جستجوی مقالات مرتبط با کلیدواژه « Durability » در نشریات گروه « آب و خاک »

Concrete mix-design specifications for concrete lining of irrigation canals in different regions are often considered the same by designers. However, the destructive factors of durability and instability of this structure are not same in different environmental conditions and so separate designs must be presented in different conditions. In this study 9 types of concrete mixes including: 3 grades of cement level, 3 ratios of (W/C) ratios and 3values of AEA were prepared. To determine specifications of durable concrete for irrigation canals in cold regions, various laboratory experiments on fresh and hardened concrete was performed. Cement grades of 325, 350 and 375 kg/m3 of concrete and w/c ratios of 0.4, 0.45 and 0.5, as well as AEA values of 0% (without AEA), 0.01 and 0.03% of cement weight was used. After preparing the concrete mixtures, different experiments on fresh concrete, including determination of slump, total air percentage, density and hardened concrete, including water absorption tests, compressive strength, modulus of elasticity and freezing-thawing cycles were performed up to 300 cycles. Based on the results, among the 9 concrete mixes samples, 3 mixes were durable in frost condition and were compatible with cold regions. These mixtures are as follows: 1- A mixture with a W/C ratio of 0.4, a cement grade of 350 kg/m3 and without AEA, 2- with a W/C ratio of 0.45 and a grade of 350 kg/m3 with 0.03% by weight of cement AEA, and 3- the W/C is 0.45 and the grade of cement is 325 kg/m3 without AEA. It was also found that using 1 to 2 kg/m3 of Concrete super plasticizer, the W/C ratio can be reduced to 0.4 and the concrete lining can be durable without using of AEA.

To evaluation of irrigation canals lining, uaually compressive strength is determined, whereas new studies proved that this paprameter cant guarantee lining durability during its lifetime. Durable concrete in cold climate can save its serving in lifetime. In this paper durability of hardened concrete in irrigation canals in Bahar plain in Hamedan province were evaluated and results were compared with prescribed standards. For this purpose, 5concrete lined canals were selected to study and field and laboratory examinations were done. Name of selected canals is Gondejin, Bahadorbeig, Abroomand, Khooshab-olia and Komooshboolaghi. Field examinations were including: 25 samples coring from these canals. Laboratory examinations were including: determination of specific gravity, initial and final water absorptions, depth of water penetration in cores. Results showed thatmean values of specific gravity, initial and final water absorptions, depth of water penetration in cores were 2.1 gr/cm3, 5.8%, 7.7% and 79 mm respectively. Based on prescribed standards mean values of these parameters must be 2.4 gr/cm3,3%, 5% and 30 mm respectively. With comparision results and prescribed standard values, it can be noted that measured mean values of specific gravity of cores is 15% less than standard. Initial and final water absorptions and depth of water penetration in cores are 3, 1.5 and 2.5 time, respectively, more than those in standards. These results express that concrete lining of studied irrigation canals is undurable for freezing-thaw condition. High permeability and high water absorption of cores is due to high porosity and low compaction. Field observations confirmed these conclusions. Because of unsuitable durability of cores, it can be concluded that concrete lining in studied canals are not secure lining in front of freeze- thaw cycles in their lifetimes.

In most civil projects، such as irrigation and drainage networks constructions، soil stabilization has an important role. Achieving maximum durability against wet-dry cycles is one of the soil stabilization objects. Therefore، depend upon project type and its importance; various hydraulic binders with different amounts are tested to obtain desirable results from technical and economical view. In this research، the effect of dry-wet cycles on engineering properties of clayey soils (low plasticity) was studied and lime، cement and lime-cement binders، with (2-6) percent of soil weight، were used. The results showed that with changing type and percent of binders، various sample durability against dry-wet cycles is different so that without binder samples did not have durability and the samples stabilized by 4% cement and 4% lime tolerance 12 wet-dry cycles. The results also showed that after dry-wet cycles، the mass and volume of sample were changed and its unconfined compressive strength was decreased so that the decrease of the unconfined compressive strength was between 40% and 60%. The present study showed that dry-wet cycles significantly cause to change the soil geotechnical properties.