Mridul Garg and Neeraj Jain, Scientists, Central Building Research Institute, Roorkee
IntroductionAppreciable 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 . 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 . 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.
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.
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
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 . 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 . 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.
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 FeasibilityNormally 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.
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.
AcknowledgementAuthors are thankful to the Director, CBRI, Roorkee for his permission to publish the present work.
- 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.