Hisahiro Matsunaga

Microfouling Studies on Experimental Test Blocks of Steel-making Slag and Concrete Exposed to Seawater off Chiba, Japan

Microfouling studies with the emphasis on microalgae (Bacillariophyceae) were carried out on test blocks of steel-making slag in comparison with concrete. Two types of slag test blocks, with and without fly-ash as an additional source of silica, and concrete test blocks of size 75 × 26 × 26 mm were used to study microfouling build-up for a period of 30 d, with intermittent samplings after 1, 2, 3, 7,14 and 21 d. The species composition, cell density, biomass and surface pH of the test pieces were determined, in addition to the hydrographic parameters of the water column. Microfouling studies showed higher numbers of algal species as well as a greater cell density on the slag than on the concrete blocks. This was true with respect to biomass measured as dry weight also. Colonization was significantly delayed in the case of concrete. Navicula spp. and Nitzschia spp. were the initial colonizers on all three types of substrata and were the dominant genera throughout the study period. While the number of species increased, several disappeared after colonization, as a part of community build-up. The surface pH of the slag blocks was near neutral, whilst that of the concrete was highly alkaline during the initial period of exposure. This alkaline surface reduced the rate of species colonization on the concrete blocks initially. The study showed severe biofouling on the slag blocks compared to concrete and thus they were considered an environmentally benign construction material for land protection. The use of slag as the construction material for land protection would greatly reduce the expense compared to concrete.

Development of Continuous Blast Furnace Slag Solidification Process for Coarse Aggregates

Recently, effective utilization of by-product slag as aggregate for concrete has been expected from the viewpoints of depletion of natural crushed stone and suppression of environmental loads. We developed a new process for continuous solidification of blast furnace slag as coarse aggregate. In this process, molten slag is continuously poured into molds, and the slag is solidified at the thickness of 20–30 mm. The flow rate of the molten slag is 1 t/min, and maximum production per ladle is about 30 t. After solidification, blast furnace slag coarse aggregate (BFG) is produced by crushing and adjusting the particle size of the solidified slag. The new BFG has water absorption of less than 1%, and concrete containing the BFG has the same fresh property and compressive strength after 28 day as concrete using natural crushed stone aggregate.