This investigation was performed to establish the effects of pozzolanic and chemical admixtures on setting behavior of cement paste at normal consistency. An ASTM Class C fly ash was used as a pozzolanic and cementitious admixture. Mixtures were proportioned to contain fly ash in the range of O-l 00% by mass of the cementitious materials using a cement replaced by fly ash in a proportion of 1: 1.25. One source of ASTM Type I cement was used. The effects of five admixtures, air-entraining agent (AEA), water reducer, retarder, high-range water-reducer (HRWRA), and hemihydrate gypsum (CaSO,. 1/2H2O) on setting characteristics of pastes, were investigated. Both initial and final setting times remained essentially the same or were slightly delayed up to 20% cement replacement with respect to the 0% fly ash mixture. Beyond this range, the times of setting were generally accelerated. Increased rate of setting occurred at cement replacement levels of 40 % and above irrespective of type of chemical admixtures used.

Concrete specimens were manufactured by completely replacing natural aggregates with recycled aggregates from a crushing plant in which rubble from building demolition was ground. Various concrete was prepared by using silica fume or fly ash as a partial fine aggregate replacement and by using an acrylic polymer based superplasticizer to achieve the prefixed workability. Three types of recycled aggregate concrete were manufactured with the same water/cement (0.40) and the same fresh workability (fluid consistency). A reference concrete was also prepared by using natural aggregates with the same particle size distribution as the recycled aggregate, and having a water/cement of 0.56 and a similar fluid consistency. The results obtained show that because of mineral addition and W/C reduction, recycled aggregates can be used instead of natural aggregates since concretes with similar compressive strength can be obtained. The use of the recycled aggregates with fly ash replacements also has significant cost and environmental advantages over ordinary concrete.

This investigation was conducted to establish database for manufacturing of concrete masonry products incorporating high volumes of ASTM Class F fly ash. A total of 15 mixture proportions for bricks, blocks, and paving stones, including reference mixture for each type of masonry product, was proportioned. The fly ash content was varied from 20 to 50% for brick and block mixtures, and from 15 to 30% for paving stone mixtures All masonry products were tested for compressive strength, density, absorption, freezing and thawing resistance, drying shrinkage, and abrasion resistance. Test results indicated that bricks and blocks with up to 30% fly ash are suitable for use in both cold and warm climates. Other brick and block mixtures containing up to 50% fly ash were appropriate for building interior walls in cold regions and both interior and exterior walls in warm regions. None of the paving stone mixtures, including the control mixture, strictly conformed to all ASTM requirements. However, all the paving stone mixtures with and without fly ash are suitable for normal construction applications.

In developed countries use of mineral admixtures such as fly ash, silica fume has already been adopted in making concrete. This includes commercial application on a large scale either for addition or for replacement of cement. In India too such replacements have been readily accepted. With the introduction of ready mixed concrete the process has been accelerated in recent times. An investigation was undertaken to study the effects of fly ash and silica fume in concrete. Compressive strengths at different levels of replacements were found. Silica fume from a local source and fly ash from Ramagundam thermal power station of the State of Andhra Pradesh were used. Maximum size of coarse aggregate was 12.5 mm. Water to cementious materials ratio was 0.32 and aggregate-cementitious materials ratio was 3.2. Cement replacement levels by fly ash were 0, 10, 20, 30, and 40 percents and by silica fume were 0,4, 8, 12, and 16 percents. Thus a total of 25 mixtures were studied. Strengths at the ages of 28 days and 56 days were found. The results are presented in tables and figures. It was found that the highest replacement level of 40 % by fly ash and 16 % by silica fume, simultaneously, i.e. a total replacement of cement to the extent of 56 % gave a 10 % increase in the 28-day compressive strength compared to that of control concrete. Maximum increase of 43 % in the 28-day compressive strength was observed at a 32 % level of cement replacement ( 20 % by fly ash and 12 % by silica fume).

In the process of a long-term study of fine cementless mortar from wastes of thermal power plants (TPP) and other industries, aspects of its tech-nology were determined which were as follows: power 1. Processing slag (also known as bottom plant to sand of 0 to 5 mm size fraction. ash) from the Abakan thermal 2. Grinding fly ash to a fineness of 700 to 750 m2/kg with the use of mechanochemical activation process. 3. Using two - stage thermal treatment of cementless mortar mixture and determining optimal regimes for secondary thermal treatment. 4. Using a model method for concrete development. The application of cementless ash slag mortars non- load - bearing concrete profitability respectively. to load - bearing and