iaetsd strength and durability characteristics of

Strength and Durability characteristics of Geopolymer concrete using GGBS and RHA

S.Subburaj,T.Anantha shagar

VV college of Engineering,tisayanvilai tutucorin

Abstract— Cement, the second most consumed product in the world, contributes nearly 7% of the global carbon dioxide emission. Several efforts are in progress to reduce the use of Portland cement in concrete in order to address the global warming issues. Geopolymer concrete is a cementless concrete. It has the potential to reduce globally the carbon emission that lead to a sustainable development and growth of the concrete industry. In this study, geo-polymer concrete is prepared by incorporating ground granulated blast furnace slag (GGBS) and black rice husk ash (BRHA) as source materials. In India RHA is used for cattle feeding, partition board manufacturing, land filling, etc. RHA is either white or black in colour. If the rice husk is burnt in controlled temperature and duration, it will result the ash in white colour. This type of RHA has high percentage of silica content. The ease availability of RHA is black in colour due to uncontrolled burning temperature and duration in various rice mills, so the resulting rice husk ash is called as black rice husk ash (BRHA). In this study GGBS used as a base material for geopolymer concrete and it is replaced upto 30% by BRHA. The strength characteristic of GGBS and BRHA based geopolymer concrete has been studied. The suitable compressive strength test is performed. The result shows that the replacement of BRHA decreases the compressive strength of geopolymer concrete, because of the unburnt carbon content present in the BRHA. Keywords— Geopolymer concrete, GGBS, Black Rice Husk Ash, Compressive strength

INTRODUCTION Concrete is the second most used material in the world after water. Ordinary Portland cement has been used traditionally as a binding material for preparation of concrete. One tone of carbon dioxide is estimated to be released to the atmosphere when one ton of ordinary Portland cement is manufactured. Also the emission by cement manufacturing process contributes 7% to the global carbon dioxide emission. It is important to find an alternate binder which has less CO2 emission than cement. Geopolymer is an excellent alternative which transform industrial waste products like flyash, GGBS and rice husk ash into binder for concrete. Al- Si materials which are used as source materials undergoes dissolutions, gel formation, setting and hardening stages to form geopolymers. There are two main constituents of geo-polymers, namely the source materials and the alkaline liquids. The source materials for geo-polymers based on alumina-silicate should be rich in silicon (Si) and aluminium (Al). These could be natural minerals such as kaolinite, clays, etc. Alternatively, by-

product materials such as fly ash, silica fume, slag, rice-husk ash, red mud, etc could be used as source materials. The choice of the source materials for making geo-polymers depends on factors such as availability, cost, type of application, and specific demand of the end users. The alkaline liquids are from soluble alkali metals that are usually sodium or potassium based. The most common alkaline liquids used in geo-polymerization are a combination of sodium hydroxide (NaOH) or potassium hydroxide (KOH) and sodium silicate (Na2SiO3) or potassium silicate (K2SiO3). The alumino silicate material which is to be used in this study is a combination of Rice husk ash and ground granulated blast furnace slag (GGBS). RHA is either white or black in color. If the rice husk is burnt in controlled temperature and duration, it will result the ash in white color. This type of RHA has high percentage of silica content. The ease availability of RHA is black in color due to uncontrolled burning temperature and duration in various rice mills, so the black color rice husk ash is called as black rice husk ash (BRHA). The RHA used in this study was black rice husk ash. This study aims to synthesize geopolymer concrete using combination of GGBS and BRHA. In this study GGBS used as a base material for geoploymer concrete. GGBS is replaced up to 30% by BRHA to understand the strength and durability characteristics.

MATERIALS The materials used for making GGBS based geopolymer concrete specimens are GGBS, Rice Husk Ash, aggregates, alkaline liquids, water and super plasticizer. Ground Granulated Blast furnace Slag was procured from JSW cements in Bellari, Karnataka. Black Rice Husk Ash was obtained from a Rice mill near Karaikudi and then it was finely grounded. The properties of GGBS and BRHA are given in Table I.

TABLE I. PROPERTIES OF GGBS AND RHA

Property GGBS BRHA SiO2 31.25 % 93.96 % Al2O3 14.06 % 0.56 % Fe2O3 2.80 % 0.43 % CaO 33.75 % 0.55 % MgO 7.03 % 0.4 % Specific gravity 2.61 2.11

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Aggregates Coarse aggregate passing through 20mm sieve and fine aggregate of river sand from a local supplier were used for the present study and their properties are given in Table II.

TABLE III. PROPERTIES OF AGGREGATES

Property Coarse Aggregate

Fine Aggregate

Specific gravity 2.73 2.60 Fineness modulus 7.36 2.63 Bulk density 1533 kg/m3 1254 kg/m3

B. Alkaline solution A mixture of Sodium hydroxide and Sodium Silicate was used as the alkaline solution in the present study. Commercial grade Sodium Hydroxide in pellets form (97%-100% purity) and Sodium silicate solution having 7.5%-8.5% of Na2O and 25% -28% and water of 67.5%- 63.5% were used in the present study. The ratio of Sodium Silicate to Sodium Hydroxide was kept as 2.5. In this study the compressive strength of geo-polymer concrete is examined for the mix of 8M of NaOH solution. The molecular weight of NaOH is 40. For example to prepare 8M of NaOH solution 320g of NaOH flakes are weighed and they can be dissolved in distilled water to form 1 litre solution. For this, volumetric flask of 1 litre capacity is taken, NaOH flakes are added slowly to distilled water to prepare 1litre solution. In order to improve the workability of fresh concrete, high-range water-reducing naphthalene based super plasticizer was used. Extra water nearly 15% of binder is added to increase the workability of the concrete.

METHODOLOGY

C. Mixing, Casting and Curing The mix proportions were taken as given in Table. III. As there are no code provisions for the mix design of geopolymer concrete, the density of geo-polymer concrete was assumed as 2400 Kg/m3 and other calculations were done based on the density of concrete [4]. The combined total volume occupied by the coarse and fine aggregates was assumed to be 77%. The alkaline liquid to binder ratio was taken as 0.40. GGBS was kept as the primary binder in which BRHA was replaced in 0, 10, 20 and 30% by weight. The normal mixing procedure was adopted. First, the fine aggregate, coarse aggregate and GGBS & BRHA were mixed in dry condition for 3-4 minutes and then the alkaline solution which is a combination of Sodium hydroxide and Sodium silicate solution with super-plasticizer was added to the dry mix. Then some extra water about 15% by weight of the binder was added to improve the workability. The mixing was continued for about 6-8 minutes. After the mixing, the concrete was placed in cube moulds of size 150mm X 150mm X 150mm by giving proper compaction. The GPC specimens were then placed in a hot air oven at a temperature of 60oC for 48 hours and then the specimens were taken out and cured under room temperature

till the time of testing.The cubes were then tested at 3, 7 and 28 days from the day of casting.

TABLE IIIII. MIX PROPOTIONS OF GEOPOLYMER CONCRETE

Materials Mass(Kg/m3) Mix1 (0%

RHA)

Mix2 (10%

RHA)

Mix3 (20%

RHA)

Mix4 (30%

RHA) GGBS 394 355 315 276 RHA 0 39 79 118 Coarse

Aggregate 647 647 647 647

Fine Aggregate

1201 1201 1201 1201

Sodium Hydroxide

45 45 45 45

Sodium Silicate

113 113 113 113

Super Plasticizer

8 8 8 8

Extra Water (15%)

59 59 59 59

RESULTS AND DISCUSSION The cubes were tested in the compressive testing machine to determine their compressive strength at the age of 3, 7 and 28 days from the day of casting. The Table IV and figure 1 shows the compressive strength variation with percentage replacement of BRHA. The table4 shows that GGBS based geopolymer concrete attained compressive strength of 69 MPa. 10 % replacement of GGBS by RHA gives compressive strength of 58 MPa. The figure1 shows that there is an increase in compressive strength if the curing time increases. The percentage of increase in strength is approximately 16 to 20 for the curing time of 3days to 28days. The percentage increase in strength from 3 to 28 days curing time is approximately 24% for mix1. The graph shows that the replacement of BRHA in GGBS based geopolymer concrete decreases the compressive strength. Because of the unburnt carbon content present in BRHA, decreases the compressive strength. The average 28 days compressive strength of mix2 and mix3 is decreases by 20% and 46% compared to mix1.

TABLE IVV. COMPRESSIVE STRENGTH TEST RESULTS

Mix Compressive strength at 3rd day(MPa)

Compressive strength at 7th day(MPa)

Compressive strength at 28th day(MPa)



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Mix 1 (100% GGBS, 0% RHA)

55.9 60.5 69.2


48.6 54.3 57.46


40.75 44.72 47.36


20.8 23.54 27.36

Fig.1 Variation of compressive strength at 3rd, 7th and 28th

days with replacement of BRHA

CONCLUSIONS

From the limited experimental study conducted on the geopolymer concrete made with GGBS and BRHA, the following conclusions are made. 1. The GGBS based geopolymer concrte gives higher

strength. 2. The replacement of GGBS by BRHA decreases the

compressive strength because of the unburnt carbon content.

3. The percentage replacement of BRHA in GGBS based geo-polymer concrete is significant only in 10%.

4. Due to the presence of high silica content in BRHA (94%) there is a fast chemical reaction occurred resulting quick setting of geo-polymer concrete.

5. In this study, the Si / Al ratio is not maintained due to low alumina content in the source materials resulting in lesser compressive strength .

6. I feel that GGBS with 10% of RHA will be well and eco friendly when compared with OPC

ACKNOWLEDGMENT

The author would like to acknowledge his Research supervisor mr.p.muthuraman for his meticulous guidance and constant motivation. The author would also like to thank the faculty members of Division of Structural Engineering, vv college of Engineering University, tisayanviai for their consent encouragement and support during the project work. The author would also like to thank his family and friends for their complete moral support.

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