Development of mix proportioning procedure for flyash concrete

S C Maiti*, National Council for Cement & Building Materials, India R C Wason, National Council for Cement & Building Materials, India H K Julka, National Council for Cement & Building Materials, India

A Maidasani, National Council for Cement & Building Materials, India

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2-rtr' Conference on OUR WORLD IN CONCRETE & STRUCTURES: 29 - 30 August 2002, Singapore

Development of mix proportioning procedure for flyash concrete

5 C Maiti*, National Council for Cement & Building Materials, India R C Wason, National Council for Cement & Building Materials, India H K Julka, National Council for Cement & Building Materials, India

A Maidasani, National Council for Cement & Building Materials, India

Abstract

Presently, no mix proportioning procedure is available for the flyash concrete for the typical Indian concrete-making materials and mix proportioning of flyash concrete is generally carried out by trial and error. An R&D project has been taken up by Authors' organization to develop a dependable mix proportioning procedure for such concretes.

The experimental work was carried out with two samples of ordinary Portland cement having different strength levels. Relationships have been developed between water/cementitious materials ratios and 28 days compressive strengths of concrete for different flyash contents in the mixes.

Taking relationship between water/cementitious materials ratio and strength of concrete as a starting pOint of the procedure, the remaining steps of the mix design procedure have been finalized. The experiments are being further conducted with cement samples having different strengths and with more flyash samples. The procedure is also being tried for proportioning of flyash mixes for commercial concretes being supplied by an RMC plant in India to various construction sites.

Keywords: Mix proportioning, Flyash, Water/cementitious materials ratio, Concrete making materials.

1. Introduction Flyash, which is produced by thermal power plants in large quantity as a waste material (about 90 million tonnes annually), is used as a mineral admixture in concrete to improve its strength and durability characteristics. Presently, good quality of fly ash conforming to IS 3812[1] is available in most of the modern thermal plants in India. In many Countries like USA, UK, Netherlands, Germany etc. flyash is being used as mineral admixture for making good quality and durable concretes[2J.

Flyash is used in concrete not only for normal building constructions, but also in high strength concretes for special structures like long span bridges, high rise structures, tunnels to achieve durability in concrete and to avoid formation of microcrakes caused by excessive heat of hydration produced due to large quantity of high grade cement required to be used for making high strength concrete. In the fourth revision recently, IS:456-2000 the code of practice for plain and reinforced concrete[3] has also included the use of flyash in concrete as part replacement of ordinary Portland cement provided uniform blending with cement is ensured.

2. Need for Mix Proportioning Procedure for Flyash Concrete The Indian Code, IS 10262[4] recommended a mix design procedure for concrete without chemical and mineral admixtures However, no mix proportioning procedure is available for the flyash concrete for the typical Indian concrete-making materials and mix proportioning of flyash concrete is generally carried out by trial and error. Extensive research has been carried out to arrive at a proper method of proportioning the flyash concrete mixes and to study the effect of flyash addition on the properties of concrete. According to Smith[5] , the water cement ratio for flyash concrete was calculated on the basis of the 'Cementing efficiency factor' for flyash. This factor depends on the curing period, strength of the mix and the type of flyash . Cannon[6] suggested that the difference in the yield due to a lager volume of cementitious material in the flyash mix should be balanced by reduction in sand content. Adoption of

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this procedure changes the gradation of the original mix. The demand for water in such mixes depended on the mix itself, increased in certain cases and decreased in others.

Lovewell and Washa[7] found that the flyash addition had to exceed the amount of cement removed in order to achieve the same strength. Additional quantity of flyash needed depended on the strength of the mix. Ghosh[8] prepared design charts suitable for design of flyash concrete. He found that the constants in Abrams' equation changed with the ratio of flyash and cement. However, these equations are not quantified. The design charts were prepared for various flyash contents and water cementitious ratios. Many other researches [9, 10, 11] have carried out studies for developing a mix design procedure for flyash concrete but still a need has been felt to develop a dependable mix design procedure for such concretes. Building research establishment[12] gives procedure for designing flyash mixes with the available quality of materials i.e. cement and flyash. This procedure provides for estimation of w/c ratio corresponding to the target strength of concrete based on cementing efficiency factor. However, it is not directly applicable for concrete mixes made with materials used in India.

3. Experimental Work 3.1 Materials used Two types of ordinary Portland cement (OPC) i.e. 43 grade OPC conforming to IS:8112[13] and 53 grade OPC conforming to IS: 12269[14] are used and their physical and chemical characteristics are given in Table 1. Crushed quartzite was used as coarse aggregate and the a pit sand known as 'Badarpur' sand conforming to grading zone II requirement as per IS 383-1970[15] was used as fine aggregate. The flyash sample collected from Talchar super thermal power station was used for the studies. The flyash sample conformed to the requirement of IS 3812 (Table 2).

3.2 Concrete Mixes Four grades of concrete i.e. M15, M20, M25, and M30 were taken up for the experimental work. The workability of 50 mm slump was chosen for all the concrete mixes. The amount of fly ash incorporated in the mixes was 0, 15, 25, and 35 % as replacement by weight of cement. The water/cementitious materials ratios in different mixes varied from 0.450 to 0.722. The water content in the mixes was varied to arrive at the required workability for the different proportions of cement, flyash and aggregates. The mix proportions adopted for the various mixes with 43 Grade OPC and 53 Grade OPC are given in Table 3 and Table 4 respectively .

Table 1 Characteristics of Cement samples

Characteristics Test Results 43 Grade 53 Grade

Fineness, m"/kg 352.4 307.4 Setting Time, min

Initial Final

87 152

105 195

Compressive Strength, N/mm" 3 Days 7 Days

28 Days

23.0 28.9 53.8

35.3 47.6 58.2

Table 2 Characteristics of Flyash sample

Characteristics Test Results Silica, Si02, % 60 Loss on Ignition, % 0.3 Lime Reactivity, N/mmz 7.2 Fineness, m"/kg 338 Specific Gravity 2.09

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Table 3 Mix Proportions With 43 Grade OPC

Grade of Flyash Cement Water Flyash Fine Coarse Water/ Concrete content

(% by wt. of cement)

Content (kg/m3)

Content (kg/m3)

Content (kg/m3)

aggregate Content (kg/m3)

aggregate Content (kg/m 3

)

cementitious materials

ratio M15 0 270 195 0 697 1140 0.722

15 229 191 41 686 1145 0.707 25 203 187 68 676 1153 0.690 35 176 183 95 667 1163 0.678

M20 0 312 195 0 630 1187 0.625 15 265 190 47 618 1186 0.609 25 233 185 79 609 1195 0.593 35 202 180 110 601 1204 0.577

M25 0 342 195 0 612 1174 0.570 15 291 191 51 600 1176 0.558 25 257 187 86 590 1182 0.547 35 222 183 120 580 1178 0.535

M30 0 375 195 0 594 1164 0.520 15 319 191 56 580 1165 0.509 25 281 187 94 571 1170 0.499 35 244 182 131 562 1177 0.485

Table 4 Mix Proportions With 53 Grade OPC

Grade of Concrete

Flyash content

(% by wt. of cement)

Cement Content (kg/m3)

Water Content (kg/m3)

Flyash Content (kg/m3)

Fine aggregate Content (kg/m3)

Coarse aggregate Content (kg/m3)

Water/ cementitious

Materials ratio

M15 0 295 194 0 636 1192 0.657 15 251 191 44 624 1196 0.647 25 221 186 74 614 1204 0.630 35 192 181 103 609 1210 0.614

M20 0 332 199 0 620 1163 0.600 15 282 190 50 613 1174 0.572 25 249 185 83 603 1182 0.557 35 216 180 116 594 1182 0.542

M25 0 364 208 0 592 1161 0.572 15 309 202 55 584 1164 0.555 25 273 195 91 577 1173 0.536 35 237 190 127 574 1175 0.522

M30 0 400 195 0 590 1155 0.488 15 340 190 60 578 1156 0.475 25 300 185 100 568 1162 0.463 35 260 180 140 558 1169 0.450

4. Test Results and discussion The 7 and 28 days compressive strength tests were carried out for the different mixes and the 28 days results are presented here in Table 5. The compressive strength results have been plotted against water/cementitious materials ratio for different flyash contents in Fig 1 and Fig 2 for mixes with 43 grade OPC and 53 grade ope respectively. On perusal of Fig 1 and Fig 2, it is seen that there exists a relationship between water/cementitious material ratio and 28 days strength of cement. It is also seen that the relationship is dependant on two other factors i.e. fly ash content in the mix and the strength of cement. Further trials have been taken up to check the validity of this relationship for various samples of flyash and cement. However, the relationship has been found suitable for establishing a mix design procedure for flyash concrete.

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Table 5 28 days compressive strength test Results for different mixes

Grade of Concrete

Flyash content

(% by wt. of cement)

With 43 Grade OPC With 53 Grade OPC

Waterl Cementitious Material ratio

28 days compressive

strength (N/mm2)

Waterl Cementitious Material ratio

28 days compressive

strength (N/mm2) M15 0 0.722 17.9 0.657 21.4

15 0.707 16.2 0.647 19.5 25 0.690 15.1 0.630 17.9 35 0.678 14.2 0.614 16.7

M20 0 0.625 23.1 0.600 28.2 15 0.609 20.9 0.572 26.1 25 0.593 19.1 0.557 24.8 35 0.577 18.2 0.542 22.7

M25 0 0.570 29.3 0.572 32.7 15 0.558 26.2 0.555 29.5 25 0.547 24.3 0.536 28.2 35 0.535 23.0 0.522 26.4

M30 0 0.520 35.1 0.488 37.1 15 0.509 32.0 0.475 35.6 25 0.499 30.1 0.463 32.8 35 0.485 27.1 0.450 30.7

With 43 grade ope40

Q) 35 ...> ..-.. L .. ''', .... ...........~ EE 30

Q) • x.. .. " "' .. ­........... ...... . '.5. g 25 """". ., ......§ Z 20 .''. ......... .. -. '-"­O'E '~" "-. '-"- .. ..........- .. '"'-... -"~A~ C» 15

'" c"C ~ 10 <0(;)

I NS o +--------,--------~--------._------_,

0.4 0.5 0.6 0.7 0.8 Water-Cementitious ratio

1- .. - 0% - .. --3i% - .j, - 25% - .)E - 35% 1

Fig. 1 : Design curve of free water/cementitious materials ratio vs 28 days compressive strength of concrete

332

With 53 grade OPC 40

35

5

O +---~----~----.---~----~---.----~

0.4 0.45 0.5 0.55 0.6 0.66 0.7 0.75

Wa1er-Cementilious ratio

1-" ()'!/, - ..... ·15%·· .. • ·25% -"*- 35% 1-

Fig. 2 : Design curve of free water/cementitious materials ratio vs 28 days compressive strength of concrete

5. Proposed Method:

The proposed method for mix proportioning of flyash concrete is based on the design curve of free water/cementitious materials ratio vs 28 days compressive strength of concrete for specified flyash content and 28 day strength of cement.

The main steps of the proposed procedure are as follows:

1) Determination of free water/cementitious material ratio. For a given target strength and percentage of flyash, determine the corresponding water/cementitious materials ratio from Fig 1 or Fig 2 depending upon the 28 day compressive strength of cement.

2) Determination of water and fine aggregate contents. Based on the maximum size and type of coarse aggregate to be used and the required level of workability, determine the water and fine aggregate contents.

3) Determination of cement and flyash contents Combining the results of step 1 and 2, determine the cement and flyash contents.

4) Determination of coarse and fine aggregate contents. Determine the coarse and fine aggregate content by absolute volume method or any other suitable method.

The procedure given in IS 10262 can be adopted for steps 2 to 4 above.

333

Acknowledgement. The paper is published with the permission of Director General of National Council for Cement

and Building Materials. The Authors thankfully acknowledge the contribution of Shri Suresh Kumar and other colleagues in the experimental work.

References. [1] IS:3812-1981, Specification for flyash for use as pozzolana and admixture, Bureau of Indian

Standards, New Delhi, 1981. [2] Jain N.K. and Mohan K., Flyash as mineral admixture for high performance concrete , Fifth

International conference on concrete technology for developing countries, vol .1, 1999 [3] IS:456-2000, Code of practice for plain and reinforced concrete, Bureau of Indian Standards,

New Delhi, 2000. [4] IS:10262-1982; Recommended guidelines for concrete mix design, Bureau of Indian

Standards, New Delhi , 1982. [5] Smith I.A., The design of flyash concrete, Proceedings, Institution of civil engineers (London) ,

vo1.36, 1967, pp 769-790. [6] Cannon R.W., Proportioning flyash concrete mixes for strength and economy, ACI journal,

proceedings, vol .65, nO.11, 1968, pp 969-979. [7] Lovewell C.E. and Washa G.W., Proportioning concrete mixtures using flyash, ACI journal,

proceedings, vol.54 no.12 July 1958, pp 1093-1102. [8] Ghosh R.S., Proportioning concrete mixes incorporating flyash, Canadian journal of civil

engineering (Ottawa) , vol.3 , 1976, pp 68-82 [9] Maiti S.C. and Jain N.K., Mix proportioning of superplasticized flyash concrete, Fifth

International conference on concrete technology for developing countries, vol.2, 1999 [101 Kumar V., Nautiyal B.D., Singh A.P. and Mohammad S. , Mix design of flyash concrete, Fifth

NCB International seminar on cement and building materials, 1996. [11 J RB-1981 , Procedure for designing flyash concrete mixes, Cement research institute of India,

1981. [12] Teychenne D.C. , Franklin R.E. and Emtroy H.C. , Design of Portland cemenUpfa mixes,

Building research establishment report, 1988, pp 33-37. [131 IS:8112-1989, Specification for 43 grade ordinary Portland cement, Bureau of Indian

Standards, New Delhi , 1989. [14] IS:12269-1987, SpeCification for 53 grade ordinary Portland cement, Bureau of Indian

Standards, New Delhi , 1987. [15] IS:383-1970, Specification for coarse and fine aggregates from natural sources for concrete,

Bureau of Indian Standards, New Delhi, 1970.

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