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Durability study on coal fly ash-blast furnace slag geopolymer concretes with bio-additives
Author’s Accepted Manuscript Durability study on Coal Fly Ash-Blast Furnace Slag geopolymer concretes with Bio-additives A. Karthik, K. Sudalaimani, C.T. Vijayakumar
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S0272-8842(17)31244-0 http://dx.doi.org/10.1016/j.ceramint.2017.06.042 CERI15564
To appear in: Ceramics International Received date: 22 March 2017 Revised date: 29 May 2017 Accepted date: 6 June 2017 Cite this article as: A. Karthik, K. Sudalaimani and C.T. Vijayakumar, Durability study on Coal Fly Ash-Blast Furnace Slag geopolymer concretes with Bioa d d i t i v e s , Ceramics International, http://dx.doi.org/10.1016/j.ceramint.2017.06.042 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Durability study on Coal Fly Ash-Blast Furnace Slag geopolymer concretes with Bioadditives A. Karthika*, K. Sudalaimanib, C.T. Vijayakumarc a
Department of Civil Engineering, Kamaraj College of Engineering and Technology, S.P.G.C. Nagar, K. Vellakulam-625701, India
b
Department of Civil Engineering, Thiagarajar College of Engineering, Madurai-625015, India
c
Department of Polymer Technology, Kamaraj College of Engineering and Technology, S.P.G.C. Nagar, K. Vellakulam-625701, India *
Corresponding author: A. Karthik. Mobile: +91 9629666291, Fax: +91 4549 278172, Email ID: [email protected]
Abstract The objective of this research was to understand the positive impact of bio-additives such as terminalia chebula and natural sugars (molasses/palm jaggery/honey) on the durability properties of coal fly ash-blast furnace slag (BFS) based geopolymer concrete under various chemical attacks. Various tests had been conducted by immersing specimens in 5% sulfuric acid, 5% sodium sulfate and 5% sodium chloride solution for different duration of 7, 14, 28, 56 and 90 days to determine the resistance of bio-additives added geopolymer concrete against chemical attacks. The durability was also related by mercury intrusion porosimetry to find out the porosity and pore size distribution. After 90 days of immersion, test results confirmed that bio-additives inclusion in coal fly ash-blast furnace slag based geopolymer concrete had undergone weight loss and compressive strength loss in the range of 2.82– 3.91%, 9.67–12.05% under sulfuric acid attack, 0.38–0.68%, 2.15–2.95% under sodium sulfate attack and 0.28–0.51%, 0.83–1.33% under sodium chloride attack respectively. 1
However in control ordinary geopolymer specimen, the weight loss and compressive strength loss was 13.97%, 33.57% under sulfuric acid attack, 1.64%, 6.45% under sodium sulfate attack and 0.86%, 2.05% under sodium chloride attack was observed.
This led to the
conclusion that bio-additives added geopolymer concretes had enhanced durability properties when compared to control ordinary geopolymer concrete examined in this study. Keywords: Durability, Bio-additives, Geopolymer. Introduction Ordinary portland cement (OPC) based concrete is the mostly used construction material and has extensive applications in residential, commercial and industrial structures. The manufacturing process of OPC hold 5–8% share of world’s greenhouse gas emissions [1]. Recent study revealed an intimidating ratio of 1 between the production of cement and CO2 gas emission (54% during calcinations and 46% during burning of fuels). Meanwhile massive amount of industrial wastes such as coal fly ash, blast furnace slag etc were being generated from power generation and steel making industry. These industrial by-products led to various disposal and storage problems. According to the recent statistics, 176 million tons of coal fly ash and 200 million tons of blast furnace slag (BFS) were not utilized worldwide and used as landfill [2]. The existing trend would increase the demand of cement in future that insists the usage of alternative cementitious materials in construction industry. Finding the environmentally and economically viable alternate for cement had now become a mandate by exploring the opportunities to consume different industrial by-products. Current literature review portrayed that concretes produced by using industrial by-products possessed better mechanical and durability properties [3–6]. The effective utilization of these industrial byproducts such as coal fly ash and BFS in concrete minimized the usage of OPC in construction applications and paved the way for sustainable building materials technology
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and eco-friendly concrete. This brings out the development of alternative concrete by adopting coal fly ash and BFS as base material by completely replacing OPC thereby less carbon foot print could be achieved. The best possible solution to address this issue is adoption of geopolymer concrete also termed as alkali-bonded ceramic/hydroceramic/lowtemperature aluminosilicate glass/ alkali-activated cement/geo-cement/inorganic polymer concrete [7]. Geopolymer synthesized predominantly from the reaction of an aluminosilicate source materials such as coal fly ash and BFS with an alkaline activator was known for its ceramic-like-properties. Coal fly ash based geopolymer concrete could be 10–30% cheaper than OPC concrete [7]. Also geopolymer concrete could be set and hardened at ambient curing conditions when coal fly ash was suitably replaced with BFS [8]. When exposed to aggressive environment geopolymer concrete exhibited high resistance to sulfate attack, acid attack and corrosion [9–12] due to the three-dimensional polymeric chain and ring like structure consisting of –Si–O–Al–O– bonds and low Ca(OH)2 content [13]. Concrete structures must be able to resist weathering action, chemical attack, abrasion or any other process of deterioration which affected the long term performance of concrete. Concrete underwent degradation under the influence of aggressive environments that induced chemical processes involving ion exchange that altered the microstructure of the binding matrix in-turn affected the serviceability of the structures. Considering the structural applications of geopolymer concrete in varying aggressive environments, it was crucial to study the durability properties of concrete. Durability of geopolymer concrete was an important aspect for its several commercial applications such as coating materials in marine concrete protection [14], industrial wastewater pipelines [15], etc. Recent studies revealed geopolymer exhibited better durability properties than OPC. The mass loss in blended ash (70% pulverized coal fuel ash+30% palm oil fuel ash) based geopolymer concrete specimens was only 8% when compared to the 20% mass loss of OPC concrete specimens in 2%
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sulfuric acid exposure for 18 months [16]. The resistance to chloride ingression was better in coal fly ash-BFS based geopolymer paste (50% coal fly ash+50% BFS) than OPC paste when immersed in 3% sodium chloride solution for 72 hours [17]. Lignite bottom ash based geopolymer mortars were less vulnerable to 3% sulfuric acid and 5% sodium sulfate solutions than OPC mortars in 120 days observation [18]. Strength loss of geopolymer concrete made with gypsum blended BFS was 33% in comparison with 47% in OPC concrete in acetic acid solution (pH=4) for 12 months [19] and 17% compared to 25% in OPC concrete in 5% sodium sulfate solutions for 12 months [20]. Previous researches conducted on geopolymers used chemical additions such as silica fume, nano silica, Na2CO3 and synthetic zeolites [21–24] to improve its durability properties. Till now very limited researches were conducted to study the effect of bio-additives on durability properties of geopolymer concrete. In ancient mortars, terminalia chebula and palm jaggery improved its functional properties when added as bio-additives along with lime mortar [25]. Addition of terminalia chebula in lime mortar increased the compressive strength and decreased the porosity [26]. Combination of bio-additives (terminalia chebula and jaggery) enriched the 28-days compressive strength of cement mortar by 88% [27]. Sugarcane bagasse ash was used as a source material for making geopolymer mortar resulted in increased compressive strength and lower porosity [28]. When BFS based geopolymer concrete specimens were immersed in 30% sugar solution for two years, it was found that the corrosion resistance was three times higher than OPC based concrete [29,30]. This research portrayed the durability performance of coal fly ash-BFS based geopolymer concrete with bio-additives when subjected to acid, sulfate and chloride attack in detail.
2. Materials
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The materials used for making geopolymer concrete specimens were aluminosilicate materials (coal fly ash and BFS), fine aggregate, coarse aggregate, alkaline activators, superplasticizer and bio-additives (terminalia chebula and natural sugars). 2.1. Aluminosilicate materials In this, both coal fly ash and BFS were used as aluminosilicate materials. Low calcium Class F coal fly ash was obtained from the silos of thermal power station, Tuticorin, Tamil Nadu was used as one of the base aluminosilicate material. BFS was obtained from local steel plant and it showed pozzolanic and binding properties in an alkaline medium [31]. Chemical compositions (percentage by weight) of coal fly ash and BFS had been identified in X-ray fluorescence spectrometry and were given in Table 1. 2.2. Aggregates Locally resourced river sand and crushed granite were used as fine and coarse aggregates. The sieve analysis test results of the fine aggregate conformed to zone II as per IS 383-1970 (Reaffirmed on 1997). It had specific gravity of 2.63, bulk density of 1721 kg/m3 and fineness modulus of 2.67. Similarly specific gravity of 2.84, bulk density of 1578 kg/m3 and fineness modulus of 7.75 were obtained for differently sized 20 mm, 12 mm, 6 mm coarse aggregates. The final combined aggregate volume was a combination of 30% of fine aggregate, 21% of 20 mm, 29% of 12 mm and 20% of 6 mm coarse aggregates. 2.3. Alkaline activators A combination of commercially available 98% pure sodium hydroxide (flakes form) and sodium silicate (liquid gel form) was used as alkaline activators for geopolymerization. For the present study 8M NaOH was used in all geopolymer specimens. The chemical composition of sodium silicate was: Na2O-14.7%, SiO2-29.4% and Water-55.9% by mass. The alkaline activator was prepared by mixing sodium silicate and sodium hydroxide
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solutions. The ratio of sodium silicate to sodium hydroxide solution was fixed as 2.5 for the alkaline activators (pH = 13). 2.4. Superplasticizer Naphthalene sulphonate based superplasticizer (Conplast SP430, Fosroc, Bengaluru, India) was used in this study to improve the workability of the fresh geopolymer mix. Superplasticizer was added 2% by the weight of aluminosilicate materials. 2.5. Bio-additives Bio-additives used here were terminalia chebula and natural sugars (molasses/palm jaggery/honey). All the bio-additives were used in raw form. Both the bio-additives were added 0.8% by the weight of aluminosilicate minerals. 2.5.1. Terminalia chebula Powdered form of terminalia chebula with particle size around 295 nm available in market was used. It contained about chebulagic acid (8–25%), chebulinic acid (15–30%) and 5–45% by weight of other low molecular weight hydrolyzable tannoids [32]. Chebulagic acid was a benzopyran tannin which was hydrolyzable while chebulinic acid was an ellagitannin. When added terminalia chebula in cement mortar, the compressive strength was enhanced by 48% [26]. 2.5.2 Natural sugars Three locally resourced different types of natural sugars such as molasses (from factory), palm jaggery and honey were individually used. Both molasses and honey were used in liquid form and palm jaggery was used in powdered form. The variable composition of molasses contained 76–84% dry substances (including 46–51% sucrose) [33]. Chemical composition of palm jaggery primarily contained 40–60% sucrose [34]. The most common carbohydrates found in honey were monosaccharides (43.3–65.5% fructose, 0.4–8.8% glucose) and disaccharide (17.2–21.6% sucrose) [35].
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3. Experimental work 3.1. Manufacturing procedure of geopolymer concrete Mix design detail for geopolymer concrete was given in Table 2. Alkaline activator to the aluminosilicate source material ratio was fixed as 0.45. Firstly the alkaline activator should be prepared 30 minutes prior to the actual mixing of the concrete. Coal fly ash, BFS and aggregates were first dry mixed in a pan mixer. To produce fresh geopolymer concrete, prepared alkaline activator solution was added to the well mixed dry materials and continued the mixing for about 5 minutes. Then the bio-additives such as terminalia chebula and natural sugar (molasses/palm jaggery/honey) were added to the wet mix. Finally superplasticizer was added to achieve workable mix. Prior casting, the inner sides of cube mould was layered with lubricating oil to prevent adhesion with the concrete specimens. The moulds were filled in three layers, each layer was well compacted. The casted specimens were kept open at the room temperature of 30±2°C and relative humidity of 65±5%. 3.2. Testing All the hardened geopolymer concrete cube specimens of size 150 mm x150 mm x150 mm were subjected to acid attack, sulfate attack and chloride attack by immersing in sulfuric acid, sodium sulfate and sodium chloride for 90 days. For sulfuric acid attack the pH of the acidic solution was checked every week and maintained at value 1.0 by adding required amount of the concentrated acid solution. The acidic solution was completely replaced every 30 days. Similarly for sulfate and chloride attack the solution replacement was done. The change in weight and compressive strength of specimens were tested at an interval of 7, 14, 28, 56 and 90 days of immersion. Tests for compressive strength were conducted on cube specimens using 2000 kN compression testing machine as per Indian Standard specifications [36]. The density of the hardened concrete before and after 90 days of immersion was found out for all the hardened concrete specimens. Pore size distributions in the specimens were analyzed by conducting mercury intrusion porosimetry (MIP) test. MIP 7
measurements were carried out with contact angle of 140° and maximum pressure of 400 MPa. 4. Results and discussions 4.1. Sulfuric acid attack 4.1.1. Weight loss due to sulfuric acid attack The 5 wt% sulfuric acid was used in the study. All geopolymer specimens were subjected to sulfuric acid attack for 90 days to study the durability of geopolymer concrete in acidic environment. The weight of GPC0, GPC1, GPC2 and GPC3 after 90 days of immersion was noted to be 6.986 kg, 8.255 kg, 8.371 kg and 8.106 kg (Fig. 1) and its corresponding percentage weight loss was found to be 13.97%, 3.47%, 2.82% and 3.91% respectively. At low pH value of 1, the positive hydrogen ions from acidic medium broke down the Si–O–Al bonds present in the geopolymer [15] and produced more number of Si– OH and Al–OH bonds along with increased amount of silicic acid in the geopolymer matrix [37]. This reaction process made the GPC0 concrete specimen weaker resulted in more weight loss of 13.97% after 90 days. Also after 90 days of immersion, GPC0 was more deteriorated and coarse aggregates were clearly exposed at the surface when observed in Fig. 3. However the bio-additives added geopolymer concrete specimens (GPC1, GPC2 and GPC3) appeared to be slightly corroded at the surface and less damaged around the edges of specimen. Bio-additives inclusion might have caused the better acid resistance of geopolymer specimens (GPC1, GPC2 and GPC3) due to the existence of stable cross-linked polymer structures that deterred the degree of chemical reaction between sulfuric acid and calcium present in geopolymer gel thereby diminishing its deterioration effects on geopolymer gel structure. This might have resulted in less surface deterioration and minimum weight loss occurred in GPC1, GPC2 and GPC3 specimens throughout the different days of immersion.
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The test results strongly implied GPC1, GPC2 and GPC3 specimens showed better resistant to acid attack when compared to GPC0. 4.1.2. Strength loss due to sulfuric acid attack After 90 days of sulfuric acid attack, compressive strength of GPC0, GPC1, GPC2 and GPC3 was reported as 18.84 Mpa, 31.11 Mpa, 33.64 Mpa and 29.20 Mpa (Fig. 2) and its equivalent percentage loss in compressive strength was noted as 33.57%, 10.71%, 9.67% and 12.05% respectively. Test results exhibited that GPC0 experienced maximum strength loss whereas GPC1, GPC2 and GPC3 experienced minimum loss at all test intervals. The compressive strength loss was in the order of GPC0 > GPC3 > GPC1 > GPC2. In general compressive strength loss was proportional to the increase in immersion duration. In the whole, GPC2 performed better against acid attack among all geopolymer specimens throughout the immersion duration. 4.2. Sodium sulfate attack 4.2.1 Weight loss due to sodium sulfate attack In this study all the specimens were subjected to 5% of sodium sulfate solution. After 90 days of immersion, the geopolymer specimens GPC0, GPC1, GPC2 and GPC3 weighed 7.997 kg, 8.456 kg, 8.540 kg and 8.378 kg (Fig. 4) and undergone percentage weight loss of 1.64%, 0.49%, 0.38% and 0.68% respectively. It was found that when geopolymer specimens were soaked in sodium sulfate solution, the diffusion of sulfate ions in geopolymer structure caused disintegration of siloxane bonds (–Si–O–Si– bonds) which decreased the silica to aluminium (Si/Al) atomic ratio in the specimens and leaching of silica (Si) in geopolymer gel structure [38]. This resulted in more weight loss in GPC0 specimen. From Fig. 6, the efflorescence effect in GPC0 was very evident in contrast to the bio-additives added specimens GPC1, GPC2 and GPC3. Test results revealed that inclusion of bio-additives in geopolymer concrete lowered the total porosity of GPC1, GPC2 and GPC3 when compared
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to GPC0 and the same was confirmed by MIP study. Less porous microstructure in GPC1, GPC2 and GPC3 inhibited the diffusion of sulfate ions and created positive effect on geopolymer microstructure which in-turn improved the resistance to weight loss in GPC1, GPC2 and GPC3. 4.2.2. Strength loss due to sodium sulfate attack After 90 days of sulfate attack, compressive strength of GPC0, GPC1, GPC2 and GPC3 was found as 26.53 Mpa, 33.96 Mpa, 36.44 Mpa and 32.22 Mpa (Fig. 5) and its equivalent percentage loss in compressive strength was reported as 6.45%, 2.53%, 2.15% and 2.95% respectively. Sulfate ions (SO4)2− had minimum deteriorating effect on compressive strength of geopolymer concrete [39]. Also the crystallization pressure of sodium sulfate developed in the specimen by absorbing (SO4)2− and possibly Na+ ions through the pores [40,13] weakened the geopolymer matrix. This mechanism resulted in the cohesion loss between geopolymer matrix and aggregate [41] that led to more strength loss in GPC0 specimen. Geopolymer matrix-aggregate interface of GPC0, GPC1, GPC2 and GPC3 was examined using SEM and the same was mentioned in Fig. 7. From the image Fig. 7(a) related to GPC0, it was clear that there was a small gap zone in the boundary between the geopolymer matrix and aggregate. This resulted in maximum strength loss in GPC0 after the sulfate attack. When examined SEM images given in Fig. 7(b), 7(c) and 7(d) correspond to the bio-additives added geopolymer specimens GPC1, GPC2 and GPC3, they showed noticeable differences in geopolymer matrix-aggregate interface. Also it was noticed that the geopolymer matrixaggregate interface was intact and geopolymer matrix was densely packed. It could be attributed to the minimum strength loss noticed in GPC1, GPC2 and GPC3 due to increase in homogeneity of bio-additives added geopolymer concrete.
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4.3. Chloride attack 4.3.1. Weight loss due to chloride attack One of the common durability issue was chloride attack on reinforced concrete. The chloride ions diffusion in geopolymer reinforced concrete would induce the steel bar corrosion by de-passivation resulting in a reduced load carrying capacity of concrete that would led to structural failure [42]. The chloride ion penetration in concrete involved various processes such as diffusion, capillary suction and convective flow through the pore system [43]. Therefore it becomes necessary to study impact of chloride attack in geopolymer concrete. At pH value of 6.5, the weight of GPC0, GPC1, GPC2 and GPC3 after 90 days of immersion was reported as 8.174 kg, 8.562 kg, 8.621 kg and 8.389 kg (Fig. 8) and its corresponding percentage weight loss was very minimal and found to be 0.86%, 0.40%, 0.28% and 0.51% respectively. The visual inspection justified the minimal chloride attack with slight colour change in the surface of all bio-additives added specimens in contrast to noticeable change in GPC0 as shown in Fig. 10. The results showed that inclusion of bioadditives in geopolymer concrete (GPC1, GPC2 and GPC3) led to the lower porosity reducing the ingress of chloride ions through pores. This in-turn slowed down the entering of chloride ions in GPC1, GPC2 and GPC3 compared with GPC0. 4.3.2. Strength loss due to chloride attack After 90 days of immersion in sodium chloride, compressive strength of GPC0, GPC1, GPC2 and GPC3 was found as 27.78 Mpa, 34.40 Mpa, 36.93 Mpa and 32.76 Mpa (Fig. 9) and its equivalent percentage loss in compressive strength was meagre and noted as 2.05%, 1.26%, 0.83% and 1.33% respectively. Thus more ordered and dense geopolymer binding gel formed in GPC1, GPC2 and GPC3 decreased the compressive strength loss compared to porous aluminosilicate gel that formed in the GPC0.
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4.4 Density Before immersion, the average density was found to be 2419 kg/m3, 2533 kg/m3, 2551 kg/m3 and 2499 kg/m3 for GPC0, GPC1, GPC2 and GPC3 specimens respectively (Table 3). These values were in better agreement with the normal concrete having density range between 2155–2560 kg/m3 [44]. There was an increasing trend in density (3.31–5.46%) for the bio-additives added geopolymer specimens compared to GPC0. It would have a direct positive effect in the durability of the concrete. Bio-additives inclusions led to the filling of micropores in geopolymer matrix which in turn led to the denser matrix in GPC1, GPC2 and GPC3. After 90 days of immersion in different immersion conditions, the density was found to be in the range of 2070–2422 kg/m3, 2446–2537 kg/m3, 2480–2554 kg/m3 and 2402–2486 kg/m3 for GPC0, GPC1, GPC2 and GPC3 specimens respectively (Table 4). By comparing the density values before and after 90 days of immersion, there was decrease in density for all specimens subjected to various chemical attacks. The decrease in density after 90 days of immersion was found to be in the range of 0.86–13.97%, 0.40–3.47%, 0.28–2.82% and 0.51– 3.91% for GPC0, GPC1, GPC2 and GPC3 specimens respectively. It was to be noted that the decrease in density of bio-additives added geopolymer concrete specimens GPC1, GPC2 and GPC3 was minimal when compared to control ordinary geopolymer concrete specimen GPC0. 4.5 Mercury intrusion porosimetry Samples of geopolymer specimens GPC0, GPC1, GPC2 and GPC3 were subjected to MIP test to measure the porosity and pore size distribution. The cumulative pore volume and differential pore volume for specimens before attack were plotted in Fig. 11 and 12 respectively and would give an idea regarding the development of pores. From Fig. 11, the total porosity of GPC0, GPC1, GPC2 and GPC3 before attack was found to be 0.068 cc/g,
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0.053 cc/g, 0.039 cc/g, and 0.056 cc/g respectively. This confirmed the addition of bioadditives lowered the total porosity of bio-additives added geopolymer (GPC1, GPC2 and GPC3) when compared to conventional geopolymer (GPC0). It could be attributed to the denser microstructure of bio-additives added geopolymer specimens. The differential curves of pore size distribution in Fig. 12 showed significant differences between samples. The critical pore diameters defined as the peaks in the differential curve gives the rate of mercury intrusion per change in pressure [45,46] were shifted to lower values for bio-additives added geopolymer (GPC1, GPC2 and GPC3). The results from MIP measurements were also consistent with durability results under different chemical attacks such as acid, sulfate and chloride which related to better permeability resistance of GPC1, GPC2 and GPC3. Thus inclusion of bio-additives would occupy the capillary pores in geopolymer matrix which would result in the refinement of pore structure of GPC1, GPC2 and GPC3. The cumulative pore volume and differential pore volume for specimens after sulfuric acid attack were plotted in Fig. 13 and 14 respectively. After 90 days of immersion in sulfuric acid, the total porosity of GPC0, GPC1, GPC2 and GPC3 was found to be 0.324 cc/g, 0.141 cc/g, 0.131 cc/g and 0.162 cc/g respectively (Fig. 13). Test results revealed that the total porosity was in the order of GPC0 > GPC3 > GPC1 > GPC2 for all geopolymer specimens before and after the chemical attack. The total porosity of the geopolymer specimens was well correlated with durability test results discussed above. Unlike the control geopolymer concrete specimen GPC0, weight loss and strength loss of bio-additives added geopolymer concrete specimens GPC1, GPC2 and GPC3 remained low after exposure to chemical attacks for 90 days. From Fig. 14, it was obvious that immersion of GPC0 specimen in sulfuric acid led to the development of highly porous system when compared to GPC1, GPC2 and GPC3. This confirmed that GPC0 contained high amount of pores that could facilitate the penetration of external chemicals. These results were in-line with the durability results where 13
the penetration of external chemical was high in GPC0. This resulted in maximum weight loss and compressive strength loss in GPC0 after the attack. 4.6 Effect of bio-additives The system was terminalia chebula with different kind of natural sugars (carbohydrates) such as molasses, palm jaggery, honey and chiefly NaOH. It had been proved that phenols react with NaOH to yield sodiumphenolates. It was found that terminalia chebula contained chebulagic acid and chebulinic acid and both the compounds were gallic acid esters [32,47]. In the presence of an alkali, these gallic acid esters might undergo hydrolysis to yield gallic acid. Hence the reaction of NaOH with both the acid and phenolic groups present in gallic acid was inevitable. All the carbohydrates used in the present investigation contained considerable amount of disaccharides like sucrose and monosaccharides like glucose and fructose. Hence it was not only the concentration of natural sugars used but also dependent on the nature of carbohydrates present in natural sugars. This included not only the configuration of monosaccharides and disaccharides but also on conformation of natural sugars. The aluminosilicate materials such as coal fly ash and BFS would be definitely containing silanol (Si–O–H) groups. Apart from several individual reactions of the terminalia chebula, carbohydrates and silanol groups, the possibility of interactions between all these groups in an alkali medium leading to the formation of highly complex structures was envisaged. The production of such networks along with silicate network with the reasonable interface interactions resulted in low porosity of GPC1, GPC2 and GPC3. This elucidated the lesser chance of foreign substance penetration through the micropores to weaken the geopolymer microstructure thereby significantly increased the durability of bio-additives added geopolymer concrete against external chemical attacks investigated in this study.
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5. Conclusions Based on the results and discussions on durability study of coal fly ash-blast furnace slag based geopolymer concrete with bio-additives, the following conclusions were made. Bio-additives added geopolymer specimens GPC1, GPC2 and GPC3 exhibited better resistance to 5% sulfuric acid attack after 90 days with weight loss ranging from 2.82– 3.91% and strength loss between 9.67–12.05% whereas control ordinary geopolymer specimen GPC0 suffered a greater weight loss of 13.97% and strength loss of 33.57%. Similarly GPC1, GPC2 and GPC3 had undergone minimal weight loss and strength loss under sulfate and chloride attack when compared to GPC0. Upon the immersion in 5% sodium sulfate and 5% sodium chloride solution after 90 days, maximum weight loss was 0.68%, 0.51% and strength loss was 2.95%, 1.33% respectively among all bioadditives added geopolymer specimens. There was a trend of increasing weight loss and strength loss for every immersion duration in all chemical attacks. Density of bio-additives added geopolymer specimens were increased upto 3.31–5.46% when compared to GPC0 before immersion. The percentage density loss in GPC1, GPC2 and GPC3 had maximum of 3.91% which was much lesser when compared to GPC0 with maximum of 13.97% in all immersion conditions after 90 days. MIP results confirmed the addition of bio-additives lowered the total porosity of the hardened geopolymer concrete before and after chemical attack. All these experimental results could be attributed to stable cross-linked polymer structures, improved homogeneity, more ordered and dense geopolymer binding gel, filling of micropores and refinement of the pore structure in bio-additives added geopolymer specimen that paved the way to enhance durability and better shielding against external chemical attacks such as acid, sulfate and chloride. It was inferred that the inclusion of bio-additives 15
such as terminalia chebula and natural sugars improved the durability properties of geopolymer concrete. In particular, addition of the palm jaggery in combination with terminalia chebula in coal fly ash-BFS based geopolymer concrete (GPC2) displayed superior durability characteristics when compared to other bio-additives used in the study.
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[7] P. Duxson, A. Fernández-Jiménez, J.L. Provis, G.C. Lukey, A. Palomo, J.S.J. van Deventer, Geopolymer technology: the current state of the art, J. Mater. Sci. 42 (2007) 2917– 2933. [8] K. Neupane, Fly ash and GGBFS based powder-activated geopolymer binders: A viable sustainable alternative of portland cement in concrete industry, Mechanics of Materials 103 (2016) 110–122. [9] G. Kürklü, The effect of high temperature on the design of blast furnace slag and coarse fly ash-based geopolymer mortar, Composites Part B 92 (2016) 9–18. [10] A. Fernandez-Jimenez, I. García-Lodeiro, A. Palomo, Durability of alkali-activated fly ash cementitious materials, J. Mater. Sci. 42 (2007) 3055–3065. [11] I. García-Lodeiro, A. Palomo, A. Fernández-Jiménez, Alkali–aggregate reaction in activated fly ash systems, Cement and Concrete Research 37 (2007) 175–183. [12] M. Criado, I. Sobrados, J.M. Bastidas, J. Sanz, Corrosion behaviour of coated steel rebars in carbonated and chloride-contaminated alkali-activated fly ash mortar, Progress in Organic Coatings 99 (2016) 11–22. [13] Z.H. Zhang, H.J. Zhu, C.H. Zhou, H. Wang, Geopolymer from kaolin in China: An overview, Appl. Clay Sci. 119 (2016) 31–41. [14] Z. Zhang, X. Yao, H. Zhu, Potential application of geopolymers as protection coatings for marine concrete I. Basic properties, Appl. Clay Sci. 49 (2010) 1–6. [15] P. Chindaprasirt, U. Rattanasak, Improvement of durability of cement pipe with high calcium fly ash geopolymer covering, Constr. Build. Mater. 112 (2016) 956–961. [16] M.A.M. Ariffin, M.A.R. Bhutta, M.W. Hussin, M.M. Tahir, N. Aziah, Sulfuric acid resistance of blended ash geopolymer concrete, Constr. Build. Mater. 43 (2013) 80–86. [17] T. Yang, X. Yao, Z. Zhang, Quantification of chloride diffusion in fly ash–slag-based geopolymers by X-ray fluorescence (XRF), Constr. Build. Mater. 69 (2014) 109–115.
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[18] V. Sata, A. Sathonsaowaphak, P. Chindaprasirt, Resistance of lignite bottom ash geopolymer mortar to sulfate and sulphuric acid attack, Cem. Concr. Compos. 34 (2012) 700–708. [19] T. Bakharev, J.G. Sanjayan, Y.-B. Cheng, Resistance of alkali-activated slag concrete to acid attack, Cem. Concr. Res. 33 (2003) 1607–1611. [20] T. Bakharev, J.G. Sanjayan, Y.-B. Cheng, Sulfate attack on alkali-activated slag concrete, Cem. Concr. Res. 32 (2002) 211–216. [21] M. Rostami, K. Behfarnia, The effect of silica fume on durability of alkali activated slag concrete, Constr. Build. Mater. 134 (2017) 262–268. [22] P.S. Deb, P.K. Sarker, S. Barbhuiya, Sorptivity and acid resistance of ambient-cured geopolymer mortars containing nano-silica, Cem. Concr. Compos. 72 (2016) 235–245. [23] D. Jeon, Y. Jun, Y. Jeong, J.E. Oh, Microstructural and strength improvements through the use of Na2CO3 in a cementless Ca(OH)2-activated Class F fly ash system, Cem. Concr. Res. 67 (2015) 215–225. [24] H. Mingyu, Z. Xiaomin, L. Fumei, Alkali-activated fly ash-based geopolymers with zeolite or bentonite as additives, Cem. Concr. Compos. 31 (2009) 762–768. [25] S. Thirumalini, R. Ravi , S.K. Sekar, M. Nambirajan, Knowing from the past– Ingredients and technology of ancient mortar used in Vadakumnathan temple, Tirussur, Kerala, India, Journal of Building Engineering 4 (2015) 101–112. [26] K.V. Bharathy, R.S. Kumar, B. Gnanasekar, K. Subash, Herbocrete - An effective use of natural admixtures in concrete, Indian Concrete Journal, Special Issue-Sustainability (2015). [27] P.V. Prabhu, S.A. Prabhakar, R. Iyappan, M. Murugan, Experimental study on mortar using natural admixtures, International Journal of Scientific & Engineering Research 7 (2016) 42–44.
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[28] S. Rukzon, P. Chindaprasirt, Strength and Porosity of Bagasse Ash-based Geopolymer Mortar, Journal of Applied Sciences 14 (2014) 586–591. [29] N.N. Gontcharov, Corrosion Resistance of Slag Alkaline Cements and Concretes in Organic Aggressive Environments, Ph.D. Thesis, Kiev Civil Engineering Institute, Kiev, USSR (1984). [30] C. Shi, P.V. Krivenko, D. Roy, Alkali-Activated Cements and Concretes, Taylor & Francis (2006) 198–199. [31] F. Puertas, S. Martínez-Ramírez, S. Alonso, T. Vázquez, Alkali-activated fly ash/slag cement strength behaviour and hydration products, Cem. Concr. Res. 30 (2000) 1625–1632. [32] S. Ghosal, M. Veeraragavan, S.R. Kalidindi, Terminalia chebula compositions and method of extracting same, US patent US2013/0266676 A1. 2013 Oct 10. [33] A.B. Bolobova, V.I. Kondrashchenko, Use of yeast fermentation waste as a biomodifier of concrete (review), Appl. Biochem. Microbiol. 36 (2000) 205–214. [34] A. Nath, D. Dutta, P. Kumar, J.P. Singh, Review on Recent Advances in Value Addition of Jaggery based Products, J. Food Process. Technol. 6 (2015) 1–4. [35] S. Saxena, S. Gautam, A. Sharma, Physical, biochemical and antioxidant properties of some Indian honeys, Food Chemistry 118 (2010) 391–397. [36] IS: 516-1959 (Reaffirmed 1999), Methods of Tests for Strength of Concrete, Bureau of Indian Standards, New Delhi. [37] T. Bakharev, Resistance of geopolymer materials to acid attack, Cem. Concr. Res. 35 (2005) 658–670. [38] Z. Baščarević, M. Komljenović, Z. Miladinović, V. Nikolić, N. Marjanović, R. Petrović, Impact of sodium sulfate solution on mechanical properties and structure of fly ash based geopolymers, Mater. Struct. 48 (2015) 683–697.
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[39] K. Komnitsas, D. Zaharaki, G. Bartzas, Effect of sulphate and nitrate anions on heavy metal immobilisation in ferronickel slag geopolymers, Appl. Clay Sci. 73 (2013) 103–109. [40] J. Zheng, C. Yang, Y. Chen, Discussion on the mechanism of the resistance of alkaliactivated cementitious material to external sulfate attack, J. Zhengzhou Univ. Eng. Sci. 33 (2012) 1–4. [41] M.B. Karakoç, İ. Türkmen, M.M. Maraş, F. Kantarci, R. Demirboğa, Sulfate Resistance of Ferrochrome Slag Based Geopolymer Concrete, Ceram. Int. 42 (2016), 1254–1260. [42] A. Neville, Chloride attack of reinforced concrete: an overview. Mater. Struct. 28 (1995) 63–70. [43] H. Zhu, Z. Zhang, Y. Zhu, L. Tian, Durability of alkali-activated fly ash concrete: Chloride penetration in pastes and mortars, Constr. Build. Mater. 65 (2014) 51–59. [44] ACI 318–14, Building Code Requirements for Structural Concrete and Commentary, American Concrete Institute (2014). [45] V.K. Bui, Y. Akkaya, S.P. Shah, Rheological model for self-consolidating concrete, ACI Mater. J. 99 (2002) 549–559. [46] P. Duan, C. Yan, W. Zhou, W. Luo, C. Shen, An investigation of the microstructure and durability of a fluidized bed fly ash–metakaolin geopolymer after heat and acid exposure, Materials and Design 74 (2015) 125–137. [47] B. Pfundstein, S.K. El Desouky, W.E. Hull, R. Haubner, G. Erben, R.W. Owen, Polyphenolic compounds in the fruits of Egyptian medicinal plants (Terminalia bellerica, Terminalia chebula and Terminalia horrida): Characterization, quantitation and determination of antioxidant capacities, Phytochemistry 71 (2010) 1132–1148.
20
9 8.614 8.515
8.479
8.552
8.5
8.412
8.461
8.394
8.372
8.436 Weight (kg)
8.12
8.265
8.245
8
8.419
8.213
8.371
8.303 8.171
8.255 8.106 GPC0 GPC1
7.656
7.565
7.5
GPC2
7.453
GPC3
7.23 7
6.986
6.5 0D
7D
14 D 28 D Immersion duration (days)
56 D
90 D
18.84
20
31.11 33.64 29.2
31.73 34.53 30
32.67 35.02 30.49
32.93 35.47 30.89
22.8
25
21.02
24.27
30
28.36
Compressive strength(Mpa)
35
23.78
40
33.11 35.96 31.16
34.84 37.24 33.2
Fig. 1. Change in weight of geopolymer specimens due to sulfuric acid attack.
GPC0 GPC1 GPC2
15
GPC3 10 5 0 0D
7D
14 D 28 D Immersion duration (days)
56 D
90 D
Fig. 2. Change in compressive strength of geopolymer specimens due to sulfuric acid attack.
21
Fig. 3. Visual appearance of geopolymer specimens subjected to 5% sulfuric acid attack after 28 and 90 days of immersion.
22
8.7 8.6
8.573
8.57
8.564
8.558
8.55
8.54
8.498
8.489
8.486
8.477
8.466
8.456
8.422
8.418
8.411
8.4
Weight (kg)
8.5 8.4
8.435
8.3
8.378
GPC0 GPC1
8.2
8.13
GPC2 8.101
8.089
GPC3
8.066
8.1
8.022
7.997
8 7.9 0D
7D
14 D 28 D Immersion duration (days)
56 D
90 D
33.96 36.44 32.22
26.53
34.09 36.62 32.49 26.93
34.27 36.8 32.62 27.24
34.58 37.02 32.89
34.4 36.93 32.8 27.47
30
27.6
Compressive strength (Mpa)
35
28.36
40
34.84 37.24 33.2
Fig. 4. Change in weight of geopolymer specimens due to sodium sulfate attack.
25 GPC0
20
GPC1 GPC2
15
GPC3 10 5 0 0D
7D
14 D 28 D Immersion duration (days)
56 D
90 D
Fig. 5. Change in compressive strength of geopolymer specimens due to sodium sulfate attack.
23
Fig. 6. Visual appearance of geopolymer specimens subjected to 5% sodium sulfate attack after 28 and 90 days of immersion.
24
(a)
(b)
25
(c)
(d)
Fig. 7. SEM images of geopolymer matrix-aggregate interface: (a) GPC0, (b) GPC1, (c) GPC2, (d) GPC3.
26
8.7
8.645
8.641
8.635
8.633
8.626
8.621
8.59
8.586
8.58
8.572
8.562
8.408
8.397
8.389
8.6 8.596
Weight (kg)
8.5 8.432
8.424
8.417
8.4
GPC0 GPC1 GPC2
8.3
8.245
GPC3 8.234
8.227
8.216 8.19
8.174
8.2
8.1 0D
7D
14 D 28 D Immersion duration (days)
56 D
90 D
34.4 36.93 32.76 27.78
34.49 37.07 32.89 27.82
34.62 37.11 33.02
34.71 37.16 33.07
27.91
28
30
28.36
Compressive strength (Mpa)
35
27.96
40
34.76 37.2 33.11
34.84 37.24 33.2
Fig. 8. Change in weight of geopolymer specimens due to sodium chloride attack.
25 GPC0
20
GPC1 GPC2
15
GPC3 10 5 0 0D
7D
14 D 28 D Immersion duration (days)
56 D
90 D
Fig. 9. Change in compressive strength of geopolymer specimens due to sodium chloride attack. 27
Fig. 10. Visual appearance of geopolymer specimens subjected to 5% sodium chloride attack after 28 and 90 days of immersion.
28
Cumulative pore volume (cc/g)
0.07 0.06 GPC0 GPC1 GPC2 GPC3
0.05 0.04 0.03 0.02 0.01 0.00 1
10
100
1000
10000
100000
Pore diameter (nm)
Fig. 11. Pore size distribution in terms of cumulative pore volume before attack.
0.07 0.06 GPC0 GPC1 GPC2 GPC3
dV/dlogD (cc/g)
0.05 0.04 0.03 0.02 0.01 0.00 1
10
100
1000
10000
100000
Pore diameter (nm)
Fig. 12. Pore size distribution in terms of differential pore volume before attack.
29
0.36
Cumulative pore volume (cc/g)
0.32 0.28 GPC0 GPC1 GPC2 GPC3
0.24 0.20 0.16 0.12 0.08 0.04 0.00 1
10
100
1000
10000
100000
Pore diameter (nm)
Fig. 13. Pore size distribution in terms of cumulative pore volume after sulfuric acid attack.
0.6
0.5 GPC0 GPC1 GPC2 GPC3
dV/dlogD (cc/g)
0.4
0.3
0.2
0.1
0.0 1
10
100
1000
10000
100000
Pore diameter (nm)
Fig. 14. Pore size distribution in terms of differential pore volume after sulfuric acid attack.
30
Table 1 Chemical compositions of coal fly ash and BFS (percentage by weight). SiO2
Al2O3
Fe2O3
CaO
MgO
Na2O
SO3
TiO2
K2O
Coal fly ash 63.53% 27.40%
3.67%
1.26%
0.35%
0.19%
0.01%
1.84%
0.85%
BFS
0.61%
38.34% 7.94%
0.29%
3.84%
0.55%
0.32%
34.26% 11.32%
Table 2 Ingredients for geopolymer concrete. Coal fly ash kg/m3
BFS
Fine aggregate
kg/m3
kg/m3
20 mm
12 mm
GPC0
237
158
547
383
GPC1
237
158
547
GPC2
237
158
GPC3
237
158
Mix ID
Coarse aggregate kg/m3
NaOH solution
Na2SiO3 solution
Superplasticizer
6 mm
kg/m3
kg/m3
kg/m3
Terminalia chebula
a
b
c
536
358
52
129
7.9
-
-
-
-
383
536
358
52
129
7.9
3.16
3.16
-
-
547
383
536
358
52
129
7.9
3.16
-
3.16
-
547
383
536
358
52
129
7.9
3.16
-
-
3.16
a-Molasses, b-Palm jaggery, c-Honey
31
Bio-additives kg/m3 Natural sugar
Table 3 Density gain of bio-additives added geopolymer specimens before immersion.
Average density before immersion (kg/m3) 2419 2533 2551 2499
Geopolymer specimen ID GPC0* GPC1 GPC2 GPC3
Density gain before immersion (%) 4.70 5.46 3.31
* denotes control specimen
Table 4 Density loss of geopolymer specimens in different immersion conditions.
Density loss after 90 D of immersion (%)
Density (kg/m3)
Before immersion
After 90 D of immersion in 5% Sulfuric acid
Before immersion
After 90 D of immersion in 5% Sodium sulfate
GPC0
2406
2070
2409
GPC1
2534
2446
GPC2
2552
GPC3
2500
Geopolymer specimen ID
Before immersion
After 90 D of immersion in 5% Sodium chloride
5% Sulfuric acid
5% Sodium sulfate
5% Sodium chloride
2369
2443
2422
13.97
1.64
0.86
2518
2505
2547
2537
3.47
0.49
0.40
2480
2540
2530
2561
2554
2.82
0.38
0.28
2402
2499
2482
2498
2486
3.91
0.68
0.51
32
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PII: DOI: Reference:
S0272-8842(17)31244-0 http://dx.doi.org/10.1016/j.ceramint.2017.06.042 CERI15564
To appear in: Ceramics International Received date: 22 March 2017 Revised date: 29 May 2017 Accepted date: 6 June 2017 Cite this article as: A. Karthik, K. Sudalaimani and C.T. Vijayakumar, Durability study on Coal Fly Ash-Blast Furnace Slag geopolymer concretes with Bioa d d i t i v e s , Ceramics International, http://dx.doi.org/10.1016/j.ceramint.2017.06.042 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Durability study on Coal Fly Ash-Blast Furnace Slag geopolymer concretes with Bioadditives A. Karthika*, K. Sudalaimanib, C.T. Vijayakumarc a
Department of Civil Engineering, Kamaraj College of Engineering and Technology, S.P.G.C. Nagar, K. Vellakulam-625701, India
b
Department of Civil Engineering, Thiagarajar College of Engineering, Madurai-625015, India
c
Department of Polymer Technology, Kamaraj College of Engineering and Technology, S.P.G.C. Nagar, K. Vellakulam-625701, India *
Corresponding author: A. Karthik. Mobile: +91 9629666291, Fax: +91 4549 278172, Email ID: [email protected]
Abstract The objective of this research was to understand the positive impact of bio-additives such as terminalia chebula and natural sugars (molasses/palm jaggery/honey) on the durability properties of coal fly ash-blast furnace slag (BFS) based geopolymer concrete under various chemical attacks. Various tests had been conducted by immersing specimens in 5% sulfuric acid, 5% sodium sulfate and 5% sodium chloride solution for different duration of 7, 14, 28, 56 and 90 days to determine the resistance of bio-additives added geopolymer concrete against chemical attacks. The durability was also related by mercury intrusion porosimetry to find out the porosity and pore size distribution. After 90 days of immersion, test results confirmed that bio-additives inclusion in coal fly ash-blast furnace slag based geopolymer concrete had undergone weight loss and compressive strength loss in the range of 2.82– 3.91%, 9.67–12.05% under sulfuric acid attack, 0.38–0.68%, 2.15–2.95% under sodium sulfate attack and 0.28–0.51%, 0.83–1.33% under sodium chloride attack respectively. 1
However in control ordinary geopolymer specimen, the weight loss and compressive strength loss was 13.97%, 33.57% under sulfuric acid attack, 1.64%, 6.45% under sodium sulfate attack and 0.86%, 2.05% under sodium chloride attack was observed.
This led to the
conclusion that bio-additives added geopolymer concretes had enhanced durability properties when compared to control ordinary geopolymer concrete examined in this study. Keywords: Durability, Bio-additives, Geopolymer. Introduction Ordinary portland cement (OPC) based concrete is the mostly used construction material and has extensive applications in residential, commercial and industrial structures. The manufacturing process of OPC hold 5–8% share of world’s greenhouse gas emissions [1]. Recent study revealed an intimidating ratio of 1 between the production of cement and CO2 gas emission (54% during calcinations and 46% during burning of fuels). Meanwhile massive amount of industrial wastes such as coal fly ash, blast furnace slag etc were being generated from power generation and steel making industry. These industrial by-products led to various disposal and storage problems. According to the recent statistics, 176 million tons of coal fly ash and 200 million tons of blast furnace slag (BFS) were not utilized worldwide and used as landfill [2]. The existing trend would increase the demand of cement in future that insists the usage of alternative cementitious materials in construction industry. Finding the environmentally and economically viable alternate for cement had now become a mandate by exploring the opportunities to consume different industrial by-products. Current literature review portrayed that concretes produced by using industrial by-products possessed better mechanical and durability properties [3–6]. The effective utilization of these industrial byproducts such as coal fly ash and BFS in concrete minimized the usage of OPC in construction applications and paved the way for sustainable building materials technology
2
and eco-friendly concrete. This brings out the development of alternative concrete by adopting coal fly ash and BFS as base material by completely replacing OPC thereby less carbon foot print could be achieved. The best possible solution to address this issue is adoption of geopolymer concrete also termed as alkali-bonded ceramic/hydroceramic/lowtemperature aluminosilicate glass/ alkali-activated cement/geo-cement/inorganic polymer concrete [7]. Geopolymer synthesized predominantly from the reaction of an aluminosilicate source materials such as coal fly ash and BFS with an alkaline activator was known for its ceramic-like-properties. Coal fly ash based geopolymer concrete could be 10–30% cheaper than OPC concrete [7]. Also geopolymer concrete could be set and hardened at ambient curing conditions when coal fly ash was suitably replaced with BFS [8]. When exposed to aggressive environment geopolymer concrete exhibited high resistance to sulfate attack, acid attack and corrosion [9–12] due to the three-dimensional polymeric chain and ring like structure consisting of –Si–O–Al–O– bonds and low Ca(OH)2 content [13]. Concrete structures must be able to resist weathering action, chemical attack, abrasion or any other process of deterioration which affected the long term performance of concrete. Concrete underwent degradation under the influence of aggressive environments that induced chemical processes involving ion exchange that altered the microstructure of the binding matrix in-turn affected the serviceability of the structures. Considering the structural applications of geopolymer concrete in varying aggressive environments, it was crucial to study the durability properties of concrete. Durability of geopolymer concrete was an important aspect for its several commercial applications such as coating materials in marine concrete protection [14], industrial wastewater pipelines [15], etc. Recent studies revealed geopolymer exhibited better durability properties than OPC. The mass loss in blended ash (70% pulverized coal fuel ash+30% palm oil fuel ash) based geopolymer concrete specimens was only 8% when compared to the 20% mass loss of OPC concrete specimens in 2%
3
sulfuric acid exposure for 18 months [16]. The resistance to chloride ingression was better in coal fly ash-BFS based geopolymer paste (50% coal fly ash+50% BFS) than OPC paste when immersed in 3% sodium chloride solution for 72 hours [17]. Lignite bottom ash based geopolymer mortars were less vulnerable to 3% sulfuric acid and 5% sodium sulfate solutions than OPC mortars in 120 days observation [18]. Strength loss of geopolymer concrete made with gypsum blended BFS was 33% in comparison with 47% in OPC concrete in acetic acid solution (pH=4) for 12 months [19] and 17% compared to 25% in OPC concrete in 5% sodium sulfate solutions for 12 months [20]. Previous researches conducted on geopolymers used chemical additions such as silica fume, nano silica, Na2CO3 and synthetic zeolites [21–24] to improve its durability properties. Till now very limited researches were conducted to study the effect of bio-additives on durability properties of geopolymer concrete. In ancient mortars, terminalia chebula and palm jaggery improved its functional properties when added as bio-additives along with lime mortar [25]. Addition of terminalia chebula in lime mortar increased the compressive strength and decreased the porosity [26]. Combination of bio-additives (terminalia chebula and jaggery) enriched the 28-days compressive strength of cement mortar by 88% [27]. Sugarcane bagasse ash was used as a source material for making geopolymer mortar resulted in increased compressive strength and lower porosity [28]. When BFS based geopolymer concrete specimens were immersed in 30% sugar solution for two years, it was found that the corrosion resistance was three times higher than OPC based concrete [29,30]. This research portrayed the durability performance of coal fly ash-BFS based geopolymer concrete with bio-additives when subjected to acid, sulfate and chloride attack in detail.
2. Materials
4
The materials used for making geopolymer concrete specimens were aluminosilicate materials (coal fly ash and BFS), fine aggregate, coarse aggregate, alkaline activators, superplasticizer and bio-additives (terminalia chebula and natural sugars). 2.1. Aluminosilicate materials In this, both coal fly ash and BFS were used as aluminosilicate materials. Low calcium Class F coal fly ash was obtained from the silos of thermal power station, Tuticorin, Tamil Nadu was used as one of the base aluminosilicate material. BFS was obtained from local steel plant and it showed pozzolanic and binding properties in an alkaline medium [31]. Chemical compositions (percentage by weight) of coal fly ash and BFS had been identified in X-ray fluorescence spectrometry and were given in Table 1. 2.2. Aggregates Locally resourced river sand and crushed granite were used as fine and coarse aggregates. The sieve analysis test results of the fine aggregate conformed to zone II as per IS 383-1970 (Reaffirmed on 1997). It had specific gravity of 2.63, bulk density of 1721 kg/m3 and fineness modulus of 2.67. Similarly specific gravity of 2.84, bulk density of 1578 kg/m3 and fineness modulus of 7.75 were obtained for differently sized 20 mm, 12 mm, 6 mm coarse aggregates. The final combined aggregate volume was a combination of 30% of fine aggregate, 21% of 20 mm, 29% of 12 mm and 20% of 6 mm coarse aggregates. 2.3. Alkaline activators A combination of commercially available 98% pure sodium hydroxide (flakes form) and sodium silicate (liquid gel form) was used as alkaline activators for geopolymerization. For the present study 8M NaOH was used in all geopolymer specimens. The chemical composition of sodium silicate was: Na2O-14.7%, SiO2-29.4% and Water-55.9% by mass. The alkaline activator was prepared by mixing sodium silicate and sodium hydroxide
5
solutions. The ratio of sodium silicate to sodium hydroxide solution was fixed as 2.5 for the alkaline activators (pH = 13). 2.4. Superplasticizer Naphthalene sulphonate based superplasticizer (Conplast SP430, Fosroc, Bengaluru, India) was used in this study to improve the workability of the fresh geopolymer mix. Superplasticizer was added 2% by the weight of aluminosilicate materials. 2.5. Bio-additives Bio-additives used here were terminalia chebula and natural sugars (molasses/palm jaggery/honey). All the bio-additives were used in raw form. Both the bio-additives were added 0.8% by the weight of aluminosilicate minerals. 2.5.1. Terminalia chebula Powdered form of terminalia chebula with particle size around 295 nm available in market was used. It contained about chebulagic acid (8–25%), chebulinic acid (15–30%) and 5–45% by weight of other low molecular weight hydrolyzable tannoids [32]. Chebulagic acid was a benzopyran tannin which was hydrolyzable while chebulinic acid was an ellagitannin. When added terminalia chebula in cement mortar, the compressive strength was enhanced by 48% [26]. 2.5.2 Natural sugars Three locally resourced different types of natural sugars such as molasses (from factory), palm jaggery and honey were individually used. Both molasses and honey were used in liquid form and palm jaggery was used in powdered form. The variable composition of molasses contained 76–84% dry substances (including 46–51% sucrose) [33]. Chemical composition of palm jaggery primarily contained 40–60% sucrose [34]. The most common carbohydrates found in honey were monosaccharides (43.3–65.5% fructose, 0.4–8.8% glucose) and disaccharide (17.2–21.6% sucrose) [35].
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3. Experimental work 3.1. Manufacturing procedure of geopolymer concrete Mix design detail for geopolymer concrete was given in Table 2. Alkaline activator to the aluminosilicate source material ratio was fixed as 0.45. Firstly the alkaline activator should be prepared 30 minutes prior to the actual mixing of the concrete. Coal fly ash, BFS and aggregates were first dry mixed in a pan mixer. To produce fresh geopolymer concrete, prepared alkaline activator solution was added to the well mixed dry materials and continued the mixing for about 5 minutes. Then the bio-additives such as terminalia chebula and natural sugar (molasses/palm jaggery/honey) were added to the wet mix. Finally superplasticizer was added to achieve workable mix. Prior casting, the inner sides of cube mould was layered with lubricating oil to prevent adhesion with the concrete specimens. The moulds were filled in three layers, each layer was well compacted. The casted specimens were kept open at the room temperature of 30±2°C and relative humidity of 65±5%. 3.2. Testing All the hardened geopolymer concrete cube specimens of size 150 mm x150 mm x150 mm were subjected to acid attack, sulfate attack and chloride attack by immersing in sulfuric acid, sodium sulfate and sodium chloride for 90 days. For sulfuric acid attack the pH of the acidic solution was checked every week and maintained at value 1.0 by adding required amount of the concentrated acid solution. The acidic solution was completely replaced every 30 days. Similarly for sulfate and chloride attack the solution replacement was done. The change in weight and compressive strength of specimens were tested at an interval of 7, 14, 28, 56 and 90 days of immersion. Tests for compressive strength were conducted on cube specimens using 2000 kN compression testing machine as per Indian Standard specifications [36]. The density of the hardened concrete before and after 90 days of immersion was found out for all the hardened concrete specimens. Pore size distributions in the specimens were analyzed by conducting mercury intrusion porosimetry (MIP) test. MIP 7
measurements were carried out with contact angle of 140° and maximum pressure of 400 MPa. 4. Results and discussions 4.1. Sulfuric acid attack 4.1.1. Weight loss due to sulfuric acid attack The 5 wt% sulfuric acid was used in the study. All geopolymer specimens were subjected to sulfuric acid attack for 90 days to study the durability of geopolymer concrete in acidic environment. The weight of GPC0, GPC1, GPC2 and GPC3 after 90 days of immersion was noted to be 6.986 kg, 8.255 kg, 8.371 kg and 8.106 kg (Fig. 1) and its corresponding percentage weight loss was found to be 13.97%, 3.47%, 2.82% and 3.91% respectively. At low pH value of 1, the positive hydrogen ions from acidic medium broke down the Si–O–Al bonds present in the geopolymer [15] and produced more number of Si– OH and Al–OH bonds along with increased amount of silicic acid in the geopolymer matrix [37]. This reaction process made the GPC0 concrete specimen weaker resulted in more weight loss of 13.97% after 90 days. Also after 90 days of immersion, GPC0 was more deteriorated and coarse aggregates were clearly exposed at the surface when observed in Fig. 3. However the bio-additives added geopolymer concrete specimens (GPC1, GPC2 and GPC3) appeared to be slightly corroded at the surface and less damaged around the edges of specimen. Bio-additives inclusion might have caused the better acid resistance of geopolymer specimens (GPC1, GPC2 and GPC3) due to the existence of stable cross-linked polymer structures that deterred the degree of chemical reaction between sulfuric acid and calcium present in geopolymer gel thereby diminishing its deterioration effects on geopolymer gel structure. This might have resulted in less surface deterioration and minimum weight loss occurred in GPC1, GPC2 and GPC3 specimens throughout the different days of immersion.
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The test results strongly implied GPC1, GPC2 and GPC3 specimens showed better resistant to acid attack when compared to GPC0. 4.1.2. Strength loss due to sulfuric acid attack After 90 days of sulfuric acid attack, compressive strength of GPC0, GPC1, GPC2 and GPC3 was reported as 18.84 Mpa, 31.11 Mpa, 33.64 Mpa and 29.20 Mpa (Fig. 2) and its equivalent percentage loss in compressive strength was noted as 33.57%, 10.71%, 9.67% and 12.05% respectively. Test results exhibited that GPC0 experienced maximum strength loss whereas GPC1, GPC2 and GPC3 experienced minimum loss at all test intervals. The compressive strength loss was in the order of GPC0 > GPC3 > GPC1 > GPC2. In general compressive strength loss was proportional to the increase in immersion duration. In the whole, GPC2 performed better against acid attack among all geopolymer specimens throughout the immersion duration. 4.2. Sodium sulfate attack 4.2.1 Weight loss due to sodium sulfate attack In this study all the specimens were subjected to 5% of sodium sulfate solution. After 90 days of immersion, the geopolymer specimens GPC0, GPC1, GPC2 and GPC3 weighed 7.997 kg, 8.456 kg, 8.540 kg and 8.378 kg (Fig. 4) and undergone percentage weight loss of 1.64%, 0.49%, 0.38% and 0.68% respectively. It was found that when geopolymer specimens were soaked in sodium sulfate solution, the diffusion of sulfate ions in geopolymer structure caused disintegration of siloxane bonds (–Si–O–Si– bonds) which decreased the silica to aluminium (Si/Al) atomic ratio in the specimens and leaching of silica (Si) in geopolymer gel structure [38]. This resulted in more weight loss in GPC0 specimen. From Fig. 6, the efflorescence effect in GPC0 was very evident in contrast to the bio-additives added specimens GPC1, GPC2 and GPC3. Test results revealed that inclusion of bio-additives in geopolymer concrete lowered the total porosity of GPC1, GPC2 and GPC3 when compared
9
to GPC0 and the same was confirmed by MIP study. Less porous microstructure in GPC1, GPC2 and GPC3 inhibited the diffusion of sulfate ions and created positive effect on geopolymer microstructure which in-turn improved the resistance to weight loss in GPC1, GPC2 and GPC3. 4.2.2. Strength loss due to sodium sulfate attack After 90 days of sulfate attack, compressive strength of GPC0, GPC1, GPC2 and GPC3 was found as 26.53 Mpa, 33.96 Mpa, 36.44 Mpa and 32.22 Mpa (Fig. 5) and its equivalent percentage loss in compressive strength was reported as 6.45%, 2.53%, 2.15% and 2.95% respectively. Sulfate ions (SO4)2− had minimum deteriorating effect on compressive strength of geopolymer concrete [39]. Also the crystallization pressure of sodium sulfate developed in the specimen by absorbing (SO4)2− and possibly Na+ ions through the pores [40,13] weakened the geopolymer matrix. This mechanism resulted in the cohesion loss between geopolymer matrix and aggregate [41] that led to more strength loss in GPC0 specimen. Geopolymer matrix-aggregate interface of GPC0, GPC1, GPC2 and GPC3 was examined using SEM and the same was mentioned in Fig. 7. From the image Fig. 7(a) related to GPC0, it was clear that there was a small gap zone in the boundary between the geopolymer matrix and aggregate. This resulted in maximum strength loss in GPC0 after the sulfate attack. When examined SEM images given in Fig. 7(b), 7(c) and 7(d) correspond to the bio-additives added geopolymer specimens GPC1, GPC2 and GPC3, they showed noticeable differences in geopolymer matrix-aggregate interface. Also it was noticed that the geopolymer matrixaggregate interface was intact and geopolymer matrix was densely packed. It could be attributed to the minimum strength loss noticed in GPC1, GPC2 and GPC3 due to increase in homogeneity of bio-additives added geopolymer concrete.
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4.3. Chloride attack 4.3.1. Weight loss due to chloride attack One of the common durability issue was chloride attack on reinforced concrete. The chloride ions diffusion in geopolymer reinforced concrete would induce the steel bar corrosion by de-passivation resulting in a reduced load carrying capacity of concrete that would led to structural failure [42]. The chloride ion penetration in concrete involved various processes such as diffusion, capillary suction and convective flow through the pore system [43]. Therefore it becomes necessary to study impact of chloride attack in geopolymer concrete. At pH value of 6.5, the weight of GPC0, GPC1, GPC2 and GPC3 after 90 days of immersion was reported as 8.174 kg, 8.562 kg, 8.621 kg and 8.389 kg (Fig. 8) and its corresponding percentage weight loss was very minimal and found to be 0.86%, 0.40%, 0.28% and 0.51% respectively. The visual inspection justified the minimal chloride attack with slight colour change in the surface of all bio-additives added specimens in contrast to noticeable change in GPC0 as shown in Fig. 10. The results showed that inclusion of bioadditives in geopolymer concrete (GPC1, GPC2 and GPC3) led to the lower porosity reducing the ingress of chloride ions through pores. This in-turn slowed down the entering of chloride ions in GPC1, GPC2 and GPC3 compared with GPC0. 4.3.2. Strength loss due to chloride attack After 90 days of immersion in sodium chloride, compressive strength of GPC0, GPC1, GPC2 and GPC3 was found as 27.78 Mpa, 34.40 Mpa, 36.93 Mpa and 32.76 Mpa (Fig. 9) and its equivalent percentage loss in compressive strength was meagre and noted as 2.05%, 1.26%, 0.83% and 1.33% respectively. Thus more ordered and dense geopolymer binding gel formed in GPC1, GPC2 and GPC3 decreased the compressive strength loss compared to porous aluminosilicate gel that formed in the GPC0.
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4.4 Density Before immersion, the average density was found to be 2419 kg/m3, 2533 kg/m3, 2551 kg/m3 and 2499 kg/m3 for GPC0, GPC1, GPC2 and GPC3 specimens respectively (Table 3). These values were in better agreement with the normal concrete having density range between 2155–2560 kg/m3 [44]. There was an increasing trend in density (3.31–5.46%) for the bio-additives added geopolymer specimens compared to GPC0. It would have a direct positive effect in the durability of the concrete. Bio-additives inclusions led to the filling of micropores in geopolymer matrix which in turn led to the denser matrix in GPC1, GPC2 and GPC3. After 90 days of immersion in different immersion conditions, the density was found to be in the range of 2070–2422 kg/m3, 2446–2537 kg/m3, 2480–2554 kg/m3 and 2402–2486 kg/m3 for GPC0, GPC1, GPC2 and GPC3 specimens respectively (Table 4). By comparing the density values before and after 90 days of immersion, there was decrease in density for all specimens subjected to various chemical attacks. The decrease in density after 90 days of immersion was found to be in the range of 0.86–13.97%, 0.40–3.47%, 0.28–2.82% and 0.51– 3.91% for GPC0, GPC1, GPC2 and GPC3 specimens respectively. It was to be noted that the decrease in density of bio-additives added geopolymer concrete specimens GPC1, GPC2 and GPC3 was minimal when compared to control ordinary geopolymer concrete specimen GPC0. 4.5 Mercury intrusion porosimetry Samples of geopolymer specimens GPC0, GPC1, GPC2 and GPC3 were subjected to MIP test to measure the porosity and pore size distribution. The cumulative pore volume and differential pore volume for specimens before attack were plotted in Fig. 11 and 12 respectively and would give an idea regarding the development of pores. From Fig. 11, the total porosity of GPC0, GPC1, GPC2 and GPC3 before attack was found to be 0.068 cc/g,
12
0.053 cc/g, 0.039 cc/g, and 0.056 cc/g respectively. This confirmed the addition of bioadditives lowered the total porosity of bio-additives added geopolymer (GPC1, GPC2 and GPC3) when compared to conventional geopolymer (GPC0). It could be attributed to the denser microstructure of bio-additives added geopolymer specimens. The differential curves of pore size distribution in Fig. 12 showed significant differences between samples. The critical pore diameters defined as the peaks in the differential curve gives the rate of mercury intrusion per change in pressure [45,46] were shifted to lower values for bio-additives added geopolymer (GPC1, GPC2 and GPC3). The results from MIP measurements were also consistent with durability results under different chemical attacks such as acid, sulfate and chloride which related to better permeability resistance of GPC1, GPC2 and GPC3. Thus inclusion of bio-additives would occupy the capillary pores in geopolymer matrix which would result in the refinement of pore structure of GPC1, GPC2 and GPC3. The cumulative pore volume and differential pore volume for specimens after sulfuric acid attack were plotted in Fig. 13 and 14 respectively. After 90 days of immersion in sulfuric acid, the total porosity of GPC0, GPC1, GPC2 and GPC3 was found to be 0.324 cc/g, 0.141 cc/g, 0.131 cc/g and 0.162 cc/g respectively (Fig. 13). Test results revealed that the total porosity was in the order of GPC0 > GPC3 > GPC1 > GPC2 for all geopolymer specimens before and after the chemical attack. The total porosity of the geopolymer specimens was well correlated with durability test results discussed above. Unlike the control geopolymer concrete specimen GPC0, weight loss and strength loss of bio-additives added geopolymer concrete specimens GPC1, GPC2 and GPC3 remained low after exposure to chemical attacks for 90 days. From Fig. 14, it was obvious that immersion of GPC0 specimen in sulfuric acid led to the development of highly porous system when compared to GPC1, GPC2 and GPC3. This confirmed that GPC0 contained high amount of pores that could facilitate the penetration of external chemicals. These results were in-line with the durability results where 13
the penetration of external chemical was high in GPC0. This resulted in maximum weight loss and compressive strength loss in GPC0 after the attack. 4.6 Effect of bio-additives The system was terminalia chebula with different kind of natural sugars (carbohydrates) such as molasses, palm jaggery, honey and chiefly NaOH. It had been proved that phenols react with NaOH to yield sodiumphenolates. It was found that terminalia chebula contained chebulagic acid and chebulinic acid and both the compounds were gallic acid esters [32,47]. In the presence of an alkali, these gallic acid esters might undergo hydrolysis to yield gallic acid. Hence the reaction of NaOH with both the acid and phenolic groups present in gallic acid was inevitable. All the carbohydrates used in the present investigation contained considerable amount of disaccharides like sucrose and monosaccharides like glucose and fructose. Hence it was not only the concentration of natural sugars used but also dependent on the nature of carbohydrates present in natural sugars. This included not only the configuration of monosaccharides and disaccharides but also on conformation of natural sugars. The aluminosilicate materials such as coal fly ash and BFS would be definitely containing silanol (Si–O–H) groups. Apart from several individual reactions of the terminalia chebula, carbohydrates and silanol groups, the possibility of interactions between all these groups in an alkali medium leading to the formation of highly complex structures was envisaged. The production of such networks along with silicate network with the reasonable interface interactions resulted in low porosity of GPC1, GPC2 and GPC3. This elucidated the lesser chance of foreign substance penetration through the micropores to weaken the geopolymer microstructure thereby significantly increased the durability of bio-additives added geopolymer concrete against external chemical attacks investigated in this study.
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5. Conclusions Based on the results and discussions on durability study of coal fly ash-blast furnace slag based geopolymer concrete with bio-additives, the following conclusions were made. Bio-additives added geopolymer specimens GPC1, GPC2 and GPC3 exhibited better resistance to 5% sulfuric acid attack after 90 days with weight loss ranging from 2.82– 3.91% and strength loss between 9.67–12.05% whereas control ordinary geopolymer specimen GPC0 suffered a greater weight loss of 13.97% and strength loss of 33.57%. Similarly GPC1, GPC2 and GPC3 had undergone minimal weight loss and strength loss under sulfate and chloride attack when compared to GPC0. Upon the immersion in 5% sodium sulfate and 5% sodium chloride solution after 90 days, maximum weight loss was 0.68%, 0.51% and strength loss was 2.95%, 1.33% respectively among all bioadditives added geopolymer specimens. There was a trend of increasing weight loss and strength loss for every immersion duration in all chemical attacks. Density of bio-additives added geopolymer specimens were increased upto 3.31–5.46% when compared to GPC0 before immersion. The percentage density loss in GPC1, GPC2 and GPC3 had maximum of 3.91% which was much lesser when compared to GPC0 with maximum of 13.97% in all immersion conditions after 90 days. MIP results confirmed the addition of bio-additives lowered the total porosity of the hardened geopolymer concrete before and after chemical attack. All these experimental results could be attributed to stable cross-linked polymer structures, improved homogeneity, more ordered and dense geopolymer binding gel, filling of micropores and refinement of the pore structure in bio-additives added geopolymer specimen that paved the way to enhance durability and better shielding against external chemical attacks such as acid, sulfate and chloride. It was inferred that the inclusion of bio-additives 15
such as terminalia chebula and natural sugars improved the durability properties of geopolymer concrete. In particular, addition of the palm jaggery in combination with terminalia chebula in coal fly ash-BFS based geopolymer concrete (GPC2) displayed superior durability characteristics when compared to other bio-additives used in the study.
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9 8.614 8.515
8.479
8.552
8.5
8.412
8.461
8.394
8.372
8.436 Weight (kg)
8.12
8.265
8.245
8
8.419
8.213
8.371
8.303 8.171
8.255 8.106 GPC0 GPC1
7.656
7.565
7.5
GPC2
7.453
GPC3
7.23 7
6.986
6.5 0D
7D
14 D 28 D Immersion duration (days)
56 D
90 D
18.84
20
31.11 33.64 29.2
31.73 34.53 30
32.67 35.02 30.49
32.93 35.47 30.89
22.8
25
21.02
24.27
30
28.36
Compressive strength(Mpa)
35
23.78
40
33.11 35.96 31.16
34.84 37.24 33.2
Fig. 1. Change in weight of geopolymer specimens due to sulfuric acid attack.
GPC0 GPC1 GPC2
15
GPC3 10 5 0 0D
7D
14 D 28 D Immersion duration (days)
56 D
90 D
Fig. 2. Change in compressive strength of geopolymer specimens due to sulfuric acid attack.
21
Fig. 3. Visual appearance of geopolymer specimens subjected to 5% sulfuric acid attack after 28 and 90 days of immersion.
22
8.7 8.6
8.573
8.57
8.564
8.558
8.55
8.54
8.498
8.489
8.486
8.477
8.466
8.456
8.422
8.418
8.411
8.4
Weight (kg)
8.5 8.4
8.435
8.3
8.378
GPC0 GPC1
8.2
8.13
GPC2 8.101
8.089
GPC3
8.066
8.1
8.022
7.997
8 7.9 0D
7D
14 D 28 D Immersion duration (days)
56 D
90 D
33.96 36.44 32.22
26.53
34.09 36.62 32.49 26.93
34.27 36.8 32.62 27.24
34.58 37.02 32.89
34.4 36.93 32.8 27.47
30
27.6
Compressive strength (Mpa)
35
28.36
40
34.84 37.24 33.2
Fig. 4. Change in weight of geopolymer specimens due to sodium sulfate attack.
25 GPC0
20
GPC1 GPC2
15
GPC3 10 5 0 0D
7D
14 D 28 D Immersion duration (days)
56 D
90 D
Fig. 5. Change in compressive strength of geopolymer specimens due to sodium sulfate attack.
23
Fig. 6. Visual appearance of geopolymer specimens subjected to 5% sodium sulfate attack after 28 and 90 days of immersion.
24
(a)
(b)
25
(c)
(d)
Fig. 7. SEM images of geopolymer matrix-aggregate interface: (a) GPC0, (b) GPC1, (c) GPC2, (d) GPC3.
26
8.7
8.645
8.641
8.635
8.633
8.626
8.621
8.59
8.586
8.58
8.572
8.562
8.408
8.397
8.389
8.6 8.596
Weight (kg)
8.5 8.432
8.424
8.417
8.4
GPC0 GPC1 GPC2
8.3
8.245
GPC3 8.234
8.227
8.216 8.19
8.174
8.2
8.1 0D
7D
14 D 28 D Immersion duration (days)
56 D
90 D
34.4 36.93 32.76 27.78
34.49 37.07 32.89 27.82
34.62 37.11 33.02
34.71 37.16 33.07
27.91
28
30
28.36
Compressive strength (Mpa)
35
27.96
40
34.76 37.2 33.11
34.84 37.24 33.2
Fig. 8. Change in weight of geopolymer specimens due to sodium chloride attack.
25 GPC0
20
GPC1 GPC2
15
GPC3 10 5 0 0D
7D
14 D 28 D Immersion duration (days)
56 D
90 D
Fig. 9. Change in compressive strength of geopolymer specimens due to sodium chloride attack. 27
Fig. 10. Visual appearance of geopolymer specimens subjected to 5% sodium chloride attack after 28 and 90 days of immersion.
28
Cumulative pore volume (cc/g)
0.07 0.06 GPC0 GPC1 GPC2 GPC3
0.05 0.04 0.03 0.02 0.01 0.00 1
10
100
1000
10000
100000
Pore diameter (nm)
Fig. 11. Pore size distribution in terms of cumulative pore volume before attack.
0.07 0.06 GPC0 GPC1 GPC2 GPC3
dV/dlogD (cc/g)
0.05 0.04 0.03 0.02 0.01 0.00 1
10
100
1000
10000
100000
Pore diameter (nm)
Fig. 12. Pore size distribution in terms of differential pore volume before attack.
29
0.36
Cumulative pore volume (cc/g)
0.32 0.28 GPC0 GPC1 GPC2 GPC3
0.24 0.20 0.16 0.12 0.08 0.04 0.00 1
10
100
1000
10000
100000
Pore diameter (nm)
Fig. 13. Pore size distribution in terms of cumulative pore volume after sulfuric acid attack.
0.6
0.5 GPC0 GPC1 GPC2 GPC3
dV/dlogD (cc/g)
0.4
0.3
0.2
0.1
0.0 1
10
100
1000
10000
100000
Pore diameter (nm)
Fig. 14. Pore size distribution in terms of differential pore volume after sulfuric acid attack.
30
Table 1 Chemical compositions of coal fly ash and BFS (percentage by weight). SiO2
Al2O3
Fe2O3
CaO
MgO
Na2O
SO3
TiO2
K2O
Coal fly ash 63.53% 27.40%
3.67%
1.26%
0.35%
0.19%
0.01%
1.84%
0.85%
BFS
0.61%
38.34% 7.94%
0.29%
3.84%
0.55%
0.32%
34.26% 11.32%
Table 2 Ingredients for geopolymer concrete. Coal fly ash kg/m3
BFS
Fine aggregate
kg/m3
kg/m3
20 mm
12 mm
GPC0
237
158
547
383
GPC1
237
158
547
GPC2
237
158
GPC3
237
158
Mix ID
Coarse aggregate kg/m3
NaOH solution
Na2SiO3 solution
Superplasticizer
6 mm
kg/m3
kg/m3
kg/m3
Terminalia chebula
a
b
c
536
358
52
129
7.9
-
-
-
-
383
536
358
52
129
7.9
3.16
3.16
-
-
547
383
536
358
52
129
7.9
3.16
-
3.16
-
547
383
536
358
52
129
7.9
3.16
-
-
3.16
a-Molasses, b-Palm jaggery, c-Honey
31
Bio-additives kg/m3 Natural sugar
Table 3 Density gain of bio-additives added geopolymer specimens before immersion.
Average density before immersion (kg/m3) 2419 2533 2551 2499
Geopolymer specimen ID GPC0* GPC1 GPC2 GPC3
Density gain before immersion (%) 4.70 5.46 3.31
* denotes control specimen
Table 4 Density loss of geopolymer specimens in different immersion conditions.
Density loss after 90 D of immersion (%)
Density (kg/m3)
Before immersion
After 90 D of immersion in 5% Sulfuric acid
Before immersion
After 90 D of immersion in 5% Sodium sulfate
GPC0
2406
2070
2409
GPC1
2534
2446
GPC2
2552
GPC3
2500
Geopolymer specimen ID
Before immersion
After 90 D of immersion in 5% Sodium chloride
5% Sulfuric acid
5% Sodium sulfate
5% Sodium chloride
2369
2443
2422
13.97
1.64
0.86
2518
2505
2547
2537
3.47
0.49
0.40
2480
2540
2530
2561
2554
2.82
0.38
0.28
2402
2499
2482
2498
2486
3.91
0.68
0.51
32