Abstract
The germicidal effectiveness of various additives when blended within a microstructure of a cement based system was studied. The relationship between the chemical and physical characteristics of concrete surfaces and their ability to have an enhanced resistance to algal growth was documented through a novel set of laboratory and field testing. The main potential areas of application for these new cement composite systems involve the lining of canal surfaces where fixed-surface biocides are desirable to control biofouling. Different biocide formulations containing class F fly ash, silica fume, Zn oxide, copper slag, ammonium chloride, sodium bromide, and cetyl-methyl-ammonium bromide were evaluated for the mitigation of algal growth on concrete surfaces. Mortar coupons treated with these formulations were tested under laboratory and field conditions.
These new cement composite systems were compared with proprietary products that are commercially available and applied using a latex paint. Laboratory scale screening experiments showed that various concentrations of zinc oxide significantly inhibited algal growth even after nine months. It was observed that 20% zinc oxide in concrete produced optimal algal inhibition compared to other additives. Copper slag, ammonium chloride, sodium bromide, and fly ash, when added singly, also showed algal inhibition capabilities. Addition of zinc oxide and ammonium chloride (10% each) in mortar mix was as effective as expensive proprietary chemicals in reducing algal growth on concrete surfaces under laboratory and field conditions.

1. Introduction
Plain or reinforced concrete has been traditionally used for covering the surfaces of many canals, pipes, irrigation channels, and water treatment structures. The surfaces of concrete provide an ideal corrosion resistant, physically and chemically stable environment for exposure to potable or waste water. There is however a lack of understanding in the correlation between the nature and composition of the concrete with its biological characteristics in terms of a medium for water transportation and delivery. The purpose of this paper is to investigate if changes in the chemical composition of paste can result in suppression of algae growth on concrete surfaces in canals.H

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