Usama H. Issa

On the compressive strength and geo-environmental properties of MC-clay soil treated with recycled bassanite

The use of recycled bassanite, produced from gypsum wastes, in ground improvement projects is initiated recently in Japan to eliminate the huge quantities of gypsum wastes. Meanwhile the use of recycled bassanite has a positive effect on the environment and economy, it has many challenges. These challenges are related to the release of fluorine more than the standard limits results in contaminated fluorine soil. This research investigates the effect of the amount of bassanite, and water content on the release of fluorine from MC-clay soil stabilized with bassanite, taking in consideration their effect on the compressive strength. Recycled bassanite was mixed with furnace cement with a ratio of 1:1 to prevent the solubility of bassanite. Different amounts of this admixture were mixed with the tested soil at different water contents. Unconfined compression test was used to determine the compressive strength while the solubility of fluorine was used to represent the geoenvironmental properties in term of the release of fluorine. Scan electron microscopic (SEM) test was done to identify the development of cementation compounds in the matrix of treated-bassanite soil. Test results showed that, the addition of bassanite had a significant effect on the improvement of compressive strength by increasing the amount of bassanite. Curing time had a significant effect on the increase of compressive strength, the strength increases with the increase of curing time, especially in the later curing time. The release of fluorine increases with increasing the amount of bassanite in soil mixture. The increase of water content had an indirect effect on the release of fluorine while it had a negative effect on the improvement of strength and consuming the amount of admixture. The increase of strength is associated with the decrease of the release of fluorine. Recycled bassanite, produced from gypsum wastes, had a potential to be used as a stabilizer material for MC-clay soil and meet the standards of environment.

DEVELOPING A DECISION-MAKING MODEL FOR REINFORCED CONCRETE COLUMNS STRENGTHENING

Steel tubes (ST) have long been used to strengthen RC columns, while the application of CFRP for this purpose is a recent practice. Both techniques have many advantages and shortcomings. In this paper, a multi-criteria decision-making model is introduced to quantify the selection of one of the two techniques. Four criteria and 28 factors affecting them are identified to develop the model. The selected criteria are cost, strengthening efficiency, durability, and project scope achievement. The model is fed by data collected from execution activities, field surveys and previous laboratory test results. The model has been validated and applied to a real case study. The detailed discussion and analysis indicated that many features support the use of CFRP in the investigated case study. Furthermore, the analysis emphasised that the strengthening efficiency and durability decide the selection while project scope achievement criterion is insignificant compared to other criteria. Ultimately, the obtained results from the case study provide the construction market with a decision that supports the use of the CFRP by 56 %, while the use of ST is only supported in 44 %.