A STUDY OF BLACK LIQUOR IN EGYPT AND ITS UTILIZATION AS CONCRETE ADMIXTURES

Abstract

Paper production industry is considered one of the national economic activities in our country; its importance is not only due to the reward of paper production, but also due to use large quantities of agricultural residues e.g., rice straw and bagasse; solving by this an enormous pollution problem. However another problem is born with this industry, this problem appears in the large quantities of industrial wastes in the form of black liquor.

An experimental program was conducted to analyze the black liquor produced from rice straw pulping from RAKTA company (Alexandria governorate), and the liquor produced from bagasse pulping from EDFU company (Aswan governorate) and QUENA pulp mill (QUENA governorate) to define the characteristics of each. A literature survey about lignin - the cementing material between cellulose cells in plants - and its wide utilities, lignin separation and black liquor treatment were also necessary in order to recognize the most useful process and optimize the best manner of using lignin in black liquor as concrete admixture.

The effect of using black liquors as it is without treatment as concrete admixtures was studied. The results record the effect of various concentrations of black liquor as replacement percentage of mixing water by volume on the properties of fresh and hardened concrete for different ages along one year; since black liquor properties change with long storage time. Also the effect of incorporating silica fume - as weight replacement percentage of cement weight - with the optimum dose of black liquor on concrete performance was studied.

The experimental results revealed that black liquor from rice straw pulping acts as set retarder, improves the concrete workability even at water cement ratio equal to 0.4. The compressive strength of hardened concrete can be increased using silica fume in very small amounts for water cement ratio equals to 0.5. The long age of black liquor had a clear affect on concrete properties, so it should be stored in shadowy places to avoid change in black liquor properties for a maximum period of time not to exceed six months. On the other hand black liquors from bagasse pulping were found to be ineffective as concrete admixtures.

Finally, chemical analyses of hardened concrete were carried out to determine the chloride ions soluble in water and sulfate content in hardened concrete as percentage of cement weight. The results revealed that black liquor from straw pulping is suitable for plain and hardened concrete within recommended dosage.