The aim of this study is to clarify the mechanism of the progressive excessive deformation observed in real underground RC box culverts of about 30 years of age. It was found by the site-inspection, monitoring and the destructive testing that the excessive deflection of top slabs for the culverts, which is almost 10 times the design estimated value, accompanies the out-of-plane shear failure. It is also computationally investigated that the coupling of subsidence of the backfill soil and the combined creep and shrinkage of concrete after cracking is closely associated with the delayed shear failure found in the culvert in service. In order to prove the delayed shear failure under higher sustained loads, the time-dependent shear crack propagation was reproduced in the laboratory test and the computational approach used in this study was examined.
Non-destructive testing is used in monitoring health of structures. In this paper, nonlinear ultrasonic test was done to analyze the sensitivity of the fundamental and higher harmonics with the internal damage in concrete. Good sensitivity produces significant quantitative changes in the nonlinear spectral amplitude parameter corresponding to the deviation of load. In actual conditions, structures have different design strength with varying water cement ratio. In addition, it is experi-encing loading and unloading. These are considered as major factors that induce effect in the behavior of ultrasonic test result in concrete. Past researches have only considered increasing application of load with single loading pattern. This study aims to investigate the effect of load application pattern in the generation of higher harmonics. Ordinary concrete specimens of size 150mm x 150mm x 150mm with water-cement ratio WC40 and WC60 were casted and tested using uniaxial compression machine with two load patterns: a.) single loading pattern from 0% to 100% and, b.) multiple loading/unloading pattern. Ultrasonic test with pitch-catch configuration was conducted at each loading state to record the fundamental and higher harmonic generation in the concrete.The experimental results showed that there was a good sensitivity for 3rd harmonic amplitude parameter DA when it was subjected to single loading pattern for both WC40 and WC60. On the other hand, good sensitivity was only observed for 2nd harmonic amplitude parameter DA when it was subjected to multiple loading/unloading pattern for both WC40 and WC60. This showed that the 2nd harmonic amplitude was consistent and sensitive when repeated load was applied for low and high water cement ratio.
This paper provides information concerning the results of test programme to investigate the properties and performance of Type General Purpose (GP) cement containing up to 12% limestone. Cement properties, including chemical and physical properties and mortar properties, such as compressive strength, drying shrinkage, and sulfate expansion were investigated comprehensively for effects of introducing higher limestone content to General Purpose (GP) cement. Test results showed that there is no significant effect on most properties due to increasing the limestone addition in cement from 7.5% to a maximum of 12%.
Volumetric changes in concrete may affect the structural performance of reinforced concrete structures and their durability. It has been revealed that autogenous shrinkage of high-strength concrete decreases reinforced concrete beam’s shear strength compared with low-shrinkage concrete. High-drying shrinkage of concrete may also decrease the shear strength of reinforced concrete beams using normal-strength concrete. In this study, the effects of drying shrinkage and expansion of normal-strength concrete on the shear strength of reinforced concrete beams with/without stirrups were investigated. Six concrete mix proportions, using different aggregates and admixtures, were used to control concrete volumetric changes. The used concrete showed a large range in volumetric change and high-shrinkage concrete caused shrinkage-induced cracking in the beams before loading. Loading test results showed that drying shrinkage and expansion decreased and increased the shear strength, respectively. The decrease or increase in measured shear strength as a result of volumetric changes was well reproduced by the proposed equation. The equation included the new concept of strain change in tension reinforcement caused by concrete shrinkage or expansion, which was proposed previously for autogenous shrinkage of high-strength concrete.
This paper presents a quantitative analysis of hydrated phase assemblage and chemical shrinkage of alkali-activated slag (AAS) as a function of pH and modulus (n= SiO2/Na2O molar ratio) of activator. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and thermodynamic modeling, provide a com-prehensive characterization of the phase assemblages and distribution in AAS microstructure. The main hydration products in AAS are calcium-alumina-silicate-hydrate (C-A-S-H) and hydrotalcite-type phases, while the formation of other hydrates is activator-dependent. For NaOH-activated slag, hydration products are preferentially formed around slag particles showing a hydrated rim, while for sodium silicate-activated slag, hydration products are initialized at both slag surface and inter-particle spaces simultaneously. However, a dark hydrated rim whose composition is similar to that of alkali-aluminosilicate-hydrate was observed around unhydrated slag in aged AAS. It indicates that the composition and spatial distribution of hydrates in AAS microstructure is heterogeneous, which cannot be predicted by thermodynamic modeling. The chemical shrinkage of AAS was quantified using buoyancy method and backscattered image analysis. The average chemical shrinkage of AAS is about 0.1211 ml/gslag and increases with the increasing modulus and pH of activator. The chemical shrinkage of AAS is about twice larger than that of portland cement, which may be attributed to the limited formation of expansive crystalline phases, such as ettringite and portlandite.
A research program was carried out to investigate the effect of heating and cooling treatment upon hydraulic property and macro-mechanical property of cement based material. Those treatments were performed on cylindrical mortar specimens (water to cement ratio of 0.5), subjected to 5, 10, 15 heating-cooling cycle times and three levels of maximum heating temperatures of 105°C, 145°C and 200°C. The hydraulic property tests were performed on a gas permeability and porosity test system. The initial permeability and porosity value of the material were measuring before the heating and cooling treatment under slightly confine (3MPa) and show the material has a good homogeneity. The damage of mortar due to the effect of heating and cooling treatment were evaluated the variation of permeability, porosity and macro-mechanical parameters by compare before and after heating and cooling treatment. Significant changes in the macro-mechanical property and hydraulic property before and after heating and cooling treatment in mortar were observed. The compressive strength and elastic modulus gradually decrease with the increase of maximum heating tem-perature and the number of heating cycles, while the porosity and permeability increases gradually.