W13_ET_Reduce Cement Consumption in Paste Fill_Kristal2011


Problem Statement:

In back fill activity we are using 14% of cement content in the paste pouring to the area in underground mine that have been finished in ore mining. In order to be able to mine an ore drive beside or underneath it, we need to back fill it first before we are allowed to do mining in relation to comply with geotechnical requirement and safety factor. The higher cement percentage being used in back fill activity, means that higher consumption in cement.

Alternatives:

Review had been done with geotechnical and mine planning team for certain drifts to use lower cement percentage in order to reduce operating cost. There are some conditions that after we back fill certain drifts, we are not going to mine under or beside for more than 3 months depending on the mine planning team.

Criterion:

Ground stability is a priority and still in mining practice. Higher cement percentage will create faster curing time to be able to mine under or beside as soon as possible to get the ore areas. But for some reasons depends on mine planning, in certain areas we don’t need to mine as soon as possible.

Analysis and Comparison:

The table below shows areas that used 14% of cement and we will mine under or beside them in some stages

                       

No.

Date

Location

%Cement

Material Usage

Paste Product

 

Vs Dry Tuff

Cement

Water

Tuff

Tuff dry

Tuff

 

  

Tons

Tons

Tons

Tons

M3

Tons

M3

 

1

5-Jul-11

K2-Sub 9’D’ Sill South OD.03

14%

83

286

774

578

846

1143

706

 

2

8-Jul-11

K2-Sub 12’B’ Sill South OD.03

14%

18

70

172

128

188

260

161

 

3

9-Jul-11

K2-Sub 12’B’ Sill South OD.03

14%

19

68

180

134

197

268

165

 

4

9-Jul-11

K2-Sub 9’D’ Sill South OD.01

14%

48

171

443

331

484

662

408

 

5

24-Jul-11

K2 – Sub 11 ‘A’ UC.1 North OD.05

14%

69

237

639

477

699

945

584

 

6

24-Jul-11

K2 – Sub 11 ‘A’ UC.1 North OD.05

14%

16

52

148

110

162

216

133

 

7

26-Jul-11

K2 – Sub 11 ‘A’ UC.1 North OD.05

14%

2

9

22

16

24

33

20

 

8

27-Jul-11

K2 – Sub 11 ‘A’ UC.1 North OD.05

14%

8

28

71

53

77

106

65

 

9

10-Sep-11

K2 – Sub 9 ‘D’ Sill South OD.1

14%

75

262

692

517

757

1029

635

 

10

28-Sep-11

K2 – Sub 12 ‘B’ Sill South OD.01 (#1)

14%

124

408

1151

859

1258

1683

1039

 

11

30-Sep-11

K2 – Sub 12 ‘B’ Sill North OD.02

14%

55

199

515

384

563

770

475

 

12

7-Oct-11

K1 – Sub 6 ‘A’ UC3 North OD.01

14%

134

453

1249

932

1365

1837

1134

 

13

8-Oct-11

K1 – Sub 6 ‘A’ UC.3 North OD.01

14%

24

89

225

168

246

338

209

 

14

8-Oct-11

K1 – Sub 6 ‘C’ UC.3 North OD.02

14%

65

232

603

450

659

899

555

 

15

8-Oct-11

K1 – Sub 6 ‘C’ UC.3 North OD.02

14%

55

183

508

379

555

746

461

 

 

The table below shows if the areas above will use 8% of cement in back fill instead of 14% cement

No.

Date

Location

%Cement

Material Usage

Paste Product

Vs Dry Tuff

Cement

Water

Tuff (wet)

Tuff dry

Tuff

Tons

Tons

Tons

Tons

M3

Tons

M3

1

40729

K2-Sub 9’D’ Sill South OD.03

8%

48

286

809

604

884

1143

706

2

40732

K2-Sub 12’B’ Sill South OD.03

8%

11

70

179

134

196

260

161

3

40733

K2-Sub 12’B’ Sill South OD.03

8%

11

68

188

140

206

268

165

4

40733

K2-Sub 9’D’ Sill South OD.01

8%

28

171

463

346

506

662

408

5

40748

K2 – Sub 11 ‘A’ UC.1 North OD.05

8%

40

237

668

499

730

945

584

6

40748

K2 – Sub 11 ‘A’ UC.1 North OD.05

8%

9

52

155

115

169

216

133

7

40750

K2 – Sub 11 ‘A’ UC.1 North OD.05

8%

1

9

23

17

25

33

20

8

40751

K2 – Sub 11 ‘A’ UC.1 North OD.05

8%

4

28

74

55

81

106

65

9

40796

K2 – Sub 9 ‘D’ Sill South OD.1

8%

43

262

724

540

791

1029

635

10

40814

K2 – Sub 12 ‘B’ Sill South OD.01 (#1)

8%

72

408

1203

898

1315

1683

1039

11

40816

K2 – Sub 12 ‘B’ Sill North OD.02

8%

32

199

538

402

588

770

475

12

40823

K1 – Sub 6 ‘A’ UC3 North OD.01

8%

78

453

1306

974

1427

1837

1134

13

40824

K1 – Sub 6 ‘A’ UC.3 North OD.01

8%

14

89

235

175

257

338

209

14

40824

K1 – Sub 6 ‘C’ UC.3 North OD.02

8%

38

232

630

470

688

899

555

15

40824

K1 – Sub 6 ‘C’ UC.3 North OD.02

8%

32

183

531

396

581

746

461

 

Selection of the preferred alternative:

     

VARIANCE AFTER IMPROVEMENT

PRICE

COST SAVING AFTER IMPROVEMENT

 

No.

Date

Location

Cement

Tuff

Cement

Tuff

 

Cement

Tuff

Tuff

USD / ton

USD / m3

IDR / ton

IDR / m3

USD

IDR

 

Tons

Tons

M3

152.23

$ 10.46

1,351,473

92,234

 

1

5-Jul-11

K2-Sub 9’D’ Sill South OD.03

35

(35)

(38)

5,364

(366)

47,311,437

(3,228,879)

$ 4,998

44,082,557

 

2

8-Jul-11

K2-Sub 12’B’ Sill South OD.03

8

(8)

(8)

1,190

(81)

10,492,380

(716,077)

$ 1,108

9,776,303

 

3

9-Jul-11

K2-Sub 12’B’ Sill South OD.03

8

(8)

(9)

1,248

(85)

11,004,183

(751,006)

$ 1,163

10,253,177

 

4

9-Jul-11

K2-Sub 9’D’ Sill South OD.01

20

(20)

(22)

3,073

(210)

27,101,057

(1,849,575)

$ 2,863

25,251,482

 

5

24-Jul-11

K2 – Sub 11 ‘A’ UC.1 North OD.05

29

(29)

(32)

4,432

(302)

39,086,282

(2,667,534)

$ 4,129

36,418,747

 

6

24-Jul-11

K2 – Sub 11 ‘A’ UC.1 North OD.05

7

(7)

(7)

1,026

(70)

9,048,054

(617,506)

$ 956

8,430,549

 

7

26-Jul-11

K2 – Sub 11 ‘A’ UC.1 North OD.05

1

(1)

(1)

150

(10)

1,326,824

(90,552)

$ 140

1,236,272

 

8

27-Jul-11

K2 – Sub 11 ‘A’ UC.1 North OD.05

3

(3)

(3)

490

(33)

4,321,161

(294,908)

$ 456

4,026,253

 

9

10-Sep-11

K2 – Sub 9 ‘D’ Sill South OD.1

31

(31)

(34)

4,800

(328)

42,337,945

(2,889,452)

$ 4,473

39,448,493

 

10

28-Sep-11

K2 – Sub 12 ‘B’ Sill South OD.01 (#1)

52

(52)

(57)

7,977

(544)

70,354,071

(4,801,478)

$ 7,432

65,552,594

 

11

30-Sep-11

K2 – Sub 12 ‘B’ Sill North OD.02

23

(23)

(25)

3,571

(244)

31,491,745

(2,149,228)

$ 3,327

29,342,517

 

12

7-Oct-11

K1 – Sub 6 ‘A’ UC3 North OD.01

56

(56)

(62)

8,657

(591)

76,352,481

(5,210,853)

$ 8,066

71,141,628

 

13

8-Oct-11

K1 – Sub 6 ‘A’ UC.3 North OD.01

10

(10)

(11)

1,558

(106)

13,744,204

(938,005)

$ 1,452

12,806,198

 

14

8-Oct-11

K1 – Sub 6 ‘C’ UC.3 North OD.02

27

(27)

(30)

4,184

(286)

36,902,386

(2,518,489)

$ 3,898

34,383,897

 

15

8-Oct-11

K1 – Sub 6 ‘C’ UC.3 North OD.02

23

(23)

(25)

3,523

(240)

31,072,337

(2,120,604)

$ 3,283

28,951,733

 
           

TOTAL SAVING FROM JUL-OCT’2011

  

$ 47,744

421,102,399

 
                         

With this initiative in reducing cement percentage from 14% to 8%, cost saving in cement consumption from July – October 2011 is $ 47,744

Performance monitoring and post-evaluation of results:

This will be permanent practice going forward for back fill areas where we will be mining in the next more than 3 months later for mining beside ore drift.

 

Reference:

  1. Sullivan William. Wicks M, Elin. Koelling C, Patrick. Engineering Economic, Fifteenth edition. Pearson International Edition, 2009

 

                                                    

 

 

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One response to “W13_ET_Reduce Cement Consumption in Paste Fill_Kristal2011

  1. Unfortunately, it really doesn’t seem that you made the changes I recommended or suggested?

    Your problem statement is better, but the alternatives should have read
    Alternative A- “Use 14% Cement Content”
    Alternative B- “Use 08% Cement Content”
    You need to make the alternatives you are testing for crystal clear. In your table below, you mention “Dry Tuff” but aren’t clear on that relationship- are you adding cement to the dry tuff and that is what you are comparing?

    In your selection criteria, you should have included the required compressed strength of the concrete at 30 days. (i.e 3000 PSI or 20 MPa) AND whatever target you were trying to achieve in terms of cost savings. Understand that as written there is a big disconnect between your criteria (compressed strength) and what you solved for (cost) You cannot have this disconnect. If cost is what you are solving for, then the acceptance criteria needs to also be stated in costs.

    The other concern I have is that when you reduce the cement content, it normally reduces the strength of the concrete. Frankly speaking, to reduce the cement content by 40% just to save money sounds downright scary to me. Surely there must be some kind of trade-off missing from this analysis?

    Bottom line- while I am willing to accept this posting, I surely hope you don’t include it in your paper unless you provide more support that reducing cement content by 43% doesn’t negatively impact the strength of the concrete below the minimum acceptable levels.

    Also, your citations are VERY weak. They do not conform to the APA standards AACE expects to see in your paper. http://owl.english.purdue.edu/owl/resource/560/02/ (where is the page number(s) showing which tool and technique you used?) and I would prefer that you cited at least two references, not just one.

    BR,
    Dr. PDG, Jakarta

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