Investigation of Fresh Concrete Behavior on Slope Lining

1. Various factors lead to the creation of cracks in the slope lining of canals and one of the most important factors is the insufficient value of slump according to the cross-slope of canal. Workability of concrete shows the condition of concrete to indicate of how easy or difficult to place and consolidate. Slump test is one of the workability tests to measure it [1, 2]. Currently in our country, the concrete canal lining is constructed without the use of vibration, thus use of concrete with higher slump helps to maintain its workability. On the other hand, because of placing concrete on a sloping surface, it is poured on the surfaces with high slump. Hence as a result, high slump value of concrete mix will be poured on the slope and low slump value causes inefficient consolidation; and maintaining of the workability and consistency of concrete on slope lining at the same time is necessary [3].2. This research investigated concrete slump values in different slopes according to workability and consistency of mixtures in lining. For this purpose, a steel mold with dimensions of 1000 × 600 × 100 mm has been made. Consistency showing the flowing ability of fresh concrete in slope lining depends on internal friction angle of aggregates, cohesion of cement mortar, coefficient of friction between the concrete and the contact surface, slope angle, and the length and thickness of the concrete panels.3. Experiments show that if a concrete mix with low slump will stay unstable on a particular slope, concrete maintains its consistency and glides down over the surface without any segregation. However, if a concrete mix with high slump value stays unstable on a particular slope, concrete pours on the surface of slope with the segregation of mix. Compressive and flexural test of samples were done and the results were compared with control samples. The results of this research demonstrate the reduction of the value of mechanical properties occuring at the bottom of some concrete panels compared to the top of the slope when concrete samples glide down or pour on the slope and we have to try keep it stable. This may be a good reason to create cracks in bottom of the slope during the serviceability of canals.Comparison of samples separated from the panel and control samples has been presented in Table 1.Table 1. Comparison of samples separated from the panel with control samplesSample properties Average of control samples Average of samples separated from the panel Comparison of panel sample and control sample Control sample with the weakest characteristics Control sample with the best characteristicsTensile strength at 28 days (MPa) 8.14 6.13 24.7% reduction 7.97 7.25 Compressive strength at 28 days (MPa) 72.6 50.7 30.2% reduction 71.75 60.62Water absorption percentage 2.7 3.61 31.3% increase 2.86 3.144. Stability of concrete on the slope is dependent on various factors such as internal friction of aggregates, cement mortar bonding, friction coefficient between the concrete and the lower surface, the angle of slope surface and the thickness of concrete panels. Comparing the control samples and panel samples demonstrated that even with the best execution, samples are not even close to satisfactory condition and it seems to be necessary to use vibration in canals concreting.