Investigation of effect of size and content of nano/SiO2 on the strength and durability of RCC in freezing-thawing cycles

RCC remains a widely used construction material over the last decade. RCC is placed in a manner similar to paving; the material is delivered by dump trucks or conveyors, spread by small bulldozers or specially modified asphalt pavers, and then compacted by vibratory rollers. By definition, Roller Compacted Concrete (RCC) is the concrete compacted by a roller in a hardened state. RCC is a special type of concrete that has essentially the same ingredients as concrete. However, at different ratios, partial substitution of fly ash is increased for Portland cement. This type of concrete has facilitated constructing many new dam and pavement projects and reducing costs by shortening the time duration of implementation. Rolled concrete materials are generally applied instead of the soil-cement mixtures in projects. Soil-cement and rolled concrete are both completely compacted mixtures of cement, aggregate, and water, while their main differences are the type and size of aggregates. Using this kind of concrete has provided a chance for the construction of many dams and new pavements with economic advantages, leading to the quick construction management. Since these structures are exposed to climatic factors, their durability, especially against alternate thawing-freezing cycles, is of paramount importance. In the current research, silica nanoparticles were added to the RCC mix of three different diameters (10, 15, and 30 nm) and three different ratios (1, 3, and 5% by cement weight) in 50, 100, and 300 cycles to investigate their effects on compressive strength, dimensions, and weights of RCC samples. The experimental results illustrated that mixtures containing nano-silica had a better durability and strength than non-additive mixtures

Reducing sediment concentration and soil loss using organic and inorganic amendments at plot scale

Various organic and inorganic mulches are used for soil conservation purposes, the effectiveness of which on soil characteristics has not been comprehensively considered from different aspects. The present study surveys the efficiency of straw mulch, manure and TA-200 polyacrylamide with respective rates of 500, 300 and 50 g m−2 in changing sediment concentration and soil loss. The experiments were conducted for sandy-loam soil taken from a summer rangeland, the Alborz Mountains, northern Iran. The experiments were performed under laboratory conditions with simulated rainfall intensities of 30, 50, 70 and 90 mm h−1 and a slope of 30%. The results showed that the straw mulch decreased soil erosion at rate of 45.60% compared to the control plots and performed better than manure (8.98% reduction) and PAM (4.74% reduction). The results showed that the maximum reduction in sediment concentration and soil loss for all soil amendments occurred at the rainfall intensity of 90 mm h−1 with the rates of 58.69 and 63.24% for straw mulch, 14.65 and 13.14% for manure and 20.15 and 23.44% for TA-200

How does land use configuration influence on sediment heavy metal pollution? Comparison between riparian zone and sub-watersheds

The effect of land use on sediment quality depends on the spatial scale. It has been found that not only the type of land use but also the landscape characteristics has a significant impact on water quality ecosystem services provided by riparian zones including filtration of sediments and pollutants. In the present study, principal component analysis and hierarchical clustering were used to investigated the relationship between land use and landscape characteristic metrics with suspended and bed sediment heavy metal pollution at sub-watershed and multi-spatial buffer zone scales (250, 500, 750 and 1000 m) in Talar watershed. The results of multi-element sediment quality indices showed a high level of heavy metal pollution (As, Be, Cd, Cr, Cu, Pb, Hg, Ni, Se, Ag, Ti and Zn) for all 10 sampling points upstream and downstream of the study river. Irrigated agriculture and residential were two land uses showed the highest positive meaningful correlation with sediment heavy metals in 250 m buffer and sub-watershed, respectively. Furthermore, the results showed that the higher level of diversity and interspersion of land use patches, the more negative effect on sediment pollution. Our study outcomes could provide useful information for managers and policymakers in land planning and development to minimize river sediment pollution and preserve the health of water resources. Graphic abstract: [Figure not available: see fulltext.]

Scale effect on runoff and soil loss control using rice straw mulch under laboratory conditions

Amendments can control the runoff and soil loss by protecting the soil surface. However, scale effects on runoff and soil loss control have not been considered yet. The present study has been formulated to determine the efficiency of two plot sizes of 6 and 0.25 m² covered by 0.5 kg m⁻² of straw mulch with regard to changing the time to runoff, runoff coefficient, sediment concentration and soil loss under laboratory conditions. The study used a sandy-loam soil taken from summer rangeland, Alborz Mountains, northern Iran, and was conducted under simulated rainfall intensities of 50 and 90 mm h⁻¹ and in three replicates. The results of the study showed that the straw mulch had a more significant effect on reducing the runoff coefficient, sediment concentration and soil loss on a 0.25 m² plot scale. The maximum effectiveness in time to runoff for both the scales was observed at a rainfall intensity of 90 mm h⁻¹. The maximum increasing and decreasing rates in time to runoff and runoff coefficient were observed at a rainfall intensity of 90 mm h⁻¹, with 367.92 and 96.71% for the 0.25 m² plot and 110.10 and 15.08% for the 6 m² plot. The maximum reduction in the runoff coefficient was in the 0.25 m² plot for the two rainfall intensities of 50 and 90 mm h⁻¹, with rates of −89.34 and −96.71%. The maximum change in soil loss at the intensities of both 50 and 90 mm h⁻¹ occurred in the 0.25 m² plot, with 100%, whereas in the 6 m² plot, decreasing rates of soil loss for the intensities of both 50 and 90 mm h⁻¹ were 46.74 and 63.24%, respectively