This paper reports on the production of masonry cement from waste chalk, Portland cement and a small quantity of phosphogypsum. It possesses good workability, water retention and greater resistance to volume changes. The new cement complied with the requirements of Indian Standard specifications. The suitability of masonry cements was examined for mortar making properties. The results showed that the strength and water-retention of 1:4 and 1:5 masonry cement-sand mortars was higher than the corresponding 1:6 cement-sand mortar. Moreover, chalk and phosphogypsum can be used without beneficiation for making masonry cement, the resulting product being economical to produce. Cost estimates for the production of this cement and the comparative cost for other traditional mortars used in buildings have been given.

Mridul Garg and Neeraj Jain, Scientists, Central Building Research Institute, Roorkee

Introduction

Appreciable quantities of cement produced in any country are consumed for masonry and plaster work. About 45% of cement produced in India is used for this purpose [1]. Use of ordinary Portland cements for plastering and masonry work would amount to improper use of material otherwise needed for structural work. Specific requirements of mortars such as plasticity, higher water retention and reduced shrinkage needed for masonary and plastering work would not be normally fully met with ordinary portland cements. This creates the need to develop masonry cements.

Masonry cement manufactured in U.S.A. and other countries mostly consists of 40-50 percent Portland cement, the rest being fillers like limestone, fly ash and granulated blast furnace slag along with a small addition of an air entraining agent. Attempts have been made to produce masonry cement from gold and zinc tailings [2, 3]. Use of fly ash and granulated blast furnace slag in making masonry cement has been claimed [4]. They are ground extremely fine and mortars prepared with masonry cement are considered somewhat superior to composite mortars in overall performance. In India because of the high cost of good quality hydrated lime and its perishable nature, scope for the development of a lime-based masonry cement is presently rather quite limited. The choice, therefore, falls on the use of cement and some cheaper materials like waste lime sludges, phosphogypsum, fluorogypsum, etc.

About 4.0 million tonnes of by-product chalk or lime sludge is produced annually from the paper, sugar, acetylene, fertilizer, soda ash and chrome sludge industries in India containing impurities of P2O5, organic matter, alkali, etc [5,6]. At present, the lime waste is being disposed of in the form of slurry in nearby places for drying.

In the present investigation, masonry cement has been produced by grinding together waste chalk, Portland cement and a small quantity of phosphogypsum. The properties of the masonry cement, its use in making masonry mortars, economic feasibility and process flow diagram have been detailed in the paper.

Experimental Procedures

Development of Masonry Cement from Waste Chalk and Phosphogypsum

The samples of Portland cement, phosphogypsum, and chalk were analysed for various constituents as per IS:1727-1967, Methods of tests for pozzolanic materials, IS:1288-1983, Methods of test for mineral gypsum, and as per standard test procedures. The results of chemical analysis are shown in Table 1.

Development of Masonry Cement from Waste Chalk and Phosphogypsum
Figure 1: SEM of unprocessed (a) chalk and (b) phosphogypsum

Development of Masonry Cement from Waste Chalk and Phosphogypsum
Figure 2: DTA of unbeneficiated (A) phosphogypsum and (B) chalk
The SEM microphotographs of chalk and phosphogypsum samples are shown in Figure1. The chalk sample exhibits formation of rounded agglomerated prismatic stillated crystals knitted round a central point. The crystal appeared like jumble of hexagonal leaves of vateritic nature. The appearance of such a crystal habit could be due to impurities of P2O5 & other unidentified ingredients present in the chalk. The phosphogypsum shows prismatic and tabular shaped crystals of variable sizes with cavities and irregular boundaries. Probably impurities of P2O5, F and organic matter have modified the crystal habit of the phosphogypsum waste.

DTA of chalk and phosphogypsum are shown in Figure 2. Phosphogypsum shows appearance of two endotherms at 140°C and 220°C due to inversion of CaSO4.2H2O-->CaSO4.1/2H2O and CaSO4.1/2H2O-->CaSO4(III). The exotherm at 450°C is due to CaSO4(III)-->CaSO4(II). In the chalk sample, two endotherms can be noted at 420° and 950°C due to decomposition of Ca(OH)2 and CaCO3 respectively.

Masonry Cement from Chalk, Portland Cement and Phosphogypsum

Development of Masonry Cement from Waste Chalk and Phosphogypsum

Portland cement, waste chalk and phosphogypsum were separately ground to a fineness of over 500 m2/kg and then mechanically mixed in various proportions (by weight) to produce masonry cement. These cements were tested as per the methods laid down in IS:4031-1996 [7]. The results are listed in Table 2. The data indicates that masonry cement mixes A & B comply with the requirements for compressive strength, water retention values as required in IS:3466-1999 [8]. However, the initial setting time of masonry cement is low. Hence, retardation of setting with tartaric acid retarder is essential to meet the standard requirements. From the test results, a mix of 55 percent of Portland cement and 45 percent chalk is most suitable.

Masonry Mortar

Development of Masonry Cement from Waste Chalk and Phosphogypsum

Suitability of masonry cements A & B was examined for mortar making properties. The compressive strength of masonry mortars are reported in Table 3. The data show that the strength of 1:4 and 1:5 masonry cement-sand mortars is higher than the corresponding 1:6 cement-sand mortar.

Economic Feasibility

Normally 1 part of masonry cement to 5 parts of sand (by volume) gives a mortar of strength comparable to that made from 1 part Portland cement and 6 parts sand (by volume). Since masonry cement contains about 40-45% of Portland cement, therefore 1:5 mortar from masonry cement contains about 6.5% Portland cement as compared to 14% in 1:6 Portland cement sand mortar thereby giving a saving of 7.5% of Portland cement.

The predesign cost estimates for the production of masonry cement for the plant of capacity 50 tonnes per day has been worked out to be Rs.2850/- against Rs. 4100/-of Portland cement. It is about 30% cheaper than Portland cement.

The process flow diagram for the production of masonry cement is shown in Figure 3.

Development of Masonry Cement from Waste Chalk and Phosphogypsum

The comparative cost data of various mortars based on estimated selling price of masonry cement and prevailing market rates of Portland cement, lime sludge, phosphogypsum and retarder are shown in Table 4. The cost of 1m3 wet mortar (1:5) based on masonry cement, is Rs. 858/- as compared to Rs.1229/- for 1:6 Portland cement-sand mortar and Rs.1337/- for 1:1:6, cement-lime-sand composite mortar. Thus, it can be deduced that there is a direct saving of Rs.371/- when 1:6 mortar is replaced by 1:5 masonry cement-sand mortar. Similarly, the saving amounts to Rs.324/- when the proposed 1:4 masonry cement–sand mortar is used in place of 1:1:6 composite mortar.

Conclusions

Development of Masonry Cement from Waste Chalk and Phosphogypsum
Figure 3: Process flow diagram for the production of the masonry cement (OPC: Ordinary Portland Cement, PG: Phosphogypsum)
A masonry cement with 40-45 % of waste chalk/lime sludge has been developed to satisfy the specific requirements of the Indian Standard Specification 3466-1999. The mortar prepared from masonry cement and sand retains greater cohesiveness, high water retentivity and workability as compared to mortar prepared from Portland cement and sand. Production of masonry cement is recommended as it will use sizable quantity of unbeneficiated waste chalk along with phosphogypsum and assures reduction in consumption of Portland cement.

Acknowledgement

Authors are thankful to the Director, CBRI, Roorkee for his permission to publish the present work.

References

  • Narang K. C., Kini, M. R., Ganapathy R. Development of masonry cement from industrial waste, National Seminar on Building Material Their Science and Technology, 15-16 April 1982, New Delhi, pp.IIA (12)-1-IIA (12)-18.
  • Rai Mohan and Jain, V. K. Utilization of zinc tailings for making masonry cement, Cement, Vol.13, No.5, Oct-Dec. 1979, pp 6-8.
  • Jain, V. K. and Rai Mohan. Gold tailings based masonry cement, National Seminar on Building Material Their Science and Technology, 15-16 April 1982, New Delhi, pp.IIA (5)-1-IIA (5)-4.
  • Taneja, C. A and Tehri, S. P. A masonry cement based on slag and fly ash. Cement, Vol. VIII, No.2, Jan. 1975, pp.10-12.
  • Dave, N. G., Pozzolanic waste and activation to produce improved lime-pozzolana mixture, 2nd Autralian Conference on Engineering Materials, University of New South Wales, Kensington, Australia, 1981, pp.71-76.
  • Singh, Manjit, Garg Mridul, Verma, C. L., Handa S. K., and Kumar R., An improved process for the purification of phosphogypsum. Construction and Building Materials, Vol.10, No.6, 1996, pp. 597-600.
  • IS:4031, Methods of physical tests for hydraulic cement, Bureau of Indian Standards, New Delhi, 1996.
  • IS: 3466, Specification for masonry cement, Bureau of Indian Standards, New Delhi, 1999.
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