The effects of addition of amorphous nanosilica particles to three grades of cement mortars Portland pozzolana cement 33, ordinary Portland cement 43, and 53 are investigated. The nanosilica particles are used as a partial replacement of cement by 0.25, 0.50, 0.75, 1.00, and 1.25 wt.%. The tests of cement mortars are carried out in water for 3rd, 14th, 28th, and 90th day. Addition of nanosilica reduces the setting time and in turn increases the compressive strength and saturated water absorption, and its digestion of calcium hydroxide crystals leads to a decrease in the size of crystals accumulated at the interface. *

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The method of microbial mineral plugging in porous media is common in nature. Physical and biochemical properties of calcium carbonate (CaCO 3 ) precipitation induced by Enterobacter and Serratia microorganisms into cement mortar specimens are studied and analysed. X-ray diffraction is used to identify the calcium carbonate crystal as calcite, vaterite, aragonite. Scanning electron microscopy (SEM) is used to verify the formations of white precipitation (calcium carbonate) in the microbial cement mortars. The improvement of strength in the concrete/cement mortar base is attributable to the formation of calcium carbonate, which fills the pores between the cement sand matrices. In the present study a noteworthy enhancement of compressive strength of 44% is observed in the biocuring Enterobactertreated specimen relative to control. This method of implanting semi-solid mixtures onto the surface of the cement paste specimens shows significant effects such as decrease of permeability and capillary water penetration.

Microbially induced calcium carbonate precipitation is a method for the protection of cement-based materials. This paper deals with the strength characteristics of microbial cement mortars, which are treated by the Enterobacter sp.FJ 973550 microorganism in different calcium sources (calcium hydroxide, calcium acetate, calcium chloride and calcium oxide). The crystalline phases of calcium carbonate crystal formation and the surface morphology of cement mortar are investigated by X-ray diffraction and scanning electron microscopy. Microbial cement mortar specimens treated in calcium hydroxide source show higher compressive strength (,29%) and tensile strength (,47%) compared to control specimens. Surface treatment of specimens with bacteria resulted in an approximately 56% decrease in water absorption and increased the resistance to water and hazard material penetration. This biological surface treatment shows promising prospects for increasing strength and durability aspects of cement mortar specimens.

Light weight concrete is an important part in the concrete technology. The use of mineral additives in light-weight concrete, to replace fine aggregate with fly ash and bagasse ash, helps to reduce the cement content. The present investigation aims to meet the performance of light weight concrete, by adding fly ash and bagasse ash, as fine aggregate replacement additives. The strength properties such as cube compressive strength, cylinder compressive strength and split tensile strength were investigated after different ages, to find the optimum addition of mineral additives such as fly ash and bagasse ash, in concrete. The strengths were compared and the optimal replacement level of cement with fly ash and bagasse ash was found. The cylinder compressive strength and split tensile strength of light weight concrete were measured, at the same replacement levels of mineral additives, at the age of 28 days curing. The mathematical equations were proposed to achieve cube compressive and tensile strengths, cylinder compressive and tensile strength and cube compressive and cylinder compressive strengths, concerning typical strength.