laboratory study of the performance of chemical grinding additive on physical properties of...

LABORATORY STUDY OF THE PERFORMANCE OF CHEMICAL GRINDING

ADDITIVE ON PHYSICAL PROPERTIES OF COMPOSITE CEMENT

S. Karthikeyan

Product Manager – Cement Additives, Ecmas Construction Chemicals Pvt. Ltd., Hyderabad,

India

ABSTRACT

This paper studies the effect of Chemical Grinding Additive (CGA) on physical properties of

Composite Cement (CC) which is prepared by inter-grinding Portland Pozzolana Cement

(PPC) with CGA and finally blending it with Ground Granulated Blast furnace Slag (GGBS).

The result indicates that CC can be successfully produced equivalent to reference PPC by

replacing PPC with 20% GGBS using CGA. Further to note, reduction in CO2 emission is

achieved by lessening clinker factor from 0.60 to 0.48.

KEYWORDS: Chemical Grinding Additive, Portland Pozzolana Cement, Composite

Cement, Ground Granulated Blast furnace Slag, CO2 emission, Energy reduction, Clinker

factor, Economic impact.

INTRODUCTION

With cement production of 285.83 MTPA, India is the second largest cement producer

accounting for around 6.7% of world’s output, as on FY15. A total of 209 large cement plants

and 365 mini & white cement plants accounts for India’s total cement production capacity of

390 MTPA. Also, we are the second largest consumer of cement at 280 MTPA, credit to the

enormous growth in the infrastructure and construction sector for last two decades. [1]

The cement production increased at a CAGR of 6.7% over FY07-15 and as per the 12th five

year plan, it is expected to reach 407 MT by FY17. The cement demand is expected to rise

greatly because of rapid growth in real estate sector and the Government’s initiative such as

building 100 smart cities, concrete road projects, housing for all, make in India, etc., The

cement production capacity is expected to increase at a CAGR of 7.9% during FY 11-20 and

reach 550 MTPA to meet the growing demand. As on 2015, the country’s per capita cement

consumption is 190 kg against world average of 350 kg, which shows great potential for

growth. [1]

To assure that the growth projections does not lead to substantial rise in CO2 emissions,

several serious initiatives are proposed to enable low-carbon technology and processes to

become the norm in cement manufacturing going forward. [2]

One such initiative was taken by BIS, by formulating a new standard for composite cement

(under IS 16415:2015[3]) permitting thereby simultaneous use of flyash and slag as mineral

additives together with clinker for its manufacture where previously only blends of either

flyash (Portland Pozzolana Cement – PPC) or slag (Portland Slag Cement – PSC) was

allowed for manufacture of cement in India.

This new Composite Cement (CC) will gain major importance because of its dual advantage

of environment impact and sustainability of cement industry.

By definition, the blended cements which are produced by using more than one mineral

additives are known as composite cement. Composite cement (under IS 16415:2015) is

mixture of clinker, certain amount of gypsum, flyash and slag. It can be produced either by

intimately inter-grinding portland cement clinker, granulated slag and flyash or intimately

and uniformly blending ordinary portland cement, finely ground granulated slag and fine

flyash with required addition of gypsum. [4]

The Indian cement industry’s average CO2 emission is 0.719/t cement in 2010 which is

substantially low compared to level of 1.12 tCO2/t cement in 1996 [5]. Clinker production is

the major contributor for CO2 emission of the industry. The current clinker-to-cement ratio in

India is estimated to 0.74 against the global average of 0.80[5]. This marginal low clinker-to-

cement is contributed because of higher blended cement production in our country. By 2014,

the share of OPC, PPC and PSC was 27%, 66% and 7% respectively of total cement

production. [6]

For the most part, CO2 is generated from two different sources during the cement

manufacturing process, particularly clinker:

1. Use of fossil fuels in the burning process

2. Calcination, when calcium carbonate is heated and broken down to calcium oxide

with the release of CO2.

Other parts of the manufacturing process such as operating mining equipment for extracting

the raw materials and transportation of the raw materials to the cement plant emit relatively

small amounts of CO2. Between 50% and 60% of the CO2 emitted is a result of calcination

and the remaining is a result of burning fossil fuels. [7]

The primary options for cement industry to reduce CO2 emission and energy reduction target

are [5]

1) Increasing the use of alternative fuels and raw materials

2) Improving thermal and electrical energy efficiency

3) Reducing clinker factor

4) Adopting state of the art newer technologies like use of mineralisers, fluidised-bed

advanced cement kiln, carbon capture, etc.

5) Adopting Waste Heat Recovery systems

Now, as CC can be manufactured in India, it will allow for greater utilization of multiple

mineral additions like flyash and slag to be incorporated together in cement production which

will help in reducing clinker factor and maintain at very low level of 0.35 as permitted in IS

16415:2015[3]

This CC standard is designed almost equivalent to existing blended cement type (both PPC

and PSC) available in our country. Therefore, it will have no impact on product performance

but will ultimately help in further reduction of CO2 emission intensity, conservation of raw

materials, reduction in thermal energy and electrical energy.

The CO2 emission intensity of CC is calculated to be 0.35 tCO2/ton of cement which is 56%

lower than that of OPC. 1Mt of OPC production requires about 1.5-1.6 Mt of limestone,

whereas production of same quantity of CC requires only 0.6 to 0.7Mt of limestone. Also the

cost of thermal energy and electrical energy for producing 1Mt of CC reduces by 52% and

34% respectively as compared to OPC production. [4]

The introduction of CC will play a major role in reducing the targeted emission level to 0.35

tCO2/ton of cement by 2050 from the level of 0.63 tCO2/ton of cement in 2010. [5]

As there will be lack of awareness among common consumers on CC and hence insufficient

demand at initial stage, we designed a CC equivalent to market prevailing PPC quality with

help of CGA (by simply inter-grinding PPC with CGA and then blending it with GGBS) to

overcome the initial barrier and successfully launch CC in Indian market. This method also

eases the manufacture of new type of cement for producer without the need for complicating

the process, installation of new set of equipment or increasing any further cost.

CGA, in general Grinding Aids (GA) are normally liquid products, traditionally formulated

as water-based solutions of organic compounds with high charge density, such as glycols,

esters of glycols, alkanolamines and carboxylates of alkanolamines. They are usually added

at the entrance of the mill together with fresh feed, composed of clinker and mineral additives [8]

Initially CGA were used in the cement manufacturing process only for increasing production

rate of cement, for reducing specific power consumption of grinding, for grinding cement

significantly finer to obtain high-early strength cement.

Over the years, Quality Improvers (QI) are intensively developed from traditional CGA to

improve the quality of cement, it can be used to obtain high-early strength cement by

promoting the hydration of cement at early ages (chemical activation) without the need of

grinding the cement to higher fineness (without increasing the specific energy consumption

or grinding cost). [9]

EXPERIMENTAL METHOD & MATERIAL

PPC according to IS 1489(Part 1):1991[10] was prepared with the recipe mentioned in Table 1.

Table 1: PPC Composition

Component Percentage (by mass)

Clinker 60

Gypsum 5

Flyash 35

4 different CGA’s were formulated based on glycols and alkanolamines. CGA’s were

formulated combining both GA and QI chemicals aiming dual benefits of increasing fineness

and quality of cement

For obtaining homogeneous representative material, clinker were size reduced using jaw

crusher passing 4.75 mm and retaining on 1 mm sieve size. The entire material (clinker,

gypsum & flyash) were dried in a hot air oven at 1000c for about 60 minutes before feeding

into lab ball mil for replicating the plant-scale cement manufacturing temperature and for

controlling gypsum dehydration. The analysis of clinker, gypsum, flyash and GGBS are given

in Table 2.

The materials were grounded in 5 kg capacity laboratory ball mill supplied by AIMIL with

standard steel balls as grinding media for a constant rotation of 6000. The ball mill operates at

a constant speed of 48 rpm, 440 volts, 3 phase, 50 Hz and AC supply.

Table 2: Analysis of clinker, gypsum, flyash & GGBS

Composition Clinker Gypsum Flyash

GGBS

Chemical and Physical Composition

SO3 1.51 43.71 0.27 0.20

CaO 64.74 29.24 2.64 36.71

SiO2 21.95 2.24 62.44 35.35

Al2O3 5.88 0.82 27.67 22.05

Fe2O3 4.87 0.38 4.85 1.15

MgO 1.26 1.20 3.44

F. CaO 0.86

LOI 0.21 0.88 0.53 0.30

LSF 0.90

AM 1.21

SM 2.04

Mineral Composition

C3S 46.73

C2S 27.69

C3A 7.34

C4AF 14.82

A total of 9 batch of ball mill grindings were done, one batch without any CGA (Reference

PPC; labelled as PPC0) and the remaining 8 batch with addition of 4 different formulated

CGA’s as mentioned in Table 3.

Table 3: Details of Cement Grounded

Name Material Grounded

PPC0 – Reference PPC PPC

PPC1 PPC + 8.75 gram CGA1








All the 9 batches of PPC were blended with GGBS individually with the proportion as

mentioned in Table 4. For obtaining homogenous mixture, PPC & GGBS were fed into lab

ball mill and blended for 1500 rotation without grinding media. The blaine’s fineness of

GGBS was 421.60 m2/kg

Table 4: PPC and GGBS blending proportion

Name Percentage (by Mass)

CC0 80% PPC0 + 20% GGBS

CC1 80% PPC1 + 20% GGBS

CC2 80% PPC2 + 20% GGBS

CC3 80% PPC3 + 20% GGBS

CC4 80% PPC4 + 20% GGBS

CC5 80% PPC5 + 20% GGBS

CC6 80% PPC6 + 20% GGBS

CC7 80% PPC7 + 20% GGBS

CC8 80% PPC8 + 20% GGBS

The cement samples PP0, CC0 to CC8 were subjected to Blaine’s fineness, normal

consistency, setting time & compressive strength testing as per relevant Indian standards.

RESULTS & DISCUSSION

BLAINE

The blaine value of cement tested are shown in Graph 1. The blaine’s fineness of PPC0 and

CC0 were found to be 375.4 and 385.10 m2/kg respectively. With the addition of CGA’s,

fineness were increased by 11.10 to 23.50 m2/kg in comparison to CC0. This indicates that all

the CGA’s tested had a significant impact on grindability of cement powder.

Graph 1: Blaine (specific surface area) of cement

NORMAL CONSISTENCY

A Normal consistency (NC) of 30.5% and 31% were obtained respectively with PPC0 and

CC0 which clearly indicates the addition of mineral additives, increases the water demand of

cement paste slightly. CC1 to CC6 exhibited the same water demand of 31% as CC0 whereas

CC7 and CC8 showed a slight higher water demand of 31.5%.

SETTING TIME

The Initial Setting Time (IST) and Final Setting Time (FST) of PPC0 were found to be 220

and 360 minutes respectively and for CC0, both IST & FST were reduced by 35 and 80

minutes respectively, this reduction in setting time could be contributed majorly because of

lower SO3 in CC0 in comparison to PPC0. Gypsum in CC0 was 4%, whereas it was 5% in

PPC0.

Lower IST of 5 to 35 minutes were obtained with CC1 to CC8 when compared to CA0 of 185

minutes. Likewise, FST were also lesser by 0 to 40 minutes compared to CA0 of 280 minutes.

Graph 2 shows the setting time of all cement paste. These results proves that CGA with

proper combination of PI chemicals accelerates both IST and FST of cement significantly.

Graph 2: Initial and Final Setting Time of cement paste

STRENGTH DEVELOPMENT

The compressive strength values were obtained by averaging of 3 cubes per age and values are

as shown in Graph 3.

PPC0 (Reference PPC) showed a strength of 8.80 Mpa at 1 day, whereas CC0 (Blank CC)

showed a value of 6.90 Mpa which clearly shows that reduction in clinker factor by 12%

reduces the one day strength in CC0 by 21.6%. CC processed with CGA’s showed higher one

day strength by upto 52.2% and 19.3% respectively in comparison to CC0 and PPC0, it proves

that CGA can impact greatly on early strength development of cement.

Similarly 3 days and 7 days strength were also lower in CC0 in comparison to PPC0. And

again, compressive strength were higher with CC1 to CC8 compared to both CC0 and PPC0.

PPC0 showed a compressive strength of 48.30 Mpa at 28 days and CC0 showed a lower

strength of 45 Mpa.

CC8 recorded a highest 1 day and 3 day strength of 10.50 Mpa and 24.0 Mpa respectively,

CC6 recorded highest 7 day strength of 35.50 Mpa and CC8 recorded the highest 28 day

strength of 52.50 Mpa

These results clearly highlights that all the CGA’s tested rapidly develops the compressive

strength of cement mortar at all ages.

Graph 3: Compressive Strength development of mortar

ECONOMICS OF CEMENT

The cost of different type of cement are shown in Graph 4 with the raw material cost obtained

from Table 5.

Table 5: Raw Material cost for manufacturing cement

Material Landed Cost (Rs/ton)

Clinker 1415

Gypsum 1420

Flyash 620

GGBS 680

PPC (PPC0) 1137

CC (CC0) 1045.60

CGA 18500 to 23000

The cost of 1 ton of PPC (PPC0) was 1137 Rupees whereas CC (CC0) was only 1045.6

rupees because of partial replacement of clinker with additional mineral additive. With the

usage of CGA, a net saving of 45.40 to 65.50 Rupees/ton was obtained in production of CC,

matching the performance of Reference PPC.

Graph 4: Cost of Cement

CONCLUSION

1. This study indicates that CC produced from PPC using CGA, by replacing PPC with

20% GGBS matches the performance of Reference PPC in all terms.

2. The test also shows that CC can be successfully introduced in Indian market without

compromising on product quality, with minimum clinker reduction of 12% and

simultaneous CO2 emission in comparison to PPC.

3. Apart from competing product performance and green value addition, CC produced

with CGA provides a net cost saving of 45.40 to 65.50 Rs/ton of cement.

FUTURE SCOPE

As an initial stage of research, this work was conducted in laboratory conditions where the

time and materials were limited and so as the number of CGA’s formulated and GGBS

addition percentage. Going forward, it is planned to study the effect of CGA on different

types of clinker and cement for promoting higher mineral additive in cement production. And

finally, to implement the experiment in plant scale cement production and evaluate the real-

time performance and cost effectiveness.

ACKNOWLEDGEMENT

The authors are thankful to their management M/s Ecmas construction chemicals pvt ltd &

A.V Institute of Technology, Vinayaka Missions University for permitting to conduct R&D

studies and their encouragement. Special thanks to M/s Penna Cement Industries Ltd for

providing raw materials for testing and their support.

REFERENCES

1. Report on Cement by IBEF, January 2016.

2. GHG reduction potentials in the Indian cement industry – a way forward.

3. IS 16415:2015, Composite cement specification, December 2015.

4. CII- Discussion paper on Composite Cement, May 2016.

5. Low carbon technology roadmap for Indian Cement Industry, developed by IEA and

WBCSD CSI members, technically supported by NCB and CII and financially

supported by IFC.

6. CII- Cement Vision 2025: Scaling New Heights.

7. Concrete CO2 fact sheet, NRMCA, June 2008.

8. Low cost grinding aids for cement, www.worldcement.com

9. Economic feasibility of new generation non-chloride vs traditional chloride based

cement additive (under publication).

10. IS 1489(Part 1):1991, Portland Pozzolana Cement specification, Part 1: Flyash based,

May 1991.

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