Throughout history, men have searched for knowledge by observing natural phenomenon, study of literature, thought, discussion and above all the integrated scientific experimentation. The twentieth century saw the advent of a large number of new materials and products accompanied by the emergence of new methods for the production and use of traditional materials. The basic incentive sprang from the vast construction programmes, which originated from the necessity for a rapid rise in the living standards and the need to provide infrastructure to the shelter less. Research on building science is much more paying than any other discipline because the buildings are repetitive in character and invoke interest of private and public sectors alike. The research done in other countries can only be a guide line as it is rarely applicable Universally. Each country has to find solution to its problems compatible with loea1/1iving conditions.
During the present century, Portland cements have reached a dominant stage and become the keynote of the development of any country. Since limes immemorial, two types of cementing materials have been in use, non-calcareous and the calcareous. The non-calcareous cementing materials include mud, clay, glue, bitumen etc. While the calcareous category comprises compounds containing essentially calcium oxide, as the basic ingredient. The only binding agent in use, in the local building industry, the Port land cement, falls into this category. It has been all along in short supply. The ever accentuating shortage has been posing great hinderance to most of the developmental works and threatening the achievements of the Annual Development Programmes of the country. This state of affairs has attracted the attention. of builders, engineers and the chemists to carry out applied research for the development of a Iternate conventional or modern cementing materials, from within t he natural resources so as to maximize the use of indigenous raw materials/technology, without jeopardising the safety or the stability of the structures.
Pakistan abounds in easily mineable high quality raw materials like gypsum, limestone and argillaceous/calcareous earths that could be usefully utilized as substitutes for Portland cement, which has a history of only about 160 years. Before its advent in 1824, the role of gypsum and lime, as cementing materials, was well recognized/established in building works. Ironically however, these have been totally omitted /relegated tot he background in Pakistan, now-a-days. Their revival, inspite of several inherent plus points and the venerable heritage in cons truction could only be possible, if these are presented in modified/improved low-in-cost forms, duly supported by scientific/technical studies/data. The work Was aimed a t achieving this. target alongwith studying the chemical -aspects of various steps involved.
In order to fulfill the responsibility of making the right choice of materials of good performance and properties, a thorough understanding of the nature and behavior of the materials is needed. The study of behavior involves the application of the principles of the nature of materials, under different conditions. The plan of work to exploit and familiarize the use of gypsum and lime as alternate materials of construction, in Pakistan comprised:-
a)conducting comprehensive literature survey on the historical background of various cementing materials including the gypsum, lime and the Portland current;
b) Finding out the composition of the mortars/plasters with particular emphasis on the ancient, pre- Moghal, Moghal and subsequent constructions in the Indo-Pakistan sub continent;
c) Assessing the cuantum /chemical quality of the natural gypsum and lime stone resources;
d)Evolving steps, ways and means to improve these raw materials to within the required limits by the physical and chemical purification/treatment ;
e)Evaluating the quality of the being manufactured gypsum plasters by chemical, physical and mechanical means;
f)Studying the chemical and physicc:1 changes in the setting process of gypsum plaster, the chemistry of reactions involved, mechanism of retardation/acceleration of the set;
g)controlling the setting limes of the gypsum plasters without jeopardising strength so as to make these acceptable to the building trade either by making improvements in the calcination operations or by the use of chemical admix tures;
h)popularizing the various forms of construction with gypsum including prefabricated low cost partition board/ sheet walling units;
i)Improving the brittle characteristics of gypsum in thin sections by fibrous reinforcement/determining their impact, flexural and fire resistance qualities.
j )Using gypsum in unit masonry cons tructionand the pi aster works instead of cement sand mortars/plasters;
k)Finding out background and the chemical steps involved in the use of various forms of lime in its old conventional putty and the modern dry hydrated powder forms;
I ) Comparing the strength values and other related criteria of gypsum, lime and cement-lime neat or sand compounded mixes /mortars, vis-a-vis common- in-practice Portland cement mixes under identical conditions;
m)Finding out the degree of fineness and the storage sensitivity of dry hydrated lime cement;
n)Comparing costs of construction- by using gypsum boards, sheets, plasters and the lime or cement lime mortars vis-a-vis Portland cement mortars/plasters.
Efforts made and progress achieved on various aspects of t he above spelled out programme are described in detail, in the following chapters.