Utilization of Oyster Shells as a Substitute Part of Cement and Fine Aggregate in the Compressive Strength of Concrete

The compressive strength of concrete depends on the physical characteristics of the concrete forming materials. Oyster shells originating from Krueng Neng, Aceh Besar are very abundant, left unattended by fishermen, causing pollution of the surrounding environment. Oyster shell dust contains CaO, which can be used as a partial substitution of cement. Therefore, it is necessary to study oyster shell ash as cement replacement and fine aggregate in concrete production. This research aims to determine the compressive strength of concrete using shell ash as cement replacement and fine aggregate. The oyster shells were obtained from Krueng Neng, Lamjamee Village, Jaya Baru, Aceh Besar District. The oyster shells were crushed with a Los Angeles Test machine and sieved with sieve size 2.36 mm for fine aggregate and sieve #200 for cement replacement. The water-cement ratios (w/c) were 0.4, 0.5 and 0.6. The results showed that concrete's compressive strength with 5% cement replacement level was higher than the concrete with cement only. Meanwhile, for other replacement levels, the compressive strengths of concrete specimens were lower than control specimens.

Study Concerning Characterization of Some Recycled Concrete Aggregates

Using recycled concrete aggregates (RCA) is a matter of high priority in the construction industry worldwide. In countries like the Netherlands, Denmark, Germany, USA, Japan, France recycled concrete aggregates obtained from demolition are valorized up to 90%, mainly for road construction and less in the manufacture of new concrete. Recycled concrete aggregates (RCA) generally result from a two-stage crushing of the concrete obtained from demolition followed by the screening and removal of contaminants (wood, plastic, metal, ceramics etc.). The literature review showed that the recycled aggregates concrete (RAC) are less resistant, with 15 to 40% versus concrete obtained using natural aggregates. The factors that play a role in the reducing of mechanical resistance are presented and analyzed in this study. This paper presents a study on the use of recycled aggregates, from a concrete of specified class, to acquire new cement concrete with different percentages of recycled aggregates. In order to evaluate the influence upon the properties of the new concrete obtained, recycled aggregates have been characterized in terms of the granulosity, the granule shape, the absorption of water, behavior to the Los Angeles test, the content of attached mortar etc.

The Use of Recycled Aggregates in Continuously Reinforced Concrete Pavements (CRCP)

The use of recycled aggregates in concrete has increased in recent decades. Increasing scarcity of natural aggregates and the growing ecological importance promote this evolution. The first test section in Belgium of a two-layer continuously reinforced concrete pavement (CRCP) with recycled aggregates in the substrate layer was built on the highway E34/N49 in 2007. Horizontal cracking at the level of the reinforcement showed up after only a few years. This is a problem which was never seen before in CRCP and was probably due to the use of recycled aggregates. Therefore it is important to understand the impact of recycled aggregates on concrete. Recycled aggregates are a two-component material consisting of natural aggregates and adhering mortar. The adhering mortar is more porous than the rock particles which insures a higher water absorption and lower density. In addition, they have a lower abrasion loss in the Los Angeles-test and less resistance against weather and temperature changes. This is due to, respectively, the less strong mortar content, and the large pores of recycled granulates. A first cause of horizontal cracking can be found in the results of high drying shrinkage, high creep and low modulus of elasticity. These properties insure larger tensions in the concrete layer. In combination with a lower tensile strength it is a possible cause for the horizontal cracking. In addition, the paper reports on laboratory testing concerning the properties of concrete with recycled aggregates and discusses an alternative method to determine the concrete mixture which takes the influence of the adhering mortar into account.