A quantitative method of approach in designing the mix proportions of fly ash and GGBS-based geopolymer concrete.
1. IntroductionThe production and manufacture of cement concrete results in high emission of [CO.sub.2] to atmosphere leading to ecological imbalance causing greenhouse effect and depletion of natural resources (Imbabi, Carrigan, and McKenna 2012). To reduce these negative effects on atmosphere, new binding materials called geopolymers for application in construction industry is preferable (Oss and Padovani 2002, 2003). The main aspect in achieving sustainable construction materials is to reduce the overuse of virgin materials used to produce concrete. To overcome these problems, geopolymer concrete (GPC) has been introduced that can completely eliminate cement with by-products and water with alkaline solution.
To produce GPC, coarse and fine aggregate used in cement concrete industry can be used along with fly ash and GGBS as base materials (Davidovits 1978; Wang et al. 1995). Fly ash is rich in alumina, silica and possesses pozzolanic properties that can react with alkaline activators to form alumino silicate hydrate. The strength of the fly ash-based GPC is due to alumino silicate hydrate, which forms due to polymeric chain process, whereas, in case of GGBS-based geopolymer concrete, the strength gain is due to formation of the calcium silicate hydrate gel. Chindaprasirt et al. (2012) reported that in high calcium-based geopolymers (with Class C fly ash and GGBFS) the reactions during setting and hardening involving precipitation can be written as:
[mathematical expression not reproducible] (1)
[mathematical expression not reproducible] (2)
It is reported that at high pH (>12) CASH gel is stable and becomes feasible at a relatively low pH range of 9-12. NASH gel (secondary gel) formed at later stages of reaction is responsible for strength development and is even stable at low pH (9-12) and it is also reported that initial formation of CASH/CSH gel responsible for early setting. For a mix with high Si[O.sub.2] more silicate species are available and the rate of condensation between silicate species is low, resulting in longer setting times. Whereas a mix with high [Al.sub.2][O.sub.3] content, more [Al[(OH).sub.4]].sup.-] species are available for reaction thus leading to higher rate of condensation between aluminate and silicate species resulting in shorter setting times (Chindaprasirt et al. 2012). Djobo et al. (2016) reported that the geopolymer system contains C-S-H, (N, C)-A-S-H, C-(N)-A-S-H, N-(C)-A-S-H gels depending on the Si, Al, Ca and Na contents. The gels C-(N)-A-S-H, N-(C)-A-S-H corresponds to gel with low Na and Ca contents, whereas (N, C)-A-S-H is a hybrid gel with chemical composition between C-(N)-A-S-H and N-(C)-A-S-H gels. Thus GGBS-based geopolymer concrete gives improved mechanical properties than fly ash-based GPC.
Alkaline solution made with the combination of sodium hydroxide (NaOH) and sodium silicate ([Na.sub.2][SiO.sub.3]) are suitable solutions as alkaline activators for the preparation of GPC. Any change in proportions of binders (fly ash and GGBS), molarity of NaOH solution, ratio of [Na.sub.2][SiO.sub.3]/NaOH solution, curing temperature will affect the concrete compressive strength (Rattanasak and Chindaprasirt 2009; Albitar, Mohamed Ali and Vistin, et al. 2017; Phoo-ngernkham et al. 2015). Previous studies have suggested that required compressive strength was achieved with NaOH solution with 8-12 M and [Na.sub.2][SiO.sub.3]/NaOH ratio as 2.5 (Hardjito et al. 2004; Pinto 2004; Mallikarjuna Rao and Gunneswara Rao 2015). Curing is also important in attaining sufficient strength. Several researchers have observed that the compressive strength of fly ash-based GPC specimens cured in oven was higher than that of ambient cured specimens (Mustafa Al Bakri et al. 2011). During the process of polymerisation, silicon oxide and aluminium oxide in fly ash reacts with alkaline solution, which forms the cementitious material. The partial replacement of fly ash with GGBS was not only found to be beneficial in avoiding oven curing condition but also improved compressive strength.
Fly ash-based geopolymers need an external energy source in the form of thermal curing for the polymerisation reaction to take place. This can be a drawback for the up scaling of the process to the industrial level, whereas, GGBS-based geopolymers avoid external energy source and attain sufficient strength at ambient curing itself (Mallikarjuna Rao and Gunneswara Rao 2015; Albitar et al. 2014). There is no existing standard mix design procedure to prepare fly ash and GGBS-based geopolymer concrete of required strength, therefore an attempt was made to develop a mix design procedure to prepare GPC of target strengths ranging from 20 to 60 MPa for outdoor curing conditions with low molarity of NaOH.
2. Research significance
The importance of sustainable environment necessitated the development of GPC, which can be an alternative to conventional concrete. The practical application of GPC in construction is lagging due to lack of proper mix design. In spite of many research works on the mix design methodology of fly ash-based GPCs, an ambiguity still arises on combination of fly ash and GGBS under different curing conditions. Hence, proper quantification for GPC materials is necessitated to use GPC with ease in practical applications. In this paper, an attempt was made to develop a mix design method for fly ash and GGBS-based GPC from experimental results.
3. Experimental programme
3.1. Materials used
Fly ash and GGBS were used as source materials in the present study. GGBS was obtained from Toshali Cements Pvt ltd, Bayyavaram, India and fly ash was collected from National thermal power plant, Ramagundam, India. Specific gravity of fly ash and GGBS were 2.17 and 2.90, respectively. The Fineness of Fly ash and GGBS were 380 [m.sup.2]/kg and 426 [m.sup.2]/kg. Chemical composition details are shown in Table 1.
The morphology of fly ash and GGBS were examined using Scanning Electron Microscope (SEM) and are shown in Figures 1 and 2. Fly ash particles were spherical in shape and are mainly composed of large percentages of silica and alumina. The shape of the GGBS grains is angular and crystalline form. From the EDXA it can be observed that GGBS is predominated with calcium and silica compared to other elements. Increase in slag content increases the CaO content and results in increased formation of C-A-S-H/C-S-H gel thereby compressive strength is improved (Chindaprasirt et al. (2012)).
The mineralogical characterisation of fly ash and GGBS sample were carried out by X-ray diffraction analysis which is presented in Figure 3. The XRD image of GGBS depicts glass content as 99%. The hydration Modulus, HM = (CaO + MgO + [Al.sub.2][O.sub.3])/[SiO.sub.2] of fly ash and GGBS were 0.52 and 1.77. Which indicates the GGBS has high Hydration Modulus thereby improving the polymerisation process (Chang 2003). The basicity coeflicient= [(CaO+MgO)/([Al.sub.2][O.sub.3]+[SiO.sub.2])] of fly ash and GGBS were 0.06 and 0.74, respectively (Bakharev 2000). Basicity of a material is the ratio between total contents of basic constituents and total contents of acidic constituents. Reactivity of a material increases with its basicity and also the addition of free-CaO content increases the basicity. The early strengths of a concrete is dependent on the basicity of binder used. The more basic the fly ash and slag, greater is its early compressive strength and hydraulic activity in presence of alkaline activators.
The local river sand was used as fine aggregate and crushed granite was used as coarse aggregate. Fine aggregate is confirming to Zone II and coarse aggregate is 20 mm well graded according to IS 383 (BIS1970).The physical properties of coarse and fine aggregates are shown in Tables 2 and 3.
Sulphonated Naphthalene formaldehyde-based superplactisizer was used for improvement of workability in concrete. Sodium silicate ([Na.sub.2][SiO.sub.3]) and sodium hydroxide (NaOH) were used as alkaline activators. The alkaline solution was prepared using distilled water in the experimented work.
3.2. Preparation of alkaline solution
NaOH pellets (320 gms) were dissolved in potable water to make one litre of 8 M sodium hydroxide solution. To achieve the required strength the ratio of sodium silicate solution to sodium hydroxide solution was set as 2.5 and the mixed solution was stored for 24 h (the dissolution of NaOH in water is an exothermic reaction which releases a substantial amount of heat when added in concrete, hence the heat liberated is to be reduced and come down to ambient temperature (Kupaei, Alengaram, and Jumaat 2014) at room temperature (25 [+ or -] 2 [degrees]C) and relative humidity of 65%, before it is used for casting.
3.3. Mix proportions
Trial mix proportions were derived by considering the guidelines of Indian Standard mix designs and from design procedures found in literature of GPC (Patankar, Ghugal, and Jamkar 2015; Talha Junaid et al. 2015). Binder content (fly ash and GGBS), alkaline/binder ratio, fly ash/GGBS ratio, type of curing and age of curing were considered as parameters of research study. Three binder contents (360, 420, 450 kg/[m.sup.3])with four alkaline/binder ratios (0.45, 0.50, 0.55 and 0.60) were studied along with 70-30, 60-40, 50-50 as different combinations of fly ash and GGBS. The final mix proportions are presented in Table 4.
Ambient temperature curing is effective if the fly ash is partially replaced by GGBS (Nath and Sarker 2014). As outdoor curing is the only possible curing method for in situ casting, it is necessitated to achieve same strength acquired by oven curing. Hence, the present study investigates on elimination of oven curing and attainment of required target strength by outdoor curing itself with replacement of fly ash by GGBS. Several trials were carried out considering the basic criterion to develop mixes of average cube strength around 20, 30, 40, 50 MPa at 28 days under outdoor curing and at the lower concentration of alkaline solution. Also it has been ensured that all these mixes have medium workability (as per IS 456:2000) at fresh state. The compressive strength of outdoor cured GPC specimens was compared with that of oven cured specimens.
3.4. Casting and curing of geopolymer concrete
The individual dry materials were weighed and mixed using a rotating drum pan mixer of 100 kg capacity. The alkaline solution and superplasticizer of required dosage was added after uniform mixing of dry materials. Proper homogenous mixing would be ensured by continuous mixing for 5 to 7 min and fresh property test were carried out to measure workability of GPC. The fresh concrete was transferred into concrete moulds (150 x 150 x 150mm) followed by table vibration for a period of 45 s and allowed to set for 24 h. The specimens were de-moulded after 24 h and cured. For outdoor curing, specimens were left out at outdoor (temperature 30 [+ or -] 5 [degrees]C and relative humidity 75%) up to specified age of testing (7 and 28 days).The outdoor temperature varied between 25 to 35 [degrees]C, as the work was carried out for six months. Temperature and humidity control were not necessary for outdoor cured specimens. In case of oven curing, the de-moulded specimens were kept in oven at a temperature of 60 [degrees]C for 24 h and specimens were taken out and allowed to cool down to room temperature. The compressive strength test was carried out on GPC specimens at ages of 7 and 28 days.
4. Results and discussions
4.1. Workability of geopolymer conerete
It becomes difficult to achieve sufficient compaction in GPC due to its stiff consistency at fresh state. GPC can only be made workable with addition of high range water reducing admixtures (preferably Naphthalene-based superplasticizer) at required dosage. The present study required a dosage of 4 per cent by mass of Binder (fly ash and GGBS content). The workability of GPC was measured using standard slump test and the slump values are presented in Table 5. From the values, it can be observed that the slump is maximum at high alkaline solution/Binder (Fly ash and GGBS) ratio, high binder content and high fly ash content. The decrease in alkaline-binder ratio at constant binder content resulted in decrease of slump value. The lower alkaline content was not sufficient to lubricate the binder particles and therefore require additional superplasticizer to attain high workability. The replacement (31 GGBS with fly ash reduced the slump value which was due to its angular shape of GGBS particles.
4.2. Testing procedure for compressive strength test
For compressive strength tests, standard cube specimens of size 150 x 150 x 150 mm are cast and tested under compression using 3000 KN testing machine at standard rate of loading suggested by IS 516 (BIS 1956). The strength values reported at 7 and 28 days are the average of three cube specimens results.
From three mix proportions and compressive strength values, the relationships are developed between Alkaline Solution/binder ratio to compressive strength and Aggregate/Binder ratio to compressive strength. These relationships help in developing mix design procedure for GPC under different curing conditions.
Figures 4-6 show the variation of compressive strength values of GPC cured under outdoor and oven for different percentages of Fly ash and GGBS
It can be observed from Figures 4-6 that the compressive strength has increased with the increase in GGBS content at all binder contents. The replacement of fly ash with GGBS has increased compressive strength; this is due to formation of rich Calcium Silicate Hydrate gel (Yip, Lukey, and Van Deventer 2005). The further replacement of fly ash increases strength but decreases setting time. It can be noted from Figures 4-6 that the optimum alkaline/binder ratio is 0.5. The same results are observed for oven curing also. It can be said that due to supply of heat, the compressive strength was increased at lower replacement of slag, i.e. 30%. As the replacement is increased (i.e. 40 and 50%), the results of outdoor curing and oven curing are similar. Although curing of the slag blended fly ash-based geopolymer in high temperatures provides high early strength, the heat curing is not usually available in cast-in situ construction. Nevertheless the same mixture can be cured in ambient condition to achieve reasonable strength gradually over the age like in OPC concrete.
For different aggregate/binder ratios, alkaline/binder ratios, fly ash & GGBS proportions at certain curing temperature, curing period and NaOH concentration (8 M), slump values and compressive strength values for three different binder contents (360, 420, 450 kg/[m.sup.3]) were obtained from laboratory tests. From these obtained three data-sets, seven more data-sets of different binder contents with different dosages of fly ash and GGBS were interpolated and tabulated in Tables 6 and 7.
Table 6 shows the predicted slump and compressive strength values for different alkaline/binder ratio (A/B), aggregate/binder (Agg/B) ratio, fly ash-GGBS proportions at outdoor curing. Similarly, Table 7 shows the predicted slump and compressive strength values of oven curing for different A/B, Agg/B, fly ash & GGBS proportion. The values in these tables were validated for 3 compressive strength values (30, 40, 50 MPa) and shown in Tables 9 and 11.
It is very important to analyse the effect of mix constituents on strength of GPC with age. Mix design is a process of selecting suitable ingredients used in a particular concrete and determining their relative proportions to reach a given target strength and workability. It is well known that increasing alkaline content improves strength of the concrete up to some extent. The strength of GPC also depends on binder content, amount of fine and coarse aggregate used in the mix. In general, with an increase in the binder content, the compressive strength of GPC increases. As Agg/binder ratio decreases, the compressive strength of GPC increases nominally. Tables 6 and 7 gives required alkaline-binder ratios, binder contents and binder proportions (Fly ash and GGBS) of fly ash and GGBS-based GPC for different compressive strength values and workability (Slump). Based on the estimated compressive strength results, a mix design method is proposed for fly ash and GGBS-based GPC which can be helpful for the design engineers to develop GPC at any required compressive strength.
5. Mix design methodology for geopolymer concrete
A simple mix design procedure is proposed for fly ash and GGBS-based GPC taking Indian standard mix designs steps of cement concrete as basis.
Step 1: Calculate Target Strength ([F.sub.t]) =[f.sub.ck] + 1.65 [S.sub.d] [f.sub.t] = Target average compressive strength of geopolymer concrete at 28 days.
[f.sub.ck] = Characteristic compressive strength at 28 days.
[S.sub.d] = Standard Deviation.
Step 2: Choice of the slump
The choice of slump depends on the type of work and the appropriate value can be assumed according to workability requirement.
Step 3: Selection of binder proportion and alkaline/binder Ratio
The selection of binder proportion mainly depends on the compressive strength and workability requirement. For lower strength, higher proportions of fly ash are sufficient and as strength requirement increases, replacement of fly ash with GGBS is incorporated. The workability of concrete is also an important parameter which changes with the proportions of binders. High proportion of GGBS decreases workability but achieves high compressive strength where as high fly ash proportion in GPC increases workability but fails in achieving required high compressive strength. The alkaline solution/binder ratio is the ratio of mass of alkaline solution (NaOH(8 M) + [Na.sub.2][SiO.sub.3]) to mass of binder (fly ash + GGBS) used in a GPC mix and has an important influence on quality of concrete produced and thus compressive strength. A lower alkaline/binder ratio leads to stiffer mix and the compressive strength is also less. Through experimental studies it was observed that increase in alkaline/binder ratio improves the compressive strength. At alkaline/binder ratio of 0.45, the mix was stiff and at 0.60, the mix was segregated. Since different binder contents and different aggregate-binder ratios, aggregate size and other characteristics may produce different compressive strength for outdoor and oven curing, the relationship between strength and alkaline-binder ratio should be preferably established for in situ conditions. Suitable alkaline-binder ratio may be selected corresponding to required compressive strength at 28 days and required workability from the values shown in Tables 6 and 7. The type of curing either outdoor and oven can also be selected according to construction condition.
Step 4: Selection of aggregate/binder ratio for the required Ft (for selected Fly ash: GGBS ratio) Tables 6 and 7 summarise the estimated compressive strength for fly ash and GGBS-based geopolymer concrete at different alkaline-binder ratios under outdoor and oven curing. The total aggregate-binder is also prescribed in Tables 6 and 7 which varies with respect to strength of GPC. Through experimental results, it is observed that the increase in aggregate-binder ratio decreases compressive strength which is as similar as that of ordinary concrete. The aggregate-binder ratio selection depends on strength requirement, binder proportion and alkaline-binder ratio. In GPC containing fly ash and GGBS with different binder contents, the difference in compressive strength is only a fraction of a per cent. Thus, aggregate content does not seem to be a factor in high strength GPC.
Step 5: Selection of binder content for the required target strength
Three binder contents with fly ash-GGBS proportions were considered in experimentation. Though this, the compressive strength re suits were obtained and intermediate binder contents are estimated for certain compressive strengths. The selection of binder content should in such a way that with maximum binder content the required strength should be obtained. It also depends on proportion of fly ash and GGBS, alkaline-binder ratio. For higher degree of GGBS, the binder content required is minimal at same compressive strength as compared to fly ash dosages. The curing temperature also effects the requirement of binder content. Hence, the selection of binder content depends on strength, availability of source materials, workability, curing temperature, etc. Step 6: Estimation of coarse aggregate and fine aggregate content
Figure 7 show the variation of binder content and coarse aggregate-total aggregate ratio obtained from Tables 6 and 7. Though these figures, the coarse aggregate-total aggregate can be estimated for selected binder contents. From the obtained values, coarse aggregate and fine aggregate can be calculated.
Quantity of coarse aggregate = [Coarse aggregate/Total aggregate] x Total aggregate content.
Quantity of fine aggregate = Total aggregate-Coarse aggregate.
Step 7: Find alkaline content
The previous steps explain the procedure for obtaining alkaline-binder ratio, binder proportion and binder contents. For 1 [m.sup.3]of concrete, when binder content, alkaline solution quantities are known, then coarse aggregate and fine aggregate contents can be calculated. Through literature and experimentation it was concluded that the optimum ratio of sodium silicate solution to sodium hydroxide solution is 2.5 by mass. Hence, from the selected alkaline-binder ratio, the quantities of NaOH and [Na.sub.2][SiO.sub.3] are calculated and the molarity of NaOH is selected as 8 M.
Alkaline solution = NaOH + [Na.sub.2][SiO.sub.3]
[Na.sub.2][SiO.sub.3]/NaOH solution = 2.5
[Na.sub.2][SiO.sub.3] = 2.5 NaOH
5. 1. Example for mix proportion using the proposed procedure
Mix design of GPC is presented here so as to serve as an example for the suggested procedure.
Assume that the fly ash and GGBS-based GPC may be prepared for a target strength required at 28 days as 30 MPa for a slump of 120 mm. The strength requirement and workability suggests that the concrete is of low grade where with lower dosages of binder and lower proportions of GGBS, the strengths can be achieved. Here, from Table 4, corresponding to target strength 30 MPa, the binder proportion 70-30, the binder content is assumed as 370 kg/[m.sup.3]. The alkaline-binder ratio is taken as 0.55 and corresponding to these values, the aggregate-binder ratio is obtained, i.e. 5.02. The optimum dosage of [Na.sub.2][SiO.sub.3]/NaOH is taken as 2.5 and 8 M NaOH solution is considered. While reducing the alkaline to binder ratio would result in less strengths, the reduction would also reduce the workability. The guidelines suggested by IS 456-2000 regarding workability the values are divided into Low, Medium and High. Based on the strength and workability the mix is selected.
The total alkali liquid is calculated by multiplying the Alkaline/Binder ratio to the total fly ash quantity: GGBS = 0.55 x 370 = 203.5 kg/[m.sup.3].
Knowing the [Na.sub.2][SiO.sub.3]/NaOH ratio of 2.5 the individual quantities of each alkaline liquid can be determined
NaOH solution = 203.5/3.5 = 58.14 kg/[m.sup.3]
[Na.sub.2][SiO.sub.3] Solution = 2.5 x 58.14 = 145.35 kg/[m.sup.3]
Total aggregate/Binder ratio = 5.02
Total aggregate = 5.02 x 370 = 1857.4 kg
From Figure 7
Coarse aggregate/Total aggregate = 0.582
Coarse aggregate = 0.582 x 1857.4 =1081 kg.
Fine aggregate = Total aggregate-Coarse aggregate
= 1857.4-1081
= 776.39 kg
Table 8 shows the mix proportions obtained for GPC of 30 MPa compressive strength cured at outdoor and oven curing. Using the obtained mix proportions, concrete cubes of size 150 x 150 x 150 mm were cast and cured under specified method of curing. The cubes are tested at different ages and results obtained are shown in Table 9. Similar method is adopted to develop 40 and 50 MPa GPCs and the mix proportions are tabulated in Table 10. The compressive strength results of 40 and 50 MPa under two different curing conditions are presented in Table 11. From the results, it can be understood that the strength required are achieved in all cases using the proposed method. It is also clear that for low strength GPC lower per cent of GGBS is sufficient whereas medium strength concretes GGBS addition to be increased.
The compressive strength results obtained for 30, 40 and 50 MPa shows that the strength development has slowed down after the 7 days age of curing in both outdoor and oven cured specimens. The per cent variation of target strength achieved for these mixes to the analytically developed results is less than 5% for all mixes. Thus, the table developed holds good for all the proposed mixes for both outdoor and oven drying conditions for a target strength of 20-60 MPa. In particular for in situ conditions, the proposed mixes with outdoor conditions provide exact results.
For GPC prepared with Fly ash and GGBS, the required target strength can be achieved under outdoor conditions, thus oven curing can be eliminated.
6. Conclusions
The present study concludes the following:
(1) Through vigorous experimental studies on fly ash and GGBS-based GPC, it is clearly evident that the replacement of fly ash with GGBS enhances the compressive strength of concrete irrespective of type of curing.
(2) The compressive strength values are maximum at Alkaline-Binder ratio 0.5 for all the three binder contents (i.e. 360, 420 and 450 kg/[m.sup.3]). It is true at all replacements of fly ash with GGBS.
(3) The level of replacement of fly ash with GGBS altered the requirement of oven curing to outdoor curing. Higher compressive strengths were observed with 50 per cent GGBS content.
(4) With a total binder content of 360 kg/[m.sup.3], the increase in compressive strength of 50FA:50GGBS is 24.7% over 60FA:40GGBS and 65.2% over 70FA:30GGBS. Similar trend was also observed with other two binder contents (420 and 450 kg/[m.sup.3])
(5) The proposed mix design method holds good for both outdoor and oven curing conditions and helps in designing the GPC in the range of compressive strength 20 to 60 MPa.
(6) The proposed method was validated with intermediate mixes and the workability and compressive strength results are reliable with developed methodology.
Disclosure statement
No potential conflict of interest was reported by the authors.
Notes on contributors
G. Mallikarjuna Rao is an associate professor in the Department of Civil Engineering, Vardhaman College of Engineering, Hyderabad, India. The author's area of research interests are geopolymer concrete, sustainable cementitious materials, fracture mechanics, steel structures.
T. D. Gunneswara Rao is an associate professor in the Department of Civil Engineering, National Institute of Technology Warangal. The authors area of research interests are fracture mechanics of concrete structures, fibre-reinforced concrete, sustainable construction materials.
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G. Mallikarjuna Rao (a) and T. D. Gunneswara Rao (b)
(a) Department of Civil Engineering, Vardhaman College of Engineering, Hyderabad, India; (b) Department of Civil Engineering, National Institute of Technology, Warangal, India
CONTACT G. Mallikarjuna Rao gmyadav25@gmail.com
ARTICLE HISTORY
Received 1 April 2017
Accepted 5 March 2018
https://doi.org/10.1080/14488353.2018.1450716
Table 1. Chemical composition of fly ash and GGBS (% by mass).
Chemical composition Fly ash GGBS
[Si.sub.O2] 60.11 34.06
[Alcomposition2][O.sub.3] 26.53 20
[Fe.sub.2][O.sub.3] 4.25 0.8
[SO.sub.3] 0.35 0.9
CaO 4.00 32.6
MgO 1.25 7.89
[Na.sub.3]O 0.22 NIL
LOI 3.25 3.72
Table 2. Physical properties of coarse and fine aggregates.
Physical properties Fine aggregate Coarse aggregate
Specific gravity 2.65 2.80
Bulk density 1.45 1.5
Fineness modulus 2.57 7.3
Water absorption 2% 0.5%
Table 3. Setting time forfly ash and GGBS combinations.
Fly ash:GGBS Final setting time (Minutes)
70:30 110
60:40 100
50:50 95
Table 4. Mix proportions of Geopolymer concrete.
Alkaline solution/ Binder (Fly ash+GGBS)
Notation binder (kg/[m.sup.3])
[A.sub.1][F.sub.70][G.sub.30] 0.45 360
[A.sub.2][F.sub.70][G.sub.30] 0.5 360
[A.sub.3][F.sub.70][G.sub.30] 0.55 360
[A.sub.4][F.sub.70][G.sub.30] 0.6 360
[B.sub.1][F.sub.70][G.sub.30] 0.45 420
[B.sub.2][F.sub.70][G.sub.30] 0.5 420
[B.sub.3][F.sub.70][G.sub.30] 0.55 420
[B.sub.4][F.sub.70][G.sub.30] 0.6 420
[C.sub.1][F.sub.70][G.sub.30] 0.45 450
[C.sub.2][F.sub.70][G.sub.30] 0.5 450
[C.sub.3][F.sub.70][G.sub.30] 0.55 450
[C.sub.4][F.sub.70][G.sub.30] 0.6 450
Coarse aggregate
Notation Fine aggregate (kg/[m.sup.3])
(kg/[m.sup.3])
[A.sub.1][F.sub.70][G.sub.30] 774 1090.8
[A.sub.2][F.sub.70][G.sub.30] 774 1090.8
[A.sub.3][F.sub.70][G.sub.30] 774 1090.8
[A.sub.4][F.sub.70][G.sub.30] 774 1090.8
[B.sub.1][F.sub.70][G.sub.30] 810.6 966
[B.sub.2][F.sub.70][G.sub.30] 810.6 966
[B.sub.3][F.sub.70][G.sub.30] 810.6 966
[B.sub.4][F.sub.70][G.sub.30] 810.6 966
[C.sub.1][F.sub.70][G.sub.30] 760.5 972
[C.sub.2][F.sub.70][G.sub.30] 760.5 972
[C.sub.3][F.sub.70][G.sub.30] 760.5 972
[C.sub.4][F.sub.70][G.sub.30] 760.5 972
Alkaline solution
Notation (kg/[m.sup.3])
[A.sub.1][F.sub.70][G.sub.30] 162
[A.sub.2][F.sub.70][G.sub.30] 180
[A.sub.3][F.sub.70][G.sub.30] 198
[A.sub.4][F.sub.70][G.sub.30] 216
[B.sub.1][F.sub.70][G.sub.30] 189
[B.sub.2][F.sub.70][G.sub.30] 210
[B.sub.3][F.sub.70][G.sub.30] 231
[B.sub.4][F.sub.70][G.sub.30] 252
[C.sub.1][F.sub.70][G.sub.30] 202.5
[C.sub.2][F.sub.70][G.sub.30] 225
[C.sub.3][F.sub.70][G.sub.30] 247.5
[C.sub.4][F.sub.70][G.sub.30] 270
Notes: A, B, C represents 360, 420, 450 kg/m, F and G represents Fly
ash and GGBS contents.
Table 5. Workability of geopolymer concrete.
Binder quantity (kg/[m.sup.3])
Alkali-binder 360 420 450
Fly ash :GGBS ratio Slump in mm
70:30 0.45 95 125 175
0.5 102 136 184
0.55 115 142 195
0.6 180 194 225
60:40 0.45 84 102 148
0.5 100 115 162
0.55 111 135 171
0.6 154 170 205
50:50 0.45 78 83 96
0.5 92 106 111
0.55 107 118 135
0.6 146 155 185
Table 6. Compressive strength and workability of outdoor curing.
0.45 0.50
Fly Binder Agg/ Slump Strength Slump Strength
ash:GGBS (kg/[m.sup.3]) Binder (mm) (MPa) (mm) (MPa)
70:30 360 5.18 95 33.83 102 36.19
370 5.02 100 34.31 108 36.52
380 4.86 105 34.79 113 36.85
390 4.70 110 35.27 119 37.18
400 4.54 115 35.76 125 37.52
410 4.38 120 36.24 130 37.85
420 4.23 125 36.69 136 38.16
430 4.10 142 35.70 152 38.43
440 3.97 160 34.89 168 38.66
450 3.85 175 33.81 184 38.96
60:40 360 5.18 84 42.32 100 47.92
370 5.02 87 42.95 103 48.47
380 4.86 90 43.58 105 47.91
390 4.70 93 44.21 108 48.75
400 4.54 96 44.85 110 49.59
410 4.38 99 45.48 113 50.43
420 4.23 102 46.08 115 51.22
430 4.10 117 46.01 131 51.04
440 3.97 133 45.96 146 50.89
450 3.85 148 45.88 162 50.69
50:50 360 5.18 78 55.37 92 59.79
370 5.02 79 55.62 94 59.88
380 4.86 80 55.85 97 59.98
390 4.70 81 56.11 99 60.08
400 4.54 81 56.36 101 60.18
410 4.38 82 56.62 104 60.28
420 4.23 83 56.86 106 60.38
430 4.10 87 54.14 108 59.75
440 3.97 92 51.90 109 59.23
450 3.85 96 48.91 111 58.53
0.55 0.60
Fly Slump Strength Slump Strength
ash:GGBS (mm) (MPa) (mm) (MPa)
70:30 115 31.11 180 25.71
120 30.27 182 25.60
124 29.43 185 25.50
129 28.60 187 25.40
133 27.77 189 25.30
138 26.95 192 25.20
142 26.17 194 25.11
160 26.01 204 23.62
177 25.88 215 22.40
195 25.71 225 20.76
60:40 111 46.87 154 43.38
115 46.49 157 46.20
119 46.12 159 46.27
123 45.75 162 46.35
127 45.38 165 46.42
131 45.02 167 46.50
135 44.67 170 46.57
147 43.71 182 46.27
159 42.91 193 46.01
171 41.85 205 45.68
50:50 107 51.61 146 46.68
109 50.73 148 46.84
111 49.86 149 46.98
113 49.00 151 47.13
114 48.14 152 47.28
116 47.28 154 47.43
118 46.48 155 47.57
124 47.15 165 47.59
129 47.71 175 47.61
135 48.45 185 47.64
Note: As per IS456:2000 Low (25-75), Medium (50-100) and High (100-150).
Table 7. Compressive strength and workability of oven curing.
0.45 0.50
Fly Binder Agg/ Slump Strength Slump Strength
ash:GGBS (kg/[m.sup.3]) Binder (mm) (MPa) (mm) (MPa)
70:30 360 5.18 95 41.53 102 42.56
370 5.02 100 41.34 108 42.72
380 4.86 105 41.15 113 42.88
390 4.70 110 40.96 119 43.03
400 4.54 115 40.78 125 43.19
410 4.38 120 40.59 130 43.35
420 4.23 125 40.41 136 43.50
430 4.10 142 39.80 152 43.84
440 3.97 160 39.19 168 44.18
450 3.85 175 38.63 184 44.49
60:40 360 5.18 84 55.57 100 57.37
370 5.02 87 56.11 103 58.20
380 4.86 90 56.66 105 59.03
390 4.70 93 57.20 108 59.86
400 4.54 96 57.75 110 60.68
410 4.38 99 58.29 113 61.51
420 4.23 102 58.80 115 62.29
430 4.10 117 58.03 131 61.95
440 3.97 133 57.27 146 61.61
450 3.85 148 56.56 162 61.30
50:50 360 5.18 78 61.96 92 65.26
370 5.02 79 61.22 94 65.09
380 4.86 80 60.47 97 64.93
390 4.70 81 59.73 99 64.76
400 4.54 81 58.98 101 64.60
410 4.38 82 58.24 104 64.43
420 4.23 83 57.54 106 64.28
430 4.10 87 56.66 108 63.47
440 3.97 92 55.78 109 62.65
450 3.85 96 54.97 111 61.90
0.55 0.60
Fly Slump Strength Slump Strength
ash:GGBS (mm) (MPa) (mm) (MPa)
70:30 115 33.94 180 28.58
120 33.49 182 28.30
124 33.03 185 28.01
129 32.58 187 27.73
133 32.12 189 27.44
138 31.67 192 27.16
142 31.24 194 26.89
160 32.59 204 27.77
177 33.95 215 28.65
195 35.20 225 29.46
60:40 111 53.39 154 51.22
115 54.32 157 52.13
119 55.26 159 53.05
123 56.19 162 53.96
127 57.12 165 54.87
131 58.06 167 55.78
135 58.93 170 56.64
147 57.37 182 54.31
159 55.82 193 51.98
171 54.38 205 49.83
50:50 107 53.39 146 52.40
109 52.93 148 51.90
111 52.46 149 51.40
113 52.00 151 50.90
114 51.54 152 50.41
116 51.07 154 49.91
118 50.64 155 49.44
124 51.92 165 50.93
129 53.20 175 52.42
135 54.38 185 53.79
Table 8. Mix proportions obtained for 30 MPa geopolymer concrete.
Quantity Outdoor Oven
Binder (kg/[m.sup.3]) 370 360
Fly ash:GGBS 70:30 70:30
Coarse aggregate(kg/[m.sup.3]) 1081 973
Fine aggregate (kg/[m.sup.3]) 776.39 770
Alkaline solution (kg/[m.sup.3]) 203.5 198
Table 9. Average compressive strength for outdoor and oven curing for
30 MPa concrete.
Ave rage compressive Average compressive
strength(Out- strength (Oven
Age of curing (Days) door) (MPa) dried) (MPa)
1 19.24 26.22
3 20.83 27.94
7 23.66 30.00
28 31.44 33.68
Table 10. Mix proportions for different compressive strength.
Compiessive strength
401 Mpa 50 MPa
Quantity Outdoor Oven Outdoor Oven
Binder (kg/[m.sup.3]) 400 360 430 370
Fly ash:GGBS 60:40 60:40 50:50 50:50
Coarse aggregate(kg/[m.sup.3]) 1042.38 973 966.12 1081
Fine aggregate (kg/[m.sup.3]) 773.6 770 796.87 776.39
Alkaline solution (kg/[m.sup.3]) 240 198 215 203.5
Table 11. Average compressive strength for outdoor and oven curing for
40 and 50 MPa concrete.
Compressive strength
40 Mpa 50 MPa
Age of curing (days) Outdoor Oven Outdoor Oven
1 23.39 32.16 33.02 40.93
3 27.29 38.89 38.36 44.22
7 34.53 46.01 48.25 55.24
28 44.89 51.53 57.84 62.25
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| |
| Author: | Rao, G. Mallikarjuna; Rao, T.D. Gunneswara |
|---|---|
| Publication: | Australian Journal of Civil Engineering |
| Geographic Code: | 9INDI |
| Date: | Apr 1, 2018 |
| Words: | 7110 |
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