STUDIES ON PAPER MILL EFFLUENTS AS A WORKABILITY AID FOR CEMENT MORTARS

Abstract

A material which either increases workability of freshly mixed mortar or concrete without increasing water content or maintains workability with a reduced amount of water is known as 'workability aid'. The materials used to increase the workability are many such as lime, foaming agents, sodium silicate• and the surfactants etc. Addition of these substances better known as plasticzers to the concrete result in better workability and higher strength than the control. However, these materials possess low order effects. However, there are some other substances such as glucose, Na-gluconates, Ca and Na-lignosulfonates, salicylic acid, hydroxy acids, carbohydrates, borates, phosphates of Pb, Zn, Cu etc. which are found more capable of reducing water requirement to the order of 10-15 percent. To achieve higher reductions, some other organic materials have been developed during last decades which are called superplasticizers. These materials are capable of reducing water contents to the order of 30 percent and at the same time resulting in improvement in the desirable properties of cement mortar. Pulp and paper" industry is an ever expanding industry which causes considerable pollution, especially during pulp making. Water requirement in paPer industry is also high of the order of 250-400 m3/tonne of paper produced. About 80-85% iv of water consumed by industry is discharged as wastewater. The characteristic of the wastewater depends upon the raw material, technology used and the environmental conditions. It has'high COD (4800 mg/1.), high BOD (1545 mg/1.); high total solids (8600 mg/1.); dark-brown colour, chlorides (380 mg/1.); sulphates (730 mg/1.), pH - 8.5-9.5. There are various testing procedure of workability for cement mortar and concrete. Viz. slump test; compaction factor test; Vee-bee consistometer and flow table test. Workability testing for cement mortar is generally done by flow table test. A study of the effluent from a paper mill with the help of UV spectra showed that it contained lignosulphonate which is a well known water reducing agent. A number of properties of the cement were studied by the additon of effluent from a small paper mill. The addition of certain quantities of this effluent to cement mortar or concrete mixes have been found to result in the reduction of water content for preparing a workable mortar or concrete. It does not have any effect on setting time as it contains very small quantities of chlorides or sugar etc. The flow values of mortar increases as the effluents percentage increase. It has been found that there is a gain of 30-50% in 7 days and 5-10% in the 28 days compressive strength by the. incorporation of effluent with 1:3 cement-sand mortar at V different workability/flow. The gain in compressive strength at same workability/flowfd)rEMmm.cubes at various dosages is from 40 to 80 percent at 7 days. However, the gain is 5 to 10 percent at 28 days. A reduction of about 18.5% in water-cement ratio can be achieved by incorporation of varying dosages of the effluent. Water reduction is desirable in a cement mortar as an increase in strength or a reduction in shrinkage and a reduction in cement content for a given strength may be achieved. The paper mill waste is capable to serve this purpose and hence is recommended as a water reducing agent for mortars and concrete. The paper mill effluents contain lignosulfonate. It is also available as such in the market. The cost of lignosulfonate base material in market is about 5-15 rupees per bag of cement. However, the small paper mills dispose their effluents without any treatment or chemical recovery since it is not economical for those plants. Therefore, the paper mill effluents may become available without any cost for use in the building industry. It has also been established in these studies that incorporation of effluents in cement mortar increases compressive strength and hence life of the structure, as well as it also reduces shirinkage and thus rendering the mortar and concrete structures impervious. This increased life of the structure will minimise the maintenance cost of the structure. Thereby the use of the paper mill effluents will be economical both from the point of view of direct materials use as well as indirectly from less expences on maintainance of the building.