During the previous decade, increased cost of energy has led to the finding alternates to traditional roofing elements. With rising incomes and awareness, grass and thatched roofing solutions have lost their importance. The traditional galvanised sheets are also losing importance due to high costs and low operating life. Micro concrete roofing tiles are designed to meet high quality standards in strength, shape and colour. Therefore, they can be used in high-end construction as well as low-cost rural houses. Tiles meet the need for efficient protection but can be suitably designed to improve the aesthetics. MCR tiles are made from a mixture of stone crusher dust, sand, cement and water.

In recent years due to the rising cost of cement, there was a need expressed by small-scale MCR manufacturers to reduce the cost of cement by suitable alternatives. This is more so since around 35 per cent of the production cost is attributed from cement alone.

Choice of additives for the replacement of cement was governed by price and easy availability. Production of MCR tiles uses ordinary portland cement. It was calculated from stoichiometric compositions that during the hydration of cement within the MCR composition, there is an appreciable release of unreacted CaO and its derived forms. If this can be suitably used for chemical reactions to form strength-giving phases, then it should reduce the requirement of cement.

Thus, for the experimentation phase, dry fly ash was used to replace cement. Dry fly ash was procured from the electrostatic precipitators of thermal power plants. Fly ash generally has an appreciable silica and alumina content with appreciable CaO.

The raw material used in the above experiment was procured locally at Datia, Madhya Pradesh. Stone dust and fine stone aggregate (<10 mm) were taken from a nearby stone crusher. Fine stone aggregate was sieved to get the required particle size of 6 mm. Coarse sand from nearby riverbed was procured and sieved in a 2.36 mm mesh to get the required particle size. Cement used was of OPC grade, ACC make. For various experimentations, both fly and pond ash was procured from Parichha Thermal Power Plant, Jhansi, Uttar Pradesh. Additionally, dry fly ash was also procured from Dadri Thermal Power Plant, Dadri, Uttar Pradesh. Properties of the various types of ash used are given in Table 1.

The equipments used for making MCR tiles include the standard system of vibrating table operated by a 0.25 HP single phase motor. Demoulding of tiles was done on polystyrene moulds, to give its unique profile.

The composition used in the experimental is given in Table 2. All values are on weight ratio basis. Seven different compositions were used with progressive replacement of cement by various types of ash.

All the materials were collected in dry state. The required quantity of raw materials were measured and batched. Initial mixing was also done in a dry state. After uniform mixing, a measured quantity of water was added. A uniform quantity of water: cement ratio of 0: 6 was maintained in all the batches, irrespective of the composition, in order to ensure uniformity. Mixing time with water was standardised at 5 minutes. The mixture was vibrated to produce the desired shape on vibrating table for about 45 seconds before being transferred to a polystyrene mould on a plastic to maintain the unique profile. After initial setting in airtight environment for 24 hours, the mixture was water cured for 14 days. After 14 days the tiles were atmosphere cured under a moist condition.

Tiles were tested for load bearing capacity and water absorption as per standard MCR tiles testing procedures.

The results of progressive addition of various types of ash replacing cement have been given in Figures 1 and 2.

It can be seen from the above results that there is a distinct benefit when fly ash is added to replace cement in MCR tiles. The strength of tiles increases by more than 25 per cent upon 4 per cent replacement of cement by ash. Even with 16 per cent replacement of cement gives an improved breaking load compared to the standard composition presently being followed. As expected, the coarser variety of ash, i.e., pond ash also has a similar effect on the properties of tiles. It can also be concluded that the development of strength is similar in all the types of ash being used and, thus, is not dependent on any physical properties of the ash being used.

1 An average person throws away 3-4 glass bottles and 13 plastic bottles/cans a week.

2 An average steel can now weighs 24 gm compared to 32 gm twenty years ago.

3 Recycling just one plastic bottle can save the same amount of energy needed to power a 60W bulb for 6 hours.

4 It can take upto 50 times more energy to produce a battery than it actually delivers.

5 50 per cent of the steel in Europe is recycled. Luxembourg has the highest steel recycling rate at 98 per cent.

6 The global net reduction of forested area in (1990s) was nearly 10 million hectares a year.

7 15 million mobile phones equates to some 1500 MT of potential landfill.

From the above study, it is recommended to add between 15-20 per cent of ash of thermal power plants replacing cement for production of MCR tiles. However, this will only be true if during production the cement being used is ordinary portland cement. The ash recommended for use can be of any type not restricted to fly ash. But, as far as possible, dry fly ash should be preferred.

Addition of recommended quantity of ash will also lower the production cost by around 7 per cent, which is expected to improve the profitability of the MCR tile business. q