiO ₃ /NaOH ) , the consistency of geopolymer decreases. Thus a ratio of 2.5 can be taken as optimum.

Compressive strength of mortar cubes:

The compressive strength of mortar cubes made with varying ratios sodium silicate to sodium hydroxide (Na ₂SiO ₃ /NaOH) is presented in table 2. With the increase in the ratio of alkaline solution compressive strength of mortar cubes increases and thereafter decreases. Higher value of compressive strength is obtained for the ratio of 2.5. Hence from strength point of view 2.5 can be taken as optimum.

Cement mortar prism Vs Geo polymer mortar prism (1:1 ratio):

The flexural strength of cement mortar plates and geo polymer mortar prisms made with 1:1 ratio of cement to fine aggregate and geo polymer to fine aggregate is presented in table 3 and 4. With increase in no. of layers from 1 to 3 flexural stress increases both in cement mortar and geo polymer mortar. The percentage of increase in flexural strength is 9.35% for 2 layers, 0.778% for 3 layers in case of Cement mortar. In case of Geo polymer mortar the increase in percentage is 3.78% for 2 layers, and for 3 Layers 154.2% . Flexural strength of geo polymer mortar is same as that of cement mortar but the percentage increase is more for geo polymer mortar. With the increase in number of layers of wire mesh flexural strength increases, hence number of layers of wire mesh play a major role in resisting the load.

Cement mortar prism Vs Geo polymer mortar prism (1:1.5 ratio):

The flexural strength of cement mortar plates and geo polymer mortar prisms made with 1:1.5 ratio of cement to fine aggregate and geo polymer to fine aggregate is presented in table 3 and 4. With increase in no. of layers from 1 to 3 flexural stress increases both in cement mortar and geo polymer mortar. The percentage of increase in flexural strength is 5.26% for 2 layers, 43.8% for 3 layers in case of Cement mortar. In case of Geo polymer mortar the increase in percentage is for 2 layers, 40.4% and For 3 Layers it is 164.2% . Flexural strength of geo polymer mortar is same as that of cement mortar but the percentage increase is more for geo polymer mortar. With the increase in number of layers of wire mesh flexural strength increases, hence number of layers of wire mesh play a major role in resisting the load.

Cement mortar prism Vs Geo polymer mortar prism (1:2 ratio):

The flexural strength of cement mortar plates and geo polymer mortar plates made with 1:2 ratio of cement to fine aggregate and geo polymer to fine aggregate is presented in table 3 and 4. With increase in no. of layers from 1 to 3 flexural stress increases both in cement mortar and geo polymer mortar. The percentage of increase in flexural strength is 37.12% for 2 layers, 82.8% for 3 layers in case of Cement mortar. In case of Geo polymer mortar the increase in percentage is for 2 layers, 25% and 30% for 3 Layers. Flexural strength of geo polymer mortar is same as that of cement mortar but the percentage increase is more for geo polymer mortar. With the increase in number of layers of wire mesh flexural strength increases, hence number of layers of wire mesh plays a major role in resisting the load.

Geo polymer mortar prisms (1:1) Vs Geo polymer mortar prisms (1:1.5 ratio)Vs Geopolymer (1:2) The Flexural strength of geopolymer mortar plates 1:1 ratio and geo polymer mortar plates 1:1.5 ratioand 1:2 of geo polymer to is presented in table 3 and 4. With increase in number of layers from 1to 3 Layers flexural strength increases for both 1:1 ratio and 1:1.5 ratio of geo polymer to fine aggregate. The flexural strength is more for 1:1 ratio of geo polymer to sand when compared to 1:1.5and1:2 ratio of geo polymer to sand, since geo polymer quantity is decreases flexural strength decreases.

Cement mortar prisms Vs Geo polymer mortar prisms (1:1 ratio ) The of cement mortar plates and geo polymer mortar plates made with 1:1 ratio of cement to sand and geo polymer to sand is presented in table 3 and 4. With increase in no. of layers from 1 to 3 toughness increases both in cement mortar and geo polymer mortar. The percentage of increase in toughness is 67.9% for 2 layers, 229.6% for 3 layers in case of Cement mortar. In case of Geo polymer mortar the increase in percentage is 9.56% for 2 Layers, 1.26% for 3 layers . Toughness of geo polymer mortar is nearly half of cement mortar but the percentage increase is more for geo polymer mortar. With the increase in number of layers of wire mesh toughness increases, hence number of layers of wire mesh play a major role in increasing toughness.

Cracking pattern:

The cracks formed in cement mortar and geo polymer are at the midpoint where the load is applied on the mortar plate. With the increase in the number of layers the formation and propagation of cracks decreased. The mesh wires resist the formation and propagation of cracks. This is the most advantage with the Ferro cement members and with that ductility is also improved. The cracking pattern is almost same for cement mortar and geo polymer mortar. With the increase in the ratio of cement to fine aggregate or geo polymer to fine aggregate, the cracking load increases and the formation of cracks also increases in 1:1.5 ratio when compared to 1:1 ratio.

CONCLUSIONS:

The geopolymer concrete specimens load carrying capacity is more than cement mortar specimens with addition of 1,2,3 layers of ferrocement . The cost of fly ash based geopolymer concrete is high compared to Ordinary Portland Concrete. Workability of geopolymer mortar decreases with the increase in concentration of sodium hydroxide. All geo polymer concrete mixes exhibited similar nature as that of ordinary Portland cement concrete 28 day flexural strengths.

REFERENCES:

1. Geopolymer Chemistry and Properties. Paper presented at the Davidovits, J. (1978b). First European Conference on Soft Mineralurgy, Compiegne, France.

2. Djwantoro Hardjito, Chua Chung Cheak and Carrie Ho Lee Ing. (2008) Strength and Setting Times of Low Calcium Fly Ash-based Geopolymer Mortar. Modern applied Science. Vol 2.

3. S. Mandal and D. Majumdar (2009). Study on the Alkali Activated Fly Ash Mortar. Paper presented at the The Open Civil Engineering Journal, 2009, 3, 98-101.

4. Mehta, P. K. (2001). "Reducing the Environmental Impact of Concrete." ACI Concrete International 23(10): 61-66.

5. R. Anuradha a , V. Sreevidya a , R. Venkatasubramania and B.V. Rangan (2011) Modified guidelines for geopolymer concrete mix design using Indian Standard, Asian Journal of Civil Engineering VOL. 13,.

Received on 06.11.2015 Accepted on 04.12.2015

Int. J. Tech. 5(2): July-Dec., 2015; Page 229-234

DOI: 10.5958/2231-3915.2015.00030.9