Controlling natural resources depletion through Montmorillonite replacement for cement-low cost construction

Construction and Building Materials 232 (2020) 117188

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Controlling natural resources depletion through Montmorillonite replacement for cement-low cost construction Safi Ur Rehman, Usman Ahmed Kiani, Muhammad Yaqub, Tariq Ali ⇑ Department of Civil Engineering, University of Engineering & Technology Taxila, Pakistan

h i g h l i g h t s
Karak Montmorillonite (K-M) fulfil all the requirements to be used as natural pozzolana.
Karak Montmorillonite (K-M) clay can be used as Supplementary cementitious material for low cost concrete.
Initial and final setting time are increased by using K-M clay as cement replacement.
Porous structure of the concrete can be improved by incorporating K-M clay.
K-M can improve the durability properties of concrete against chemical attacks.

a r t i c l e

i n f o

Article history: Received 23 October 2018 Received in revised form 17 September 2019 Accepted 6 October 2019

Keywords: Bentonite SAI Workability Permeability Acid Attack Sulphate Attack Carbonation pH Karak-Montmorillonite

a b s t r a c t This research is aimed to evaluate Montmorillonite clay (commercially known as Bentonite clay) available in Karak, 33°70 1200 N 71°50 410 0 E, (KPK, Pakistan) as cement replacement material. In this study the clay was incorporated (5%, 10%, 15%, 20%, and 25%) by mass of cement keeping other constituents of concrete constant. The morphology of Karak-Montmorillonite was studied using Scanning Electron Microscope (SEM). All samples of K-M satisfied the Strength Activity Index (SAI) requirements of ASTM C 618. Results revealed that workability of concrete decreased with an increase of K-M content. Consequently, initial and final setting time was increased. The mechanical compression and Nondestructive testing (NDT) were performed to evaluate the compressive strength. The results disclosed that increase in K-M content significantly reduced the compressive strength. Concrete with 15% K-M gave competent results relative to control mix. The tensile and flexural strength of concrete also decreased with the increase of K-M content. Concrete with K-M as replacement for cement showed better performance in durability tests i.e. water absorption, permeability, acid attack, sulphate attack, carbonation test and pH test. Acid and salt cured samples containing K-M performed better than normal control samples. Utilization of the Karak-Montmorillonite (K-M) as cement replacement is low-cost, eco-friendly and produce durable concrete. Ó 2019 Elsevier Ltd. All rights reserved.

1. Introduction Now a days a great deal of construction is going on in Khyber Pakhtunkhwa province of Pakistan due to natural and man made hazards in last two decades. Earthquake, floods and imposed terrorism resulted in the severe damage of different concrete structures throughout the region [1]. Rehabilitation work is going on a large scale in the region, which demands for the low cost, durable concrete materials [2]. The most expensive construction material ⇑ Corresponding author. Tel.: +92 314 9894986. E-mail addresses: [email protected] (S.U. Rehman), [email protected] (U.A. Kiani), [email protected] (M. Yaqub), [email protected] (T. Ali). https://doi.org/10.1016/j.conbuildmat.2019.117188 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.

for concrete is cement, thus alternatives for cement is highly desired in order to produce low cost concrete [3]. Cement industry is considered in the primary list of industries, which are producing greenhouse gases. The previous studies indicate that cement industry contribute almost 7% to the total carbon dioxide production annually. Furthermore energy (1.6 MW h) is required for the production of one ton cement [4,5]. In order to cater the above mentioned problems, it is necessary to explore all the available options of natural pozzolans available in the region. In the past several studies were made in order to evaluate different industrial waste such as fly ash, bagasse ash and rice husk ash etc. as an alternative binding material for the concrete [6– 8]. Different clays possess pozzolanic characteristic depend upon the clay mineral types and has a long history of being used as an

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admixture and binding material for concrete [9]. Based upon clay minerals there are Kaolinite, Smectite, Illite, Chlorite & Vermiculite clay groups [10]. Montmorillonite belongs to smectite group of clay. It has a three layered structure, where two tetrahedral layers sandwiches an alumina octahedral layer [11,12]. Most of Montmorillonite in Pakistan is widely deposited in Khyber Pakhtunkhwa Province. One of the Montmorillonite mine explored in this study is situated in Karak, 33°70 1200 N 71°50 4100 E, Pakistan. It is estimated that in district Karak there are approximately 36 million ton of Montmorillonite clay exists [13]. 2. Experimental program Fig. 1. Karak-Montmorillonite (K-M) used in the research.

2.1. Materials used 2.1.1. Cement Locally available cement (Fauji Brand) was used in the research conforming to ASTM standard C150-07 (ASTM, 2009). In order to detect any uncombined lime in cement, Soundness test was done on the cement. Cement have specific gravity of 3.14, fineness modulus of 3198 cm2/gm and consistency of 30%. All the other properties are depicted in Table 2. Fig. 2. XRD pattern of Karak-Montmorillonite (K-M) used in the research [2].

2.1.2. Fine and coarse aggregate Fine aggregates used were collected locally form Lawrencepur, the sand used was having fineness modulus of 2.45, specific gravity of 2.71 and water absorption of 1.22%. For coarse aggregates, Margalla mine aggregates were chosen, having specific gravity of 2.685 and water absorption of 0.8%. As per ASTM C136-06 sieve analysis of fine and coarse aggregates has been done and shown in Table 1. 2.1.3. Montmorillonite/Bentonite clay Montmorillonite/Bentonite clay was obtained from district Karak, (KPK, Pakistan) which contains million tons of such minerals as shown in Fig. 1. The XRD pattern of the Pakistani Montmorillonite (K-M) is reported by Mirza et al [2]. Both the crystalline minerals and amorphous phases were reported in the XRD pattern of the K-M as shown in the Fig. 2. K-M after collection were passed through ball mill for proper grinding, then passed through sieve #200 and packed in polythene bags. Karak-Montmorillonite (K-M) were made moisture free & dried in the oven up to 100 °C. Properties of K-M are illustrated in Table 2. As per ASTM C618-08, K-M meets the requirements for natural pozzolana to be used as binding material. 2.2. Mix design and preparation of test samples For Strength activity index mortar cubes of 50 mm  50 mm  50 mm were cast. The cement-to-sand ratio of 1:3 was used with

water-to-Binder = 0.45. Concrete mixes (cement: sand: coarse aggregates ratio = 1:2:4, commonly used in Pakistan) were prepared using a constant W/B of 0.6. (B = Binder). Nomenclature of mixes is given in Table 3. For Compression test cylinders of 150 mm dia  300 mm height were cast as per ASTM C39. For split tensile test cylinders of 150 mm dia  300 mm height were cast as per ASTM C496, similarly for flexural strength test prisms of 100 mm  100 mm  500 mm were cast as per ASTM C293. Samples were prepared according to experimental program enlisted in Table 4. 3. Experimental results and discussions 3.1. Scanning electron microscope (SEM) Scanning electron microscope was used to find out the chemical composition of Karak-Montmorillonite by EDS (energy dispersive x-ray spectroscopy) listed in Table 2. An average EDS range is depicted as a plot of X-beam numbers versus vitality (in keV), vitality tops narrate the different components in the specimen. Fig. 3 shows the peaks of different chemicals in original graph. Scanning electron microscope images of different resolution are shown in Fig. 4. It shows that Karak-Montmorillonite has flaky, elongated, angular and sub angular shape particles and average

Table 1 Sieve analysis of fine and coarse aggregate. BS (mm or lm)

ASTM (No./inch)

Mass retained (g)

Retained percentage

Cumulative percentage passing

ASTM limits for percentage passing

Fine aggregate

4.75 mm 2.36 mm 1.18 mm 600 lm 300 lm 150 lm

# # # # # #

0 16 26 220 460 214

0 1.60 2.60 22.00 46.00 21.40

100 98.40 95.80 73.80 27.80 6.40

95–100 80–100 50–85 25–60 10–30 2–10

Coarse aggregate

25 mm 20 mm 9.5 mm 4.75 mm Pan

1 ¾ 3/8 3/16 Pan

0 45 2185 751 19

0 1.50 72.83 25.03 0.63

100 98.50 25.67 0.64 0

90–100 60–85 20–55 0–10

4 8 16 30 50 100

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S.U. Rehman et al. / Construction and Building Materials 232 (2020) 117188 Table 2 Chemical and physical properties of cement & Karak-Montmorillonite (K-M). Chemical Composition (%) Cement

K-M

Sodium oxide (Na2O) Magnesium oxide (MgO) Aluminum oxide (Al2O3) Silicon dioxide (SiO2) Potassium oxide (K2O) Calcium oxide (CaO) Titanium oxide (TiO2) Ferric oxide (Fe2O3) Sulphur tri oxide (SO3) (SiO2)+(Al2O3)+ (Fe2O3)

0.84 1.63 9.87 19 1.19 60 – 3.46 2.6 –

1.44 3.06 20.49 52.89 7.81 2.08 0.94 11.33 – 84.68

Physical Properties Materials specific gravity Average particle size Initial setting time Final setting time

3.06 20 mm 45 min 260 min

2.60 5–7 mm 206 min 38 min

ASTM C 618 Class N requirements 5 max

Fig. 3. Chemical Composition of the K-M clay (EDS). 70 min

3.2.3. Workability of concrete Slump test was performed as per ASTM C143 to measure the workability of concrete. Slump value was found to be decreasing with the increase of Karak-Montmorillonite. The possible decrease may be due to less density and higher fineness of substitution material. Workability of normal control mix was measured to be more than the mix with Karak-Montmorillonite, as shown in Fig. 7.

Table 3 Details of mixed design. Sr. No.

Mix ID

K-M % replacement with cement

Water to Binder Ratio

1 2 3 4 5 6

CM 5% BC 10% BC 15% BC 20% BC 25% BC

0% 5% 10% 15% 20% 25%

0.6 0.6 0.6 0.6 0.6 0.6

3.3. Mechanical properties of concrete 3.3.1. Strength activity index (SAI) As per standard ASTM C618, for any material to be considered as pozzolanic, its SAI should be minimum 75% of the average compressive strength of control cement mortars both at 7 and 28 days. The results show that all Karak-Montmorillonite samples having more than 75% compressive strength of control cement mortar confirming the ASTM C618 standard for all replacements levels (5% to 25%) but the specimens at all levels of replacement show lower strength than that of control specimen. At 15% replacement level, the strength of Karak-Montmorillonite concrete found to be more at all ages, than that of all other replacement levels (Fig. 8). At 15% replacement level of Karak-Montmorillonite, the increase in compressive strength of mortar cube is due to the maximum pore filling and packing effects. After 7 days reduction in strength for different levels (5%, 10%, 15%, 20% & 25%) of replacement as compared to control mix was found to be 8.56%, 7.2%, 6.3%, 17.1%, & 21.25% respectively, while after 28 days reduction in strength was found to be 7%, 6.2%, 5%, 14%, & 17% respectively. The results also show that at 28 days SAI values are more than that of 7 days values as the pozzolanic reaction takes place initially at slower rate. Marsh and Day in 1988 reported that pozzolans are not effective at initial ages and they start to be active somewhere near after 14 days of casting. The trend of the results are same like the previous research done in past on different sources of Montmorillonite. It is also observed that the Montmorillonite contributes more to the delayed strength rather than early strength. Fig. 9 shows the higher values of SAI after 28 days.

size is 5–7 mm. The Karak-Montmorillonite particles shape and size resembles the cement particles to be used as replacement of cement in concrete. 3.2. Rheological properties of Karak-Montmorillonite concrete (K-M-C)/Bentonite concrete (BC) 3.2.1. Initial & final setting time Initial and final setting time tests as described in (EN1963:1987) were performed. Results (Fig. 5) show that both initial and final setting time increased with the increase in KarakMontmorillonite content, due to low heat of hydration of Montmorillonite [14]. 3.2.2. Consistency test Consistency test was performed as per (EN196-3:1987) with the help of Vicat’s apparatus. Consistency test results of normal and modified cement paste are shown in Fig. 6. The results illustrate that the consistency increases with the increase of KarakMontmorillonite content, due the increase in surface area of paste because of smaller particle size of Karak-Montmorillonite.

Table 4 Sample casting schedule and testing days. Test details

Specimen details

Compressive strength test SAI test Split/tensile Strength test Flexural Strength test Acid attack H2SO4 Acid attack HCL Sulphate attack Na2SO4 Permeability test Permeability test

Cylinders (150 mm u  300 mm) Cubes (50 mm  50 mm 50 mm) Cylinders (150 mm u  300 mm) Beams (100 mm  100 mm  500 mm) Cylinders (150 mm u  300 mm) Cylinders (150 mm u  300 mm) Cylinders (150 mm u  300 mm) Cylinders (100 mm u  150 mm) Cubes (100 mm 100 mm 100 mm)

Age (days)

Total for 1 mix

3

7

28

56

– – – – – – – – –

3 3 – – – – – – –

3 3 3 3 – – – – –

3 9 – 6 – 3 – 3 3 3 3 3 3 3 1 1 1 1 Grand Total

Total for 6 mixes

54 36 18 18 18 18 18 6 6 192

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S.U. Rehman et al. / Construction and Building Materials 232 (2020) 117188

7

80

6

70 Slump value (mm)

Time(hours)

Fig. 4. SEM images of Karak-Montmorillonite particles.

5 4

Initial setting

3

Final setting

2 1

60 50 40 30 20 10

0 CM

0

05%BC 10%BC 15%BC 20%BC 25%BC

CM

Fig. 5. Initial & Final setting time.

Fig. 7. Workability Test.

40

120

35

100

30 25

SAI value in %

Consistency values in %

05%BC 10%BC 15%BC 20%BC 25%BC

20 15 10 5

80 60 40 20

0 CM

05%BC 10%BC 15%BC 20%BC 25%BC Fig. 6. Consistency values.

0 CM

05%BC

10%BC

15%BC

20%BC

25%BC

Fig. 8. 7 Days SAI Values.

3.3.2. Compressive strength test Compressive strength test was performed on the cylinder of 300 mm height and 150 mm diameter at 7, 28 and 56 days as per ASTM C39. NDT testing both ultrasonic pulse velocity & Schmidt hammer test were also performed as per (ASTM C805, ASTM C597-02) in order to validate the results of 28 and 56 days compressive strength. The compressive strength results for 7, 28 and

56 days show that samples with Karak-Montmorillonite exhibit lower strength than that of controlled samples. Replacement level 15% of Karak-Montmorillonite shows higher compressive strength in comparison to other replacement levels at all ages (7, 28, 56 days) of testing. In this particular replacement level KarakMontmorillonite provides maximum packing reducing voids. Also

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Compressive strength (Mpa)

120 SAI value in %

100 80 60 40 20 0 CM

30 25

CM

20

5%BC

15

10%BC

10

15%BC 20%BC

5 0

05%BC 10%BC 15%BC 20%BC 25%BC

25%BC 0

20

40

60

Age (Days)

Fig. 9. 28 Days SAI values.

during hydration of cement a byproduct calcium hydroxide (CH) is produced. The K-M mixed with cement possess silica, so in the presence of moisture the silica component of the K-M react with the produced CH and form an additional calcium silicate hydrate (C-S-H) gel which helps concrete to gain more strength [15]. The overall results of compressive strength for all ages are depicted in Fig. 10. For all levels of replacement, the compressive strength was found to be increasing with the increase of curing period from 7 to 56 days. Fig. 11 shows the trend of compressive strength, corresponding to the different ages of concrete, while the Fig. 12, illustrate the relative decrease in strength with respect to the different levels of replacement. Schmidt hammer test result are shown below in Table 5, which includes R value of specimens. The compressive strength of specimens was found on a given graph of strength versus R or rebound hammer value in the laboratory manual of that instrument. Ultrasonic pulse velocity test was also performed for 28 and 56 days and the values of velocities were calculated from direct transmission of waves, which are tabulated in Tables 6 and 7. The Velocity flow rate depends upon the solidification of the concrete samples, higher velocity indicates the low porosity of the sample. By comparison of destructive and nondestructive testing a slight difference in results was found due to instrument limitations. Ultrasonic pulse velocity results were in good agreement with the original results obtained from destructive testing of controlled samples.

Compressive strength (Mpa)

3.3.3. Tensile strength/split cylinder test The tensile strength found by split tensile test as per ASTM C496-71 specifications was found to be decreasing with the addition of Karak-Montmorillonite. Total 18 samples of 150 mm diameter and 300 mm height were tested. Split tensile strength was calculated at each age by taking the average of 3 samples. The trend of tensile strength against every replacement level is shown in Fig. 13.

30 25 20

7 DAYS

15

35 30 25 20

7 days % loss

15

28days% loss

10

56days%loss

5 0

Fig. 12. Percentage loss of strength.

Table 5 Rebound Hammer ‘R’ Values. MIX

28 Days R value

56 Days R value

C-M 5% K-M 10% K-M 15% K-M 20% K-M 25% K-M

28.15 27.5 27.8 28 26 25.3

34.5 33.3 33.6 34 31 30.4

Table 6 Velocity values  28 day’s. MIX

T(mSec)

Distance(m)

velocity(km/sec)

CM 5% K-M 10% K-M 15% K-M 20% K-M 25% K-M

80.5 81 80.9 80.8 84 85

0.304 0.304 0.304 0.304 0.304 0.304

3.78 3.74 3.76 3.77 3.6 3.55

Table 7 Velocity values  56 day’s. MIX

T(mSec)

Distance (m)

velocity(km/sec)

CM 5% K-M 10% K-M 15% K-M 20% K-M 25% K-M

77 78 77.8 77.9 80 81

0.304 0.304 0.304 0.304 0.304 0.304

3.95 3.87 3.88 3.9 3.81 3.75

28 DAYS

10

56 DAYS

5 0

Percentage loss of strength (%)

Fig. 11. Rate of gain of compressive strength.

CM

05%BC

10%BC

15%BC

20%BC

25%BC

Fig. 10. Compressive strength of specimens at all ages.

3.3.4. Flexural strength Concrete beams (100 mm  100 mm  500 mm) were caste for six mixes and then tested for 28-days flexural strength as per ASTM C 78-02 specifications. It was concluded that Flexural strength decreases with the addition of Karak-Montmorillonite as shown in Fig. 14.

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S.U. Rehman et al. / Construction and Building Materials 232 (2020) 117188

up to 15% replacement level, onward this level the trend get reversed. The reason for this behavior is that as KarakMontmorillonite content increases, it fills the concrete pores and hence decreases water absorption. But as Karak-Montmorillonite content increases above 15%, the excess Karak-Montmorillonite absorbs water thus increasing water absorption. Fig. 15 shows water absorption test results of Karak-Montmorillonite concrete in comparison with control mix.

Tensile strength (Mpa)

2.5 2 1.5 1 0.5 0 CM

05%BC 10%BC 15%BC 20%BC 25%BC Fig. 13. Tensile strength.

Modulus of rupture (Mpa)

6 5 4 3 2 1 0 CM

05%BC

10%BC

15%BC

20%BC

25%BC

Fig. 14. Flexural Strength Results.

3.4. Durability results of bentonite concrete

3.4.3. Acids and sulphate attack For the evaluation of acid and sulphate attack 5% solutions of HCL, H2SO4 and Na2SO4 were used as shown in Fig. 18. Initially, all specimens were cured in normal water for 7 days to gain sufficient strength. After 7 days samples were cured in 5% solutions of HCL, H2SO4 and Na2SO4 in separate containers. After 56 days samples were tested in compression. Results show (Fig. 19) that Karak-Montmorillonite based concrete perform better against acid and sulphate attack than that of control mix. The presence of silica in Montmorillonite results in the formation of silica gel, which resists the acid attack better than the control mix samples. Similarly in sulphate attack Karak-Montmorillonite based concrete perform better than that of controlled concrete samples due to lower concentration of calcium hydroxide. The reason for

Coeffiecent of permeability

3.4.1. Water absorption test Water absorption for Karak-Montmorillonite concrete was measured in accordance to ASTM C642-06 after 28 days. The trend is found similar to the previous research on Jahangira bentonite conducted by Memon et al. [3]. Karak-Montmorillonite concrete showed less absorption in comparison to the control samples. The results exhibit that the water absorption keep on decreasing

Water absorption%

3.4.2. Permeability of concrete test Permeability of concrete test was performed on Automatic Permeability Apparatus (EN12390-B-2000). Two specimens for each mix were prepared and cured for 28 days, after that samples are painted along the sides and tested. The test apparatus with sample assembly is shown in Fig. 16. The results (Fig. 17) show that there is no significant difference in coefficient of permeability values. Coefficient of permeability of concrete reduces up to a certain level of Karak-Montmorillonite content (15%). After filling the pores the surplus content above this replacement level is unable to form a strong bond with other concrete constituents. Due to the hydrostatic pressure, K-M may disperse and hence its dosage increase the coefficient of permeability.

0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0

8E-08 7E-08 6E-08 5E-08 4E-08 3E-08 2E-08 1E-08 0 CM

CM

05%BC 10%BC 15%BC 20%BC 25%BC

Fig. 15. Water absorption test results after 28 days.

Fig. 16. Permeability test apparatus assembly.

05%BC 10%BC 15%BC 20%BC 25%BC Specimens

Fig. 17. Permeability test results.

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S.U. Rehman et al. / Construction and Building Materials 232 (2020) 117188 Table 8 Percentage loss of strength in control mix compared to 15% BC mix at 56 days. % Loss of strength in control mix compared to 15% BC mix Mix

HCL

H2SO4

Na2SO4

CM

5%

9%

8%

Table 9 Percentage loss in strength of specimens compared to normal strength. Percentage loss in strength at 56 days

Fig. 18. Surface conditions of different cured samples.

MIX

HCL

H2SO4

Na2SO4

CM 05%BC 10%BC 15%BC 20%BC 25%BC

15.38 11.93 11.34 9.67 9.01 9.18

20.13 15.20 14.02 12.49 8.19 7.33

23.51 17.94 15.61 15.18 11.74 9.18

Compressive strength (Mpa)

HCL CURED 30

H2SO4 CURED

25

Na2SO4 CURED

20 15 10 5 0 CM

05%BC 10%BC 15%BC 20%BC 25%BC

are not carbonated. Acid solution cured concrete shows no pink color because surface of concrete is carbonated as shown in Fig. 21. The concrete specimens with broken internal surfaces were tested again by spraying phenolphthalein and a darker pink shade was observed. Concrete specimens with Karak-Montmorillonite content shows a darker pink shade than concrete with ordinary portland cement indicating Karak-Montmorillonite resists the carbonation better than normal concrete.

Fig. 19. Comparison of strength after acids and sulphate attack.

the strength loss is the formation of sulfoaluminate (ettringite), which increase in volume resulting in low strength [16]. Comparison of compressive strength against the normally cured specimens is shown in Fig. 20. It was found that compressive strength of samples cured in acids were less than the normally cured specimens. Reduction in strength of CM with respect to maximum strength of 15% BC mix at 56 days is depicted in Table 8, while the overall reduction in strength with different replacement level at 56 days is described in Table 9. 3.4.4. Carbonation depth test Concrete cured in normal potable water and sulphate solution shows pink color which indicates the surfaces of these samples

3.4.5. Surface pH ASTM F710-11 ‘‘Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring” procedure was used to find the acceptability of surface of concrete as shown in Fig. 22. After 56 days, samples were removed from curing tanks containing solutions of acids, sulphates and potable water. Their surfaces were cleaned by spraying distilled water and then tested for pH value by pasting pH paper and matching the color coding from pH paper. The results of sulphuric acid cured concrete specimens show lower surface range of pH values from 3 to 4. While hydrochloric acid cured samples show a range from 4 to 6. Normally cured concrete values are from 11 to 13 and sulphate solution cured concrete values show 10–14 pH. Concrete specimens with Karak-Montmorillonite content shows more pH values than concrete with ordinary portland

NORMAL CONCRETE

35

CONTACT WITH 5%HCL CONTACT WITH 5%H2SO4

Compressive strength (Mpa)

30

CONTACT WITH 5% Na2SO4 25 20 15 10 5 0

CM

05%BC

10%BC

15%BC

20%BC

25%BC

Fig. 20. Comparison of strength against normally water cured specimens.

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S.U. Rehman et al. / Construction and Building Materials 232 (2020) 117188

Fig. 21. Carbonation test.

Fig. 22. Surface pH test.

cement which indicates that Karak-Montmorillonite concrete having more passivity against acidic and sulphate solutions than ordinary concrete as shown in Fig. 23. 4. Cost analysis Cost analysis of 100 cubic feet concrete was made for mixes of 15% replacement of Karak-Montmorillonite with cement. It was NORMAL CONCRETE CONTACT WITH 5% HCL

16

CONTACT WITH 5% H2SO4

14

CONTACT WITH 5%Na2SO4

PH

values

12 10 8 6 4 2 0 CM

05%BC

10%BC 15%BC Specimens

Fig. 23. pH values of specimens.

20%BC

25%BC

found that the reduction in cost of concrete produced by 15% replacement of Karak-Montmorillonite with cement is 10.5% cheaper in comparison to conventional concrete. The cost analysis is summarized in Table 10. The cost of fine and coarse aggregates in both mixes were constant. 5. Conclusions and recommendations 5.1. Conclusions
Consistency values increases (29%–35%) as KarakMontmorillonite percentage increases (0%–25%) due to increase in surface area.
When Karak-Montmorillonite fraction increases (0%–25%), initial setting time increases (1.5–3.6) h and final setting time increases (4–6.4) h, due to low heat of hydration.
Workability of concrete decreases as Karak-Montmorillonite increases (0%–25%), slump values reduces (75–55 mm) respectively.
Water absorption of concrete decreases with partial replacement of Karak-Montmorillonite till 15%. The measured values of water absorption at 0% and 15% were 0.46% and 0.14%. Moreover further replacement of Karak-Montmorillonite increases water absorption. At 25% replacement measured value was 0.36%. Increase in water absorption may be due to unreacted Karak-Montmorillonite which absorbs water.

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S.U. Rehman et al. / Construction and Building Materials 232 (2020) 117188 Table 10 Cost analysis of concrete with 15% replacement of K-M/Bentonite with cement. Description

Control Mix Mix with 15% replacement of K-M/Bentonite

Quantity (kg)

Unit rate (Rs/kg)

Cost (Rs)

Cement

K-M

Cement

880 748

0 132

10 3 10 3 Difference in cost (Rs)


Coefficient of permeability of concrete decreases with increase in Karak-Montmorillonite content up to 15%. The measured values of control mix and 15% replacement level were 6.5E-08 and 5.75E-08 respectively. After 15% replacement of KarakMontmorillonite increase in coefficient of permeability was observed due to weak zone created by unreacted KarakMontmorillonite. Measured value at 25% was 7.5E-08.
Strength Activity Index of all specimens fulfills the ASTM C618 criteria.
Tensile and flexural strength of concrete decreases with increase in Karak-Montmorillonite content, at 25% replacement both strengths reduced up to 27% of control mix strength.
Generally decline in compressive strength is observed for all replacements. However due to packing effect at 15% replacement the maximum strength was observed which is close to the strength of control mix. Karak-Montmorillonite mixes perform better than control mix against acids and Sulphate attack due to formation of silica gel. Loss of strength in control mix, compared to the mix with 15% replacement of K-M, at 56 days was measured to be 5%, 9%, and 8% in HCL, H2SO4 and Na2SO4 solutions respectively.
pH of samples are found to be increasing from 11 to 13 as Karak-Montmorillonite increases 0% to 25%.
Carbonation depth also increases as Karak-Montmorillonite increases, and surface of acids cured specimens show no pink color but inside portion of those specimens show a good pink color.

5.2. Recommendations
Karak-Montmorillonite up to 15% replacement can be easily used to produce environment friendly, low cost concrete and can be used to obtain compressive strength up to 3000 psi.
Concrete samples with Karak-Montmorillonite fraction perform better against acid and sulphate attack. Karak-Montmorillonite up to 20% can be used in lean concrete, curb stones, plinth protections to reduce Sulphate and acids attack or weathering action of environment.
Overall durability of concrete improves with addition of KarakMontmorillonite.
Reduction in cost of cement for 15% replacement of KarakMontmorillonite is 10.5%.

K-M

Total Cost (Rs)

Cement

K-M

8800 7480

0 396

8800 7876 924

6. Future work suggestions Concrete with different cement ratio and use of admixtures are suggested for better strength results. Other sources of Montmorillonite in Pakistan need to be explored for sustainable engineering works. Fire resistance of concrete modified with KarakMontmorillonite also needs evaluation. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References [1] S. Ahmad, S.A. Barbhuiya, A. Elahi, J. Iqbal, Effect of Pakistani bentonite on properties of mortar and concrete, Clay Miner. 46 (2011) 85–92. [2] J. Mirza, M. Riaz, A. Naseer, F. Rehman, A.N. Khan, Q. Ali, Pakistani bentonite in mortars and concrete as low cost construction material, Appl. Clay Sci. 45 (2009) 220–226. [3] S.A. Memon, R. Arsalan, S. Khan, T.Y. Lo, Utilization of Pakistani bentonite as partial replacement of cement in concrete, Constr. Build. Mater. 30 (2012) 237–242. [4] J.M. Justice, L.H. Kennison, B.J. Mohr, S.L. Beckwith, L.E. McCormick, B. Wiggins, et al., Comparison of two metakaolins and a silica fume used as supplementary cementitious materials SP-228, ACI, Farmington Hills, Mich, 2005, pp. 213– 236. [5] Z. Ahmad and R.A. Siddiqi, Minerals and Rocks for Industry, pp. 202–245, 1995. [6] E. Badshah, ‘‘Use of Jehangira bentonite as partial replacement of cement.” MSc. Thesis, Department of Civil Engineering, University of Engineering and Technology, Peshawar, 2003. [7] J.-T. Ding, Z. Li, Effects of metakaolin and silica fume on properties of concrete, Mater. J. 99 (2002) 393–398. [8] F. P. Torgal, A. Shahsavandi, S. Jalali, Using metakaolin to improve the compressive strength and the durability of fly ash based concrete. [9] S.N. Patil, A.K. Gupta, S.S. Deshpande, Metakaolinpozzolanic material for cement in high strength concrete, J. Mech. Civ. Eng. 2 (2011) 46–49. [10] P.J. Sasturkar, FRC–A new sustainable option for construction to mitigate earthquakes, World Acad. Sci. Eng. Technol. 73 (2011) 926–931. [11] R. Siddique, J. Klaus, Influence of metakaolin on the properties of mortar and concrete: a review, Appl. Clay Sci. 43 (2009) 392–400. [12] C. Meyer, The greening of the concrete industry, Cem. Concr. Compos. 31 (2009) 601–605. [13] E. Gartner, Industrially interesting approaches to ‘‘low-CO2” cements, Cem. Concr. Res. 34 (2004) 1489–1498. [14] T. Akram, S. A. Memon, M. N. Khan, Utilization of Jehangira bentonite as partial replacement of cement, pp. 301–311. [15] A.M. Neville, Properties of Concrete, 4, Longman, London, 1995. [16] A. Chakchouk, L. Trifi, B. Samet, S. Bouaziz, Formulation of blended cement: Effect of process variables on clay pozzolanic activity, Constr. Build. Mater. 23 (2009) 1365–1373.