LECA

This research evaluates the effect of both organic and ammonia loading rates and the presence of plants on the removal of chemical oxygen demand and ammonia nitrogen in horizontal subsurface flow constructed wetlands, 2 years after the start-up. Two sets of experiments were carried out in two mesocosms at different organic and ammonia loading rates (the loads were doubled); one without plants (control bed), the other colonized with Phragmites australis. Regardless of the organic loading rate, the organic mass removal rate was improved in the presence of plants (93.4 % higher for the lower loading rate, and 56 % higher for the higher loading rate). Similar results were observed for the ammonia mass removal rate (117 % higher for the lower loading rate, and 61.3 % higher for the higher loading rate). A significant linear relationship was observed between the organic loading rate and the respective removal rates in both beds for loads between 10 and 13 g m−2 day−1. The presence of plants markedly increase removal of organic matter and ammonia, as a result of the role of roots and rhizomes in providing oxygen for aerobic removal pathways, a higher surface area for the adhesion and development of biofilm and nitrogen uptake by roots.

In the paper, the effects of different percentages of additives (perlite, LECA, pumice) on the mechanical properties of structural lightweight aggregate concrete were tested and evaluated. For the research, 14 mixing designs with different amounts of aggregate, water, and cement were made. Experimental results showed that the specific gravity of lightweight structural concrete made from a mixture of LECA, pumice, and perlite aggregates could be 25-30% lighter than conventional concrete. Lightweight structural concrete with a standard specific gravity can be achieved by using a combination of light LECA with perlite lightweight aggregates (LA) and pumice with perlite in concrete. The results indicated that LECA lightweight aggregates show more effective behavior in the concrete sample. Also, the amount of cement had a direct effect on increasing the strength regardless of the composition of LAs. The amount of cement causes compressive strength to increase. Furthermore, the stability of different experimental models increased from 156 to 345 3 kg m while increasing the amount of cement from 300 to 400 3 kg m in the mixing designs of LECA and perlite for W/C ratios of 0.3, 0.35, and 0.4. For a fixed amount of cement equal to 300 kg, the compressive strength is reduced by 4% by changing the water to cement ratio from 0.5 to 0.4. The compression ratios of strength for 7 to 28 days obtained in this study for lightweight concrete were between 0.67-0.8. Based on the 2 Corresponding 140 Mehdi KHOSHVATAN, Majid POURAMINIAN rate of tensile strength to the compressive strength of ordinary concretes, which is approximately 10, this ratio is about 13.5 to-17.8 in selected and optimal lightweight concretes in this research, which can be considered good indirect tensile strength for structural lightweight concretes.

Reducing the weight of structural materials is an important issue in the construction materials engineering, because it results in a decrease in the amount of dead loads imposed on the structure. Semi-light-weight concrete may be created with LECA. Industrial LECA is made from expanded clay particles and possesses a low unit weight yet it has acceptable strength properties. However, light-weight concrete is porous. Therefore the durability of this type of concrete is a source of concern. The addition of pozzolanic materials improves the strength properties and durability of this type of concrete. In this study microsilica was added to structural lightweight concrete and the resulting changes in compressive strength were recorded. The weight of the cementitious materials were held constant and the cement was partially replaced by microsilica. The replacements were equal to 5, 10, 15, and 20 percent by weight of cementitious materials. Absorption was selected as an indicator of durability. All tests were carried out at the ages of 7 and 28 days and then comparisons were made. Based on the results, addition of silica fume will improve mechanical and durability properties of light weight aggregate concrete. According to the improvements made in the light-weight concrete by micro-silica and by cost considerations, score were given to each design mix. The economic feasibility of using this pozzolan was then discussed.