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Abstract This paper investigates the effects on the physical and mechanical properties and microstructure of lime-hemp concrete (LHC) materials at different binder mass ratios. A mixture of three cementitious materials, slaked lime, cement, and coal gangue powder, was used as binder, and hemp shives were used as concrete aggregate, and five test groups were designed, i.e., binder/hemp shives (B/H) mass ratios of 1.2, 1.4, 1.6, 1.8, and 2.0. The physical properties of LHC, including density, drying rate, water absorption, thermal conductivity coefficients, and mechanical properties (compressive strength and flexural strength) with different binder ratios were investigated. In addition, the microstructural properties of 56d LHC were investigated by SEM, XRD, and TG-DTG micro-scale analysis methods. The results showed that with the increase in binder content, the drying speed of LHC became faster, the thermal conductivity coefficients, compressive strength, and flexural strength increased, and the water absorption was just the opposite. With a fit ratio of 2.0, the strength is the greatest and the toughness is the best; with a fit ratio of 1.2, the thermal conductivity coefficient is the smallest and the insulation effect is the best. In addition, the hydration of the binder produced different forms of hydration products (CaCO3 and C-S-H), and the hydration products increased in quantity with the increase of the binder, resulting in stronger CaCO3 and C-S-H diffraction peaks. The hydration products produce a better bond with the rough cannabis particle surface, filling the internal voids of the LHC, improving the density of the material, and enhancing the mechanical properties of the material.

Conventional bridge expansion joints have the disadvantages of easy damage and lengthy maintenance period. Polyurethane concrete, as a polymer material, is gradually being applied to the repair of expansion joints. However, polyurethane-based repair materials are susceptible to a variety of factors during the early strength-building phase. In this regard, a Polyurethane-Fly Ash Composite (PU-FAC) for rapid repair was proposed in this paper and the effects of different factors on early mechanical performance were investigated. The orthogonal test was first used to determine the optimal mixing ratio of PU-FAC. Then the effects of temperature, catalyst, and curing time on the performance of PU-FAC were investigated by temperature rise curve, maturity index, SEM, and response surface method. The results showed that temperature and catalyst at different curing times had both positive and negative effects on the failure pattern, curing rate, degree of foaming, and mechanical performance. Finally, the optimum values of temperature and catalyst were determined by gray correlation analysis as 15 °C and 0.6 %. By analyzing the effects of different factors on the performance of PU-FAC, it provides a basis for the rapid repair construction of bridge expansion joint anchorage area.

For the study of the applicability of polyurethane concrete (PUC) in the anchorage zone of expansion joints, the construction process of PUC was summarized through the on-site construction of the anchorage zone of bridge expansion joints. The mechanical response of anchorage zones with different materials under vehicle loading was also analyzed by finite element modeling. The linear fatigue cumulative damage of expansion joint anchorage zone materials PUC, steel fiber concrete (SFC), and silicate cement concrete (PCC) were analyzed respectively by traffic investigation of bridge sections under construction and Miner's linear fatigue damage accumulation theory. The results show that the vertical displacement of PUC is 13 times that of SFC and PCC, the stress is reduced by 36%, and the annual cumulative fatigue damage value of PUC is 1.06E-07, which is only 1/10 of that of SFC, and PUC has excellent load cushioning capacity and fatigue performance, which can effectively improve the service life of the anchorage zone of expansion joints.

The use of polyurethane concrete (PUC) with a high compressive strength together with a corrugated steel plate (CSP) with a high tensile strength can improve the bending capacity of the corrugated steel-concrete composite structures. Although the PUC is lighter than normal concrete, its compressive, tensile, and bond strengths are much higher. In the paper, two groups of corrugated steel-concrete composite structure specimens with the PUC were designed, and the positive and negative bending capacities of the composite structure specimens were tested by a symmetrical four-point loading test and compared with that of the composite structure specimens using the normal concrete. The test results show that the bending capacity and deformation property of the composite structure specimens with the PUC are greatly improved compared with those using the normal concrete. Compared with the positive and negative bending capacities of the corrugated steel-normal concrete composite structure specimens, the composite structure specimens using PUC in the compression zone increased by 137.88 % and 136.42 %, while the corrugated steel-PUC composite structure specimens increased by 311.69 % and 283.39 %. Since the PUC has high bond strength, the test results of the negative flexural rigidity of the corrugated steel-PUC composite structure specimens were evaluated higher than the derived theoretical results. The test results of the corrugated steel-normal concrete composite structure specimens and the composite structure specimens using PUC in the compression zone are consistent with the theoretical results. In addition, using the PUC in the compression zone greatly improves the negative bending performance of the composite structure.

The development of irrigated agriculture in northwest China is restricted by shortages of fresh water and groundwater salinization. Saline water irrigation may cause salt accumulation in the soil, which results in salt stress to roots. The effects of water salinity and irrigation amount on wheat root distribution and yield, as well as soil salt distribution, were evaluated in field experiments conducted in 2014 and 2015 at the Shiyanghe Experimental Station of the China Agricultural University (102°52'E, 37°52'N), located in the Liangzhou District, in the city of Wuwei in northwest China. A total of 12 treatments including 4 levels of irrigation water salinity as indicated by electrical conductivity (0.65, 3.2, 5.2, and 7.1 dSm-1) and 3 levels of irrigation amount (205, 280, and 355 mm), were established using a randomized block design. Freshwater with an electrical conductivity of 0.65 dSm-1 and an irrigation amount of 355 mm was used as the control for salinity and irrigation level. The results showed that the influence of irrigation amount and water salinity on root distribution was mainly in the top 40-cm. Irrigation amount had no statistically significant (p > 0.05) effects on the average root length density (RLD) in the 2-year experiment. A decrease in irrigation amount reduced root biomass (RB) at maturity when water salinity ranged from 0.65 to 5.2 dSm-1. Water salinity less than 3.2 dSm-1 stimulated root growth in the soil layers 10-40-cm at the heading stage without obvious yield reduction or salt accumulation. However, water salinities of 5.2 and 7.1 dSm-1 led to decreases in RLD in the 0-10-cm layer and RB at the maturity stage, and a significant decrease in yield (p < 0.05) in both years. The interaction effects of irrigation amount and water salinity had no statistically significant (p > 0.05) effects on root parameters and yield. In the absence of rainfall, a regime with irrigation amounts between 205 and 355 mm and water salinity between 0.65 and 5.2 dSm-1 can ensure a 70% yield. [ABSTRACT FROM AUTHOR]