Reinforced concrete--Environmental testing

The purpose of this research project is to compare the strength and durability
characteristics of rice husk ash-modified concrete with those of normal concrete in
the marine environment. Specimens prepared from concrete mixes with watercementitious
ratios of 0.40 and 0.55, and rice husk ash content of 0%, 10%, and 20%
were tested. The rice husk ash used was obtained from Agrilectric, power plant
located in Lake Charles, Louisiana. The grinding of the ash to particle size of 7-J..tm
to 45-J..tm was done by Process Research ORTECH Inc., Ontario, Canada. Strength
and durability tests were performed, following ASTM (American Society for Testing
and Materials) Standards. The significant fmdings are that the properties and quality
of the rice husk ash-modified concrete are as good, if not better than normal concrete.

Durability of marine reinforced and unreinforced concretes was tested under accelerated environmental conditions. The specimens were subjected to alternate wet and dry cycles in specially constructed durability testing tanks. The specific objective was to evaluate the durability of different types of concretes with varying water-cementitious material ratios (0.3, 0.4, and 0.6), cement types (Types I and II), mineral admixtures (blast furnace slag, fly ash, microsilica), and steel types (black, galvinized and epoxy-coated rebars). The unreinforced cylindrical specimens were tested for compressive and splitting tensile strengths and the reinforced prismatic specimens for corrosion. The test results after 300 cycles of accelerated exposure indicated the adverse effects of the marine environment on the durability of concretes, resulting in loss of strength and corrosion resistance. The specimens with lower w/c ratios (0.3 and 0.4) showed good performance, whether or not they were admixture modified. However, mineral admixture inclusions improved the properties of strength and corrosion resistance of the specimens even with high w/c ratios (0.6). The specimens with regular rebars indicated least resistance to corrosion induced from the accelerated marine exposure compared to the ones with galvanized and epoxy-coated rebars.