effect of water-binder ratio and naoh molarity … · an early age and at least 30 mpa at 28 days...

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International Journal of Civil Engineering and Technology (IJCIET)

Volume 9, Issue 10, October 2018, pp. 1339–1352, Article ID: IJCIET_09_10_134

Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=9&IType=10

ISSN Print: 0976-6308 and ISSN Online: 0976-6316

©IAEME Publication Scopus Indexed

EFFECT OF WATER-BINDER RATIO AND

NAOH MOLARITY ON THE PROPERTIES OF

HIGH CALCIUM FLY ASH GEOPOLYMER

MORTARS AT OUTDOOR CURING

Sani Haruna

Department of Civil and Environmental Engineering, Universiti Teknologi PETRONAS,

32610, Bandar Seri Iskandar, Perak, Malaysia

Department of Civil Engineering, Bayero University Kano, PMB 3011, Kano, Nigeria

Bashar S Mohammed



Muhd Shahir-Liew



Wessam Salah Alaloul



Abdulrahman Haruna



ABSTRACT

In this article, strength development high calcium fly ash geopolymer mortar

cured at ambient temperature was investigated. The outcome of HCFA fly ash

geopolymer mortars on the flow ability and strength improvement of geopolymer

mortars were predicted by an established statistical models using response surface

methodology (RSM). The ambient cured geopolymer mortars were triggered with a

solution of sodium hydroxide (NaOH) and sodium silicate. The investigation reveals

that increase in alkaline solution to binder ratio reduces the compressive strength of

the mortars and subsequently improves the workability. All the geopolymer mortars

were able to achieve more than 15 N/mm2 at an early age. At 28 days curing, the

compressive strength of outdoor curing range between 30 to 70 N/mm2 for all the

mixes. All the models developed appeared to be significant with percentage error of

less than 5%. The predicted and real data’s were found to be in good agreement. It

Effect of Water-Binder Ratio and Naoh Molarity on the Properties of High Calcium Fly Ash

Geopolymer Mortars at Outdoor Curing


was also observed that the setting time of the designed geopolymer mortar increases

at higher concentration of NaOH for both final and initial setting time. This makes

high calcium fly ash suitable for repair and cast in situ applications as it exhibit

enhanced early age strength growth in comparison with low calcium fly ash

geopolymers.

Key words: Geopolymer mortar, molarity, water-binder ratio, response surface.

Cite this Article: Sani Haruna, Bashar S Mohammed, Muhd Shahir-liew, Wessam

salah Alaloul, Abdulrahman Haruna, Effect of Water-Binder Ratio and Naoh Molarity

on the Properties of High Calcium Fly Ash Geopolymer Mortars at Outdoor Curing,

International Journal of Civil Engineering and Technology (IJCIET) 9(10), 2018, pp.

1339–1352.

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=9&IType=10

1. INTRODUCTION

Development of geopolymer binder as a substitute cement less binder to OPC was one of the

important findings in the field of concrete technology in the 20th century. Geopolymer

technology is a new approach of concrete production by exclusion of ordinary Portland

cement entirely with pozzolanic material. Davidovits initially introduced the term

geopolymer. Geopolymer is an inorganic alumino-silicate polymer synthesized mainly from

silicon and aluminium ingredients like fly ash, Metakaolin, GGBS, rice husk ash, etc. It can

be synthesized with low energy consumption process at room temperature or higher. Cement

production is energy consuming and yields greenhouse gas discharging product. Geopolymer

cements production releases less than 20% of CO2 greenhouse effect gas while Portland

cement releases immense CO2 to the surrounding environment [1].Geopolymers are gaining

wider attention as binders with low carbon dioxide emission compared to Portland cement.

Geopolymer also possess resembling and remarkable engineering properties compared to

cement. Over the past three decades Geopolymer has been developed and its utilizations in

civil infrastructures begin to gain reputation by replacing high-carbon concrete materials with

the greener material.

Production of geopolymer concrete does not require the use of any OPC but, the binder is

produce by the reaction of an aluminosilicate material with strong alkaline liquids. There is

rapid consumption of concrete due to increase in volume of the built environment as people

tends to migrate from rural to urban cities for socio-economic activities, this result in high

carbon dioxide emissions as a result of so many factors among which ordinary Portland

cement production is among the CO2 producers. It is evident that besides depleting the natural

resources in the production of OPC huge quantity of carbon dioxide was emitted to the

surrounding atmosphere. To mitigate these effects a substitute green materials is required. It is

therefore, essential to utilize a substitute materials for the production of environmental

favorable concrete [1]. Collectively, geopolymer cement gel binds the aggregates and

unreacted material to yield Geopolymer concrete [2, 3]. It is worth mentioning that

geopolymer cements production releases 80 to 90% less CO2 (greenhouse effect gas) as

compared to Portland cement production.

Geopolymer technology display distinguished achievement for utilization in concrete

production as a substitute binder to the Portland cement [4]. With regard to global warming,

the scientific knowledge of geopolymer could aid greatly to lower the CO2 discharge to the

surrounding environment produced by the cement companies [5]. Adoption of green materials

for construction of infrastructure will reduce the carbon footprint and would be helping the

surrounding environment. The requirement for elevated temperature curing of the geopolymer

Sani Haruna, Bashar S Mohammed, Muhd Shahir-liew, Wessam salah Alaloul, Abdulrahman Haruna


concrete makes it a challenge for mass production which limits its application to only precast

applications[6]. Notwithstanding the reality that geopolymer system was established over a

set of decades in the past and has numerous beneficial attributes, yet it is not been utilized in

concrete broadly as compared to Ordinary Portland cement. Broad utilization of low calcium

fly-ash geopolymers is limited owing to its constraints such as slow hardening, high porosity

and following slow strength growth. However, various researchers [7-10] reported the

potential to produce ambient cured geopolymer with high calcium fly ash as the primary

ingredient. The HCFA mortar can be cured at outdoor temperature due to the presence of high

percentage of calcium in the structure.

This study explores the properties of high calcium fly ash-based geopolymer mortar under

outdoor curing mode by performing workability, compressive strength and evaluating their

uncovered relationships. This article reports the outcomes of investigation that deals with

compressive strength, final and initial setting time of geopolymer mortar at ambient curing

mode. High calcium fly ash was utilized as the primary ingredient and activated with an

alkaline solutions to produce the geopolymer mortar at three various molar concentration of

NaOH that is 10M, 14M and 16M respectively. The proportion of sodium silicate to sodium

hydroxide is maintained as 2.

2. EXPERIMENTAL METHODS

2.1. Materials

High calcium fly ash was utilized as the primary binder in this investigation. The chemical

constituents of the fly ash was obtained by X- Ray fluorescence (XRF) and presented in table

1. The alkaline stimulator used in this work was a coalescence of sodium silicate and sodium

hydroxide solutions. Sodium hydroxide solution was formed by dissolving the NaOH pellets

in potable water. Three various solutions of 10 M, 14 M and 16 M concentrations were

processed and stabilize at ambient condition a day prior to mixing. The sodium hydroxide and

sodium silicate solutions were combined at various mass ratios prior to be used in the

preparation of mortar specimens. Locally obtainable river sand of 2.61 specific gravity was

utilized as fine aggregate.

Table 1 High calcium Fly Ash Chemical Composition

Oxide Percentages (%)

SiO2 25.9 %

Al2O3 12.30 %

Fe2O3 32.20 %

CaO 20.9 %

MgO 2.08 %

SO3 0.7 %

K2O 2.8 %

Na2O 0.26 %

LOI 2.86

2.2. Experimental Procedures

The high calcium fly ash was supplied from the manjung power plant Perak Malaysia.

Sodium hydroxide (NaOH) with purity of more than 98% and sodium silicate solution

(29.43% of SiO2, 14.26% of Na2O and 56.31% of H2O by mass ratios) was supplied by Sino

chemicals industry Malaysia and utilized as the alkaline actuator, triggering the activation of

the fly ash. Foregoing investigations disclosed that mixing an alkaline solution with sodium

silicate of, 9–10% of Na2O and 30% of SiO2 with a solid composition of about 40% and a




density of 1.39 g/cm3 can trigger the geopolymerisation process greater than the use of a

lonely alkaline actuator [11-13]. Geopolymer mortar was produce from high calcium fly ash

to sand ratio of 1:2. The mix parameters were concentration of sodium hydroxide and ratio of

alkaline solution to binder as presented in Table 2. HCFA was mixed with the alkaline

solutions at 0.5, 0.55, and 0.6 alkaline solution to HCFA ratio for all the mixes. The HCFA

was then mixed with the alkaline solutions in an automatic Hobart mixer for about 2 minutes.

Sand was then added into the mixer and mixed continuously for 3 more minutes until a

homogenous mix was obtained. The wet geopolymer mortars produce are unified and flow

able. Conventional vibrating table was employed for compaction of the mortar. Steel cube

molds of dimension 50 mm are used for casting mortar specimens. The specimens were

removed from the molds after 24 hours and cured outdoor. In open-air curing, the specimens

are left out-door until stipulated period of testing. Control of temperature and humidity are not

essential for outdoor-cured samples. Specimens are left alone in open-air until testing period

after casting. The parameters regarded in this investigation are: (i) modification in

concentration of sodium hydroxide solution as 10, 14, and 16M; (ii) variation in solution to

binder ratio.

The setting time of the geopolymer mortar was also examined in conformity to ASTM

C807 [14]. The fresh mortars were designed with a unique sodium silicate to sodium

hydroxide proportion of 2 and cast in 50mm cubes and then cured at an ambient temperature.

Then, the specimens were remove from the molds and kept outside on the shelve and tested

for compressive strength on 3, 7, and 28 days. At least 3 specimens were tested and the mean

values were recorded at each age. Flow table was used to obtain the flowability of the fresh

geopolymer mortars based on ASTM standards C230[15], each mix was examined twice and

the average value was recorded.

Table 2 Mix proportions of HCFA geopolymer mortars

Mix. No. Fly ash Sand Na2SiO3 NaOH

NaOH

Molarity Soln/binder

ratio [g] [g] [g] [g] [M]

M1 270 540 90 45 10 0.5

M2 270 540 90 45 14 0.5

M3 270 540 90 45 16 0.5

M4 270 540 99 49.5 10 0.55

M5 270 540 99 49.5 14 0.55

M6 270 540 99 49.5 16 0.55

M7 270 540 108 54 10 0.6

M8 270 540 108 54 14 0.6

M9 270 540 108 54 16 0.6

Table 3 RSM boundaries of variables

Factor code units Levels

-1 0 1

Molarity of NaOH A M 10 14 16

s/b ratio B 0.5 0.55 0.6



Table 4. Established experimental mix design and responses of geopolymer mortars

Run

Factors

Responses

Coded Values

Actual Values

A:

molarity of

NaOH

B: w/b

ratio

A:

molarity of

NaOH

B: w/b

ratio

Compressive

strength (MPa)

Flowability

(mm)

1 0 0

14 0.55

46.7 37

2 -1 0 10 0.55 55.25 41

3 0 0 14 0.55 47.25 38

4 1 -1 16 0.5 56.55 25

5 0 0 14 0.55 47 39

6 0 1 14 0.6 38.75 75

7 0 -1 14 0.5 60.75 30

8 -1 1 10 0.6 43.85 78

9 -1 -1 10 0.5 68.25 37

10 0 0 14 0.55 45.75 38

11 0 0 14 0.55 47.35 40

12 1 1 16 0.6 30.25 66

13 1 0 16 0.55 42.65 30

3. RESULT AND DISCUSSION

3.1. Flowability of Fresh Geopolymer

The flowability of the geopolymer mortar was reliant on the concentration of NaOH and the

proportion of solution to fly ash ratio as portrays in Table 3. Increasing the ratio of solutions

to fly ash of the geopolymer mortar result in an acceptable flowability while at lower solution

to binder ratio, the mix becomes stiffer. Similarly at particular solutions to fly ash ratio, the

workability of the mix reduces with an increase in sodium hydroxide concentration. This is

attributed to the higher molecular weight of the NaOH which makes the solution more viscous

and hence reduced the workability of the mix. Practically, at higher NaOH concentration the

flow resistance of the mix improved and therefore retrenches the flowability[16, 17]. As

shown in figure 3, mixes with higher alkaline concentration were much thicker than that of

lower concentration at a specific solution to binder ratio. The workability range from 25 mm

to 78 mm at lower and higher solution to binder proportion. The flow of the geopolymer

mortar at 0.5 alkaline solution to binder ratio decreases by 18.92% from 10M to 14 M NaOH

and the percentage doubles at 16 M NaOH concentration. Moreover, at 0.55 solution to binder

ratio the flow reduces 9% from 10 M to 14 M NaOH and also the percentage doubled at 16 M

NaOH molarity. The workability follows the same pattern at higher alkaline solution to binder

ratio.

3.2. Setting Time of Geopolymer Mortar

Setting time attributes of HCFA geopolymer mortars were investigated by modifying sodium

hydroxide concentration and alkaline solution to binder ratio. Setting time disclosed in this

article is the setting time of the designed geopolymer mortar. The methodology considered is

identical to that of OPC mortars. The changes in setting time of geopolymer mortars with

respect to NaOH concentration for various mixes of HCFA is depicted in table 3. The initial

setting time of the various mixes recognized in this investigation ranges from 55 to 132

minutes for all the mixes while the final setting time varied from 85 to 193 minutes. It was

also observed that the setting time of the designed geopolymer mortar increases at higher

concentration of NaOH for both final and initial setting time.

Furthermore, the setting time increases with an increase in solution to fly ash ratio. At

lower concentration of NaOH, the final setting occurred just immediately in less than 1 hour




after the initial setting time for almost all the mixes. However, the setting behaviour is directly

proportional to the alkaline solution to binder ratio for all the mixes.

3.3. Compressive Strength

Compressive strength growth of various geopolymer mortar combinations were evaluated up

to 28 days of outdoor curing. Figure 2 shows the results in form of 3D response surface plot

of 28-day compressive strength of HCFA geopolymer mortars at various mix parameters. The

results shown in figure 2 are the mean value of three specimens tested at the test age. It is

worth to mention that all the geopolymer mortars were able to achieve more than 15 MPa at

an early age and at least 30 MPa at 28 days outdoor curing was achieved for all the mixes.

The highest strength occurred at 10 M NaOH concentration at 0.5 solution to binder ratio.

However, the flowability of the mix becomes stiff at this ratio. Higher concentration of NaOH

solution yields to decrease in compressive strength similar to the known circumstance

reported by [18-20]. It is also noticed that increasing the concentration of NaOH from 10 to

16 M improved the strength by almost 17% and at the same time decreasing the flow of the

mixes by 37%. Similarly same pattern of strength improvement were observed on all the

mixes. This is anomalous to the known behaviour of class F fly ash geopolymers in which

strength was improved as the concentration of NaOH is increased. This findings are in

consistence with the work of [21].

Figure 1 Compressive strength of HCFA geopolymer mortars

3.4. Effect of Alkaline Solution to Binder Ratio

It is observed that altering the solution to binder ratio affect the compressive strength. At

higher solution to binder ratio the strength decreases due to the excess amount of alkaline

solution in the mixes and therefore, showed similar behaviour with that of OPC mortars this

study is in agreement with that of Nath [22] . The excess alkaline solution in the mix result in

providing additional OH- ions to the geopolymer mortar which later react with calcium to

form calcium hydroxide and thus, decrease its strength [21]. It is noted that geopolymer

mortars at ambient temperature with high humidity suffered intense efflorescence, but curing

at outdoor temperature reduces the rate of efflorescence on the surface of the mortars due to

the rapid dry of the moisture on the surface of the mortars.

0

10

20

30

40

50

60

70

80

M1 M2 M3 M4 M5 M6 M7 M8 M9

com

pre

ssiv

e s

tre

ngt

h (

MP

a)

Mixes

compressive strength [Mpa] compressive strength [Mpa] compressive strength [Mpa]



Moreover, surplus amount of Na+ ions in the mix react with CO2 within the surrounding to

form a white precipitate on the surface of the specimens which significantly contributed to the

lower strength evolution at higher concentration and solution to binder proportions

particularly at ambient temperature. This is due to the fact that geopolymer mortars contains

higher soluble alkaline ions concentrations than Portland cement as such when it comes in

contact with water or at higher humidity efflorescence due occurred and this study is in

agreement with that of [23].

3.5. Statistical Models Analysis using RSM Design Experts

Statistical analysis was employed using Design of Experiment software which is commonly

known as response surface methodology (RSM). A response surface design is a set of

progressive statistical analysis procedures that aid researchers better perceive and optimize

their rejoinder. RSM is customarily used statistical approach for investigating and establishing

designs between solitary or more separate parameters and responses [24, 25]. RSM was has

been in used in various field of studies for models establishment and optimization of

mixtures. This technique is also used to examine the effect of independent variables and their

interaction effect on the dependent variable. Mohammed et al [26] predicted the compressive

strength of a blended paper concrete by using RSM and maximize the model using numerical

optimization, the research was supported by [27-29]. In recent studies by [24] used the RSM

to establish mix design models for roller compacted concrete. They have further optimized the

RCR mixtures by minimizing the water absorption and enhancing the strength. Table 3 and 4

represents the RSM boundaries of variables and established experimental mix design and

responses of HCFA geopolymer mortars respectively.

Table 5 Anova response models

Responses factors S.S Df M.S F-Value P-Value Remark

Compressive

strength(MPa) Model 1141.18 5 228.2368 173.4354

3.53E-

07 significant

A-molarity of

NaOH 0.68 1 0.68 0.51 0.4966

B-w/b ratio 15.34 1 15.34 11.65 0.0112

AB 0.32 1 0.32 0.24 0.636

A

2 2.68 1 2.68 2.04 0.1963

B

2 9.92 1 9.92 7.54 0.0287

Lack of fit 7.55 3 2.52 6.08 0.0569 insignificant

Flowability(mm) Model 3560.53 5 712.11 378.61 < 0.0001 significant

A-molarity of

NaOH 14.06 1 14.06 7.48 0.0292

B-w/b ratio 533.95 1 533.95 283.89 < 0.0001

AB 0.19 1 0.19 0.1 0.7596

A

2 40.52 1 40.52 21.55 0.0024

B

2 622.86 1 622.86 331.16 < 0.0001

Lack of fit 7.97 3 2.66 2.04 0.2506 insignificant

Df: degree of freedom,: P: Probability; F: Fisher statistical value; SS; sum of squares; MS: mean square

Analysis of variance was used to evaluate the connections between the independent

variables and their responses as depicts in Table 5. Level of significance of 5% was adopted

to assess the importance of the model. All models are choose according to the highest level in

which the supplementary terms are important and not aliased by the RSM software. P-values

of less than 0.05 was obtained for all the response models, consequently, all the models are

significant at 95% confidence level as shown in Table 5. The desirability function was

established after establishing the response surface for each dependent variable through a




regression model. The quality of the model was assess based on the lack of fit, the smaller

lack of fit value indicates models worthiness. As noticed in Table 5, the lack of fit P-value for

all the models was more than 0.05 i.e. (0.0569 and 0.2506), which indicates insignificancy,

and thus implies excellent fitness for all the models response. The relationships and effects

between the variables (molarity of NaOH and w/b ratio with regards to their real values) and

the responses was achieved by the analysis of variance and presented in equations 1 & 2.

Similarly, the difference between predicted R-squared and adjusted R-squared for individual

response was less than 0.2 and the response models can therefore be describe to be in good

aggrement with each other as depicts in table 6.

As illustrated in Figure. 1, data points are nearly coincided with straight line and the

predicted against Actual plot is nearly 45° and therefore, the predicted values are in good

agreement with real values. The three dimensional graph showing the synergistic effect of

NaOH molarity and water-binder ratio on the compressive strength and flowability were

presented in figure 2 and 3. Similarly, the 2D contour plots are also presented and the contour

lines appeared nearly incline in figure 2 indicating less interaction while in figure 4, the 2D

contour plots appeared elliptical implying an excellent interaction between concentration of

NaOH and w/b ratio in flowability response while the interaction is very weak in terms of

compressive strength represented by a straight contour lines as depicts in figure 2.

Perturbation plot is shown in Figure 5 represented by factor, A (NaOH molarity) and B (w/b

ratio) with a Steep inclination illustrating the sensitivity of both factors.

Figure 2 Measure of concurrency between experimental and predicted plots for the establish models

(1)

(2)



Table 6Validation of response model

Response Compressive

strength (MPa)

Flowability

(mm)

standard deviation 1.15 1.37

mean 48.49 44.15

C.V % 2.37 3.11

R2 0.992 0.9963

Predicted R2 0.9424 0.9768

Adjusted R2 0.9863 0.9937

Adequate precision 47.225 57.907

(a) 3-dimensional response (b) Fig. contour plot

Figure 3 Compressive strength against molarity and w/b ratio

(a) 3-dimensional response (b) contour plot

Figure 4 Flowability versus molarity and w/b ratio




Figure 5 Perturbation plot for the established model

Figure 6 Ramps of numerical multi- objective optimized mix

3.6. Optimization

In this findings Multi-objective optimization was accomplished using numerical method to

obtain the desired values of molarity and water binder ratio for achieving maximum

compressive strength within the flowability range. The main purpose of the optimisation was

to findout the suitable combination of independent parameters (molarity and water binder

ratio) and maximising the performance properties of the mortars. The optimized range of

variables and responses was depicted in Table 7.

A:Molarity of NaOH = 10

10 16

B:w/b ratio = 0.5

0.5 0.6

Compressive strength = 68.2221

30.25 68.25

Flowability = 36.0772

25 78

Desirability = 1.000



Table 7 Optimization bench mark

Variables and responses purpose lower

limit upper limit

molarity of NaOH (M) minimize 10 16

w/b ratio in range 0.5 0.6

compressive strength(MPa) maximise 30.25 68.25

flowability (mm) in range 25 78

The numerical optimisation outcomes for the established models are shown table 8. Five

different solutions were obtained from the response surface optimisation process and the best

desired mix combinations was selected base on the highest desirability. Therefore, 10 M

sodium hydroxide concentration with 0.5 w/b ratio was chosen to yield maximum

compressive strength within the range of flowability with combined desirability of 1. The

independent variables and responses are illustrated by ramps of optimisation in Figure 6. To

verify the appropiatness of the optimization results and the whole response models, additional

set of experiments were conducted using the enhanced mixture proportions and different

concentration of NaOH and w/b ratio to validate the optimised mixture proportion within the

design mixes. The error between experimental and predicted values was calculated using

equation 3 and express in percentage.

(3)

The percentage error variation was found to be less than 5% in all the responses evaluated,

implying that the predicted values for the established models are in good understanding with

the experimental datas. The outcomes of the optimisation and percentage error are pointed out

in table 8.

Table 8. Model verification

Responses solutions

NaOH

Molarit

y(M)

w/b

ratio

Predicted

outcomes

Experimenta

l outcomes

Error

(%)

Compressive strength

(MPa) 1 10 0.5 68.22 66.55 2.51

2 14 0.55 49.45 47.73 3.6

3 16 0.5 58.35 57.01 2.35

Flowability (mm) 1 10 0.5 36.08 37.5 3.79

2 14 0.55 41.5 40 3.75

3 16 0.5 25.33 24.5 3.39




4. CONCLUSIONS

In this study, 13 mortar mixes were obtained using RSM with five duplications at various

parameters. Workability, compressive strength and effect of solutions to fly ash ratio were

envisaged. The results showed that increasing the solution to fly ash ratio reduces the strength

of the geopolymer mortars and consequently improved the flowability of the mortars.

Furthermore, higher concentration of NaOH result in worsening the compressive strength

result at outdoor curing. All the geopolymer mortars were able to achieve more than 15

N/mm2 at an early age and at 28 days curing, the compressive strength of outdoor curing

range between 30 to 70 N/mm2 for all the mixes. The outcomes of the RSM investigation

shows a strong correlation between the established models and their counterpart experimental

values as all possessed quadratic relationships, with a higher degree of correlations. All the

models developed appeared to be significant with percentage error of less than 5%. The

predicted and real data’s were found to be in good agreement.

It can also be concluded that high calcium fly ash can be utilized for repair works as it

exhibited high early strength development at early age without the application of heat.

However, the issue related to efflorescence formation at ambient curing need to be addressed.

ACKNOWLEDGEMENTS

The authors would like to admit the assistance offers by Universiti Teknologi PETRONAS,

Malaysia for the research financial support.

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effect of water-binder ratio and naoh molarity … · an early age and at least 30 mpa at 28 days...

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