This paper investigates the bond strength of tension lap splice in the ordinary concrete (OC)beam and self-compacted concrete (SCC) beam. A total of six beam specimens were cast for thebending test. Results indicate that the SCC beam and OC beam present similar bond strength at thelap splice of tension bar. Current code for the tension lap splice is available for the SCC beam. Bothof the SCC and OC beams with transverse stirrups could have ductile flexural behavior in the regionof tension lap splicer. Only minor spalling between reinforcing steel and concrete was found underservice loading, such that the corrosion resistance of the tension lap splice in the SCC and OC beamscould be preserved.
Structural lightweight aggregate concrete (LWAC) members have demonstrated greater fire endurance periods than equivalent thickness members made with normal-weight aggregates. Superior performance is due to a combination of lower thermal conductivity, lower coefficient of thermal expansion, and the inherent thermal stability developed by aggregates that have been exposed temperature greater than 1050°C during preprocessing. Furthermore, LWAC exhibits relatively high thermal insulating value, of which the thermal conductivity can be half as much as that of ordinary normal-weight concrete (NWC). Therefore, the main objective of this paper is to implement fire resistance testing for structural and non-structural elements made of LWAC and NWC to assess and compare their fire behavior.
The present study experimentally investigated the pre-failure and post-fatigue behavior of reinforced concrete (RC) beams constructed with lightweight aggregate concrete (LWAC) in comparison with that constructed of normal weight concrete (NWC) of the same compressive strength (40 MPa). A total of twelve RC beams were tested under different fatigue loadings. Based on the experimental observations, the midspan total deflection measured in the fatigue testing consisted of the elastic and plastic components. The mechanismof the two deflection components developed with load cycles was different. The experimental results showed that the fatigue resistance of LWAC beams was better than that of NWC beams for the same fatigue loading levels. It was reflected in both the lower evolution of fatigue damage and the smaller growth of midspan residual deflection. After 2 million cycles, an average increase in residual load capacity of about 8% was found in the NWC beams, while that in the LWA beams remained virtually unchanged.
In recent years, the reservoir sediments have been a disturbance to Taiwan government, and are getting worse due to the climate change. Consequently, it becomes an urgent issue for the authority to dredge and dispose reservoir sludge effectively. Material researchers in civil engineering and environmental engineering, cooperating with microbiologists and geochemists, have recently attempted the solidification of sludge granules into sandstone-like materials employing microorganisms. The aim of this study is to investigate the approach to solidify sludge or soil particle rapidly to attain strength through the growth of bacteria and apply the technique in practical. In this research, we used Bacillus pasteurii in the solidification of reservoir sludge. The sludge used in the experiment has a moisture content of 40%. The change of bacteria broth culture concentration (0%, 25%, 50%, 75%, and 100%) and CaCl2 ratio in the culturing Urea-CaCl2 medium (10%, 30% and 70%) were used as the experimental variables. The culture broth was mixed directly with reservoir sludge to form a cubic specimen (50 mm x 50 mm x 50 mm), which was then used in compressive strength, XRD and SEM test. The test results showed that being cultured in 70%-CaCl2 medium, the specimen blended with 100% bacteria broth had the highest compressive strength. Compared with the blank samples (0% bacteria broth), the compressive strength was enhanced by approximately 13.48%. Also, it was suggested that the solidification by bacteria can indeed enhance the compressive strength of the cube. The sludge solidified with bacteria cultured in 70%-CaCl2 medium has the highest compressive strength. The result also showed that the higher the content of CaCl2 used in the culturing medium is, the more CaCO3 deposit is induced by the bacteria.
As one of the most popular materials used in construction, concrete is prone to superficial flaws, such as crack, due to the load-bearing and external environment. This research manually made cracks of 2 mm with 100 mm length and 30 mm depth on concrete vessels as specimens. Subsequently, bacteria, specifically B. pasteurii, was used in crack rehabilitation to enhance the compression strength of the repaired concrete. The mixture of microbes, urea medium, and urea-CaCl2 medium was added to a sludge and fine aggregate with a weight ratio of 0.6:1:1 to be the repairing material for crack rehabilitation. Crack rehabilitation was conducted by injected the mixture into the test samples after 90 days curing in saturated lime solution. In addition to the traditional test – compression test, scanning electron microscope (SEM) was used to examine the structure composition of the microbe-repaired concrete for calcium carbonate crystal formation. Various rectangular and polygonal crystals were observed in the SEM photographs of the microbe-repaired concrete samples with high bacterial concentrations demonstrated that bacteria can induce calcium carbonate precipitation to complete crack rehabilitation. The results prove that high concentration of bacterial broth induced a great amount of calcium carbonate precipitate and improved the concrete strength of the microbe-repaired samples.
This study aims to develop the mix proportion of concrete incorporating water purification sludge (WPS), as parts of fine aggregate and consequently investigate its mechanical properties and durability. The experiments involve three sludges from Da-Nan, Lin-Nei and Nan-Hua water treatment plants in Taiwan. In addition to the control mixture without WPS, four replacement levels of 20%, 40%, 60% and 80% of fine aggregate were selected for preparing the concrete mixture. The concretes tested were designed to have three target compressive strengths of 14MPa, 18MPa and 21MPa. Test results show that the compressive strengths of the Da-Nan and Lin-Nei WPS concretes meet the design requirements, and the strength of the Nan-Hua WPS concrete is lower to be only suitable for application in low strength concretes. The shrinkage deformation of the Da-Nan and Lin-Nei WPS concretes increase with the increase of sludge replacement level, however, the shrinkage deformation decreases with the increase of the compressive strength of concrete. If the sludge replacement ratio is less than 40%, its effect on the compressive strength of the Da-Nan and Lin-Nei WPSs concrete is limited whether they are cured in water or in the air.
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