Construction and Building Materials 133 (2017) 128–134

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Construction and Building Materials

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Comparative study using Portland cement and calcium carbide residueas a promoter in bottom ash geopolymer mortar

http://dx.doi.org/10.1016/j.conbuildmat.2016.12.0460950-0618/� 2016 Elsevier Ltd. All rights reserved.

⇑ Corresponding author.E-mail address: tanakorn.ph@rmuti.ac.th (T. Phoo-ngernkham).

Sakonwan Hanjitsuwan a, Tanakorn Phoo-ngernkhamb,⇑, Nattapong Damrongwiriyanupap c

a Program of Civil Technology, Faculty of Industrial Technology, Lampang Rajabhat University, Lampang 52100, ThailandbResearch Center for Advances in Civil Engineering and Construction Materials, Department of Civil Engineering, Faculty of Engineering and Architecture, Rajamangala Universityof Technology Isan, Nakhon Ratchasima 30000, ThailandcCivil Engineering Program, School of Engineering, University of Phayao, Phayao 56000, Thailand

h i g h l i g h t s

� Sustainable masonry units using waste materials.� Role of calcium promoter on strength development of BA geopolymer.� PC provided more reaction products and degree of geopolymerization than CCR.� Both PC and CCR replacement met the strength requirement for masonry units.

a r t i c l e i n f o

Article history:Received 26 June 2016Received in revised form 20 November 2016Accepted 13 December 2016Available online 23 December 2016

Keywords:Bottom ashCalcium promotersStrength developmentMicrostructureGeopolymer

a b s t r a c t

This article presents the comparative study using Portland cement (PC) and calcium carbide residue (CCR)as a promoter on properties of bottom ash (BA) geopolymer cured at ambient temperature. Two calciumpromoters: PC and CCR were used to replace BA at the amount of 10%, 20%, and 30% by weight of binder.Sodium hydroxide and sodium silicate solutions were used as liquid alkaline activation in all mixtures.The setting time and strength development of BA geopolymer mortars were studied. XRD, SEM andFTIR analyses were used on the BA geopolymer pastes with calcium promoters for investigating the reac-tion products. The results showed that the use of calcium promoters to replace BA resulted in decreasingof setting time whereas its strength development enhanced. The highest compressive strength of BAgeopolymer mortars could be observed at the BA replacement with 30% of PC and 30% of CCR which were13.8 and 11.4 MPa, respectively. The difference in strength development of BA geopolymer mortars withcalcium promoters was due to degree of geopolymerization. The results of XRD, SEM and FTIR analysesagreed well with strength behaviors that the use of PC provided more reaction products and degree ofgeopolymerization than that of CCR. The 28-day compressive strengths of both PC and CCR replacementmet the strength requirement for non-load-bearing and load-bearing brick masonry units as specified byASTM standard. In addition, the outcome of this research could help divert significant quantity of wastematerials from landfills and considerably reduce environmental damage caused by carbon emissions dueto PC production.

� 2016 Elsevier Ltd. All rights reserved.

1. Introduction

The production of Portland cement increases every year all overthe world and this process causes the emission of CO2 which is aprimary problem of global warming. Turner and Collins [1] men-tioned that every ton of Portland cement production releasedapproximately 0.82 ton of CO2 to the atmosphere. To solve this

problem, alternative pozzolanic materials were used to reducethe Portland cement content in concrete mixture [2]. Other effortshave made to develop a new binding material. This is called‘‘alkali-activated aluminosilicate material” and also known as‘‘geopolymer”, which consists of SiO4 and AlO4 tetrahedral withhighly alkaline conditions to form three-dimensional structures.

In Thailand, by-product or waste materials from coal combus-tion for electricity generation such as fly ash and bottom ash areproduced approximately 3 and 0.8 million tons, respectively, eachyear [3–5]. Fly ash is comprised of fine particles that are dispelled

S. Hanjitsuwan et al. / Construction and Building Materials 133 (2017) 128–134 129

of the incinerator and captured by electrostatic precipitators. Ashthat falls in the bottom of the incinerator called bottom ash. Nowa-days, bottom ash has been less used in concrete/geopolymer mate-rials compared to fly ash. So, it is mainly disposed of to landfillwhich leads to environmental problems as reported by previousstudies [5,6]. Both fly ash and bottom ash contain a large amountof silica, alumina and calcium oxide; thus, these waste materialscan be used for producing geopolymer. Over the past few years,there have been several studies on fly ash and bottom ash geopoly-mer, for instance, two different types of precursors were used tomanufacture geopolymer masonry units. One was made from flyash and water treatment sludge [7] and another was producedfrom fly ash based geopolymer incorporating recycled glass [8].Chindaprasirt et al. [6] reported that fly ash geopolymer had ahigher strength development than bottom ash geopolymer, dueto the difference of geopolymerization degree. Another reason isdue to large particles and high porous of bottom ash resulting inlower reactivity [5,6]. To improve the reaction degree of bottomash, Jaturapitakkul and Cheerarot [9] improved the pozzolanicreaction of bottom ash by grinding into small particles. The resultsshowed that bottom ash with higher fineness obtained highstrength of concrete. However, the use of bottom ash as sourcematerial for producing geopolymer is in low strength comparedto fly ash geopolymer [6]. Recently, many researchers [10–17] havetried to improve the properties of geopolymer matrix cured atambient temperature to obtain higher strength. It is known thatgeopolymerization reaction can be improved by curing at temper-ature of 40–75 �C [18,19] but this is not practical to use in con-struction work except in precast system. As mentionedpreviously, some studies [12,15] claimed that the use of Portlandcement as a promoter could enhance the strength developmentof geopolymer cured at ambient temperature and resulted in goodgeopolymer properties.

Calcium carbide residue is also one of waste materials consist-ing of substantial calcium oxide; therefore, it is interesting to useas a promoter in similar to Portland cement. Calcium carbide resi-due is a by-product of acetylene production process through thehydrolysis of calcium carbide (CaC2) regarded as a sustainablecementing agent. Calcium carbide residue is mainly composed ofcalcium hydroxide in a slurry form [20–23]. In Thailand, thedemand of calcium carbide for producing acetylene gas is about18,500 tons/year, consequently this implies that more than21,500 tons/year of calcium carbide residue is released[20,23,24]. Usually, calcium carbide residue is mainly disposed inlandfills, which causes various environmental problems due to itshigh alkalinity. Recently, calcium carbide residue was used as anew cementitious material with rice husk ash to form calciumsilicate hydrate (C-S-H) similar to the hydration products ofPortland cement [25]. Makaratat et al. [26] investigated the useof calcium carbide residue and fly ash in concrete without Portlandcement and found that the properties were satisfactorily comparedto normal concrete. Moreover, calcium carbide residue was alsoused to improve strength characteristics of soil [21,22]. Forinstance, Phetchuay et al. [23] used calcium carbide residuecombined with fly ash as a binder for making geopolymer matrixto stabilize strength development in soft marine clay, and calciumcarbide residue was also employed as an alkaline activator in flyash geopolymer for subgrade stabilization [27]. In addition, otherby-products have been recently used in geopolymer cements. Forexample, a novel geopolymeric material comprised of spent coffeeground as a base material together with blast furnace slag and flyash as precursors was used to stabilize subgrade soil [28]. Thestabilization of recycled demolition aggregates used in pavementbase/subbase by geopolymers was investigated by Mohammediniaet al. [29]. The results showed that both the resilient modulus andcompressive strength were improved by geopolymer binders. The

similar results were found by Arulrajah et al. [30] that the strengthproperties of pavement were enhanced by fly ash-slag-calcium car-bide residue based geopolymer.

However, from the above review, several works have beeninvestigated on fly ash based geopolymer but there is no researchinvestigated on the utilization of bottom ash as a binder stabilizedby calcium admixtures to improve the strength of geopolymer.Thus, this research focuses mainly on a comparison betweenPortland cement and calcium carbide residue as a promoter forenhancing the strength development of bottom ash geopolymer.The setting time, compressive strength, X-ray diffractometry(XRD), scanning electron microscopic (SEM) and Fourier transforminfrared spectroscopy (FTIR) were examined. The results of thisstudy would lay a foundation for the future use of bottom ashgeopolymer with calcium promoters as non-load-bearing andload-bearing brick masonry units as described in ASTM C129 [31]and ASTM C90 [32], respectively, instead of treating bottom ashand calcium carbide residue as waste materials. Also, the outcomesfrom this study could help divert significant quantity of wastematerials from landfills and considerably reduce environmentaldamage caused by carbon emissions due to Portland cementproduction.

2. Experimental details and testing analysis

2.1. Materials

The staring materials used in this study were bottom ash (BA),Portland cement type I (PC) and calcium carbide residue (CCR). TheBA was obtained from the Mae Moh power plant in the northernThailand. The BA was ground by a Los Angeles abrasion machine,and passed through a sieve No. 100 (150 lm) with a specific grav-ity and median particle size of 2.12 and 32.3 lm, respectively. TheCCR was oven-dried at 100 �C for 24 h and then it was ground by aLos Angeles abrasion machine. The CCR passed through a sieve No.100 (150 lm) with a specific gravity and median particle size of2.25 and 21.2 lm, respectively. While, the commercial PC used inthis study has a specific gravity and median particle size of 3.15and 14.6 lm, respectively. Fig. 1 shows the scanning electronmicrographs (SEM) of ground BA and CCR. The BA consists of irreg-ular shapes whereas the CCR particles are generally irregular insimilar to the previously published results [33]. The chemical com-positions of BA, PC and CCR are summarized in Table 1. The BAmainly consists of SiO2 Al2O3, CaO and some impurities. The sumof SiO2, Al2O3 and Fe2O3 is 56.25%, with 28.51% of CaO content, thusBA used in this study conformed to Class C as per ASTM C618-15[34]. The PC comprises of CaO and SiO2 whereas the major compo-nent of CCR is CaO. River sand with a specific gravity of 2.63 andfineness modulus of 2.05 in saturated surface dry condition wasused as fine aggregate for mixing BA geopolymer mortars (BAGMs).

2.2. Sample preparation for bottom ash geopolymer mortars

Commercial grade sodium silicate solution (Na2SiO3) with13.45% Na2O, 32.39% SiO2, and 54.16% H2O by weight and 10 Msodium hydroxide solution (NaOH) were used to produce theBAGMs. The 10 M NaOH solution was selected for this studybecause it provided high-strength geopolymer as reported byRattanasak and Chindaprasirt [35] and Somna et al. [36]. The10 M NaOH was obtained from 400 g of sodium hydroxide pelletsin 1 L of distilled water and then allowed it to cool down for 24 hbefore use [3]. The ratios of liquid to solid binder, Na2SiO3 to NaOH,and sand to binder were fixed at 0.70, 2.0, and 1.5, respectively.

The BA and promoters were mixed at various BA:PC and BA:CCRratios of 100:0, 90:10, 80:20 and 70:30 with an abbreviation of

(a) ground BA (b) CCR

Fig. 1. SEM photos of ground BA and CCR.

Table 1Chemical compositions of BA, PC and CCR (by weight).

Materials SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O P2O5 TiO2 MnO LOI SO3

BA 26.17 15.79 14.21 28.51 2.98 1.43 1.05 0.25 0.31 0.12 7.68 1.50PC 20.80 4.70 3.40 65.30 1.50 0.10 0.40 – – – 2.90 0.90CCR 5.94 3.42 – 86.14 0.36 0.10 0.39 – – – 2.79 0.87

130 S. Hanjitsuwan et al. / Construction and Building Materials 133 (2017) 128–134

100BA, 90BA10PC, 80BA20PC, 70BA30PC, 90BA10CCR, 80BA20CCR,and 70BA30CCR, respectively. The mix proportions of the BAGMs inthis study are summarized in Table 2. For the mixing of the BAGMs,binder and sand were dry mixed for 1 min or until the mixture washomogenous. The Na2SiO3 and NaOH solutions were then addedand the mixing was done for another 3 min.

2.3. Testing procedure for bottom ash geopolymer mortars

The setting time of the BAGMs was tested in accordance withASTM C191 [37]. For the compressive strength test, the freshBAGMs were placed into a 50 � 50 � 50 mm cube mold and com-pacted as described in ASTM C109 [38]. The BAGMs weredemoulded at the age of 1 day and immediately wrapped withvinyl sheet to protect moisture loss and kept in the ambient roomtemperature. The compressive strengths are determined at the ageof 28 days. The results are reported as an average of three samples.

In order to observe a growth of cementitious products,microstructure evaluation techniques were conducted that theBA geopolymer pastes with calcium promoters at 28-day age werebroken into small pieces approximately 3–6 mm for scanningelectron microscopic (SEM) analysis. While, the pastes wereground into fine powder for X-ray diffractometry (XRD) andFourier transform infrared spectroscopy (FTIR) analyses. For theFTIR testing, each sample was mixed with KBr before testing. TheFTIRs were conducted in the wave number region of between

Table 2Mix proportions of Bottom Ash Geopolymer Mortars.

Symbol BA (g) PC (g) CCR (g)

100BA 100 – –90BA10PC 90 10 –80BA20PC 80 20 –70BA30PC 70 30 –90BA10CCR 90 – 1080BA20CCR 80 – 2070BA30CCR 70 – 30

400 and 4000 cm�1 whereas the XRDs were performed for 2 thetafrom 10� to 60�.

3. Results and discussion

3.1. Setting time and compressive strength

The setting time of the BAGMsmade from BA and promoters, PCand CCR, is illustrated in Fig. 2 whereas the 28-day compressivestrength is shown in Fig. 3. The setting time of the BAGMs obvi-ously decreases while compressive strength of the BAGMs substan-tially increase with the increase of promoter replacement ratio.The final setting time of 100BA, 90BA10PC, 80BA20PC, 70BA30PC,90BA10CCR, 80BA20CCR, and 70BA30CCR mortars are 675, 100,60, 35, 165, 65, and 35 min, respectively. While, the compressivestrengths are 5.8, 7.6, 9.6, 13.8, 6.4, 7.4 and 11.4 MPa with corre-sponding to 100BA, 90BA10PC, 80BA20PC, 70BA30PC, 90BA10CCR,80BA20CCR, and 70BA30CCR mortars, respectively. According toFig. 2, the setting time of the BAGMs containing PC is found to berapid setting similar to the BAGMs containing CCR. It is noticedthat the BAGMs containing PC shows a higher strength than thoseof the BAGMs containing CCR. The highest strength of 13.8 MPa isobtained with the 70BA30PC mix. The compressive strengths ofBAGMs gained from the present study are lower than those ofprevious experiments conducted by Chindaprasirt et al. [6] andBoonserm et al. [39] that the strengths were approximately 15.0and 25.0 MPa, respectively. However, those of previous studies

Sand (g) NaOH (g) Na2SiO3 (g) SiO2/Al2O3

150 23.3 46.7 4.44150 23.3 46.7 4.71150 23.3 46.7 5.03150 23.3 46.7 5.40150 23.3 46.7 4.58150 23.3 46.7 4.75150 23.3 46.7 4.95

0

100

200

300

400

500

600

700

800Se

tting

tim

e (m

in)

BA Geopolymer Mortar

Initial Setting Time Final Setting Time

Fig. 2. Setting time of the BAGMs.

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

0 10 20 30

Com

pres

sive

stre

ngth

(MPa

)

Calcium Promoters (%)

PC replacement CCR replacement

Fig. 3. 28-day compressive strength of the BAGMs.

S. Hanjitsuwan et al. / Construction and Building Materials 133 (2017) 128–134 131

were done with the temperature curing at 65 �C and 40 �C for 48 hbut, in this study, it was performed in ambient temperature. Aspreviously mentioned by Chindaprasirt et al. [16], the temperaturecuring could accelerate the degree of geopolymerization withingeopolymer matrix. Still, the heat curing is not economical andenvironmentally unfriendly practices for the construction industry.

0 10 20 302theta (d

Inte

nsity

(cou

nts)

= quartz (SiO2), =anorthite (CaAl2Si2O8), = calcium carbonate (CaCO3), = ferric oxide (Fe2O3= calcium silicate hydrate (CaSiO3.H2O)

(a) ground BA

(b) 70BA30PC

(c) 70BA30CCR

Fig. 4. XRD patterns of ground BA and BA geop

Differences in trend of setting time and strength behavior ofBAGMs are due to the characteristic of promoters. The CCR ismainly consisted of calcium hydroxide (Ca(OH)2), whereas themajor components of PC are Tricalcium Silicate (C3S) and Dical-cium Silicate (C2S). Normally, the degree of geopolymerization ofBA geopolymer matrix is found to be low [6]. Thus, the use of cal-cium promoters such as PC and CCR to replace BA can enhancecompressive strength of geopolymer mortars. That is tricalcium sil-icate (C3S) and dicalcium silicate (C2S) in PC react with water cre-ating hydration products and the Ca(OH)2 from hydration productschemically react with SiO2 and/or Al2O3 from BA to form poz-zolanic reaction. On the other hand, only pozzolanic reaction istaken place in BAGMs containing CCR that is Ca(OH)2 existing inCCR reacts with SiO2 and/or Al2O3 from BA [26]. Thus, the strengthdevelopment of the BAGMs containing PC are higher than that ofusing CCR replacement in BA geopolymer system. Moreover, theaddition of calcium oxide in BAGM can accelerate the setting andhardening time similarly found in FA geopolymer containing PC[12]. It can be concluded that the use of BA geopolymer with cal-cium promoters can produce a new binding material similar toFA geopolymer, but the compressive strength is lower comparedto FA based geopolymer [15].

The SiO2/Al2O3 ratio is one of the significant factors affecting onthe strength development of geopolymermatrix. As seen in Table 2,the BA geopolymer without promoters has the lowest SiO2/Al2O3

ratio of 4.44 resulting in the lowest compressive strength of5.80 MPa. While, the strength increases with increasing of SiO2/Al2O3 ratio. This is similar to the previous result investigated ongeopolymer synthetized from bottom coal ash [40]. The highestcompressive strength of 13.8 MPa and 11.4 MPa for BA-PC andBA-CCR geopolymer are found at SiO2/Al2O3 ratio of 5.40 and4.95, respectively. In addition, the results from other studies havebeen confirmed that the appropriate SiO2/Al2O3 ratio depends onthe properties of geopolymer precursor materials and stronglyinfluences on the optimum strength. For example, the suitableSiO2/Al2O3 ratio of high calcium FA and metakaolin based geopoly-mer was found to be approximately 3.20–3.70 [41] and 3.0–3.8[42] that produce the optimum strength of 64.0 MPa and28.0 MPa, respectively. Nimwinya et al. [43] reported that calcinedwater treatment sludge and rice husk ash geopolymers provide theoptimum SiO2/Al2O3 ratio of 4.9 providing the highest strength of16.0 MPa.

40 50 60egree)

= auguite (Ca(Mg,Fe,Al)(Si,Al)2O6), ), = gypsum (CaSO4.2H2O),

olymer pastes with promoters at 28 days.

(a) 100BA

(b) 70BA30PC

(c) 70BA30CCR

Fig. 5. SEM photos of BA geopolymer pastes with promoters at 28 days.

132 S. Hanjitsuwan et al. / Construction and Building Materials 133 (2017) 128–134

The maximum 28-day compressive strength of BAGMs with cal-cium promoters cured at room temperature satisfies the ASTMspecifications for non-load-bearing and load-bearing brickmasonry units. This result is similar to the compressive strengthof high fire resistance blocks containing coal combustion fly ashesand bottom ash investigated by Carcia Arenas et al. [44].

3.2. XRD analysis

The XRD analysis is one of characterization techniques toobserve the reaction products within geopolymer matrix. Accord-ing to Fig. 3, the 70BA30PC and 70BA30CCR show the highest com-pressive strength, therefore, they were selected to investigate themicrostructure, the development of geopolymerization products,and the effect of calcium promoters compared to BA geopolymer.The XRD patterns of ground BA, 70BA30PC, and 70BA30CCR areshown in Fig. 4a–c. The ground BA (Fig. 4a) consists of amorphousphase at the hump around 20–38� 2theta, crystalline phases ofquartz (SiO2), anorthite (CaAl2Si2O8), auguite (Ca(Mg,Fe,Al)(Si,Al)2O6), calcium carbonate (CaCO3), ferric oxide (Fe2O3) and gyp-sum (CaSO4�2H2O). When ground BA was mixed with alkali solu-tions and promoters, the glassy phase was dissolved to form anew phase of alkali aluminosilicate gel. This is confirmed by a shiftof broad hump peak at around 25-35� 2theta which is similarlyfound in FA geopolymer [45–47]. The presence of amorphousphases are generally corresponded to the coexist between calciumsilicate hydrate (C-S-H) and sodium alumino silicate hydrate (N-A-S-H) as reported by Escalante-Garcia et al. [48]. As mentioned in[49], the additional C-S-H is essential for an increasing of thestrength development of geopolymer matrix. With regard to effectof calcium promoters, the 70BA30PC paste (Fig. 4b) illustrates areduction in crystal phase compared to the 70BA30CCR paste(Fig. 4c). In 70BA30PC paste, C-S-H is found and anorthite existingin BA disappears, but its pattern still has peaks of quart, calciumcarbonate, and ferric oxide. While, the anorthite and strong peakof calcium carbonate are still found in 70BA30CCR paste.

3.3. SEM analysis

The SEM photos of hardened BA geopolymer paste with calciumpromoters cured at 28 days are illustrated in Fig. 5. The 100BApaste (Fig. 5a) contains a number of nonreacted and/or partiallyreacted BA particles embedded in a continuous matrix. For themixes with promoters (Fig. 5b and c), the pastes show densematrix with additional reaction products within geopolymer sys-tem. This is because the samples containing PC provide additionalhydration products generating by the chemical reaction of PC andwater as seen in Fig. 5b. While, CCR is mainly comprised of calciumhydroxide (Ca(OH)2), which reacts with SiO2 and Al2O3 from BAthrough pozzolanic reaction and create C-S-H and C-A-S-H gelcoexisting with N-A-S-H as reported by Ismail et al. [50]. This leadsto the overall improvement in strength development as shown inFig. 3. These results also agree well with the previous studies[11,12,15,51]. For the photo of the 70BA30PC paste (Fig. 5b), thepaste exhibits a denser matrix than that of the 70BA30CCR paste(Fig. 5c) because the hydration products from tricalcium silicate(C3S), dicalcium silicate (C2S), and water taken place in 70BA30PCaccelerate the geopolymerization process [49]. Hence, the use of PCcan improve compressive strength of BA geopolymer matrix.While, the geopolymerization mechanism in 70BA30CCR is mainlydue to Ca(OH)2 as previously described.

3.4. FTIR analysis

FTIR spectroscopic was used to study the geopolymerizationdegree of BA geopolymer paste with calcium promoters at

28-day age as illustrated in Fig. 6. All samples are located in therange between 400 and 4000 cm�1. The distinct band is essentialfor the understanding of reaction products within geopolymermatrix. The results of FTIR spectra changed in both of spectra bandand wave number from ground BA to the 70BA30PC and the70BA30CCR pastes. It is implied that ground BA can react with cal-cium oxides from PC and CCR in alkali system. The broad bands arelocated at approximately 3450 and 1650–1600 cm�1 indicated toO-H stretching and O-H bending of water molecule [6,52]. Thepresence of structural water when the starting materials reactedwith alkali solution in mixture [45,53], could be observed in

4006008001000120014001600180020002200240026002800300032003400360038004000

Wavenumber (cm-1)

(a) ground BA

(b) 100BA

(c) 90BA10PC

(d) 80BA20PC

(e) 70BA30PC

(f) 90BA10CCR

(g) 80BA20CCR

(h) 70BA30CCR

3405.01448.0

1620.9

874.0967.6

430.5670.5

3312.5 1640.9 1396.9

946.5

432.8

3251.11641.6

1389.9

947.9

3255.2 1639.2 1396.7

946.3

434.5

3233.0 1639.1

960.6

1386.4

432.83288.6 1642.5 1388.0

964.6

430.7

3258.731641.4 1393.4

955.8

3245.81639.9 1390.4

939.8

Fig. 6. FTIR spectra of ground BA and BA geopolymer pastes with promoters at 28 days.

S. Hanjitsuwan et al. / Construction and Building Materials 133 (2017) 128–134 133

Fig. 6c–h. The wave number range between of 1200 and 950 cm�1

can be attributed to the Si-O-Si and Si-O-Al stretching vibration[45,53]. This wave number indicates the degree of geopolymeriza-tion within the matrix and is more prominent than that of O-Si-Obending mode as reported by Chindaprasirt et al. [6]. This isbecause the O-Si-O bending mode near 460 cm�1 represents theremain of unreacted quartz in mixture [54]. The carbonate(CO3

2�) band can be observed at around 1400–1450 cm�1 especiallyin BA-CCR geopolymers (Fig. 6f–h). At 670 cm�1, it is indicated thatS@O in BA is similar as found in the XRD results which show thepresence of gypsum (CaSO4�2H2O) [54]. With regard to effect ofpromoters, the BA-PC geopolymers (Fig. 6c–e) exhibits less in theO-H stretching, O-H bending, and carbonate compared to the BA-PC geopolymers (Fig. 6f–h). The reduction in water molecule andcarbonate in the 70BA30PC paste is the main reason for the highercompressive strength gain. In addition, the presence of carbonatepotentially results in the carbonation as reported by Barbosaet al. [53] and Chindaprasirt et al. [6]. The results from FTIR spectraanalysis corresponded well with the compressive strength andmicrostructure analysis results.

4. Conclusion

This study presents the comparative study on the use of Port-land cement (PC) and calcium carbide residue (CCR) as a promoterin BA geopolymer mortars (BAGMs). The study shows that PC andCCR are suitable promoters for enhancing the strength develop-ment of BAGMs. The results of compressive strength andmicrostructure investigation via XRD, SEM and FTIR analyses showthat the use of PC as a promoter provides more reaction productsand degree of geopolymerization than that of CCR. The CCR ismainly consisted of calcium hydroxide (Ca(OH)2) while the majorcomponents of PC are Tricalcium Silicate (C3S) and Dicalcium Sili-cate (C2S). The reaction between PC and water creating hydrationproducts, whereas the samples containing CCR can react with

SiO2 and/or Al2O3 existing in BA and form pozzolanic reactionproducts. This is the main reason why these two promoters pro-vide additional strength for geopolymer matrix. It is also foundin the present study that the use of PC shows less in carbonatecompared to those of CCR geopolymer. The relatively high com-pressive strength of BAGM can be obtained with the replacementof 30%PC, which is 13.8 MPa. While, the use of CCR as a promoterat 30% by weight of binder gives the compressive strength of11.4 MPa. These BAGMs with 10% to 20% of promoter replacement,PC and CCR, meet the strength requirement to be considered asnon-load bearing whereas 30%PC and 30%CCR geopolymer samplesare satisfied the strength requirement for load bearing brickmasonry units as specified by ASTM standards. Furthermore, theoutcome of this research can play a significant role in divertingof waste materials from landfills and considerably reduce carbonemissions due to PC production industry.

Acknowledgements

The authors gratefully acknowledge the financial support fromFaculty of Industrial Technology, Lampang Rajabhat University(Grant no. 008/2559); the National Research Council of Thailand(NRCT) under Lampang Rajabhat University (Grant no.006/2559); the TRF New Research Scholar, Grant no.MRG5580222; and European Commission Research ExecutiveAgency, via a research grant (H2020-MSCA-RISE-2015-689857).The authors also would like to acknowledge the support of the Pro-gram of Civil Technology, Faculty of Industrial Technology, Lam-pang Rajabhat University.

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